全文获取类型
收费全文 | 929篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 837篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 63篇 |
物理学 | 41篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 29篇 |
2011年 | 33篇 |
2010年 | 13篇 |
2009年 | 22篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1966年 | 36篇 |
1965年 | 85篇 |
1964年 | 117篇 |
1963年 | 4篇 |
1956年 | 85篇 |
1955年 | 91篇 |
1954年 | 16篇 |
排序方式: 共有950条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
56.
Gerhard Quinkert Erhard Fernholz Peter Eckes Doris Neumann Gerd Dürner 《Helvetica chimica acta》1989,72(8):1753-1786
Synthesis of (+)-Aspicilin Using Building Blocks from Renewable Resources The 18-membered lichen macrolide (+)-aspicilin ( 1 ) is easily built up from compounds 14 , 16 , 3 , and 24 following the C3 + C7 + C6 + C2 = C18 pattern (see Schemes). The synthesis requires 15 steps and gives 1 in 13% overall yield from D -mannose ( 2 ). The latter compound provides the stereogenic centers C(4), C(5), and C(6). The stereogenic center C(17) is supplied by building block 14 (from (?)-(S)-ethyl lactate). 相似文献
57.
58.
59.
Andreas Mautner Xiaohua Qin Harald Wutzel Samuel C. Ligon Barbara Kapeller Doris Moser Guenter Russmueller Juergen Stampfl Robert Liska 《Journal of polymer science. Part A, Polymer chemistry》2013,51(1):203-212
Monomers for radical photopolymerization based on vinyl esters (VEs) have recently been identified as suitable alternatives to (meth)acrylates on account of their low irritancy and cytotoxicity. The drawback of most VEs with abstractable hydrogens is their relatively low reactivity compared with (meth)acrylates. Within this article, we proved by photo‐differential scanning calorimetry measurements and real‐time Fourier transform infrared spectroscopy that the thiol‐ene concept is able to improve the photoreactivity of these VEs to a large extent to a level between those of acrylates and methacrylates. Other VEs have now a reactivity of at least the level of similar acrylates. Mechanical properties as determined by Dynamic Mechanical Analysis and Charpy impact tests showed significant toughening of these materials. Furthermore, we were able to confirm low toxicity of all components by osteoblast cell culture experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
60.
Jairo Quijano Jorge David Claudia Snchez Elizabeth Rincon Doris Guerra Luis A. Len Rafael Notario Jos L. Abboud 《Journal of Molecular Structure》2002,580(1-3):201-205
Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G* levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions. 相似文献