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1.
A comparative study of the dynamics of Heterotrophic bacteriocenoses was carried out in three springs in the territory of
Krylatskie Kholmy reserve in Moscow. The effect of abiotic (including anthropogenic) factors was assessed. Overall, the abundance
of heterotrophic bacteria in springs in Krylatskie Kholmy reserve is at the level common for spring water. However, despite
the relative closeness of springs, the microbiological characteristics of the “Svyatoi istochnik” spring radically differed
from those in the other two springs. In particular, the number of bacteria by inoculation in this spring was always lower.
This suggests the higher quality of water in the “Svyatoi istochnik” spring in terms of microbiological characteristics, which
is likely due to a lesser anthropogenic effect. 相似文献
2.
Jean-Claude Tanguy Michel Condomines Maxime Le Goff Vito Chillemi Santo La Delfa Giuseppe Patanè 《Bulletin of Volcanology》2007,70(1):55-83
A careful re-examination of the well-known written documents pertaining to the 2,750-year-long historical period of Mount
Etna was carried out and their interpretation checked through the high-accuracy archeomagnetic method (>1,200 large samples),
combined with the 226Ra-230Th radiochronology. The magnetic dating is based upon secular variation of the direction of the geomagnetic field (DGF) and
estimated to reach a precision of ±40 years for the last 1,200 years, and ±100 to 200 years up to circa 150 B.C. Although
less precise, the 226Ra-230Th method provides a unique tool for distinguishing between historic and prehistoric lavas, which in some cases might have
similar DGFs. We show that despite the abundance of details on ancient historical eruptions, the primary sources of information
are often too imprecise to identify their lava flows and eruptive systems. Most of the ages of these lavas, which are today
accepted on the geological maps and catalogues, were attributed in the 1800s on the basis of their morphology and without
any stratigraphical control. In fact, we found that 80% of the “historically dated” flows and cones prior to the 1700s are
usually several hundreds of years older than recorded, the discrepancies sometimes exceeding a millennium. This is proper
the case for volcanics presumed of the “1651 east” (actually ∼1020), “1595” (actually two distinct flows, respectively, ∼1200
and ∼1060), “1566” (∼1180), “1536” (two branches dated ∼1250 and ∼950), “1444” (a branch dated ∼1270), “1408” (lower branches
dated ∼450 and ∼350), “1381” (∼1160), “1329” (∼1030), “1284” (∼1450 and ∼700), “1169 or 812” (∼1000) eruptions. Conversely,
well-preserved cones and flows that are undated on the maps were produced by recent eruptions that went unnoticed in historical
accounts, especially during the Middle Ages. For the few eruptions that are recorded between A.D. 252 and 750 B.C., none of
their presumed lava flows shows a DGF in agreement with that existing at their respective dates of occurrence, most of these
flows being in fact prehistoric. The cinder cones of Monpeloso (presumed “A.D. 252”) and Mt. Gorna (“394 B.C.”), although
roughly consistent magnetically and radiochronologically with their respective epochs, remain of unspecified age because of
a lack of precision of the DGF reference curve at the time. It is concluded that at the time scale of the last millennia,
Mount Etna does not provide evidence of a steady-state behavior. Periods of voluminous eruptions lasting 50 to 150 years (e.g.,
A.D. 300–450, 950–1060, 1607–1669) are followed by centuries of less productive activity, although at any time a violent outburst
may occur. Such a revised history should be taken into account for eruptive models, magma output, internal plumbing of the
volcano, petrological evolution, volcano mapping and civil protection. 相似文献
3.
Metallogenic geodynamic background of Mesozoic gold deposits in granite-greenstone terrains of North China Craton 总被引:4,自引:0,他引:4
The spatial distribution map of 65 mid-large gold-deposits hosted in the granite-greenstone terrains of the North China Craton
is first drawn. These gold deposits mainly concentrate in the Mesozoic remobilized Yinshan-Yan-shan-Liaoning-Jilin intracontinental
collisional orogenic belt, the northern Qinling and the Jiaodong Mesozoic collisional orogenic belts, and the Mesozoic intracontinental
fault-magmatic belts developed along the Taihangshan and the Tan-Lu faults; their mineralizing time is predominantly Jurassic-Cretaceous,
i. e. the Yanshanian. The metallogenic geodynamic background is exactly the compression-to-extension transition regime during
continental collision.
