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991.
C. N. Cascaval I. A. Schneider I. C. Poinescu 《Journal of polymer science. Part A, Polymer chemistry》1975,13(10):2259-2268
Pyrolysis, in combination with gas-chromatography technique, was used in the determination of the structure and study of the thermal degradation mechanism of the condensation polymers obtained by Friedel-Crafts reactions of poly(vinyl chloride) with benzene, toluene, and naphthalene. The separation of the pyrolysis products was made using a column packed with chromosorb W (80–100 mesh) coated with 15% silicone SE-52. The identification of the pyrolysis products resulted as a consequence of the thermal decomposition of condensation polymers and their semiquantitative estimation led to the final conclusion that the initial normal chlorine substitution in the macromolecular chain of poly(vinyl chloride) is followed by an important intramolecular cyclization reaction yielding 1,3-methyleneindan units. 相似文献
992.
C. Strazielle 《European Polymer Journal》1979,15(1):55-59
This paper presents the results of a study of the thermodynamic properties of a ternary system viz. solvent (ethylacetate or benzene)-polydimethylsiloxane-polystyrene. The interaction parameter between the two polymers χ23, determined both from light scattering and studies of the critical conditions of phase separation, has been studied as a function of the molecular weights of the two polymers. Using a polystyrene of fixed molecular weight, we observe a large decrease in χ23 for increasing molecular weight of polydimethylsiloxane. When the molecular weights of the two polymers are very high, the parameter χ23 becomes very small (of the order of 0.01). The values of χ23 obtained for these two polymers are compared to those found for comparable systems, viz. polystyrene-polyisobutene and polydimethylsiloxane-polyisobutene. 相似文献
993.
An expression for the impedance frequency dependence in the case of d.c. superposition has been derived and analyzed for the crystallization process of metals taking into account the two-dimensional diffusion of ions in solution and the surface diffusion of adatoms and using the simplest surface model with parallel step lines. It is shown that in the general case it is impossible to present the crystallization impedance as the sum of the surface diffusion impedance and the Warburg impedance. It has been found that in the case of anode polarization an unusual effect of the impedance increasing with agitation intensity takes place which is typical of this mechanism. Possible methods for determination of the model parameters from impedance measurements are discussed. The authors suggest an iteration procedure which permits to determine all the parameters of the model under consideration including the surface diffusion coefficient of adatoms and the spacing between the growth step lines. 相似文献
994.
D. H. Beebe C. E. Gordon R. N. Thudium M. C. Throckmorton T. L. Hanlon 《Journal of polymer science. Part A, Polymer chemistry》1978,16(9):2285-2301
A quantitative procedure has been developed for characterizing the complete microstructure of polymers of 1,3-pentadiene, including the tacticity of any crystalline component. This can be accomplished by a combination of infrared spectroscopy, X-ray crystallinity, and 300-MHz NMR spectroscopy. A series of high structural purity polymers were synthesized with a series of previously unreported mixed microstructures. These samples were characterized by using the three techniques mentioned, including the previously unreported 300-MHz NMR data. With those results a 60-MHz NMR/IR method of spectroscopy was developed to determine the composition of poly(1,3-pentadiene)s in terms of percent cis-1,2-, cis-1,4-, trans-1,4-, and 3,4-pentadiene units. 相似文献
995.
This work reports the experimental results of the uniaxial pressure dependence at various temperatures of the spin-lattice relaxation time, T1, in paradichlorobenzene single crystals.The directionality of the pressure dependence, together the temperature dependence ot T1 near room temperature, give us some information about the dependence of the molecular torsional frequencies and lifetimes of the oscillations ground levels with the intermolecular crystalline potential. 相似文献
996.
D. Bagatti M. C. Cantone A. Giussani S. Ridone C. Birattari M. L. Bonardi F. Groppi A. Martinotti S. Morzenti M. Gallorini E. Rizzio 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(2):515-520
Summary The nuclear properties of 186gRe make it a useful agent for radionuclide therapy and imaging. The coordination compound [186gRe]Re-HEDP has proved to be a successful bone seeking agent for palliation of metastatic bone pain. Chemical, radiochemical and radionuclidic purity of commercial radiopharmaceutical [186gRe]Re-HEDP have been checked by means by γ- and β-spectrometries, INAA and paper radio-chromatography. The results indicate a good radionuclidic purity, with levels of contamination from the short-lived 188Re well below the required specifications. After injection of the radiopharmaceutical, the radiochemical measurements conducted in vivo, on biological matrices, blood, plasma and urine, have shown that, entering the systemic circulation, 186gRe dissociates from the bis-phosphonate complex as hydrosoluble [186gRe]ReO4-, and the two chemical species follow different biokinetics. 相似文献
997.
The structures and energetics of Li(6) (+), Li(6) (-) and three isomers of Li(6) are investigated using the coupled-cluster singles, doubles and perturbative triples [CCSD(T)] method with valence and core-valence correlation consistent basis sets of double- to quadruple-zeta quality (cc-pVXZ and cc-pCVXZ, where X=D-Q). These results are compared with qualitatively different predictions by less reliable methods. Our results conclusively show that the D(4h) isomer is the global minimum structure for Li(6). It is energetically favored over the C(5v) and D(3h) structures by about 5.1 and 7.1 kcal mol(-1), respectively, after the inclusion of the zero-point vibrational energy (ZPVE) correction. Our most accurate total atomization energies are 123.2, 117.6, and 115.7 kcal mol(-1) for the D(4h), C(5v), and D(3h) isomers, respectively. Comparison of experimental optical absorption spectra with our computed electronic spectra also indicate that the D(4h) isomer is indeed the most stable structure. The cation, anion, and some higher spin states are investigated using the less expensive cc-pCVDZ basis set. Adiabatic ionization energies and electron affinities are reported and compared with experimental values. Predictions of molecular properties are found to be sensitive to the basis set used and to the treatment of electron correlation. 相似文献
998.
When surfaces are structured on the scale of the wavelength, we can expect incident light to be strongly modified by the surface. This is especially the case when the surface is metallic. We have developed a formalism for computing these modifications, closely analogous to electron scattering theory, which we briefly review and present some results for optical properties of, and electron energy loss in, colloids. Our main theme is another effect associate with rough or structured metallic surfaces: Surface Enhanced Raman Scattering, or SERS. We model the rough surface by a periodic array of spheres and obtain the correct magnitude for the enhancement and for the frequency shifts observed. 相似文献
999.
1000.
Oxidative addition of 1-chloro-1-nitroethane to trans-IrCl(CO)-[P(CH3)2C6H5]2 followed by treatment of the initial product with pyridine yields a new iridium(III) complex IrCl(py)[COC(NO2)CH3][P(CH3)2C6H5]2, whose structure has been confirmed by X-rays crystallography. Two intermediate products have been observed by NMR spectroscopy; their structures have been tentatively assigned. The reaction of the corresponding bromine derivatives yields two isomers of the composition IrBr2(CO)[CH(NO2)CH3][P(CH3)2C6H5]2, and these are not affected by pyridine. The reaction of 1-chloro-1-nitroethane with Pt[P(C6H5)3]4 takes a completely different course in that yields nitrorethane and cis-PtCl2[P(C6H5)3]2 as the main products, with no detectable formation of the products of oxidation addition. A brief mechanistic investigation points towards the participation of radicals and radical anions as transient intermediates and a mechanism is proposed which explains most of the experimental results. 相似文献