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41.
卡尔曼滤波分光光度法同时测定钛锡钼钨 总被引:5,自引:0,他引:5
以两性表面活性剂溴化十六烷基二甲基氨基乙酸作为新增效试剂,研究了钛、锡、钼、钨邻氯苯基荧光酮显色体系的光度性质,并用卡尔曼滤波分光光度法进行同时测定。合成试样中钛、锡、钼、钨的回收率范围及相对标准偏差分别为96.2%~106.3%、96.7%~104.5%、92.2%~107%、97.7%~105.6%和3.76%、3.24%、5.09%、2.81%;合金钢样中微量钛、锡、钼、钨测定的相对误差为5.0%~11.8%。 相似文献
42.
43.
P. Da Costa C. Potvin J.-M. Manoli M. Breysse G. Djega-Mariadassou 《Catalysis Letters》2003,86(1-3):133-138
Hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene on alumina-supported Mo2C has been studied. These catalysts are stable and active under deep HDS conditions (0-250 wt ppm S). However, although they are well known to have hydrogenation properties, they lead preferentially to a non-hydrogenated product of the HDS reaction: dimethylbiphenyl. For the same reaction, supported platinum and sulfided molybdenum oxide lead to the hydrogenated products dimethyldicyclohexyl and methylcyclohexyltoluene, respectively. The ranking of HDS activity is as follows: MoS2/Al2O3 < Mo2C/Al2O3 < Pt/SiO2. 相似文献
44.
Michael Kmetz Steven L. Suib Francis S. Galasso 《Journal of the American Ceramic Society》1989,72(8):1523-1524
The strength and toughness of fibrous composites depend on the interface properties which control the bonding between the fibers and matrices. One method of controlling the interface involves coating the fiber with an appropriate material. In a previous study, it was found that there is a definite advantage in using low coating temperatures to prevent fibers from degrading. We therefore were interested in a report that Mo2 C could be deposited from Mo(CO)6 at temperatures as low as 300° to 475°C. Our studies indicated that the material was not Mo2 C, but an oxycarbide, which, with an analogous tungsten oxycarbide coating, was applied to SiC yarns. Both oxycarbides could be converted to the metals by heat-treating in N2 . 相似文献
45.
A set of Co promoted 10% Mo/Al2O3 samples have been characterized by means of Raman spectroscopy under ambient as well as in situ dehydrated conditions. Under ambient conditions, the degree of the polymerization of surface molybdenum oxide species decreases with increasing Co loading. Under dehydrated conditions, the polymeric molybdenum oxide species is absent with the addition of only 0.2% Co. At low Co loadings (2%), before the formation of CoMoO4 compound, the spectral features are very similar under ambient conditions. Dehydration causes the upward shift of the Mo=O symmetric stretching mode. A broad band around 920–930 cm–1 was thus observed. This band has been suggested to be associated with the Co-Mo interaction species. In contrast to crystalline CoMoO4, this species shows a reversibility on H2 reduction-O2 reoxidation treatments. From the results obtained, it is proposed that cobalt oxide interacts with the most polymerized molybdenum oxide species to form Co-Mo interaction species and/or crystalline CoMoO4; therefore, the amount of the surface molybdenum oxide species decreases with a change in the molecular structure as a function of the Co concentration. 相似文献
46.
Gang Wang Wan Jiang Guangzhao Bai Libin Wu 《Journal of the American Ceramic Society》2003,86(4):731-34
A type of aluminosilicate that has a good wetting property for molybdenum disilicide (MoSi2 ) was added to a MoSi2 matrix to study the effects on the microstructure and low-temperature oxidation. It was found that the composites had not only good low-temperature oxidation resistance but also high thermal shock resistance when the added oxides formed a network microstructure in the matrix. There was no appreciable oxidation gain for MoSi2 /oxide composites with a network microstructure at 773 K for 2500 h. The results indicate that microstructure design is a simple and effective solution to preventing the low-temperature oxidation of MoSi2 . 相似文献
47.
T.M. Egelkraut D.E. Kissel M.L. Cabrera W. Adkins 《Nutrient Cycling in Agroecosystems》2003,66(1):1-12
The N mineralized from soil organic matter provides an important portion of N available for crop production. The objective of this study was to determine the amount of spatial variability in N mineralization potential in a field and to evaluate three different methods that might be used to estimate this variability. The three methods tested included predicting the N mineralized from surface soil properties as well as from a biological and a chemical procedure. Three soils varying in N mineralization potential were selected for the study from a field in the Georgia Coastal Plain. The N mineralized from these soils was determined by an N balance of unfertilized and cropped plots. The amount of N mineralized could not be reliably predicted from surface soil organic C, although surface soil clay concentration was positively correlated with the N mineralized. The N mineralized that was predicted using mineralization parameters determined by aerobic incubation, adjusted daily for soil water content and temperature, was approximately 50% of the field measurements of N mineralized. The values of NH4-N extracted with hot 2 M KCl were related significantly to N mineralized in the field (r2= 0.60) and also to the zero order rate constant of mineralization, k0 (r2= 0.77), determined from the N mineralized in the aerobic laboratory incubation. 相似文献
48.
A simulation model for winter wheat growth, crop nitrogen dynamics and soil nitrogen supply was tested against experimental data. When simulations of dry matter production agreed with measurements, nitrogen uptake was simulated accurately. The total amount of soil mineral nitrogen as well as the distribution of mineral nitrogen over the various soil layers were generally simulated well, except for experiments in which fertilizer was applied late in spring. In these experiments, applied nitrogen disappeared because it could not be accounted for by the model. Some explanations for this disappearance are briefly discussed. 相似文献
49.
通过结构设计和负荷计算,研制出适合于实验室使用的以钼丝为电热体,电熔镁砂或镁铝尖晶石为沪芯材料,H2-N2混合气体为保护气氛和最高使用温度达1950℃的内挂式氢气钼丝炉。 相似文献
50.
Dehydroaromatization of methane to benzene occurs over a 2 wt% Mo/ZSM-5 catalyst at 700C under non-oxidizing conditions. Following an initial induction period, during which CH4 reactant reduces the original Mo6+ ions in the zeolite to Mo2C and deposition of coke occurs, a benzene selectivity of 70% at a CH4 conversion of 8–10% could be sustained for more than 16 h. X-ray photoelectron spectroscopy and X-ray powder diffraction measurements indicate that the reduced Mo is highly dispersed in the channels of the zeolite. Initial activation of CH4 reactant occurs on Mo2C sites, leading to the formation of C2H4 as the primary product. The latter then undergoes subsequent oligomerization reactions on acidic sites of the zeolite to form aromatic products. 相似文献