全文获取类型
收费全文 | 553449篇 |
免费 | 4739篇 |
国内免费 | 1497篇 |
专业分类
化学 | 285476篇 |
晶体学 | 7751篇 |
力学 | 26577篇 |
综合类 | 18篇 |
数学 | 72905篇 |
物理学 | 166958篇 |
出版年
2021年 | 5259篇 |
2020年 | 5763篇 |
2019年 | 6484篇 |
2018年 | 8659篇 |
2017年 | 8821篇 |
2016年 | 12150篇 |
2015年 | 6730篇 |
2014年 | 11016篇 |
2013年 | 24748篇 |
2012年 | 19516篇 |
2011年 | 23219篇 |
2010年 | 17240篇 |
2009年 | 16994篇 |
2008年 | 21900篇 |
2007年 | 21762篇 |
2006年 | 19925篇 |
2005年 | 17794篇 |
2004年 | 16589篇 |
2003年 | 14898篇 |
2002年 | 14743篇 |
2001年 | 15131篇 |
2000年 | 11713篇 |
1999年 | 9089篇 |
1998年 | 7939篇 |
1997年 | 7855篇 |
1996年 | 7278篇 |
1995年 | 6562篇 |
1994年 | 6611篇 |
1993年 | 6333篇 |
1992年 | 6652篇 |
1991年 | 7154篇 |
1990年 | 6833篇 |
1989年 | 6741篇 |
1988年 | 6561篇 |
1987年 | 6334篇 |
1986年 | 6093篇 |
1985年 | 7735篇 |
1984年 | 8106篇 |
1983年 | 6817篇 |
1982年 | 7130篇 |
1981年 | 6612篇 |
1980年 | 6314篇 |
1979年 | 6751篇 |
1978年 | 7016篇 |
1977年 | 6887篇 |
1976年 | 6800篇 |
1975年 | 6484篇 |
1974年 | 6315篇 |
1973年 | 6580篇 |
1972年 | 4812篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
22.
Peter Imkeller 《Probability Theory and Related Fields》1996,106(1):105-135
Summary. The analytic treatment of problems related to the asymptotic behaviour of random dynamical systems generated by stochastic
differential equations suffers from the presence of non-adapted random invariant measures. Semimartingale theory becomes accessible
if the underlying Wiener filtration is enlarged by the information carried by the orthogonal projectors on the Oseledets spaces
of the (linearized) system.
We study the corresponding problem of preservation of the semimartingale property and the validity of a priori inequalities
between the norms of stochastic integrals in the enlarged filtration and norms of their quadratic variations in case the random
element F enlarging the filtration is real valued and possesses an absolutely continuous law. Applying the tools of Malliavin’s calculus,
we give smoothness conditions on F under which the semimartingale property is preserved and a priori martingale inequalities are valid.
Received: 12 April 1995 / In revised form: 7 March 1996 相似文献
23.
Myagchenkov V. A. Chichkanov S. V. Proskurina V. E. Myagchenkov A. V. 《Russian Journal of Applied Chemistry》2002,75(9):1485-1488
The Thoms effect observed with water-soluble cationic copolymer of acrylamide was studied in relation to the concentration, molecular weight, and molecular weight polydispersity of the polymeric additive, with its composition and composition polydispersity being constant. 相似文献
24.
A. M. Nikitin 《Journal of Mathematical Sciences》1997,87(6):4138-4146
An explicit way for producing invariants for 6-valent graphs with rigid vertices within the framework of Kauffman's approach
to graph invariants is presented. These invariants can be used to detect the chirality of a 6-valent graph with rigid vertices.
A relevant example is considered. Bibliography: 19 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 223, 1995, pp. 251–262.
Translated by A. M. Nikitin 相似文献
25.
26.
A. K. Lopatin 《Ukrainian Mathematical Journal》1997,49(1):51-74
We consider the method of normal forms, the Bogolyubov averaging method, and the method of asymptotic decomposition proposed by Yu. A. Mitropol’skii and the author of this paper. Under certain assumptions about group-theoretic properties of a system of zero approximation, the results obtained by the method of asymptotic decomposition coincide with the results obtained by the method of normal forms or the Bogolyubov averaging method. We develop a new algorithm of asymptotic decomposition by a part of the variables and its partial case — the algorithm of averaging on a compact Lie group. For the first time, it became possible to consider asymptotic expansions of solutions of differential equations on noncommutative compact groups. 相似文献
27.
28.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity,
which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish
at a critical density n
c
, 2∼2×1012 cm−2, and then to have the opposite sign at n>n
c
,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the
critical point, G
c
,2∼120e
2/h, sets an upper (low-temperature) limit on its conductivity.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
29.
30.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献