全文获取类型
收费全文 | 884篇 |
免费 | 34篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 121篇 |
地球物理 | 191篇 |
地质学 | 369篇 |
海洋学 | 30篇 |
天文学 | 191篇 |
综合类 | 4篇 |
自然地理 | 25篇 |
出版年
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 28篇 |
2014年 | 28篇 |
2013年 | 44篇 |
2012年 | 41篇 |
2011年 | 42篇 |
2010年 | 34篇 |
2009年 | 40篇 |
2008年 | 48篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 31篇 |
2003年 | 24篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1972年 | 6篇 |
1960年 | 4篇 |
排序方式: 共有939条查询结果,搜索用时 343 毫秒
851.
Klaus Wyrtki 《Ocean Dynamics》1952,5(1):21-27
Zusammenfassung Es werden die Beziehungen zwischen den über der südlichen Nordsee herrschenden Winden und den durch die Straße von Dover stattfindenden Wasserbewegungen abgeleitet. Diese werden einerseits durch den unmittelbaren Windeinfluß und andererseits durch das im wesentlichen auch windbedingte Gefälle vom Kanal zur Nordsee bestimmt. Der Jahresgang und im Zusammenhang damit das Vorrücken salzreichen Wassers im Kanal werden untersucht. Die bei Feuerschiff Varne auftretenden Richtungsänderungen des mittleren jährlichen Reststromes werden durch Schwankungen der Windgeschwindigkeit erklärt. An Hand von Salzgehaltskarten aufeinanderfolgender Monate werden Bewegungen von Wasserkörpern und Fronten im Kanal unter dem Einfluß des Windes verfolgt. Auf die Bedeutung solcher Untersuchungen synoptischer Art zum Studium der Wasserbewegungen wird hingewiesen.
The wind's influence on the flow of water through the Straits of Dover
Summary The relations between the winds blowing over the southern North Sea and the flow of water through the Straits of Dover are derived; this flow of water depends on both the immediate influence of the wind and the slope of the sea surface between the Channel and the North Sea which, too, is mainly produced by the wind. The annual variation and, in connection with it, the advance of Atlantic water into the Channel are investigated. The changes of directions the mean annual residual current is subjected to according to the observations made near the light vessel Varne are found to be due to variations in the wind velocity. The shifting of water bodies and fronts in the Channel as dependent on the wind is studied by means of salinity charts over consecutive months. Finally, attention is drawn to the significance of such synoptical investigations for the study of water movements.
L'influence du vent sur les mouvements de l'eau dans le Pas de Calais
Résumé Les relations entre les vents dominant au sud de la mer du Nord et les mouvements de l'aeu dans le Pas de Calais sont dérivées. Ces mouvements sont causés par l'action immédiate du vent ainsi que par la pente de la surface entre la Manche et la mer du Nord; celle-ci, de sa part, est de même essentiellement causée par le vent. La marche annuelle et, en conséquence, la progression de l'eau atlantique dans la Manche sont étudiées. Les changements de direction du courant résiduel moyen par an dérivés des observations du bateau feu Varne sont expliqués en fonction des changements de vitesse du vent. À l'aide des cartes de salinité sur des mois consécutifs les mouvements des masses d'eau et des fronts dans la Manche sont étudiés par rapport à leur dépendance du vent. En résumé, l'attention est attirée sur l'importance de telles investigations synoptiques pourl'étude des mouvements de l'eau.相似文献
852.
