全文获取类型
收费全文 | 139篇 |
免费 | 3篇 |
专业分类
化学 | 108篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 6篇 |
物理学 | 22篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 13篇 |
2007年 | 5篇 |
2006年 | 12篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有142条查询结果,搜索用时 15 毫秒
101.
1H n.m.r. spectra of N-phenylmaleimide have been investigated in isotropic as well as nematic phases; the chemical shifts, the direct dipolar and the indirect spin–spin coupling constants have been determined. The direct dipolar coupling constants are consistent with rapidly interconverting energetically equivalent twisted conformations of C2 symmetry. Under the assumption that only two such conformers are predominantly present, the angle between the phenyl and the maleimide planes is determined as 52.9±0.9°. 相似文献
102.
Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A d'Olivera AB Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1992,69(22):3147-3150
103.
Rao IN Boruah A Kumar SK Kunwar AC Devi AS Vyas K Ravikumar K Iqbal J 《The Journal of organic chemistry》2004,69(6):2181-2184
An acyclic tripeptide based on a heterochiral D-pro-L-pro template shows a propensity to exist as a 3(10) helical conformation and can be cyclized, via ring-closing metathesis, to the corresponding cyclic tetrapeptides without disrupting the helical conformations in CDCl(3) as well as in DMSO-d(6) solutions. The detailed conformational studies were carried out by using NMR spectroscopy, X-ray crystallography, molecular dynamic simulations, and circular dichroism spectroscopy. 相似文献
104.
J.S. Yadav B.V.S. ReddyG. Satheesh A. PrabhakarA.C. Kunwar 《Tetrahedron letters》2003,44(10):2221-2224
2-Methylindole and its N-substituted derivatives react smoothly with 2,3-dihydrofuran (DHF) in the presence of a catalytic amount of InCl3 under mild conditions to afford the corresponding 2-methyl-3-perhydrofuro[2,3-b]oxepin-4-yl-1H-indole derivatives in fairly good yields with high diastereoselectivity, while 3,4-dihydro-2H-pyran (DHP) affords exclusively 5,5-di(1H-3-indolyl)-1-pentanol derivatives in high yields under similar reaction conditions. 相似文献
105.
Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Costa I Cremaldi LM Darling C Denisenko K Fernandez A Gagnon P Gerzon S Gobel C Gounder K Granite D Halling AM Herrera G Hurvits G James C Kasper PA Kondakis N Kwan S Langs DC Leslie J Lichtenstadt J Lundberg B Manacero A MayTal-Beck S Meadows B de Mello Neto JR Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV 《Physical review letters》1996,76(3):364-367
106.
Bizau J Esteva J Cubaynes D Wuilleumier FJ Blancard C La Fontaine AC Couillaud C Lachkar J Marmoret R Remond C Bruneau J Hitz D Ludwig P Delaunay M 《Physical review letters》2000,84(3):435-438
Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series. 相似文献
107.
108.
Sharma GV Manohar V Dutta SK Subash V Kunwar AC 《The Journal of organic chemistry》2008,73(10):3689-3698
Hybrid peptides are prepared from a C-linked carbo-beta-amino acid ester (R-beta-Caa) and an alpha-aminoxy acid (R-Ama) derived from S-lactic acid. Extensive NMR (in CDCl 3 solution), CD, and MD studies on the tetra- and hexapeptides led to identification of robust 12/10-mixed helices. The dipeptide repeat having an R-beta-Caa and an R-Ama thus provides a "new motif" to realize a 12/10-mixed helix, for the first time, in oligomers containing R-Ama. To understand the impact of side chains in the mixed helix formation, R-beta-Caa/Ama (with no substitution in Ama) and S-beta-hAla/R-Ama oligomers were investigated. NMR studies revealed the existence of 12/10-helices in these hybrid peptides, and the side chains of monomers were found to have a profound influence on their stabilities. These observations imply that the propensity of beta-amino acid to prefer a mixed 12/10-helix governs the structural behavior in these peptides. The structural consequences of the lone-pair repulsion between nitrogen and oxygen atoms result in a new and interesting structural motif which behaves like "pseudo" beta (3),beta(2)-peptides in generating 12/10-mixed helices. 相似文献
109.
J.S. Yadav B.V. Subba Reddy T. Pandurangam K.V. Raghavendra Rao K. Praneeth G.G.K.S. Narayana Kumar C. Madavi A.C. Kunwar 《Tetrahedron letters》2008,49(27):4296-4301
Various 1,3-dicarbonyl compounds reacted readily with benzylic and propargylic alcohols in the presence of 10 mol % of phosphomolybdic acid supported on silica gel (PMA/SiO2) under mild reaction conditions to produce 2-benzylic- and 2-propargylic-1,3-dicarbonyl compounds in excellent yields and with high selectivity. 相似文献
110.
Jhillu S. Yadav Basi V. Subba Reddy Nagendra Nath Yadav Ashutosh Pratap Singh Madavi Choudhary Ajit C. Kunwar 《Tetrahedron letters》2008,49(42):6090-6094
Baylis-Hillman acetates undergo smooth alkynylation with aryl-susbstituted iodoalkynes in the presence of indium metal in refluxing dichloromethane to furnish 1,4-enynes in high yields with (E)-stereoselectivity. In the absence of Lewis acid, the reaction follows both SN2 and SN2′ pathways affording 1:1 mixtures of 1,4-enynes. Upon addition of 10 mol % of InBr3, the reaction proceeds preferably in the SN2′ manner. In the case of adducts derived from acrylonitrile, the corresponding products are obtained in fairly good yields and with (Z)-stereoselectivity. 相似文献