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451.
O. Blasco M. D. Contreras S. Díaz-Madrigal J. Martínez A. G. Siskakis 《Integral Equations and Operator Theory》2008,61(1):45-62
In this paper we deal with the maximal subspace in BMOA where a general semigroup of analytic functions on the unit disk generates a strongly continuous semigroup of composition
operators. Particular cases of this question are related to a well-known theorem of Sarason about VMOA. Our results describe analytically that maximal subspace and provide a condition which is sufficient for the maximal subspace
to be exactly VMOA. A related necessary condition is also proved in the case when the semigroup has an inner Denjoy-Wolff point. As a byproduct
we provide a generalization of the theorem of Sarason.
This research has been partially supported by the Ministerio de Educación y Ciencia projects n. MTM2006-14449-C02-01 and MTM2005-08350-C03-03 and by La Consejería de Educación y Ciencia de la Junta de Andalucía. 相似文献
452.
Solvent effects on oxygen-17 chemical shifts in methyl formate: linear solvation shift relationships
de Kowalewski DG Kowalewski VJ Contreras RH Díez E Casanueva J San Fabián J Esteban AL Galache MP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(1):1-10
A multiple linear regression analysis has been carried out using the Kamlet-Abboud-Taft solvatochromic parameters in order to quantify the solvent effects on the (17)O chemical shifts of methyl formate (MF). The influence of the solvents upon the carbonyl oxygen chemical shifts is smaller for MF than for N-methylformamide (NMF). The influence (in parts per million) of the solvent polarity-polarizability reduces from -21.9pi* in amides to -9.6pi* in MF. The influence of the solvent hydrogen-bond-donor acidities reduces from -42.0alpha in formamides to -16.9alpha in MF. The solvent effects upon the dicoordinated oxygen chemical shifts of MF are smaller in magnitude and opposite in direction, i.e., 4.8pi* and 2.6alpha, than those for the carbonyl oxygen. (17)O hydration shifts have been calculated for the NMF + (H(2)O)(6) and MF + (H(2)O)(5) complexes by the ab initio GIAO method at the 6-311 + G** level. The hydration shifts calculated for the carbonyl oxygens of NMF and MF and for the dicoordinated oxygen of MF, -102.4, -64.7, and 17.6 ppm, respectively, show the same trend as the corresponding empirical hydration shifts, -101.7, -42.0, and 14.2 ppm. 相似文献
453.
Cerda-Monje A Aizman A Tapia RA Chiappe C Contreras R 《Physical chemistry chemical physics : PCCP》2012,14(28):10041-10049
Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction. 相似文献
454.
Cross-efficiency evaluation is an extension of Data Envelopment Analysis (DEA) that permits not only the determination of a ranking of Decision Making Units (DMUs) but also the elimination of unrealistic weighting schemes, thereby rescinding the necessity for the inclusion of individual judgements in the models. The main deficiency of the procedure is the non-uniqueness of the optimal weights, which results in the peer evaluations dependences, for instance, on the software used to determine DMU’s efficiencies. This shortfall justifies the inclusion of secondary goals in order to determine cross-efficiency values. In this paper a new proposal of a secondary goal is studied. The idea is related with that proposed in Wu et al. (2009), in which the objective is the optimization of the rank position of the DMU under evaluation. In the procedure proposed here, an incentive to break level-pegging ties between alternatives is introduced by considering that efficiency scores induce a weak order of alternatives. The model is illustrated with a preference-aggregation application. 相似文献
455.
Rodrigo Ormazábal‐Toledo Enrique A. Castro José G. Santos Daniela Millán Alvaro Cañete Renato Contreras Paola R. Campodónico 《Journal of Physical Organic Chemistry》2012,25(12):1359-1364
In nucleophilic substitution reactions at carbonyl centres, there are two possible channels. The first one occurs when the attack of nucleophilic agents takes place simultaneously with the departure of the nucleofuge. This process is named as concerted. The second possibility is the formation of a reaction intermediate, typically a tetrahedral intermediate from which the nucleofuge departs after passing through a second transition state. This second mechanism is defined as stepwise. Whether a concerted or stepwise mechanism is to be expected for a given reaction depends on several factors. Among these determinants are the nucleophilicity of the attacking group, the leaving group ability of the nucleofuge, and the solvent, which affects both the stability of the intermediate or the transition states involved. The role of the electrophilic centre can however become an important factor that can determine the reaction mechanism. In this work we show that the group nucleophilic Fukui function model may be used to rationalize and to predict the reaction mechanism of the title compounds towards alicyclic amines. In general, when the electrophilic carbon centre is attached to the soft sulfur atom, the reaction mechanism is predicted to follow a stepwise route. When the electrophilic carbon atom is attached to a harder oxygen centre, the reaction mechanism is determined by chemical substitution at the nucleofuge moiety. Experimental verification for a set of four substrates is presented. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
456.
Robles J. Herrera Montes H. Camacho Casillas P. E. García Velasco-Santos C. Martínez-Hernández A. L. Herrera O. Raymond Aquino J. A. Matutes Coba L. Fuentes Contreras L. Alvarez Bordia R. K. 《Journal of Solid State Electrochemistry》2023,27(8):2207-2216
Journal of Solid State Electrochemistry - The increasing demands for higher energy density and higher power capacity of Li-ion secondary batteries have led to a search for electrode materials whose... 相似文献
457.
The three component mixture of HCl: HNO3: CH3COOH in the volumetric proportion of 3: 1: 4 was found to be a satisfactory etchant for various surfaces of Bi4Ge3O12. The correlation between etch pits and dislocations was established by means of repeated etching and optical observations. 相似文献
458.
Agueda E. Ceniceros‐Gmez Angel Ramos‐Organillo Julio Hernndez‐Díaz Jonathan Nieto‐Martínez Rosalinda Contreras Silvia E. Castillo‐Blum 《Heteroatom Chemistry》2000,11(6):392-398
The coordination sites of 2,6‐bis(benzimidazol‐2′‐yl)pyridine ( 1 ) toward protons and the diamagnetic metal ions Li+, Na+, and Co3+ were investigated by NMR spectroscopy. Variable temperature 1H and 13C NMR experiments were performed on 1 in order to evaluate the tautomeric equilibrium and hydrogen bonding. Imidazole dicoordinated aromatic nitrogen atoms were protonated by trichloroacetic acid and the three N‐dicoordinated atoms by fuming H2SO4. Reactions of the ligand 1 and benzimidazole 2 with metallic sodium or LiH afforded anionic species; the alkali metal ions appeared solvated by THF, but not by the ligands 1 or 2 . In contrast, reaction of 1 with Co(III) produces the stable cation [Co( 1 ‐H)2]+ with cobalt ion coordinated by two molecules of the monodeprotonated ligand. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:392–398, 2000 相似文献
459.