White, pale-yellow and brown deposits occur on surfaces of fragments of the Norton County enstatite achondrite. X-ray powder analysis of these materials indicates that they consist of several calcium-bearing minerals: portlandite [Ca(OH)2], vaterite (CaCO3, hexagonal), calcite (CaCO3, trigonal) and bassanite (CaSO4-1/2 H2O). We suggest that these minerals formed by weathering of oldhamite (CaS), which we found to occur in Norton County. The occurrence of portlandite suggests that at low temperatures and in the terrestrial environment, hydrolysis of oldhamite is the most important first step in the weathering sequence. Subsequent carbonation of portlandite is thought to produce vaterite, and vaterite in turn might transform into calcite. Thus, we suggest a weathering sequence in the terrestrial environment of oldhamite portlandite vaterite calcite. The mineral bassanite is clearly also a terrestrial weathering product but its precise mode of origïn is somewhat uncertain: in the system CaSO4-H2O, bassanite forms from gypsum at about 100 °C (an unlikely high T for the weathering environment of Norton County). 相似文献
853.
R.J. Floran Martin Prinz P.F. Hlava Klaus Keil C.E. Nehru J.R. Hinthorne 《Geochimica et cosmochimica acta》1978,42(8):1213-1229
The Chassigny meteorite is a moderately shocked olivine achondrite or chassignite with features indicative of a cumulate origin with some subsolidus annealing. Chassigny is an iron-rich dunite (Fo68) with minor amounts of Ca-rich and Ca-poor pyroxene, alkalic feldspar, chromite, and melt inclusions in olivine. Accessory phases include chlorapatite, troilite, marcasite, kaersutite amphibole, pentlandite, ilmenite, rutile and baddeleyite. The meteorite experienced shock pressures of ~150–200 kbar as evidenced by planar and irregular fractures in olivine, local recrystallization in pyroxene and reduced birefringence and rare deformation lamallae in feldspar. Kaersutitic amphibole (K0.05 Na0.45)0.50 (Ca1.71 Na0.29)2.00 (Mg2.73 ‘Fe’1.19 Ti0.73 A10.23 Cr0.08 Mn0.03)4.99 (Si6.05Al1.95)8.00 O22 (OH, F)2 containing hydrogen and lesser amounts of fluorine represents the first extraterrestrial occurrence of hydrous amphibole and the first meteoritic amphibole type other than fluorichterite. Kaersutite is found only in melt inclusions.Melt inclusion bulk compositional data suggest crystallization from a low-Ca melt that may have been similar in major element abundances to the silicate portion of LL group chondrites. However, Chassigny has a fractionated pattern for REE and the lack of metallic iron, possible presence of minor Ni in the olivine and Fe3+ in the chromites indicates that Chassigny formed under relatively more oxidizing conditions than most other achondrites. Therefore its parental melt could not have been directly derived from a chondritic composition in a simple single-stage process. The iron-rich bulk composition, cumulate texture and abundance as well as alkalic nature of the interstitial feldspar indicate that Chassigny could not have generated eucritic magmas. This places further constraints on its relationship to other meteorites and the parent body from which it is derived. The Brachina meteorite is similar to Chassigny except that it is finer grained, more feldspathic and is unshocked. It extends the fractionation range of this group which now represents two unusual meteorites. 相似文献
854.
855.
Time series of hydrographic sections in the northern North Atlantic from the period 1990 to 2004 are analyzed for changes
in the characteristics and distribution of water masses that are involved in the thermohaline circulation (THC). During the
1990s, the North Atlantic Oscillation (NAO) alternates from a positive phase (strong westerlies) to a negative phase (weak
westerlies). The reduced ocean heat loss confined the convection in the Labrador Sea to the upper 1,200 m, generating a new
salinity minimum layer characterizing the Upper Labrador Sea Water (ULSW), and led to a warming and salinization of the older
LSW below due to lateral mixing. The Lower LSW, formed in the first half of the 1990s, spread in the subpolar gyre and reached
the Newfoundland and Irminger basins after about 1 to 2 years, where the associated isopycnal doming contributed to eastward
frontal shifts in the upper layer. After 5 and 6 years, it arrived in the Iceland and West European basins, respectively.
