全文获取类型
收费全文 | 11994篇 |
免费 | 1386篇 |
国内免费 | 1349篇 |
专业分类
化学 | 6038篇 |
晶体学 | 60篇 |
力学 | 719篇 |
综合类 | 167篇 |
数学 | 3412篇 |
物理学 | 4333篇 |
出版年
2024年 | 24篇 |
2023年 | 107篇 |
2022年 | 220篇 |
2021年 | 282篇 |
2020年 | 322篇 |
2019年 | 311篇 |
2018年 | 290篇 |
2017年 | 362篇 |
2016年 | 357篇 |
2015年 | 400篇 |
2014年 | 512篇 |
2013年 | 819篇 |
2012年 | 547篇 |
2011年 | 607篇 |
2010年 | 624篇 |
2009年 | 688篇 |
2008年 | 746篇 |
2007年 | 887篇 |
2006年 | 697篇 |
2005年 | 625篇 |
2004年 | 520篇 |
2003年 | 543篇 |
2002年 | 596篇 |
2001年 | 436篇 |
2000年 | 386篇 |
1999年 | 376篇 |
1998年 | 363篇 |
1997年 | 225篇 |
1996年 | 252篇 |
1995年 | 220篇 |
1994年 | 166篇 |
1993年 | 156篇 |
1992年 | 141篇 |
1991年 | 104篇 |
1990年 | 76篇 |
1989年 | 75篇 |
1988年 | 62篇 |
1987年 | 57篇 |
1986年 | 58篇 |
1985年 | 65篇 |
1984年 | 45篇 |
1983年 | 34篇 |
1982年 | 49篇 |
1981年 | 59篇 |
1980年 | 43篇 |
1979年 | 45篇 |
1978年 | 37篇 |
1976年 | 27篇 |
1975年 | 30篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
在Brueckner-Hartree-Fock理论框架内, 研究了同位旋非对称核物质中质子和中子单粒子势的动量相关性及其随同位旋非对称度的变化, 在此基础上计算了同位旋对称势, 并讨论了三体核力的影响. 结果表明同位旋对称势对于同位旋非对称度的依赖性很弱, 但对于动量和密度均有较强的依赖性. 当密度固定时, 同位旋对称势随动量增加而减小. 尽管三体核力对于质子和中子单粒子势的动量相关性有较大影响, 但对同位旋对称势的影响很小. 还与目前重离子碰撞输运理论模型中所使用的各种参数化的唯象对称势进行了比较. 相似文献
142.
利用Ditzian-Totik光滑模对于[0,1]上定义的非角连续函数f(x),且f(x)≠0,文中证明存在正系数多项式Pn(x)及常数C,使得|f9x)-1/Pn(x)|≤Cωψ^λ(f,n^-1/2(ψ(x) 1/√n)^1-λ)。当λ=1时,上述结果导出已有的整体估计,而当0≤λ<1时,得到倒数逼近一个新的点态局部估计。 相似文献
143.
《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):241-244
The helicity dependence of the γ
p↦pη reaction has been measured for the first time at a center-of-mass angle θ*
η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector
system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section
is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
Received: 19 December 2002 / Accepted: 10 March 2003 / Published online: 20 May 2003 相似文献
144.
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
145.
A Kind of direct methods is presented for the solution of optimal control problems with state constraints.These methods are sequential quadratic programming methods.At every iteration a quadratic programming which is obtained by quadratic approximation to Lagrangian function and Linear approximations to constraints is solved to get a search direction for a merit function.The merit function is formulated by augmenting the Lagrangian funetion with a penalty term.A line search is carried out along the search direction to determine a step length such that the merit function is decreased.The methods presented in this paper include continuous sequential quadratic programming methods and discreate sequential quadrade programming methods. 相似文献
146.
W. Götze 《Journal of statistical physics》1996,83(5-6):1183-1197
147.
148.
The performance evaluation of many complex manufacturing, communication and computer systems has been made possible by modeling
them as queueing systems. Many approximations used in queueing theory have been drawn from the behavior of queues in light
and heavy traffic conditions. In this paper, we propose a new approximation technique, which combines the light and heavy
traffic characteristics. This interpolation approximation is based on the theory of multipoint Padé approximation which is
applied at two points: light and heavy traffic. We show how this can be applied for estimating the waiting time moments of
the GI/G/1 queue. The light traffic derivatives of any order can be evaluated using the MacLaurin series analysis procedure. The heavy
traffic limits of the GI/G/1 queue are well known in the literature. Our technique generalizes the previously developed interpolation approximations
and can be used to approximate any order of the waiting time moments. Through numerical examples, we show that the moments
of the steady state waiting time can be estimated with extremely high accuracy under all ranges of traffic intensities using
low orders of the approximant. We also present a framework for the development of simple analytical approximation formulas.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
149.
150.
An efficient time-domain algorithm for plane non-linear flexural vibrations of multi-layered composite beams, which are driven into the inelastic range by severe transverse loadings, is presented. The influence of an axial static preload is considered in the sense of the quasi-linear second-order theory of structures. The inelastic parts of strain are treated as additional sources of selfstress in the linear elastic background-structure, driving the elastic response into the inelastic one. The efficiency of this exact formulation lies in the fact that linear solution techniques can be used in their most powerful form: Rubin's useful formulation for the quasi-static second-order transfer-matrix of linear elastic structures is applied in combination with modal analysis. Having in mind multi-metal beams, the classical lamination theory is assumed to be valid. Beams with overhang composed of ideal elastic-plastic and viscoplastic layers are studied as example structures. The fictitious sources of selfstress are calculated from the different material laws of the layers in a numerical time-stepping procedure, where a generalized midpoint-rule in combination with Crisfield's secant-Newton procedure is used. 相似文献