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31.
V. N. Manuilov T. Idehara M. Kamada T. Hayashi La Agusu T. Kanemaki K. Yatsui Wiehua Jiang 《International Journal of Infrared and Millimeter Waves》2006,27(9):1183-1193
High power Large Orbit Gyrotron (LOG) [1] is now under development at FIR FU. First version of this device was recently manufactured
and then assembled with power supply ETIGO-IV [2]. Results of preliminary tests of electron-optic system are presented. The
conditions when stableflat form of current pulse realized are discussed. Analytical estimations of cathode-anode distance
to achieve small influence of cathode plasma during high voltage (HV) pulse are performed.
Two new electron gun versions with decreased influence of the cathode plasma on its impedance and pulse form are suggested
and optimized. New optimal magnetic field distributions are found. First gun has quiasi-flat cathode configuration near the
anode diaphragm and provides operating current about 60 A. Second one uses blade cathode with operating current about 30 A.
Beam quality for both guns is suitable for LOG operation. 相似文献
32.
J. Lí nares M. V. P Rez R. E. La Fuente X. Prieto C. Montero L. Gato J. I. Rodriguez C. G mez-Reino 《Fiber and Integrated Optics》1993,12(3):231-245
An experimental analysis of graded-index (GRIN) planar waveguides produced by ion exchange in soda-lime glass is presented. This study is based on a recent model describing nonlinear diffusion. Likewise the modal coupling between planar waveguides, produced in the same substrate, is analyzed in order to design efficient integrated optical components. Finally, waveguiding structures induced by Kerr effect in glass are proposed and analyzed. 相似文献
33.
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35.
Würthwein EU Lang G Schappele LH Mayr H 《Journal of the American Chemical Society》2002,124(15):4084-4092
A literature survey on the kinetics of hydride abstractions from CH-groups by carbocations reveals a general phenomenon: Variation of the hydride acceptor affects the rates of hydride transfer to a considerably greater extent than an equal change of the thermodynamic driving force caused by variation of the hydride donor. The origin of this relationship was investigated by quantum chemical calculations on various levels of ab initio and DFT theory for the transfer of an allylic hydrogen from 1-mono- and 1,1-disubstituted propenes (XYC=CH-CH(3)) to the 3-position of 1-mono- and 1,1-disubstituted allyl cations (XYC=CH-CH(2)(+)). The discussion is based on the results of the MP2/6-31+G(d,p)//RHF/6-31+G(d,p) calculations. Electron-releasing substituents X and Y in the hydride donors increase the exothermicity of the reaction, while electron-releasing substituents in the hydride acceptors decrease exothermicity. In line with Hammond's postulate, increasing exothermicity shifts the transition states on the reaction coordinate toward reactants, as revealed by the geometry parameters and the charge distribution in the activated complexes. Independent of the location of the transition state on the reaction coordinate, a value of 0.72 is found for Hammond-Leffler's alpha = deltaDeltaG/deltaDelta(r)G degrees when the hydride acceptor is varied, while alpha = 0.28 when the hydride donor is varied. The value of alpha thus cannot be related with the position of the transition state. Investigation of the degenerate reactions XYC=CH-CH(3) + XYC=CH-CH(2)(+) indicates that the migrating hydrogen carries a partial positive charge in the transition state and that the intrinsic barriers increase with increasing electron-releasing abilities of X and Y. Substituent variation in the donor thus influences reaction enthalpy and intrinsic barriers in the opposite sense, while substituent variation in the acceptor affects both terms in the same sense, in accord with the experimental findings. Marcus theory is employed to treat these effects quantitatively. 相似文献
36.
José Fernández Bertrán Boris La Serna Klaus Doerffel Klaus Dathe Gunther Kabish 《Journal of Molecular Structure》1982
The Fermi doublet V2?V3 + V4 of CH3CN in basic, inert and acidic solvents has been studied by IR and Raman spectroscopy. The values of W, the Fermi coupling coefficient, obtained from IR spectra varies with the nature of the solvent while W evaluated from Raman data remains constant at 12.5 ± 0.5 cm?1. The similar effects of Bronsted and Lewis acids on the band frequencies and intensities is evidence that the CN group complexes with acids via the N atom “n” electron pair and not the π bond. 相似文献
37.
Spoto G Gribov E Bordiga S Lamberti C Ricchiardi G Scarano D Zecchina A 《Chemical communications (Cambridge, England)》2004,(23):2768-2769
Cu(I) ions in Cu-ZSM-5 form Cu+(H2) complexes, stable at room temperature and sub-atmospheric H2 pressure, which do not have any homogeneous analogue except for matrix-isolated [Cu(eta2-H2)Cl]. Comparison with the unstable Na+(H2) adducts formed in the parent Na-ZSM-5 zeolite allow the conclusion that the Cu(I)/H2 bond is governed by sigma-pi overlap forces. 相似文献
38.
Since its inception five decades ago, imprinted sol-gel materials went practically unnoticed, until in the 1970s the conceptual introduction of molecular imprinting in synthetic polymers triggered a new interest in this field. The recent growth in interest in organic–inorganic hybrid materials prepared by sol-gel chemistry and the development of a variety of new strategies for imprinting polymeric matrices have led to a growing activity in what became known as molecularly imprinted sol-gel materials. This paper intends to give an overview of recent progress in molecular imprinting in sol-gel matrices, the potential analytical applications of these tailor-made materials and their limitations, with the aim of drawing attention to useful information and to enhancing interest in this practically unexplored but promising field. 相似文献
39.
Gabriele Proietti Stefano Corsano Enzo Castagnino 《Journal of heterocyclic chemistry》1981,18(2):415-416
The synthesis of cis- and trans-2-methyl-3-phenyl-1,4-benzodioxans 4 and 5 , from 1-phenyl-2-[2-(hydroxy)-phenoxy]propanols threo 2 and erythro 3 are described. 相似文献
40.
The linking of pyrimidines to polystyrene supports via either a 2- or 4-thioether provides access to pteridines through solid-phase synthesis. Oxidative cleavage (dimethyldioxirane) followed by nucleophilic substitution by amines, azide, or water completes a traceless synthesis of pteridines. 相似文献