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971.
The redox reaction between N-vinylcarbazole (NVC) and various oxidants including Ce(Ⅳ), Fe(Ⅲ)and benzoylperoxide in methanol proceeds via the initial formation of the NVC N-cation radical which in turn leads to the formation of the NVC cyclic dimer, trans-1,2-dicarbazylcyclobutane. Molecular oxygen and a few arylamines are able to accelerate the rate of the formation and increase the yield of the dimer. The mechanism of this process and the functions of oxygen and arylamines are presented as follows: The participation of molecular oxygen is to facilitate the dissociation of the resulting reduced metal ion and the NVC N-cation radical ion pair or charge transfer complex, thereby releasing the free NVC N-cation radical and increase the rate of the formation and yield of the dimer. The arylamine in this reaction between NVC and oxidants can be viewed as electron transfer agent between NVC and the oxidant. Because the amines are present in small amount relative to the oxidants and can be regenerated in pr 相似文献
972.
G.-M. Kim H. Qin X. Fang F. C. Sun P. T. Mather 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3299-3313
Polyhedral oligosilsesquioxane (POSS)-reinforced thermosets based on octaglycidyl epoxy polyhedral oligosilsesquioxane cured with 4,4′-diaminodiphenyl sulfone (DDS) were prepared and studied for their cure, thermomechanical, and microstructural characteristics. Particular attention was paid to nanometer-scale deformation processes responsible for toughening, as revealed by transmission electron microscopy (TEM) in conjunction with the thermal properties. A cure analysis investigated with calorimetry and rheometry showed a significant dependence of the cure mechanism and kinetics on the DDS content, but all hybrid thermosets reacted completely below 300 °C into rigid solids. A dynamic mechanical analysis of this hybrid resin system showed that increasing the DDS concentration used during cure increased the dynamic storage modulus in the glassy (temperature < glass-transition temperature) and rubbery (temperature > glass-transition temperature) states, simply through an increase in the crosslink density. The phase structures revealed by TEM with selective POSS staining were drastically affected by the DDS concentration and manifested as altered nanomechanical deformation structures. It was qualitatively found that the main toughening mechanism in the studied POSS-reinforced thermosets was void formation at the nanometer scale, possibly templated by limited POSS aggregation. As the crosslinking density increased with the DDS concentration, microshear yielding between voids prevailed, providing a balance of stiffness, strength, and toughness. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3299–3313, 2003 相似文献
973.
Zhong Xue Yang Yan Jun Wu Feng Zhu YaFei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):395-398
A novel one-dimensional helical nanocable structure has been synthesized through the reaction of carbon fiber with SiO vapor. The crystalline SiC core typically has diameters of 10–20 nm with a helical periodicity of 30–40 nm and is covered by a uniform layer of 10–20 nm thick amorphous SiO2. A growth mechanism is proposed on the basis of difference in the growth rate between crystalline SiC core and amorphous SiO2 shell. 相似文献
974.
975.
多胺型螯合树脂对重金属离子的吸附研究 总被引:11,自引:1,他引:10
研究了含有三乙烯四胺功能基的酚醛树脂(FQ—34)对Cu2 、Ni2 ,Zn2 、Co2 的静态吸附动力学、等温吸附等过程。结果表明,液膜扩散是吸附的主控步骤,可用G.E.Boyd膜扩散方程来描述;等温吸附属单分子层吸附,可用Langmuir等温方程描述。同时,还对吸附机理作了初步探讨。 相似文献
976.
A straightforward, high-yielding procedure has been developed for the manufacture of substituted vinylphenols from 2- and 4-hydroxybenzaldehydes utilising classical Knoevenagel condensation reaction conditions. 相似文献
977.
Shuzhen Fan Qingpu Wang Shutao Li Shuanghong Ding Fufang Su 《Optics Communications》2006,266(2):620-626
A method of more precise determination of the focal length of equivalent thermal lens (TL) is presented in this paper. The method is based on the diffraction theory of aberrations. By numerically calculating the optical path difference (OPD) distribution and the Strehl ratio, the focal lengths for “top-hat” pumping and Gaussian pumping are obtained and the equations for the focal lengths are presented by curve fitting. Also the equations for average pump radii are presented. The experiment on a fiber-coupled LD pumped Nd:YAG laser is carried out. The experimental results verify the validity of the method. 相似文献
978.
Valérie Sciannamea Jean‐Marie Catala Robert Jérôme Christophe Detrembleur 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1219-1235
Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10?10 mol L?1 at 110 °C. At this temperature, the dissociation rate constant (kd) is 3.7 × 10?3 s?1, the recombination rate constant (kc) is 4.3 × 106 L mol?1 s?1, whereas the activation energy (Ea,diss.), for the dissociation of the alkoxyamine at the chain‐end is ~125 kJ mol?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007 相似文献
979.
We studied the influence of CO poisoning of the anode in the polymer electrolyte membrane fuel cell (PEMFC) using electrochemical impedance spectroscopy (EIS). The anode impedance was found by first feeding neat hydrogen gas and next hydrogen with CO into one of the electrodes, keeping neat hydrogen gas on the other electrode as a reference. The electrodes were E-TEK Elat gas-diffusion electrodes with 0.5 mg Pt/cm2, and the membrane was Nafion® 117. The CO concentration was 103 ppm, and the total pressures were 1, 2.5 and 4 bar. Operating temperatures were kept constant, 30.0 °C or 50.0 ± 0.1 °C. Bias voltages of 0 and 0.05 V were used. Three steps were revealed in the reaction mechanism, the slow adsorption/diffusion step, the charge transfer step and the proton hydration step, confirming earlier results. Carbon monoxide affects the charge transfer step by blocking active sites and by affecting the surface polarisation. We further conclude that CO adsorbs to the porous carbon matrix, and reduces significantly the rate of surface diffusion of hydrogen to the surface. 相似文献
980.