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41.
K. -P. Arnold K. -P. Döring M. Gladisch N. Haas D. Herlach W. Jacobs M. Krauth S. Liebke H. Metz H. Orth H. -E. Schaefer A. Seeger 《Hyperfine Interactions》1984,17(1-4):219-224
We have measured the transverse spin relaxation of positive muons
+ in Al single crystals after irradiation at 150 K with 3 MeV electrons. The relaxation functions agree with those expected for diffusion-limited trapping of the
+ in monovacancies. Between 215 K and 60 K the
+ diffusivity is well described by the Flynn-Stoneham law (multi-phonon incoherent tunnelling between ground states) with an activation enthalpyH
a = (30±2) meV. At lower temperatures, few-phonon (in particular one-phonon) processes become important. The decrease of the vacancy concentration by a factor of 100 during annealing between 227 K and 267 K has been studied. 相似文献
42.
Howard C. Haas Ruby L. Macdonald Alan N. Schuler 《Journal of polymer science. Part A, Polymer chemistry》1970,8(5):1213-1226
The polymerization kinetics in water of acrylylglycinamide (AG) initiated by K2S2O8 was studied over the temperature range 40.0 to 60.0°C. Monomer concentration was varied from 7.8 × 10?3 to 31.2 × 10?3M and catalyst from 1.85 × to 11.10 × 10?5M. The rate expression is ?d[M]/dt = Rp, = k1.22[K2S2O8]0.5[M]1.22, and the overall empirical rate constant, k1.22 = 1.14 × 1011e?15,800/RT 1.0.72 mole?0.72 min?1. To explain the dependence on monomer, a kinetic scheme which includes a bimolecular reaction (k2) between monomer and initiator is suggested. The simplified expression which describes the initial rate of polymerization is: ?d[M]/dt = Rp, = k4(2[I]/k5)1/2[M](k1 + k2[M])1/2, where k1, k2, k4 and k5 are rate constants for S2O8 = decomposition, a bimolecular reaction between monomer and initiator, propagation, and termination, respectively. Individual bimolecular rate constants are expressed in liter/mole-min. The equation predicts a dependence on monomer concentration between 1.0 and 1.5 with 1.5 being approached a t high monomer concentrations. Plots of RP2/[M]2 versus [M] are linear, as predicted by the postulated reaction route and values for k2 and k4/k51/2 were obtained from the slopes and intercepts of these plots. The temperature dependence of the bimolecular monomer-initiator reaction is k2 = 5.19 × 1021e?36,000/RT. Instead of the usual behavior, the k4/k51/2 ratio was found to decrease with temperature and the difference of activation energies, (E4 ? E5/2), is ?1.50 kcal. The temperature dependence of the propagation to square root of the termination rate constant ratio is k4/k51/2 = 6.16e1500/RT. These rather unusual results may be related to the ability of AG polymers in water to form thermally reversible gels; even above the gel melting points, the polymers are considerably aggregated in solution. This would tend to make the bimolecular termination reaction more temperature dependent and also account for the high values (59–69) for the k4/k51/2 ratios. For similar temperatures, the overall rate constants for AG are approximately four times those for acrylamide. 相似文献
43.
A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.
(), , , , -. Pt , .相似文献
44.
The comparative reaction chemistry between first and second derivative paraelement analogs ( (CF3)2PH, (CF3S)2PH, CF3SH, CF3SSH, CF3SNH2, (CF3S)2NH, (CF3S) 3N) and F-N-isopropylacetimidoyl chloride [CF3CCl=NCF(CF3)2, I] has been investigated. Reaction schemes are presented. The reactions of I with NH3 and NaI are also reported. Analytical data is provided for previously unreported compounds along with more detailed analysis of known compounds. 相似文献
45.
The following substances could be prepared by Grignard reactions or by conversions with trichlorosilane: C6F5CH2CHCH2, C6F5(CH2)3SiCl3, CF3(CF2)9CH2CHCH2, CF3(CF2)7(CH2)2SiCl3, CF3(CF2)11(CH2)3CHCH2 und CF3(CF2)11(CH2)5SiCl3.They were characterized by spectroscopical and microanalytical methods. 相似文献
46.
Silvia Dorn Peter Eggenberg Michael R. C. Gerstenberger Alois Haas Ulrich Niemann Peter Zobrist 《Helvetica chimica acta》1979,62(5):1442-1450
(Perhalomethylthio)heterocycles. X 1 IX. Mitt.: s. [1]. . Acid-catalyzed substitutions on (perchlorofluoromethylthio)pyrroles and their agro-biological activities In the presence of C4F9SO3H the (perhalomethylthio)pyrroles 1a–c react with Cl3?nFnCSCl (n = 1–3) to give mixtures of the 2,5- and 2,4-disubstituted pyrroles 2a–f and 3a–h . 2a and 3a react with CF3SCl (catalyst CF3SO3H) yielding 2,3,5-tris (trifloromethylthio)pyrrole ( 4a ), which under similar conditions reacts further to give 2,3,4,5-tetrakis (trifluoromethylthio)pyrrole ( 5 ). As a by-product during the conversion of 3a to 4a 2,3,4-tris (trifluoromethylthio)pyrrole ( 4b ) is formed. The pyrroles 2a , 4a and 5 form the mercury salts 6a–c ; compound 5 yields also a silver salt 7 . The 1H- and 19F-NMR. spectra are discussed and the agro-biological properties of the compounds investigated. 相似文献
47.
