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   9476篇
  免费   1763篇
  国内免费   597篇
化学   2123篇
晶体学   80篇
力学   857篇
综合类   147篇
数学   4333篇
物理学   4296篇
  2024年   9篇
  2023年   89篇
  2022年   210篇
  2021年   277篇
  2020年   291篇
  2019年   326篇
  2018年   302篇
  2017年   395篇
  2016年   424篇
  2015年   353篇
  2014年   493篇
  2013年   854篇
  2012年   551篇
  2011年   602篇
  2010年   537篇
  2009年   569篇
  2008年   636篇
  2007年   566篇
  2006年   501篇
  2005年   456篇
  2004年   380篇
  2003年   398篇
  2002年   355篇
  2001年   300篇
  2000年   265篇
  1999年   256篇
  1998年   183篇
  1997年   202篇
  1996年   197篇
  1995年   130篇
  1994年   98篇
  1993年   72篇
  1992年   68篇
  1991年   57篇
  1990年   49篇
  1989年   45篇
  1988年   32篇
  1987年   35篇
  1986年   32篇
  1985年   50篇
  1984年   31篇
  1983年   18篇
  1982年   27篇
  1981年   24篇
  1980年   9篇
  1979年   19篇
  1978年   14篇
  1977年   13篇
  1976年   11篇
  1973年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
This paper focus on the event-triggered sliding mode controller design for discrete-time switched genetic regulatory networks (GRNs) with persistent dwell time (PDT) switching. Firstly, the observation error dynamics of switched GRNs with PDT is constructed in the light of event-triggered sliding mode control (SMC) scheme. Next, sufficient conditions are derived to ensure the exponential stability of the augmented plant. Moreover, an event-triggered SMC law is synthesized to impel the system trajectories onto the sliding surface in a finite time. Finally, a verification example is provided to illustrate the effectiveness and potential of the proposed method.  相似文献   
122.
In this paper, we investigate the Novikov equation with weak dissipation terms. First, we give the local well-posedness and the blow-up scenario. Then, we discuss the global existence of the solutions under certain conditions. After that, on condition that the compactly supported initial data keeps its sign, we prove the infinite propagation speed of our solutions, and establish the large time behavior. Finally, we also elaborate the persistence property of our solutions in weighted Sobolev space.  相似文献   
123.
The single machine group scheduling problem is considered. Jobs are classified into several groups on the basis of group technology, i.e. jobs of the same group have to be processed jointly. A machine set-up time independent of the group sequence is needed between each two consecutive groups. A schedule specifies the sequence of groups and the sequence of jobs in each group. The quality of a schedule is measured by the criteriaF 1, ...,F m ordered by their relative importance. The objective is to minimize the least important criterionF m subject to the schedule being optimal with respect to the more important criterionF m–1 which is minimized on the set of schedules minimizing criterionF m–2 and so on. The most important criterion isF 1, which is minimized on the set of all feasible schedules. An approach to solve this multicriterion problem in polynomial time is presented if functionsF 1, ...,F m have special properties. The total weighted completion time and the total weighted exponential time are the examples of functionsF 1, ...,F m–1 and the maximum cost is an example of functionF m for which our approach can be applied.The research of the authors was partially supported by a KBN Grant No. 3 P 406 003 05, the Fundamental Research Fund of Belarus, Project N 60-242, and the Deutsche Forschungsgemeinschaft, Project Schema, respectively. The paper was completed while the first author was visiting the University of Melbourne.  相似文献   
124.
The minimum time problem associated with a nonlinear control system is considered, and the unicity of the lower semicontinuous solution of the corresponding Bellman equation is investigated. A main tool in our approach is the Kruzkov transformation that enables us to work on n –{0}, where {0} is the target set, instead of the unknown reachable set.This research was carried out while the first author was visiting the Department of Mathematics, University of Genova, Genova, Italy.  相似文献   
125.
We establish the large deviation principle (LDP) for the virtual waiting time and queue length processes in the GI/GI/1 queue. The rate functions are found explicitly. As an application, we obtain the logarithmic asymptotics of the probabilities that the virtual waiting time and queue length exceed high levels at large times. Additional new results deal with the LDP for renewal processes and with the derivation of unconditional LDPs for conditional ones. Our approach applies in large deviations ideas and methods of weak convergence theory.This work was supported in part by AT&T Bell Labs.  相似文献   
126.
Considering an infinite string of i.i.d. random letters drawn from a finite alphabet we define the cover timeW n as the number of random letters needed until each pattern of lenghtn appears at least once as a substring. Sharp weak and a.s. limit results onW n are known in the symmetric case, i.e., when the random letters are uniformly distributed over the alphabet. In this paper we determine the limit distribution ofW n in the nonsymmetric case asn. Generalizations in terms of point processes are also proved.Dedicated to Endre Csáki on his 60th birthday.  相似文献   
127.
Noise effects on phase lockings in a system consisting of a piecewise-linear van der Pol relaxation oscillator driven by a periodic input are studied. The problem of finding the period of the oscillator is reduced to the first-passage-time problem of the Ornstein-Uhlenbeck process with time-varying boundary. The probability density functions of the first-passage time are used to define the operator which governs a transition of an input phase density after one cycle of the oscillator. Phase lockings in a stochastic sense are investigated on the basis of the density evolution by the operator.  相似文献   
128.
Three-dimensional systems possessing a homoclinic orbit associated to a saddle focus with eigenvalues ±i, – and giving rise to homoclinic chaos when the Shil'nikov condition < is satisfied are studied. The 2D Poincaré map and its 1D contractions capturing the essential features of the flow are given. At homoclinicity, these 1D maps are found to be piecewise linear. This property allows one to reduce the Frobenius—Perron equation to a master equation whose solution is analytically known. The probabilistic properties such as the time autocorrelation function of the state variablex are explicitly derived.  相似文献   
129.
LetW be a Wiener process of dimensiond3, starting from 0, and letX(t) be the total time spent byW in the ball centered at 0 with radiust. We give an affirmative answer to a conjecture of Taylor and Tricot(16) on the tail distribution ofX(t). Lévy's lower functions ofX(t) are characterized by an integral test.  相似文献   
130.
LetR be the radial part of ad-dimensional Wiener process, starting from 0. In this paper, small ball probabilities are evaluated for sup0<11(t –p R(t)) and sup t 0(e –1 R(t)), withp[0, 1/2]. Chung's law of the iterated logarithm is established for the supremum of the local times of a two-dimensional Bessel process.  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