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   568542篇
  免费   3506篇
  国内免费   1276篇
化学   264005篇
晶体学   8390篇
力学   32339篇
综合类   11篇
数学   97315篇
物理学   171264篇
  2020年   4670篇
  2019年   5458篇
  2018年   17748篇
  2017年   17730篇
  2016年   16350篇
  2015年   6174篇
  2014年   9936篇
  2013年   20495篇
  2012年   19407篇
  2011年   28685篇
  2010年   20127篇
  2009年   20463篇
  2008年   24275篇
  2007年   26130篇
  2006年   16718篇
  2005年   15753篇
  2004年   15150篇
  2003年   14477篇
  2002年   13734篇
  2001年   13282篇
  2000年   10607篇
  1999年   7964篇
  1998年   7334篇
  1997年   7178篇
  1996年   6726篇
  1995年   6025篇
  1994年   6152篇
  1993年   5908篇
  1992年   6281篇
  1991年   6609篇
  1990年   6472篇
  1989年   6378篇
  1988年   6251篇
  1987年   6220篇
  1986年   5780篇
  1985年   7288篇
  1984年   7699篇
  1983年   6532篇
  1982年   6774篇
  1981年   6473篇
  1980年   6283篇
  1979年   6626篇
  1978年   6976篇
  1977年   6956篇
  1976年   7151篇
  1975年   6625篇
  1974年   6525篇
  1973年   6816篇
  1972年   5263篇
  1971年   4570篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Structural hierarchy of rock masses and the mechanisms of its formation   总被引:1,自引:0,他引:1  
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed.  相似文献   
42.
The paper addresses the problem of calculation of the local stress field and effective elastic properties of a unidirectional fiber reinforced composite with anisotropic constituents. For this aim, the representative unit cell approach has been utilized. The micro geometry of the composite is modeled by a periodic structure with a unit cell containing multiple circular fibers. The number of fibers is sufficient to account for the micro structure statistics of composite. A new method based on the multipole expansion technique is developed to obtain the exact series solution for the micro stress field. The method combines the principle of superposition, technique of complex potentials and some new results in the theory of special functions. A proper choice of potentials and new results for their series expansions allow one to reduce the boundary-value problem for the multiple-connected domain to an ordinary, well-posed set of linear algebraic equations. This reduction provides high numerical efficiency of the developed method. Exact expressions for the components of the effective stiffness tensor have been obtained by analytical averaging of the strain and stress fields.  相似文献   
43.
The chlorination of benzene, toluene, and o-xylene with molecular chlorine in the presence of the phthalocyanine complexes of different structures was studied. The transformations of the catalysts during the reaction were investigated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1644–1647, August, 2008.  相似文献   
44.
45.
The kinetics of unhindered sedimentation of a titanium dioxide suspension (as model dispersed system) was studied, and the effect of the concentration and mode of addition of various formulations based on anionic and cationic acrylamide copolymers on their flocculation properties in aqueous salt (NaCl) solutions was evaluated.  相似文献   
46.
Oximes of 4-(4-pyrazolyl)-3-buten-2-onees obtained by successive reaction of 3-aryl-4-formylpyrazoles with acetone and hydroxylamine at the treatment with iodine suffered an oxidative cyclization yielding 3-aryl-4-(5-isoxazolyl)pyrazoles.  相似文献   
47.
48.
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested.  相似文献   
49.
50.
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