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91.
Air was injected through a well in a thin transparent tank filled with saturated glass beads to study how the size and air
saturation of air sparging plumes are affected by particle size and gradation; operational parameters such as injection pressure,
well depth, injection pressure pulsing; and well outlet configuration. V-shaped air plumes with an apex between 40° and 60°
were obtained for all tests. The air pressure required to initiate sparging agreed closely with the sum of the air entry pressure
and the hydrostatic pressure, with higher initiation pressures required in the fine and well-graded beads. Higher air flow
rates and air saturations were obtained in coarser beads at a given pressure, and the variation in flow rate was consistent
with estimated air permeabilities. Peak average air saturations were 28–56% for the coarse-medium beads, 10% for the well-graded
beads, and 8% for the fine beads. Air saturation and the radius of influence increased modestly (<40%) as the normalized injection
pressure exceeded 0.1. Radius of influence increased by approximately a factor of two as the well depth increased, but leveled
off once the ratio of radius of influence to well depth reached 0.60–1.05. Pulsing of injection pressure had no effect on
the initiation pressure, air flow rate, or air saturation, but increased the size of the air plume and the radius of influence
slightly (<15%). Well outlet configuration had only a slight affect the radius of influence (<10%), air saturation (<10%),
or air flow rate (<12%). Dye testing showed that water surrounding the air plume circulated during continuous and pulsed sparging.
However, pulsed sparging resulted in greater and more defined circulation of water within and adjacent to the air plume, which
should reduce mass transfer limitations during sparging. 相似文献
92.
Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals 总被引:1,自引:0,他引:1
Jorge Pousa Luigi Tosi Eduardo Kruse Dardo Guaraglia Maurizio Bonardi Andrea Mazzoldi Federica Rizzetto Enrique Schnack 《Environmental Geology》2007,51(8):1307-1316
The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic
aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors.
These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree
of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach
mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting
and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage
to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions
based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations
on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented
here. 相似文献
93.
Potential hyperaccumulation of Pb, Zn, Cu and Cd in endurant plants distributed in an old smeltery, northeast China 总被引:1,自引:0,他引:1
The absorption and accumulation of Pb, Zn, Cu and Cd in some endurant weed plant species that survived in an old smeltery
in Liaoning, China, were systematically investigated. Potential hyperaccumulative characteristics of these species were also
discussed. The results showed that metal accumulation in plants differed with species, tissues and metals. Endurant weed plants
growing in this contaminated site exhibited high metal adaptability. Both the metal exclusion and detoxification tolerance
strategies were involved in the species studied. Seven species for Pb and four species for Cd were satisfied for the concentration
time level standard for hyperaccumulator. Considering translocation factor (TF) values, one species for Pb, seven species
for Zn, two species for Cu and five species for Cd possessed the characteristic of hyperaccumulator. Particularly, Abutilon theophrasti Medic, exhibited strong accumulative ability to four heavy metals. Although enrichment coefficients of all samples were lesser
than 1 and the absolute concentrations didn’t reach the standard, species mentioned above were primarily believed to be potential
hyperaccumulators. 相似文献
94.
Enis Morkoc Legovic Tarzan Oya Okay Huseyin Tufekci Vildan Tufekci Leyla Tolun Fatma Karakoc 《Environmental Geology》2007,53(1):103-112
The Izmit Bay is an elongated semi-enclosed bay in the Marmara Sea. It is being increasingly polluted by both domestic and
industrial waste discharge since 1970’s. A monitoring program was conducted between 1999-2000 to document the state of pollution
in the bay. This includes the effect of Marmara (Izmit) earthquake (magnitude 7.4) that occurred in August 1999. A stable
two-layer ecosystem exists in the bay throughout the year due to continuous inflows of the saltier Mediterranean and brackish
Black Sea waters to the Marmara basin. Therefore, the principal biochemical characteristics of the bay are governed by the
two-layer flow system over the basin. Dissolved oxygen (DO) is generally at a saturated levels in the surface layer which
is 10 to 15 m thick, but it is depleted to 60–70 μM in the lower layer, exhibiting a steep gradient in the sharp halocline.
When the earthquake occurred, great loads of industrial wastes were released into the bay surface waters, which enhanced primary
production in the upper layer and thus large export of particulate organic matter to lower layer and eventually to the bottom.
Accordingly, DO was consumed and anoxic condition was established even in the upper layer/halocline interface, the halocline
and bottom waters of the eastern and central bay. In this period, concurrent increases were observed in phosphate and ammonia
contents at the halocline and in deep waters whilst the nitrate was almost consumed via denitrification processes in the anoxic
water. Recently, the industrial C, N and P loads increased by as much as 8 fold within five years (1995–2000) whilst domestic
inputs increased by 50%. Total organic matter discharged to the bay increased more than double within the last 15 years. Besides,
most factories in the region release toxic wastes into the bay after only partial treatment. 相似文献
95.
Tomonori Naya Yoshihiro Tanimura Yutaka Kanai Fujio Kumon Kazuo Amano 《Journal of Paleolimnology》2007,37(4):547-563
In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past
few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility
measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the
lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic
environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707)
are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater
species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the
Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could
arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change.
In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase
rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide
gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm−2 y−1) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data
gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment
of the lake after the 1970s exceed rates during the period concerned in this study. 相似文献
96.
97.
