全文获取类型
收费全文 | 103365篇 |
免费 | 10264篇 |
国内免费 | 8189篇 |
专业分类
化学 | 28786篇 |
晶体学 | 365篇 |
力学 | 7319篇 |
综合类 | 1550篇 |
数学 | 29562篇 |
物理学 | 28378篇 |
无线电 | 25858篇 |
出版年
2024年 | 169篇 |
2023年 | 920篇 |
2022年 | 1619篇 |
2021年 | 1999篇 |
2020年 | 2186篇 |
2019年 | 2185篇 |
2018年 | 2032篇 |
2017年 | 2608篇 |
2016年 | 3014篇 |
2015年 | 2950篇 |
2014年 | 4667篇 |
2013年 | 6593篇 |
2012年 | 5187篇 |
2011年 | 5554篇 |
2010年 | 4619篇 |
2009年 | 5764篇 |
2008年 | 6379篇 |
2007年 | 6748篇 |
2006年 | 6249篇 |
2005年 | 5356篇 |
2004年 | 4816篇 |
2003年 | 4803篇 |
2002年 | 4234篇 |
2001年 | 3548篇 |
2000年 | 3427篇 |
1999年 | 2965篇 |
1998年 | 2721篇 |
1997年 | 2250篇 |
1996年 | 2061篇 |
1995年 | 1809篇 |
1994年 | 1644篇 |
1993年 | 1419篇 |
1992年 | 1304篇 |
1991年 | 1025篇 |
1990年 | 868篇 |
1989年 | 753篇 |
1988年 | 653篇 |
1987年 | 500篇 |
1986年 | 408篇 |
1985年 | 506篇 |
1984年 | 494篇 |
1983年 | 250篇 |
1982年 | 388篇 |
1981年 | 426篇 |
1980年 | 324篇 |
1979年 | 319篇 |
1978年 | 243篇 |
1977年 | 221篇 |
1976年 | 171篇 |
1974年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献
252.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
253.
RUAN Manqi XU Gang & ZENG Jinyan Department of Physics Tsinghua University Beijing China Department of Physics Peking University Beijing China Correspondence should be addressed to Zeng Jinyan 《中国科学G辑(英文版)》2004,47(1):36-41
Foratwo-particle(spin1/2)systemthespinstateisdescribedusingavectorinafour-dimensionalHilbertspace.Inangularmomentumcouplingtheory[1],theangularmomentumuncouplingandcouplingrepresentationsareusuallyadopted.WhilethesimultaneouseigenstatesoftheCSCO(s1z,s2z),12,12,12and12,arechosenasthebasisofangularmomentumuncouplingscheme,thesimultaneouseigenstatesoftheCSCO(2,zSS),,SM(12=+Sss),arechosenasthebasisofangularmomentumcouplingscheme,1212100,2轾=-臌1212110,2轾=+臌121211,1,1.=-=Thefo… 相似文献
254.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献
255.
256.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献
257.
N. A. Lockerbie 《General Relativity and Gravitation》2004,36(3):593-600
By using a novel free-flying, rotating, optical bench aboard the International Space Station (ISS) as the basis for a measurement of differential acceleration between two gravitating bodies, in principle the Newtonian inverse-square law and the constant of gravitation, G, can be determined at the parts in 106 level. 相似文献
258.
介绍了PHS网呼入成功率和短消息流程,依据短消息模型和性能统计结果分析了群发短信对PHS网呼入成功率的影响,并建议选择合理的时间进行短消息群发以减少对网络负荷的影响。 相似文献
259.
软交换技术的发展及其应用 总被引:1,自引:0,他引:1
软交换是下一代网络NGN的核心技术,本文从软交换的概念入手,介绍了软交换的基本功能及其优点.软交换的网络系统结构、软交换的对外接口等内容,并探讨了软交换技术的应用。 相似文献
260.
Vincenzo Santagada Ferdinando FiorinoElisa Perissutti Beatrice SeverinoSara Terracciano Giuseppe CirinoGiuseppe Caliendo 《Tetrahedron letters》2003,44(6):1145-1148
A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating. 相似文献