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51.
Ce对Fe-Cr合金高温氧化行为的影响   总被引:1,自引:0,他引:1  
Fe-15Cr 和 Fe-30Cr 合金在1000至1200℃空气中氧化时,表面富铁氧化伤的发展导致保护性Cr_2O_3层衰退,氧化速率增大。添加 Ce 可延迟衰退过程的发生,从而大幅度减低氧化速率。随氧化温度和合金成份变化,Cr_2O_3层衰退的开始时间和发展特征随之改变,Ce 对氧化行为的影响因而呈现出规律性的变化。研究发现,合金中 Cr 的内氧化使 Cr_2O_3层形成小舌包卷合金并使其氧化成富铁氧化物。这是Cr_2O_3层衰退的原因之一。含 Ce 合金中 Ce 的优先内氧化则降低自氧化层进入合金的氧浓度,抑制Cr 的内氧化。氧浓度降低还能促进 Si 的内氧化物在氧化层/合金界面集聚。  相似文献   
52.
Existing commercial CAD/CAM systems allow the user to generate the cutter-path for machining a 2-1/2D pocket by using only a single cutting-tool size. Therefore, to avoid potential problems, such as gouging and unmachined areas, the user tends to choose the size of the cutting-tool in a conservative manner. This can result in longer processing time and higher production cost than those that can be achieved by using multiple cutting-tool sizes to machine a given pocket. The key to cutter-path generation using multiple cutting-tool sizes lies in having an efficient mechanism for representing the material volumes that can be removed by a specified cutting-tool size and the unmachined material volumes that will remain after its use. In this paper, we develop a novel concept called the Voronoi mountain and describe its application to cutter-path generation using multiple cutting-tool sizes. The theoretical significance of this approach stems from its ability to: (i) to create a Voronoi mountain representation of unmachined material volumes without having to construct the corresponding Voronoi diagram; and (ii) to accommodate generalized pocket geometries.  相似文献   
53.
A one-unit photovoltaic electrolyzer, fabricated from double-stacked amorphous silicon cells (pin-pin), is described. A solar energy conversion efficiency to hydrogen of 2.6% has been achieved, which, with recent technological developments, can be raised to 6%. A one-unit array (with storage) capable of supplying solar hydrogen to power tractors on the average farm would give rise to a cost of ca. 6.2¢/kWh, using the expected 1990 value of $1 per peak W for amorphous silicon photovoltaics. The cost of the hydrogen derived from the system is ca. two to three times that of conventional gasoline per gallon equivalent.  相似文献   
54.
The results of flow visualization in a rectangular test cell during the melting of n-octadecane are reported. The experiments provide information on buoyancy-induced fluid motion and its effect on the shape of the solid-liquid interface.  相似文献   
55.
The estimation algorithm described in this note solves the linear estimation problem as a two-stage estimator consisting of two consecutive Kalman filters. The interconnections between this estimator structure and the more familiar one-stage optimal Kalman filter are discussed. Applications to decentralized estimation, bias estimation, and parameter identification are described.  相似文献   
56.
The adsorption of a solute by porous solid particles can be represented with good accuracy by a simple approximate formula of the “penetration” type. The corresponding “kinetic” model makes use of average lumped concentrations of the two phases. It can be applied, by introduction of the fluid—solid slip velocity, either to the agitated vessel, or to the co- or counter-current moving bed. With the external specific area of the particle sample, the formula also represents correctly the, absorption by particles of any shape and any size distribution.  相似文献   
57.
本文系统地分析了步行车辆在坡道上行走时的稳定性问题。利用本文的分析方法,可以方便地求解步行车辆沿纵向坡道、横向坡道以及在坡道上沿任意方向行走时的稳定性,还可以方便地求出步行车辆能够稳定行走的最大纵向坡度和最大横向坡度以及能够在坡道上沿任意方向稳定行走时坡道的最大坡度角。  相似文献   
58.
Biscationic quaternary phosphonium compounds (bisQPCs) represent a promising class of antimicrobials, displaying potent activity against both Gram-negative and Gram-positive bacteria. In this study, we explored the effects of structural rigidity on the antimicrobial activity of QPC structures bearing a two-carbon linker between phosphonium groups, testing against a panel of six bacteria, including multiple strains harboring known disinfectant resistance mechanisms. Using simple alkylation reactions, 21 novel compounds were prepared, although alkene isomerization as well as an alkyne reduction were observed during the respective syntheses. The resulting bisQPC compounds showed strong biological activity, but were hampered by diminished solubility of their iodide salts. One compound (P2P-10,10 I) showed single-digit micromolar activity against the entire panel of bacteria. Overall, intriguing biological activity was observed, with less rigid structures displaying better efficacy against Gram-negative strains and more rigid structures demonstrating slightly increased efficacy against S. aureus strains.  相似文献   
59.
Experiments are performed to study slot air jet impingement cooling flow and the heat transfer along triangular rib-roughened walls. Both flow visualization and local heat transfer measurements along the ribbed wall are made. The effect of different rib protrusions (heights) on the impinging flow and heat transfer along the wall is studied, which is achieved by using different sizes of nozzles. Two different ribbed walls with different rib pitches are selected which have a rib pitch-to-height ratio of 2 and 4, respectively. The widely opened cavity between neighboring ribs make more intense transport of momentum between the wall jet and cavity flow so that recirculation cell in the cavity is hardly observed. This leads to a higher heat transfer around the cavity wall than in the case with rectangular ribs. However, in the region of laminar wall jet, a number of air bubbles enclosing the cavities are formed which prevent penetration of the wall jet into the cavities. This leads to a significant reduction in the heat transfer. The geometric shape of the triangular ribs is more effective in rebounding the wall jet away from the wall than in the case with rectangular ribs. The rebound of the jet away from the wall causes a significant reduction in the heat transfer. A comparison and correlations of the stagnating point Nusselt number under different conditions are presented and discussed. During the experiments, the Reynolds number varies from 2500 to 11,000, the slot width-to-rib height ratio from 1.17 to 6.67, and nozzle-to-plate spacing from 2 to 16.  相似文献   
60.
In this paper, we address the problem of optimizing the tool path plan for patchby-patch machining of parts having multiple surface patches. The tool path plan defines the sequence in which the patches are to be machined and the entry and exit points for the cutting-tool within each patch. Curent CAD/CAM systems require the user to select the tool path plan. When the number of surface patches increases and alternative machining strategies need to be evaluated, it is often difficult for the user to select the optimal tool path plan that minimizes the total time to machine the part. In this paper, we address three cases of this optimization problem, and present models that can be used to incorporate tool path plan evaluation and optimization capabilities in CAD/CAM systems.  相似文献   
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