The results are partly from the project entitled “The main types of gold mineralizations in China and their metallogenic model”
(89-El) supported by the Ministry of Metallurgical Industry of China, and projects “Geology and metallogenesis of the main
type gold deposits in East Chinan” (Grant No. 9488010) and “Study on ore-forming fluids of the Wangfeng gold deposit, Xinjiang” supported by the National Natural
Science Foundation of China (Grant No. 49672119). 相似文献
4.
Study on the pattern and mode of vertical crustal deformation during the seismogenic process of intraplate strong earthquakes 总被引:3,自引:0,他引:3
Studyonthepatternandmodeofverticalcrustaldeformationduringtheseismogenicprocessofintraplatestrongearthquakes杨国华,桂昆长,巩曰沐,杨春花,韩... 相似文献
5.
Case histories of water level subsidence in bore-holes as a precursor of earthquakes are given here. Based on the examples,
a testable quantitative theory for causative mechanism of the precursor—“draining-injecting water model with variable discharge”
is proposed (abbreviated to DIW model). Through analysing the constitution law of which the deformation changes in the porous,
water-saturated media under the effect of exterior stress, as first step of all, the authors suggested first a simple “drainage-natural
restoration model” (abbreviated to DNR model), calculated and gave a group of theoretical precursor curve by using DNR model,
compared the theoretical precursor curves of DNR model with the observational curves, found out the differences of the two
curves, studied the causative physical factors that caused the differences then, revised the DNR model, and finally, the theory
on “draining-injecting water model with variable discharge” in the paper was obtained. The authors deduced general equation
of the two dimensions “draining-injecting water linear source drawdown field” in the paper, suggested and developed the concept
on “domain”. DIW model can also give a possible explanation for both regularity and complexity of this precursor. DIW theory
can quantitatively divide the seismogenic process of the foci on the short-term and impending process into several phases,
and by inversing the discharge functionq(τ) curve, the time values by which the phases are divided were obtained. They will be helpful to predicting the occurrence
time of earthquake and judging the DD and IPE model of the seismogenesis.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 194–201, 1993. 相似文献
6.
In this paper, based on the previous study of practical use of seismic regime windows and seismic regime belts, the problem
of establishing a “seismic regime network” consisting of “windows” and “belts” is further posed and discussed according to
the observed fact that many “windows” and “belts” make responses to one earthquake. For the convenience of usage, the “seismic
regime network” is divided into two classes, the first class and the second one. The former can be used in tendency prediction
for long-term seismic activity in a large area, the latter used in short-term prediction in a small area. In this paper, after
briefly discussing the physical significance of “seismic regime network”, it is pointed out that this simple and easily used
method can be used to observe and extract seismic precursory information from a large area before a great earthquake, thus
it can provide a reliable basis for the analysis and judgement of seismic regime tendency in time and space. No doult, this
method is of certain practical significance.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 161–169, 1991.
The English version of this paper is improved by Prof. Shaoxie Xu. 相似文献
7.
Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland, USA 总被引:2,自引:0,他引:2
Carolyn A. Klocker Sujay S. Kaushal Peter M. Groffman Paul M. Mayer Raymond P. Morgan 《Aquatic Sciences - Research Across Boundaries》2009,71(4):411-424
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects
of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in
Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of
stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to
its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some
stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable
across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was
low in the restored streams during summer baseflow conditions. Uptake length of NO3
−–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3
−–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m
in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank
Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may
be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with
hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary,
however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in
response to the “flashy” hydrologic flow conditions during storms common in urban streams. 相似文献
8.