The collapse of the isopycnal dome in the Labrador Sea, associated with the drainage of the Lower LSW, resulted in a slowing
of the cyclonic circulation of the subpolar gyre. This was accompanied in the upper layer by a westward shift of the southeastern
extension of the gyre and a northward advection of warm and saline subtropical water in its eastern part, which finally reached
the Labrador Sea after about 7 years. In the upper layer of the Labrador Sea, the advection of warm and saline water dominated
over the heat loss to the atmosphere and the freshwater gain from melting ice and precipitation in the NAO-low period, so
that no accumulation of freshwater but an increase of the heat and salt contents were observed, as in the whole eastern part
of the subpolar gyre. Within 1 to 2 years after the drop of the NAO in the winter of 1995/1996, the Subarctic (Subpolar) Front
shifted northward and westward north of about 50°N, favored by the retreat of the low-salinity tongue extending eastward from
the southern Labrador Sea, and it shifted southward and eastward in the Newfoundland Basin. Therefore, the enhanced northward
advection of subtropical waters in the northeastern North Atlantic is balanced by the enhanced southward advection of subarctic
waters, including Lower LSW in the Newfoundland Basin, indicating a strong response of the gyre component of the THC. 相似文献
856.
High-resolution sea floor imaging (narrow beam sediment profiler) yields evidence for an offshore rupture along a strand of
the Carboneras Fault Zone (CFZ) in the Gulf of Almería off southern Spain. The observed faults affect the seafloor and cut
the Late Holocene sedimentary cover, hence the faults are regarded as active and the escarpments as relatively fresh. Seafloor
faulting is associated with escarpments, fissures, pressure ridges, folds, and reverse faults indicating sinistral strike-slip
faulting with a significant vertical displacement. Adjacent to the major fault zone secondary phenomena such as submarine
slumps and slides are observed. The observed fresh escarpments imply an offshore rupture during a major earthquake along the
CFZ. The southern Iberian margin and the Afro-Eurasian convergence zone form an area of moderate seismicity. However, some
major events occurred, such as the 1522 Almería earthquake (EMS IX; [IGN (2005) Instituto Geografico Nacional, www.ign.es]),
which affected large areas in the western Mediterranean. Different epicentral areas have been suspected, mainly along the
50 km long sinistral CFZ; however, no on-shore surface ruptures and paleoseismological evidences for this event have been
found. Based on our data, a new epicentral area is proposed in the Gulf of Almería precisely along the observed sea floor
rupture area, where the CFZ extend at least for 100 km offshore. Our findings suggest a specific seismic hazards and tsunami
potential for offshore active and seismogenic faults in the Alborán Sea. 相似文献
857.
Most antibiotics are only partially metabolised by patients before being discharged into the municipal sewage system along with patient excreta. Studies have shown that the majority of antibiotics pass through sewage treatment and are then released into the environment. Accordingly, investigations conducted in various countries have detected a number of antibiotics in the low μg or ng per litre range in different environmental compartments. Studies connecting mass balances of use on a local scale and of input and analysis of the antibiotic concentrations present in municipal sewage treatment plants are scarce. Data on local use of antibiotics and their relation to nationwide consumption are not available. This study investigated the use, input, and fate of antibiotics on a local scale and this data were compared with the German nationwide consumption. 42 antibiotics and 15 antimycotics were used in the mass balance consideration over a period of one year. It was found that the local pattern of usage differed only little from that found nationwide. Seasonal changes were minor and the concentrations actually measured were found to be in the expected range. Differences in both the identified occurrence and the concentrations of the target compounds were observed within and between the three sampling periods. 相似文献
858.
