全文获取类型
收费全文 | 135608篇 |
免费 | 35018篇 |
国内免费 | 30586篇 |
专业分类
化学 | 52671篇 |
晶体学 | 1471篇 |
力学 | 5619篇 |
综合类 | 509篇 |
数学 | 11283篇 |
物理学 | 57362篇 |
综合类 | 72297篇 |
出版年
2024年 | 636篇 |
2023年 | 1102篇 |
2022年 | 1660篇 |
2021年 | 1735篇 |
2020年 | 2544篇 |
2019年 | 5396篇 |
2018年 | 5453篇 |
2017年 | 6528篇 |
2016年 | 6702篇 |
2015年 | 7149篇 |
2014年 | 7503篇 |
2013年 | 8866篇 |
2012年 | 8848篇 |
2011年 | 10359篇 |
2010年 | 14056篇 |
2009年 | 13911篇 |
2008年 | 7405篇 |
2007年 | 6927篇 |
2006年 | 5990篇 |
2005年 | 5883篇 |
2004年 | 6910篇 |
2003年 | 5294篇 |
2002年 | 4908篇 |
2001年 | 4701篇 |
2000年 | 3795篇 |
1999年 | 3422篇 |
1998年 | 2590篇 |
1997年 | 2385篇 |
1996年 | 2544篇 |
1995年 | 2995篇 |
1994年 | 3110篇 |
1993年 | 3249篇 |
1992年 | 2840篇 |
1991年 | 2545篇 |
1990年 | 2064篇 |
1989年 | 2134篇 |
1988年 | 2177篇 |
1987年 | 1329篇 |
1986年 | 1360篇 |
1985年 | 947篇 |
1984年 | 1027篇 |
1982年 | 909篇 |
1981年 | 750篇 |
1980年 | 791篇 |
1979年 | 540篇 |
1978年 | 534篇 |
1977年 | 634篇 |
1976年 | 1043篇 |
1973年 | 437篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
陈泽乾 《数学物理学报(B辑英文版)》2002,22(3)
A new framework of Gaussian white noise calculus is established, in line with generalized expansion in [3, 4, 7]. A suitable frame of Fock expansion is presented on Gaussian generalized expansion functionals being introduced here, which provides the integral kernel operator decomposition of the second quantization of Koopman operators for chaotic dynamical systems, in terms of annihilation operators dt and its dual, creation operators t*. 相似文献
52.
A three-dimensional quasiclassical trajectory study of the dynamics of the light atom transfer reaction O(3P) + HCl(ν=0)→ OH + Cl was carried out employing two LEPS potential energy surfaces (I and II). Attention was focused mainly on three-dynamical properties; the oscillatory behavior of partial cross sections as a function of collision energy; the rotational excitation of the products; and the influence of reagent rotation on reactivity. Distinct differences were found between surfaces I and II with respect to these properties. The examination of individual trajectories indicated that there is a significant difference in the nature of these surfaces. While surface I is governed by weak repulsive forces, surface II is governed by strong attractive forces which tend to direct the reactants toward a collinear geometry. The present results confirm conclusions reached from an earlier study of the reaction Cl+HCl→ClH+Cl concerning correlations between dynamical properties and features of potential energy surfaces. For surfaces of the type that we termed HREP, since they are of repulsive nature and they lead to highly rotationally excited products, no significant oscillations of partial cross sections are obtained and reagent rotation promotes the reaction. On the other hand, for surfaces of the type that we termed COLD (collinearly directing), since they tend to direct the reactants toward a collinear geometry and form rotationally “cold” products, significant oscillations of partial cross sections are obtained and reagent rotation causes a decline in reactivity. 相似文献
53.
54.
用增量有限元法计算金属流动 总被引:1,自引:0,他引:1
利用增量有限元理论 ,对金属材料的变形过程进行模拟。为了模拟工程中塑性变形较大的构件的变形规律 ,在每个加载步迭代完成后自动实现坐标更新。 相似文献
55.
56.
57.
非傍轴平顶高斯光束M2因子两种定义的比较研究 总被引:1,自引:1,他引:0
基于功率密度的二阶矩方法,推导出了非傍轴平顶高斯(FG)光束束宽和远场发散角的解析表达式.研究表明,当w0/λ→0时,远场发散角趋于渐近值θmax=63.435°,与阶数无关.使用非傍轴高斯光束代替傍轴高斯光束作为理想光束,研究了非傍轴FG光束的M2因子,并与传统定义的M2因子作了比较.在非傍轴范畴,非傍轴FG光束的M2因子不仅与阶数N有关,而且与w0/λ有关.按照定义,当w0/λ→0时,非傍轴FG光束的M2因子不等于0,对阶数N=1, 2, 3时,M2因子分别趋于0.913,0.882和0.886.当N→∞时,M2因子取最小值M2min=0.816. 相似文献
58.
59.
ON THE UNIQUENESS OF THE WEAK SOLUTIONS OF A QUASILINEAR HYPERBOLIC SYSTEM WITH A SINGULAR SOURCE TERM 下载免费PDF全文
This paper is a continuation of the authors'previous paper[1].In this paper the authorsprove,assuming additional conditions on the initial data,some results about the existence anduniqueness of the entropy weak solutions of the Cauchy problem for the singular hyperbolicsystem a_t+(au)_x_2au/x=0,u_t+1/2(a~2+u~2)_x=0,x>0,t≥0. 相似文献
60.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献