Alexander Bartholomä Adam Kubicki Thomas H. Badewien Burghard W. Flemming 《Ocean Dynamics》2009,59(2):213-225
The German Wadden Sea (southern North Sea) sediments are composed of both cohesive and non-cohesive deposits. The spatial
distribution patterns are mainly driven by wind-induced waves and tidal currents. Transport intensity and duration depend
on the hydrodynamic conditions, which vary over time. In this paper, the transport of suspended sediment was investigated
on seasonal, tidal and hourly time scales in the back-barrier system of Spiekeroog Island. Long- and short-term data of fair
weather periods and two storm events were investigated based on stationary and mobile measurements of currents and waves by
Acoustic Doppler Current Profiler (ADCP), in situ particle size and suspended sediment concentration (SSC) measurements by
laser in situ scattering and transmissometry (LISST) as well as wind records. The ADCP backscatter intensities were calibrated
by means of LISST volume concentration data in order to quantify longer term SSCs and fluxes in the back-barrier system. Values
up to 120 mg l−1 were recorded, but concentrations more commonly were below 60 mg l−1. The long-term results confirm former observations of a balanced budget during low-energy (fair weather) conditions in the
study area. In general, SSCs were higher during spring tides than during neap tides. The data also clearly show the remobilisation
of sediment by tidal current entrainment. The records include two severe storm events, “Britta” (1st November 2006) and “Kyrill”
(18th January 2007). The data reveal very complex temporal flow and transport patterns. During both storm events, the export
of material was mainly controlled by the interaction of wind, waves and tidal phase. The typical ebb-dominance occurring during
fair-weather conditions was temporarily neutralised and even reversed to a flood-dominated situation. During “Kyrill”, the
wind and high-waves setup in conjunction with the tidal phase was even able to compress the duration of two successive ebb
cycles by over 70%. Although SSCs increased during both storms and higher turbulence lifted particle clouds upwards, an export
of suspended matter towards the North Sea was only observed under the conditions taking place during “Britta”. Such fluxes,
however, are currently still difficult to quantify because the backscatter intensity during high energy events includes a
substantial amount of noise produced by the high turbulence, especially near the water surface. 相似文献
9.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献
10.
The purpose of the research was to determine parameters of ground-motion models for two areas characterized by considerable
induced seismicity and different geology. Fifty-nine events collected from surface seismological stations of coal mine “Bielszowice”
(at the Main Anticline, South Poland) and 144 events from coal mine “Ziemowit” (at the Main Syncline, South Poland) were used
for computation. For both areas, simple ground-motion prediction equations (GMPEs) without site effects were derived, but
the model was acceptable only for “Bielszowice” area. The GMPE was calculated once again for “Ziemowit”, but this time we
took into consideration the amplification coefficient, which significantly improved the model solution. Finally, the theoretical
value of amplification was calculated. Knowing that the amplification is associated with subsurface layers, we used three
different models of overburden: (i) with Quaternary sediments only, (ii) with a complex of Quaternary-Tertiary sediments,
and (iii) with a complex of Quaternary-Tertiary-Triassic sediments and Carboniferous as a basement. Usually, the amplification
of vibrations appears in the Quaternary sediments. However, theoretical calculations of amplification were consistent with
the results obtained from GMPE when a rigid Carboniferous substratum was applied. 相似文献
11.
Early Paleozoic subduction of the Paleo-Asian Ocean: Geochronological and geochemical evidence from the Dashizhai basalts,Inner Mongolia 总被引:10,自引:0,他引:10
Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted
at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns
(i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic
Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high
TiO2, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions
(87Sr/86Sr(i)=0.7028−0.7032, εNd(t)=+9.8−+11.2, εHf(t)=+16.1−+18.4). Group 2 has lower TiO2, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (87Sr/86Sr(i)=0.7037−0.7038, εNd(t)=+5.7−+7.3, εHf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction
of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by
predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The
petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and
the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts
were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation”
volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the
previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions
of different volcano-sedimentary associations.
Supported by National Basic Research Program of China (Grant No. 2006CB403504) 相似文献
12.
D. N. Osokina 《Izvestiya Physics of the Solid Earth》2010,46(5):419-432
In the work 2D and 3D fields of stresses of several scale levels close to the off of the main fault (vertical strike-slip
fault) in conditions of compression are mathematically calculated and investigated. The solution is found for the elastic
task for a 2D “horizontal” field; a 3D field of stresses is obtained by the imposition of a “vertical” unaxis compression.
