全文获取类型
收费全文 | 4139篇 |
免费 | 85篇 |
国内免费 | 22篇 |
专业分类
化学 | 2705篇 |
晶体学 | 25篇 |
力学 | 161篇 |
数学 | 651篇 |
物理学 | 704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 | 74篇 |
2014年 | 86篇 |
2013年 | 229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 | 177篇 |
2005年 | 196篇 |
2004年 | 158篇 |
2003年 | 145篇 |
2002年 | 157篇 |
2001年 | 61篇 |
2000年 | 70篇 |
1999年 | 65篇 |
1998年 | 47篇 |
1997年 | 73篇 |
1996年 | 75篇 |
1995年 | 65篇 |
1994年 | 55篇 |
1993年 | 59篇 |
1992年 | 50篇 |
1991年 | 54篇 |
1990年 | 39篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1985年 | 79篇 |
1984年 | 62篇 |
1983年 | 50篇 |
1982年 | 65篇 |
1981年 | 72篇 |
1980年 | 53篇 |
1979年 | 66篇 |
1978年 | 68篇 |
1977年 | 78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4246条查询结果,搜索用时 15 毫秒
21.
22.
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
23.
24.
25.
N Bernard G Cuisinaud C Jozefczak M Seccia N Ferry J Sassard 《Journal of chromatography. A》1980,183(1):99-103
26.
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
27.
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
28.
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
29.
Pirard B 《Journal of computer-aided molecular design》2003,17(11):785-796
The Peroxisome Proliferator-Activated Receptors (PPARs) are nuclear receptors which over the last couple of years have been the focus of considerable research efforts aiming to identify compounds with well-defined selectivity profiles for the treatment of metabolic diseases. The ligand binding domains (LBD) of the three known PPAR subtypes exhibit between 60 and 70% sequence identity. To gain insight into the structural determinants of selectivity for the PPAR subtypes, a set of 13 crystal structures of PPAR LBD were classified, using the GRID/CPCA approach. As a result, nearly all of the crystal structures of each different PPAR subtype were found clustered in different regions of the CPCA score plots, and hydrophobic as well as steric interactions were identified as the major determinants of PPAR subtypes selectivity. Furthermore, interpretation of the GRID/CPCA model in structural terms led to the identification of LBD regions which could be targeted to improve the selectivity for a given PPAR subtype. Our findings are consistent with published structure-activity relationships for PPAR ligands as well as with site-directed mutagenesis results. 相似文献
30.
A series of normal mode analyses of bovine pancreatic trypsin inhibitor (BPTI) has been performed. The results of modifying the long-range truncation of electrostatics, reducing the conformational space of the system (reduced basis normal mode analysis), and using different parameter sets and models for the potential function are reported. Both explicit (904 atoms) and polar hydrogen (580 atoms) representations of BPTI were examined and produced nearly identical normal mode vectors but slightly modified vibrational frequencies. The truncation methods—no cutoff, shift, and switch—were examined, and the use of a short switching function was found to alter harmonic motion greatly. A table relating the different cutoff methods to several previously published frequencies for BPTI indicates that the diversity of published lowest frequencies is due to the use of different electrostatic models rather than to inherent differences in the models or energy parameters. Examining reduced basis results demonstrates that a dihedral basis yields similar normal mode vectors, though the vibrational frequencies are shifted to higher values. The analysis of BPTI harmonic dynamics using a spherical harmonic reduced basis set yields significantly altered dynamics, indicating that BPTI is not well represented as a homogeneous object at low temperatures. © 1995 John Wiley & Sons, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America. 相似文献