全文获取类型
收费全文 | 9979篇 |
免费 | 1826篇 |
国内免费 | 630篇 |
专业分类
化学 | 2112篇 |
晶体学 | 80篇 |
力学 | 1010篇 |
综合类 | 148篇 |
数学 | 4783篇 |
物理学 | 4302篇 |
出版年
2024年 | 10篇 |
2023年 | 96篇 |
2022年 | 216篇 |
2021年 | 278篇 |
2020年 | 305篇 |
2019年 | 342篇 |
2018年 | 309篇 |
2017年 | 415篇 |
2016年 | 440篇 |
2015年 | 368篇 |
2014年 | 511篇 |
2013年 | 903篇 |
2012年 | 580篇 |
2011年 | 652篇 |
2010年 | 565篇 |
2009年 | 602篇 |
2008年 | 662篇 |
2007年 | 595篇 |
2006年 | 533篇 |
2005年 | 483篇 |
2004年 | 404篇 |
2003年 | 413篇 |
2002年 | 371篇 |
2001年 | 322篇 |
2000年 | 291篇 |
1999年 | 276篇 |
1998年 | 198篇 |
1997年 | 218篇 |
1996年 | 168篇 |
1995年 | 143篇 |
1994年 | 99篇 |
1993年 | 79篇 |
1992年 | 74篇 |
1991年 | 59篇 |
1990年 | 52篇 |
1989年 | 46篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 49篇 |
1984年 | 36篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 9篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
23.
E. A. Bailov N. Temirgaliev 《Computational Mathematics and Mathematical Physics》2006,46(9):1515-1525
Sharp estimates (in the power scale) are obtained for the discretization error in the solutions to Poisson’s equation whose right-hand side belongs to a Korobov class. Compared to the well-known Korobov estimate, the order is almost doubled and has an ultimate value in the power scale. 相似文献
24.
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
25.
26.
FJZ-250型高速分幅相机时间测量不确定度分析 总被引:2,自引:1,他引:1
FJZ-250型高速转镜分幅相机因转镜速度的不可重复性,光机结构的构造原理和控制系统各路高压触发时间的漂移,导致了时间测量的不确定度。为此,须对相机测量数据进行校正。阐述了校正方法、提供了逐幅校正位置误差的修正系数。若以预置转速对应的名义周期值去处理测量结果,则相机的时间测量合成小确定度将达1%,对名义周期值和名义幅间间隔时间值进行修正后,则可降至0.3%。 相似文献
27.
Jeong Ryeol Choi 《International Journal of Theoretical Physics》2004,43(4):947-958
We derived the WKB wave function for the general time-dependent quadratic Hamiltonian system using a unitary transformation method. We applied our research to sinusodially drived Caldirola–Kanai oscillator and confirmed that the time evolution of our approximated WKB wave function is similar to that of the exact one. This wave function can be used to analyze the interference between the probability amplitudes contributed by the area of overlap in phase space of quantum states. 相似文献
28.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
29.
A new prediction technique is proposed for chaotic time series. The usefulness of the technique is thatit can kick off some false neighbor points which are not suitable for the local estimation of the dynamics systems. Atime-delayed embedding is used to reconstruct the underlying attractor, and the prediction model is based on the timeevolution of the topological neighboring in the phase space. We use a feedforward neural network to approximate thelocal dominant Lyapunov exponent, and choose the spatial neighbors by the Lyapunov exponent. The model is testedfor the Mackey-Glass equation and the convection amplitude of lorenz systems. The results indicate that this predictiontechnique can improve the prediction of chaotic time series. 相似文献
30.
Ashish Goel Monika R. Henzinger Serge Plotkin Eva Tardos 《Journal of Algorithms in Cognition, Informatics and Logic》2003,48(2):314-332
In this paper we consider the online ftp problem. The goal is to service a sequence of file transfer requests given bandwidth constraints of the underlying communication network. The main result of the paper is a technique that leads to algorithms that optimize several natural metrics, such as max-stretch, total flow time, max flow time, and total completion time. In particular, we show how to achieve optimum total flow time and optimum max-stretch if we increase the capacity of the underlying network by a logarithmic factor. We show that the resource augmentation is necessary by proving polynomial lower bounds on the max-stretch and total flow time for the case where online and offline algorithms are using same-capacity edges. Moreover, we also give polylogarithmic lower bounds on the resource augmentation factor necessary in order to keep the total flow time and max-stretch within a constant factor of optimum. 相似文献