In Arbuzov-type reactions CFnCl3?nSCl reacts with ROPCl2 (R = CH3, C2H5) to give CFnCl3?nSP(O)Cl2 (n = 3,2,1,0). The corresponding reaction with CF3SeX (X = Cl, Br) produces CF3SeP(O)Cl2 in good yields only in the presence of catalysts such as SbCl5 or BCl3. Reactions between P4 and the sulfenylchlorides produce (CFnCl3?nS)xPCl3?n (n = 3,2,1 and x = 1,2). On heating CFn′ Cl3?n′ SP(O)Cl2 (n′ = 2,1,0) decompose to P(O)Cl3 and SCFn′ Cl2?n′. During this process fluorination of P(O)Cl3 to P(O)F3 by SCF2 is observed. A Cl/Br exchange between CFnCl3?nSP(O)Cl2 (n = 3,2) and PBr3 was proved 19F? and 31P-NMR-spectroscopically.Chemical and physical properties of the newly synthesized compounds will be discussed. 相似文献
48.
Lower Chalcogen Fluorides V. Unusual Chemical Equilibria F3S? SF ? 2 SF2 and CF3SF2? SCF3 ? 2 CF3SF SF2 and CF3SF form unusual chemical equilibria with their dimers F3SSF and CF3SF2 SCF3 involving two different bonds (SF and SS). The equilibrium between F3SSF and SF2 is disturbed by a decomposition reaction of these compounds yielding SF4 and SSF2 · Kp (298) = 2.5 · 10?3atm, ΔH°298 = 68.5 kJ/mol for the system F3SSF ? 2SF2 and Kp(298) = 1.3 × 103 atm, δH298 = 42.5 kJ/mol for the system CF3SF2SCF3 ? 2CF3SF have been determined as the equilibrium constants and the dissociation enthalpies. In both systems kinetic hindrance delays the achievement of the equilibrium. The rates for dissociation and decomposition are strongly surface dependent. Under favourable conditions the half-lives at 298 K for the dissociation of F3SSF and CF3SF2SCF3 are found to be ca. 8 h and ca. 2 h respectively, and for the decomposition of SF2 and CF3SF (p ~ 13 mbar) the values are ca. 10 h and 1 year respectively. 相似文献
49.
The pseudohalide CF3SO2NCO has been synthesized by means of a new reaction involving trifluoromethanesulphonamide and chlorosulphonylisocyanate. This method may be used for preparing other perfluorinated alkanesulphonyl-, arenesulphonyl- and alkanecarbonyl-amides. Reactions of CF3SO2NCO with alcohols, thiols, phenols and amines lead to the corresponding carbonic acid esters, thio-esters, phenyl esters and ureas. Reactions with carbonic acids, aldehydes and dimethylsulphoxide gave CO2 and the corresponding acid amides, azomethines and imino-dimethylsulphurane. Under pressure at 160°C, CF3SO2NCO reacts with phosphorus pentasulphide to give the previously unknown compound CF3SO2NCS; with phosphorus pentachloride under the same conditions, CF3SO2NCCl2 is formed. 相似文献
50.
Howard C. Haas Ruby L. Macdonald Alan N. Schuler 《Journal of polymer science. Part A, Polymer chemistry》1971,9(4):959-973
Polymethacrylylglycinamides (PMG), like polyacrylylglycinamides (PAG), form thermally reversible aqueous gels, but higher molecular weights and/or concentrations are required and the melting points of the gels are lower. The heats of crosslinking for aqueous PMG gels fall in the range of ?5 to ?10 kcal/mole of crosslinks, the same as for aqueous PAG gels, implying that the crosslinks are chemically similar. PMG and PAG are incompatible with each other but both are individually compatible with some types of gelatin. The solubilities of PMG and PAG are similar. Various reagents, however, affect PMG and PAG gels in quite different manners. Aqueous PMG solutions, just outside conditions required for gelation, are rheopectic. Intrinsic viscosities [η] of PMG in 2M NaCNS are about 2.5 times those in water. The Huggins' k′ value for PMG in 2M NaCNS has a value of 0.39–0.40, and both it and [η] are essentially temperature-independent over the range 25–45°C. In water at 25°C for PMG, k′ has an average value of about 1.4. With increasing temperature, for H2O, there is a considerable increase in [η] which is accompanied by a decrease in the value of k′. Osmotic molecular weight measurements on unfractionated PMG in H2O at 40°C yield π/c versus c plots having essentially zero slope, implying a value of close to zero for the second virial coefficient, a value of about 0.5 for the polymer–solvent interaction parameter, and a condition close to a θ condition. An approximate viscosity–M n relationship for polydisperse PMG is [η]2M NaCNS, 25deg;C = 1.7 × 10?8 M n1.5. The low value of K and high value of the exponent do not result from large differences in polydispersity but rather from a stiff, rodlike configuration in solution. This steric hindrance to rotation also manifests itself in the extreme brittleness of PMG films and in a ΔHp for homopolymerization of only ?6 kcal/-mole. The infrared spectra of MG monomer and PMG are recorded as well as the density and refractive index for PMG. PMG has a glass transition at 226°C by DTA and by TGA, thermal decomposition sets in at about 300°C. From copolymerization with acrylic acid, values of 1.66 and +0.06, respectively, were obtained for the resonance factor Q and the electrical factor e for MG monomer. 相似文献