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111.
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The separation performance of two different commercially available tubular inorganic membranes was studied for solvent dehydration. The separation layers consisted of A-type zeolite and microporous silica. The membrane characteristics were determined as function of operating conditions such as feed composition, temperature, and permeate pressure in pervaporation and vapor permeation. Among different membranes of the same batch, flux and selectivity were reproducible within 10%. The partial flux of water as the preferentially permeating component increases linearly with the water vapor pressure difference between feed and permeate and depends only marginally (viscosity influence) upon the properties of the organic component. The flux of the organic (retained) component is low and can best be described by assuming a substance and membrane specific permeance (flux over partial pressure difference) that is independent of composition. At very low water concentration in the feed one would expect a strong increase in permeability of the retained component through non-zeolite pores and larger silica pores as predicted by pure component measurements. However, this effect was not observed in mixtures within the concentration range studied here. A temperature rise improves flux rates exponentially while selectivity remains high. Thus, higher module cost in comparison to polymeric membranes can be compensated by reduced membrane area if a higher operating temperature can be chosen. Flux and selectivity decline as a function of permeate pressure with decreasing driving force. In vapor permeation with inorganic membranes superheating of the vaporous feed improves their performance while for polymeric materials a steep flux decline is observed. High flux and selectivity are obtained in the separation of water from alcohols. The normalized flux values of the A-type zeolite membrane are roughly 10 kg/m2 h bar with a mixture selectivity of 2000 for methanol, 4000 for ethanol and 8000 for n-butanol. The average permeance of the amorphous silica membrane lies above 12 kg/m2 h bar with mixture selectivity of 50 for methanol, 500 for ethanol and 2000 for n-butanol. The separation mechanism is mainly based on adsorption and diffusion enhanced by shape selectivity and size exclusion in some cases. The transport characteristics could be described with a simple transport model based on normalized permeate fluxes. With regard to the operation stability of the membranes, no deterioration of the performance was observed for the A-type zeolite in solvent dehydration or in separation of water from reaction mixtures. The silica membrane showed an initial conditioning effect involving a rearrangement of Si-OH groups with an increase in selectivity and decrease in flux of about 30%. After a few hours the performance stabilized and remained constant during further operation. 相似文献
114.
通过对硅溶胶泥浆的流变性实验确定了硅溶胶泥浆的流变模型,验证并分析了加入少量经过低温氧化过的甘油三酸脂(GTO)不改变硅溶胶泥浆的流变模型,但能有效地改善其流变性能。因此,GTO可作为硅溶胶结合浇注料的高效减水剂。 相似文献
115.
综述了近年来硅胶载体经甲基铝氧烷(MAO)化学处理后负载茂金属催化剂的一些研究进展,指出硅胶的化学活化是茂金属催化剂负载化的关键,单组分化学处理剂处理硅胶载体不能完全满足人们对负载型茂金属催化剂烯烃聚合的需求,采用含MAO的多组分化学处理剂化学活化硅胶后负载催化剂是该领域发展的趋势。 相似文献
116.
磷钨酸/硅胶催化剂催化合成环己酮1,2-丙二醇缩酮 总被引:2,自引:0,他引:2
以溶胶-凝胶法制备的磷钨酸/硅胶为催化剂、通过环己酮和1,2-丙二醇反应合成了环己酮1,2-丙二醇缩酮,探讨磷钨酸/硅胶对缩酮反应的催化活性,较系统地研究了酮醇量比、催化剂用量、反应时间、带水剂用量对产品收率的影响。实验表明:磷钨酸/硅胶是合成环己酮1-2-丙二醇缩酮的良好催化剂,在门(酮):门(醇)=1:1.5、催化剂用量为反应物料总质量的0.5%、环己烷为带水剂、反应时间45min的优化条件下,环己酮1,2-丙二醇缩酮的收率可达79.8%. 相似文献
117.
Wu -Hsun Cheng 《Catalysis Letters》1996,38(1-2):135-141
Selectivities in methanol oxidation over silica supported molybdenum oxide catalysts were investigated in relation with the phase distribution. The supported catalysts were prepared by impregnation with ammonium heptamolybdate. In addition to crystalline MoO3, Mo containing cluster species of 1–2 nm size were observed by STEM even from a used catalyst with 13% catalyst loading. The percentage of Mo present as crystalline MoO3 increases with the catalyst loading. An ESCA study indicates that part of surface Mo in the supported catalysts is reduced to Mo5+. The dimethyl ether selectivity increases with the catalyst loading and its formation occurs over the crystalline MoO3 phase. The Selectivities to CO and methyl formate are greatly enhanced because of the presence of support, and are relatively independent of the catalyst loading and phase distribution. The dependence and independence of the Selectivities of different byproducts on the loading make the silica supported catalysts with high catalyst loadings less selective for the partial oxidation of methanol to formaldehyde. 相似文献
118.
Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene 总被引:1,自引:0,他引:1
Megumu Inaba Yoshiaki Kintaichi Masaaki Haneda Hideaki Hamada 《Catalysis Letters》1996,39(3-4):269-274
Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO2 prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co2+ ions on silica are responsible for the catalytic activity. 相似文献
119.
Colloidal silica particles are prepared via a sol gel technique carried out in an inverse microemulsion of water in a toluene solution of tetraethoxysilane (TEOS), stabilized by either an anionic surfactant AOT or isopropanol. Functionalized material was obtained using a functional coupling agent (RO)3Si(CH2)3
X, X being a functional group such as methacryloyl, thiol, vinyl, amino group, or a chlorine atom. Functionalization can be carried out either directly via the direct copolycondensation of TEOS and the coupling agent, or in a two-step process involving a core-shell polycondensation of the coupling agent onto preformed silica particles. Kinetic studies of the copolycondensation are carried out using either29Si NMR analysis or liquid chromatography. They show that the consumption of TEOS is more rapid than that of the coupling agent. The materials are characterized both chemically (elemental analysis, FTIR,13C and29Si NMR CPMAS analysis), and by their particle size. The silica functionalized with a polymerizable methacryloyl group is encapsulated by a polymer layer in an inverse emulsion polymerization of acrylic acid. After inversion of the emulsion in water, the resulting material is covered with a layer of hydrophobic polymer in a conventional emulsion polymerization. 相似文献
120.
Jacques Jupille Anne-Marie Flank Pierre Lagarde 《Journal of the American Ceramic Society》2002,85(5):1041-1046
The local structure centered on sodium after diffusion in silica (Na-SiO2 samples) has been determined by means of extended X-ray absorption fine structure (EXAFS) studies. The Na-SiO2 samples are of particular interest because (i) their sodium content can be varied over a wide range of concentration and (ii) their local structure is representative of that of soda–silica glass. EXAFS analyses reveal the existence of a well-defined local structure involving oxygen, sodium, and silicon neighbors. The Na-O, Na-Na, and Na-Si bonds lengths, which amount to 0.23, 0.30, and 0.38 nm, respectively, do not depend on sodium concentration. This environment closely resembles that found in soda–silica glass. Moreover, it is compatible with the "target site" and "the site memory effect" suggested by recent theories of the ionic conductivity in oxide glasses. 相似文献