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   97350篇
  免费   3282篇
  国内免费   3423篇
测绘学   2617篇
大气科学   7889篇
地球物理   18850篇
地质学   36614篇
海洋学   9675篇
天文学   20970篇
综合类   1205篇
自然地理   6235篇
  2022年   1217篇
  2021年   1785篇
  2020年   1752篇
  2019年   1931篇
  2018年   3301篇
  2017年   3051篇
  2016年   3450篇
  2015年   2022篇
  2014年   3382篇
  2013年   5251篇
  2012年   3607篇
  2011年   4527篇
  2010年   4096篇
  2009年   4957篇
  2008年   4373篇
  2007年   4452篇
  2006年   4127篇
  2005年   2889篇
  2004年   2765篇
  2003年   2651篇
  2002年   2690篇
  2001年   2378篇
  2000年   2258篇
  1999年   1884篇
  1998年   1862篇
  1997年   1756篇
  1996年   1485篇
  1995年   1481篇
  1994年   1253篇
  1993年   1172篇
  1992年   1072篇
  1991年   1061篇
  1990年   1004篇
  1989年   913篇
  1988年   818篇
  1987年   937篇
  1986年   820篇
  1985年   977篇
  1984年   1098篇
  1983年   1056篇
  1982年   970篇
  1981年   906篇
  1980年   807篇
  1979年   762篇
  1978年   735篇
  1977年   626篇
  1976年   635篇
  1975年   627篇
  1974年   597篇
  1973年   668篇
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
201.
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   
202.
203.
A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with two wide-band filter combinations. One of these combinations isolates C2 emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C2 emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion. On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 105 km from the nucleus. It is possible that this peak is related to the extended source of the C2 molecules. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
204.
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   
205.
 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   
206.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
207.
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   
208.
209.
210.
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   
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