全文获取类型
收费全文 | 104265篇 |
免费 | 1468篇 |
国内免费 | 632篇 |
专业分类
测绘学 | 2466篇 |
大气科学 | 6991篇 |
地球物理 | 19442篇 |
地质学 | 39499篇 |
海洋学 | 9048篇 |
天文学 | 23102篇 |
综合类 | 370篇 |
自然地理 | 5447篇 |
出版年
2022年 | 658篇 |
2021年 | 1114篇 |
2020年 | 1172篇 |
2019年 | 1323篇 |
2018年 | 4416篇 |
2017年 | 3986篇 |
2016年 | 3783篇 |
2015年 | 1524篇 |
2014年 | 2833篇 |
2013年 | 4801篇 |
2012年 | 3664篇 |
2011年 | 5553篇 |
2010年 | 4966篇 |
2009年 | 6067篇 |
2008年 | 5180篇 |
2007年 | 5618篇 |
2006年 | 3822篇 |
2005年 | 2932篇 |
2004年 | 2838篇 |
2003年 | 2734篇 |
2002年 | 2614篇 |
2001年 | 2140篇 |
2000年 | 2127篇 |
1999年 | 1644篇 |
1998年 | 1717篇 |
1997年 | 1571篇 |
1996年 | 1322篇 |
1995年 | 1329篇 |
1994年 | 1121篇 |
1993年 | 1067篇 |
1992年 | 981篇 |
1991年 | 1034篇 |
1990年 | 1008篇 |
1989年 | 866篇 |
1988年 | 801篇 |
1987年 | 962篇 |
1986年 | 824篇 |
1985年 | 1022篇 |
1984年 | 1142篇 |
1983年 | 1118篇 |
1982年 | 1015篇 |
1981年 | 965篇 |
1980年 | 884篇 |
1979年 | 814篇 |
1978年 | 790篇 |
1977年 | 681篇 |
1976年 | 675篇 |
1975年 | 659篇 |
1974年 | 653篇 |
1973年 | 708篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
821.
The mechanism of the effect of a collapsing turbulent eddy on diapycnal transport in a stably stratified fluid is considered. It is shown that at small Richardson turbulent numbersRi
0 the mixing efficiency increases asRi
0, and at large numbers it decreases in proportion toRi
0
–1/2
.Translated by Mikhail M. Trufanov. UDK 551.465.15. 相似文献
822.
Peculiarities of the dynamics and the structure formation in the estuary run-off lenses have been analysed based on field data obtained at the Guinean coast (the central eastern Atlantic Ocean). Attention was paid to the processes of restratification, internal mixing, and exchange in the areas of the frontal zone of the run-off lens and the tidal frontal zone. The stabilization of the front of the estuary run-off lens by means of the periodic washing out of its forepart by tidal upwelling is described. The mechanisms of the energy transformation in the leading part of the lens have been revealed. Effects of run-off and loczalization of transformed waters in the small-scale frontal zones are found. The energy estimations represented will be useful in considering analogous phenomena in other coastal regions.Translated by Mikhail M. Trufanov. 相似文献
823.
M. I. Fortus 《Izvestiya Atmospheric and Oceanic Physics》2007,43(5):555-568
In connection with the problem of revealing cause-effect relations among different climatic characteristics, methods for determining the dependence between time series on the basis of selected auto-and cross-covariance functions and periodograms expressed in terms of the Fourier coefficients of the initial series are discussed. Real time series do not always satisfy the conditions of statistical stationarity, so that their analysis requires a combination of statistical and deterministic approaches. The possibility of using the above numerical characteristics in relation to such series is considered. Characteristic features of describing finite segments of time series with the use of their Fourier coefficients is studied in detail. The main emphasis is on the determination of the time shifts (delays) at which the covariance between the series is maximal. The problems that appear during a practical implementation of the periodogram method for shift estimation are discussed. A previously unknown formula that is necessary for further studies and relates the Fourier transform of a selected correlation function to the periodogram of the series is derived. 相似文献
824.
825.
The data on the species composition, trophic structure, and distribution of macrozoobenthos in Amur Bay obtained in 2001 are presented. Long-term changes in the benthos are analyzed. In 2001, the total benthos biomass significantly increased, although the parameters of the species richness declined as compared to 1986–1989. In 2001, as well as in the 1970s and 1980s, the benthos trophic structure was characterized by the prevalence of deposit feeders. The entire structure of the benthos is evaluated as an eutrophic one. Eutrophication of the bay is considered to be the most probable cause of the negative changes in the benthic communities of the bay in 2001, as well as 15 years ago. 相似文献
826.
827.
Martina A. Doblin Stephen B. Baines Lynda S. Cutter Gregory A. Cutter 《Estuarine, Coastal and Shelf Science》2006,67(4):681-694
As part of a study of estuarine selenium cycling, we measured the concentration, chemical form (speciation), and distribution of particulate selenium under various river flow conditions in the North San Francisco Bay (from the Golden Gate to the Sacramento and San Joaquin Rivers). We also conducted laboratory studies on the accumulation of selenium by phytoplankton, the critical first step in the transformation of dissolved to particulate selenium. Total particulate selenium concentration in the North SF Bay was relatively constant between high and low flow periods, ranging spatially from 0.05 to 0.35 nmol l−1 and comprising between 5 and 12% of the total water column selenium inventory. Mean concentrations were generally highest in the Carquinez Strait–Suisun Bay region (salinity 0–17) and lowest in Central Bay. However, selenium content of suspended particles varied with river flow, with higher content during low flow (9.76 ± 4.17 nmol g−1; mean ± sd; n = 67) compared to high flow (7.10 ± 4.24 nmol g−1; n = 39). Speciation analyses showed that most particulate selenium is organic selenide (45 ± 27%), with a smaller proportion (typically <30%) of adsorbed selenite + selenate and a varying proportion (35 ± 28%) of elemental selenium. Based on the amount of elemental selenium in the seston (total suspended material), we calculate that resuspension of estuarine sediments could contribute 29–100% of particulate selenium in the water column. While selenium content of SF Bay seston (>0.4 μm) is relatively unenriched compared to phytoplankton (13.6–155 nmol g−1 dry weight) on a mass basis, when normalized to carbon or nitrogen, seston contains a similar selenium concentration to SF Bay sediments or phytoplankton cultures. SF Bay seston is thus comprised of selenium-rich phytoplankton and phyto-detritus, but also inorganic clay mineral particles that effectively “dilute” total particulate selenium. Selenium concentrations in algal cultures (11 species) exposed to 90 nmol l−1 selenite show relatively large differences in selenium accumulation, with the diatoms, chlorophytes and cryptophytes generally having lower selenium cell content (3.8 ± 2.7 × 10−9 nmol selenium cell−1) compared to the dinoflagellates (193 ± 73 × 10−9 nmol selenium cell−1). Because phytoplankton are such a rich (but variable) source of selenium, their dynamics could have a profound effect on the particulate selenium inventory in the North SF Bay. 相似文献
828.
The paper presents a non-linear buckling analysis of ring stiffened cylindrical shells subject to external pressure. The collapse pressure is calculated by assuming failure to occur when the material reaches a plastic stress state defined by the Ilyushin criterion. It is shown in the paper that use of the non-linear theory can reduce the estimated first yield by up to 25% in comparison to the linear buckling analysis used up to now. Comparison of predicted failure loads are in good agreement with the lower bound of test results. 相似文献
829.
Long-term changes in ray populations in the North Sea 总被引:2,自引:3,他引:2
830.