It is shown that the surroundings of the fault are subdivided into three (not two, as is usually considered) regions of types
of predictable secondary fractures: “extension,” “strike-slip fault,” and “compression.” In regions close to the off of the
main fault, three different microregions occur. The type of destruction in these microregions depends on the parameters of
the outer load. Natural and model data of second order fractures that are compared with the calculated data are examined and
generalized. The performed investigation is important for the determination of the genesis of secondary fractures, located
close to the main fault. The calculated parageneses of secondary fractures may be used for the estimation of the stress tensor
type of the regional field. 相似文献
13.
赵和云 《地震学报(英文版)》1994,7(3):465-474
ThepatterncharacteristicsofthetendencyvariationsofearthresistivityanditsrelationtoearthquakesHe-YunZHAO(赵和云)(EarthquakeResear... 相似文献
14.
Following a new train of thinking, this paper has explored first the potential information in the ground resistivity data observed by the existing geoelectric observation system, investigated and proposed a new dimensionless geoelectric precursor factor, the degree of ground resistivity anisotropy, S, and studied the characteristics of dynamic evolution pattern of S during the seismogenic process. The results show that, during the seismogenic process, the degree of ground resistivity anisotropy (S) displays a process of 'normal' →'abnormal strengthening (amplitude, range)' →abnormal weakening' → 'earthquake occurrence'→ 'normal'. The earthquake would occur at the time when the S value has entered the late stage of strengthening and turns to weaken and in the gradient belt on the margin of S anomaly region. The dynamic evolution pattern of S reflects the changes of the tectonic stress field during the seismogenic process. Therefore, it would be possible to trace the process of earthquake generation and occurrence from the dynamic evolution pattern of S so as to service earthquake prediction. 相似文献
15.
Climatic and environmental changes over the last millennium recorded in the Malan ice core from the northern Tibetan Plateau 总被引:3,自引:0,他引:3
WANG Ninglian YAO Tandong PU Jianchen ZHANG Yongliang SUN Weizhen 《中国科学D辑(英文版)》2006,49(10):1079-1089
In this paper, climatic and environmental changes were reconstructed since 1129A.D. based on the Malan ice core from Hol Xil, the northern Tibetan Plateau. The record of δ 18O in the Malan ice core indicated that the warm-season air temperature variations displayed a general increase trend, the 20th-century warming was within the range of natural climate variability, and the warmest century was the 17th century while the warmest decade was the 1610s, over the entire study period. The “Medieval Warm Epoch” and “Little Ice Age” were also reflected by the ice core record. The dust ratio in the Malan ice core is a good proxy for dust event frequency. The 870-year record of the dust ratio showed that dust events occurred much frequently in the 19th century. Comparing the variations of δ 18O and the dust ratio, it is found that there was a strong negative correlation between them on the time scales of 101―102 years. By analyses of all the climatic records of ice cores and tree rings from the northern Tibetan Plateau, it was revealed that dust events were more frequent in the cold and dry periods than in the warm and wet periods. 相似文献
16.
Gradient-based similarity in the atmospheric boundary layer 总被引:2,自引:0,他引:2
Zbigniew Sorbjan 《Acta Geophysica》2008,56(1):220-233
The “flux-based” and “gradient-based” similarity in the stable boundary layer and also in the interfacial part of the convective
boundary layer is discussed. The stable case is examined on the basis of data collected during the CASES-99 experiment. Its
interfacial counterpart is considered in both the quasi-steady (mid-day) and non-steady states, utilizing the results of large-eddy
simulations.
In the stable regime, the “gradient-based” approach is not unique and can be based on various master length scales. Three
local master length scales are considered: the local Monin-Obukhov scale, the buoyancy scale, and the Ellison scale. In the
convective “quasi-steady” (mid-day) case, the “mixed layer” scaling is shown to be valid in the mixed layer and invalid in
the interfacial layer. The temperature variance profile in non-steady conditions can be expressed in terms of the convective
temperature scale in the mixed layer. The analogous prediction for velocity variances is not valid under non-steady conditions. 相似文献
17.
Dev K. Niyogi Janet M. Bandeff Cem Selman Drew E. Menke 《Aquatic Sciences - Research Across Boundaries》2010,72(2):203-212
We examined nutrient flux, uptake, and transformation along a spring-fed stream in the Ozark region of Missouri, USA, over
the year 2006. Water in Mill Creek originates from several springs, with a single spring contributing over 90% of the stream
discharge during much of the year of study. Soluble reactive phosphate concentrations were usually low (<10 μg L−1) along Mill Creek, but peaked during high discharge. Concentrations of dissolved inorganic nitrogen (DIN) were relatively
high in the spring water, mainly as nitrate, but usually declined across a small pond and the 10-km length of Mill Creek.
