全文获取类型
收费全文 | 260276篇 |
免费 | 6916篇 |
国内免费 | 5125篇 |
专业分类
化学 | 139239篇 |
晶体学 | 4190篇 |
力学 | 12409篇 |
综合类 | 325篇 |
数学 | 30779篇 |
物理学 | 85375篇 |
出版年
2022年 | 2525篇 |
2021年 | 3211篇 |
2020年 | 3572篇 |
2019年 | 3906篇 |
2018年 | 4649篇 |
2017年 | 4620篇 |
2016年 | 6368篇 |
2015年 | 4177篇 |
2014年 | 6351篇 |
2013年 | 12256篇 |
2012年 | 10411篇 |
2011年 | 11780篇 |
2010年 | 8869篇 |
2009年 | 8876篇 |
2008年 | 10572篇 |
2007年 | 10195篇 |
2006年 | 9543篇 |
2005年 | 8516篇 |
2004年 | 7810篇 |
2003年 | 7031篇 |
2002年 | 6951篇 |
2001年 | 7490篇 |
2000年 | 5660篇 |
1999年 | 4438篇 |
1998年 | 3878篇 |
1997年 | 3581篇 |
1996年 | 3440篇 |
1995年 | 3117篇 |
1994年 | 3146篇 |
1993年 | 2988篇 |
1992年 | 3255篇 |
1991年 | 3244篇 |
1990年 | 3167篇 |
1989年 | 3026篇 |
1988年 | 2918篇 |
1987年 | 2932篇 |
1986年 | 2781篇 |
1985年 | 3442篇 |
1984年 | 3488篇 |
1983年 | 3086篇 |
1982年 | 3165篇 |
1981年 | 2905篇 |
1980年 | 2848篇 |
1979年 | 3110篇 |
1978年 | 3155篇 |
1977年 | 3071篇 |
1976年 | 3221篇 |
1975年 | 3046篇 |
1974年 | 3051篇 |
1973年 | 3230篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
M Lepère R Gobeille V.Malathy Devi M.A.H Smith B Aoaeh A.W Mantz 《Journal of Molecular Spectroscopy》2004,224(1):7-12
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. 相似文献
72.
We investigate the dynamics of the Λ system driven by two resonant laser fields in presence of dissipation for coupling strengths where the rotating‐wave approximation starts to break down. This regime is characterised by Rabi frequencies being approximately equal or smaller than the field frequencies. A systematic procedure to obtain an expansion for the solution of the Bloch evolution equations of the system is presented. The lowest contribution results to be the well‐known rotating‐wave approximation. The method is based on a semi‐classical treatment of the problem, and its predictions are interpreted fully quantum mechanically. The theory is illustrated by a detailed study of the disappearance of coherent population trapping as the intensities of the fields increase. 相似文献
73.
74.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
75.
Belov V. V. Dobrokhotov S. Yu. Maksimov V. A. 《Theoretical and Mathematical Physics》2003,135(3):765-791
Different versions of the Darboux–Weinstein theorem guarantee the existence of action–angle-type variables and the harmonic-oscillator variables in a neighborhood of isotropic tori in the phase space. The procedure for constructing these variables is reduced to solving a rather complicated system of partial differential equations. We show that this system can be integrated in quadratures, which permits reducing the problem of constructing these variables to solving a system of quadratic equations. We discuss several applications of this purely geometric fact in problems of classical and quantum mechanics. 相似文献
76.
Yu. M. Dyukarev 《Mathematical Notes》2004,75(1-2):66-82
In this paper, we obtain criteria for the indeterminacy of the Stieltjes matrix moment problem. We obtain explicit formulas for Stieltjes parameters and study the multiplicative structure of the resolvent matrix. In the indeterminate case, we study the analytic properties of the resolvent matrix of the moment problem. We describe the set of all matrix functions associated with the indeterminate Stieltjes moment problem in terms of linear fractional transformations over Stieltjes pairs. 相似文献
77.
Q. B. Li 《Optics and Lasers in Engineering》1989,11(2)
The smoothing spline function has been used for differentiation of photomechanical data in experimental stress analysis. However, since the available software packages use the algorithm with the so-called natural boundary conditions which are not necessarily suitable in many circumstances, errors tend to occur in both the first and second derivatives. In this paper we have modified the algorithm so that the user can have more freedom in selecting boundary conditions which suit the problem best and therefore, as a result, improve the accuracy of the analysis. Two examples are given to show the improvement achievable using the new scheme. 相似文献
78.
We show that, in dimensions equal or greater than three, classical strings do not join or split. This is part of a no-interaction theorem that is also proved. The quantum theory is considered. 相似文献
79.
Yu. P. Kalmykov 《Radiophysics and Quantum Electronics》1989,32(9):826-835
Radio Engineering and Electronics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1113–1124, September, 1989. 相似文献
80.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献