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   741456篇
  免费   5968篇
  国内免费   2329篇
化学   361275篇
晶体学   10668篇
力学   39569篇
综合类   18篇
数学   117325篇
物理学   220898篇
  2021年   5849篇
  2020年   6409篇
  2019年   7286篇
  2018年   19233篇
  2017年   19026篇
  2016年   19131篇
  2015年   8375篇
  2014年   12946篇
  2013年   30240篇
  2012年   26224篇
  2011年   36832篇
  2010年   25299篇
  2009年   25676篇
  2008年   31532篇
  2007年   33399篇
  2006年   23682篇
  2005年   22227篇
  2004年   20914篇
  2003年   19354篇
  2002年   18365篇
  2001年   19033篇
  2000年   14805篇
  1999年   11530篇
  1998年   9939篇
  1997年   9692篇
  1996年   9231篇
  1995年   8319篇
  1994年   8245篇
  1993年   8072篇
  1992年   8514篇
  1991年   8990篇
  1990年   8562篇
  1989年   8438篇
  1988年   8313篇
  1987年   8073篇
  1986年   7666篇
  1985年   9983篇
  1984年   10437篇
  1983年   8646篇
  1982年   9051篇
  1981年   8637篇
  1980年   8252篇
  1979年   8770篇
  1978年   9021篇
  1977年   8886篇
  1976年   8863篇
  1975年   8379篇
  1974年   8263篇
  1973年   8577篇
  1972年   6221篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically.  相似文献   
62.
Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate.  相似文献   
63.
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   
64.
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   
65.
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   
66.
Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed.  相似文献   
67.
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   
68.
69.
70.
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