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271.
Amino acids have been used as catalysts for the study of kinetic of enolisation of m-Methylacetophenone, in which iodination has been the chosen method. Several parameters like effect of ketone concentration, effect of dielectric constant, effect of catalysts etc. have been investigated for their effect on enolisation kinetics. The study is focused on β-alanine, dl-alanine, l-alanine and Glycine for their effects on the rate. The order of the rate constants obtained has been found to be in the order of increasing dipole moments of the amino acids i.e. l-alanine < Glycine < dl-alanine < β-alanine. With an increase in the temperature from 323 K to 338 K, an increase in the rate was from 1.3 to 2.12 mol?1 min?1. The ongoing reaction was found to be bimolecular in nature. The values of different thermodynamic parameters like Entropy (ΔS≠), Enthalpy (ΔH≠), Energy of activation (ΔEa) and Gibbs free energy (ΔF≠) were found to be 6.20 e.u., 24.74 cal mol?1, 25.20 k cal mol?1 and 24.54 cal mol?1 respectively. 相似文献
272.
Summary The aim of this work was to study the utilisation of coordinative europium compounds as stationary phase additives in gas
chromatography.
The following series of aliphatic nucleophilic compounds were used as solutes: n-alcohols, carboxylic acid methyl esters,
ketones, ethers and 1-alkenes.
A correlation was established between the chromatographic retention values and the NMR chemical shift changes induced by interactions
of the organic molecules with the europium chelate.
The agglomerate formation between the europium chelates and nucleophilic compounds involves changes in the NMR spectra and
selective increases in the GC retention values when adding europium chelates to the stationary phases.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
273.
Hai Hua Tang 《Surface science》2007,601(16):3293-3302
The interaction of ethyl vinyl ketone (EVK) with Si(1 1 1)-7 × 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH2 (3099 cm−1) and CO (1684 cm−1) coupled with the appearance of new CC stretching mode (1660 cm−1) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC1H2C2HC3(C4H2C5H3)OSi surface species via [4 + 2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C1/C2 and C3 upon chemisorption display chemical downshifts of 0.8 eV and 2.2 eV, respectively, further confirming the proposed [4 + 2]-like cycloaddition reaction for the EVK/Si(1 1 1)-7 × 7 system. DFT theoretical calculations suggest that the proposed [4 + 2]-like cycloadduct is thermodynamically most favorable. 相似文献
274.
The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral PxNy-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)5] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP2N4 (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee. 相似文献
275.
Luca Salvi Francesca Micoli Werner Oberhauser 《Journal of organometallic chemistry》2007,692(7):1442-1450
Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)2(OAc)2(PnBu3)[P(p-XC6H4)3] (OAc = acetate, X = CH3O, CH3, H, F or Cl), containing different phosphine ligands trans to PnBu3, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO)2(OAc)2(PnBu3)2 and Ru(CO)2(OAc)2(PPh3)2. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to PnBu3 as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)2(H)(OAc)(PnBu3)[P(p-XC6H4)3], or dihydride, Ru(CO)2(H)2(PnBu3)[(p-XC6H4)3], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the CC double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto CO bond. 相似文献
276.
Four new N-heterocyclic carbene (NHC)-rhodium and iridium complexes derived from 2,2′-diaminobiphenyl have been successfully synthesized and their structures have been unambiguously characterized by X-ray diffraction. Their catalytic activities for hydrosilylation of ketones with diphenylsilane were investigated. It was found that NHC-rhodium complex (6) is the best one among the four catalysts for the reduction of ketones. 相似文献
277.
