全文获取类型
收费全文 | 10794篇 |
免费 | 587篇 |
国内免费 | 1085篇 |
专业分类
化学 | 9365篇 |
晶体学 | 148篇 |
力学 | 105篇 |
综合类 | 47篇 |
数学 | 1132篇 |
物理学 | 1669篇 |
出版年
2024年 | 7篇 |
2023年 | 83篇 |
2022年 | 223篇 |
2021年 | 185篇 |
2020年 | 184篇 |
2019年 | 535篇 |
2018年 | 264篇 |
2017年 | 500篇 |
2016年 | 299篇 |
2015年 | 315篇 |
2014年 | 344篇 |
2013年 | 672篇 |
2012年 | 577篇 |
2011年 | 663篇 |
2010年 | 470篇 |
2009年 | 683篇 |
2008年 | 752篇 |
2007年 | 682篇 |
2006年 | 633篇 |
2005年 | 549篇 |
2004年 | 562篇 |
2003年 | 489篇 |
2002年 | 446篇 |
2001年 | 318篇 |
2000年 | 274篇 |
1999年 | 212篇 |
1998年 | 196篇 |
1997年 | 192篇 |
1996年 | 181篇 |
1995年 | 172篇 |
1994年 | 142篇 |
1993年 | 117篇 |
1992年 | 123篇 |
1991年 | 69篇 |
1990年 | 57篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 34篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 28篇 |
1982年 | 14篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
Luc M. H. Koymans Nico P. E. Vermeulen Allard Baarslag Gabriëlle M. Donné-Op den Kelder 《Journal of computer-aided molecular design》1993,7(3):281-289
Summary A homology model building study of cytochrome P450 2D6 has been carried out based on the crystal structure of cytochrome P450 101. The primary sequences of P450 101 and P450 2D6 were aligned by making use of an automated alignment procedure. This alignment was adjusted manually by matching -helices (C, D, G, I, J, K and L) and -sheets (3/4) of P450 101 that are proposed to be conserved in membrane-bound P450s (Ouzounis and Melvin [Eur. J. Biochem., 198 (1991) 307]) to the corresponding regions in the primary amino acid sequence of P450 2D6. Furthermore, -helices B, B and F were found to be conserved in P450 2D6. No significant homology between the remaining regions of P450 101 and P450 2D6 could be found and these regions were therefore deleted. A 3D model of P450 2D6 was constructed by copying the coordinates of the residues from the crystal structure of P450 101 to the corresponding residues in P450 2D6. The regions without a significant homology with P450 101 were not incorporated into the model. After energy-minimization of the resulting 3D model of P450 2D6, possible active site residues were identified by fitting the substrates debrisoquine and dextrometorphan into the proposed active site. Both substrates could be positioned into a planar pocket near the heme region formed by residues Val370, Pro371, Leu372, Trp316, and part of the oxygen binding site of P450 2D6. Furthermore, the carboxylate group of either Asp100 or Asp301 was identified as a possible candidate for the proposed interaction with basic nitrogen atom(s) of the substrates. These findings are in accordance with a recently published predictive model for substrates of P450 2D6 [Koymans et al., Chem. Res. Toxicol., 5 (1992) 211]. 相似文献
272.
273.
Mounir Maafi Belkacem Laassis Jean-Jacques Aaron M. Carmen Mahedero Arsenio Muñoz De La Peña Francisco Salinas 《Journal of inclusion phenomena and macrocyclic chemistry》1995,22(3):235-247
The photooxidation of Azure A and fluorescence properties of Azure A and its photoproduct have been investigated in aqueous media and in the presence of-cyclodextrin (-CD). The fluorescence intensity of the complex formed between the photoproduct and -CD was found to be three times higher than that of the uncomplexed Azure A photoproduct. A complex formation constant of 110±40 M–1 was calculated using the Benesi-Hildebrand treatment of the fluorescence emission data. Although the stoichiometry of the Azure A photoproduct: -CD complex was found to be 1: 1, it seems that the Azure A structure is only partially included. Calibration graphs were plotted for the free Azure A photoproduct and the photogenerated product included in -CD. The analytical parameters and quantification limits were determined. 相似文献
274.
The activity coefficients at infinite dilution have been measured at 25°C for cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, benzene, n-hexane, 1-hexene, 1-hexyne, n-heptane, 1-heptene and 1-heptyne in decahydronaphthalene, bicyclohexyl, 1,2,3,4-tetrahydronaphthalene and cyclohexylbenzene. These results, together with previously determined H
m
E
and V
m
E
have been used to calculate the partial molar excess thermodynamic properties of mixing at infinite dilution. 相似文献
275.
276.
Two new series of Nb6 bromides, CsRENb6Br18 (RE = all the lanthanides excepted Eu and Yb, + Y) (type H ) and M2RENb6Br18 (M = Cs, Rb, Tl; RE = Eu, Yb) (type R ) have been isolated. The crystal structures of CsErNb6Br18 and Cs2EuNb6Br18, isotypic with the corresponding chlorides, have been determined by single crystal X-ray diffraction data. The (Nb6Br18) intra-unit strength is related to the nature and the charge of the counter cation. A comparison between the corresponding chlorides and bromides series, based on the chemical properties and the size of the halogen is discussed. 相似文献
277.
2,6—二甲基吡啶在Y型分子筛的Bronsted和Lewis酸中心上的吸附动力学董玉林,杨孔章(山东大学胶体与界面化学研究所,济南250100)关键词Y型分子筛,酸中心,Lewis酸中心,2,6—二甲基吡啶,吸附动力学沸石分子筛是一类固体酸催化剂,在... 相似文献
278.
Summary The enantiomers of diphenylalanine (DPA) were well separated by chiral HPLC and NMR spectroscopy on the chiral stationary
phase (CSP) derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA). The chromatographic parameters such as separation
factors and retention times were greatly influenced by the mobile phase conditions. The (+)-18-C-6-TA used in the CSP was
also employed as a chiral solvating agent for the enantiodiscrimination of the DPA enantiomers by NMR spectroscopy. The proton
of the DPA analyte showing the chemical shift nonequivalences was used in determining the enantiomeric composition of the
analyte. 相似文献
279.
The intramolecular electrophilic substitution in 6-functionalized 1,3-dimethyl-1H-pyrrolo[3,4-d]pyrimidine-2,4(3H,6H)-diones was used for the synthesis of pyrimido[4′,5′:3,4]-pyrrolo[1,2-a]quinoxaline-8,10(7H,9H)-dione, pyrimido[4′,5′:3,4]pyrrolo[2,1-c][1,2,4]benzo-triazine-8,10(7H,9H)-dione, and 2H-pyrimido[4′,5′:3,4]pyrrolo[1,2-a]indole-2,4,11(1H, 3H)-trione derivatives.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2180–2185, December, 2006. 相似文献
280.
The areas of the fusion and crystallization peaks of K3TaF8 and K3TaOF6 have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K3TaF8 at temperature of fusion 1039 K: ΔfusHm(K3TaF8; 1039 K) = (52 ± 2) kJ mol−1 and of K3TaOF6 at temperature of fusion 1055 K: ΔfusHm(K3TaOF6; 1055 K) = (62 ± 3) kJ mol−1 have been determined. 相似文献