全文获取类型
收费全文 | 507399篇 |
免费 | 5161篇 |
国内免费 | 1600篇 |
专业分类
化学 | 255173篇 |
晶体学 | 7175篇 |
力学 | 25073篇 |
综合类 | 13篇 |
数学 | 79921篇 |
物理学 | 146805篇 |
出版年
2021年 | 3768篇 |
2020年 | 4185篇 |
2019年 | 4519篇 |
2018年 | 15593篇 |
2017年 | 15321篇 |
2016年 | 14495篇 |
2015年 | 6318篇 |
2014年 | 8783篇 |
2013年 | 20408篇 |
2012年 | 19016篇 |
2011年 | 28840篇 |
2010年 | 18652篇 |
2009年 | 18912篇 |
2008年 | 23684篇 |
2007年 | 25471篇 |
2006年 | 16413篇 |
2005年 | 15705篇 |
2004年 | 14901篇 |
2003年 | 13714篇 |
2002年 | 12633篇 |
2001年 | 13622篇 |
2000年 | 10323篇 |
1999年 | 8031篇 |
1998年 | 6721篇 |
1997年 | 6431篇 |
1996年 | 6260篇 |
1995年 | 5579篇 |
1994年 | 5462篇 |
1993年 | 5283篇 |
1992年 | 5878篇 |
1991年 | 5984篇 |
1990年 | 5711篇 |
1989年 | 5524篇 |
1988年 | 5546篇 |
1987年 | 5431篇 |
1986年 | 5142篇 |
1985年 | 6604篇 |
1984年 | 6734篇 |
1983年 | 5335篇 |
1982年 | 5425篇 |
1981年 | 5404篇 |
1980年 | 5000篇 |
1979年 | 5389篇 |
1978年 | 5525篇 |
1977年 | 5403篇 |
1976年 | 5344篇 |
1975年 | 4928篇 |
1974年 | 4896篇 |
1973年 | 4904篇 |
1972年 | 3472篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
142.
143.
M. S. Nikol'skii 《Differential Equations》2003,39(11):1603-1608
144.
Stephen M. Robinson 《Mathematical Programming》2003,97(1-2):245-265
This is an expository paper about the analysis of variational conditions over sets defined in finite-dimensional spaces by
fairly smooth functions satisfying a constraint qualification. The primary focus is on results that can provide quantitative
and computable sensitivity information for particular instances of the problems under study, and our objective is to give
a personal view of the state of current knowledge in this area and of gaps in that knowledge that require future work. The
writing style is informal, in keeping with the objective of focusing the reader's attention on the basic concepts and the
relationships between them, rather than on details of the particular results themselves.
Received: December 1, 2002 / Accepted: April 25, 2003
Published online: May 28, 2003
Key words. variational condition – variational inequality – complementarity – sensitivity – stability – nondegeneracy
Mathematics Subject Classification (2000): Primary: 90C31. Secondary: 47J20, 49J40, 49J53, 90C33 相似文献
145.
In this paper political and economic rationality is modelled regarding an economic problem with a four-dimensional dynamical system taking into consideration the information about the problem spread among the people who support the political alternatives. Under special parameter conditions velcro bifurcation occurs, which destabilizes the equilibrium points when information is going to spread. The last stable equilibrium point is related to the economically rational equilibrium point. 相似文献
146.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
147.
A crystalline quartz plate of thickness 1.070 mm is calibrated between 370 and 794 nm. Throughout this spectral interval, the retardance varied by 32π and the plate introduced quarterwave retardance 16 times at different wavelengths. The birefringence (ne−no) of crystalline quartz was calculated as a single quantity and varied from 0.00971 at 370 nm to 0.00891 at 794 nm. All measurements were carried out at 23°C. 相似文献
148.
Until recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering 1 ns pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to >100 kHz.Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to >1 W average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser. 相似文献
149.
A fully quantum mechanical approach to the calculation and normalization of the Franck–Condon factors for diatomic species is described. The treatment is based on the fundamental demand of completeness of the energy eigenfunctions, which results in the rigorous sum rule for the Franck–Condon overlap integrals. The importance of this general rule has been discussed and thoroughly illustrated in the case of diatomic xenon molecules. Exactly solvable reference potentials for this system have been constructed and a complete basis of the actual energy eigenstates (including both bound and scattering states) has been created. Several direct spectroscopic applications to xenon excimers are presented, and their good agreement with relevant experimental data demonstrated. In particular, a kinetic model is proposed to explain the observed oscillatory structures in the fluorescence spectra of Xe2* [Chem. Phys. Lett. 117 (1985) 301] related to their classical left turning points. The same model gives a uniform explanation to the well-known first and second emission continua of rare gases. 相似文献
150.
Yu. M. Pechatnikov 《Technical Physics》2003,48(12):1522-1526
Transition (molecular-viscous) isothermal channel flow of rarefied gases is considered. Present-day engineering physical models of transition gas flow and methods of simulation are analyzed and verified in terms of the kinetic theory on the micro-and macrolevels. 相似文献