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1.
The average and local heat transfer at the base surface of a cylindrical cavity whose opening is perpendicular to an oncoming freestream have been determined experimentally. During the course of the experiments, the cavity depth was varied from zero to 65% of the diameter, while the freestream Reynolds number ranged between about 5000 and 50,000. The average heat transfer coefficient decreased sharply with increasing cavity depth, the reduction being slightly greater than 50% at a depth-diameter ratio of 0.10 and greater than 90% when the depth-diameter ratio was 0.65. For the finite-depth cavities, the local heat transfer coefficient attained its maximum value at the center of the base surface and decreased with increasing radial distance from the center until a minimum was reached, after which there was a moderate increase adjacent to the outer edge of the base. The minimum occurred at the location where the radial outflow along the base separated from the surface, and a toroidal-shaped recirculation zone occupied the corner region at the intersection of the cavity base and side wall. In contrast, for the zero-depth cavity (i.e. a free disk oriented perpendicular to the oncoming flow), the local coefficient attained its minimum at the center of the surface and increased with increasing radial distance from the center. 相似文献
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P. Balle H. Bockhorn B. Geiger N. Jan S. Kureti D. Reichert T. Schrder 《Chemical Engineering and Processing: Process Intensification》2006,45(12):1065-1073
This study deals with the development of a laboratory bench for the practical evaluation of catalysts that are useful for the direct conversion of NOx and soot in the exhaust of diesel engines. The employed model exhaust is generated by using a diffusion burner with additionally dosing some gaseous components to the burner gas to obtain a realistic feed composition. The produced soot is extensively characterized by employing thermogravimetry, transmission electron microscopy, N2 physisorption and temperature programmed techniques. The results of the different characterization methods show that the present soot is suitable for the intended catalytic investigations. The simultaneous conversion of NOx and soot is examined like in practice, i.e. the soot is separated from the tail gas by a diesel particulate filter (DPF) that is coated with the catalyst. The deposited soot is then catalytically converted by NOx and O2 to form N2 and CO2. The conversions of NOx and soot are measured by exclusively applying gas analysers, whereby a special experimental procedure is developed to determine the soot removal. Hence, additional soot related analytics are not required. To show the suitability of the constructed bench a Pt/Fe2O3/β-zeolite sample is taken as test catalyst that is reported to be very active in NOx/soot reaction. The measurements performed with and without catalyst clearly show the effect of the used sample in simultaneous NOx/soot conversion. We therefore consider the constructed laboratory bench to be a useful tool for testing and ranking catalytic materials. 相似文献
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The medullary raphe system of sheep and goat can be divided in the solitary nuclei raphe magnus and pallidus besides the impaired Nucleus raphe paramedianus. The nucleus raphe magnus begins in the caudal end of the medulla oblongata running far to the pons. On the other hand you can follow the nucleus raphe pallidus and paramedianus only in distinct area near the obex. Different types of neurons are isolated and described in light- and electronmicroscopical investigations. All three nuclei are poor of synapses. 相似文献
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Journal of Mathematical Imaging and Vision - A correction to this paper has been published: https://doi.org/10.1007/s10851-021-01028-0 相似文献
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The synthesis of thiophene-containing second (G2) and third generation (G3) dendronized macromonomers with methacrylate polymerizable units as well as their corresponding dendronized polymers is reported. The dendrons are prepared from branched thiophene oligomers and are decorated with straight alkyl chains for solubility reasons. The polymerization reactions were done with AIBN as initiator and the polymers were characterized by NMR spectroscopy, elemental analysis and GPC. Molar masses are in the range of 2.2-5.4 × 105 g mol−1 (G2) and 1.3-3.0 × 104 g mol−1 (G3) for different runs. These polymers are investigated by cyclic voltammetry and optical spectroscopy. 相似文献
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It is time that universities stop using the excuse that industry does not want a five-year-engineering-degree graduate. Industry does not have any choice since it can only select from the available talent pool. At present, materials graduates with four-year degrees often lack the critical tools necessary to perform the non-engineering jobs that are frequently offered. Courses such as statistics, process control and management will help remedy this situation. Today, the individual with a master of science degree, having spent over five years in school, still lacks many essential non-engineering skills. Worse, many students in master’s degree programs graduate with a primarily science background and have not taken the full basic engineering curriculum. For this reason, there is no comparison between the current, research-oriented M.S. degree and the proposed master of engineering degree. The outlined curriculum allows for a continuation of many current programs in materials while providing a transition to a five-year, first professional degree. The program allows the student to choose, after four years of education, whether he or she really wants to obtain a professional degree. Further, the four-year degree recipient enters the field with a better education than is available at present, and industry is supplied with a better-educated mix of degree recipients. 相似文献
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Using a laser system for local heat treatment, it is possible to adjust the mechanical properties of aluminum blanks in a restricted area by influencing the precipitation structure to manufacture so called Tailored Heat Treated Blanks (THTB). These blanks are characterized by a distribution of the mechanical properties adapted particularly for the forming conditions during deep drawing.This paper presents a finite element (FE) based procedure to determine adequate laser parameters for the heat treatment process to enhance the forming limits. Both FE and experimental results show the improved process compared to the conventional drawing of homogeneous aluminum blanks. 相似文献
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