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   79295篇
  免费   896篇
  国内免费   715篇
测绘学   1909篇
大气科学   4992篇
地球物理   15177篇
地质学   28852篇
海洋学   7286篇
天文学   19027篇
综合类   268篇
自然地理   3395篇
  2022年   667篇
  2021年   1046篇
  2020年   1123篇
  2019年   1218篇
  2018年   2628篇
  2017年   2473篇
  2016年   2894篇
  2015年   1414篇
  2014年   2679篇
  2013年   4182篇
  2012年   2925篇
  2011年   3635篇
  2010年   3299篇
  2009年   4036篇
  2008年   3527篇
  2007年   3694篇
  2006年   3377篇
  2005年   2255篇
  2004年   2222篇
  2003年   2125篇
  2002年   2015篇
  2001年   1854篇
  2000年   1695篇
  1999年   1301篇
  1998年   1345篇
  1997年   1289篇
  1996年   1066篇
  1995年   1069篇
  1994年   937篇
  1993年   813篇
  1992年   808篇
  1991年   815篇
  1990年   877篇
  1989年   689篇
  1988年   713篇
  1987年   733篇
  1986年   640篇
  1985年   845篇
  1984年   910篇
  1983年   807篇
  1982年   774篇
  1981年   684篇
  1980年   687篇
  1979年   633篇
  1978年   650篇
  1977年   531篇
  1976年   495篇
  1975年   504篇
  1974年   451篇
  1973年   507篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%.  相似文献   
94.
The laboratory simulation experiments on volatilization from the melts formed due to micrometeoroid impacts on the lunar surface were carried out. The simulation was performed using modulated laser pulses incident on rocks and minerals in vacuum; in so doing microcraters on the targets, glass particles, condensates were formed and gases solved in the bulk of the rock and mineral grains were released. It is shown that volatilization from only the crater glass layers is negligible, which fully confirms the theoretical predictions of Nussinov and Chernyak.The volatilizations from the drops formed by the micrometeoric impacts can be noticeable. For micron-sized drops, predominant among the others after the impact, the volatilization of Na, K and other volatiles can be up to 10 to 20%. For larger-sized (d102 m) drops the volatilization should lead to the appearance of the significant gradients of the element concentrations over the particle cross-section and as a result of their normalization it leads to the surface enrichment by some elements (Si and others).The mechanism of dust formation due to the surface rocks attack by volatilizing alkaline metals (Naughtonet al.) on the Moon probably is not effective. It is the consequence of such a fact that the condensate of the target materials evaporated due to other simultaneous micrometeoric impacts and had the same (as the target has) elemental composition is the very strong background for volatilizing and condensating alkaline elements.Preliminary conclusions about a possible correlation between the composition and the sizes of dust particles in the Solar system and in the Universe (at similar initial composition) have been drawn.  相似文献   
95.
F.A. Gifford  R.P. Hosker  K.S. Rao 《Icarus》1978,36(1):133-146
The spreading angle of a number of light and dark Martian streaks is determined from selected Mariner 9 images. The resulting frequency distributions of spreading half-angles have maxima at ~5° for light, and ~7° for dark streaks; however the dark streaks have a secondary maximum spreading angle at ~14°. The smaller values, which include most streaks, are interpreted as crater-wake spreading phenomena. The larger value, found in only a few dark streaks or “tails,” may result from atmospheric diffusion and subsequent deposition of material from isolated sources such as vents or blowouts. An atmospheric diffusion-deposition analysis is presented, assuming this streak origin, from which it is possible to deduce the eddy diffusivity, K, in Mars' boudary layer. Calculated K values are found to agree with various theoretical estimates. They lie in the range 107 and 109 cm2 sec?1 and exhibit the proper scale dependence. Thus it appears that, in addition to streak-derived wind direction patterns and speed information, it is possible in a few cases to derive information on Mars' boundary-layer turbulence from streak-spreading measurements.  相似文献   
96.
97.
98.
99.
100.
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