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291.
Armstrong FA Camba R Heering HA Hirst J Jeuken LJ Jones AK Léger C McEvoy JP 《Faraday discussions》2000,(116):191-203; discussion 257-68
A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on an electrode surface. By carrying out cyclic voltammetry over a wide range of scan rates and exploiting the ability to poise or pulse the electrode potential between cycles, data are obtained that are conveniently (albeit simplistically) analysed in terms of plots of peak potentials against scan rate. A simple reversible electron-transfer process gives rise to a 'trumpet'-shaped plot because the oxidation and reduction peaks separate increasingly at high scan rate; the electrochemical kinetics are then determined by fitting to Butler-Volmer or Marcus models. Much more interesting though are the ways in which this 'trumpet plot' is altered, often dramatically, when electron transfer is coupled to biologically important processes such as proton transfer, ligand exchange, or a change in conformation. It is then possible to derive particularly detailed information on the kinetics, energetics and mechanism of reactions that may not revealed clearly or even at all by other methods. In order to interpret the voltammetry of coupled systems, it is important to be able to define 'ideal behaviour' for systems that are expected to show simple and uncoupled electron transfer. Accordingly, this paper describes results we have obtained for several proteins that are expected to show such behaviour, and compares these results with theoretical predictions. 相似文献
292.
Streubel R Schiemann U Jones PG Tran Huy NH Mathey F 《Angewandte Chemie (International ed. in English)》2000,39(20):3686-3688
293.
[reaction: see text] Synthesis and structure of a novel [6.6]metacyclophane with enediyne bridges is reported. 相似文献
294.
Bryant WS Jones JW Mason PE Guzei I Rheingold AL Fronczek FR Nagvekar DS Gibson HW 《Organic letters》1999,1(7):1001-1004
[formula: see text] Inspired by folded, nonpseudorotaxane complexes of bis(m-phenylene)-32-crown-10 systems, we synthesized a new bicyclic crown ether containing two 1,3,5-phenylene units linked by three tetra(ethyleneoxy) units. The new cryptand forms a "pseudorotaxane-like" inclusion complex with N,N'-dimethyl-4,4'-bipyridinium bis(hexafluorophosphate) with association constant Ka = 6.1 x 10(4) M-1, 100-fold greater than that of an analogous simple crown ether. 相似文献
295.
The laser-induced fluorescence excitation spectra of zinc phthalocyanine, chloroaluminum phthalocyanine, magnesium phthalocyanine, and free-base phthalocyanine have been investigated under jet-cooled conditions, by using pulsed infrared laser desorption as the means of vaporization. Assignment of the observed vibronic transitions reveals that many of them gain intensity from coupling of the S1(Q) state with the S2(B) and Q' states. Low-frequency out-of-plane modes of the macrocycle are observed in the region below 100 cm-1; the vibronic structure in this region of the spectrum is sensitive to deviation of the molecule from a planar geometry. The S1-S0 excitation energy shows a weak dependence on the hole size of the macrocycle. Copyright 1999 Academic Press. 相似文献
296.
297.
298.
Lipschitzian optimization without the Lipschitz constant 总被引:30,自引:0,他引:30
D. R. Jones C. D. Perttunen B. E. Stuckman 《Journal of Optimization Theory and Applications》1993,79(1):157-181
We present a new algorithm for finding the global minimum of a multivariate function subject to simple bounds. The algorithm is a modification of the standard Lipschitzian approach that eliminates the need to specify a Lipschitz constant. This is done by carrying out simultaneous searches using all possible constants from zero to infinity. On nine standard test functions, the new algorithm converges in fewer function evaluations than most competing methods.The motivation for the new algorithm stems from a different way of looking at the Lipschitz constant. In particular, the Lipschitz constant is viewed as a weighting parameter that indicates how much emphasis to place on global versus local search. In standard Lipschitzian methods, this constant is usually large because it must equal or exceed the maximum rate of change of the objective function. As a result, these methods place a high emphasis on global search and exhibit slow convergence. In contrast, the new algorithm carries out simultaneous searches using all possible constants, and therefore operates at both the global and local level. Once the global part of the algorithm finds the basin of convergence of the optimum, the local part of the algorithm quickly and automatically exploits it. This accounts for the fast convergence of the new algorithm on the test functions. 相似文献
299.
M. Convery W. L. Davis K. DelSignore T. L. Jenkins E. Kangas M. Knepley K. L. Kowalski C. C. Taylor C. H. Wang S. H. Oh W. D. Walker P. L. Colestock B. Hanna M. A. Martens J. M. Streets R. C. Ball H. R. Gustafson L. W. Jones M. J. Longo J. D. Bjorken N. Morgan C. Pruneau 《Il Nuovo Cimento C》1996,19(6):1045-1049
Summary A small experiment, ?MiniMax?, has been set up in the C0 intersection region of the Fermilab Tevatron to seek evidence for
disoriented chiral condensates and to study other forward physics phenomena. The experiment consists of a proportional wire
chamber telescope accompanied by scintillation (trigger) counters, a lead converter, and followed by an electromagnetic calorimeter.
The solid angle accepted is a cone centered at pseudorapidity (η) of 4.1 and of radius (in η-ϕ space) of about 0.6. Over 2.5
million events thus far have demonstrated the successful operation of the apparatus, however to date the analysis has not
progressed sufficiently to permit any conclusions concerning disoriented chiral condensates.
presented byL. W. Jones
Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International
Cosmic-Ray Conference, Rome, August 28–September 8, 1995. 相似文献
300.
Fibre-optic beam delivery systems for particle image velocimetry 总被引:2,自引:0,他引:2
The role of fibre-optics in the formation of light sheets for particle image velocimetry is reviewed, concentrating on the power handling capacities of fibres and their effect on laser beam quality. It is shown that when continuous wave lasers are used, chopped to form a pulsed light sheet, then it is feasible to use a single multimode optical fibre to deliver the beam. Conversely, with Q-switched lasers, the peak power densities are so high that to achieve an adequate compromise between pulse energy and beam quality, delivery systems based on bundles of multimode fibres have been developed. 相似文献