全文获取类型
收费全文 | 254篇 |
免费 | 7篇 |
学科分类
数理化 | 261篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 14篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 16篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 6篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 0 毫秒
1.
Studies in the field of development of polymeric oligoalkenesulfonate additives derived from sulfonated oligomers and exhibiting multifunctional effect when added to petroleum oils are summarized. 相似文献
2.
The magnetization and paramagnetic susceptibility of the system of compounds Zn1−x
CuxCr2S4 (0<x⩽1) are investigated at low temperatures. It is shown that as the content of Cu increases the system exhibits a transition
from an antiferromagnetic to a ferromagnetic state.
Fiz. Tverd. Tela (St. Petersburg) 40, 278–279 (February 1998) 相似文献
3.
Katritzky AR Nair SK Khokhlova T Akhmedov NG 《The Journal of organic chemistry》2003,68(14):5724-5727
Enynes 5a-g were prepared in moderate to good yields from 1-(triphenylphosphoranylideneaminoalkyl)benzotriazoles. Ring-closing metathesis of 5a-f afforded functionalized dienes 6a-f, respectively, which were used in a Diels-Alder cycloaddition reaction in the synthesis of the corresponding hexahydroisoquinoline derivatives 7a-f. 相似文献
4.
Katritzky AR Wang Z Hall CD Akhmedov NG Shestopalov AA Steel PJ 《The Journal of organic chemistry》2003,68(23):9093-9099
Reactions of oximes 9, 17, and 19 with electrophiles 15a-f and 24 in the presence of anhydrous potassium carbonate or triethylamine give 2-substituted condensed ring oxazoles 10, 16a-c, 18a-d, 20a-c, and 25 in a new general route to these compounds. 相似文献
5.
6.
7.
8.
9.
Katritzky AR Akhmedov NG Abdel-Fattah AA Wang M Rostek CJ Maender OW 《Magnetic resonance in chemistry : MRC》2004,42(5):424-435
Nucleophilic addition of alkyl- and benzylthiols to benzoquinone diimine (1) gave the corresponding 3-alkylthio- or 3-benzylthio-1,4-phenylenediamines (2-5). However, addition of aryl- or heteroarylthiols to 1 formed 2-arylthio- or 2-heteroarylthio-1,4-phenylenediamines (6-14). The structures of 2-14, obtained in 55-91% yields, were confirmed in CDCl3 or DMSO-d6 solution using 1D (NOE difference, coupled 13C NMR spectra, APT and DEPT) and 2D NMR techniques [DQCOSY, NOESY, HETCOR and heteronuclear multiple bond coherence (HMBC)] that resulted in unambiguous proton and carbon NMR resonance assignments. The substituent-induced 13C NMR chemical shift differences were calculated in 2-14 relative to carbon atoms in the model compound N1-(1,3-dimethylbutyl)-N4-phenyl-1,4-phenylenediamine (DMBPPD) (15) (a reduced form of benzoquinone diimine). 相似文献
10.
Katritzky AR Akhmedov NG Wang M Rostek CJ Steel PJ 《Magnetic resonance in chemistry : MRC》2004,42(7):648-658
The 1H and 13C NMR spectra of compounds 1-11 and 16-22 in CDCl3 and DMSO-d6 solutions allowed structural assignment to regioisomers 1/5 and 2/6 and their regioselective cyclization products 16-18 utilizing one- and two-dimensional NMR techniques (APT, DEPT, NOE difference, COSY, NOESY, HETCOR and gHMQC, gHMBC). Temperature-dependent 1H NMR spectra of 8-anilino-5-(4-methyl-2-pentyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (18) indicated a free energy of activation (deltaG++) of ca 17 kcal mol(-1) for interconversion between rotamers. The 1H and 13C NMR spectra of 20 and 22 containing two chiral centers exhibit duplication of several signals, indicating the existence of two diastereomeric forms. The structure of 4 was unambiguously confirmed by x-ray crystallography. 相似文献