首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   103988篇
  免费   2029篇
  国内免费   958篇
测绘学   2585篇
大气科学   7383篇
地球物理   21253篇
地质学   37195篇
海洋学   8957篇
天文学   23375篇
综合类   346篇
自然地理   5881篇
  2022年   584篇
  2021年   1003篇
  2020年   1099篇
  2019年   1148篇
  2018年   2677篇
  2017年   2505篇
  2016年   3134篇
  2015年   1865篇
  2014年   3095篇
  2013年   5504篇
  2012年   3289篇
  2011年   4376篇
  2010年   3835篇
  2009年   5096篇
  2008年   4541篇
  2007年   4340篇
  2006年   4075篇
  2005年   3228篇
  2004年   3150篇
  2003年   2930篇
  2002年   2734篇
  2001年   2519篇
  2000年   2376篇
  1999年   1974篇
  1998年   2082篇
  1997年   1951篇
  1996年   1479篇
  1995年   1632篇
  1994年   1403篇
  1993年   1282篇
  1992年   1217篇
  1991年   1154篇
  1990年   1281篇
  1989年   1079篇
  1988年   1000篇
  1987年   1257篇
  1986年   1028篇
  1985年   1336篇
  1984年   1451篇
  1983年   1412篇
  1982年   1282篇
  1981年   1197篇
  1980年   1063篇
  1979年   991篇
  1978年   1012篇
  1977年   910篇
  1976年   880篇
  1975年   841篇
  1974年   826篇
  1973年   853篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
Rostov State Pedagogical Institute; All-Union Scientific Research Institute Gradient. Translated from Astrofizika, Vol. 33, No. 3, pp. 379–393, November–December, 1990.  相似文献   
95.
The interaction of free convection with thermal radiation of the oscillatory flow past a vertical plate is studied. The Rosseland approximation is used to describe the radiative heat flux in the energy equation.  相似文献   
96.
It is shown that the kinematical parameters associated with the congruence formed by tachyonic motion can be defined in the manner of Greenberg, but not that of Ehlers. The space-like counterpart of Raychaudhuri's equation has also been obtained.  相似文献   
97.
Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR 1 =I(854.8 Å)/I(786.9 Å),R 2 =I(852.2 Å)/I(786.9 Å),R 3 =I(849.2 Å)/I(786.9 Å), andR 4 =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR 1, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed.  相似文献   
98.
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm.  相似文献   
99.
Transport by southeastern rivers has insignificant influence on the lead concentration of southeastern shelf waters. If the rate of mobilization and transport of lead by these rivers is representative of uncontaminated fluvial transport during the Pleistocene, only about 5% of the prehistoric output of lead to the North Atlantic can be accounted for by river input.Lead concentrations in southeastern shelf waters are similar to those of North Atlantic Water from the upper 1000 m, which is probably similar to the intrusion source water for the shelf. Atmospheric inputs to the shelf of the same magnitude as observed for the Western North Atlantic are difficult to reconcile given the residence time of shelf waters and their lead concentration unless the rate of loss of lead to shelf sediments is about the same as the atmospheric flux.  相似文献   
100.
A coupled continuum‐discrete hydromechanical model was employed to analyse the liquefaction of a saturated loose deposit of cohesionless particles when subjected to a dynamic base excitation. The pore fluid flow was idealized using averaged Navier–Stokes equations and the discrete element method was employed to model the solid phase particles. A well established semi‐empirical relationship was utilized to quantify the fluid–particle interactions. The conducted simulations revealed a number of salient micro‐mechanical mechanisms and response patterns associated with the deposit liquefaction. Space and time variation of porosity was a major factor which affected the coupled response of the solid and fluid phases. Pore fluid flow was within Darcy's regime. The predicted response exhibited macroscopic patterns consistent with experimental results and case histories of the liquefaction of granular soil deposits. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号