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961.
Franke A Hessenauer-Ilicheva N Meyer D Stochel G Woggon WD van Eldik R 《Journal of the American Chemical Society》2006,128(41):13611-13624
A new model for the P450 enzyme carrying a SO(3)(-) ligand coordinated to iron(III) (complex 2) reversibly binds NO to yield the nitrosyl adduct. The rate constant for NO binding to 2 in toluene is of the same order of magnitude as that found for the nitrosylation of the native, substrate-bound form of P450(cam) (E.S-P450(cam)). Large and negative activation entropy and activation volume values for the binding of NO to complex 2 support a mechanism that is dominated by bond formation with concomitant iron spin change from S = (5)/(2) to S = 0, as proposed for the reaction between NO and E.S-P450(cam). In contrast, the dissociation of NO from 2(NO) was found to be several orders of magnitude faster than the corresponding reaction for the E.S-P450(cam)/NO system. In a coordinating solvent such as methanol, the alcohol coordinates to iron(III) of 2 at the distal position, generating a six-coordinate, high-spin species 5. The reaction of NO with 5 in methanol was found to be much slower in comparison to the nitrosylation reaction of 2 in toluene. This behavior can be explained in terms of a mechanism in which methanol must be displaced during Fe-NO bond formation. The thermodynamic and kinetic data for NO binding to the new model complexes of P450 (2 and 5) are discussed in reference to earlier results obtained for closely related nitrosylation reactions of cytochrome P450(cam) (in the presence and in the absence of the substrate) and a thiolate-ligated iron(III) model complex. 相似文献
962.
The anionic polymerization of acrylonitrile in DMF initiated by lithium 1,2-bis(diethylamino)-2-oxoethanolate in the range ?60 to 0°C has been studied. The initiator efficiency at low temperatures (?60 to ?40°C) is 2–6%; it remains nearly invariable with conversion owing to the associated state of the initiator. The low concentration of growing active centers is constant throughout the process; as a result, polymers with M > 3 × 105 are produced. The polymers are characterized by a narrow molecular-mass distribution, M w/M n = 1.3–1.6, and contain insignificant amounts of low-molecular-mass fractions. It has been shown that controlled polymerization processes can be carried outat moderately low temperatures (?30 to 0°C), and experimental conditions for freezing of polymerization and its recommencement have been ascertained. Optimum conditions for the synthesis of a high-molecular-mass polyacrylonitrile with M > 3 × 105 have been established, and the method for preparing polymers with M = (6.50–8.5) × 105 on an enlarged scale using high concentrations of the monomer has been developed. 相似文献
963.
E. A. Vinogradov G. I. Vinogradova V. I. Golovanov V. G. Veselago A. A. Mel’nikov A. V. Kapustyan A. A. Zhukov 《Physics of Wave Phenomena》2012,20(4):264-269
A design of the two-beam hybrid microwave interferometer for measuring refractive indices of metamaterials is described. It is based on the branching of radiation using a waveguide directional coupler. Radiations of the interferometer waveguide arms are summed and the phase disbalance of the interferometer arms is counted on the waveguide measuring line. The frequency dispersion of the negative refractive indices of the metamaterial samples with a variable distance between its constituent plates is experimentally investigated. A possibility of controlling the refractive index of a metamaterial is demonstrated. 相似文献
964.
Yuri Roiter Volodymyr Samaryk Sergiy Varvarenko Natalya Nosova Igor Tarnavchyk Jürgen Pionteck Petra Pötschke Stanislav Voronov 《Macromolecular Symposia》2004,210(1):209-217
An approach to synthesize interfacial active peroxide graft copolymers, so called precompatibilizers, which are suitable for the universal compatibilization of one special polymer with a number of other polymers, has been presented. As example, this approach is illustrated by the reactive fusion of a random peroxide copolymer (VO) with polypropylene (PP) resulting in a VOgPP precompatibilizer. A mathematical model of the process of the VOgPP synthesis and the conduction of a full-factorial experiment have allowed both the optimization of the synthesis conditions and the prediction of its proceeding. During blending PP with other polymers VOgPP localizes across the blend interphases and initiates radical processes leading to the in situ formation of final compatibilizer macromolecules, which are efficient just for the blends where they are formed. The universality of the precompatibilizer concept is demonstrated in PP blends of the thermoplastic/thermoplastic type (with polystyrene and polyethylene) and of the thermoplastic/thermoset type (with unsaturated polyester resin). 相似文献
965.
Natalya Nosova Yuri Roiter Volodymyr Samaryk Sergiy Varvarenko Yuri Stetsyshyn Sergiy Minko Manfred Stamm Stanislav Voronov 《Macromolecular Symposia》2004,210(1):339-348
Method of polyolefin surface activation via covalent grafting of polyperoxide nanolayer by free radical mechanism has been presented. The features of such the nanolayer formation under the thermoprocessing conditions, i.e.: formation of 3D crosslinked network in polyperoxide bulk; and its grafting with complete coating of polyolefin surface, -- is considered. The method provides an availability of uniformly placed peroxide groups of one type over the polyolefin surface activated, which may further be utilized for the tailored modification of polymer surfaces using the “grafting to” and “grafting from” techniques in that time when it is necessary. 相似文献
966.
Natalya Permyakova Tatyana Zheltonozhskaya Nikolay Strilchyk Nina Zagdanskaya Lesya Momot Vladimir Syromyatnikov 《Macromolecular Symposia》2003,203(1):247-258
Complex formation in the model three-component system, including polymer-polymer complex of poly(styrene-alt-maleic acid) (PSMA) and poly(ethylene oxide) (PEO), and also silica sol (SiO2) in aqueous solution as a function of molecular weight of PEO and the order of component mixing, were investigated. The degree of binding of PSMA links with PEO and SiO2 as well as the Gibbs energy of formation of the polymer-polymer complex and polymer-colloid complexes were defined. It was shown that the main factor of stabilization of the structure is hydrogen bonds. The conditions of three-component polymer-colloid system are practically independent of the order of component mixing. The spontaneous formation of polymer-colloid complexes between chemically complementary polymers and small dispersed particles is considered as the main reason for the abnormally high binding ability of colloid particles to the polymer-polymer complex. 相似文献
967.
Alexander V. Yakimansky Ludmila V. Vinogradova Boris L. Erussalimsky 《Macromolecular theory and simulations》1994,3(3):633-637
The energetic and electronic parameters of various mono- and bidentate complexes of CH3Li with N- and O-containing electron donors were calculated by the MNDO method. It was shown that N,N,N′,N′-tetramethylethylenediamine (TMD) forms a more stable bidentate complex with CH3Li than 1,2-dimethoxyethane (DME). However, DME, in contrast to TMD, may form a bis-bidentate complex with CH3Li in which the C Li bond is weakened to a higher degree than in complexes of CH3Li with N-containing electron donors. Much lower steric hindrance of DME, as compared to that of TMD, makes an easy formation of bis- and tris-monodentate complexes of DME with CH3Li possible; in these bis- and tris-monodentate complexes DME was simulated by (CH3)2O. Parameters of the C Li bond in the tris-monodentate complexes of (CH3)2O and tetrahydrofuran (THF) with CH3Li are comparable to those of the bis-bidentate complex CH3Li · 2 DME. These results are in qualitative agreement with experimental data, according to which THF and DME, in contrast to TMD, can favor the formation of separated ion pairs as active sites in anionic polymerization. 相似文献