全文获取类型
收费全文 | 394篇 |
免费 | 12篇 |
国内免费 | 6篇 |
专业分类
化学 | 269篇 |
晶体学 | 3篇 |
力学 | 2篇 |
数学 | 86篇 |
物理学 | 52篇 |
出版年
2020年 | 5篇 |
2019年 | 4篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 3篇 |
1965年 | 6篇 |
1963年 | 3篇 |
排序方式: 共有412条查询结果,搜索用时 15 毫秒
1.
2.
Riedl Z Kövér P Soós T Hajós G Egyed O Fábián L Messmer A 《The Journal of organic chemistry》2003,68(14):5652-5659
2-Arylsulfanyl and 2-benzylsulfanylpyridinium N-arylimides (2) easily prepared from 3-aryltetrazolopyridinium salts (1) with aryl and benzylthiolates, respectively, reacted with various dipolarophiles yielding cycloadducts that underwent transformation to give tetrahydropyrrolo[3,2-b]pyridines (5, 6, and 8) in good yields. A similar rearrangement (formation of 15) was also observed in the case of parent derivatives being unsubstituted in position 2 (12). The abscence of any significant solvent effect, comparison of the sulfur and non-sulfur analogues, as well as the stereoselective nature of the observed ring transformation seem to support a sigmatropic mechanism. Structure elucidation of the products has been carried out by single-crystal X-ray diffraction and (1)H NMR experiments. 相似文献
3.
Gröger H Hummel W Buchholz S Drauz K Nguyen TV Rollmann C Hüsken H Abokitse K 《Organic letters》2003,5(2):173-176
[reaction: see text] An enzyme-compatible biphasic reaction media for the asymmetric biocatalytic reduction of ketones with in situ cofactor regeneration has been developed. In this biphasic reaction media, which is advantageous for reactions at higher substrate concentrations, both enzymes (alcohol dehydrogenase and FDH from Candida boidinii) remain stable. The reductions with poorly water-soluble ketones were carried out at substrate concentrations of 10-200 mM, and the optically active (S)-alcohols were formed with moderate to good conversions and with up to >99% ee. 相似文献
4.
The chemical reactivity of the [1,2,3]triazolo[1,5-a]- and [1,5-c]-pyrimidinium salts towards morpholine, water and sodium methoxide have been studied. Among others, new 1-aza and 2-azabutadienes substituted by a [1,2,3]-triazole ring were obtained in the course of the opening of the positively charged pyrimidine ring. 相似文献
5.
A comparison of some results from Xα-scattered wave (Xα-SW) and extended Hückel (EH) calculations for metal clusters is given. It is found that small clusters of atoms (≈ 13 atoms) using the Xα-SW method reproduce many of the features of the electronic structure of the bulk metals, whereas this is not the case for the same clusters using the EH method. A more systematic approach to EH parametrizations is suggested in order to make this method a more viable approach to treating metal clusters. 相似文献
6.
Electron deficient 1,2-diacylcyclopropenes represent synthetic equivalent for both acylcarbenes and vinylcarbenes; in their cycloreaction with ynamines aminofuranes and/or aminocyclopentadienes are formed. 相似文献
7.
The spironaphthalen-2-ones 2, 10 and 18 were prepared by N-bromosuccinimide (NBS) oxidation of 1, 9 and 17 respectively, whereas spironaphthalen-1-ones 24 and 25 were obtained by treating 23 with NBS. The stereoisomeric reduction products 29, 30 and 32 obtained from 24 and 25 , gave the pentacyclic compound 33 on treatment with polyphosphoric acid. 相似文献
8.
9.
10.
The SCF Xα SW method can be used to obtain uniquely all the multiplets arising from the d → d transitions in the square planar metal complex PtCl2?4. The agreement with the experimental absorption spectrum and the singlet transition assignments in the region ≈ 3.0–4.5 eV is excellent. 相似文献