全文获取类型
收费全文 | 1200篇 |
免费 | 17篇 |
国内免费 | 8篇 |
专业分类
化学 | 787篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 235篇 |
物理学 | 188篇 |
出版年
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 44篇 |
2012年 | 53篇 |
2011年 | 53篇 |
2010年 | 38篇 |
2009年 | 32篇 |
2008年 | 61篇 |
2007年 | 65篇 |
2006年 | 60篇 |
2005年 | 46篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 43篇 |
2001年 | 10篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1996年 | 12篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 16篇 |
1989年 | 7篇 |
1985年 | 11篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1935年 | 7篇 |
1927年 | 9篇 |
1926年 | 7篇 |
1913年 | 7篇 |
1912年 | 11篇 |
1911年 | 7篇 |
1910年 | 9篇 |
1909年 | 19篇 |
1903年 | 8篇 |
1898年 | 7篇 |
1890年 | 8篇 |
1885年 | 11篇 |
排序方式: 共有1225条查询结果,搜索用时 671 毫秒
71.
Expressions are derived for the spectrum of the field generated by a planar, homogeneous, secondary source of any spectral distribution and of any state of spatial coherence. It is shown that the state of coherence affects the contributions of the homogeneous as well as the evanescent waves of the emitted field. The near-field spectra are studied in detail. The analysis is illustrated by examples. 相似文献
72.
73.
The lithium diisopropylamide-mediated 1,2-elimination of 1-bromocyclooctene to provide cyclooctyne is investigated using approximately 50 potentially hemilabile polyethers and amino ethers. Rate laws for selected ligands reveal chelated monomer-based pathways. The dependence of the rates on ligand structure shows that anticipated rate accelerations based on the gem-dimethyl effect are nonexistent and that substituents generally retard the reaction. With the aid of semiempirical and DFT computational studies, the factors influencing chelation are discussed. It seems that severe buttressing within chelates of the substitutionally rich ligands precludes a net stabilization of the chelates relative to nonchelated (eta(1)-solvated) forms. One ligand-MeOCH(2)CH(2)NMe(2)-appears to promote elimination uniquely by a higher-coordinate monomer-based pathway. 相似文献
74.
Veige AS Wolczanski PT Lobkovsky EB 《Angewandte Chemie (International ed. in English)》2001,40(19):3629-3632
75.
76.
77.
78.
Emil Gottlieb J. Neumann Lezé und Allard 《Fresenius' Journal of Analytical Chemistry》1893,32(1):252-253
Ohne Zusammenfassung 相似文献
79.
80.
Karel indel JiÍ Holubek Emil Svtek Olue Matouov Jiina Metyov Miroslav Protiva 《Journal of heterocyclic chemistry》1989,26(5):1325-1330
Reactions of dibenzo[b,e]thiepin-11(6H)-one (4) with 2-, 3- and 4-(dimethylaminomethyl)phenylmagnesium bromide afforded the tertiary alcohols 5a,b,c. The aldehydes 7 and 8 gave similarly the secondary alcohols 9a,b,c and 10c . Numerous attempts to prepare the corresponding ketones, especially by oxidation of 9a,b,c and 10c were unsuccessful. Only the oxidation of 9c with tetrabutylammonium chromate in chloroform afforded the desired ketone 16 . Its formation was accompanied by an important side reaction consisting in a cleavage of the “retro-ene-reaction” type leading to compound 11 and the aldehyde 13c which reacted with the chloroform present to give the alcohol 17 . Compounds 5a,b,c, 9a,b,c and 16 were tested as potential antidepressants but with the exception of some effects in the test of potentiation of yohimbine toxicity in mice, they proved inactive in this line. 相似文献