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   88620篇
  免费   1508篇
  国内免费   609篇
测绘学   1884篇
大气科学   5839篇
地球物理   17148篇
地质学   32004篇
海洋学   8151篇
天文学   20440篇
综合类   238篇
自然地理   5033篇
  2022年   644篇
  2021年   1074篇
  2020年   1157篇
  2019年   1300篇
  2018年   2616篇
  2017年   2441篇
  2016年   2812篇
  2015年   1443篇
  2014年   2720篇
  2013年   4700篇
  2012年   2964篇
  2011年   3881篇
  2010年   3510篇
  2009年   4431篇
  2008年   3908篇
  2007年   4002篇
  2006年   3700篇
  2005年   2649篇
  2004年   2553篇
  2003年   2411篇
  2002年   2380篇
  2001年   2033篇
  2000年   2028篇
  1999年   1584篇
  1998年   1653篇
  1997年   1511篇
  1996年   1293篇
  1995年   1281篇
  1994年   1085篇
  1993年   1042篇
  1992年   965篇
  1991年   997篇
  1990年   960篇
  1989年   845篇
  1988年   781篇
  1987年   912篇
  1986年   807篇
  1985年   988篇
  1984年   1104篇
  1983年   1070篇
  1982年   992篇
  1981年   938篇
  1980年   834篇
  1979年   783篇
  1978年   763篇
  1977年   641篇
  1976年   649篇
  1975年   633篇
  1974年   619篇
  1973年   682篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
We study the ion dynamics in a magnetic field reversal with a constant electric field and with a model of three dimensional magnetic turbulence. By computing the mean square displacements in the plane of the current sheet we find superdiffusive and superballistic transport regimes. Since velocity increases with the length of the free path, we have accelerated Lévyflights. The possibility to generate power law velocity distribution functions is pointed out, as well as the long memory effects and non local properties of ion transport. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
192.
International programs of observations of selected minor planets have lasted about 50 years and the last one comes to the end in 2000. The main aim of these observational programs consists in obtaining the orientation of the stellar reference frame with respect to the dynamical one using observations of the bright minor planets. The observations are also useful for the orbital improvements of the asteroids themselves. They are available from the author via e-mail at the address .During the above mentioned period more than 23 000 observations of minor planets, referred to different reference star catalogues, have been obtained. The reduction procedure of observations to the PPM star catalogue is described. The orientation parameters are given and discussed.  相似文献   
193.
194.
We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that, in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations also indicate that the dust driven winds may only occur in cool, luminous, low mass objects. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   
195.
 Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need for detailed analysis and intercomparison in order to understand and reduce the disagreements. Received: 1 September 2000 / Accepted: 20 April 2001  相似文献   
196.
Indonesia is one of the most rapidly developing nations in the world. One important component of its transformation is an industrialisation policy which sees its people utilised by transnational corporations as sources of cheap labour for export goods processing. This has both positive and negative outcomes. This paper explores these issues in a review of Indonesian development strategy with particular reference to Batam Island in Riau Province.  相似文献   
197.
198.
199.
We review the present understanding of interstellar CH+. We show that the essential chemistry was correctly identified by Bates and Spitzer in 1951. More recent work has been concerned with defining appropriate venues within which this chemistry can function efficiently. This process had led to a much fuller understanding of the nature of the interstellar medium.  相似文献   
200.
Robe's restricted three-body problem is reanalyzed with a view to incorporate a new assumption, namely that the configuration of the fluid body is that described by an hydrostatic equilibrium figure (Roche's ellipsoid). In the concomitant gravitational field a full treatment of the buoyancy force is given. The pertinent equations of motion are derived, the linear stability of the equilibrium solution is studied and the connection between the effect of the buoyancy forces and a perturbation of the Coriolis force is pointed out.  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