全文获取类型
收费全文 | 13936篇 |
免费 | 1432篇 |
国内免费 | 713篇 |
专业分类
化学 | 704篇 |
晶体学 | 45篇 |
力学 | 764篇 |
综合类 | 108篇 |
数学 | 4083篇 |
物理学 | 3230篇 |
无线电 | 7147篇 |
出版年
2024年 | 32篇 |
2023年 | 139篇 |
2022年 | 187篇 |
2021年 | 221篇 |
2020年 | 279篇 |
2019年 | 203篇 |
2018年 | 238篇 |
2017年 | 328篇 |
2016年 | 409篇 |
2015年 | 446篇 |
2014年 | 877篇 |
2013年 | 985篇 |
2012年 | 839篇 |
2011年 | 1079篇 |
2010年 | 860篇 |
2009年 | 871篇 |
2008年 | 1010篇 |
2007年 | 1035篇 |
2006年 | 813篇 |
2005年 | 668篇 |
2004年 | 617篇 |
2003年 | 570篇 |
2002年 | 477篇 |
2001年 | 401篇 |
2000年 | 362篇 |
1999年 | 299篇 |
1998年 | 268篇 |
1997年 | 207篇 |
1996年 | 211篇 |
1995年 | 200篇 |
1994年 | 166篇 |
1993年 | 112篇 |
1992年 | 102篇 |
1991年 | 72篇 |
1990年 | 62篇 |
1989年 | 52篇 |
1988年 | 44篇 |
1987年 | 24篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 36篇 |
1979年 | 35篇 |
1978年 | 22篇 |
1977年 | 21篇 |
1976年 | 8篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
61.
Luis L. Bonilla 《Journal of statistical physics》1987,46(3-4):659-678
A nonlinear Fokker-Planck equation is derived to describe the cooperative behavior of general stochastic systems interacting via mean-field couplings, in the limit of an infinite number of such systems. Disordered systems are also considered. In the weak-noise limit; a general result yields the possibility of having bifurcations from stationary solutions of the nonlinear Fokker-Planck equation into stable time-dependent solutions. The latter are interpreted as non-equilibrium probability distributions (states), and the bifurcations to them as nonequilibrium phase transitions. In the thermodynamic limit, results for three models are given for illustrative purposes. A model of self-synchronization of nonlinear oscillators presents a Hopf bifurcation to a time-periodic probability density, which can be analyzed for any value of the noise. The effects of disorder are illustrated by a simplified version of the Sompolinsky-Zippelius model of spin-glasses. Finally, results for the Fukuyama-Lee-Fisher model of charge-density waves are given. A singular perturbation analysis shows that the depinning transition is a bifurcation problem modified by the disorder noise due to impurities. Far from the bifurcation point, the CDW is either pinned or free, obeying (to leading order) the Grüner-Zawadowki-Chaikin equation. Near the bifurcation, the disorder noise drastically modifies the pattern, giving a quenched average of the CDW current which is constant. Critical exponents are found to depend on the noise, and they are larger than Fisher's values for the two probability distributions considered. 相似文献
62.
Fully and partially observed stochastic control of systems with nonlinear dynamics and terminal and running costs are considered.
Measure changes are introduced which allow both state and observation dynamics to be thought of as linear. In the case when
the terms of the cost have a special form the measure change transformation “cancels out” the nonlinearities and changes the
original nonlinear problem into a classical LQG one and standard results can be applied. We also consider unnormalized conditional
densities of the whole path as state variables and obtain dynamic programming and verification results.
R. J. Elliott wishes to acknowledge support of the Natural Sciences and Engineering Research Council of Canada, Grant A7964. 相似文献
63.
64.
A Modified SQP Method and Its Global Convergence 总被引:6,自引:0,他引:6
Guanglu Zhou 《Journal of Global Optimization》1997,11(2):193-205
The sequential quadratic programming method developed by Wilson, Han andPowell may fail if the quadratic programming subproblems become infeasibleor if the associated sequence of search directions is unbounded. In [1], Hanand Burke give a modification to this method wherein the QP subproblem isaltered in a way which guarantees that the associated constraint region isnonempty and for which a robust convergence theory is established. In thispaper, we give a modification to the QP subproblem and provide a modifiedSQP method. Under some conditions, we prove that the algorithm eitherterminates at a Kuhn–Tucker point within finite steps or generates aninfinite sequence whose every cluster is a Kuhn–Tucker point.Finally, we give some numerical examples. 相似文献
65.
本文介绍了EltctronicWorkbench软件和计算机虚拟仪器系统,采用计算机模拟仿真技术对电子线路实验加以辅助设计和探索。 相似文献
66.
刘崇新 《微电子学与计算机》1996,13(6):9-11
本文提出了以电流跟随器CF为基本电路元件的全集成MOSFET-C精确连续时间六阶低通滤波器电路,并应用PSPICE-Ⅱ通用模拟电路程序,对其幅频特性和相频特性进行了计算机仿真分析,得出了实用的结论。 相似文献
67.
声表面波滤波器的匹配电路设计 总被引:1,自引:0,他引:1
介绍了通过测试仪器采集的声表面波(SAW)滤波器的Sij(i,j=1,2)参数来优化匹配电路的方法。首先将采集的Sij(i,j=1,2)参数转换为SAW滤波器Yij(i,j=1,2)参数,然后建立新的S12(或S21)参数与匹配电路的依赖关系,通过优化匹配电路元件值,而使滤波器的插入损耗和通带波动满足目标值,该方法的主要优点是考虑整个通带特性,而不是考虑通带内的某一点(如中心频率)。 相似文献
68.
Using the path integral method we derive quantum wave function and quantum fluctuations of charge andcurrent in the mesoscopic RLC circuit. We find that the quantum fluctuation of charge decreases with time, oppositely,the quantum fluctuation of current increases with time monotonously. Therefore there is a squeezing effect in the circuit.If some more charge devices are used in the mesoscopic-damped circuit, the quantum noise can be reduced. We also findthat uncertainty relation of charge and current periodically varies with the period π/2 in the under-damped case. 相似文献
69.
本文阐述了真空断路器用RC保护装置的原理。分析了用RC保护装置保护电力系统及其设备的试验结果。RC保护装置主要参数的选择。最后,讨论了有关RC保护装置的一些问题。 相似文献
70.
This paper considers a problem of nonlinear programming in which the objective function is the ratio of two linear functions and the constraints define a bounded and connected feasible region. Using a coordinate transformation, this problem is transformed into a simpler one, whose geometric interpretation is of particular significance. The transformation leads to a characterization of some special vertices of the feasible region from both the theoretical and operational points of view. 相似文献