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31.
平面应变板料拉弯成形回弹理论分析 总被引:1,自引:0,他引:1
基于平面应变假设,采用服从Hill平方屈服准则和指数强化材料模型,建立了板料拉弯成形回弹量预测的理论模型。应用该模型计算了一个拉弯成形回弹实例,分析了单位宽度切向拉力、凸模圆角半径、摩擦因数及各向异性参数对板料回弹量的影响。分析结果表明,只有当中性层偏移距离超过板厚的四分之一时,增大切向拉力才能有效地控制板料回弹量,而且弯曲半径越大,增大切向拉力控制板料的回弹量越为有效,然而拉力不能无限制的增大,它的计算准则为板料最外层的等效应变应不大于极限应变。同时还表明,摩擦因数对板料回弹量的影响随切向拉力的增大变得更为显著,而各向异性参数对板料拉弯成形回弹量的影响也较为明显。与有限元数值模拟预测结果的对比表明,理论模型预测板料拉弯成形回弹量与有限元数值模拟结果很接近。 相似文献
32.
Mechanical blends of thermoplastic medium density polyethylene (MDPE) and elastomeric ethylene propylene diene monomer (EPDM) have been prepared with a fixed composition of 60/40 wt%. They have been used either in their gum form or loaded with two different reinforcing fillers, high abrasion furnace (HAF) carbon black or precipitated SiO2 (Hi Sil) of concentration 25–100 phr (parts per hundred parts of resin) with respect to the blend. Curing was achieved by gamma irradiation. Yielding properties (yield stress, yield strain and cold drawing) have been followed as a function of irradiation dose for different blend compositions. Yield stress values increased with irradiation dose and with the content of the reinforcing filler, but yield strain and cold drawing values decreased with irradiation dose and also with the filler content. The data obtained reveal that Hi Sil is more effective as a reinforcing filler, and the prepared blends are suitable for load‐bearing applications. © 2001 Society of Chemical Industry 相似文献
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35.
产酯酵母产酯条件的研究 总被引:1,自引:0,他引:1
用收集到的三株不同产酯酵母,从中优选产酯力最高的酵母菌株进行产酯条件(温度、pH、磷盐、基质浓度、乙酸、乙醇、通风)的试验,在试验得出的产酯最佳条件下,酵母产酯能力比对照样提高11.2%。 相似文献
36.
长细比对钢筋混凝土长柱受力性能的影响 总被引:1,自引:0,他引:1
通过对24根钢筋混凝土正方形截面长柱的试验研究,表明长细比是影响钢筋混凝土长柱受力和变形性能的重要因素.随着长细比的增加,构件的极限承载力明显降低,大偏压构件的屈服荷载与其极限荷载的比值增加,混凝土的极限压应变值则明显降低. 相似文献
37.
本文研究了工业纯 α-Fe 中晶内同晶界对氢致软化同氢致硬化效应的不同贡献,发现其中仍以晶内贡献为主,并提出了相应的新机制。 相似文献
38.
Spherical void expansion in plastics and rubber-modified plastics is investigated under radial traction conditions. The plastics
are modeled as elastic-plastic pressure-sensitive materials and the rubbers are modeled as nonlinearly elastic materials.
First, the growth of a spherical void in an infinite plastic matrix is investigated under remote radial traction conditions.
The results show that the cavitation stress of the plastic decreases significantly as the pressure sensitivity increases.
Then, the growth of a spherical void located at the center of a spherical rubber particle in an infinite plastic matrix is
investigated under remote radial traction conditions. The results indicate that without any failure criteria for the rubber,
the cavitation stress does not exist when the void is small and the rubber is characterized by high-order strain energy functions.
However, when a failure criterion for the rubber is considered at a finite stretch ratio, the results show that the cavitation
stress for the plastic with the rubber particle becomes close to that for the plastic without the rubber particle.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
39.
T.L. Becker Jr. J.M. McNaney R.M. Cannon R.O. Ritchie 《Mechanics of materials : an international journal》1997,25(4):3969-308
The mixed-mode delaminating beam (MMDB) is a widely used test geometry designed to measure the fracture resistance of bimaterial interfaces under mixed-mode loading conditions. In the present work, linear-elastic finite element analyses are employed to determine the complex stress intensity factor, K, for an interfacial crack in this sample; results are found to confirm those of previous studies of the bilayer specimen. However, the numerical results further reveal that the region of K-dominance near the crack tip is very limited, extending merely 1/100 to 1/1000 of the sample height, about an order of magnitude smaller than for other common fracture-mechanics test samples. Analyses performed for this specimen geometry modified to include a thin sandwiched interlayer also indicate a very limited region of K-dominance, for example, extending 1/10 of the height of the sandwiched layer from the crack tip for very thin sandwiched layers. For the sandwiched geometry, two situations leading to a useful small scale yielding condition are described. Examples of the use of this specimen in the evaluation of the fracture toughness of ceramic joints are cited from the literature and comparisons are made between the size of the K-dominant region and the extent of crack tip plasticity. Based on these comparisons, the geometry-independent predictive power of linear-elastic fracture mechanics for common bimaterial couples and specimen dimensions using this geometry is challenged. 相似文献
40.
Displacement‐dependent dampers with relatively low post‐yielding stiffness exhibits abrupt stiffness loss and can even induce notable damage concentrations under strong vibrations. A lattice‐shaped friction unit (LSFU) composed of steel strips and friction discs is proposed and it can dissipate most input energy through translational friction and rotational friction and provide post‐yielding stiffness through the axial strength of vertical strips. Measurements of the friction coefficient and torque coefficient ratio and quasi‐static analysis of the LSFU are conducted, the results indicate that the ratio rises first and then drops to a constant value. Under cyclic loading, the two friction mechanisms could work together effectively and the contribution of each component contained in the restoring force could be controlled by adjusting design parameters of the LSFU; the assembly accuracy of the components affect the resistance of vertical strips. The experiment results of two specimens are compared with those obtained from the developed formulas and numerical simulations. A design procedure and applicable style are proposed. Nonlinear seismic response analysis results show that these devices can reduce the displacement response effectively under small and moderate earthquakes and can also prevent concentrated damage and weak‐story occurrence in the structure relative to friction‐damped brace frame in strong earthquakes. 相似文献