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   2077篇
  免费   50篇
  国内免费   6篇
化学   1183篇
晶体学   48篇
力学   75篇
数学   358篇
物理学   469篇
  2022年   17篇
  2021年   37篇
  2020年   35篇
  2019年   47篇
  2018年   85篇
  2017年   95篇
  2016年   82篇
  2015年   64篇
  2014年   70篇
  2013年   141篇
  2012年   169篇
  2011年   163篇
  2010年   111篇
  2009年   111篇
  2008年   97篇
  2007年   78篇
  2006年   68篇
  2005年   120篇
  2004年   85篇
  2003年   60篇
  2002年   27篇
  2001年   29篇
  2000年   23篇
  1999年   20篇
  1998年   14篇
  1997年   12篇
  1996年   24篇
  1995年   13篇
  1994年   17篇
  1993年   9篇
  1992年   12篇
  1991年   11篇
  1990年   11篇
  1989年   8篇
  1988年   15篇
  1987年   9篇
  1986年   8篇
  1985年   8篇
  1984年   8篇
  1983年   8篇
  1982年   7篇
  1981年   6篇
  1980年   6篇
  1979年   5篇
  1978年   9篇
  1977年   10篇
  1976年   8篇
  1974年   6篇
  1973年   9篇
  1968年   5篇
排序方式: 共有2133条查询结果,搜索用时 58 毫秒
1.
2.
3.
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
4.
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach.  相似文献   
5.
We extend the previously found accelerated Kerr-Schild metrics for Einstein-Maxwell-null dust and Einstein-Born-Infeld-null dust equations to the cases including the cosmological constant. This way we obtain the generalization of the charged de Sitter metrics in static space-times. We also give a generalization of the zero acceleration limit of our previous Einstein-Maxwell and Einstein-Born-Infeld solutions.  相似文献   
6.
Montgomery and Vaughan improved a theorem of Erd?s and Fuchs for an arbitrary sequence. Sárközy extended this theorem of Erd?s and Fuchs for two arbitrary sequences which are "near" in a certain sense. Using the idea of Jurkat (differentiation of the generating function), we will extend similarly the result of Montgomery and Vaughan for "sufficiently near" sequences.  相似文献   
7.
Wave-hierarchy problems appear in a variety of applications such as traffic flows, roll waves down an open inclined channel and multiphase flows. Usually, these are described by the compressible Navier-Stokes equations with specific non-linearities; in a fluidized bed model they contain an additional pressure gradient term and are supplemented by an elliptic equation for this unknown pressure. These equations admit solutions periodic in space as well as in time, i.e. periodic travelling waves. Therefore, the corresponding initial value problem with periodic boundary conditions is solved locally in time in appropriate Sobolev spaces. Some remarks are made concerning global solutions, the occurrence of clusters or voids and the bifurcation of time periodic solutions, respectively.  相似文献   
8.
The possibility of using an Auger peak height in the dN (E) /dE spectrum and an integrated N (E) spectrum as a measure of the Auger current is discussed and necessary relations are presented. The methods of the background determination are reviewed and discussed.

The relation between the Auger current and the atomic cancentration of a corresponding sample component is derived and the state of art in the field of theoretical and experimental determination of factors appearing in this relation (ionization cross-section, Auger transition probability. backscattering factor, and inelastic mean free path of Auger electrons) is presented.

Approaches to the quantitative Auger analysis (QAA) of homogeneous, isotropic samples, including corrections for matrix factors, are presented and discussed. Problems arising when heterogeneous samples are analyzed are discussed and practical approaches to such an analysis are presented.

The role of crystalline effects (the dependence of the Auger signal from crystalline samples on the direction of the primary electron beam and angular distribution of Auger electron emission from such samples) in QAA is discussed and examples of such crystalline effects are presented together with their physical foundation.

Some rules are suggested allowing the quantitative Auger analysis to be performed with the smallest possible error.  相似文献   

9.
The determination of the sensitivity of the acoustical characteristics of vibrating systems with respect to the variation of the design parameters predicting these characteristics is a necessary and important step of the acoustic design and optimization process. Acoustic design sensitivity analysis includes the computation and evaluation of the sensitivity information required for this procedure. In this study, a boundary element code performing the sensitivity analysis of the acoustic pressure by using the matrix sensitivities with respect to different design variables has been developed. The effect of the precision of boundary element discretization on the acoustic pressure sensitivity is examined via this code. The formulation is applied to a multi-source system and the dimension sensitivity analysis of near field pressures of two-dilating-spherical source is performed. The last application is devoted to a real sound source: a washing machine sitting on the floor. Sensitivity of the field pressures to the machine’s dimensions (size), surface velocity and frequency is examined on the bases of the boundary element model of the machine and half-space condition. The impacts of these variables are compared; and a limiting speed for the machine responding both the acoustical and operational requirements is determined.  相似文献   
10.
Summary It is shown that certain singular integral operators with variable kernels leave invariant theL v, -spaces studied by Campanato, Stampacchia, Peetre and others. Our results extend Peetre's work on convolution operators.  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