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   23623篇
  免费   2177篇
  国内免费   3147篇
测绘学   1158篇
大气科学   3033篇
地球物理   4933篇
地质学   10645篇
海洋学   2887篇
天文学   3062篇
综合类   1027篇
自然地理   2202篇
  2024年   126篇
  2023年   340篇
  2022年   770篇
  2021年   1045篇
  2020年   945篇
  2019年   1012篇
  2018年   1287篇
  2017年   1200篇
  2016年   1268篇
  2015年   941篇
  2014年   1193篇
  2013年   1450篇
  2012年   1274篇
  2011年   1446篇
  2010年   1288篇
  2009年   1331篇
  2008年   1235篇
  2007年   1222篇
  2006年   1097篇
  2005年   689篇
  2004年   636篇
  2003年   637篇
  2002年   714篇
  2001年   570篇
  2000年   487篇
  1999年   467篇
  1998年   399篇
  1997年   389篇
  1996年   345篇
  1995年   339篇
  1994年   322篇
  1993年   255篇
  1992年   252篇
  1991年   178篇
  1990年   149篇
  1989年   161篇
  1988年   136篇
  1987年   115篇
  1986年   113篇
  1985年   113篇
  1984年   106篇
  1983年   117篇
  1982年   98篇
  1981年   93篇
  1980年   79篇
  1979年   96篇
  1978年   68篇
  1977年   52篇
  1975年   50篇
  1973年   47篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Various measures including material experiments, centrifuge modeling tests and FEM numerical analyses were performed to study systematically the action mechanism of the geotextile-reinforced cushion under breakwater on soft ground and the effects of the strata characterization and the reinforcement condition on the stability of the breakwater-ground system. In the aspect of controlling the deformation, the geotextile-reinforced cushion under breakwater constrains the lateral displacement of both the embankment and the ground. From the viewpoint of stress, the reinforcement suppressed the range of high stress level in the system. In general, the weaker the ground is and the greater the modulus of the geotextile is, the more effective the reinforcement is. The tensile force in the geotextile is greater in the range of the main part of the embankment.  相似文献   
32.
33.
A small, inexpensive, and easily deployable meteorological buoy is described. Buoy motion is greatly reduced by appropriate ballast techniques; vector averaging further removes buoy motion effects from wind data. Data is transmitted to the GOES satellite and is retrieved by telephone. Measurements are vector-averaged wind components, wind speed, wind direction, water temperature, air temperature, and compass direction. Data from two field trials are discussed. Speed comparisons averaged 0.2 m sec−1 with a standard deviation of 0.6 m sec−1. Direction comparisons were different due to local topography, but they indicate a probable accuracy of ±5°.  相似文献   
34.
35.
This paper presents a method to evaluate statistical properties of half-cycle excursions including extreme values. The probability density function for half-cycle excursions for an arbitrarily given wave spectrum is developed based on the Gaussian assumption. The results of numerical computations carried out using wave data obtained during hurricane Camille show that the half-cycle probability density function agrees well with the histogram constructed from the data. The extreme wave height for design consideration computed with risk parameter 0.01 is approximately 20% greater than the observed extreme height.  相似文献   
36.
The model of the pulsar magnetosphere filled with massless charged particles (rest massm=0) is considered. The gas of charged massless particles can be found in two different phases: (1) dynamical phase (DP), when the particles move with nonvanishing energy along some base line, determined by the electromagnetic field only, (2) statical phase (SP), when the particles have vanishing energy =0. The pulsar magnetosphere occurs to be divided into regions of different types: (a) the accelerating regions (DP-regions) containing only DP, (b) the capture regions, containing only SP, (3) leaky capture regions, where DP moves through SP. The leaky capture regions are the active regions, which are responsible for the pulsar radioemission. In the case of oblique magnetic moment the equation for the capture surface has been obtained. The capture region is formed around this surface. Expressions for jumps of the electromagnetic field, the current density and the charge density on the capture region boundary have been obtained. The problem of the pulsar magnetosphere is stated mathematically in the case of oblique magnetic moment and ejection of only electrons.  相似文献   
37.
38.
39.
40.
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