全文获取类型
收费全文 | 472897篇 |
免费 | 3146篇 |
国内免费 | 813篇 |
专业分类
化学 | 230420篇 |
晶体学 | 7490篇 |
力学 | 24498篇 |
综合类 | 14篇 |
数学 | 61690篇 |
物理学 | 152744篇 |
出版年
2021年 | 4146篇 |
2020年 | 4664篇 |
2019年 | 5532篇 |
2018年 | 8157篇 |
2017年 | 8579篇 |
2016年 | 10719篇 |
2015年 | 5438篇 |
2014年 | 9666篇 |
2013年 | 19774篇 |
2012年 | 15975篇 |
2011年 | 18645篇 |
2010年 | 14615篇 |
2009年 | 14748篇 |
2008年 | 17143篇 |
2007年 | 16831篇 |
2006年 | 15352篇 |
2005年 | 15884篇 |
2004年 | 15186篇 |
2003年 | 13140篇 |
2002年 | 11934篇 |
2001年 | 12832篇 |
2000年 | 9948篇 |
1999年 | 7494篇 |
1998年 | 6553篇 |
1997年 | 6398篇 |
1996年 | 5958篇 |
1995年 | 5397篇 |
1994年 | 5363篇 |
1993年 | 5242篇 |
1992年 | 5876篇 |
1991年 | 6106篇 |
1990年 | 6030篇 |
1989年 | 6028篇 |
1988年 | 5780篇 |
1987年 | 5850篇 |
1986年 | 5460篇 |
1985年 | 6632篇 |
1984年 | 6888篇 |
1983年 | 5651篇 |
1982年 | 5915篇 |
1981年 | 5670篇 |
1980年 | 5302篇 |
1979年 | 6072篇 |
1978年 | 6092篇 |
1977年 | 6348篇 |
1976年 | 6252篇 |
1975年 | 5739篇 |
1974年 | 5650篇 |
1973年 | 5709篇 |
1972年 | 4557篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers. 相似文献
64.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献
65.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
66.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this
addendum is to present a correct argument for it. 相似文献
67.
Mark L. Agranovsky E. K. Narayanan 《Proceedings of the American Mathematical Society》2006,134(7):2117-2123
A test for a function to be a solution of an elliptic PDE is given in terms of extensions, as solutions, from the boundaries inside the domains belonging to an isotopic family. It generalizes a result of Ehrenpreis for spheres moved along a straight line.
68.
69.
M. V. Kartikeyan G. Singh E. Borie B. Piosczyk M. Thumm 《International Journal of Infrared and Millimeter Waves》2006,27(5):657-670
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode
competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic
roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried
out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of
well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector. 相似文献
70.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献