全文获取类型
收费全文 | 4170篇 |
免费 | 87篇 |
国内免费 | 22篇 |
专业分类
化学 | 2699篇 |
晶体学 | 25篇 |
力学 | 161篇 |
数学 | 651篇 |
物理学 | 743篇 |
出版年
2021年 | 27篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 39篇 |
2017年 | 38篇 |
2016年 | 61篇 |
2015年 | 73篇 |
2014年 | 86篇 |
2013年 | 231篇 |
2012年 | 170篇 |
2011年 | 199篇 |
2010年 | 124篇 |
2009年 | 116篇 |
2008年 | 171篇 |
2007年 | 165篇 |
2006年 | 178篇 |
2005年 | 196篇 |
2004年 | 160篇 |
2003年 | 147篇 |
2002年 | 159篇 |
2001年 | 67篇 |
2000年 | 72篇 |
1999年 | 65篇 |
1998年 | 48篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 67篇 |
1994年 | 56篇 |
1993年 | 60篇 |
1992年 | 53篇 |
1991年 | 54篇 |
1990年 | 39篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 33篇 |
1985年 | 81篇 |
1984年 | 64篇 |
1983年 | 51篇 |
1982年 | 67篇 |
1981年 | 73篇 |
1980年 | 54篇 |
1979年 | 67篇 |
1978年 | 68篇 |
1977年 | 79篇 |
1976年 | 52篇 |
1975年 | 53篇 |
1974年 | 50篇 |
1973年 | 38篇 |
1971年 | 36篇 |
1968年 | 27篇 |
排序方式: 共有4279条查询结果,搜索用时 265 毫秒
31.
Edward R. T. Tiekink Tomas Kurucsev Bernard F. Hoskins 《Journal of chemical crystallography》1989,19(5):823-839
The preparation, characterization, and X-ray structure analysis of (adeninatoN9)triethylphosphinegold(I) is reported. The crystal structure consists of discrete molecules, the adeninate anion coordinates via the N(9) atom with a Au-N(9) bond distance of 2.057(5) Å and the linear geometry about the Au atom is completed by the P atom of a disordered Et3P ligand; the Au-P(1) bond distance is 2.238(2) Å and the N(9)-Au-P(1) bond angle is 178.8(2)°. The crystals are orthorhombic, space groupPbca, with unit cell dimensionsa=8.528(1),b=17.797(3),c=18.526(2) Å andZ=8. The structure was refined by a full-matrix least-squares procedure to finalR=0.030 andR
w
=0.033 for 1749 reflections withI>2.5a(I). The electronic spectrum of the complex dissolved in water in the near ultraviolet is consistent with essentially separate -electron systems of the adenine and phosphinegold moieties; a conclusion which corroborates the X-ray structural results. 相似文献
32.
33.
The first reported synthesis of 3-formyltetronic acid and its conversion to enamine derivatives is described. 3-Dimethylaminomethylene-2,4-dioxotetrahydrofuran derivatives were also prepared by treatment of tetronic acids with dimethylformamide diethyl acetal. Nmr spectral studies are included. 相似文献
34.
35.
36.
Henriques ES Floriano WB Reuter N Melo A Brown D Gomes JA Maigret B Nascimento MA Ramos MJ 《Journal of computer-aided molecular design》2001,15(4):309-322
We present the search for a new model of -factor XIIa, a blood coagulation enzyme, with an unknown experimental 3D-structure. We decided to build not one but three different models using different homologous proteins as well as different techniques and different modellers. Additional studies, including extensive molecular dynamics simulations on the solvated state, allowed us to draw several conclusions concerning homology modelling, in general, and -factor XIIa, in particular. 相似文献
37.
N Bernard G Cuisinaud C Jozefczak M Seccia N Ferry J Sassard 《Journal of chromatography. A》1980,183(1):99-103
38.
Bernard A. Mikrut Krishan K. Khullar Pamela Y. P. Chan John M. Kokosa Ludwig Bauer Richard S. Egan 《Journal of heterocyclic chemistry》1974,11(5):713-718
The reaction of pyridine 1-oxide with 1-adamantanethiol in acetic anhydride produced a mixture of 2- and 3-(1-adamantanethio)pyridines, 1-aeetyl-2-(1-adamantanethio)-3-hydroxy-4-acetoxy-1,2,3,4-telrahydropyridine and the corresponding 3-acetoxyderivative. Pure substances were separated by means of column chromatography on alumina. The tetrahydropyridines were identified by means of their proton magnetic and mass spectra. 4-(1-Adamantanethio)pyridine was synthesized from 4-chloropyridinc and 1-adamantanethiol. The three isomeric (1-adamantanethio)-pyridines were, each, cleaved by concentrated hydrochloric acid to give 1-chloroadamantane and the corresponding pyridinethiol. 相似文献
39.
Steric and electronic influences of various substituted pyridines support the hypothesis of the coordination of pyridine in the manganese porphyrin-catalysed epoxidation of olefins with sodium hypochlorite solution. 相似文献
40.
Luis JM Torrent-Sucarrat M Solà M Bishop DM Kirtman B 《The Journal of chemical physics》2005,122(18):184104
Our new simple method for calculating accurate Franck-Condon factors including nondiagonal (i.e., mode-mode) anharmonic coupling is used to simulate the C2H4+X2B3u<--C2H4X1A(g) band in the photoelectron spectrum. An improved vibrational basis set truncation algorithm, which permits very efficient computations, is employed. Because the torsional mode is highly anharmonic it is separated from the other modes and treated exactly. All other modes are treated through the second-order perturbation theory. The perturbation-theory corrections are significant and lead to a good agreement with experiment, although the separability assumption for torsion causes the C2D4 results to be not as good as those for C2H4. A variational formulation to overcome this circumstance, and deal with large anharmonicities in general, is suggested. 相似文献