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   41626篇
  免费   815篇
  国内免费   272篇
测绘学   790篇
大气科学   2839篇
地球物理   8271篇
地质学   15081篇
海洋学   3815篇
天文学   9143篇
综合类   96篇
自然地理   2678篇
  2022年   266篇
  2021年   472篇
  2020年   531篇
  2019年   616篇
  2018年   1065篇
  2017年   1069篇
  2016年   1138篇
  2015年   644篇
  2014年   1092篇
  2013年   2009篇
  2012年   1266篇
  2011年   1749篇
  2010年   1565篇
  2009年   1938篇
  2008年   1741篇
  2007年   1780篇
  2006年   1657篇
  2005年   1147篇
  2004年   1153篇
  2003年   1178篇
  2002年   1064篇
  2001年   931篇
  2000年   832篇
  1999年   766篇
  1998年   765篇
  1997年   759篇
  1996年   640篇
  1995年   604篇
  1994年   539篇
  1993年   489篇
  1992年   452篇
  1991年   465篇
  1990年   480篇
  1989年   427篇
  1988年   412篇
  1987年   441篇
  1986年   448篇
  1985年   564篇
  1984年   608篇
  1983年   613篇
  1982年   546篇
  1981年   493篇
  1980年   477篇
  1979年   451篇
  1978年   419篇
  1977年   422篇
  1976年   377篇
  1975年   380篇
  1974年   367篇
  1973年   400篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
221.
The southwest monsoon that dominated Central Himalaya has preserved loessic silt deposits preserved in patches that are proximal to periglacial areas. The occurrence of such silts suggests contemporary prevalence of cold and dry northwesterly winds. Field stratigraphy, geochemistry, mineral magnetism, infrared stimulated luminescence (IRSL) and radiocarbon dating has enabled reconstruction of an event chronology during the past 20 ka. Three events of loess accretion could be identified. The first two events of loess deposition occurred betweem 20 and 9 ka and were separated by a phase of moderate weathering. Pedogenesis at the end of this event gave rise to a well‐developed soil that was bracketed around 9 to > 4 ka. This was followed by the third phase of loess accretion that occurred around 4 to > 1 ka. Episodes of loess deposition and soil formation are interpreted in terms of changes in the strength of the Indian southwest monsoon. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
222.
223.
224.
225.
CO maps of the Bok globule B335 are presented and used to derive its density profile, mass distribution, and rotational velocity structure. It is found that the cloud is in nearly hydrostatic equilibrium with a density profile that varies roughly as r?1 in the core and r?3 in the envelope. The observed rotation is unimportant in the force balance at the present stage of evolution.  相似文献   
226.
227.
228.
The BATSE and OSSE instrument teams have modified flight software to promptly (within 2 min of trigger) slew the OSSE detectors to burst locations determined on-board by BATSE. This enables OSSE to make sensitive searches for prompt and delayed post-burst line and continuum emission above 50 keV. In the best cases our sensitivity will be more than an order of magnitude better than any other search in this energy range. We expect to slew to 1–2 bursts per month, based on the OSSE FOV and BATSE event rate. Detections or limits from continued operation of this system may provide significant constraints on burst models. As an example of the observations made using this system, we present preliminary limits for post-burst emission from GRB 950223 on several time scales.  相似文献   
229.
230.
We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702  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