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   131995篇
  免费   2386篇
  国内免费   932篇
测绘学   3050篇
大气科学   9248篇
地球物理   26340篇
地质学   46505篇
海洋学   11925篇
天文学   29594篇
综合类   325篇
自然地理   8326篇
  2021年   1269篇
  2020年   1471篇
  2019年   1610篇
  2018年   3197篇
  2017年   2998篇
  2016年   3674篇
  2015年   2076篇
  2014年   3576篇
  2013年   6835篇
  2012年   3845篇
  2011年   5217篇
  2010年   4696篇
  2009年   6169篇
  2008年   5441篇
  2007年   5345篇
  2006年   5142篇
  2005年   3940篇
  2004年   3911篇
  2003年   3678篇
  2002年   3584篇
  2001年   3140篇
  2000年   3094篇
  1999年   2574篇
  1998年   2594篇
  1997年   2440篇
  1996年   2159篇
  1995年   2103篇
  1994年   1843篇
  1993年   1748篇
  1992年   1631篇
  1991年   1567篇
  1990年   1683篇
  1989年   1489篇
  1988年   1331篇
  1987年   1606篇
  1986年   1417篇
  1985年   1729篇
  1984年   2002篇
  1983年   1910篇
  1982年   1750篇
  1981年   1651篇
  1980年   1440篇
  1979年   1405篇
  1978年   1410篇
  1977年   1267篇
  1976年   1215篇
  1975年   1187篇
  1974年   1168篇
  1973年   1223篇
  1972年   747篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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   
22.
23.
24.
25.
26.
27.
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   
28.
29.
30.
The surface digital photometry for NGC 5253 and NGC 2915 is given. The luminosity profiles and colour gradients are discussed and compared. It is concluded that NGC 2915 differs from NGC 5253, both in the extension and intensity of the star burst event because of the kinematical behaviour of the captured gas.CONICET, Buenos Aires, Visiting Astronomer, Cerro Tololo Inter-American Observatory, La Serena, Chile, operated by NSF  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