全文获取类型
收费全文 | 83625篇 |
免费 | 7099篇 |
国内免费 | 5261篇 |
专业分类
化学 | 10304篇 |
晶体学 | 140篇 |
力学 | 5253篇 |
综合类 | 635篇 |
数学 | 11287篇 |
物理学 | 15022篇 |
综合类 | 53344篇 |
出版年
2024年 | 176篇 |
2023年 | 632篇 |
2022年 | 1392篇 |
2021年 | 1503篇 |
2020年 | 1637篇 |
2019年 | 1400篇 |
2018年 | 1325篇 |
2017年 | 1727篇 |
2016年 | 2091篇 |
2015年 | 2252篇 |
2014年 | 3905篇 |
2013年 | 4254篇 |
2012年 | 4460篇 |
2011年 | 5081篇 |
2010年 | 4127篇 |
2009年 | 4617篇 |
2008年 | 5079篇 |
2007年 | 6330篇 |
2006年 | 5599篇 |
2005年 | 5190篇 |
2004年 | 4679篇 |
2003年 | 4146篇 |
2002年 | 3550篇 |
2001年 | 2964篇 |
2000年 | 2492篇 |
1999年 | 2312篇 |
1998年 | 1863篇 |
1997年 | 1696篇 |
1996年 | 1516篇 |
1995年 | 1357篇 |
1994年 | 1153篇 |
1993年 | 1014篇 |
1992年 | 840篇 |
1991年 | 795篇 |
1990年 | 675篇 |
1989年 | 546篇 |
1988年 | 487篇 |
1987年 | 357篇 |
1986年 | 209篇 |
1985年 | 124篇 |
1984年 | 77篇 |
1983年 | 45篇 |
1982年 | 61篇 |
1981年 | 46篇 |
1980年 | 32篇 |
1979年 | 42篇 |
1978年 | 26篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1957年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
具有种内互惠作用的Lotka-Volterra互惠共存模型 总被引:1,自引:0,他引:1
对具有种内互惠作用的Lotka-Volterra互惠共存模型进行了完整的全局分析,得到了一些新的结果。 相似文献
142.
This paper uses the method of linear approximation for impulsive systems and gets a theorem which guarantees a fishery modei to be asymptotically stable at its equilibrium point and gives the ecological explanation. 相似文献
143.
In this article, we define stochastic dynamics for a system coupled to reservoirs. The rules for forward and backward transitions are related by a generalized detailed balance identity involving the system and its reservoirs. We compare the variation of information and of entropy. We define the Carnot dissipation and prove that it can be expressed in terms of cyclic transformations. Lower bounds for partial dissipations are also studied, as well as the effect of switching off certain reservoirs. We also study the near degeneracy of the stochastic matrix, relate it to phase transitions and we show that the reduced dynamics on the set of phases is a permutation. Finally, we relate these concepts to heat, work and more generally to the dissipation and creation of resources, in general systems. 相似文献
144.
M.B. Xu 《Applied Acoustics》2003,64(7):731-752
The forced vibration of an infinite elastic circular cylindrical shell filled with fluid is studied. Three methods are employed to analyze the forced vibration problem of this shell-fluid coupled system, that is, wave propagation approach (wave mode superposition), theorem of residues and a numerical integral method. In order to explain these methods more explicitly, before being used to investigate the vibration of an infinite fluid-filled elastic circular cylindrical shell, all these three methods are employed firstly to analyze the forced vibration problem of an infinite beam and an infinite elastic circular cylindrical shell in vacuo. Advantage and disadvantage of these three methods are discussed and their interesting relationship is revealed. That is, to any circumferential wavenumber and frequency of the external force, there is an unchangeable relationship between the general coordinates of various waves in the wave propagation approach and the residuals in the theorem of residues. 相似文献
145.
146.
Jin Cheng Ching-Lung Lin Gen Nakamura 《Proceedings of the American Mathematical Society》2005,133(8):2359-2367
In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.
147.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
148.
Nikolaos S. PAPAGEORGIOU Nikolaos YANNAKAKIS 《数学学报(英文版)》2005,21(5):977-996
This is the first part of a work on second order nonlinear, nonmonotone evolution inclusions defined in the framework of an evolution triple of spaces and with a multivalued nonlinearity depending on both x(t) and x(t). In this first part we prove existence and relaxation theorems. We consider the case of an usc, convex valued nonlinearity and we show that for this problem the solution set is nonempty and compact in C^1 (T, H). Also we examine the Isc, nonconvex case and again we prove the existence of solutions. In addition we establish the existence of extremal solutions and by strengthening our hypotheses, we show that the extremal solutions are dense in C^1 (T, H) to the solutions of the original convex problem (strong relaxation). An example of a nonlinear hyperbolic optimal control problem is also discussed. 相似文献
149.
J. Wang J. Kono A. Oiwa H. Munekata C. J. Stanton 《Superlattices and Microstructures》2003,34(3-6):563
We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons. 相似文献
150.