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   34011篇
  免费   1451篇
  国内免费   1461篇
测绘学   782篇
大气科学   3335篇
地球物理   7349篇
地质学   12554篇
海洋学   2904篇
天文学   6954篇
综合类   574篇
自然地理   2471篇
  2022年   316篇
  2021年   436篇
  2020年   384篇
  2019年   490篇
  2018年   872篇
  2017年   799篇
  2016年   987篇
  2015年   729篇
  2014年   1066篇
  2013年   1653篇
  2012年   1142篇
  2011年   1450篇
  2010年   1321篇
  2009年   1663篇
  2008年   1465篇
  2007年   1446篇
  2006年   1366篇
  2005年   1115篇
  2004年   1089篇
  2003年   1064篇
  2002年   942篇
  2001年   879篇
  2000年   864篇
  1999年   828篇
  1998年   836篇
  1997年   820篇
  1996年   656篇
  1995年   626篇
  1994年   541篇
  1993年   524篇
  1992年   434篇
  1991年   367篇
  1990年   378篇
  1989年   362篇
  1988年   314篇
  1987年   388篇
  1986年   331篇
  1985年   393篇
  1984年   433篇
  1983年   417篇
  1982年   382篇
  1981年   345篇
  1980年   343篇
  1979年   311篇
  1978年   328篇
  1977年   284篇
  1976年   286篇
  1975年   294篇
  1974年   250篇
  1973年   258篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
31.
An empirical kinematic method developed by Hakamada and Akasofu (1982) is calibrated on the basis of a one-dimensional MHD solution. The calibrated results are used to simulate the stream-stream interaction and the background corotating structure in a simple situation and also during 22 November–6 December 1977. The solar wind disturbances caused by solar activities during this period are then introduced into the above background stream in simulating the heliospheric disturbance event which was observed by an aligned set of spacecraft at distances between 0.6 and 1.6 a.u. The observations and the simulated results are satisfactory, and a little more refinement in the simulation could reconstruct reasonably well the data by filling the data gaps in the solar wind speed, the density and the IMF magnitude.  相似文献   
32.
33.
34.
利用钻孔测井资料并运用地层倾角测量信息分析法,给出了江汉盆地地应力最大水平主压应力方向为NE60~65°  相似文献   
35.
An updated Lagrangian finite-element formulation has been developed for time-dependent problems of soil consolidation involving finite deformations. Large plastic strains as well as rotations occur in such problems and nominal stress measures are introduced in the formulation to redefine stresses. This leads to corrective terms for equilibrium and yield violations in addition to geometric stiffening terms in the governing integral equations. The soil is considered to be either a linear elastic or an elastoplastic, critical-state material. Some simple numerical examples are studied to validate the formulation, followed by a detailed analysis of the problem of penetration of a pile into soil. The results of this problem are viewed with emphasis on the physical interpretation and practical significance.  相似文献   
36.
37.
38.
39.
We have derived the galaxy luminosity function in various regions of the cluster of galaxies Abell 496 from a wide field image in the I band. A Schechter function fit in the 17≤ IAB ≤22(–19.5≤ MIAB ≤ –14.5) magnitude interval gives a steep power law index, which is somewhat steeper in the outer regions than in the inner zones. This result agrees with previous findings obtained by several teams on the Coma cluster and can be interpreted as due to the fact that faint galaxies are accreted by large ones in the central regions. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
40.
We have developed a method for analytically solving the porous medium flow equation in many different geometries for horizontal (two‐dimensional), homogeneous and isotropic aquifers containing impermeable boundaries and any number of pumping or injection wells located at arbitrary positions within the system. Solutions and results are presented for rectangular and circular aquifers but the method presented here is easily extendible to many geometries. Results are also presented for systems where constant head boundary conditions can be emulated internal to the aquifer boundary. Recommendations for extensions of the present work are briefly discussed. Copyright © 2003 John Wiley & Sons, Ltd.  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