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51.
Under the applied high reaction temperatures (900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (O) apart from O atoms dissolved in the bulk (O). Methanol oxidation to formaldehyde proceeds through this O species as demonstrated by application of a variety of spectroscopic techniques. 相似文献
52.
J.-M. Giraudon A. Elhachimi F. Wyrwalski S. Siffert A. Aboukaïs J.-F. Lamonier G. Leclercq 《Applied catalysis. B, Environmental》2007,75(3-4):157-166
Calcined and reduced catalysts Pd/LaBO3 (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO3 > Pd/LaMnO3+δ > Pd/LaCoO3 > Pd/LaNiO3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO3 (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO3 and either 200 or 250 °C for LaCoO3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B3+ (B = Mn) or B2+ even to B0 (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd2+/Pd4+ and Pd0/Pd2+/Pd4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity. 相似文献
53.
54.
Yan Song Wenming Qiao Seong‐Ho Yoon Isao Mochida Quangui Guo Lang Liu 《应用聚合物科学杂志》2007,106(4):2151-2157
Adsorption of low concentration formaldehyde on pitch‐based, rayon‐based, and PAN‐based activated carbon fibers (ACFs) and an unactivated PAN‐based carbon fiber (PAN‐CF) was investigated by a dynamic method. The pore structure and surface chemistry of these samples were characterized by liquid nitrogen adsorption, elemental analysis, and X‐ray photoelectron spectroscopy. Results revealed that the pore structure, especially surface chemical composition, greatly influence the formaldehyde adsorption. PAN‐based ACFs showed the highest formaldehyde adsorption capacity because there are more abundant nitrogen‐containing groups, especially pyrrolic, pyridonic, pyridinic, and quaternary on the surface. The breakthrough time and formaldehyde adsorption capacity of one kind of PAN‐ACF were 361 min and 0.478 mmol/g, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
55.
Due to their superior thermal and chemical stability, polyimides are often used as adhesives in harsh environments. This study examines the effect on bond strength of thioether sulfur in the polyimide backbone. Bonds were made using steel that was believed to catalyze the oxidation of sulfur. In addition, non-sulfur containing polyimides with similar Tg were also studied for comparison. The polymer/metal interface was studied using both the T-peel and wedge tests. No apparent effect was observed in the T-peel test with steel where the T-peel strengths of non-sulfur and sulfur containing polyimides were similar. In the wedge test, however, the sulfur-containing BDSDA/ODA bonded to steel had the smallest initial crack length of 34 mm. However, the BTDA/APB bonds tested in a dry environment had the smallest crack growth. The sulfur-containing BTDA/ASD performed best of the bonds tested in a wet environment. Metal-catalyzed oxidation of sulfur was observed to take place in the steel case, but not to an extent to have a noticeable effect on peel strength. 相似文献
56.
The methanation of CO2 has been investigated over a special Ru/TiO2 catalyst suggested by Thampi, Kiwi and Graetzel [4]. This paper deals with the analysis of the material and the investigation of the reported photoenhancement of the activity. The catalyst is characterised by in situ UV-VIS spectroscopy and by XPS. Conversion experiments at atmospheric pressure were carried out with and without UV light irradiation. The irradiation increases the conversion significantly. From various experiments it can be shown, however, that this effect is due to a thermal effect and does not involve an intrinsic photochemical step. Localised Ti3+ states sensitise the support to convert visible light into heat resulting in the observed increase in conversion. 相似文献
57.
聚合物—铝酸—钙界面组成与结构的XPS研究 总被引:3,自引:0,他引:3
从复合材料界面的角度,采用XPS综合方法研究了水泥基聚合物复合材料的高强特别是高抗弯强度的微观机理。结果表明,在材料界面上存在明显的电子结合能化学位移效应,并被证实为聚合物与无机水泥的化学键合所致。界面层的深度分析发现,掺加聚合物的材料界面具有良好的化学和物理结构。作者认为这种材料的高强机理主要是由于两种基质界面间的有效化学键合作用,形成了良好的界面结构,因此,可认为这种作用大于有的学者所解释的聚合物的单一物理作用。 相似文献
58.
The catalysts of Co/Zr-SiO2 were prepared by precipitation and the promoter of Pt was supported by impregnation. The reducibility of the cobalt oxide and the other physicochemical properties of the catalysts were characterized by TPR, TPD, BET and XPS. With the evaluation of the reduction temperature, the reduction degree increased but the surface area of the catalysts and the adsorption property for reactant CO distinctly decreased; The addition of Pt resulted in the improvement of the reducibility by decreasing the reduction temperature of cobalt oxide species. The FT-synthesis has been performed in a quartz fixed-bed reactor, and the experimental results showed that the best activity for promoted catalyst has been found at the reduction temperature of 400℃, in spite of its uncompleted reduction. 相似文献
59.
Electrochemical Ni-Mo alloying of the surface of a nickel substrate was investigated using alternating pulsed electrolysis in an aqueous solution containing only molybdate ions (MoO42−) as a metal ion component. In this electrochemical process, the nickel substrate was slightly dissolved during the anodic pulses, providing nickel ions into the solution in the vicinity of the substrate, while Ni and Mo were both electrodeposited on the substrate surface during the subsequent cathodic pulses. Through the optimization of anodic and cathodic conditions independently based on a set of direct-current electrolysis data, amorphous Ni-Mo alloy layers were found to be formed at the surface of the nickel substrate by the alternating pulsed electrolysis using the MoO42− solution of pH 3.0-5.0. The conditions for Ni-Mo alloy formation were discussed in terms of the dissolving regime of ionic species in the electrolytes determined by an equilibrium calculation. 相似文献
60.
LiNi0.5Mn1.5O4 spinels coated with various amounts of fumed silica have been synthesized and investigated as cathode materials for high-voltage lithium-ion batteries at the elevated temperature (55 °C). The morphology and structure of the coated LiNi0.5Mn1.5O4 samples were characterized by XRD, TEM and EDX. It was found that the surfaces of the coated LiNi0.5Mn1.5O4 samples are covered with a porous, amorphous, nanostructured SiO2 layer. The results of electrochemical experiments showed that the SiO2-coated LiNi0.5Mn1.5O4 samples display obviously improved capacity retention rate, and the improvement effect enhances with the increase of SiO2 content. The XPS results revealed that the surfaces of the SiO2-coated LiNi0.5Mn1.5O4 cathode materials have relatively low content of LiF, and this is mainly responsible for their improved electrochemical cycling stability. 相似文献