全文获取类型
收费全文 | 17864篇 |
免费 | 2628篇 |
国内免费 | 1229篇 |
专业分类
化学 | 3432篇 |
晶体学 | 100篇 |
力学 | 1520篇 |
综合类 | 299篇 |
数学 | 10590篇 |
物理学 | 5780篇 |
出版年
2024年 | 26篇 |
2023年 | 142篇 |
2022年 | 319篇 |
2021年 | 409篇 |
2020年 | 433篇 |
2019年 | 500篇 |
2018年 | 475篇 |
2017年 | 614篇 |
2016年 | 687篇 |
2015年 | 522篇 |
2014年 | 849篇 |
2013年 | 1478篇 |
2012年 | 987篇 |
2011年 | 1005篇 |
2010年 | 910篇 |
2009年 | 1028篇 |
2008年 | 1153篇 |
2007年 | 1107篇 |
2006年 | 1005篇 |
2005年 | 918篇 |
2004年 | 781篇 |
2003年 | 751篇 |
2002年 | 731篇 |
2001年 | 647篇 |
2000年 | 570篇 |
1999年 | 557篇 |
1998年 | 426篇 |
1997年 | 416篇 |
1996年 | 338篇 |
1995年 | 289篇 |
1994年 | 222篇 |
1993年 | 173篇 |
1992年 | 165篇 |
1991年 | 140篇 |
1990年 | 110篇 |
1989年 | 98篇 |
1988年 | 75篇 |
1987年 | 81篇 |
1986年 | 72篇 |
1985年 | 97篇 |
1984年 | 83篇 |
1983年 | 33篇 |
1982年 | 61篇 |
1981年 | 41篇 |
1980年 | 29篇 |
1979年 | 41篇 |
1978年 | 25篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
可变抽样区间的非参数控制图 总被引:1,自引:1,他引:0
最近几年一些学者研究了可变抽样区间的质量控制图。Amin等提出了可变抽样区间(VSI)的非参数控制图———符号 (Sign)统计量图〔1〕。本文在此基础上研究位置VSI符号控制图的制定方法 ,并设计离散VSI符号控制图。符号控制图的优点是对非正态总体亦可应用 ,并且不需要过程方差的信息。本文将所设计的VSI符号控制图同固定抽样区间 (FSI)的常规图作比较 ,并举实例说明符号控制图的应用 相似文献
32.
最速下降规则不失为一可用规则 总被引:5,自引:4,他引:1
本从统计意义上平均迭代次数的观点出发,指出求解线性规划的最速下降规则是可取的,好用的。 相似文献
33.
A Dirac picture perturbation theory is developed for the time evolution operator in classical dynamics in the spirit of the Schwinger–Feynman–Dyson perturbation expansion and detailed rules are derived for computations. Complexification formalisms are given for the time evolution operator suitable for phase space analyses, and then extended to a two-dimensional setting for a study of the geometrical Berry phase as an example. Finally a direct integration of Hamilton's equations is shown to lead naturally to a path integral expression, as a resolution of the identity, as applied to arbitrary functions of generalized coordinates and momenta. 相似文献
34.
线性分式规划最优解集的求法 总被引:5,自引:0,他引:5
薛声家 《应用数学与计算数学学报》2002,16(1):90-96
本文使用多面集的表示定理,导出了线性分式规划最优解集的结构,并给出确定全部最优解的计算步骤。 相似文献
35.
Evolutionary algorithms are applied as problem-independent optimization algorithms. They are quite efficient in many situations. However, it is difficult to analyze even the behavior of simple variants of evolutionary algorithms like the (1+1) EA on rather simple functions. Nevertheless, only the analysis of the expected run time and the success probability within a given number of steps can guide the choice of the free parameters of the algorithms. Here static (1+1) EAs with a fixed mutation probability are compared with dynamic (1+1) EAs with a simple schedule for the variation of the mutation probability. The dynamic variant is first analyzed for functions typically chosen as example-functions for evolutionary algorithms. Afterwards, it is shown that it can be essential to choose the suitable variant of the (1+1) EA. More precisely, functions are presented where each static (1+1) EA has exponential expected run time while the dynamic variant has polynomial expected run time. For other functions it is shown that the dynamic (1+1) EA has exponential expected run time while a static (1+1) EA with a good choice of the mutation probability has polynomial run time with overwhelming probability. 相似文献
36.
基于FPGA并行处理的实时图像相关速度计 总被引:3,自引:1,他引:2
研究制作了一种采用高速线阵CCD的实时相关速度计,其测量数据的输出速率可达每秒一万次。针对以往光学相关测速方法的问题进行了讨论,探讨了适合FPGA并行处理的算法,制作了高速线阵CCD摄像机及其处理装置。通过实验验证了系统的可行性和可实现性。 相似文献
37.
Haifeng Yang Guangming XieTianguang Chu Long Wang 《Nonlinear Analysis: Theory, Methods & Applications》2006
In the paper, commuting and stable feedback design for switched linear systems is investigated. This problem is formulated as to build up suitable state feedback controller for each subsystem such that the closed-loop systems are not only asymptotically stable but also commuting each other. A new concept, common admissible eigenvector set (CAES), is introduced to establish necessary/sufficient conditions for commuting and stable feedback controllers. For second-order systems, a necessary and sufficient condition is established. Moreover, a parametrization of the CAES is also obtained. The motivation comes from stabilization of switched linear systems which consist of a family of LTI systems and a switching law specifying the switching between them, where if all the subsystems are stable and commuting each other, then the total system is stable under arbitrary switching. 相似文献
38.
Quantization of Underdamped, Critically Damped, and Overdamped Electric Circuits with a Power Source
Jeong-Ryeol Choi 《International Journal of Theoretical Physics》2002,41(10):1931-1939
We have investigated the quantum mechanical effect of the underdamped, critically damped, and overdamped electric circuits with a power source. The charge of the underdamped circuit oscillates while those of the critically damped and overdamped ones don't. The wave function of the system of overdamped circuit represented parabolic cylinder function while underdamped circuit was represented by well-known Hermite polynomial. The eigenvalues of underdamped circuit is discrete while those of the critically damped and overdamped ones are given as continuously. 相似文献
39.
40.
Mingxin Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):424-436
This paper deals with positive solutions of degenerate and quasilinear parabolic systems not in divergence form: ut=up(Δu+av), vt=vq(Δv+bu), with null Dirichlet boundary conditions and positive initial conditions, where p, q, a and b are all positive constants. The local existence and uniqueness of classical solution are proved. Moreover, it will be proved that all solutions exist globally if and only if ab?λ12, where λ1 is the first eigenvalue of −Δ in Ω with homogeneous Dirichlet boundary condition. 相似文献