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571.
572.
Xiuju Liu Steven M. Colman Erik T. Brown Andrew C. G. Henderson Josef P. Werne Jonathan A. Holmes 《Journal of Paleolimnology》2014,51(2):223-240
We inferred the climate history for Central Asia over the past 20,000 years, using sediments from core QH07, taken in the southeastern basin of Lake Qinghai, which lies at the northeastern margin of the Tibetan Plateau. Results from multiple environmental indicators are internally consistent and yield a clear late Pleistocene and Holocene climate record. Carbonate content and total organic carbon (TOC) in Lake Qinghai sediments are interpreted as indicators of the strength of the Asian summer monsoon. Warm and wet intervals, associated with increased monsoon strength, are indicated by increased carbonate and TOC content. During the glacial period (~20,000 to ~14,600 cal year BP), summer monsoon intensity remained low and relatively constant at Lake Qinghai, suggesting cool, dry, and relatively stable climate conditions. The inferred stable, cold, arid environment of the glacial maximum seems to persist through the Younger Dryas time period, and little or no evidence of a warm interval correlative with the Bølling–Allerød is found in the QH07 record. The transition between the late Pleistocene and the Holocene, about 11,500 cal year BP, was abrupt, more so than indicated by speleothems in eastern China. The Holocene (~11,500 cal year BP to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the late Pleistocene. The warmest, wettest part of the Holocene, marked by increased organic matter and carbonate contents, occurred from ~11,500 to ~9,000 cal year BP, consistent with maximum summer insolation contrast between 30°N and 15°N. A gradual reduction in precipitation (weakened summer monsoon) is inferred from decreased carbonate content through the course of the Holocene. We propose that changes in the contrast of summer insolation between 30°N and 15°N are the primary control on the Asian monsoon system over glacial/interglacial time scales. Secondary influences may include regional and global albedo changes attributable to ice-cover and vegetation shifts and sea level changes (distance from moisture source in Pacific Ocean). The abruptness of the change at the beginning of the Holocene, combined with an increase in variability, suggest a threshold for the arrival of monsoonal rainfall at the northeastern edge of the Tibetan Plateau. 相似文献
573.
Federico Manzini Virginio Oldani Roberto Crippa José Borrero Erik Bryssink Martin Mobberley Joel Nicolas 《Astrophysics and Space Science》2014,351(2):435-450
Extensive observations of comet 260P/McNaught were carried out between August 2012 and January 2013. The images obtained were used to analyze the comet’s inner coma morphology at resolutions ranging from 250 to about 1000 km/pixel. A deep investigation of the dust features in the inner coma allowed us to identify only a single main active source on the comet’s nucleus, at an estimated latitude of ?50°±15°. A thorough analysis of the appearance and of the motion of the morphological structures, supported by graphic simulations of the geometrical conditions of the observations, allowed us to determine a pole orientation located within a circular spot of a 15°-radius centered at RA=60°, Dec=0°. The rotation of the nucleus seems to occur on a single axis and is not chaotic, furthermore no precession effects could be estimated from our measurements. The comet’s spin axis never reached the plane of the sky from October 2012 to January 2013; during this period it did not change its direction significantly (less than 30°), thus giving us the opportunity to observe mainly structures such as bow-shaped jets departing from the single active source located on the comet’s nucleus. Only during the months of August 2012 and January 2013 the polar axis was directed towards the Earth at an angle of about 45° from the plane of the sky; this made it possible to observe the development of faint structures like fragments of shells or spirals. A possible rotation period of 0.340±0.01 days was estimated by means of differential photometric analysis. 相似文献
574.
