全文获取类型
收费全文 | 268107篇 |
免费 | 1580篇 |
国内免费 | 530篇 |
专业分类
化学 | 120758篇 |
晶体学 | 4359篇 |
力学 | 14036篇 |
综合类 | 3篇 |
数学 | 43597篇 |
物理学 | 87464篇 |
出版年
2020年 | 1430篇 |
2019年 | 1586篇 |
2018年 | 10701篇 |
2017年 | 11602篇 |
2016年 | 7189篇 |
2015年 | 2757篇 |
2014年 | 3253篇 |
2013年 | 7821篇 |
2012年 | 9983篇 |
2011年 | 19097篇 |
2010年 | 12066篇 |
2009年 | 12126篇 |
2008年 | 16928篇 |
2007年 | 20339篇 |
2006年 | 6280篇 |
2005年 | 12081篇 |
2004年 | 8447篇 |
2003年 | 7944篇 |
2002年 | 5839篇 |
2001年 | 5378篇 |
2000年 | 4176篇 |
1999年 | 3004篇 |
1998年 | 2528篇 |
1997年 | 2406篇 |
1996年 | 2415篇 |
1995年 | 2223篇 |
1994年 | 2191篇 |
1993年 | 2086篇 |
1992年 | 2378篇 |
1991年 | 2322篇 |
1990年 | 2272篇 |
1989年 | 2202篇 |
1988年 | 2213篇 |
1987年 | 2210篇 |
1986年 | 2101篇 |
1985年 | 2722篇 |
1984年 | 2791篇 |
1983年 | 2479篇 |
1982年 | 2582篇 |
1981年 | 2397篇 |
1980年 | 2379篇 |
1979年 | 2534篇 |
1978年 | 2573篇 |
1977年 | 2416篇 |
1976年 | 2506篇 |
1975年 | 2412篇 |
1974年 | 2377篇 |
1973年 | 2596篇 |
1972年 | 1661篇 |
1971年 | 1362篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Recently commercial equipment using sedimentation field flow fractionation (SFFF) has become available for analysis of particulate materials in the sub-micron range. This paper describes the DuPont instrument and discusses its performance. A particular study is described on the comparison of the SFFF technique with that of quasi-elastic light scattering (QELS). The paper concludes that the instrument is capable of measuring particle size distributions with high resolution and precision, provided that no particles above the upper size limit — about 1 μm — are present. 相似文献
992.
B. Sanjeeva Rao M. Ramakrishna Murthy 《Journal of Polymer Science.Polymer Physics》1989,27(6):1187-1194
Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH3? CH? CH2 ~ and/or ~ CH2? CH? CH2 ~. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the Cα? Cβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption. 相似文献
993.
994.
We prove both geometric ergodicity and regular variation of the stationary distribution for a class of nonlinear stochastic recursions that includes nonlinear AR-ARCH models of order 1. The Lyapounov exponent for the model, the index of regular variation and the spectral measure for the regular variation all are characterized by a simple two-state Markov chain. 相似文献
995.
Kaon production is studied within the Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) model. Results are compared with experiment and with other models. The influence of the kaon potential on the kaon azimuthal distributions at SIS energies is considered. We also discuss the role of the many-body collisions at high-density phase of reaction. 相似文献
996.
Praveen K. Tandon Gayatri Sumita Sahgal Manish Srivastava Santosh B. Singh 《应用有机金属化学》2007,21(3):135-138
Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H2O2. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
A. I. Maksimov 《Thermophysics and Aeromechanics》2007,14(4):469-492
The paper briefly describes the life and activities of F.A. Zander and Yu.V. Kondratyuk (A.I. Shargei), pioneers of domestic
rocket engineering who made a significant contribution to the development of cosmonautics and rocket technologies. The main
ideas and proposals of these prominent scientists and inventors in the field of rocket and space engineering, which found
their application in space conquering, are considered.
To the 120th anniversary of F.A. Zander and 110th anniversary of Yu.V. Kondratyuk 相似文献
998.
999.
The solid solubility in the systems Y2O2S---La2O2S, Y2O2S---Gd2O2S, and Gd2O2S---La2O2S has been investigated. Solid solutions of all compounds, throughout the whole composition range, were readily obtained, using coprecipitated oxalates and a polysulfide flux. 相似文献
1000.
Stadia are popular models of chaotic billiards introduced by Bunimovich in 1974. They are analogous to dispersing billiards
due to Sinai, but their fundamental technical characteristics are quite different. Recently many new results were obtained
for various chaotic billiards, including sharp bounds on correlations and probabilistic limit theorems, and these results
require new, more powerful technical apparatus. We present that apparatus here, in the context of stadia, and prove “regularity”
properties.
相似文献