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   3586篇
  免费   150篇
  国内免费   180篇
化学   333篇
晶体学   4篇
力学   420篇
综合类   11篇
数学   1966篇
物理学   1182篇
  2024年   5篇
  2023年   53篇
  2022年   53篇
  2021年   41篇
  2020年   77篇
  2019年   78篇
  2018年   74篇
  2017年   96篇
  2016年   89篇
  2015年   101篇
  2014年   228篇
  2013年   361篇
  2012年   184篇
  2011年   248篇
  2010年   261篇
  2009年   311篇
  2008年   292篇
  2007年   287篇
  2006年   175篇
  2005年   116篇
  2004年   121篇
  2003年   77篇
  2002年   86篇
  2001年   77篇
  2000年   60篇
  1999年   48篇
  1998年   50篇
  1997年   38篇
  1996年   28篇
  1995年   33篇
  1994年   15篇
  1993年   18篇
  1992年   24篇
  1991年   14篇
  1990年   8篇
  1989年   10篇
  1988年   9篇
  1987年   6篇
  1986年   8篇
  1985年   11篇
  1984年   7篇
  1983年   6篇
  1982年   12篇
  1981年   2篇
  1980年   5篇
  1979年   3篇
  1978年   5篇
  1977年   2篇
  1972年   1篇
  1971年   1篇
排序方式: 共有3916条查询结果,搜索用时 14 毫秒
991.
Summary This paper considers discrete distributions of orderk based on a binary sequence which is defined as an extension of independent trials with a constant success probability and is more practical than the independent trials. Some results on calculation of probabilities and characteristics of the distributions are obtained as well as their formal expressions. Examples and an application are also given. The Institute of Statistical Mathematics  相似文献   
992.
本文讨论了一类广义非自治离散松驰系统的时间最优控制问题,将R^n中点曲线的目标约束推广为凸集值函数的超曲线约束.在证明了松驰系统与原系统可达集相等的基础上,得到了最优控制的存在性.由凸集分离定理及终端时间闺值函数方程,我们获得了最大值原理及最优控制时间的确定方法.较之Hamilton方法,本文的条件更一般.离散松驰系统的相关结论可以用于分散控制.  相似文献   
993.
该文利用拓扑度方法研究了一类时滞依赖状态的广义Duffing型泛函微分方程x'(t)$ 该文利用拓扑度方法研究了一类时滞依赖状态的广义Duffing型泛函微分方程x'(t)$ 该文利用拓扑度方法研究了一类时滞依赖状态的广义Duffing型泛函微分方程x'(t) g(x(t-τ(t,x(t))))=f(t)周期解的存在性,得到了方程周期解存在的充分条件和必要条件.研究了当滞量为常值时,方程周期解的存在唯一性.并且给出了所研究问题的一个应用实例.  相似文献   
994.
We consider the Hermite trigonometric interpolation problem of order 1 for equidistant nodes, i.e., the problem of finding a trigonometric polynomial t that interpolates the values of a function and of its derivative at equidistant points. We give a formula for the Fourier coefficients of t in terms of those of the two classical trigonometric polynomials interpolating the values and those of the derivative separately. This formula yields the coefficients with a single FFT. It also gives an aliasing formula for the error in the coefficients which, on its turn, yields error bounds and convergence results for differentiable as well as analytic functions. We then consider the Lagrangian formula and eliminate the unstable factor by switching to the barycentric formula. We also give simplified formulae for even and odd functions, as well as consequent formulae for Hermite interpolation between Chebyshev points.  相似文献   
995.
We use Brouwer degree to prove existence and multiplicity results for the periodic solutions of some nonlinear second order difference equations involving discrete -Laplacian. We obtain in particular upper and lower solutions theorems, Ambrosetti–Prodi type multiplicity results, sharp existence conditions for nonlinearities which are bounded from below or from above and necessary and sufficient conditions for the existence of positive periodic solutions when the nonlinearity is singular at 0.  相似文献   
996.
It is first observed that a uniformly bounded cosine operator function C() and the associated sine function S() are totally non-stable. Then, using a zero-one law for the Abel limit of a closed linear operator, we prove some results concerning strong mean stability and uniform mean stability of C(). Among them are: (1) C() is strongly (C,1)-mean stable (or (C,2)-mean stable, or Abel-mean stable) if and only if 0ρ(A)σc(A); (2) C() is uniformly (C,2)-mean stable if and only if S() is uniformly (C,1)-mean stable, if and only if , if and only if , if and only if C() is uniformly Abel-mean stable, if and only if S() is uniformly Abel-mean stable, if and only if 0ρ(A).  相似文献   
997.
Intuition suggests that the variance of additive noise contaminating a signal can be estimated by investigation of the highest resolution level in a local Nonlinear Multiresolution Analysis. In the case of the Discrete Pulse Transforms with LULU-operators well known elegant identities between B-splines lead to some surprisingly simple and useful results.  相似文献   
998.
Coherent multiperiod risk adjusted values and Bellman’s principle   总被引:1,自引:0,他引:1  
Starting with a time-0 coherent risk measure defined for “value processes”, we also define risk measurement processes. Two other constructions of measurement processes are given in terms of sets of test probabilities. These latter constructions are identical and are related to the former construction when the sets fulfill a stability condition also met in multiperiod treatment of ambiguity as in decision-making. We finally deduce risk measurements for the final value of locked-in positions and repeat a warning concerning Tail-Value-at-Risk.  相似文献   
999.
The classical discrete location problem is extended here, where the candidate facilities are subject to failure. The unreliable location problem is defined by introducing the probability that a facility may become inactive. The formulation and the solution procedure have been motivated by an application to model and solve a large size problem for locating base stations in a cellular communication network. We formulate the unreliable discrete location problems as 0–1 integer programming models, and implement an enhanced dual-based solution method to determine locations of these facilities to minimize the sum of fixed cost and expected operating (transportation) cost. Computational tests of some well-known problems have shown that the heuristic is efficient and effective for solving these unreliable location problems.  相似文献   
1000.
The classical vehicle routing problem involves designing a set of routes for a fleet of vehicles based at one central depot that is required to serve a number of geographically dispersed customers, while minimizing the total travel distance or the total distribution cost. Each route originates and terminates at the central depot and customers demands are known. In many practical distribution problems, besides a hard time window associated with each customer, defining a time interval in which the customer should be served, managers establish multiple objectives to be considered, like avoiding underutilization of labor and vehicle capacity, while meeting the preferences of customers regarding the time of the day in which they would like to be served (soft time windows). This work investigates the use of goal programming to model these problems. To solve the model, an enumeration-followed-by-optimization approach is proposed which first computes feasible routes and then selects the set of best ones. Computational results show that this approach is adequate for medium-sized delivery problems.  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