全文获取类型
收费全文 | 8799篇 |
免费 | 1542篇 |
国内免费 | 2736篇 |
专业分类
化学 | 7418篇 |
晶体学 | 173篇 |
力学 | 870篇 |
综合类 | 116篇 |
数学 | 540篇 |
物理学 | 3960篇 |
出版年
2024年 | 27篇 |
2023年 | 180篇 |
2022年 | 405篇 |
2021年 | 400篇 |
2020年 | 460篇 |
2019年 | 329篇 |
2018年 | 295篇 |
2017年 | 371篇 |
2016年 | 458篇 |
2015年 | 380篇 |
2014年 | 447篇 |
2013年 | 710篇 |
2012年 | 518篇 |
2011年 | 594篇 |
2010年 | 504篇 |
2009年 | 667篇 |
2008年 | 600篇 |
2007年 | 658篇 |
2006年 | 657篇 |
2005年 | 539篇 |
2004年 | 530篇 |
2003年 | 451篇 |
2002年 | 358篇 |
2001年 | 327篇 |
2000年 | 347篇 |
1999年 | 228篇 |
1998年 | 289篇 |
1997年 | 223篇 |
1996年 | 190篇 |
1995年 | 175篇 |
1994年 | 165篇 |
1993年 | 133篇 |
1992年 | 121篇 |
1991年 | 62篇 |
1990年 | 54篇 |
1989年 | 39篇 |
1988年 | 42篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
本文在内生信息成本的基础上,通过引入投资银行的信息成本函数,考察了国际上主要股票发售机制的内在机理,并用一个统一的框架比较了各种发售机制的差异及演进趋势。本研究表明,在投资银行和投资者信息成本相同的情况下,由于固定价格发售机制须用额外的折价去解决投资者之间的信息问题,因而相对于累计投标询价制是一种处于劣势的机制选择。同时指出,具有信息成本优势的机构投资者的出现和发展,是固定价格发行向询价发行过渡的一个必要条件。 相似文献
62.
63.
The engineering of many modern electronic devices demands control over a crystal down to the thickness of a single layer of atoms—and future demands will be even more challenging. Such control is achieved by the method of crystal growth known as epitaxy, and that makes this method the subject of intense study. More than that, recent advances are revolutionizing our knowledge of how surfaces grow. In fact, growing surfaces show a beautifully rich variety of phenomena, many of which are only now beginning to be uncovered. In the past few years many surface imaging techniques have been used to give us a close look at how crystals grow—while they are growing. The purpose of this article will be to illustrate some of the ways real surfaces grow and change as revealed by some of the latest in situ microscopic imaging technologies.
It is often said that crystal growth is more of an art than a science. Here we will show that it is emphatically both. 相似文献
64.
Hui-Ling Li De-Jiang Qi Qing-Quan Jiang Shu-Zheng Yang 《International Journal of Theoretical Physics》2006,45(12):2428-2436
An extension of the Parikh-Wilczek's semi-classical quantum tunneling method, the tunneling radiation of the charged particle from a torus-like black hole is investigated. Difference from the uncharged mass-less particle, the geodesics of the charged massive particle tunneling from the black hole is not light-like, but determined by the phase velocity. The derived result shows that the tunneling rate depends on the emitted particle's energy and electric charge, and takes the same functional form as uncharged particle. It proves also that the exact emission spectrum is not strictly pure thermal, but is consistent with the underlying unitary theory.
PACS Numbers: 04.70.Dy, 97.60.Lf, 05.30.Ch. 相似文献
65.
T. N. Sokolova V. R. Kartashov I. V. Timofeev Yu. K. Grishin N. S. Zefirov 《Russian Chemical Bulletin》1994,43(3):461-465
The dependence of the regiochemistry of the mercuration of bornylene on the nature of the mercurating reagent and on the solvent has been found. The structures of the intermediate and transition state in these reactions have been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 501–505, March, 1994. 相似文献
66.
67.
A. S. Peregudov L. N. Usatova E. I. Smyslova E. I. Fedin D. N. Kravtsov 《Russian Chemical Bulletin》1995,44(8):1513-1519
It has been shown by the19F NMR method that the relative polarities of nitrogenelement bonds in 2-(4-fluorophenyl)benzimidazole and its PhHg and PPh3Au derivatives increase in the order N-H19F NMR. It has been found that these reactions occur by a bimolecular associative mechanism and that the N-H bond is substantially less reactive than the N-Hg and N-Au bonds, which have identical reactivities within the limits of sensitivity of the method used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1580, August, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-5528). 相似文献
68.
The nature of the propagation center in the cationic polymerization of N-benzoyl-8-octanelactam initiated by octanoylium hexachlcroantimonate, SbCl5, and Ph3CAsF6 in perdeuterated tetrachloroethane or its mixture with o-dichlorobenzene was studied using 1H, 13C, 19F, 31P, 75As, and 121Sb nuclear magnetic resonance (NMR) of model oligomers and the products of their end-capping with triphenylphosphine. In all cases, the nature of the propagation center has been found to be of an acylium ion pair with an SbCl6? or AsF6? counterion coordinated with the nearest benzoylamide group and cosolvated by the solvent. © 1994 John Wiley & Sons, Inc. 相似文献
69.
70.
The role of filamentation instability of quark-gluon plasma, in explaining collective phenomena in relativistic heavy-ion
collisions, has been analyzed. Using equations of SU(2) two fluid color hydrodynamics it is shown that this instability can
significantly enhance nuclear stopping and might contribute to collective sideward flows. 相似文献