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   351383篇
  免费   2351篇
  国内免费   1098篇
化学   172711篇
晶体学   4900篇
力学   17842篇
综合类   7篇
数学   61447篇
物理学   97925篇
  2021年   2401篇
  2020年   2667篇
  2019年   3072篇
  2018年   14433篇
  2017年   14268篇
  2016年   11701篇
  2015年   3950篇
  2014年   5414篇
  2013年   12121篇
  2012年   12730篇
  2011年   20988篇
  2010年   13506篇
  2009年   13726篇
  2008年   16762篇
  2007年   18796篇
  2006年   9927篇
  2005年   9980篇
  2004年   9360篇
  2003年   9139篇
  2002年   8140篇
  2001年   7945篇
  2000年   6249篇
  1999年   4621篇
  1998年   4101篇
  1997年   4000篇
  1996年   3732篇
  1995年   3139篇
  1994年   3179篇
  1993年   3229篇
  1992年   3379篇
  1991年   3486篇
  1990年   3306篇
  1989年   3332篇
  1988年   3191篇
  1987年   3114篇
  1986年   2991篇
  1985年   3817篇
  1984年   4036篇
  1983年   3276篇
  1982年   3582篇
  1981年   3358篇
  1980年   3131篇
  1979年   3393篇
  1978年   3622篇
  1977年   3640篇
  1976年   3534篇
  1975年   3364篇
  1974年   3349篇
  1973年   3471篇
  1972年   2374篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
A new method was developed for studying voids and channels in crystal structures based on the Voronoi-Dirichlet partition of crystal space, and 822 structurally characterized ternary compounds Li p X q O r were analyzed for the first time. For these compounds, the dimensionality was determined and the migration patterns of channel systems capable of providing lithium-ion transport were constructed. The calculated coordinates of lithium atoms in the centers of the voids are consistent (within 0.4 ?) with the known structural data. Among these compounds, 113 compounds have infinite channel systems, 60 compounds (18 structural types, STs) have been described earlier in the literature as solid electrolytes, and 53 compounds (23 STs) can be considered as potential one-, two-, or three-dimensional ionic conductors (13, 3, and 7 STs, respectively). Original Russian Text ? N.A. Anurova, V.A. Blatov, G.D. Ilyushin, O.A. Blatova, A.K. Ivanov-Shitz, L.N. Dem’yanets, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 987–993.  相似文献   
24.
We propose a dislocation model of a nanotwin, which is used to calculate the stress fields in the nanotwin. We consider the role of these stresses in the process of interdislocation interaction and nanotwin growth.  相似文献   
25.
The aim of this study is to construct a quantitative characteristic for the degree of gaze stabilization on a visual target with consideration of physiological constraints. A quality criterion for visual tracking during optokinetic vestibulocervical nystagmus is proposed. The index of imaginary tracking during rotation in the dark allows one to speak of a difference in the image stabilization quality between a healthy person and a patient. Experimental nystagmus data are used to calculate the quality index of visual tracking and the index of imaginary tracking.  相似文献   
26.
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   
27.
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   
28.
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   
29.
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.  相似文献   
30.
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL.  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