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   59351篇
  免费   922篇
  国内免费   415篇
测绘学   1260篇
大气科学   3920篇
地球物理   11619篇
地质学   21267篇
海洋学   5648篇
天文学   13643篇
综合类   106篇
自然地理   3225篇
  2022年   385篇
  2021年   708篇
  2020年   708篇
  2019年   809篇
  2018年   1688篇
  2017年   1525篇
  2016年   1796篇
  2015年   907篇
  2014年   1637篇
  2013年   3108篇
  2012年   1872篇
  2011年   2505篇
  2010年   2303篇
  2009年   2961篇
  2008年   2493篇
  2007年   2705篇
  2006年   2440篇
  2005年   1746篇
  2004年   1698篇
  2003年   1656篇
  2002年   1629篇
  2001年   1459篇
  2000年   1300篇
  1999年   1075篇
  1998年   1071篇
  1997年   1090篇
  1996年   830篇
  1995年   841篇
  1994年   786篇
  1993年   693篇
  1992年   666篇
  1991年   639篇
  1990年   648篇
  1989年   641篇
  1988年   581篇
  1987年   690篇
  1986年   620篇
  1985年   765篇
  1984年   799篇
  1983年   745篇
  1982年   674篇
  1981年   703篇
  1980年   602篇
  1979年   592篇
  1978年   571篇
  1977年   544篇
  1976年   489篇
  1975年   487篇
  1974年   480篇
  1973年   521篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In connection with the celebration of the centennial of the Institute of Electrical and Electronics Engineers (UEEE) in 1984, the history of electrical engineering in relation to the world's oceans is traced, with emphasis on the 20-year period from the 1960's to the present. Note is taken of the breadth of the cross-disciplinary interests involved, as exemplified by the active participation of a score of IEEE Societies and Professional Groups, how they organized to cooperate, the periodic meetings and annual conferences they sponsored, the publications they undertook, the tokens of recognition they adopted, and how they adapted to changes in emphasis to reflect shifts in the areas of technology served. Finally, an assessment is made of the future of the recently organized IEEE Oceanic Engineering Society.  相似文献   
52.
53.
54.
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   
55.
Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole.  相似文献   
56.
57.
58.
59.
High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D1&D2, He i D3, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics.  相似文献   
60.
OSIRIS (OH-Suppressing Infra-Red Integral-field Spectrograph) is a new facility instrument for the Keck Observatory. After seeing first light in February 2005, OSIRIS is currently undergoing commissioning. OSIRIS provides the capability of performing three-dimensional spectroscopy in the near-infrared z, J, H, and K bands at the resolution limit of the Keck II telescope, which is equipped with adaptive optics and a laser guide star. The science case for OSIRIS is summarized, and the instrument and associated data reduction software are described.  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