全文获取类型
收费全文 | 1332篇 |
免费 | 69篇 |
国内免费 | 4篇 |
专业分类
化学 | 1107篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 147篇 |
物理学 | 136篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 17篇 |
2020年 | 34篇 |
2019年 | 28篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 62篇 |
2015年 | 47篇 |
2014年 | 58篇 |
2013年 | 73篇 |
2012年 | 116篇 |
2011年 | 102篇 |
2010年 | 66篇 |
2009年 | 51篇 |
2008年 | 97篇 |
2007年 | 74篇 |
2006年 | 91篇 |
2005年 | 66篇 |
2004年 | 84篇 |
2003年 | 62篇 |
2002年 | 50篇 |
2001年 | 30篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1937年 | 1篇 |
1935年 | 2篇 |
1931年 | 1篇 |
1919年 | 2篇 |
排序方式: 共有1405条查询结果,搜索用时 15 毫秒
101.
The [6pi]-photocyclization of the anilides 1a and 5 was studied in the absence and in the presence of the enantiomerically pure chiral lactam 4. The relative configuration of the products was unambiguously established by single-crystal X-ray crystallography and by NMR spectroscopy. A significant enantiomeric excess was observed upon reaction of compound 1a to its photocyclization products at -55 degrees C employing lactam 4 as a chiral complexing agent in toluene as the solvent (66% yield). The trans product ent-3a was obtained in 57% ee, and the minor diastereoisomer (trans/cis = 73/27), cis product ent-2a, was obtained in 30% ee. DFT calculations were conducted modeling the complexation of intermediates 8 and ent-8 to host 4. In agreement with steric arguments concerning the conrotatory ring closure of 1a, the formation of ent-8 is favored leading to the more stable complex 4.ent-8 as compared to 4.8. Whereas the enantioselectivity in the photocyclization to trans compound ent-3a increased upon reduction in the reaction temperature, the enantiomeric excess in the formation of cis compound ent-2a went through a maximum at -15 degrees C (45% ee) and decreased at lower temperatures. Deuteration experiments conducted with the pentadeuterated analogue of 1a, d(5)-1a, revealed that the protonation of the intermediates 8 and ent-8 is influenced by chiral amide 4. In the formation of ent-3a/3a, both the enantioselective ring closure and the enantioselective protonation by amide 4 favor the observed (6aS,10aS)-configuration of the major enantiomer ent-3a. In the formation of ent-2a/2a, the enantioselective ring closure (and the subsequent diastereoselective protonation) favors the (6aR,10aS)-configuration that is found in compound 2a. Contrary to that, the enantioselective protonation by amide 4 shows a preference for ent-2a with the (6aS,10aR)-configuration. 相似文献
102.
103.
104.
Yu L Oost TK Schkeryantz JM Yang J Janowick D Fesik SW 《Journal of the American Chemical Society》2003,125(15):4444-4450
A method is described for the NMR-based screening for the discovery of aminoglycoside mimetics that bind to Escherichia coli A-site RNA. Although aminoglycosides are clinically useful, they exhibit high nephrotoxicity and ototoxicity, and their overuse has led to the development of resistance to important microbial pathogens. To identify a new series of aminoglycoside mimetics that could potentially overcome the problems associated with toxicities and resistance development observed with the aminoglycosides, we have prepared large quantities of E. coli 16 S A-site RNA and conducted an NMR-based screening of our compound library in search for small-molecule RNA binders against this RNA target. From these studies, several classes of compounds were identified as initial hits with binding affinities in the range of 70 microM to 3 mM. Lead optimization through synthetic modifications of these initial hits led to the discovery of several small-molecule aminoglycoside mimetics that are structurally very different from the known aminoglycosides. Structural models of the A-site RNA/ligand complexes were prepared and compared to the three-dimensional structures of the RNA/aminoglycoside complexes. 相似文献
105.
106.
Schneppensieper T Zahl A van Eldik R 《Angewandte Chemie (International ed. in English)》2001,40(9):1678-1680
107.
Eichhorn C Scherer OJ Sögding T Wolmershäuser G 《Angewandte Chemie (International ed. in English)》2001,40(15):2859-2861
108.
109.
Eann A. Patterson Erwin Hack Philippe Brailly Richard L. Burguete Qasim Saleem Thorsten Siebert Rachel A. Tomlinson Maurice P. Whelan 《Optics and Lasers in Engineering》2007,45(5):550
The design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards. 相似文献
110.