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151.
The load dependence of the Vickers microhardness of SrLaAlO4 and SrLaGaO4 single crystals, using a PMT-3 hardness tester, has been investigated and analysed from the standpoint of various theoretical
models. On the (100) and (001) planes of these crystals, reverse indentation size effect was observed. Analysis of the experimental
data revealed: (1) the indentation size effect is best described by Meyer's law and the proportional specimen resistance model
of Li and Bradt, (2) indentation-induced cracking model for reverse indentation size effect and Meyer's law cannot be used
to determine the hardness of the crystals, (3) as shown by the negative values of the load-dependent quantities in Hays-Kendall's
approach and Li-Bradt model, the origin of indentation size effect is associated with the processes of relaxation of indentation
stresses, and (4) the load-dependent and load-independent quantities of different models are interrelated and are intimately
connected with the orientation and chemical composition of the crystals. It was also found that the plots of the ratio of
indentation load to indentation diagonal against indentation diagonal for a sample exhibit two different slopes with a transition
in the slopes occurring at an indentation diagonal, whose value depends on the indenter orientation, indented plane and chemical
composition of the crystals. The physical significance of the appearance of these transitions and the nature of load-independent
indentation microhardness are discussed.
Electronic Publication 相似文献
152.
K. Kurabayashi 《International Journal of Thermophysics》2001,22(1):277-288
This paper discusses the thermal conduction anisotropy in polymers by reviewing currently available theories and experimental methods for studying oriented polymers. The anisotropic thermal conductivity and diffusivity of oriented polymers originate from the difference between the thermal energy transport mechanisms parallel and perpendicular to their molecules. Recent progress in the development of experimental techniques for studying the thermal conduction anisotropy of polymer films with thicknesses near 1 m is discussed in connection with modern microelectronics applications. The data obtained from these techniques are expected to serve for developing sophisticated thermal conduction theories that account for the polymer anisotropy and for performing precise thermal design of organic electronic devices that incorporate highly oriented polymer structures. 相似文献
153.
A combinatorial method to calculate the mean square end-to-end distance R
2 of a polymer on a Bethe lattice is used. The case of an anisotropic lattice and semiflexible polymers is considered. The distance on the Cayley tree is defined by embedding the tree on an N-dimensional Euclidean space considering that every bend of the polymer defines a direction orthogonal to all the previous ones. The semiflexible polymer is effectively equivalent to a flexible one if one considers an effective (noninteger) coordination number. Although an analytical calculation is performed, a closed expression for R
2 is possible only for the isotropic case. Numerical results are shown for the anisotropic case. Plots of R
2 against N for different values of the anisotropy parameter y are shown. The power dependence for N does not depend on the anisotropy as expected, but the linear coefficient increases on increasing the anisotropy. The anisotropy tends to stretch the polymer. 相似文献
154.
The initial texture and anisotropy of alloyed tool steel specimens are studied by constructing pole figures and conducting
compression tests. Scattered initial axial crystallographic growth texture and weak anisotropy of yield stress and ultimate
strength are established. A relationship between deformability and texture is determined.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 26–31, 2007. 相似文献
155.
针对81-02型198Au短程治疗源的临床应用,用蒙特卡罗方法计算了在一半径为30cm的理论球体模型中,AAPMTG43U1所推荐剂量计算参数的数值,包括剂量率常数、径向剂量函数和各向异性函数。所得单个81-02型198Au短程治疗源的剂量率常数为1.113 cGy·h-1·U-1,与Dauffy等的理论计算值和TLD实测值分别相差0.18%和1.62%。在源中垂轴0.1~10.0cm距离范围内计算径向剂量函数的数值,在角度0°~90°(10°间隔)、距离0.5~9.0cm(1cm间隔)范围内计算各向异性函数的数值,最后对径向剂量函数和各向异性函数进行拟合,得到实用性较强的经验公式。 相似文献
156.
157.
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
158.
Wolff法则是指骨骼通过重建/生长,保证骨小梁方向趋于与主应力方向一致以不断地适应它的力学环境。根据Wolff法则,建立了一种新的拓扑优化的准则法。该方法的基本思想是:(1)将待优化的结构看作是一块遵从Wolff法则生长的骨骼,骨骼的重建过程作为三维连续体结构寻找最优拓扑的过程;(2)用构造张量描述正交各向异性材料的弹性本构;(3)重建规律为结构中材料的更新规律。通过引入参考应变区间,材料更新规律可解释为:设计域内一点处主应变的绝对值不在该区间时,该点处构造张量出现变化;否则,构造张量不变化,该点处于生长平衡状态。(4)当设计域内所有点都处于生长平衡状态时,结构拓扑优化结束。采用各向同性本构模型,即令二阶构造张量与二阶单位张量成比例,分析三维结构拓扑优化。实例进一步验证基于Wolf法则的连续体结构优化方法的正确性和可行性。 相似文献
159.
160.
Cold-drawn prestressing steel wires exhibit strength anisotropy in the form of fracture path deflection towards a direction
approaching the wire axis, or cold drawing line, as a consequence of the pearlitic microstructure orientation induced by the
manufacturing procedure. Such a crack path deflection is initiated at certain nuclei (fracture origins) at which axial cracking
appears in the cold drawing direction (or wire axis) in the form of micro-cleavage units that produce in the load-displacement
curve a macroscopic phenomenon of pop-in. This paper shows that such fracture initiators appear at a certain distance from the fatigue pre-crack tip at which a local
maximum of the cleavage stress is located. 相似文献