Carlos Augusto França Schettini Klaus Ricklefs Eliane Cristina Truccolo Volker Golbig 《Ocean Dynamics》2006,56(3-4):308-319
This study investigates the hydrodynamic characteristics of the lower, middle, and upper sectors of a highly stratified estuary, the Itajaí-Açu river estuary (south of Brazil ∼27° S/48.5° W). The study is based on a 25-h field campaign with three sampling stations positioned at 2, 17, and 38 km inward from the river mouth, during low river discharge condition and spring tide. The experimental data gathered was reduced and analyzed in terms of distribution of variables in time and space tide average vertical profiles and decomposition of the advective transport of salt and suspended particulate matter (SPM). Tidal range was nearly constant along the estuary, presenting time lag of about 2 h between lower and upper estuary. The ebb discharge peaks were about twice the discharge flood peaks and occurred simultaneously. The tide was the main determining agent in the lower estuary, where currents, salt stratification, and SPM distributions presented a repetitive behavior. In the middle estuary, the tide effects were also observed, but the presence of saline waters decreased along the time due to increasing river discharge during the campaign. The distribution of SPM in the mid- and upper estuary presented patched pattern not associated with tides and may be attributed to short-term flood contributions of tributaries. Currents presented ebb dominance in all three sectors; in the middle and upper estuary, they presented also a time asymmetry, with ebb currents longer than flood. The advective transport of salt in the lower estuary was upstream, with dominance of gravitational circulation term. In the mid-estuary, there was practically no transport, with balance between fluvial discharge (downstream) and tidal correlation (upstream). The advective transport of SPM was upstream in the lower estuary and downstream in the mid- and upper estuary, being dominated by gravitational circulation in the former and fluvial discharge in the others. 相似文献
859.
We present numerical results of thermal-mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly
different character of an olivine mantle. In the numerical experiments quartz is found to have a very strong tendency for
short-time-scale instabilities, while our numerical experiments show that olivine has a decisive tendency for a stable thermally
lubricated slip. At the same time, olivine can also go through a transitional period of creep bursts, which are physically
caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear
zone. Since olivine has this strong propensity to self organize in a large apparently stable fault system, it lacks the dynamics
of interacting ductile faults evident in other minerals. Quartz behaves totally different and keeps its jerky slip behavior
for prolonged deformation. An example is shown here in which a 30 × 50 km piece of a wet quarzitic crust is extended for about
2 Ma. The associated total displacement field clearly shows the unstable slipping events, which have a characteristic time
frame of one to several years, In contrast, olivine is very stable and has a much longer time scale for thermal instability
of 100 kyrs. 相似文献
860.
Judit Zádor Tamás Turányi Klaus Wirtz Michael J. Pilling 《Journal of Atmospheric Chemistry》2006,55(2):147-166
It is essential to quantify the background reactivity of smog-chambers, since this might be the major limitation of experiments carried out at low pollutant concentrations typical of the polluted atmosphere. Detailed investigation of three chamber experiments at zero-NO
x
in the European Photoreactor (EUPHORE) were carried out by means of rate-of-production analysis and two uncertainty analysis tools: local uncertainty analysis and Monte Carlo simulations with Latin hypercube sampling. The chemical mechanism employed was that for methane plus the inorganic subset of the Master Chemical Mechanism (MCMv3.1). Newly installed instruments in EUPHORE allowed the measurement of nitrous acid and formaldehyde at sub-ppb concentrations with high sensitivity. The presence of HONO and HCHO during the experiments could be explained only by processes taking place on the FEP Teflon walls. The HONO production rate can be described by the empirical equation W(HONO)EUPHORE
dry = a × j
NO
2× exp (− T
0/T) in the low relative humidity region (RH < 2%, a = 7.3×1021 cm−3, T
0 = 8945K), and by the equation W(HONO)EUPHORE
humid = W(HONO)EUPHORE
dry+ j
NO
2× b × RH
q
in the higher relative humidity region (2% < RH < 15%, b = 5.8×108 cm−3 and q = 0.36, and RH is the relative humidity in percentages). For HCHO the expression W(HCHO)EUPHORE = c × j
NO
2exp (− T′0/T) is applicable (c = 3.1×1017 cm−3 and T′0 = 5686 K). In the 0–15% relative humidity range OH production from HONO generated at the wall is about a factor of two higher than that from the photolysis of 100 ppb ozone. Effect of added NO2 was found to be consistent with the dark HONO formation rate coefficient of MCMv3.1. 相似文献