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   5244篇
  免费   502篇
  国内免费   820篇
化学   3309篇
晶体学   72篇
力学   136篇
综合类   99篇
数学   1220篇
物理学   1730篇
  2023年   41篇
  2022年   76篇
  2021年   92篇
  2020年   110篇
  2019年   116篇
  2018年   117篇
  2017年   147篇
  2016年   169篇
  2015年   120篇
  2014年   197篇
  2013年   356篇
  2012年   302篇
  2011年   301篇
  2010年   245篇
  2009年   321篇
  2008年   332篇
  2007年   363篇
  2006年   302篇
  2005年   306篇
  2004年   278篇
  2003年   248篇
  2002年   204篇
  2001年   182篇
  2000年   174篇
  1999年   158篇
  1998年   142篇
  1997年   128篇
  1996年   124篇
  1995年   110篇
  1994年   102篇
  1993年   64篇
  1992年   96篇
  1991年   73篇
  1990年   59篇
  1989年   54篇
  1988年   44篇
  1987年   38篇
  1986年   42篇
  1985年   31篇
  1984年   26篇
  1983年   12篇
  1982年   29篇
  1981年   27篇
  1980年   20篇
  1979年   15篇
  1978年   14篇
  1977年   10篇
  1976年   24篇
  1973年   10篇
  1972年   4篇
排序方式: 共有6566条查询结果,搜索用时 31 毫秒
31.
加速牛顿迭代收敛的新方法   总被引:2,自引:0,他引:2  
提出了加速牛顿迭代收敛的新思想,构造出一类加权牛顿迭代格式,通过选取最优加权因子,使得该格式具有高阶收敛性和较小的渐近误差常数。  相似文献   
32.
The results of studies on electrosynthesis involving carb- and heteroanions generated by cathodic deprotonation of acids (CDA), carried out in the laboratory headed by the author, are surveyed. These studies resulted in the elaboration of efficient electrochemical versions of the known Michaelis-Becker, Wittig-Horner, and Perkin reactions; electrochemical analogs of homolytic aromatic substitution, alkylation, heterocyclization,etc. were developed. Based on CDA, convenient and promising methods for preparing variousN-, O-, P-, S-, andC-alkylated and arylated substances have been developed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1411–1422, August, 1995.The author is grateful to Professor V. A. Dorokhov, Professor V. P. Litvinov, and researchers from the laboratories of N. D. Zelinsky Institute of Organic Chemistry headed by them, who participated in joint studies.The work was carried out with financial support from the International Science Foundation (Grant No. MHYOO).  相似文献   
33.
We give a number of characterizations of bodies of constant width in arbitrary dimension. As an application, we describe a way to construct a body of constant width in dimension n, one of its (n – 1)‐dimensional projection being given. We give a number of examples, like a four‐dimensional body of constant width whose 3D‐projection is the classical Meissner's body. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
34.
We give some sufficient conditions for the Domínguez-Lorenzo condition in terms of the James constant, the Jordan-von Neumann constant, and the coefficient of weak orthogonality. As a consequence, we obtain fixed point theorems for multivalued nonexpansive mappings.  相似文献   
35.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities, temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease with electric field.  相似文献   
36.
In this note we consider a variable G cosmology which is consistent with observation and which had successfully predicted an ever expanding accelerating universe with a small cosmological constant amongst other things. Three further tests are proposed in this note: First, the inexplicable anomalous accelerations of the Pioneer spacecrafts can be explained. It is then shown that the observed shortening of the orbital periods of binary pulsars is in good agreement with this model. Finally, more general changes in orbital parameters are deduced, which may be observed in the future.  相似文献   
37.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.

  相似文献   

38.
Given a constant of motion for the one-dimensional harmonic oscillator with linear dissipation in the velocity, the problem to get the Hamiltonian for this system is pointed out, and the quantization up to second order in the perturbation approach is used to determine the modification on the eigenvalues when dissipation is taken into consideration. This quantization is realized using the constant of motion instead of the Hamiltonian. PACS: 03.20.+i, 03.30.+p, 03.65.−w,03.65.Ca  相似文献   
39.
Two games of interacting between a coalition of players in a marketplace and the residual players acting there are discussed, along with two approaches to fair imputation of gains of coalitions in cooperative games that are based on the concepts of the Shapley vector and core of a cooperative game. In the first game, which is an antagonistic one, the residual players try to minimize the coalition's gain, whereas in the second game, which is a noncooperative one, they try to maximize their own gain as a coalition. A meaningful interpretation of possible relations between gains and Nash equilibrium strategies in both games considered as those played between a coalition of firms and its surrounding in a particular marketplace in the framework of two classes of n-person games is presented. A particular class of games of choosing partners and forming coalitions in which models of firms operating in the marketplace are those with linear constraints and utility functions being sums of linear and bilinear functions of two corresponding vector arguments is analyzed, and a set of maximin problems on polyhedral sets of connected strategies which the problem of choosing a coalition for a particular firm is reducible to are formulated based on the firm models of the considered kind.  相似文献   
40.
采用反应射频磁控溅射方法,在Si (100) 基片上制备了具有高c轴择优取向的ZnO薄膜.利用 原子力显微镜、透射电子显微镜、X射线衍射分析、拉曼光谱等表征技术,研究了沉积温度 对ZnO薄膜的表面形貌、晶粒尺度、应力状态等结晶性能的影响;通过沉积温度对透射光谱 和光致荧光光谱的影响,探讨了ZnO薄膜的结晶特性与光学性能之间的关系.研究结果显示, 在室温至500℃的范围内,ZnO薄膜的晶粒尺寸随沉积温度的增加而增加,在沉积温度为500 ℃时达到最大;当沉积温度为750℃时,ZnO薄膜的晶粒尺度有所减小;在室温至750℃的范 围内,薄膜中ZnO晶粒与Si基体之间均存在着相对固定的外延关系;在沉积温度低于500℃时 ,制备的ZnO薄膜处于压应变状态,而750℃时沉积的薄膜表现为张应变状态.沉积温度的不 同导致ZnO薄膜的折射率、消光系数、光学禁带宽度以及光致荧光特性的变化,沉积温度对 紫外光致荧光特性起着决定性的作用.此外,探讨了影响薄膜近紫外光致荧光发射的可能因 素. 关键词: ZnO薄膜 表面形貌 微观结构 光学常数  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