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   22473篇
  免费   2499篇
  国内免费   2185篇
化学   2345篇
晶体学   37篇
力学   1924篇
综合类   541篇
数学   15472篇
物理学   6838篇
  2024年   21篇
  2023年   181篇
  2022年   284篇
  2021年   392篇
  2020年   445篇
  2019年   461篇
  2018年   488篇
  2017年   645篇
  2016年   732篇
  2015年   545篇
  2014年   1148篇
  2013年   1449篇
  2012年   1146篇
  2011年   1423篇
  2010年   1284篇
  2009年   1530篇
  2008年   1528篇
  2007年   1649篇
  2006年   1445篇
  2005年   1349篇
  2004年   1149篇
  2003年   1051篇
  2002年   862篇
  2001年   782篇
  2000年   724篇
  1999年   642篇
  1998年   564篇
  1997年   536篇
  1996年   384篇
  1995年   332篇
  1994年   268篇
  1993年   206篇
  1992年   179篇
  1991年   152篇
  1990年   153篇
  1989年   109篇
  1988年   102篇
  1987年   92篇
  1986年   75篇
  1985年   98篇
  1984年   77篇
  1983年   54篇
  1982年   70篇
  1981年   69篇
  1980年   44篇
  1979年   42篇
  1978年   36篇
  1977年   31篇
  1976年   35篇
  1973年   24篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
Derivation of the elementary Fowler-Nordheim equation is based on several strong physical assumptions (e.g. smooth flat surface and uniform work function across emitting surface, constant emission area and a uniform distribution of the applied field over it). A real emitter, however, definitely does not fulfill these assumptions. In spite of it the total emission current follows the FN equation and is frequently used for an estimation of the "average" work-function. The physical basis of this procedure and of the terms "average" work function and "emission area" are analyzed from the experimentalist's point of view. Thus some of the older - more or less intuitive - conclusions are substantiated.  相似文献   
992.
Analogy is used to treat the system of non-interacting integrate-and-fire neurons as an ideal Fermi gas. It allows to obtain the nonlinear gain curve in the form of sigmoid in agreement with biological findings. As the by-product the gain-threshold mechanism in neurons is presented. Surprisingly enough, this is in agreement with new biological findings, too. Besides, the application of this mechanism to the dynamics of neurons leads to the non-monotone transfer function.  相似文献   
993.
Our main aim from this work is to see which theorems in classical probability theory are still valid in fuzzy probability theory. Following Gudder's approach [Demonestratio Mathematica 31(3), 1998, 235–254; Foundations of Physics, 30, 1663–1678] to fuzzy probability theory, the basic concepts of the theory, that is of fuzzy probability measures and fuzzy random variables (observables), are presented. We show that fuzzy random variables extend the usual ones. Moreover, we prove that for any separable metrizable space, the crisp observables coincide with random variables. Then we prove the existence of a joint observable for any collection of observables, and we prove the weak law of large numbers and the central limit theorem in the fuzzy context. We construct a new definition of almost everywhere convergence. After proving that Gudder's definition implies ours and presenting an example that indicates that the converse is not true, we prove the strong law of large numbers according to this definition.  相似文献   
994.
引用1984年尹克震提出的“开关函数的反演公式”,采用伪随机序列技术的思想,提出移位寄存器型时序逻辑网络的一种快速设计方法。  相似文献   
995.
Brui  I. N. 《Mathematical Notes》2002,71(1-2):166-176
Necessary and sufficient conditions for an orthogonal series to be the Fourier series of a function in the space , , are obtained. In the special case of regular summation methods we recover the classical results of Orlicz and Lomnicki.  相似文献   
996.
狭缝法测量X射线斑点大小   总被引:3,自引:3,他引:3       下载免费PDF全文
 应用狭缝光阑成像法测量X射线斑点大小,通过狭缝成像获得光源的线扩展函数和调制传递函数MTF,而后从MTF为0.5所对应的空间频率之值确定出光源的光斑大小。应用该方法测量得到12 MeV 直线感应加速器(LIA)X射线斑点大小为3.2 mm,及磁透镜在不同焦距下的X射线斑点大小。该项测量为12 MeV LIA电子束聚焦调试实验提供有效判据。  相似文献   
997.
The radial wave functions of inner electron shell and outer electron shell of a Ne atom were obtained by the approximate analytical method and tested by calculating the ground state energy of the Ne atom. The equivalent volume of electron cloud and the refractive index of Ne were calculated. The calculated refractive index agrees well with the experimental result. Relationship between the refractive index and the wave function of Ne was discovered. Supported by the New Star Program of Beijing Science and Technology, China (Grant No. 952870400), the Beijing Municipal Commission of Education, and the Excellent Young Teachers Program of Ministry of Education, China  相似文献   
998.
可能性理论的推广方法及合理性研究   总被引:1,自引:0,他引:1  
本文通过引入二维可能性分布函数的概念,将可能性测度推广到二维的情形。并给出了二维可能性测度的一些重要性质。文中还重点证明了该推广方法的合理性。  相似文献   
999.
We study the equidistribution on spheres of the n-step transition probabilities of random walks on graphs. We give sufficient conditions for this property being satisfied and for the weaker property of asymptotical equidistribution. We analyze the asymptotical behaviour of the Green function of the simple random walk on 2 and we provide a class of random walks on Cayley graphs of groups, whose transition probabilities are not even asymptotically equidistributed.  相似文献   
1000.
The main result of the paper is as follows.Theorem. Suppose that G(z) is an entire function satisfying the following conditions: 1) the Taylor coefficients of the function G(z) are nonnegative: 2) for some fixed C>0 and A>0 and for |z|>R0, the following inequality holds:
Further, suppose that for some fixed α>0 the deviation DN of the sequence xn={αn}, n=1, 2, ..., as N→∞ has the estimate DN=0(lnB N/N). Then if the function G(z) is not an identical constant and the inequality B+1<A holds, then the power series converging in the disk |z|<1 cannot be analytically continued to the region |z|>1 across any arc of the circle |z|=1. Translated fromMatematicheskie Zametki, Vol. 66, No. 4, pp. 540–550, October, 1999.  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