全文获取类型
收费全文 | 481020篇 |
免费 | 4609篇 |
国内免费 | 1490篇 |
专业分类
化学 | 252993篇 |
晶体学 | 7529篇 |
力学 | 21469篇 |
综合类 | 12篇 |
数学 | 58178篇 |
物理学 | 146938篇 |
出版年
2020年 | 3968篇 |
2019年 | 4511篇 |
2018年 | 5841篇 |
2017年 | 5695篇 |
2016年 | 8679篇 |
2015年 | 5445篇 |
2014年 | 8353篇 |
2013年 | 20824篇 |
2012年 | 15911篇 |
2011年 | 19324篇 |
2010年 | 13603篇 |
2009年 | 13422篇 |
2008年 | 17959篇 |
2007年 | 17995篇 |
2006年 | 16916篇 |
2005年 | 15286篇 |
2004年 | 14023篇 |
2003年 | 12490篇 |
2002年 | 12230篇 |
2001年 | 13311篇 |
2000年 | 10331篇 |
1999年 | 8076篇 |
1998年 | 7028篇 |
1997年 | 6866篇 |
1996年 | 6638篇 |
1995年 | 6017篇 |
1994年 | 6138篇 |
1993年 | 5931篇 |
1992年 | 6385篇 |
1991年 | 6505篇 |
1990年 | 6230篇 |
1989年 | 5994篇 |
1988年 | 6102篇 |
1987年 | 5876篇 |
1986年 | 5580篇 |
1985年 | 7584篇 |
1984年 | 7890篇 |
1983年 | 6534篇 |
1982年 | 6795篇 |
1981年 | 6697篇 |
1980年 | 6596篇 |
1979年 | 6622篇 |
1978年 | 6993篇 |
1977年 | 6800篇 |
1976年 | 6944篇 |
1975年 | 6412篇 |
1974年 | 6417篇 |
1973年 | 6617篇 |
1972年 | 4625篇 |
1971年 | 3887篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Robert G. Parr 《International journal of quantum chemistry》1994,49(3):135-144
The helium atom in its ground state, subject to strong magnetic fields, is treated using a variational method. Trial functions consisting of Gaussians with nonlinear parameters variationally optimized are used. The form of these functions is a generalized s-symmetry-state properly modified to admit spatial deformation along the direction on which the magnetic field is applied. © 1994 John Wiley & Sons, Inc. 相似文献
52.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc. 相似文献
53.
54.
F. G. Vagizov 《Hyperfine Interactions》1995,95(1):85-95
We present the results of an experimental investigation of a RF splitting of57Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field. 相似文献
55.
A. J. Maroulis P. D. Akrivos C. P. Hadjiantoniou-Maroulis 《Journal of heterocyclic chemistry》1993,30(4):913-916
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity. 相似文献
56.
57.
The electrical conductivity of hydrosols of ultradispersed diamonds was studied. The electromembrane method for cleaning and concentrating of ultradispersed diamonds in hydrosols was considered. The influence exerted by the concentration of the dispersed phase on the electrical characteristics of the cleaning process was analyzed. A mathematical relation making it possible to evaluate the output characteristics of the process and to determine the geometrical characteristics of the apparatus was proposed. 相似文献
58.
Eduard Feireisl Antonín Novotný Hana Petzeltov 《Mathematical Methods in the Applied Sciences》2002,25(12):1045-1073
We prove a general compactness result for the solution set of the compressible Navier–Stokes equations with respect to the variation of the underlying spatial domain. Among various corollaries, we then prove a general existence theorem for the system in question with no restrictions on smoothness of the spatial domain. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
59.
The radiation emitted by charged, scalar particles in a Schwarzschild field with maximal acceleration corrections is calculated classically and in the tree approximation of quantum field theory. In both instances the particles emit radiation that has characteristics similar to those of gamma-ray bursters. 相似文献
60.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献