全文获取类型
收费全文 | 562篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
化学 | 347篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 88篇 |
物理学 | 139篇 |
出版年
2023年 | 7篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 14篇 |
2013年 | 41篇 |
2012年 | 35篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 22篇 |
2008年 | 22篇 |
2007年 | 24篇 |
2006年 | 25篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1973年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有582条查询结果,搜索用时 15 毫秒
91.
Inês C.B. Martins Mariana Sardo Tomaž Čendak José R.B. Gomes João Rocha M. Teresa Duarte Luís Mafra 《Magnetic resonance in chemistry : MRC》2019,57(5):243-255
Hydrogen bonds (HBs) play a key role in the supramolecular arrangement of crystalline solids and, although they have been extensively studied, the influence of their strength and geometry on crystal packing remains poorly understood. Here we describe the crystal structures of two novel protic gabapentin (GBP) pharmaceutical salts prepared with the coformers methanesulfonic acid (GBP:METHA) and ethanesulfonic acid (GBP:ETHA). This study encompasses experimental and computational electronic structure analyses of 1H NMR chemical shifts (CSs), upon in silico HB cleavage. GBP:METHA and GBP:ETHA crystal packing comprise two main structural domains: an ionic layer (characterized by the presence of charge-assisted +NHGBP⋯ O−METHA/ETHA HB interactions) and a neutral layer generated in a different way for each salt, mainly due to the presence of bifurcated HB interactions. A comprehensive study of HB networks is presented for GBP:METHA, by isolating molecular fragments involved in distinct HB types (NH⋯ O, OH⋯ O, and CH⋯ O) obtained from in silico disassembling of an optimized three-dimensional packing structure. Formation of HB leads to calculated 1H NMR CS changes from 0.4 to ~5.8 ppm. This study further attempts to assess how 1H NMR CS of protons engaged in certain HB are affected when other nearby HB, involving bifurcated or geminal/vicinal hydrogen atoms, are removed. 相似文献
92.
93.
The linear equivalence method (LEM), introduced by [Bull. Math. Soc. Sci. Math. de la Roumanie 24 (72) (1980) 4417; An. Univ. Bucure
ti, ser. Matematica 31 (1982) 75] to get solutions of nonlinear ODEs, was used so far to get differential type representations. New LEM representations of integral type are presented here and used for the study of the nonlinear elastic bar; a good approximating formula for the rotation of the cross-section at the bar end is also obtained, in case of a simply supported bar. A parallel old–new results is made by means of a programming code. 相似文献
94.
Toma Albu 《Journal of Number Theory》2003,99(1):222-224
This note presents corrections and additions to my paper (J. Number Theory 41 (1992) 322-358). 相似文献
95.
96.
Henrique E. Toma Herenilton P. Oliveira Hercílio R. Rechenberg 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(4):351-363
The intercalation ofmeso-tetrapyridylporphyrins into hydrated vanadium(V) pentoxide has been studied using X-ray diffraction; FTIR, electronic and Mössbauer spectroscopy; cyclic voltammetry and spectroelectrochemistry. The intercalation compound containing iron tetrapyridylporphyrin exhibits pronounced electrocatalytical activity in the reduction of molecular dioxygen, reflecting an enhanced reactivity of the catalyst in a confined medium. 相似文献
97.
The [RuIII(edta)(benzotriazole)]− complex has been investigated in aqueous solution, by means of cyclic voltammetry, stopped-flow
kinetics and spectroelectrochemistry. The formation reaction, starting from [RuIII(edta)H2O]− and benzotriazole, leads essentially
to the N(1) coordinated isomer. In the case of the RuII species, the products exhibit an intramolecular isomerization equilibrium
involving the N(1) and N(2) binding sites, with K12=0.33. A complete set of acid/base and association constants has been obtained
for the RuII and RuIII complexes. The data are coherent with theoretical calculations, reflecting the importance of π-backbonding
interactions in the reduced species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
98.
A modification of the Weiner index which properly takes into account the symmetry of a graph is proposed. The explicit formulae for the modified Wiener index of path, cycle, complete bipartite, cube and lattice graphs are derived and compared with their standard Wiener index. 相似文献
99.
We describe non-orientable, octagonal embeddings for certain 4-valent, bipartite Cayley graphs of finite metacyclic groups, and give a class of examples for which this embedding realizes the non-orientable genus of the group. This yields a construction of Cayley graphs for which
is arbitrarily large, where and
are the orientable genus and the non-orientable genus of the Cayley graph.Work supported in part by the Research Council of Slovenia, Yugoslavia and NSF Contract DMS-8717441.Supported by NSF Contract DMS-8601760. 相似文献
100.
Ultrasound effects on photochemical reactions, part 1: photochemical reactions of ketones with alkenes 总被引:3,自引:0,他引:3
Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Büchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction. 相似文献