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11.
Since bromides are well-known precursors of primary amines, diethylaluminum 12 bromo-1-dodecyl oxide has been prepared and used as an initiator for the ring-opening polymerization of ?-caprolactone and L-lactide. Uner strictly controlled conditions, the end-functionalization of the polyesters in quantitative and the bromo end-group is easily converted into an azide group whatever the polymeric backbone. The subsequent reduction of the azide into the expected primary amine has been investigated by catalytic transfer hydrogenation (CTH) in DMF and by hydrolysis in the presence of triphenylphosphine in THF, respectively.The hydrolysis reaction (PΦ3/H2O) is perturbed by a coupling reaction, which involves a protonate secondary amine and leads to a twofold increase in the polyester molecular weight. The CTH method gives rise to the expected ω-NH2 poly (?-caprolactone), in contrast to polylactide which seems to be unstable toward the nascent amine end group. Whatever the polarity of the medium (DMF or THF), aminolysis of polylactides is observed to occur and leads to the formation of an internal amide. © 1994 John Wiley & Sons, Inc.  相似文献   
12.
Differential scanning calorimetry has been used to study the heats of fusion and melting transitions of n-octadecyl derivatives of polyvinyl alcohol. These derivatives were obtained by grafting paraffinic chains on polyvinyl alcohol, at various proportions. The melting transitions are independent of the degree of substitution; the heats of fusion are proportional to the fraction of crystallizable units. Using Flory's equilibrium crystallization theory, it is possible to interpret these results assuming, as demonstrated previously, that the chemical grafting is sequential with two unreacted hydroxyl groups between two adjacent paraffinic side-chains.  相似文献   
13.
Improvements of a CAMECA IMS 300 ion microanalyzer are described: ion source, resolution, ion detector and counting system. Comparison with the performances of an electron microprobe is presented. Examples of application are given.  相似文献   
14.
Résumé Une étude théorique ab initio SCF-LCAO-MO de la méthylène imine et de l'anion vinyle a été effectuée. Les barrières d'énergie calculées pour l'inversion de l'azote et pour la rotation autour de la liaison C=N sont respectivement de 26–28 kcal/mole et de 57 kcal/mole.La barrière d'inversion du carbanion calculée pour l'anion vinyle est de 39 kcal/mole et l'isomérisation des imines se fait donc par inversion de l'azote. Les anions vinyliques ont une configuration stable.L'origine physique de ces barrières d'inversion est étudiée et caractérisée par les variations des termes énergétiques, de la composition de l'OM du doublet libre et des populations électroniques.La comparaison des processus d'inversion du carbanion, de l'azote et de l'oxonium dans la série CH2=CH, CH2=NH et CH2=OH a permis de mettre en évidence l'évolution des termes énergétiques, de la hauteur de la barrière et des transferts de population.
Theoretical conformational analysisIV. An ab initio SCF-LCAO-MO study of methylenimine and of vinyl anion
An ab initio SCF-LCAO-MO study of methylenimine and vinyl anion has been performed. The calculated barriers to nitrogen inversion and to rotation about the C=N bond are equal to 26–28 kcal/mole and 57 kcal/mole respectively.The calculated barrier to carbanion inversion in the vinyl anion amounts to 39 kcal/mole. Thus isomerization of imines occurs by a nitrogen inversion process and vinyl anions are configurationally stable.The physical origin of these inversion barriers is studied and characterized by the changes in the energy terms, in lone pair MO composition, and in electron populations.Comparison of the carbanion, nitrogen and oxonium inversion processes in the isoelectronic series CH2=CH, CH2=NH and CH2=OH permits to delineate general trends in the energy terms, barrier height and population transfers.

Zusammenfassung Für Methylenimin und das Vinylanion wird eine ab initio SCF-LCAO-MO-Studie durchgeführt. Die berechneten Barrieren für die Stíckstoffinversion und die Rotation um die C=N-Bindung betragen 26–28 kcal/Mol bzw. 57 kcal/Mol.Die berechnete Barriere für die Inversion des Carbanions im Vinylanion beträgt 39 kcal/Mol. Daher wird die Isomerisation von Iminen durch einen Stickstoffinversionsprozeß hervorgerufen, und die Konfigurationen von Vinyl-Anionen sind stabil.Der physikalische Ursprung dieser Inversionsbarrieren wird studiert und durch Änderungen in den Energietermen, in der Zusammensetzung von Ione pair-MO's und in den Besetzungszahlen der Elektronen charakterisiert.Ein Vergleich der Inversionsprozesse des Carbanions, des Stickstoffs und des Oxonium-Ions in der isoelektronischen Reihe CH2=CH, CH2=NH and CH2=OH+ ermöglicht es, allgemeine Züge in den Energietermen, in den Höhen der Barrieren und den Besetzungsübergängen abzuleiten.


Précédent article de cette série: cf. Réf. [1].

Laboratoire associé au C.N.R.S.  相似文献   
15.
The condensation of 1,5-diaminoimidazoles with ethyl aceto-acetate gives two types of compounds: imidazo[1,5-b]-1,2,4-triazepinones and imidazo[4,5-b]pyridinones. The structure of these compounds is demonstrated by rmn and mass spectroscopy. The formation of imidazo[4,5-b]pyridinones from imidazo[1,5-b]-triazepinones through a new transposition is also shown.  相似文献   
16.
We study Schrödinger operators of the form on d , whereA 2 is a strictly positive symmetricd×d matrix andV(x) is a continuous real function which is the Fourier transform of a bounded measure. If n are the eigenvalues ofH we show that the theta function is explicitly expressible in terms of infinite dimensional oscillatory integrals (Feynman path integrals) over the Hilbert space of closed trajectories. We use these explicit expressions to give the asymptotic behaviour of (t) for smallh in terms of classical periodic orbits, thus obtaining a trace formula for the Schrödinger operators. This then yields an asymptotic expansion of the spectrum ofH in terms of the periodic orbits of the corresponding classical mechanical system. These results extend to the physical case the recent work on Poisson and trace formulae for compact manifolds.Partially supported by the USP-Mathematisierung, University of Bielefeld (Forschungsprojekt Unendlich dimensionale Analysis)  相似文献   
17.
18.
We describe here the synthesis of the enantiomerically pure phosphohomoserine lactone which will serve as an haptenic structure in catalytic antibody preparation.  相似文献   
19.
We investigate the interatomic Coulombic decay (ICD) of neon dimers following photoionization with simultaneous excitation of the ionized atom (shakeup) in a multiparticle coincidence experiment. We find that, depending on the parity of the excited state, which determines whether ICD takes place via virtual dipole photon emission or overlap of the wave functions, the decay happens at different internuclear distances, illustrating that nuclear dynamics heavily influence the electronic decay in the neon dimer.  相似文献   
20.
The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.  相似文献   
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