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   3027篇
  免费   101篇
  国内免费   130篇
测绘学   20篇
大气科学   40篇
地球物理   455篇
地质学   358篇
海洋学   47篇
天文学   2193篇
综合类   29篇
自然地理   116篇
  2024年   3篇
  2023年   2篇
  2022年   19篇
  2021年   22篇
  2020年   25篇
  2019年   22篇
  2018年   21篇
  2017年   22篇
  2016年   19篇
  2015年   32篇
  2014年   53篇
  2013年   40篇
  2012年   47篇
  2011年   56篇
  2010年   35篇
  2009年   252篇
  2008年   261篇
  2007年   269篇
  2006年   261篇
  2005年   263篇
  2004年   253篇
  2003年   261篇
  2002年   171篇
  2001年   169篇
  2000年   181篇
  1999年   139篇
  1998年   196篇
  1997年   27篇
  1996年   30篇
  1995年   20篇
  1994年   9篇
  1993年   10篇
  1992年   16篇
  1991年   7篇
  1990年   8篇
  1989年   17篇
  1988年   7篇
  1987年   5篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1981年   2篇
  1954年   1篇
排序方式: 共有3258条查询结果,搜索用时 15 毫秒
1.
2.
3.
We present high-resolution echelle spectroscopy of 20 stars in 16 systems catalogued as members of the TW Hydrae association, and 16 stars identified as possible new members. We have calibrated the range of coronal and chromospheric activity expected for such young stars as a function of spectral type by combining our observations with literature data for field and open cluster stars. We also compute space motions for TWA members and candidate members with proper motion measurements, using two techniques to estimate distances to stars lacking direct trigonometric parallax measurements. The mean space motion of the four TWA members with known parallaxes is  ( U , V , W : −10.0, −17.8, −4.6) km s−1  . 14 of the candidates have properties inconsistent with cluster membership; the remaining two are potential new members, although further observations are required to confirm this possibility.  相似文献   
4.
With the rapid development of space technology, earth observation technology and sky observatory technolo-gy, they have played a more and more important part in monitoring and predicting of earthquakes and volcanoes in the terres-trial land. In recent years, the related agencies have done the experiments and researches on monitoring and predicting ofearthquakes and volcanoes in the forewarning period by means of many approaches, such as satellite thermal infrared re-mote sensing (TIRS), Global Positioning System (GPS), differential interferometric synthesis aperture radar (D-INSAR),astronomical time-latitude residual anomaly, and Geographic Information Systems (GIS), etc. A quite large number of re-search foundation has been built in the fundamental theories and application methods. The experiments and researcheshave shown that these technology is efficient methods for high frequency crust movement. If the existed separate scientificforces and results are possibly assembled together to form a more complete integration monitoring system with the combina-tion of space, sky observation, ground, deep geology and macro anomaly, it will come into a new stage of monitoring andpredicting of earthquakes and volcanic eruptions.  相似文献   
5.
6.
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars.  相似文献   
7.
8.
9.
10.
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