During low flows in summer and early autumn, the stream removed over 300 μg L−1 of DIN over its 10-km length, or about 80% of the initial amount. DIN retention along the stream, as a percentage of the
DIN upstream, was related mainly to discharge, with higher flows having much higher DIN concentrations. The net uptake rate
of DIN uptake was 0.91 μg m−2 s−1 in the stream during summer baseflow. The uptake rate declined downstream for different reaches and was closely related to
DIN concentration. In experimental channels, uptake by epilithic algae was one significant sink for nitrate-N in Mill Creek.
In 2006, inorganic nutrient export during a single day after a spring storm was similar to export during 40–100 days of low
flow conditions in summer and early autumn. Our results suggest that significant nutrient retention can occur during baseflow
periods via biological uptake, whereas substantial export occurs during high flow conditions. 相似文献
18.
An alternative “direct method” to “mean dynamic topography” (MDT) computations using satellite altimetry-derived “mean sea
surface” (MSS) and “global geopotential model” (GGM), without direct application of the geoid, is devised. The developed approach,
which is based on derivation of an equipotential surface of the gravity field of the Earth that fits to global MSS in least
squares sense, is formulated via a constrained optimization problem. The validity of our method is numerically tested by computing
a global MDT model based on DNSC08 MSS model and EGM2008 GGM as input data. 相似文献
19.
Chiara Turino Paola Morasca Gabriele Ferretti Davide Scafidi Daniele Spallarossa 《Journal of Seismology》2010,14(2):393-411
Reliable automatic procedure for locating earthquake in quasi-real time is strongly needed for seismic warning system, earthquake
preparedness, and producing shaking maps. The reliability of an automatic location algorithm is influenced by several factors
such as errors in picking seismic phases, network geometry, and velocity model uncertainties. The main purpose of this work
is to investigate the performances of different automatic procedures to choose the most suitable one to be applied for the
quasi-real-time earthquake locations in northwestern Italy. The reliability of two automatic-picking algorithms (one based
on the Characteristic Function (CF) analysis, CF picker, and the other one based on the Akaike’s information criterion (AIC),
AIC picker) and two location methods (“Hypoellipse” and “NonLinLoc” codes) is analysed by comparing the automatically determined
hypocentral coordinates with reference ones. Reference locations are computed by the “Hypoellipse” code considering manually
revised data and tested using quarry blasts. The comparison is made on a dataset composed by 575 seismic events for the period
2000–2007 as recorded by the Regional Seismic network of Northwestern Italy. For P phases, similar results, in terms of both
amount of detected picks and magnitude of travel time differences with respect to manual picks, are obtained applying the
AIC and the CF picker; on the contrary, for S phases, the AIC picker seems to provide a significant greater number of readings
than the CF picker. Furthermore, the “NonLinLoc” software (applied to a 3D velocity model) is proved to be more reliable than
the “Hypoellipse” code (applied to layered 1D velocity models), leading to more reliable automatic locations also when outliers
(wrong picks) are present. 相似文献
20.
Physicochemical and microbiological characteristics of the bathing waters in Varna’s Black Sea coastal area were investigated
during year 2007 at 23 monitoring stations. Most of the determined physicochemical parameters—pH, mineral oils, surface active
substances, phenols, dissolved oxygen, nutrients and microbiological parameters—“Total coliforms”, “Faecal coliforms”, “Faecal
streptococci” were in compliance with the guidline’ limits and exhibited good water quality. Ammonium and phosphate’s pollution
above the limits was determined at the South beach, Officers beach and Central beach situated in Varna’s central bathing zone.
For the period of 13.08 to 24.10.2007—70% of the South beach samples analyzed for NH4+ exceeded the limits 60 times and the concentrations of PO43− exceeded the limits 17.5 times. Some deviations from the guidline’ limits regarding the microbiology were exhibited at the
same beaches. A conclusion is made that the area of study is not yet seriously threatened, in spite of the rapid recreation
during the last years. 相似文献