全文获取类型
收费全文 | 12374篇 |
免费 | 905篇 |
国内免费 | 749篇 |
专业分类
化学 | 1453篇 |
晶体学 | 46篇 |
力学 | 455篇 |
综合类 | 82篇 |
数学 | 4106篇 |
物理学 | 2026篇 |
综合类 | 5860篇 |
出版年
2024年 | 26篇 |
2023年 | 91篇 |
2022年 | 159篇 |
2021年 | 188篇 |
2020年 | 232篇 |
2019年 | 237篇 |
2018年 | 203篇 |
2017年 | 277篇 |
2016年 | 302篇 |
2015年 | 318篇 |
2014年 | 439篇 |
2013年 | 673篇 |
2012年 | 580篇 |
2011年 | 558篇 |
2010年 | 467篇 |
2009年 | 662篇 |
2008年 | 725篇 |
2007年 | 802篇 |
2006年 | 807篇 |
2005年 | 701篇 |
2004年 | 608篇 |
2003年 | 552篇 |
2002年 | 520篇 |
2001年 | 466篇 |
2000年 | 465篇 |
1999年 | 413篇 |
1998年 | 304篇 |
1997年 | 280篇 |
1996年 | 220篇 |
1995年 | 232篇 |
1994年 | 176篇 |
1993年 | 161篇 |
1992年 | 181篇 |
1991年 | 152篇 |
1990年 | 110篇 |
1989年 | 121篇 |
1988年 | 111篇 |
1987年 | 87篇 |
1986年 | 60篇 |
1985年 | 48篇 |
1984年 | 37篇 |
1983年 | 21篇 |
1982年 | 37篇 |
1981年 | 20篇 |
1980年 | 49篇 |
1979年 | 36篇 |
1978年 | 25篇 |
1977年 | 35篇 |
1976年 | 24篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
51.
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
52.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
53.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
54.
本文给出了一个数据流图的存贮模型。并在此基础上,给出了数据流图的操作算法。可以解决SA方法中的文档管理。 相似文献
55.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
56.
57.
研究了柔性变截面滑移式机械手臂的控制。首先,基于有限元法导出系统的动力学方程,然后分别建立了两种控制方式的状态方程:1)以加速度和角加速度作为控制变量:2)以力和力矩作为控制变量。控制过程分为“粗控”和“精控”两步进行。“精控”过程采用线性二次型高斯控制。最后给出了数值模拟的结果。 相似文献
58.
The application of some recently proposed algebraic multilevel methods for the solution of two-dimensional finite element problems on nonuniform meshes is studied. The locally refined meshes are created by the newest vertex mesh refinement method. After the introduction of this refinement technique it is shown that, by combining levels of refinement, a preconditioner of optimal order can be constructed for the case of local refinement along a line. Its relative condition number is accurately estimated. Numerical tests demonstrating the performance of the proposed preconditioners will be reported in a forthcoming paper. 相似文献
59.
胡健生 《解放军理工大学学报(自然科学版)》1992,(1)
本文利用作者最近提出的一种新的算子方法——W-算子方法,从理论和应用方面探讨了电气传动控制系统的设计问题,并对算法的收敛性进行了分析。该算法具有结构简单,算法严密,计算方便的特点,避免了实际应用中用传统最优控制方法设计所带来的困难。 相似文献
60.
对拟线性椭圆变分不等式的障碍最优控制问题(即以障碍为控制变量)进行了研究.指标泛函为Lagrange型,其中含有控制变量二阶导数的p次幂,这使得最优性条件的推导颇为不易.对所考虑的问题给出了最优控制的存在性定理以及必要条件. 相似文献