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951.
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953.
So-called cathodic delamination is one of the major modes of failure for organic coatings immersed in electrolyte solutions (e.g. seawater). Cathodic delamination occurs as a result of the electrochemical reactions, which takes place on a corroding steel surface. This means that reactants must continuously be transported from the bulk solution to the cathodic areas. The transport of sodium ions from a defect in the coating to the cathodic areas is generally considered the rate-determining step for cathodic delamination because the transport of oxygen and water through the coating is sufficient for the corrosion processes. In this work, a novel practical method, which allows direct estimation of the apparent diffusion coefficient of sodium ions in the ultrathin aqueous layer at the coating–steel interface, is described. The apparent diffusion coefficients estimated are of similar magnitude as previously reported values and show an acceptable repeatability. The method was used to obtain the apparent diffusion coefficients of sodium ions in the coating–steel interface for three commercial inert-pigmented epoxy coatings. The delamination rates predicted using the apparent interfacial diffusion coefficients and Fick's second law, under the assumption of a transport controlled mechanism, show qualitative agreement with the observed delamination rates in 0.5 M sodium chloride. This confirms that the rate-determining step of cathodic delamination is the transport of sodium ions along the coating–steel interface. 相似文献
954.
One of the most important factors in corrosion prevention by protective coatings is the coating adhesion loss under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In order to improve the adhesion of organic coating the metal substrate is often pretreated in some way. In this work, the adhesion of polyester coatings on differently pretreated aluminium surface (by anodizing, with and without sealing, by phosphating and by silane film deposition) was examined. The dry and wet adhesion of polyester coatings were measured by a direct pull-off standardized procedure, as well as indirectly by NMP test. It was shown that under dry test conditions all polyester coatings showed very good adhesion, but that aluminium surface pretreated by silane film showed superior adhesion. The overall increase of wet adhesion for polyester coating on aluminium pretreated by silane film was maintained throughout the whole investigated time period. The different trends in the change of adhesion of polyester coatings were observed for different aluminium pretreatments during exposure to the corrosive agent (3% NaCl solution). The highest adhesion reduction was obtained for polyester coating on aluminium pretreated with phosphate coating. The corrosion stability of polyester coated aluminium was investigated by electrochemical impedance spectroscopy in 3% NaCl solution. The results confirmed good protective properties of polyester coating on aluminium pretreated with silane film, i.e. greater values of pore resistance and smaller values of coating capacitance were obtained in respect to other protective systems, whereas charge-transfer resistance and double-layer capacitance were not measurable during 2 months of exposure to a corrosive agent. 相似文献
955.
Cathodic delamination is one of the major modes of failure for organic coatings immersed in seawater and refers to the weakening or loss of adhesion between the coating and the substrate. The diminished adhesion is the result of electrochemical reactions occurring at the coating–steel interface, where solid iron is oxidized to ferrous ions and oxygen is reduced to hydroxyl ions. In this work, the effects of various parameters on cathodic delamination have been investigated. The parameters are: permeability of the coating, concentration of dissolved oxygen and cations, polarization potential, type of binder, degree of curing, and pigment loading, shape and type. The results show that cathodic delamination increases with increasing concentration of cations up to the point where the concentration of dissolved oxygen becomes insufficient to maintain the corrosion rate. The rate of cathodic delamination is inversely proportional to the magnitude of polarization potential when ions can penetrate the coating, while cathodic polarization does not affect cathodic delamination when the ionic transport is restricted to the coating–steel interface. Increasing the pigment loading or partial replacement of spherical pigments with flake-shaped micaceous iron oxide or aluminium pigments reduces the rate of cathodic delamination. Finally, binders with an increasing amount of secondary hydroxyl groups in the polymer backbone reduce the rate of cathodic delamination while increasing the initial molar ratio of amide to epoxide increases cathodic delamination. 相似文献
956.
Preparation and characterization of flame retardant solvent base and emulsion paints 总被引:1,自引:0,他引:1
In this research solvent base alkyd and emulsion paint formula were made flame retardant (FR) by incorporation of hexachlorodiphosh (V) azane of types (I–III). Elemental analysis was used to characterize the structure of these compounds. These additives are physically incorporated into the paint formula through grinding in a pebble mill until all particulates have a size below 38 μm. Experimental coatings were manufactured on a laboratory scale, applied by brush on wood and steel panels. Results of an oxygen index value indicated that coating with these compounds containing chlorine, nitrogen and phosphorus exhibit very good flame retardant effect when mixed with solvent base alkyd and emulsion paint. The physical, mechanical and corrosion resistance were studied to evaluate the additives drawbacks. The additives did not affect the flexibility and pinholes of paint formula. The gloss and the impact strength were decreased by the additives, the hardness and adhesion resistance increased by the additives. However, corrosion resistance was not significantly changed by these additives. 相似文献
957.
探讨自润滑复合镀层的摩擦学性能及其增强相的摩擦磨损强化机理;分析经具有自润滑性能的石墨、二硫化钼、聚四氟乙烯及碳纳米管等改性的复合镀层的摩擦学行为;并探讨该类复合镀层的摩擦磨损强化机制。 相似文献
958.
文章简单介绍了PU漆黄变的机理,并通过人工老化实验,对比分析不同因素对PU白面漆耐黄性能的影响。 相似文献
959.
文章介绍了一种新型胶体复合流变剂的制备以及在重防腐涂料等高固含涂料体系中的应用。结果表明,该防沉剂能够有效的提高重防腐涂料的储存稳定性,提高防沉抗流挂效果,与普通膨润土流变剂相比,该防沉剂能够降低对涂料光泽度的影响。 相似文献
960.