全文获取类型
收费全文 | 23863篇 |
免费 | 1695篇 |
国内免费 | 1081篇 |
专业分类
化学 | 1530篇 |
晶体学 | 30篇 |
力学 | 2571篇 |
综合类 | 310篇 |
数学 | 19645篇 |
物理学 | 2553篇 |
出版年
2024年 | 41篇 |
2023年 | 238篇 |
2022年 | 348篇 |
2021年 | 526篇 |
2020年 | 512篇 |
2019年 | 537篇 |
2018年 | 608篇 |
2017年 | 704篇 |
2016年 | 666篇 |
2015年 | 505篇 |
2014年 | 1034篇 |
2013年 | 1672篇 |
2012年 | 1230篇 |
2011年 | 1215篇 |
2010年 | 1114篇 |
2009年 | 1474篇 |
2008年 | 1517篇 |
2007年 | 1598篇 |
2006年 | 1363篇 |
2005年 | 1131篇 |
2004年 | 940篇 |
2003年 | 985篇 |
2002年 | 863篇 |
2001年 | 689篇 |
2000年 | 703篇 |
1999年 | 584篇 |
1998年 | 570篇 |
1997年 | 521篇 |
1996年 | 390篇 |
1995年 | 366篇 |
1994年 | 273篇 |
1993年 | 228篇 |
1992年 | 226篇 |
1991年 | 185篇 |
1990年 | 154篇 |
1989年 | 102篇 |
1988年 | 90篇 |
1987年 | 81篇 |
1986年 | 81篇 |
1985年 | 110篇 |
1984年 | 102篇 |
1983年 | 40篇 |
1982年 | 53篇 |
1981年 | 45篇 |
1980年 | 36篇 |
1979年 | 52篇 |
1978年 | 34篇 |
1977年 | 43篇 |
1976年 | 26篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
121.
Using a method of uniform approximations, necessary and sufficient conditions for a nonsmooth constrained vector-valued minimax problem are established in terms of Mordukhovich subdifferentials. 相似文献
122.
ELSO is an environment for the solution oflarge-scale optimization problems. With ELSO the user is required to provide only code for the evaluation of a partially separable function. ELSO exploits the partialseparability structure of the function to computethe gradient efficiently using automatic differentiation.We demonstrate ELSO's efficiency by comparing thevarious options available in ELSO.Our conclusion is that the hybrid option in ELSOprovides performance comparable to the hand-coded option, while having the significantadvantage of not requiring a hand-coded gradient orthe sparsity pattern of the partially separable function.In our test problems, which have carefully coded gradients,the computing time for the hybrid AD option is within a factor of two of thehand-coded option. 相似文献
123.
本文证明了周期单元中带有某些硬相互作用的相对论Boltzmann方程初值问题在初值满足质量、能量和熵有限的条件下具有一个整体温和解. 相似文献
124.
We develop a production policy that controls work-in-process (WIP) levels and satisfies demand in a multistage manufacturing system with significant uncertainty in yield, rework, and demand. The problem addressed in this paper is more general than those in the literature in three aspects: (i) multiple products are processed at multiple workstations, and the capacity of each workstation is limited and shared by multiple operations; (ii) the behavior of a production policy is investigated over an infinite-time horizon, and thus the system stability can be evaluated; (iii) the representation of yield and rework uncertainty is generalized. Generalizing both the system structure and the nature of uncertainty requires a new mathematical development in the theory of infinite-horizon stochastic dynamic programming. The theoretical contributions of this paper are the existence proofs of the optimal stationary control for a stochastic dynamic programming problem and the finite covariances of WIP and production levels under the general expression of uncertainty. We develop a simple and explicit sufficient condition that guarantees the existence of both the optimal stationary control and the system stability. We describe how a production policy can be constructed for the manufacturing system based on the propositions derived. 相似文献
125.
In this paper, we investigate a constrained optimization problem with a quadratic cost functional and two quadratic equality constraints. It is assumed that the cost functional is positive definite and that the constraints are both feasible and regular (but otherwise they are unrestricted quadratic functions). Thus, the existence of a global constrained minimum is assured. We develop a necessary and sufficient condition that completely characterizes the global minimum cost. Such a condition is of essential importance in iterative numerical methods for solving the constrained minimization problem, because it readily distinguishes between local minima and global minima and thus provides a stopping criterion for the computation. The result is similar to one obtained previously by the authors. In the previous result, we gave a characterization of the global minimum of a constrained quadratic minimization problem in which the cost functional was an arbitrary quadratic functional (as opposed to positive-definite here) and the constraints were at least positive-semidefinite quadratic functions (as opposed to essentially unrestricted here). 相似文献
126.
UCINSKI DARIUSZ; JAI ABDELHAQ EL 《IMA Journal of Mathematical Control and Information》1997,14(2):153-174
In this paper, the concept of weak spreadability is introduced.It constitutes an extension of the idea developed by El Jai& Kassara. In the case of linear distributed systems weconsider quadratic control techniques with a conveniently penalizedcriterion which makes the system weakly spreadable. The approachis outlined for a convectiondiffusion system, and theresults of a numerical study are also included to illustratethe main features of the considered problem. 相似文献
127.
Yoshikazu Takada 《Annals of the Institute of Statistical Mathematics》1998,50(2):325-335
This paper gives a condition which implies the nonexistence of parametric statistical procedures with bounded risk or error performance characteristics. Many examples for which such a condition is satisfied are considered. 相似文献
128.
IGCC空气侧整体综合优化的研究 总被引:4,自引:1,他引:3
主要符号表X。。氮气回注系数如空分整体化系数E。;c燃气轮机压气机效率G。l回注氮气流量万燃气轮机透平前温尼。”系统相对效率G。。煤气氮气掺混流量Ea;,c空气专用压缩机效率N。”系统相对功率1前言整体煤气化联合循环(IGCC)系统模拟与优化逐步受到重视,开展了许多相关研究[‘-‘]。但是,现有的方法[‘,‘]一个突出的问题,它是在设定的具体流程方案下的数值分析,这常常导致落入“局部优化掩盖了整体最优”的误区。本文是研究以空分系统为中心的空气侧子系统的整体优化,阐述基本概念,尝试新方法,并结合大型商业化装… 相似文献
129.
130.
一类经典”秘书问题”的推广 总被引:2,自引:0,他引:2
”秘书问题”在最优停时理论的发展中曾起过重要作用 ,实际中的一类问题与”秘书问题”有类似之处 ,但比”秘书问题”更复杂 .本文将经典”秘书问题”进行推广 ,建立了一类比经典”秘书问题”更有实际意义的模型 ,并给出了该类模型的解 . 相似文献