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   265853篇
  免费   4371篇
  国内免费   3409篇
测绘学   7191篇
大气科学   19489篇
地球物理   55534篇
地质学   92915篇
海洋学   22036篇
天文学   57331篇
综合类   1054篇
自然地理   18083篇
  2021年   2269篇
  2020年   2621篇
  2019年   2860篇
  2018年   4290篇
  2017年   3996篇
  2016年   6210篇
  2015年   4281篇
  2014年   7022篇
  2013年   14338篇
  2012年   6851篇
  2011年   8600篇
  2010年   7628篇
  2009年   10239篇
  2008年   8857篇
  2007年   8407篇
  2006年   9688篇
  2005年   7892篇
  2004年   7762篇
  2003年   7270篇
  2002年   6838篇
  2001年   6069篇
  2000年   5995篇
  1999年   5223篇
  1998年   5254篇
  1997年   5050篇
  1996年   4714篇
  1995年   4446篇
  1994年   4135篇
  1993年   3882篇
  1992年   3670篇
  1991年   3613篇
  1990年   3781篇
  1989年   3534篇
  1988年   3312篇
  1987年   3860篇
  1986年   3422篇
  1985年   4243篇
  1984年   4762篇
  1983年   4431篇
  1982年   4324篇
  1981年   3942篇
  1980年   3653篇
  1979年   3514篇
  1978年   3507篇
  1977年   3283篇
  1976年   3048篇
  1975年   2965篇
  1974年   2914篇
  1973年   3084篇
  1972年   2028篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Free flexural-gravity waves unevenly compressed in an ice-covered basin have been studied using a linear formulation. The conditions were specified allowing determination of the bounds of the angular area of wave disturbances and of the oscillation frequency intervals due to compression. The paper considers the distribution of the wave characteristics over frequency depending on compressive stresses and the direction of wave propagation.Translated by Vladimir A. Puchkin.  相似文献   
992.
993.
994.
Seasonal variation of global surface pressure and water vapor   总被引:1,自引:0,他引:1  
Previous studies have shown that the seasonal variation of global-mean surface pressure ( p s) results from variation of global-mean water vapor pressure ( p w). The current study, employing the global data generated by Version 1 of the Goddard Earth Observing System (GEOS-1) Data Assimilation System, shows that seasonal variations of regional p s and p w tend to be out of phase (particularly in the subtropics of the two hemispheres) and that the magnitude of the former variation is generally much larger than that of the latter. The seasonal variations of these two quantities are maintained by airmass and water vapor transports by the global divergent circulation, which is driven by the latent heat released by cumulus convection over the water vapor sink, as the "water mass forcing" mechanism predicted. Since p w and p s are used often in depicting the climate system, assessments of climate change in terms of the global-mean and regional variations of these two variables should be interpreted with caution.  相似文献   
995.
996.
A series of eight tracer experiments were carried out over one year (1983) on a low energy, macro-tidal beach in South Wales, UK. Tracer movement was monitored and 30 pebbles adjacent to coloured tracer pebbles were measured. Measurements were of the A, B, and C axes, roundness, Maximum Projection Sphericity and Oblate-Prolate indices. Analysis shows that through time, the percentage rejection of these properties increased. It is theorised that the surface tracers are 'misfits' or 'rejects' which have not found their equilibrium position in the pebble facies.  相似文献   
997.
998.
999.
1000.
The bedrock morphology of Start Bay, Southwest England, and the Structures within overlying sediments have been determined by a combined geophysical and geological survey. It has been established that the Skerries Bank consists of a drape of possibly coarse, unconsolidated material (bank deposits) overlying medium- to fine-grained silty sand (bay deposits). A break of slope in the bedrock surface, traced along the entire length of the Bay, and a step profile in the southern part of the Bay, may be either a legacy of submerged topography produced by vigorous tidal action, or alternatively the product of subaerial and marine processes. Other significant geological features in the Bay include infilled valleys, and “terraces” possibly pertaining to relict barrier beaches.  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