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   204077篇
  免费   1309篇
  国内免费   428篇
化学   105192篇
晶体学   3396篇
力学   10336篇
综合类   10篇
数学   22056篇
物理学   64824篇
  2020年   2016篇
  2019年   2579篇
  2018年   3669篇
  2017年   3672篇
  2016年   4827篇
  2015年   2362篇
  2014年   4308篇
  2013年   8682篇
  2012年   6849篇
  2011年   8064篇
  2010年   6466篇
  2009年   6656篇
  2008年   7642篇
  2007年   7599篇
  2006年   6710篇
  2005年   5921篇
  2004年   5646篇
  2003年   5161篇
  2002年   5171篇
  2001年   5617篇
  2000年   4152篇
  1999年   3151篇
  1998年   2719篇
  1997年   2776篇
  1996年   2567篇
  1995年   2223篇
  1994年   2344篇
  1993年   2237篇
  1992年   2541篇
  1991年   2665篇
  1990年   2565篇
  1989年   2641篇
  1988年   2554篇
  1987年   2567篇
  1986年   2429篇
  1985年   3053篇
  1984年   3120篇
  1983年   2621篇
  1982年   2584篇
  1981年   2546篇
  1980年   2350篇
  1979年   2728篇
  1978年   2694篇
  1977年   2894篇
  1976年   2903篇
  1975年   2691篇
  1974年   2625篇
  1973年   2741篇
  1972年   2112篇
  1971年   1978篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
V stat'e izuchayutsya klassy periodicheskikh funktsii mnogikh peremennykh s zadannoi mazhorantoi smeshannykh modulei nepreryvnosti, prichem mazhoranta imeet spetsial'nyi vid. Rassmotreny nailuchshie priblizheniya ukazannykh klassov i vozmozhnost' kharakterizatsii 'etikh klassov cherez nailuchshie priblizheniya.  相似文献   
62.
Molecules of the title compound, C12H13ClN4, are linked by two independent N—H...N hydrogen bonds into a chain of edge‐fused R22(8) rings. The significance of this study lies in its attempt to rationalize the patterns of supramolecular aggregation in the title compound and in a range of analogous 4,6‐disubstituted 2‐aminopyrimidines.  相似文献   
63.
The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λmax= 350 nm.  相似文献   
64.
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   
65.
This paper addresses the issue of energy propagation features in ribbed panels over a wide frequency range. First, a tool for estimating the wave propagation characteristics of one- and two-dimensional structures by k-space analysis is presented. This tool uses a concept of Inhomogeneous Wave Correlation with sparse measured or extracted data, and leads to the estimation of θ-dependent wavenumbers. Here, the method is employed with the sparse simulated and measured normal velocities of a set of ribbed panels and new insights into their k-space behavior are highlighted. Behavior is essentially characterized at low frequencies by structural orthotropy. Comparisons with homogenized data show very good agreement. At higher frequencies, a new behavior pattern is observed and explained both numerically and experimentally. This is a multi-modal waveguide type of propagation in a direction parallel to the ribs.  相似文献   
66.
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   
67.
68.
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   
69.
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   
70.
The alternative: equivalence-singularity on the conic sigma-field is established for a pair of centered Gaussian distributions and a corresponding criterion is given. The behavior of the logarithmic variation is established for the Radon–Nikodym derivative on the conic sigma-subfield. Bibliography: 6 titles.  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