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   138049篇
  免费   10560篇
  国内免费   8254篇
化学   69548篇
晶体学   1620篇
力学   6562篇
综合类   505篇
数学   13585篇
物理学   39610篇
无线电   25433篇
  2023年   1700篇
  2022年   2620篇
  2021年   3479篇
  2020年   3577篇
  2019年   3775篇
  2018年   3974篇
  2017年   4027篇
  2016年   4992篇
  2015年   4034篇
  2014年   5540篇
  2013年   7478篇
  2012年   7965篇
  2011年   8285篇
  2010年   6569篇
  2009年   6585篇
  2008年   7048篇
  2007年   6449篇
  2006年   6028篇
  2005年   5454篇
  2004年   4581篇
  2003年   4197篇
  2002年   4363篇
  2001年   3723篇
  2000年   3032篇
  1999年   2490篇
  1998年   2240篇
  1997年   1922篇
  1996年   1850篇
  1995年   1528篇
  1994年   1516篇
  1993年   1403篇
  1992年   1369篇
  1991年   1366篇
  1990年   1306篇
  1989年   1182篇
  1988年   1025篇
  1987年   989篇
  1986年   953篇
  1985年   997篇
  1984年   959篇
  1983年   861篇
  1982年   834篇
  1979年   820篇
  1978年   817篇
  1977年   816篇
  1976年   924篇
  1975年   815篇
  1974年   848篇
  1973年   849篇
  1972年   755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.  相似文献   
72.
Estimates of a rate of convergence of orderO(n –1) are obtained for integral functionals of an empirical process.Translated fromTeoriya Sluchainykh Protsessov, Vol. 15, pp. 10–16, 1987.  相似文献   
73.
Translated fromProblemy Ustoichivosti Stokhasticheskikh Modelei. Trudy Seminara, 1988, pp. 84–92.  相似文献   
74.
75.
In this paper, symbolic code matrix ,constant matrix and count matrix are defined .The first twomatrices are used to describe the elemental expression of augmented matrix and the nede admittance equa-tion is thus obtained. The third matrix is used to obtain the incoming degree matrix, and according to thematrix all the 1- factors of the Coates graph are given. By using the data code, the determinant is expandedand the same items in the expansion are merged. Thus the symbolic network function in which no term can-cellation occurs is generated.  相似文献   
76.
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   
77.
78.
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   
79.
An expression for the ratio of the glass transition temperature to the melting temperature, T g/T m, was derived with allowance for fluctuations of the packing factor in the amorphous state. This relationship made it possible to describe the actual range of variation in T g/T m depending on a change in the packing factor in the crystalline state k o, cr. The proposed approach forms the basis for the method of determination of increments in the packing ratio k o, cr and formulation of the principles of selection of experimental data for calculations. The glass transition temperatures in polyethylene depending on the type of unit cell were calculated.  相似文献   
80.
A three-dimensional (3D) finite-difference time-domain (FDTD) scheme is introduced to model the scattering from objects in continuous random media. FDTD techniques have been previously applied to scattering from random rough surfaces and randomly placed objects in a homogeneous background, but little has been done to simulate continuous random media with embedded objects where volumetric scattering effects are important. In this work, Monte Carlo analysis is used in conjunction with FDTD to study the scattering from perfectly electrically conducting (PEC) objects embedded in continuous random media. The random medium models under consideration are chosen to be inhomogeneous soils with a spatially fluctuating random permittivities and prescribed correlation functions. The ability of frequency averaging techniques to discriminate objects in this scenarion is also briefly investigated. The simulation scheme described in this work can be adapted and used to help in interpreting the scattered field data from targets in random environments such as geophysical media, biological media, or atmospheric turbulence  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