全文获取类型
收费全文 | 67664篇 |
免费 | 1466篇 |
国内免费 | 503篇 |
专业分类
测绘学 | 1829篇 |
大气科学 | 5396篇 |
地球物理 | 14182篇 |
地质学 | 21986篇 |
海洋学 | 5819篇 |
天文学 | 15483篇 |
综合类 | 155篇 |
自然地理 | 4783篇 |
出版年
2020年 | 520篇 |
2019年 | 531篇 |
2018年 | 1052篇 |
2017年 | 1003篇 |
2016年 | 1489篇 |
2015年 | 1120篇 |
2014年 | 1534篇 |
2013年 | 3377篇 |
2012年 | 1615篇 |
2011年 | 2390篇 |
2010年 | 2038篇 |
2009年 | 3010篇 |
2008年 | 2719篇 |
2007年 | 2443篇 |
2006年 | 2506篇 |
2005年 | 2156篇 |
2004年 | 2279篇 |
2003年 | 2088篇 |
2002年 | 2000篇 |
2001年 | 1796篇 |
2000年 | 1761篇 |
1999年 | 1520篇 |
1998年 | 1515篇 |
1997年 | 1494篇 |
1996年 | 1282篇 |
1995年 | 1223篇 |
1994年 | 1101篇 |
1993年 | 1000篇 |
1992年 | 953篇 |
1991年 | 805篇 |
1990年 | 1021篇 |
1989年 | 853篇 |
1988年 | 760篇 |
1987年 | 928篇 |
1986年 | 819篇 |
1985年 | 1026篇 |
1984年 | 1185篇 |
1983年 | 1131篇 |
1982年 | 1021篇 |
1981年 | 979篇 |
1980年 | 839篇 |
1979年 | 818篇 |
1978年 | 874篇 |
1977年 | 793篇 |
1976年 | 749篇 |
1975年 | 700篇 |
1974年 | 704篇 |
1973年 | 710篇 |
1972年 | 450篇 |
1971年 | 387篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
J.F.A. Sleath 《Coastal Engineering》1985,9(2):159-170
Measurements of energy dissipation have been made with an oscillating tray apparatus similar to that of Bagnold (1946). Two different bed profiles were examined: one was sinusoidal and the other consisted of fins projecting perpendicularly fromthe plate in a regular two-dimensional pattern. The tests with the sinusoidal profile showed that significant variation in energy dissipation coefficient with Reynolds number occurs near the point at which vortex formation first starts to take place. It is suggested that Bagnold did not observe this effect because of the particular profile used in his tests. The tests with the finned beds showed that even when vortex formation is fully developed there is still some variation in energy dissipation coefficient with Reynolds number, at constant a/ks, at high Reynolds numbers. 相似文献
163.
164.
165.
J.D. Pos 《Coastal Engineering》1985,9(2):101-123
An experimental technique and configuration has been developed by the author to simulate and measure (using short range photogrammetric techniques) the wave heights of waves diffracting into a model basin of infinite extent. The finite and infinite element program “WAVE” developed in the Department of Civil Engineering, University College of Swansea, Wales, has been modified to run on the UNIVAC 1100 at the University of Cape Town. The program is used to model the experimental configuration being tested mathematically. Two configurations, namely a symmetrical and an asymmetrical breakwater gap configuration, are analysed both experimentally and numerically. It is concluded that there is a good correlation between the finite element and experimental results and that the “WAVE” program is a very useful tool for the prediction of wave heights in large harbour basins. 相似文献
166.
167.
Sean J. McKenna 《Astrophysics and Space Science》1985,108(1):31-66
A general treatment of the transfer of polarized radiation in spectral lines assuming a Rayleigh phase function and a general law of frequency redistribution is derived. It is shown how nine families of coupled integral equations for the moments of the radiation field arise which are necessary to fully describe the state of polarization of the emergent radiation from a plane-parallel, semi-infinite atmosphere. The special case of angle independent redistribution functions is derived from the general formalism, and it is shown how the nine families of integral equations reduce to the six linearly independent integral equations derived by Collins (1972). To serve as a test of the formulation, solutions for isothermal atmospheres are given. 相似文献
168.
169.
J.LR. Touret 《地学学报》1992,4(1):87-98
The CO2 atmospheric content has shown large variations over geological times. High contents (up to one order of magnitude more than present-day values) ultimately correspond to discrete episodes of mantle degassing, either juvenile, or subduction-related (carbon recycling). A number of arguments (e.g. the continuous volume increase of carbonate-bearing sediments with time) suggest that, throughout the Earth's history, juvenile CO2 has formed a major contribution to the global carbon budget of the Earth.
The absence of a direct relationship between major volcanic episodes and the average CO2 atmospheric content suggests that volcanoes might not be the only way by which mantle CO2 is transported to the surface. It is proposed that large quantities of juvenile CO2 could temporarily be stored in the lower continental crust during major episodes of granulite formation. These are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of CO2 -bearing, mantle-derived magmas. Most of the CO2 migrates through the crust during post-metamorphic evolution and isostatic restoration of the normal continental thickness. However, large quantities of CO2 can still be present in some areas, notably as high-density fluids enclosed in minerals. 相似文献
The absence of a direct relationship between major volcanic episodes and the average CO
170.
J. D. Leatherdale 《The Photogrammetric Record》1994,14(83):759-769
Some of the economic and operational aspects of mapping are discussed, including the conditions that may offer air survey a competitive advantage over other methods. The financing of national mapping programmes around the world is increasingly market oriented, driven by the need to provide the end users with information that they can turn into sustainable economic growth and social progress. Despite these economic pressures, map makers seem to find their work more enjoyable and rewarding than most professionals. 相似文献