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   4812篇
  免费   408篇
  国内免费   158篇
化学   627篇
晶体学   3篇
力学   358篇
综合类   92篇
数学   3126篇
物理学   1172篇
  2024年   5篇
  2023年   65篇
  2022年   87篇
  2021年   112篇
  2020年   104篇
  2019年   93篇
  2018年   74篇
  2017年   147篇
  2016年   158篇
  2015年   106篇
  2014年   258篇
  2013年   396篇
  2012年   301篇
  2011年   269篇
  2010年   213篇
  2009年   307篇
  2008年   309篇
  2007年   285篇
  2006年   217篇
  2005年   185篇
  2004年   148篇
  2003年   144篇
  2002年   112篇
  2001年   118篇
  2000年   102篇
  1999年   101篇
  1998年   118篇
  1997年   77篇
  1996年   88篇
  1995年   71篇
  1994年   52篇
  1993年   49篇
  1992年   35篇
  1991年   37篇
  1990年   45篇
  1989年   28篇
  1988年   21篇
  1987年   32篇
  1986年   24篇
  1985年   59篇
  1984年   31篇
  1983年   27篇
  1982年   35篇
  1981年   26篇
  1980年   20篇
  1979年   25篇
  1978年   29篇
  1977年   8篇
  1976年   7篇
  1973年   4篇
排序方式: 共有5378条查询结果,搜索用时 62 毫秒
71.
本文研究指数分布卷积形式参数的点估计,区间估计以及经验分布函数与分布函数最大偏差的概率估计.  相似文献   
72.
半变系数模型PLS估计的渐近正态性   总被引:1,自引:1,他引:0  
半变系数模型在统计建模中具有重要的应用.最近几年,人们提出了许多方法来估计其常系数和函数系数,但是估计的渐近性质还没有被系统的研究.本文介绍了半变系数模型的PLS估计,在Fan和Huang对常系数渐近性质研究的基础上,给出了函数系数的渐近正态性。  相似文献   
73.
This paper addresses the statistical problem of density deconvolution under the condition that the density to be estimated has compact support. We introduce a new estimation procedure, which establishes faster rates of convergence for smooth densities as compared to the optimal rates for smooth densities with unbounded support. This framework also allows us to relax the usual condition of known error density with non-vanishing Fourier transform, so that a nonparametric class of densities is valid; therefore, even the shape of the noise density need not be assumed. These results can also be generalized for fast decaying densities with unbounded support. We prove optimality of the rates in the underlying experiment and study the practical performance of our estimator by numerical simulations.   相似文献   
74.
In the paper, the simple method of laser chirp parameters estimation is presented. It is based on measuring time-domain distortions of chirped signal transmitted through dispersive fiber and finding laser chirp parameters by matching measured distortions to calculated ones. Experiments undertaken with 1.55 μm telecommunication grade distributed feedback (DFB) lasers and standard single-mode fiber are described, together with some practical remarks on measurement setup and main conclusions.  相似文献   
75.
本文对广义风险过程中的渐近方差作了非参数估计,得出并证明了两个定理,为广义风险过程中破产概率的区间估计作了理论准备.  相似文献   
76.
Epilepsy is among the most common brain disorders. Approximately 25–30% of epilepsy patients remain unresponsive to anti-epileptic drug treatment, which is the standard therapy for epilepsy. In this study, we apply optimization-based data mining techniques to classify the brain's normal and epilepsy activity using intracranial electroencephalogram (EEG), which is a tool for evaluating the physiological state of the brain. A statistical cross validation and support vector machines were implemented to classify the brain's normal and abnormal activities. The results of this study indicate that it may be possible to design and develop efficient seizure warning algorithms for diagnostic and therapeutic purposes. Research was partially supported by the Rutgers Research Council grant-202018, the NSF grants DBI-980821, CCF-0546574, IIS-0611998, and NIH grant R01-NS-39687-01A1.  相似文献   
77.
Functional central limit theorems for triangular arrays of rowwise independent stochastic processes are established by a method replacing tail probabilities by expectations throughout. The main tool is a maximal inequality based on a preliminary version proved by P. Gaenssler and Th. Schlumprecht. Its essential refinement used here is achieved by an additional inequality due to M. Ledoux and M. Talagrand. The entropy condition emerging in our theorems was introduced by K. S. Alexander, whose functional central limit theorem for so-calledmeasure-like processeswill be also regained. Applications concern, in particular, so-calledrandom measure processeswhich include function-indexed empirical processes and partial-sum processes (with random or fixed locations). In this context, we obtain generalizations of results due to K. S. Alexander, M. A. Arcones, P. Gaenssler, and K. Ziegler. Further examples include nonparametric regression and intensity estimation for spatial Poisson processes.  相似文献   
78.
An evolutionary method for optimization of plate buckling resistance   总被引:9,自引:0,他引:9  
Optimization of plate buckling resistance is very complicated, because the in-plane stress resultants in the prebuckled state of a plate are functions of thickness distribution. This paper discusses the problem of finding the optimum thickness distribution of isotropic plate structures, with a given volume and layout, that would maximise the buckling load. A simple numerical method using the finite-element analysis is presented to obtain the optimum thickness distribution. Optimum designs of compression-loaded rectangular plates with different boundary conditions and plate aspect ratios are obtained by using the proposed method. Optimum designs from earlier studies and the methods of buckling analysis used to attain these results are discussed and compared with the designs from the proposed method. This paper also examines the reliability of the optimality criterion generally used for plate buckling optimization, which is based on the uniform strain energy density.  相似文献   
79.
Optimization techniques are finding increasingly numerous applications in process design, in parallel to the increase of computer sophistication. The process synthesis problem can be stated as a largescale constrained optimization problem involving numerous local optima and presenting a nonlinear and nonconvex character. To solve this kind of problem, the classical optimization methods can lead to analytical and numerical difficulties. This paper describes the feasibility of an optimization technique based on learning systems which can take into consideration all the prior information concerning the process to be optimized and improve their behavior with time. This information generally occurs in a very complex analytical, empirical, or know-how form. Computer simulations related to chemical engineering problems (benzene chlorination, distillation sequence) and numerical examples are presented. The results illustrate both the performance and the implementation simplicity of this method.Nomenclature c i penalty probability - cp precision parameter on constraints - D variation domain of the variablex - f(·) objective function - g(·) constraints - i,j indexes - k iteration number - N number of actions - P probability distribution vector - p i ith component of the vectorP as iterationk - r number of reactors in the flowsheet - u(k) discrete value or action chosen by the algorithm at iterationk - u i discrete value of the optimization variable in [u min,u max] - u min lowest value of the optimization variable - u max largest value of the optimization variable - Z random number - x variable for the criterion function - xp precision parameter on criterion function - W(k) performance index unit output at iterationk - 0, 1 reinforcement scheme parameters - p sum of the probability distribution vector components  相似文献   
80.
Let l be the critical exponent associated with the probability thatl independentN-step ordinary random walks, starting at nearby points, are mutually avoiding. Using Monte Carlo methods combined with a maximum-likelihood data analysis, we find that in two dimensions 2=0.6240±0.0005±0.0011 and 3=1.4575±0.0030±0.0052, where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second error bar represents statistical error (classical 95% confidence limits). These results are in good agreement with the conformal-invariance predictions 2=5/8 and 3=35/24.  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