The simulation of European heat waves from an ensemble of regional climate models within the EURO-CORDEX project 总被引:4,自引:1,他引:3
Robert Vautard Andreas Gobiet Daniela Jacob Michal Belda Augustin Colette Michel Déqué Jesús Fernández Markel García-Díez Klaus Goergen Ivan Güttler Tomáš Halenka Theodore Karacostas Eleni Katragkou Klaus Keuler Sven Kotlarski Stephanie Mayer Erik van Meijgaard Grigory Nikulin Mirta Patarčić John Scinocca Stefan Sobolowski Martin Suklitsch Claas Teichmann Kirsten Warrach-Sagi Volker Wulfmeyer Pascal Yiou 《Climate Dynamics》2013,41(9-10):2555-2575
The ability of a large ensemble of regional climate models to accurately simulate heat waves at the regional scale of Europe was evaluated. Within the EURO-CORDEX project, several state-of-the art models, including non-hydrostatic meso-scale models, were run for an extended time period (20 years) at high resolution (12 km), over a large domain allowing for the first time the simultaneous representation of atmospheric phenomena over a large range of spatial scales. Eight models were run in this configuration, and thirteen models were run at a classical resolution of 50 km. The models were driven with the same boundary conditions, the ERA-Interim re-analysis, and except for one simulation, no observations were assimilated in the inner domain. Results, which are compared with daily temperature and precipitation observations (ECA&D and E-OBS data sets) show that, even forced by the same re-analysis, the ensemble exhibits a large spread. A preliminary analysis of the sources of spread, using in particular simulations of the same model with different parameterizations, shows that the simulation of hot temperature is primarily sensitive to the convection and the microphysics schemes, which affect incoming energy and the Bowen ratio. Further, most models exhibit an overestimation of summertime temperature extremes in Mediterranean regions and an underestimation over Scandinavia. Even after bias removal, the simulated heat wave events were found to be too persistent, but a higher resolution reduced this deficiency. The amplitude of events as well as the variability beyond the 90th percentile threshold were found to be too strong in almost all simulations and increasing resolution did not generally improve this deficiency. Resolution increase was also shown to induce large-scale 90th percentile warming or cooling for some models, with beneficial or detrimental effects on the overall biases. Even though full causality cannot be established on the basis of this evaluation work, the drivers of such regional differences were shown to be linked to changes in precipitation due to resolution changes, affecting the energy partitioning. Finally, the inter-annual sequence of hot summers over central/southern Europe was found to be fairly well simulated in most experiments despite an overestimation of the number of hot days and of the variability. The accurate simulation of inter-annual variability for a few models is independent of the model bias. This indicates that internal variability of high summer temperatures should not play a major role in controlling inter-annual variability. Despite some improvements, especially along coastlines, the analyses conducted here did not allow us to generally conclude that a higher resolution is clearly beneficial for a correct representation of heat waves by regional climate models. Even though local-scale feedbacks should be better represented at high resolution, combinations of parameterizations have to be improved or adapted accordingly. 相似文献
575.
Abstract This paper examines implementation of the Kyoto Protocol without Russia. It concludes that implementation without Russia is possible, although it requires political will on the part of the countries that wish to proceed with the Protocol. It would lead to higher compliance costs for Annex B buyer regions, but other regions, except Russia, would benefit financially. Russia would forego revenue of at least $20 billion for the first commitment period. Implementation without Russia could improve the environmental performance of the Protocol. It would reduce reliance on Annex B sinks, use of surplus assigned amount units (AAUs) for compliance, and the quantity of Kyoto units banked for subsequent commitment periods. Actual emissions by Kyoto Protocol Parties would fall, but the reduction may be offset by leakage to the US and Russia. 相似文献
576.
Hansson T Schiedek D Lehtonen KK Vuorinen PJ Liewenborg B Noaksson E Tjärnlund U Hanson M Balk L 《Marine pollution bulletin》2006,53(8-9):451-468
A battery of biochemical biomarkers and the SigmaPCB concentration in adult female perch (Perca fluviatilis) verified an aquatic pollution gradient with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included both an upstream gradient, 46 km westwards through Lake M?laren, and a downstream gradient, 84 km eastwards through the Stockholm archipelago. Besides the main gradient from Stockholm, there were strong indications of pollution coming from the Baltic Sea. The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch, characterised by increased specific EROD activity in the liver, increased liver EROD somatic index, decreased AChE activity in the muscle, increased amount of DNA adducts in the liver, and a high concentration of biliary 1-pyrenol. In addition, laboratory exposure to common EROD inducers elicited an abnormal response, suggestive of chronic intoxication. 相似文献