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   432490篇
  免费   4186篇
  国内免费   1326篇
化学   223013篇
晶体学   7039篇
力学   19690篇
综合类   12篇
数学   49673篇
物理学   138575篇
  2021年   3546篇
  2020年   3876篇
  2019年   4270篇
  2018年   5702篇
  2017年   5877篇
  2016年   8409篇
  2015年   4953篇
  2014年   8101篇
  2013年   19862篇
  2012年   15031篇
  2011年   18239篇
  2010年   13143篇
  2009年   12880篇
  2008年   16295篇
  2007年   16231篇
  2006年   15216篇
  2005年   13585篇
  2004年   12493篇
  2003年   11105篇
  2002年   11023篇
  2001年   12917篇
  2000年   9621篇
  1999年   7615篇
  1998年   6423篇
  1997年   6288篇
  1996年   5946篇
  1995年   5298篇
  1994年   5062篇
  1993年   4983篇
  1992年   5550篇
  1991年   5703篇
  1990年   5464篇
  1989年   5386篇
  1988年   5199篇
  1987年   5291篇
  1986年   5025篇
  1985年   6488篇
  1984年   6648篇
  1983年   5511篇
  1982年   5879篇
  1981年   5445篇
  1980年   5444篇
  1979年   5694篇
  1978年   5832篇
  1977年   5740篇
  1976年   5753篇
  1975年   5456篇
  1974年   5266篇
  1973年   5485篇
  1972年   3756篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems.  相似文献   
44.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis  相似文献   
45.
46.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers.  相似文献   
47.
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin.  相似文献   
48.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography: 5 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23.  相似文献   
49.
Using the method of the tensor Green’s function of the wave equation, the differential and total cross sections for the scattering of surface optical electromagnetic waves (surface plasmon polaritons) by a spherical nanoparticle into surface plasmon polaritons and light have been obtained with the inclusion of the magnetic dipole contribution. Using the example of noble metal systems, it has been shown that the magnetic dipole contribution may significantly affect the angular dependence of the differential cross sections and increase their anisotropy as the plasmon wavelength increases.  相似文献   
50.
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De  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