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   74532篇
  免费   1406篇
  国内免费   1316篇
测绘学   1920篇
大气科学   5332篇
地球物理   15225篇
地质学   26629篇
海洋学   6555篇
天文学   16965篇
综合类   341篇
自然地理   4287篇
  2022年   481篇
  2021年   809篇
  2020年   834篇
  2019年   892篇
  2018年   1768篇
  2017年   1671篇
  2016年   2020篇
  2015年   1251篇
  2014年   2009篇
  2013年   3763篇
  2012年   2390篇
  2011年   3201篇
  2010年   2815篇
  2009年   3787篇
  2008年   3170篇
  2007年   3213篇
  2006年   3024篇
  2005年   2254篇
  2004年   2183篇
  2003年   2029篇
  2002年   1937篇
  2001年   1694篇
  2000年   1651篇
  1999年   1365篇
  1998年   1416篇
  1997年   1355篇
  1996年   1164篇
  1995年   1144篇
  1994年   1005篇
  1993年   876篇
  1992年   865篇
  1991年   842篇
  1990年   957篇
  1989年   819篇
  1988年   765篇
  1987年   955篇
  1986年   776篇
  1985年   978篇
  1984年   1140篇
  1983年   1043篇
  1982年   957篇
  1981年   945篇
  1980年   852篇
  1979年   780篇
  1978年   768篇
  1977年   719篇
  1976年   678篇
  1975年   663篇
  1974年   653篇
  1973年   726篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
G. R. Isaak 《Solar physics》1983,82(1-2):235-235
The size of the rotational splitting recently observed (Claverie et al., 1981) is correlated with the 12.2d variation in the measurements of solar oblateness observed by Dicke (1976) and implies a convection zone of depth of 0.1 R . The near equality of amplitudes of global velocity oscillations (Claverie et al., 1981) of the various m components of the l = 1 and l = 2 modes as seen from the Earth viewing the Sun nearly along the equator is unexpected for pure rotational splitting. It is suggested that a magnetic perturbation is present and an oblique asymmetric magnetic rotator with magnetic fields of a few million gauss is responsible. A more detailed account was submitted to Nature.Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1–5 September, 1981.  相似文献   
132.
133.
The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence.  相似文献   
134.
Samples were studied from each color change along six gravity cores from nearshore to deep-sea areas in the Gulf of Mexico. Analytical methods and techniques used to characterize the sediments were X-ray diffraction, differential thermal analysis, cation exchange capacity, particle size distribution and fractionation of the clay-size material with the supercentrifuge.  相似文献   
135.
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results.  相似文献   
136.
137.
138.
139.
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported.  相似文献   
140.
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