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   16079篇
  免费   2377篇
  国内免费   710篇
化学   2008篇
晶体学   42篇
力学   2291篇
综合类   280篇
数学   9940篇
物理学   4605篇
  2023年   198篇
  2022年   238篇
  2021年   402篇
  2020年   427篇
  2019年   377篇
  2018年   403篇
  2017年   635篇
  2016年   722篇
  2015年   586篇
  2014年   795篇
  2013年   1379篇
  2012年   848篇
  2011年   843篇
  2010年   762篇
  2009年   887篇
  2008年   955篇
  2007年   943篇
  2006年   830篇
  2005年   702篇
  2004年   621篇
  2003年   659篇
  2002年   564篇
  2001年   494篇
  2000年   479篇
  1999年   414篇
  1998年   369篇
  1997年   298篇
  1996年   259篇
  1995年   248篇
  1994年   195篇
  1993年   151篇
  1992年   137篇
  1991年   140篇
  1990年   119篇
  1989年   91篇
  1988年   104篇
  1987年   84篇
  1986年   70篇
  1985年   114篇
  1984年   81篇
  1983年   45篇
  1982年   69篇
  1981年   48篇
  1980年   69篇
  1979年   65篇
  1978年   44篇
  1977年   62篇
  1976年   58篇
  1974年   19篇
  1957年   13篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
We present an existence result for Lévy‐type processes which requires only weak regularity assumptions on the symbol with respect to the space variable x. Applications range from existence and uniqueness results for Lévy‐driven SDEs with Hölder continuous coefficients to existence results for stable‐like processes and Lévy‐type processes with symbols of variable order. Moreover, we obtain heat kernel estimates for a class of Lévy and Lévy‐type processes. The paper includes an extensive list of Lévy(‐type) processes satisfying the assumptions of our results.  相似文献   
52.
53.
This paper considers the consensus tacking problem for nonlinear fractional‐order multiagent systems by presenting a PDα‐type iterative learning control update law with initial learning mechanisms. The asymptotical convergence of the proposed distributed learning algorithm is strictly proved by using the properties of fractional calculus. A sufficient condition is derived to guarantee the whole multiagent system achieving an asymptotic output consensus. An illustrative example is given to verify the theoretical results.  相似文献   
54.
Birnbaum and Saunders introduced a two‐parameter lifetime distribution to model the fatigue life of a metal, subject to cyclic stress. Since then, extensive work has been done on this model providing different interpretations, constructions, generalizations, inferential methods, and extensions to bivariate, multivariate, and matrix‐variate cases. More than 200 papers and one research monograph have already appeared describing all these aspects and developments. In this paper, we provide a detailed review of all these developments and, at the same time, indicate several open problems that could be considered for further research.  相似文献   
55.
56.
We consider systems of stochastic differential equations of the form d X t i = j = 1 d A i j ( X t ? ) d Z t j for i = 1 , ? , d with continuous, bounded and non‐degenerate coefficients. Here Z t 1 , ? , Z t d are independent one‐dimensional stable processes with α 1 , ? , α d ( 0 , 2 ) . In this article we research on uniqueness of weak solutions to such systems by studying the corresponding martingale problem. We prove the uniqueness of weak solutions in the case of diagonal coefficient matrices.  相似文献   
57.
闫熙  马昌凤 《计算数学》2019,41(1):37-51
本文针对求矩阵方程AXB+CXD=F唯一解的参数迭代法,分析当矩阵A,B,C,D均是Hermite正(负)定矩阵时,迭代矩阵的特征值表达式,给出了最优参数的确定方法,并提出了相应的加速算法.  相似文献   
58.
ABSTRACT

The single input single output (SISO) system with known strong interference is widely used in various occasions. Due to its strong interference, the control accuracy is hard to guarantee. To solve this problem, an improved generalized predictive control (IGPC) algorithm is developed. The IGPC firstly builds the difference equation CARIMA (Controlled Auto-Regressive Integrated Moving-Average) model of the SISO system and then treats the system as a two input single output (TISO) system and calculates its predictive vector, then transforms it into a SISO system and uses the TISO system predictive vector to calculate the SISO system control increment. A new parameter called phase coefficient is added to inhibit the control lag. Simulations are performed to make the comparison among the traditional GPC, PID control, velocity synchronization control (VSC), fuzzy adaptive PID control (FAPID), model-based robust PID control (BPID) and the IGPC. Results show that IGPC has best performance compared to the others. Finally, experiments are developed which proved that the IGPC algorithm has a higher accuracy in the SISO system with known strong interference than that of VSC.  相似文献   
59.
It is shown that for , there exists an optimal packing with triples on points that contains no Pasch configurations. Furthermore, for all (mod 6), there exists a pairwise balanced design of order , whose blocks are all triples apart from a single quintuple, and that has no Pasch configurations amongst its triples.  相似文献   
60.
ABSTRACT

An optimization problem of maximizing an integral of a function over a family of probability measures is considered. The problem is a generalization of a well-studied variational problem in mathematical economics, concerning optimal allocations. The specific generalization that we examine arises also in the limit of singularly perturbed optimal control problems. We examine the mathematical problem and allude to the singular perturbation motivation.  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