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   503843篇
  免费   4650篇
  国内免费   1662篇
化学   253248篇
晶体学   8241篇
力学   23959篇
综合类   8篇
数学   60661篇
物理学   164038篇
  2021年   4198篇
  2020年   4553篇
  2019年   5160篇
  2018年   6960篇
  2017年   7114篇
  2016年   9963篇
  2015年   5838篇
  2014年   9728篇
  2013年   23397篇
  2012年   17622篇
  2011年   21506篇
  2010年   15662篇
  2009年   15563篇
  2008年   19456篇
  2007年   19404篇
  2006年   18076篇
  2005年   15976篇
  2004年   14864篇
  2003年   13147篇
  2002年   13107篇
  2001年   15339篇
  2000年   11585篇
  1999年   9099篇
  1998年   7615篇
  1997年   7381篇
  1996年   7010篇
  1995年   6224篇
  1994年   6127篇
  1993年   6086篇
  1992年   6562篇
  1991年   6851篇
  1990年   6515篇
  1989年   6370篇
  1988年   6193篇
  1987年   6215篇
  1986年   5817篇
  1985年   7670篇
  1984年   7902篇
  1983年   6427篇
  1982年   6678篇
  1981年   6397篇
  1980年   6203篇
  1979年   6569篇
  1978年   6609篇
  1977年   6586篇
  1976年   6667篇
  1975年   6193篇
  1974年   6166篇
  1973年   6256篇
  1972年   4422篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
63.
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   
64.
65.
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   
66.
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   
67.
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   
68.
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   
69.
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   
70.
We give a coring version for the duality theorem for actions and coactions of a finitely generated projective Hopf algebra. We also provide a coring analogue for a theorem of H.-J. Schneider, which generalizes and unifies the duality theorem for finite Hopf algebras and its refinements. This paper was written while the first author visited the Mathematics Departments of Syracuse University and California State University Dominguez Hills. He would like to thank both departments for their hospitality.  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