全文获取类型
收费全文 | 23768篇 |
免费 | 3079篇 |
国内免费 | 1579篇 |
专业分类
化学 | 11437篇 |
晶体学 | 132篇 |
力学 | 1759篇 |
综合类 | 247篇 |
数学 | 10165篇 |
物理学 | 4686篇 |
出版年
2024年 | 35篇 |
2023年 | 437篇 |
2022年 | 472篇 |
2021年 | 511篇 |
2020年 | 701篇 |
2019年 | 689篇 |
2018年 | 688篇 |
2017年 | 745篇 |
2016年 | 997篇 |
2015年 | 1054篇 |
2014年 | 1391篇 |
2013年 | 2026篇 |
2012年 | 1332篇 |
2011年 | 1481篇 |
2010年 | 1296篇 |
2009年 | 1459篇 |
2008年 | 1566篇 |
2007年 | 1527篇 |
2006年 | 1224篇 |
2005年 | 906篇 |
2004年 | 881篇 |
2003年 | 896篇 |
2002年 | 765篇 |
2001年 | 554篇 |
2000年 | 550篇 |
1999年 | 542篇 |
1998年 | 469篇 |
1997年 | 331篇 |
1996年 | 339篇 |
1995年 | 364篇 |
1994年 | 294篇 |
1993年 | 218篇 |
1992年 | 203篇 |
1991年 | 144篇 |
1990年 | 130篇 |
1989年 | 109篇 |
1988年 | 111篇 |
1987年 | 79篇 |
1986年 | 70篇 |
1985年 | 121篇 |
1984年 | 81篇 |
1983年 | 43篇 |
1982年 | 88篇 |
1981年 | 67篇 |
1980年 | 76篇 |
1979年 | 80篇 |
1978年 | 60篇 |
1977年 | 60篇 |
1976年 | 65篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
The existence of an attractor for a 2D-Navier-Stokes system with delay is proved. The theory of pullback attractors is successfully applied to obtain the results since the abstract functional framework considered turns out to be nonautonomous. However, on some occasions, the attractors may attract not only in the pullback sense but in the forward one as well. Also, this formulation allows to treat, in a unified way, terms containing various classes of delay features (constant, variable, distributed delays, etc.). As a consequence, some results for the autonomous model are deduced as particular cases of our general formulation. 相似文献
62.
M Gubinelli 《Journal of Functional Analysis》2004,216(1):86-140
We formulate indefinite integration with respect to an irregular function as an algebraic problem which has a unique solution under some analytic constraints. This allows us to define a good notion of integral with respect to irregular paths with Hölder exponent greater than 1/3 (e.g. samples of Brownian motion) and study the problem of the existence, uniqueness and continuity of solution of differential equations driven by such paths. We recover Young's theory of integration and the main results of Lyons’ theory of rough paths in Hölder topology. 相似文献
63.
风力发电机组变速恒频控制系统研究 总被引:2,自引:0,他引:2
全面介绍了一种最新应用于风力发电中的新型电机—无刷双馈电机,并分析了这种新型电机作变速恒频运行的原理并对这种电机进行了动态特性仿真研究,给出了形式简洁的控制方程和易于实现的控制方案。 相似文献
64.
光突发交换的交换控制策略和光缓存配置 总被引:4,自引:2,他引:2
光突发交换是面向下一代互联网的光交换模式.讨论了异步光突发交换系统的交换控制策略以及相应光缓存的优化配置策略.除了传统预约模式的交换策略,还研究了非预约和改进型预约模式,它们的性能评估由计算机仿真给出.结果表明:在条件相当情况下,改进型预约模式具有最低的丢包率.同时光缓存的配置对上述几类交换控制策略的性能都有很大影响,仿真结果指出:光缓存的粒度对系统性能具有重要影响,所讨论的几类交换模式都存在最佳时延粒度,研究结果对光交换矩阵的设计有指导意义. 相似文献
65.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
66.
67.
基于CSCW的协同编著系统的设计 总被引:3,自引:0,他引:3
讨论了计算机支持的协同工作(CSCW)的主要技术,其中重点讨论了协同编著系统设计中的并发控制技术,指出了其与传统的并发控制技术的区别。根据CSCW的基本原理设计出了一个基于Browse/Server结构的协同编著系统的系统模型。该系统模型比传统的模型更加方便了用户之间通过Internet的浏览器进行协作。 相似文献
68.
This paper derives the optimal trajectories in a general fluid network with server control. The stationary optimal policy in the complete state space is constructed. The optimal policy is constant on polyhedral convex cones. An algorithm is derived that computes these cones and the optimal policy. Generalized Klimov indices are introduced, they are used for characterizing myopic and time-uniformly optimal policies.Received: November 2004 / Revised: February 2005The research of this author has been supported by the project ‘‘Stochastic Networks’’ of the Netherlands Organisation for Scientific Research NWO. 相似文献
69.
《Magnetic resonance in chemistry : MRC》2003,41(1):37-41
The oxidation of symmetrical disulfides [D ,L ‐cystine ( 1 ) and 3,3′‐dithiobis(propionic acid) ( 2 )] with hydrogen peroxide in D2O–NaOH solution (pH 10–11) was studied by NMR spectroscopy. Assignments of the proton and carbon NMR signals of starting materials ( 1 and 2 ) and products of oxidation are based on conventional 1D NMR methods (DEPT, selective spin decoupling). Formation of C—S bond cleavage products or, in case of 2 , partially oxidized intermediates was not detected. The accelerating effect of Cu2+ cations, but not Fe3+ cations, on the oxidation rate of 1 in basic medium was demonstrated. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
70.
Jocelyn Sabatier Serge Poullain Patrick Latteux Jean Luc Thomas Alain Oustaloup 《Nonlinear dynamics》2004,38(1-2):383-400
Robust speed control of a low damped electromechanical system with backlash is studied, controlled load angular speed being not measured. The proposed control strategy combines a Luenberger observer (load angular speed and load torque disturbance estimations) and a robust CRONE controller. The observer provides estimation of the load angular speed and of the disturbance torque applied on the load. Through the computation of only three independent parameters (as many as a PID controller), the CRONE controller permits to ensure the robust speed control of the load in spite of plant parametric variations and speed observation errors. The proposed control strategy is applied to a four mass experimental test bench. 相似文献