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81.
Three natural basaltic samples were collected and used as efficient catalysts for the liquid‐phase synthesis of n‐butyl acetate. The samples were characterized by X‐ray fluorescence analysis (XRF), X‐ray diffraction (XRD), thermogravimetry (TG), differential thermal analysis (DTA), Fourier transform infrared (FT‐IR), scanning electron microscopy (SEM), and N2 sorption. The acidity of the samples was determined using isopropanol dehydration, and the strength of the acid sites was measured using chemisorption of basic probes. The catalytic activity of the samples towards the esterification of acetic acid with n‐butanol was extensively examined. The influence of different parameters, such as the reaction refluxing time, molar ratio, catalyst loading, reusability, and calcination temperature, on the esterification reaction was studied in detail. The results revealed that all samples had high catalytic activity with a selectivity of 100% to n‐butyl acetate formation. In addition, the sample obtained from the top hill of Volcano had the highest activity with a 80% yield of n‐butyl acetate. Moreover, the significant catalytic performances were well correlated with the acidity of the samples and to the reaction rate constants. 相似文献
82.
83.
Magdi M. Naoum Nadia H. Metwally Manal M. Abd eltawab Hoda A. Ahmed 《Liquid crystals》2013,40(10):1351-1369
Eight homologous series of 2- (or 3-) substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (Ina–h) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH3, H, F, Br and CN. Compounds prepared were characterised by infrared and 1H-NMR spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and identified by polarised light microscopy. The results were discussed in terms of polarity and steric effects. The stability of the mesophase was correlated once with the dipolar anisotropy of the whole molecule and another with the dipolar anisotropy of the substituent, X. A comparative study was made between the investigated compounds and their previously prepared linear 4-substituted isomers, namely 4-substituted phenyl 4?-(4?-alkoxy phenylazo) benzoates (Ini–k). 相似文献
84.
85.
86.
The adsorption of Cu(II) and Cr(III) ions by pure clay mineral, vermiculite, was examined in aqueous solution with respect
to the adsorbent dose, initial metal ion concentration, pH, and contact time. The studies showed that vermiculite can be used
as an adsorbent material for the moderate removal of Cr(III) and Cu(II) from aqueous solutions. Lagergren first-order, pseudo-second-order,
and intraparticle diffusion models were used to describe the kinetic data. The kinetics of adsorption indicates that the process
fitted well the intraparticle diffusion model. 相似文献
87.
E.A MahmoudM.M El-Samanoudy A.S Abd Rabo 《Journal of Physics and Chemistry of Solids》2002,63(11):2003-2010
Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated GexFexSe100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap Eopt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(EF), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature Tg cohesive energy C.E and number of constraints NCo with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers. 相似文献
88.
Mohamed M. M. Abd El-Wahab Abd El-Aziz A. Said Shar S. Al-Shihry 《Monatshefte für Chemie / Chemical Monthly》2004,135(4):357-370
Summary. A series of AlPO4-V2O5 (APV) systems with various vanadia amounts 1–30mol% were prepared by the impregnation method and calcinated at 400 and 600°C for 4h. The catalysts were characterized by TG/DTG, DSC, IR spectroscopy, XRD, N2 adsorption, and electrical conductivity measurements. The surface acidity and basicity of the catalysts were studied by the dehydration-dehydrogenation of isopropyl alcohol and the adsorption of pyridine. The catalytic gas phase esterification of acetic acid with ethyl alcohol was carried out at 210°C in a flow system at 1atm using air as a carrier gas. The results showed that the catalysts calcinated at 400°C were active and selective towards the formation of ethyl acetate whereas the calcination of samples at 600°C led to a drastic reduction in both activity and selectivity. Good correlations were obtained between catalytic activities towards ester formation and acidity of the prepared catalysts. 相似文献
89.
The longitudinal ultrasonic attenuation measurements have been made using pulse echo method at fundamental frequencies of 2, 4, 6 and 8 MHz in 20WO3–(80−x) TeO2–xPbO ternary tellurite glasses (x=10, 12.5, 15, 17.5 and 20 mol%) in the temperature range 160–280 K. The results showed the presence of a broad peak which shifts to higher temperature with increasing frequency. The ultrasonic attenuation peaks suggest that the experimental behavior is controlled by thermally activated structural relaxations. The internal friction, acoustic activation energy, deformation potential, relaxation strength, number of loss centers and density of state have been calculated both as a function of temperature and PbO content. The acoustic activation energy was found to decrease from 0.156 to 0.135 eV with the increase of PbO content. The results showed that both the number of loss centers and their activation energy decrease with the atomic ring size. An increase in the density of state is observed with addition of PbO content at the same frequency in the whole range of temperature which is associated with structural units formed when PbO is added. 相似文献
90.
A linear and nonlinear study has been made of cylindrical interface, carrying a uniform surface charge in the presence of a finite rate of charge relaxation, is investigated by using multiple scales method. The linear stability flow is analyzed by deriving a dispersion relation for the growth waves, and solving it analytically and numerically to find marginal stability curves. We investigate the electric charge relaxation effects on the stability of the flow by considering various limiting cases. We also examine the effects of finite charge relaxation times in axisymmetric and nonaxisymmetric modes. In the nonlinear approach, it is shown that the evolution of the amplitude is governed by a Ginzburg–Landau equation. There is also obtained a nonlinear modified Schrödinger equation describing the evolution of wave packets for small charge relaxation time. Further, the classic Schrödinger equation is obtained when the influence of relaxation time charge is neglected. On the other hand, the complex amplitude of quasi-monochromatic standing waves near the cutoff wavenumber is governed by a similarly type of nonlinear Schrödinger equation in which the roles of time and space are interchanged. This equation makes it possible to estimate the nonlinear effect on the cutoff wavenumber. The nonlinear theory, when used to investigate the stability of charged liquid jet, appears accurately to predict a new unstable regions. The effects of the surface charge and charge relaxation on the stability are identified. The various stability criteria are discussed both analytically and numerically and the stability diagrams are obtained. 相似文献