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   132216篇
  免费   2425篇
  国内免费   928篇
测绘学   3097篇
大气科学   9357篇
地球物理   26420篇
地质学   46676篇
海洋学   11971篇
天文学   29390篇
综合类   337篇
自然地理   8321篇
  2021年   1256篇
  2020年   1469篇
  2019年   1596篇
  2018年   3341篇
  2017年   3148篇
  2016年   3737篇
  2015年   2121篇
  2014年   3611篇
  2013年   6825篇
  2012年   3910篇
  2011年   5267篇
  2010年   4682篇
  2009年   6160篇
  2008年   5431篇
  2007年   5335篇
  2006年   5139篇
  2005年   4221篇
  2004年   4274篇
  2003年   3930篇
  2002年   3601篇
  2001年   3137篇
  2000年   3085篇
  1999年   2564篇
  1998年   2588篇
  1997年   2417篇
  1996年   1926篇
  1995年   2062篇
  1994年   1805篇
  1993年   1698篇
  1992年   1585篇
  1991年   1532篇
  1990年   1642篇
  1989年   1424篇
  1988年   1290篇
  1987年   1554篇
  1986年   1364篇
  1985年   1697篇
  1984年   1975篇
  1983年   1880篇
  1982年   1719篇
  1981年   1623篇
  1980年   1425篇
  1979年   1372篇
  1978年   1392篇
  1977年   1247篇
  1976年   1192篇
  1975年   1166篇
  1974年   1152篇
  1973年   1212篇
  1972年   737篇
排序方式: 共有10000条查询结果,搜索用时 195 毫秒
61.
62.
63.
The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause.  相似文献   
64.
65.
66.
67.
68.
69.
Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit.  相似文献   
70.
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