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151.
A large class of queuing systems have a stationary probability vector of matrix-geometric form. The essential step in the computation algorithm is the evaluation of a matrix R, the unique nonnegative solution of a matrix quadratic equation. The matrix R is usually determined by successive approximations.An explicit form of R is proposed, for systems that resemble the M/PH/1 queue. 相似文献
152.
153.
In recent publications from this laboratory, we have shown that the fragmentation of photoexcited olefinic molecules in the vacuum UV region leads mainly to the cleavage of a C—C bond located in the ß position relative to the double bond. The allyl fragment bears away part of the excess energy of the photon. At low pressure, this excited radical is capable of undergoing further decomposition. From the pressure effect, we were able to measure the first order rate constant for this secondary fragmentation. In this paper we shall use RRKM calculations in order to get a better idea on how the energy is distributed among the primary fragments. In cases where α- and β;-methallyl radicals were involved, the results show that an important part of the excess energy is located in the methallyl fragment in the 7.1 and 7.6 eV photolysis of 3-methyl-1-butene, 2-methyl-1-butene, and cis-2-pentene. 相似文献
154.
155.
Roland Guy 《Annali di Matematica Pura ed Applicata》1970,86(1):331-355
Résumé Le calcul des jets devenant rapidement presqu'inextricable, un calcul matriciel partiel est proposé qui pallie en partie à
cet inconvénient et permet de mieux saisir la structure algebrique des jets holonomes (chap1). Cet algorithme est ensuite utilisé dans le calcul des jets et permet de définir des connexions d'ordre supériéur ainsi
que les différentielles absolues correspondantes de manière très simple (chap2). Ceci généralise naturellement l'algorithme classique mis sous forme adéquate (voir introduction).
Entrata in Redazione il 13 dicembre 1969. 相似文献
156.
Lavallo V Mafhouz J Canac Y Donnadieu B Schoeller WW Bertrand G 《Journal of the American Chemical Society》2004,126(28):8670-8671
Stable tert-butyl diisopropylamino carbene is more nucleophilic but also more electrophilic than diamino carbenes; it undergoes cyclopropanation reactions and easily binds to metal fragments. 相似文献
157.
Guy Solladié Christine Greck Gilles Demailly Arlette Solladié-Cavallo 《Tetrahedron letters》1982,23(48):5047-5050
It is shown that reductions of β-ketosulfoxides of identical chirality (R) at sulfur, lead to reduction products of opposite stereochemistry according to the reducing agent used. The high enantiomeric excesses obtained (80 to 100%) provide a general route to both enantiomers of methylcarbinols from the corresponding esters. 相似文献
158.
The enthalpies of dissolution and dilution of LiBH4 and LiAlH4 in THF have been determined.Dissolutions are exothermic. The endothermic dilution of LiAlH4 suggests for this compound, either a dissociation or an association equilibrium. 相似文献
159.
Lateral diffusion measurements, most commonly accomplished through Fluorescence Photobleaching Recovery (FPR or FRAP), provide
important information on cell membrane molecules' size, environment and participation in intermolecular interactions. However,
serious difficulties arise when these techniques are applied to weakly expressed proteins of either of two types: fusions
of membrane receptors with visible fluorescent proteins or membrane molecules on autofluorescent cells. To achieve adequate
sensitivity in these cases, techniques such as interference fringe FPR are needed. However, in such measurements, cytoplasmic
species contribute to the fluorescence recovery signal and thus yield diffusion parameters not properly representing the small
number of surface molecules. A new method helps eliminate these difficulties. High Probe Intensity (HPI)-FPR measurements
retain the intrinsic confocality of spot measurements to eliminate interference from fluorescent cytoplasmic species. However,
HPI-FPR methods lift the previous requirement that FPR procedures be performed at probe beam intensities low enough to not
induce bleaching in samples during measurements. The high probe intensities now employed provide much larger fluorescence
signals and thus more information on molecular diffusion from each measurement. We report successful measurement of membrane
dynamics by this technique. 相似文献
160.
Harris SE Orpen AG Bruno IJ Taylor R 《Journal of chemical information and modeling》2005,45(6):1727-1748
Metal-ligand (M-L) bond lengths for a range of ligands (carboxylates, chlorides, pyridines, water, tertiary phosphines, and alkenes) and a variety of metals have been retrieved from the Cambridge Structural Database, CSD. Analysis of the factors which affect M-L bond lengths (for example, ligand coordination mode, oxidation state, metal coordination number and geometry, spin and Jahn-Teller effects, and ligand trans to M-L bond) shows that it is generally possible to subdivide the M-L data sets systematically to obtain better defined, unimodal, bond length distributions with means and sample standard deviations (SSDs) which reflect the nature of the bond in question. Typically, the SSDs for the M-L data sets can be reduced to 0.04-0.05 A by these methods. This work is an extension to tables of bond lengths in organometallic compounds and coordination complexes published in 1989. The importance of the factors which affect M-L bond lengths for particular metal-ligand groups are discussed. From the case studies reported, an algorithm is proposed by which compilation of a library of molecular geometry for metal complexes may be automated. The points that need to be considered to produce such a molecular library from the data stored in the CSD are discussed. The development of such a library would allow users to retrieve chemically well-defined geometric data rapidly and accurately. This should be of use, for example, to crystallographers and molecular modelers. 相似文献