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21.
Adolfo Ensuncho M. Jennifer Lafont Alexandra Rotinov Rosa M. Domínguez Armando Herize Gabriel Chuchani Jairo Quijano 《国际化学动力学杂志》2001,33(8):465-471
The gas‐phase elimination kinetics of the ethyl ester of two α‐amino acid type of molecules have been determined over the temperature range of 360–430°C and pressure range of 26–86 Torr. The reactions, in a static reaction system, are homogeneous and unimolecular and obey a first‐order rate law. The rate coefficients are given by the following equations. For N,N‐dimethylglycine ethyl ester: log k1(s?1) = (13.01 ± 3.70) ? (202.3 ± 0.3)kJ mol?1 (2.303 RT)?1 For ethyl 1‐piperidineacetate: log k1(s?1) = (12.91 ± 0.31) ? (204.4 ± 0.1)kJ mol?1 (2.303 RT)?1 The decompositon of these esters leads to the formation of the corresponding α‐amino acid type of compound and ethylene. However, the amino acid intermediate, under the condition of the experiments, undergoes an extremely rapid decarboxylation process. Attempts to pyrolyze pure N,N‐dimethylglycine, which is the intermediate of dimethylglycine ethyl ester pyrolysis, was possible at only two temperatures, 300 and 310°C. The products are trimethylamine and CO2. Assuming log A = 13.0 for a five‐centered cyclic transition‐state type of mechanism in gas‐phase reactions, it gives the following expression: log k1(s?1) = (13.0) ? (176.6)kJ mol?1 (2.303 RT)?1. The mechanism of these α‐amino acids differs from the decarbonylation elimination of 2‐substituted halo, hydroxy, alkoxy, phenoxy, and acetoxy carboxylic acids in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:465–471, 2001 相似文献
22.
Gildas Bertho Imed Eddine Oumezziane Cédric Caradeuc Louis Guibout Christine Balducci Laurence Dinan Pierre J. Dilda Serge Camelo René Lafont Nicolas Giraud 《Magnetic resonance in chemistry : MRC》2022,60(5):504-514
We report the analysis of complex samples obtained during the microwave irradiation/heating of norbixin, which has been identified as a potential therapeutic target for age-related macular degeneration (AMD). In this context, identifying the different isomers that are obtained during its degradation is of primary importance. However, this characterization is challenging because, on the one hand, some of these isomers are unstable, and on the other hand, the 1H spectra of these isomeric mixtures are poorly resolved. We could successfully apply 1D pure shift experiments to obtain ultrahigh-resolution 1H nuclear magnetic resonance (NMR) spectra of the norbixin isomer samples and exploit their information content to analyze complementary 2D NMR data and describe accurately their isomeric composition. 相似文献
23.
24.
Laurent N Lafont D Dumoulin F Boullanger P Mackenzie G Kouwer PH Goodby JW 《Journal of the American Chemical Society》2003,125(50):15499-15506
Several 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 5a-e with various carbohydrate heads (beta-D-gluco, beta-D-galacto, beta-lacto, beta-D-xylo, and alpha-D-manno) have been synthesized. The key step was the formation of phenyldiazonium tetrafluoroborates 2a-e from the per-O-acetylated 4-aminophenyl glycosides 1a-e. These salts were condensed with N,N-didodecylaniline under phase transfer conditions and the per-O-acetylated 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 4a-e were fully de-O-acetylated by the Zemplén method. The self-organizing liquid crystal properties of the compounds were investigated by a variety of techniques, including polarized light microscopy, differential scanning calorimetry, and X-ray diffraction. All but one of the materials exhibited smectic A, lamellar phases. Remarkably, the glucose derivative exhibited a rectangular disordered columnar phase. This result has implications with respect to the induced curvature created by the recognition processes of the glucose headgroup relative to the other sugar moieties and to the prevalence of various glycolipids in cell membranes 相似文献
25.
Line Lucry Ferdinand Enoma Franois Estour Sabine Mnager Olivier Lafont Hassan Oulyadi 《Journal of heterocyclic chemistry》2002,39(4):663-670
A series of 46 3‐phenyloctahydropyrimido[1,2‐a]‐s–triazine derivatives were synthesized. This synthesis was performed via iminodimethylation of dialkylated 2‐aminopyrimidinedione synthons by substituted primary arylamines. In vitro pharmacological evaluation of these compounds is reported. One of them exhibited antifungal activity against Microsporum canis (10?65010?5 mol/L), and another showed affinity for serotoninergic 5‐HT1A and 5‐HT2b receptors (10?85010?7 mol/L). 相似文献
26.
