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171.
The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m–3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m–3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity. 相似文献
172.
The crystal structure of urea-polyethylene complex in the hexagonal form, obtained by one of our preparation methods, is analysed by X-ray power diffractometry. In this analysis, the fixed molecular parameters of urea are used, and three models with respect to rotational disorder of the guest polyethylene molecule are assumed. It is shown that the host lattice structure constructed by urea molecules is essentially the same as that of urea-n-paraffin complex. Effects of the disorder structure of the guest on X-ray scattering of the complex are presented. However, there is a difficulty in identifying the disorder structure by X-ray analysis. With the aid of a potential energy calculation between the hexagonal urea tunnel and the guest molecule, a rotational disorder model is preferred. 相似文献
173.
David Merrick 《Fuel》1983,62(5):547-552
Mathematical models are proposed to predict the true density of coal, semi-coke and coke and the porosity of a coke oven charge during carbonization. These models are combined in a further model which predicts the hitherto unexplained ‘twin-peaked’ contraction curve observed for semi-coke. It is found that the first contraction peak results from the relatively high rate of mass loss occurring towards the end of the primary devolatilization stage. The second peak occurs because of the increase in true density arising from the elimination of hydrogen from the semi-coke. 相似文献
174.
2,6-萘二甲酸二甲酯与一些二甲基萘所形成的激基复合物 总被引:1,自引:0,他引:1
2,6-萘二甲酸二甲酯与一些二甲基萘可以形成激基复合物。本文通过稳态和动态荧光光谱研究了这类激基复合物的形成与分子结构的关系。结果表明,尽管这些二甲基萘的电离能基本相同,但因取代基位置不同使分子中电荷分布不同,从而影响了激基复合物的形成能力。 相似文献
175.
An isothermal model for hydrodemetallation (HDM) of crude oils in catalytic fixed-bed reactors is proposed. This model involves a consecutive reaction mechanism, which is capable of accounting for particle deposit profiles with interior maxima. Consistent with the fact that HDM catalysts are conglomerates formed by precipitation, the porous catalyst itself is modeled as randomly overlapping spheres of equal size. The metal is deposited as growing metal sulfide crystallites on the inner surface of the catalyst. These crystallites originate from a certain number of randomly scattered nuclei and increase in size as the deposition proceeds. The random sphere model for the catalyst and the deposit provides the changes in the catalyst pore structure—local porosity and surface area.
The mass transport within the domain of the particle is due to restricted liquid diffusion, since the diameter of the metal bearing compound (porphyrin) and the intermediate are comparable to the pore size. The diffusion restrictions taken into account are the enhanced drag imposed on a molecule by adjacent pore walls and steric partitioning.
Since the deposition process is much slower than diffusion and reaction, the pseudo-steady-state assumption can be justified. The equations of conservation for mass are solved by orthogonal collocation on finite elements. Based on this solution technique a computer simulation program of HDM is designed that allows two modes of operation: constant temperature and constant conversion. The simulation program “SIMULA” is highly flexible with regard to reaction kinetics, catalyst structure, reactor design, and operating conditions. In comparison to a base case with uniform activity, the effect of intraparticle (radial) and bed (axial) activity profiles on the conversion rate is discussed. For the case investigated, a radial distribution of activity higher at the center of the particle than at the edge can increase catalyst life by 25%, but axial distribution was less successful. 相似文献
The mass transport within the domain of the particle is due to restricted liquid diffusion, since the diameter of the metal bearing compound (porphyrin) and the intermediate are comparable to the pore size. The diffusion restrictions taken into account are the enhanced drag imposed on a molecule by adjacent pore walls and steric partitioning.
Since the deposition process is much slower than diffusion and reaction, the pseudo-steady-state assumption can be justified. The equations of conservation for mass are solved by orthogonal collocation on finite elements. Based on this solution technique a computer simulation program of HDM is designed that allows two modes of operation: constant temperature and constant conversion. The simulation program “SIMULA” is highly flexible with regard to reaction kinetics, catalyst structure, reactor design, and operating conditions. In comparison to a base case with uniform activity, the effect of intraparticle (radial) and bed (axial) activity profiles on the conversion rate is discussed. For the case investigated, a radial distribution of activity higher at the center of the particle than at the edge can increase catalyst life by 25%, but axial distribution was less successful. 相似文献
176.
177.
从四边固定正方形板受均布载荷的经典问题入手,结合不同类型单元的特点,探讨应用三维实体单元分析薄壁箱型结构时应注意的几个问题,纠正三维实体单元分析和应用的误区,为提高结构分析计算结果精度提供参考. 相似文献
178.
Isao Mochida Yozo Korai Hiroshi Fujitsu Kenjiro Takeshita Yoshinobu Komatsubara Kei-Ichiro Koba Harry Marsh 《Fuel》1984,63(1):136-139
Cokes were prepared from nine coals of different rank and characterized by surface area measurement, reactivity to carbon dioxide at 1473K and Raman-laser spectroscopy. Rates of gasification of cokes on a unit surlface area basis (K1 = g m?2 min?1) decreased with increasing rank of parent coal based on maximum oil reflectances. However rates of gasification could not be related to coke structure as measured by Raman-laser spectroscopy. 相似文献
179.
180.
Phase transitions of canola oil sediment 总被引:3,自引:0,他引:3
H. Liu C. G. Biliaderis R. Przybylski N. A. M. Eskin 《Journal of the American Oil Chemists' Society》1993,70(5):441-448
Canola sediment was obtained from an industrial filter cake by solvent extraction. When heated in the differential scanning
calorimeter (DSC) (5–100°C), the sediment exhibited a single narrow melting peak at around 74.8°C. No solid-state polymorphic
transformation of the material could be detected over this temperature range. The X-ray powder diffraction pattern of canola
sediment resembled waxes from other sources with an orthorhombic unit cell. The phase transition behavior of canola sediment
in oil was studied by both DSC and polarizing microscopy. With increasing ratio of oil/sediment, a reduction in both melting
temperature and transition enthalpy was observed. The shape of the supercooling curve resembled that of the melting curve.
The induction time was determined by spectrophotometry and was used to calculate the interfacial free energyσ between sediment and oil; σ=4.71 erg/cm2. The effect of temperature and sediment concentration on the clouding time of canola oil was studied; the clouding time was
the shortest at 5°C. 相似文献