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91.
Kanchan Ghosal Rey T. Chern Benny D. Freeman Raj Savariar 《Journal of Polymer Science.Polymer Physics》1995,33(4):657-666
CO2, CH4, O2, and N2 permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N2, O2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc. 相似文献
92.
十二烷基苯的硝化选择性 总被引:1,自引:0,他引:1
借助气相色谱发现正十二烷基苯在硝硫混酸和硝磷混酸中硝化时,一硝化产物中对位异构体可达60%,较在硝酸乙酸酐中硝化时的对位选择性高10%,利用1HNMR测定了工业十二烷基苯和正十二烷基苯在高浓度硫酸(98%)的硝硫混酸中的硝化选择性,发现前者的硝化中对位异构体的高达80%。 相似文献
93.
We have examined the environments of the three phenol rotamers about the C–C bond in tyrosinamide by fluorescence quenching. Steady-state acrylamide quenching yields a nonlinear stern-Volmer plot. With three distinct emitting species and no other information about the system, it is impossible to analyze the data due to the number of variables which have to be determined. We therefore reduced the number of variables by independently determining the fractional intensity and dynamic quenching constant for each rotamer through time-resolved fluorescence quenching studies. These parameters were then used to analyze the steady-state data for any contribution of static quenching. We conclude that the nonlinear Stern-Volmer plot for the quenching of tyrosinamide by acrylamide is a consequence of each rotamer having a distinct dynamic quenching constant and the presence of static quenching. The static quenching can be represented by either the sphere-of-action model involving two of the three rotamers or the ground-state complex model involving all three rotamers. 相似文献
94.
The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6 were synthesized by nitration reaction and catalytic hydrogenation with high selectivity. The chemical structures were determined by FTIR, 1H NMR, 13C NMR, and UV. Regarding the mixture of Ac2O and HNO3 as nitrating agent, the reaction exhibited commendable trans-isomer selectivity. Effects of nitrating agent ratio, reaction temperature and reaction time on yield of trans-di(nitrobenzo)-18-crown-6 were investigated. The yield of trans-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1, reaction temperature of 50?°C and reaction time of 5?h. Moreover, effect of reaction time on trans-di(aminobenzo)-18-crown-6 was also studied. 相似文献
95.
The oxidation of 2-acetyl-5-methyl-4-R-furans (R = H, NO2) by selenious acid was studied. Derivatives substituted at the C=O groups of the corresponding glyoxals were obtained. The nitration of 2-(5-methyl-2-furyl)quinoxaline was carried out at C(4'). Oxidative splitting of the -nitrofuryl group occurs at the C(4)-C(5) and C(5)-O bonds. 相似文献
96.
97.
Oligomers of leucine, methionine, phenylalanine, and tyrosine were prepared enzymatically (using papain) from the respective methyl esters, with yields ranging from 51–96%. The effect of pH, buffer and salt concentration, and addition of alcohol on the oligomerization of leucine methyl ester was examined. The limits and potentialities of the enzymatic reaction as a method for obtaining monodisperse oligomers are discussed. 相似文献
98.
谷胱甘肽和Ebselen对胰岛素硝化的抑制及其相互作用机理的研究 总被引:3,自引:0,他引:3
生物体内NO和超氧阴离子快速反应生成的过氧亚硝酸根离子(ONOO-,peroxynitrite)是一种强细胞毒性物质,它诱导蛋白质酪氨酸残基硝化是其损伤生物系统的重要途径之一。为了探讨谷胱甘肽和ebselen对胰岛素硝化的抑制及其相互作用机理,采用UV-Vis、HPLC和ESI-MS等方法,研究了ONOO-对胰岛素的硝化作用、小分子抗氧化剂谷胱甘肽(GSH)和ebselen对ONOO-硝化胰岛素的影响以及它们之间的相互作用。结果表明单独的GSH和ebselen对ONOO--引发的胰岛素硝化均有明显的抑制,而作为谷胱甘肽过氧化物酶(GPx)的底物GSH 与GPx的模型化合物ebselen之间存在相互拮抗作用,经过对其产物分析,确定其机理是GSH和ebselen能够直接反应生成一种加合物,从而抑制了GSH和ebselen各自的抗硝化能力。 相似文献
99.
E. N. Khodot I. M. Petrova O. V. Anikin I. E. Chlenov 《Russian Chemical Bulletin》1995,44(11):2183-2185
The possibilities for stabilization of compounds with the A-B-NO2 fragment, where A is an atom containing a lone electron pair, were examined. It was shown thatN-methyl-O-2,4-dinitro- and 2,4,6-trinitrophenylhydroxylamines undergo nitration with nitronium tetrafluoroborate or with a mixture of nitric acid and acetic anhydride to give the correspondingN-nitrohydroxylamines in high yields.N-Nitro-2,4-dinitrohydroxylamine that contains no methyl group at the nitrogen atom is unstable and forms a product ofO-alkylation upon reaction with diazomethane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2276–2278, November, 1995.The work was supported by the International Science Foundation (Grant NGN 000). 相似文献
100.
A. I. Kazakov Yu. I. Rubtsov L. P. Andrienko G. B. Manelis 《Russian Chemical Bulletin》1997,46(10):1694-1699
The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10−3 to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by
the interaction of NO2 withn-decane. The equilibrium constants of dissociation of N2O4 inn-decane and Henry's constants of NO2 and N2O4 in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO2—n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N2O4 with intermediate oxidation products. The rate constants of the reaction of NO2 withn-decane were compared with analogous values determined in its mixtures with HNO3 solutions.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997. 相似文献