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   50033篇
  免费   637篇
  国内免费   1118篇
测绘学   1918篇
大气科学   3894篇
地球物理   9661篇
地质学   20440篇
海洋学   3157篇
天文学   7660篇
综合类   2203篇
自然地理   2855篇
  2021年   171篇
  2020年   208篇
  2019年   218篇
  2018年   5182篇
  2017年   4456篇
  2016年   3130篇
  2015年   666篇
  2014年   703篇
  2013年   1261篇
  2012年   1710篇
  2011年   3685篇
  2010年   2861篇
  2009年   3473篇
  2008年   2908篇
  2007年   3370篇
  2006年   1052篇
  2005年   1017篇
  2004年   1236篇
  2003年   1203篇
  2002年   986篇
  2001年   739篇
  2000年   686篇
  1999年   586篇
  1998年   599篇
  1997年   578篇
  1996年   442篇
  1995年   425篇
  1994年   385篇
  1993年   344篇
  1992年   312篇
  1991年   279篇
  1990年   310篇
  1989年   280篇
  1988年   237篇
  1987年   312篇
  1986年   262篇
  1985年   354篇
  1984年   384篇
  1983年   373篇
  1982年   336篇
  1981年   324篇
  1980年   329篇
  1979年   274篇
  1978年   306篇
  1977年   258篇
  1976年   269篇
  1975年   271篇
  1974年   233篇
  1973年   242篇
  1972年   155篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
31.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars.  相似文献   
32.
33.
1 Introduction Inrecentyearstherehasbeengrowingresearchin terestinthetwo dimensional (2 D )systemtheory .The 2 Dsystemsmayfindapplicationsinareassuchasmarineseismicdataprocessingandimageprocessing .Althoughmoreandmorevaluableresultshavebeengained ,mos…  相似文献   
34.
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.
Wetlands in the Jianghan Plain are important components of wetland types in lake area in the middle and lower reaches the Changjiang (Yangtze) River and they fulfill many uses and functions related to hydrology,waste assimilation, ecosystem productivity and biodiversity. Owing to natural factors and human activities, especially excessive reclamation from lakes, the shrinking process of the lakes has been accelerated. Wetland ecosystem has shown the characteristics of vulnerability. According to the analysis of wetland ecological function in the Jianghan Plain, this paper presented an index system related to productivity, stability and environmental capacity. By using the method of Analytic Hierarchy Process, we computed the values of the relative weights of the indexes, and evaluated the vulnerability level of the wetland ecosystem by the method of multi-indexes. The case study showed that the fragile extent of wetland ecosystem in the Jianghan Plain is 5.6. This means that the wetland ecosystem in the Jiang-han Plain is laid to the state of middle vulnerability. Therefore, the wetland conservation and eco-rehabilitation in the JiangJaan Plain should be paid attention to.  相似文献   
40.
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   
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