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71.
72.
Concurrent surface- and edge-flaw populations are often observed in strength testing of ceramics The overall strength distribution in such ceramic samples has been analyzed in terms of a modified Weibull distribution function. The junction provides an upper and lower strength limit and is characterized by two shape and location parameters. To evaluate the parameters of the distribution function, the type of flaw that causes failure need not be identified. The applicability of the function has been evaluated in terms of experimental results on SiC specimens. The analysis also shows that the relative values of shape parameters determine which flaw type dominates. 相似文献
73.
N. De Belie J. Monteny A. Beeldens E. Vincke D. Van Gemert W. Verstraete 《Cement and Concrete Research》2004,34(12):2223-2236
New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity). 相似文献
74.
In some industrial fluidized bed processes, notably coal combustion, the bed contains a very wide size range (50 – 5000 μm) of equal density particles. In others the particles change their density as the reaction proceeds, giving a bed of particles having similar sizes but densities varying by a factor of up to 2.
Experiments have been done in a bed 0.29 m diam. at velocities up to 5 m/s, using coarse particles up to 6 mm. They show that segregation by density difference can be reduced to negligible proportions by using high velocities, but that segregation by size appears to be an intrinsic feature of coarse particle systems at all velocities when a very wide size range is present. A tentative form of equation is proposed for segregation by size; the equations of Rowe are useful predictors for segregation by density difference. 相似文献
75.
Composites consisting of a fine-grained, polycrystalline zinc oxide matrix and <10 vol% coarse, rigid silicon carbide inclusions were prepared by the same mixing procedure and then compacted to produce samples with matrix densities of 0.45 and 0.68 of the theoretical. The samples were sintered under identical temperature profiles in separate experiments that employed either a constant rate of heating of 4°C/min or near isothermal heating at 735°C. The ratio of the densification rate of the composite matrix to the densification rate of the unreinforced zinc oxide was found to be independent of the initial matrix density. This ratio increased significantly with temperature in the constant-heating-rate experiments but was relatively constant in the isothermal experiments. The results indicate that microstructural coarsening may be an important mechanism for explaining the reduced sinterability of polycrystalline matrix composites. 相似文献
76.
Germplasm with shorter duration than that of the currently grown varieties is being generated to maximize productivity of irrigated rice. However, short-duration varieties often produce yields lower than the medium- and long-duration varieties. Experiments were conducted during the 1980–82 dry and wet seasons to increase productivity through the use of very early-maturing rices and the improved management of nitrogen (N) fertilizers.Results over three years showed that IR58 and IR9729-67-3 (growth duration 100 ± 5 days) yield as well as or higher than IR36 although earlier maturing. They generally had a higher productivity (kg ha–1 day–1) than IR36 (110 ± 5 days).Three years' data suggest that the improved timing of broadcast applications of urea in split doses increased grain yield comparable with the basal incorporation of slow-release sulfur-coated urea (SCU) or deep point-placement of urea supergranules (USG).Results on elite breeding lines showed that the early-maturing IR9729-67-3 produced higher protein yield ha–1 than longer duration varieties such as IR8 and IR42 in the dry season. Furthermore, contrary to earlier results, single basal incorporation of slow-release SCU increased the protein yield of rice by 53 kg ha–1 and deep point-placement of USG by 43 kg ha–1 over split application of prilled urea. 相似文献
77.
Chromium was deposited on steel specimens and on electroplated steel specimens covered with a Watts nickel layer. The influence of the substrate and of the crack pattern of the electrodeposited chromium layer on the passivation and the reactivation behaviour has been studied by means of potentiodynamic polarization curve measurements and cyclic voltammetry. In the results of the above mentioned electrochemical measurements a strong influence of the substrate was found for a cracked chromium layer deposited on the steel specimen and for a cracked chromium layer deposited on a 30 m Watts nickel layer. No influence of the substrate was found in the case of a crack-free chromium layer deposited on the steel substrate or on a Watts nickel layer. It is thus possible to determine whether the chromium layer is cracked or crack free by recording a polarization curve or a cyclic voltammogram for a chromium-plated system. A mechanism is proposed for the passivation and repassivation of cracked chromium layers electrodeposited on a steel substrate or on a Watts nickel layer. 相似文献
78.
The conditions for obtaining recrystallization in more ordered modifications are described for an uniaxially oriented sample of isotactic polypropylene, annealed with fixed ends. These recrystallization conditions are related to the conditions of a lamination process. 相似文献
79.
Ozonation of purine and pyrimidine bases and of carbohydrates was studies in laboratory experiments. The results showed that nucleobases are much more reactive with molecular ozone in aqueous solution than carbohydrates. Second order rate constants for direct reaction of ozone on purines (adenine and guanine) and on pyrimidines (cytosine, thymine and uracil) ranged from 0.76 × 103 to 6.8 × 103 M-1s-1at 2°C. The difference of reactivity between these solutes may be attributed to their substituents. As far as carbohydrates are concerned, direct reactions of ozone are very slow k03 ? 0.1 – 0.3 M-1s-1 at 20°C, and the results indicated that free radical reactions are predominant in the degradation pathway of carbohydrates by ozone. Some ozonation by-products of monosaccharides (glucose, xylose) and disaccharides (cellobiose) also were identified in this study by means of GC/MS analyses. 相似文献
80.