全文获取类型
收费全文 | 32969篇 |
免费 | 886篇 |
国内免费 | 244篇 |
专业分类
化学 | 21830篇 |
晶体学 | 150篇 |
力学 | 751篇 |
综合类 | 1篇 |
数学 | 5898篇 |
物理学 | 5469篇 |
出版年
2021年 | 298篇 |
2020年 | 379篇 |
2019年 | 348篇 |
2018年 | 302篇 |
2017年 | 319篇 |
2016年 | 667篇 |
2015年 | 672篇 |
2014年 | 718篇 |
2013年 | 1601篇 |
2012年 | 1574篇 |
2011年 | 1903篇 |
2010年 | 1058篇 |
2009年 | 904篇 |
2008年 | 1642篇 |
2007年 | 1699篇 |
2006年 | 1752篇 |
2005年 | 1605篇 |
2004年 | 1544篇 |
2003年 | 1246篇 |
2002年 | 1173篇 |
2001年 | 562篇 |
2000年 | 513篇 |
1999年 | 457篇 |
1998年 | 429篇 |
1997年 | 489篇 |
1996年 | 466篇 |
1995年 | 414篇 |
1994年 | 456篇 |
1993年 | 426篇 |
1992年 | 429篇 |
1991年 | 388篇 |
1990年 | 358篇 |
1989年 | 347篇 |
1988年 | 308篇 |
1987年 | 279篇 |
1986年 | 309篇 |
1985年 | 463篇 |
1984年 | 461篇 |
1983年 | 387篇 |
1982年 | 416篇 |
1981年 | 395篇 |
1980年 | 392篇 |
1979年 | 335篇 |
1978年 | 368篇 |
1977年 | 337篇 |
1976年 | 275篇 |
1975年 | 257篇 |
1974年 | 264篇 |
1973年 | 244篇 |
1972年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
111.
We carry out a careful study of operator algebras associated with Delone dynamical systems. A von Neumann algebra is defined using noncommutative integration theory. Features of these algebras and the operators they contain are discussed. We restrict our attention to a certain C
*-subalgebra to discuss a Shubin trace formula. 相似文献
112.
113.
Capillary gas chromatography coupled to microwave-inducedplasma detection furnishes sensitivity adequate for trace analysis when the signal is monitored at a carbon emission line. Work performed with one of these systems at high electronic gain for the carbon signal has revealed solvent band widths in excess of four minutes; these impeded quantification of peaks eluting after the solvent. This report discusses two phenomena which could be related to the unexpected intensity of this solvent response: photomultiplier tube saturation and carbon deposits in the quartz plasma discharge tube. 相似文献
114.
115.
The transmission and diffraction of radiation through dense monolayers of monodisperse opaque spheres were studied for the Fraunhofer domain. Theoretical considerations, numerical calculations and experiments on ultrasonic transmission and on laser light transmission and diffraction yielded corresponding results. Complementary studies included the cases of sterically non-interacting particles (by numerical simulation) and of small particle size parameters (by ultrasonic extinction). Transmission was found to be, in general, a non-linear function of the monolayer density. Secondary effects on the transmission can be attributed to the effect of the monolayer structure (characterized by the pair correlation function) on the angular distribution of diffracted intensity. The results were found to be in accordance with experimental results on extinction in three-dimensional systems. 相似文献
116.
Graham R. Knox Peter L. Pauson Debra Willison 《Journal of organometallic chemistry》1993,450(1-2):177-184
Phenylazoferrocene undergoes nickelation and palladation exclusively on the phenyl group. Lithium phenylazocyclopentadienide has been converted into derivatives of Mo, Mn, Fe, Ru and Rh. 相似文献
117.
A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine. 相似文献
118.
119.
120.
Future pathways for combinatorial chemistry 总被引:1,自引:0,他引:1
David Brown 《Molecular diversity》1997,2(4):217-222
Summary Investment in combinatorial chemistry (combichem) in the pharmaceutical industry is being driven by the need for increased efficiency. Results from pioneers in the field have demonstrated where mixture or discrete compound synthesis is useful, and what mixture sizes and compound concentrations are appropriate. To make the techniques of combichem of general utility in drug discovery, a broad range of advances is still required. Conversion of organic chemistry to solid phase conditions is key, as are developments in linkers and resins. Library design methodology requires further development. Combinatorial biosynthesis of focused libraries of natural products holds great promise for capitalising on hardwon natural product leads. Miniaturisation of screens is required to reduce the cost of screening combinatorial libraries. Developments in the processes preceding and following synthesis are required to enable the flow of increased numbers of compounds without new bottlenecks developing. The impact of combinatorial chemistry will be greatly enhanced by synergy with ongoing parallel developments in genetic technologies, screening technologies and bioinformatics. 相似文献