全文获取类型
收费全文 | 396496篇 |
免费 | 3141篇 |
国内免费 | 1196篇 |
专业分类
化学 | 201357篇 |
晶体学 | 6579篇 |
力学 | 19520篇 |
综合类 | 11篇 |
数学 | 45171篇 |
物理学 | 128195篇 |
出版年
2020年 | 3451篇 |
2019年 | 4108篇 |
2018年 | 5649篇 |
2017年 | 5592篇 |
2016年 | 7799篇 |
2015年 | 4329篇 |
2014年 | 7446篇 |
2013年 | 17163篇 |
2012年 | 13066篇 |
2011年 | 15837篇 |
2010年 | 11850篇 |
2009年 | 11956篇 |
2008年 | 14822篇 |
2007年 | 14740篇 |
2006年 | 13516篇 |
2005年 | 12054篇 |
2004年 | 11437篇 |
2003年 | 10233篇 |
2002年 | 10131篇 |
2001年 | 11507篇 |
2000年 | 8718篇 |
1999年 | 6742篇 |
1998年 | 5685篇 |
1997年 | 5698篇 |
1996年 | 5346篇 |
1995年 | 4821篇 |
1994年 | 4854篇 |
1993年 | 4809篇 |
1992年 | 5221篇 |
1991年 | 5421篇 |
1990年 | 5140篇 |
1989年 | 5158篇 |
1988年 | 5108篇 |
1987年 | 4987篇 |
1986年 | 4776篇 |
1985年 | 6286篇 |
1984年 | 6551篇 |
1983年 | 5305篇 |
1982年 | 5524篇 |
1981年 | 5403篇 |
1980年 | 5163篇 |
1979年 | 5549篇 |
1978年 | 5586篇 |
1977年 | 5660篇 |
1976年 | 5758篇 |
1975年 | 5286篇 |
1974年 | 5255篇 |
1973年 | 5386篇 |
1972年 | 3934篇 |
1971年 | 3425篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
12.
13.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed. 相似文献
14.
15.
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
16.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
17.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
18.
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
19.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen相似文献
20.