M. Mastalerz C. Souch G. M. Filippelli N. L. Dollar S. M. Perkins 《International Journal of Coal Geology》2001,46(2-4)
Cores from the Great Marsh area of the Indiana Dunes National Lakeshore were examined in order to document variations in concentration, type and size of anthropogenic organic matter (AnOM—coal, coke, etc.) and discuss their relationship to the concentration of such trace elements as Pb, Zn, and Mn in the near-surface sediment section. The results indicate that the first appearance of AnOM corresponds to the onset of industrialization in the area. There is also a general relationship between the occurrence of AnOM and Zn, Pb, and Mn. Trace metals were likely transported from the industrial sites to the area of their deposition as sulfur-bearing coatings on small anthropogenic particles. After deposition, these sulfur-bearing compounds reacted with organic matter within the marsh. As a result of bacterial reduction, the pyrite was produced, as suggested by a close relationship between the pyrite and AnOM. Distance from the industrial complex upwind as well as local hydrologic conditions are among the major factors controlling distribution of AnOM and trace elements. At the same distance from the source, types and sizes of AnOM are influenced by the duration and frequency of flooding. 相似文献
98.
Generation of Deccan Trap magmas 总被引:1,自引:0,他引:1
Gautam Sen 《Journal of Earth System Science》2001,110(4):409-431
Deccan Trap magmas may have erupted through multiple centers, the most prominent of which may have been a shield volcano-like
structure in the Western Ghats area. The lavas are predominantly tholeiitic; alkalic mafic lavas and carbonatites are rare.
Radioisotope dating, magnetic chronology, and age constraints from paleontology indicate that although the eruption started
some 68 Ma, the bulk of lavas erupted at around 65–66 Ma. Paleomagnetic constraints indicate an uncertainty of ± 500,000 years
for peak volcanic activity at 65 m.y. in the type section of the Western Ghats. Maximum magma residence times were calculated
in this study based on growth rates of “giant plagioclase” crystals in lavas that marked the end phase of volcanic activity
of different magma chambers. These calculations suggest that the > 1.7 km thick Western Ghats section might have erupted within
a much shorter time interval of ∼ 55,000 years, implying phenomenal eruption rates that are orders of magnitude larger than
any present-day eruption rate from any tectonic environment. Other significant observations/conclusions are as follows: (1)
Deccan lavas can be grouped into stratigraphic subdivisions based on their geochemistry; (2) While some formations are relatively
uncontaminated others are strongly contaminated by the continental crust; (3) Deccan magmas were produced by 15–30% melting
of a Fe-rich lherzolitic source at ∼ 3–2 GPa; (4) Parent magmas of the relatively uncontaminated Ambenali formation had a
primitive composition with 16%MgO, 47%SiO2; (5) Deccan magmas were generated much deeper and by significantly more melting than other continental flood basalt provinces;
(6) The erupted Deccan tholeiitic lavas underwent fractionation and magma mixing at ∼ 0.2 GPa. The composition and origin
of the crust and crust/mantle boundary beneath the Deccan are discussed with respect to the influence of Deccan magmatic episode. 相似文献
99.
Pollution vulnerability of the Quaternary aquifer near Cairo, Egypt, as indicated by isotopes and hydrochemistry 总被引:2,自引:1,他引:2
The present study was conducted to delineate the pollution vulnerability of the Quaternary aquifer in two areas, Imbaba and
Shobra El-Khima, near Cairo, Egypt. Environmental isotopes combined with hydrochemistry were used for this purpose. The groundwater
in the Imbaba area (average total dissolved solids about 900 mg/L; sodium/chloride, sulfate, and bicarbonate water types)
is more mineralized than groundwater in the Shobra El-Khima area (average total dissolved solids 500 mg/L; calcium and sodium/bicarbonate
water type). A high nitrate content and significant mineralization in the groundwater are probably due to contamination of
recharge to the aquifer by irrigation drainage, deteriorated sewage networks, and septic tanks. The deuterium and oxygen-18
compositions of the groundwater are depleted compared to Nile River water, which is the main source of aquifer recharge. This
less isotopically enriched water probably represents older Nile water recharge that flooded the region before construction
of the Aswan High Dam in 1963, or it is a mixture of a young water and originally deposited paleowater that was in deeper
horizons at a time of cooler and more humid climate. Intensive pumping has moved the paleowater higher in the aquifer. Groundwater
in the Shobra El-Khima area has higher residence time, based on the tritium concentration, than groundwater in the Imbaba
area. The percentage of the isotopically depleted water equals 75% in the Shobra El-Khima and 35% in Imbaba, and the thickness
of the clay cap above the aquifer is 38 m in Shobra El-Khima and 20 m in Imbaba. These factors are indicative of the rate
of recharge to the aquifer and were used to evaluate the pollution vulnerability in the two areas.
Electronic Publication 相似文献
100.
Groundwater samples collected from both open and bore wells in an area of about 270 km2 from Madras City, India, have been analyzed for major ions (HCO3, Cl, Si, Na, Ca, and Mg) and trace elements (As, Se, B, V, Cr, Fe, Co, Pb, Cu, Zn, Cd, Mn, Ni, Mo, and Ba). The study reveals that the quality of potable water has deteriorated to a large extent. Seawater intrusion into the aquifer has been observed in nearly 50 percent of the study area. The toxic elements (As and Se) have already exceeded the maximum permissible limits of drinking water in almost the entire city. A positive correlation of As and Se with other toxic metals such as V, Cr, Fe, B, etc., indicates that all these elements are anthropogenic in origin. Applying multivariate analysis, the source for trace elements in groundwater has been grouped into two major factors: pollution and mobilization factors. The groundwater in the study area is largely contaminated by organic effluents and reflects the intensity of pollution caused by the overlying soil sediment and rapid infiltration of the pollutants. 相似文献