Jordi Vill Jrg Bentzien ngels Gonzlez‐Lafont Jos M. Lluch Juan Bertran Arieh Warshel 《Journal of computational chemistry》2000,21(8):607-625
A general methodology for the study of chemical catalysis is presented and demonstrated in a study of Friedel–Crafts‐type alkylation reactions that are constrained to collinear configurations. Ab initio potential energy surfaces in solution and relevant experimental results are used to calibrate general empirical valence bond (EVB) potential surfaces for studies of such reactions. The EVB surfaces allow one to interpolate the ab initio results to studies of the effect of different solvents, substituents, and catalysts on the alkylation reactions. This implicit approach introduces such effects by shifting the diagonal energies of the corresponding resonance structures. Such an EVB/shift approach appears valuable for assessing the effects of different catalysts and solvents on complex chemical reactions. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 607–625, 2000 相似文献
27.
Liliany Espitia Ruby Meneses Rosa M. Dominguez Maria Tosta Armando Herize Jesus Lezama Jennifer Lafont Gabriel Chuchani 《国际化学动力学杂志》2009,41(3):145-152
The gas‐phase elimination kinetics of ethyl 2‐furoate and 2‐ethyl 2‐thiophenecarboxylate was carried out in a static reaction system over the temperature range of 623.15–683.15 K (350–410°C) and pressure range of 30–113 Torr. The reactions proved to be homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are expressed by the following Arrhenius equations: ethyl 2‐furoate, log k1 (s?1) = (11.51 ± 0.17)–(185.6 ± 2.2) kJ mol?1 (2.303 RT)?1; ethyl 2‐thiophenecarboxylate, log k1 (s?1) = (11.59 ± 0.19)–(183.8 ± 2.4) kJ mol?1 (2.303 RT)?1. The elimination products are ethylene and the corresponding heteroaromatic 2‐carboxylic acid. However, as the reaction temperature increases, the intermediate heteroaromatic carboxylic acid products slowly decarboxylate to give the corresponding heteroaromatic furan and thiophene, respectively. The mechanisms of these reactions are suggested and described. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 145–152, 2009 相似文献
28.
Jean-François Cavalier Dominique Lafont Paul Boullanger David Houisse Jacqueline Giallo Jean-Michel Ballester Frédéric Carrière 《Journal of chromatography. A》2009,1216(37):6543-6548
A general and easily accessible method for the extraction followed by the simultaneous separation and quantitative determination of triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids has been improved and optimized based on existing protocols using liquid-phase extraction and thin-layer chromatography coupled to flame ionization detection (TLC/FID Iatroscan). After lipid extraction in the presence of a suitable new synthetic internal standard, namely CholE1, a single elution step using n-heptane/diethyl ether/formic acid (55:45:1, v/v/v) was applied. This method was validated in line with international bioanalytical method validation guidelines using two different matrix systems: purified water and human gastro-intestinal fluid. Overall, the assay was found to have high levels of precision with coefficients of variation ranging from 1.48% to 11.0% and accuracy ranging from −13.3% to +5.79% RE. The confidence limits of the lipid mean recovery rates varied between 89.9% and 104%. This method is therefore highly suitable for quantifying the lipolysis products generated in vitro during the hydrolysis of various fats and oils by digestive lipases, as well as those collected from the gastro-intestinal tract in the course of human clinical studies on lipid digestion. 相似文献
29.
N. Z. Mamadalieva L. N. Zibareva R. Lafont L. Dainan Z. Saatov 《Chemistry of Natural Compounds》2004,40(6):574-578
Research results on the isolation and identification of ecdysteroids from plants of the Silene L. genus were presented.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 472–475, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
30.
Z. Sadikov Z. Saatov M. Garcia J.-P. Girault R. Lafont 《Chemistry of Natural Compounds》2001,37(3):262-265
The ecdysteroid content ofSilene claviformishas been analyzed and the four major compounds have been identified as 20-hydroxyecdysone, 2-deoxy-20-hydroxyecdysone, 2-deoxyecdysone, and integristerone A. Two new minor compounds have also been identified
An erratum to this article can be found at 相似文献