全文获取类型
收费全文 | 3001篇 |
免费 | 80篇 |
国内免费 | 22篇 |
专业分类
化学 | 1918篇 |
晶体学 | 21篇 |
力学 | 59篇 |
数学 | 587篇 |
物理学 | 518篇 |
出版年
2023年 | 16篇 |
2022年 | 69篇 |
2021年 | 73篇 |
2020年 | 71篇 |
2019年 | 81篇 |
2018年 | 67篇 |
2017年 | 58篇 |
2016年 | 121篇 |
2015年 | 108篇 |
2014年 | 129篇 |
2013年 | 224篇 |
2012年 | 192篇 |
2011年 | 204篇 |
2010年 | 145篇 |
2009年 | 147篇 |
2008年 | 179篇 |
2007年 | 172篇 |
2006年 | 137篇 |
2005年 | 115篇 |
2004年 | 93篇 |
2003年 | 70篇 |
2002年 | 80篇 |
2001年 | 31篇 |
2000年 | 37篇 |
1999年 | 27篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 12篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 11篇 |
1970年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有3103条查询结果,搜索用时 15 毫秒
11.
12.
13.
Bombek S Lenarsic R Kocevar M Saint-Jalmes L Desmurs JR Polanc S 《Chemical communications (Cambridge, England)》2002,(14):1494-1495
An electrophilic amination of halogenated phenols with diisopropyl diazenedicarboxylate in the presence of ZrCl4 as a Lewis acid, accompanied by a halogen migration, was demonstrated for the first time; the fluorine, chlorine, bromine, or iodine atom migrated during the amination process under mild reaction conditions. 相似文献
14.
15.
Jonathan S. Dordick K. C. Backman R. Balakrishnan R. Brent M. S. Ptashne L. P. Casson S. A. Goff A. L. Goldberg P. A. Cornelius R. M. Hochstrasser N. R. Kallenbach H. Rubin G. J. Todaro H. A. De Boer J. C. Delgoffe M. Lobmann N. ZyGraich L. Gehrke T. Kunkel A. Paau S. G. Platt L. Sequeira M. A. Palladino H. G. Roman D. Hultmark T. T. Rasmusan H. Steiner 《Applied biochemistry and biotechnology》1990,26(1):107-113
Protein engineering and site-directed mutagenesis is becoming immensely important in both fundamental studies and commercial applications involving proteins and enzymes in biocatalysis. Protein engineering has become a powerful tool to help biochemists and molecular enzymologists elucidate structure-function relationships in enzymic active sites, to understand the intricacies of protein folding and denaturation, and to alter the selectivity of enzymatic catalysis. Commercial applications of engineered enzymes are being developed to increase protein stability, widen or narrow substrate specificity, and to develop novel approaches for use of enzymes in organic synthesis, drug design, and clinical applications. In addition to protein engineering, novel expression systems have been designed to prepare large quantities of genetically engineered proteins. Recent US patents and scientific literature on protein engineering, site-directed mutagenesis, and protein expression systems related to protein engineering are surveyed. Patent abstracts are summarized individually and a list of literature references are given. 相似文献
16.
Easily accessible N-acyl-2-triphenylphosphonioglycinate tetrafluoroborates react smoothly with trimethylphosphite in the presence of methyltriphenylphosphonium iodide to give N-acyl-2-(dimethoxyphosphoryl)glycinates in good or very good yields. The dimethoxyphosphorylglycinates may be isolated by column chromatography, or used directly for the Wadsworth-Emmons synthesis of α,β-dehydro-α-amino acids in a one-pot procedure without purification. 相似文献
17.
Roman Dziembaj 《Journal of solid state chemistry》1978,26(2):159-165
Measurements of oxygen equilibrium pressure above the V2O5?x oxide system have been performed within the temperature range 575 to 615°C. The results have been used to determine the standard enthalpy and entropy in the reaction V6O13 + O2 = 3 V2O5. The thermodynamic properties of the V2O5?x system (at x < 1) cited in the literature have been discussed for all the equilibria postulated. 相似文献
18.
Suspensions of cellulose nanocrystals form colloidal chiral nematic phases. The liquid crystalline order in these suspensions can be captured in solid films by slow evaporation of the liquid. Studies of the microstructure of such chiral nematic solid films revealed parabolic focal conic (PFC) defects, a symmetric form of focal conic defects in which the line defects form a pair of perpendicular, antiparallel, and confocal parabolas. The cellulose films with PFC defects were characterized by polarized-light and atomic force microscopy. The film surface showed a regular array of large and small elevations resulting from the displacement of the structural layers. Film fracture lines showed a series of layered half-cones. The microstructure of the films was modeled by computer. The model revealed that many structural layers terminate at the film surface. 相似文献
19.
20.