全文获取类型
收费全文 | 10795篇 |
免费 | 1683篇 |
国内免费 | 482篇 |
专业分类
化学 | 1935篇 |
晶体学 | 44篇 |
力学 | 1721篇 |
综合类 | 208篇 |
数学 | 5658篇 |
物理学 | 3394篇 |
出版年
2024年 | 16篇 |
2023年 | 145篇 |
2022年 | 288篇 |
2021年 | 307篇 |
2020年 | 259篇 |
2019年 | 244篇 |
2018年 | 244篇 |
2017年 | 462篇 |
2016年 | 530篇 |
2015年 | 469篇 |
2014年 | 591篇 |
2013年 | 807篇 |
2012年 | 573篇 |
2011年 | 582篇 |
2010年 | 526篇 |
2009年 | 646篇 |
2008年 | 680篇 |
2007年 | 685篇 |
2006年 | 532篇 |
2005年 | 424篇 |
2004年 | 427篇 |
2003年 | 437篇 |
2002年 | 379篇 |
2001年 | 276篇 |
2000年 | 290篇 |
1999年 | 278篇 |
1998年 | 245篇 |
1997年 | 190篇 |
1996年 | 182篇 |
1995年 | 161篇 |
1994年 | 123篇 |
1993年 | 99篇 |
1992年 | 76篇 |
1991年 | 81篇 |
1990年 | 68篇 |
1989年 | 55篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 68篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 47篇 |
1979年 | 46篇 |
1978年 | 27篇 |
1977年 | 37篇 |
1976年 | 38篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Jong Dae Lee Dong-Hwal Lee No-Kuk Park Si Ok Ryu Tae Jin Lee 《Current Applied Physics》2006,6(6):1040
The reduction–carburization of tungsten trioxide (WO3) under carbon monoxide flow was studied in the temperature range of 300–750 °C. The reduction–carburization of WO3 was improved by mechanically mixing with zeolite-HX, -NaX and -KX. The interaction between cation in zeolite-X and oxygen in WO3 affected the improvement of the reduction–carburization of WO3 to WC. Moreover, the improved reduction–carburization of WO3 could lead to the decrease of reaction temperature. Because the particle size of WC is in contact with a reaction temperature, the nanophase WC can be prepared at low temperature. In particular, the particle size of WC was controlled by reaction temperature. The particle sizes of produced WC at 550, 650 and 700 °C were 25, 50 and 100 nm respectively. 相似文献
942.
We consider the control of an infinite capacity shuttle which transports passengers between two terminals. The passengers
arrive at each terminal according to a compound Poisson process and the travel time from one terminal to the other is a random
variable following an arbitrary distribution. The following control limit policy is considered: dispatch the shuttle at terminali, at the instant that the total number of passengers waiting at terminali reaches or exceeds a predetermined control limitm
i
. The objective of this paper is to obtain the mean waiting time of an arbitrary passenger at each terminal for given control
valuesm
1 andm
2. We also discuss a search procedure to obtain the optimal control values which minimize the total expected cost per unit
time under a linear cost structure. 相似文献
943.
模糊控制已在一类缓变的过程控制中得到成功的应用,本文将它引入到柴油机这一高速系统的性能控制,研究了相应的模糊控制器的设计方法,研制了以微计算机为核心的增压空气泄放控制系统,并在B6135-ZG20涡轮增压柴油机上实现了最大爆发压力的闭环控制。这一研究进一步改善了增压系统的性能,也为模糊控制开辟了一个新的应用领域。 相似文献
944.
J. P. Raymond 《Journal of Optimization Theory and Applications》1990,67(1):109-132
We give existence theorems of solutions for Lagrange and Bolza problems of optimal control. These results are obtained without convexity assumptions on the cost function with respect to the control variable. We extend a Cesari's theorem to cost functions which are nonlinear with respect to the space variable and to problems which are governed by a differential inclusion. Moreover, we consider the case where the control variable belongs to a space of measurable functions and the case where this variable belongs to a Lebesgue space. 相似文献
945.
F. Blanchini 《Journal of Optimization Theory and Applications》1990,65(1):29-40
The problem of control in the presence of unknown but limited disturbance for a discrete-time linear system with polyhedral input and state bounds is investigated. Two problems are considered: that of reaching an assigned target set in the state space; and that of keeping the state in a given region using the available controls. In both cases, a solution is given via linear programming. A computational procedure for the control synthesis is proposed which can be implemented to obtain a feedback control.The author thanks Professor G. Leitmann for his helpful suggestions. 相似文献
946.
Zhi-Chi Zhu 《Acta Mechanica Solida Sinica》1990,3(4):457-468
Researches on sound propagation problems in ducts done by the author and other investigators in recent years are briefly discussed in this paper. The finite difference method used in fluid mechanics is used for solving these problems thus presenting an aspect of the development of research work in this field at home and abroad.The project supported by National Natural Science Foundation of China. 相似文献
947.
V. S. Borkar 《Journal of Optimization Theory and Applications》1990,66(2):289-309
The Kumar-Becker-Lin scheme introduces a slowly vanishing cost bias in the parameter estimation part of self-tuning control in order to improve its performance. This paper establishes the a.s. optimality of a variant of this scheme for Markov chains on a countable state space when the action space is compact metric and the parameter space is a compact subset ofR
m
. 相似文献
948.
We consider a finite-horizon control model with additive input. There are two convex functions which describe the running cost and the terminal cost within the system. The cost of input is proportional to the input and can take both positive and negative values. It is shown that there exists a deterministic control problem whose optimal cost is the same as the one in the stochastic control problem. The optimal policy for the stochastic problem consists of keeping the process as close to the optimal deterministic trajectory as possible.This research is supported by NSERC Grant A4619, MRCO, NSF Grant DMS-86-01510, and AFOSR Grant 87-0278. 相似文献
949.
We consider time discrete systems which are described by a system of difference equations. The related discrete optimal control problems are introduced. Additionally, a gametheoretic extension is derived, which leads to general multicriteria decision problems. The characterization of their optimal behavior is studied. Given starting and final states define the decision process; applying dynamic programming techniques suitable optimal solutions can be gained. We generalize that approach to a special gametheoretic decision procedure on networks. We characterize Nash equilibria and present sufficient conditions for their existence. A constructive algorithm is derived. The sufficient conditions are exploited to get the algorithmic solution. Its complexity analysis is presented and at the end we conclude with an extension to the complementary case of Pareto optima.Dmitrii Lozovanu was Supported by BGP CRDF-MRDA MOM2-3049-CS-03. 相似文献
950.
M. Majewski 《Journal of Optimization Theory and Applications》2006,128(3):635-651
In this paper, some results concerning the existence of optimal solutions to an optimal control problem are derived. The problem involves a quasilinear hyperbolic differential equation with boundary condition and a nonlinear integral functional of action. The assumption of convexity, under which the main theorem is proved, is not connected directly with the convexity of the functional of action. In the proof, the implicit function theorem for multimappings is used.Communicated by L. D. Berkovitz 相似文献