全文获取类型
收费全文 | 12861篇 |
免费 | 1969篇 |
国内免费 | 510篇 |
专业分类
化学 | 3333篇 |
晶体学 | 72篇 |
力学 | 1790篇 |
综合类 | 276篇 |
数学 | 5371篇 |
物理学 | 4498篇 |
出版年
2024年 | 16篇 |
2023年 | 186篇 |
2022年 | 310篇 |
2021年 | 413篇 |
2020年 | 327篇 |
2019年 | 303篇 |
2018年 | 304篇 |
2017年 | 533篇 |
2016年 | 606篇 |
2015年 | 539篇 |
2014年 | 697篇 |
2013年 | 918篇 |
2012年 | 698篇 |
2011年 | 770篇 |
2010年 | 619篇 |
2009年 | 794篇 |
2008年 | 790篇 |
2007年 | 796篇 |
2006年 | 623篇 |
2005年 | 519篇 |
2004年 | 535篇 |
2003年 | 523篇 |
2002年 | 442篇 |
2001年 | 336篇 |
2000年 | 347篇 |
1999年 | 328篇 |
1998年 | 281篇 |
1997年 | 213篇 |
1996年 | 224篇 |
1995年 | 179篇 |
1994年 | 140篇 |
1993年 | 121篇 |
1992年 | 87篇 |
1991年 | 90篇 |
1990年 | 79篇 |
1989年 | 62篇 |
1988年 | 62篇 |
1987年 | 58篇 |
1986年 | 40篇 |
1985年 | 68篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 33篇 |
1981年 | 29篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 26篇 |
1977年 | 36篇 |
1976年 | 37篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
91.
92.
Decentralized iterative learning control for a class of large scale interconnected dynamical systems
Hansheng Wu 《Journal of Mathematical Analysis and Applications》2007,327(1):233-245
The problem of decentralized iterative learning control for a class of large scale interconnected dynamical systems is considered. In this paper, it is assumed that the considered large scale dynamical systems are linear time-varying, and the interconnections between each subsystem are unknown. For such a class of uncertain large scale interconnected dynamical systems, a method is presented whereby a class of decentralized local iterative learning control schemes is constructed. It is also shown that under some given conditions, the constructed decentralized local iterative learning controllers can guarantee the asymptotic convergence of the local output error between the given desired local output and the actual local output of each subsystem through the iterative learning process. Finally, as a numerical example, the system coupled by two inverted pendulums is given to illustrate the application of the proposed decentralized iterative learning control schemes. 相似文献
93.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
94.
Rolando Cavazos-Cadena 《Annals of Operations Research》1991,28(1):169-184
We consider a class of Markov decision processes withfinite state and action spaces which, essentially, is determined by the following condition: The state space isirreducible under the action of any stationary policy. However, except by this restriction, the transition law iscompletely unknown to the controller. In this context, we find a set of policies under which thefrequency estimators of the transition law are strongly consistent and then, this result is applied to constructadaptive asymptotically discount-optimal policies.Dedicated to Professor Truman O. Lewis, on the occasion of his sixtieth birthdayThis research was supported in part by the Third World Academy of Sciences (TWAS) under Grant TWAS RG MP 898-152, and in part by the Consejo Nacional de Ciencia y Tecnología (CONACYT) under Grant A128CCOEO550 (MT-2). 相似文献
95.
Decisions concerning a project’s expedition, traditionally involved considerations regarding time and cost tradeoff. It was recently suggested that the quality of a project should also be taken into considerations. In this paper, we propose a meta-heuristic solution procedure for the discrete time, cost and quality tradeoff problem. This problem involves the scheduling of project activities in order to minimize the total cost of the project while maximizing the quality of the project and also meeting a given deadline. We apply a so called electromagnetic scatter search to solve this problem. In this process, we initially generate a population of feasible solutions. In so doing, we use frequency memory to well sample the feasible region. A number of these solutions are then selected and improved locally. The improved solutions are then combined to generate new set of solutions. The combination process utilizes attraction–repulsion mechanisms borrowed from the electromagnetism theory. The whole process is stopped when no significant improvement in the set of solutions are observed. The validity of the proposed solution procedure is demonstrated, and its applicability is tested on a randomly generated large and complex problem having 19,900 activities. 相似文献
96.
从大型复杂武器装备系统的具体特点出发,运用基于神经网络的评价方法,构建了大型复杂武器装备质量综合评价模型。实证分析的结果表明该方法得出的结果与实际情况相符。 相似文献
97.
魏立平 《数学的实践与认识》2004,34(4):1-4
综合运用国内外多种测量量表对大学生的心理素质进行诊断与测试 ,并应用多元统计分析方法对其心理素质结构主因素进行定量分析 ,在此基础上建立了心理素质诊断模型 ,并运用该模型对实际问题进行了分析 . 相似文献
98.
HT—6M闭环反馈平衡控制系统 总被引:1,自引:1,他引:0
本文描述HT-6M托卡马克装置闭环反馈平衡控制系统的结构组成,通过对各个环节的简化,得到了有效实用的数学模型,进而分析了系统稳态和动态性能。实验结果表明,该系统运行可靠;并且,将等离子体环水平位移控制在2mm以内。 相似文献
99.
This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically. 相似文献
100.
SXDG—1型汽车前照灯全自动检测仪是用于检测汽车前照大灯光轴的偏斜情况及发光强度并进行定量检验的专用设备。它可以自动测出有关参数,并予以数字显示和打印输出。本文介绍了该仪器的主要性能、工作原理及微机控制系统(包括硬件结构和软件设计思想等)。 相似文献