全文获取类型
收费全文 | 79600篇 |
免费 | 6690篇 |
国内免费 | 8362篇 |
专业分类
化学 | 34300篇 |
晶体学 | 487篇 |
力学 | 7952篇 |
综合类 | 1341篇 |
数学 | 25435篇 |
物理学 | 25137篇 |
出版年
2024年 | 117篇 |
2023年 | 731篇 |
2022年 | 1642篇 |
2021年 | 1821篇 |
2020年 | 1854篇 |
2019年 | 1998篇 |
2018年 | 1655篇 |
2017年 | 2012篇 |
2016年 | 2315篇 |
2015年 | 2112篇 |
2014年 | 3006篇 |
2013年 | 5327篇 |
2012年 | 3326篇 |
2011年 | 3836篇 |
2010年 | 3212篇 |
2009年 | 4464篇 |
2008年 | 4877篇 |
2007年 | 5052篇 |
2006年 | 4683篇 |
2005年 | 4005篇 |
2004年 | 3712篇 |
2003年 | 3659篇 |
2002年 | 3307篇 |
2001年 | 2777篇 |
2000年 | 2721篇 |
1999年 | 2441篇 |
1998年 | 2255篇 |
1997年 | 1855篇 |
1996年 | 1643篇 |
1995年 | 1468篇 |
1994年 | 1354篇 |
1993年 | 1172篇 |
1992年 | 1125篇 |
1991年 | 872篇 |
1990年 | 715篇 |
1989年 | 622篇 |
1988年 | 577篇 |
1987年 | 451篇 |
1986年 | 385篇 |
1985年 | 447篇 |
1984年 | 435篇 |
1983年 | 215篇 |
1982年 | 356篇 |
1981年 | 407篇 |
1980年 | 309篇 |
1979年 | 305篇 |
1978年 | 222篇 |
1977年 | 208篇 |
1976年 | 156篇 |
1974年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Yoshiyuki Hino 《Journal of Mathematical Analysis and Applications》2003,286(2):741-752
For abstract linear functional differential equations with an almost automorphic forcing term, we establish a result on the existence of almost automorphic solutions, which extends the classical theorem due to Massera on the existence of periodic solutions for linear periodic ordinary differential equations. 相似文献
952.
J. M. Cuevas J. M. Laza M. Correa J. L. Vilas M. Rodríguez L. M. Len 《Journal of Polymer Science.Polymer Physics》2003,41(17):1965-1977
The reticulation process of an epoxy resin using an amine as a cure agent was studied at different temperatures and concentrations of the cure agent with dynamic mechanical thermal analysis. The study was performed under both isothermal and nonisothermal conditions, and a temperature–time–transformation diagram was obtained. The measurements from the two modes gave similar results, although the nonisothermal mode required fewer experiments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1965–1977, 2003 相似文献
953.
Taking into account the effects of quantum interference and interface scattering, combining the electron current with hole current contribution to tunnel current,we study the coherent quantum transport in normal-metal/d-wave superconductor/normal-metal (NM/d-wave SC/NM) double tunnel junctions by using extended Blonder-Tinkham-Klapwijk (BTK) approach. It is shown that all quasiparticle transport coefficients and conductance spectrum exhibit oscillating behavior with the energy, in which periodic vanishing of Andreev reflection (AR) above superconducting gap is found.In tunnel limit for the interface scattering strength taken very large, there are a series of bound states of quasiparticles formed in SC. 相似文献
954.
In this paper we present a new method for the solution of optimization problems with PDE constraints. It is based on simultaneous pseudo-time stepping for evolution equations. The new method can be viewed as a continuous reduced SQP method in the sense that it uses a preconditioner derived from that method. The reduced Hessian in the preconditioner is approximated by a pseudo-differential operator, whose symbol can be investigated analytically. We apply our method to a boundary control model problem. The new optimization method needs 3.2-times the overall computational effort of the solution of simulation problem alone. 相似文献
955.
In this paper we describe the experimental analysis of a novel ion-exchange polymer metal composite (IPMC) actuator under
large external voltage. The experimental analysis is supplemented with a coupled thermodynamic model, which includes mass
transport across the thickness of the polymer actuator, chemical reactions at boundaries, and deformation as a function of
the solvent (water) distribution. In this paper, the case of large electrode potentials (over 1.2 V) has been analyzed experimentally
and theoretically. At these voltage levels, electrochemical reactions take place at both electrodes. These are used in the
framework of overpotential theory to develop boundary conditions for the water transport in the bulk of polymer. The model
is then simplified to a three-component system comprised of a fixed negatively charged polymeric matrix, protons, and free
water molecules within the polymer matrix. Among these species, water molecules are considered to be the dominant species
responsible for the deformation of the IPMC actuators. Experiments conducted at different initial water contents are described
and discussed in the context of the proposed deformation mechanism. Comparison of numerical simulations with experimental
data shows good agreement. 相似文献
956.
957.
耦合双原子Jaynes-Cummings模型的腔场谱H 总被引:14,自引:8,他引:6
研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n>0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显. 相似文献
958.
959.
光照与彩陶俑表面色变关系的实验研究 总被引:1,自引:0,他引:1
本文以秦彩俑表面色彩为研究对象,通过光照实验与色彩变化的色度测量,分析了光照引起彩俑颜料色变的规律,为秦彩俑这一大型重点文物的色彩保护提供了科学理论依据. 相似文献
960.