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   3646篇
  免费   335篇
  国内免费   261篇
化学   733篇
晶体学   5篇
力学   263篇
综合类   44篇
数学   2353篇
物理学   844篇
  2024年   10篇
  2023年   50篇
  2022年   83篇
  2021年   96篇
  2020年   133篇
  2019年   113篇
  2018年   107篇
  2017年   115篇
  2016年   120篇
  2015年   111篇
  2014年   192篇
  2013年   416篇
  2012年   179篇
  2011年   202篇
  2010年   187篇
  2009年   222篇
  2008年   255篇
  2007年   213篇
  2006年   170篇
  2005年   194篇
  2004年   144篇
  2003年   121篇
  2002年   119篇
  2001年   71篇
  2000年   94篇
  1999年   80篇
  1998年   59篇
  1997年   58篇
  1996年   54篇
  1995年   39篇
  1994年   33篇
  1993年   39篇
  1992年   16篇
  1991年   14篇
  1990年   11篇
  1989年   13篇
  1988年   13篇
  1987年   20篇
  1986年   17篇
  1985年   7篇
  1984年   10篇
  1983年   4篇
  1982年   9篇
  1981年   6篇
  1980年   4篇
  1979年   2篇
  1978年   3篇
  1977年   4篇
  1974年   2篇
  1970年   2篇
排序方式: 共有4242条查询结果,搜索用时 15 毫秒
21.
纵横扩张的优化   总被引:4,自引:0,他引:4  
得到了最小折数纵横扩张的判别准则.针对4-正则图的平面嵌入的纵横扩张的特殊性,给出了它的最小折数纵横扩张判别准则.  相似文献   
22.
In this paper, we investigate the Hausdorff measure for level sets of N-parameter Rd-valued stable processes, and develop a means of seeking the exact Hausdorff measure function for level sets of N-parameter Rd-valued stable processes. We show that the exact Hausdorff measure function of level sets of N-parameter Rd-valued symmetric stable processes of index α is Ф(r) = r^N-d/α (log log l/r)d/α when Nα 〉 d. In addition, we obtain a sharp lower bound for the Hausdorff measure of level sets of general (N, d, α) strictly stable processes.  相似文献   
23.
24.
In this note, the local spectral properties of unilateral operator weighted shifts arestudied.  相似文献   
25.
This paper proposes a method for estimation of a class of partially linear single-index models with randomly censored samples. The method provides a flexible way for modelling the association between a response and a set of predictor variables when the response variable is randomly censored. It presents a technique for “dimension reduction” in semiparametric censored regression models and generalizes the existing accelerated failure-time models for survival analysis. The estimation procedure involves three stages: first, transform the censored data into synthetic data or pseudo-responses unbiasedly; second, obtain quasi-likelihood estimates of the regression coefficients in both linear and single-index components by an iteratively algorithm; finally, estimate the unknown nonparametric regression function using techniques for univariate censored nonparametric regression. The estimators for the regression coefficients are shown to be jointly root-n consistent and asymptotically normal. In addition, the estimator for the unknown regression function is a local linear kernel regression estimator and can be estimated with the same efficiency as all the parameters are known. Monte Carlo simulations are conducted to illustrate the proposed methodology.  相似文献   
26.
We consider the estimation of multivariate regression functions r(x1,…,xd) and their partial derivatives up to a total order p1 using high-order local polynomial fitting. The processes {Yi,Xi} are assumed to be (jointly) associated. Joint asymptotic normality is established for the estimates of the regression function r and all its partial derivatives up to the total order p. Expressions for the bias and variance/covariance matrix (of the asymptotic distribution) are given.  相似文献   
27.
This document presents theoretical considerations about the solution of dynamic optimization problems integrating the Benders Theory, the Dynamic Programming approach and the concepts of Control Theory. The so called Generalized Dual Dynamic Programming Theory (GDDP) can be considered as an extension of two previous approaches known as Dual Dynamic Programming (DDP): The first is the work developed by Pereira and Pinto [3–5], which was revised by Velásquez and others [8,9]. The second is the work developed by Read and others [2,6,7].  相似文献   
28.
Multi-objective optimization using evolutionary algorithms identifies Pareto-optimal alternatives or their close approximation by means of a sequence of successive local improvement moves. While several successful applications to combinatorial optimization problems are known, studies of underlying problem structures are still scarce.  相似文献   
29.
We deal with the differential conditions for local optimality. The conditions that we derive for inequality constrained problems do not require constraint qualifications and are the broadest conditions based on only first-order and second-order derivatives. A similar result is proved for equality constrained problems, although the necessary conditions require the regularity of the equality constraints.  相似文献   
30.
In this paper, we study the Maslov-type index theory for linear Hamiltonian systems with brake orbits boundary value conditions and its applications to the existence of multiple brake orbits of nonlinear Hamiltonian systems.  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