Acetone plays an important role in the chemistry of both the atmosphere and the ocean, due to its potential effect on the
tropospheric HOx (= HO + HO2) budget, as well as its environmental and health effects. We discuss the development of a mobile, sensitive, selective, economical
and facile method for the determination of acetone in seawater. The method consists of derivatizing acetone to its pentafluorobenzyl
oxime using 1,2,3,4,5-pentafluorobenzylhydroxylamine (PFBHA), followed by solid-phase microextraction (SPME) and analysis
by gas chromatography/mass spectrometry (GC/MS). A detection limit of 3.0 nM was achieved. The buffering capacity of seawater
imposes challenges in using the method’s optimum pH (3.7) on seawater samples, requiring calibration standards to be made
in buffered salt water and the acidification of seawater samples and standards prior to extraction. We employed the technique
for analysis of selected surface seawater samples taken on the Nordic seas during the ARK-XX/1 cruise (R.V. Polarstern). An upper limit of 5.5–9.6 nM was observed for acetone in these waters, the first acetone measurements reported for far
North Atlantic and Arctic waters.
Simplified schematic of transformations of organic compounds at the atmosphere–ocean interface 相似文献
278.
The quantitative analysis of ketones using DNPH is usually conducted in the presence of an acid catalyst. However, this method may cause an analytical error because 2,4-dinitrophenylhydrazones have both E- and Z-stereoisomers. Purified ketone-2,4-dinitrophenylhydrazone comprised only the E-isomer. However, under the addition of acid, both E- and Z-isomers were seen. In the case of 2-butanone-, 2-pentanone- and 2-hexanone-2,4-dinitrophenylhydrazone, the equilibrium Z/E isomer ratios were 0.20, 0.21 and 0.22, respectively. In addition, when trace water was added to the hydrazone derivatives in acetonitrile solution, the concentration of ketone derivatives were seen to decrease and the concentration of free DNPH was seen to increase. The decomposition rate of 2-butanone-2,4-dinitrophenylhydrazone was dependent on the concentration of acid-catalysis and reached an equilibrium state - carbonyl, DNPH, hydrazone-derivative and H2O - within 10 h at 0.1 mol L−1 phosphoric acid solution. The equilibrium constants of ketone-2,4-dinitrophenylhydrazones, [carbonyl] [DNPH]/[hydrazone] [H2O], were relatively large and ranged from 0.74 × 10−4 to 5.9 × 10−4. Hydrazone derivatives formed from 2-ketones such as 2-pentanone, 2-hexanone and 4-methyl-2-pentanone showed lower equilibrium constants than corresponding 3-ketones. Consequently, only a minimum concentration of catalytic acid must be added. The best method for the determination of ketone-2,4-dinitrophenylhydrazones by HPLC or GC is to add phosphoric acid to both the standard reference solution and samples, forming a 0.001 mol L−1 acid solution, and analyze after 27 h. 相似文献
279.
José Vicente María Teresa ChicoteAntonio Jesús Martínez-Martínez 《Tetrahedron letters》2011,52(47):6298-6302
Spontaneously or under various heating conditions, 2-alkyl- or 2-aryl-(iminoalkyl)benzenamines react with ketones and triflic acid (1:1:1) to give quinolinium salts. When working under milder thermal conditions, intermediate 1,2-dihydroquinazolinium derivatives can be isolated or detected in solution but decompose upon standing or heating to give the corresponding quinolinium salts. 相似文献
280.
The densities ρ, viscosities η, and refractive indices nD of binary mixtures of dimethyl carbonate (DMC) with acetophenone, cyclopentanone, cyclohexanone, and 3-pentanone have been measured over the entire range of composition at the temperatures 303.15, 308.15 and 313.15 K and at atmospheric pressure. The density values were used to calculate excess molar volumes VE, and other excess functions of interest such as deviations in viscosity Δη, excess Gibb's free energies of activation of viscous flow ΔGE and deviations in molar refraction ΔR. The measured viscosities were compared with those predicted using the Grunberg-Nissan, Eyring-Margules, Soliman-Marshall, and McAllister four body models. Furthermore the refractive indices data have been correlated using Lorentz-Lorentz, Weiner, Newton, Gladstone-Dale, Eykman, and Eyring-John equations and a satisfactory agreement was found for all the binary systems studied in the present work. 相似文献