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1.
The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK).  相似文献   
2.
针对忽略岩土体非均质和各向异性将导致边坡稳定性评价产生误差的问题,应用极限分析上限理论及抗剪强度系数折减法,推导土体强度非均质和各向异性影响下隧道洞口含裂缝仰坡稳定性解析式,探究土体强度非均质和各向异性对仰坡稳定性系数、坡顶裂缝位置、隧道拱顶失稳范围及仰坡安全系数的影响。结果表明,裂缝深度及坡角越大,仰坡稳定性系数越小;非均质系数越大和各向异性系数越小,维持仰坡稳定的临界坡高越大;非均质系数及各向异性系数越大,裂缝距坡顶边缘越远,隧道拱顶失稳范围越大;非均质系数增大有利于仰坡稳定,而各向异性系数越大仰坡越易失稳。  相似文献   
3.
基于紧凑拉伸剪切结构的复合型疲劳裂纹扩展研究   总被引:1,自引:0,他引:1  
针对含I-II型复合裂纹的紧凑拉伸剪切(CTS)试样,研究了不同加载角度下的裂纹扩展路径及裂纹扩展寿命,通过实验数据给出了适宜于CTS试样的等效应力强度因子关系式,并基于此提出了一种新的I-II型复合裂纹扩展模型。研究表明,CTS试样的裂纹沿与加载方向近垂直的方向扩展,基于Tanaka公式的等效应力强度因子更适合于本文CTS试件的裂纹扩展寿命评估。当加载角度处于0°~45°之间时,提出的复合型裂纹扩展模型预测误差控制在5.49%之内,验证了分析模型的可行性和准确性。  相似文献   
4.
At the Leipzig Technical University a method was developed, which allows to determine nondestructive the crack depth in concrete up to 15 cm. Based on a radiotracer technique the access to only one side of the object is required. The labelling of artificial-made cracks was carried out by use of a transport medium (not miscible with water) on the base of methyl isobutyl ketone (MIBK) and In- 113m as radionuclide. For the calculation of crack depth, measure-geometrical parameters were used. The improvement of the reliability of building-diagnostical interpretation using radio-physical parameters is described. A first application is provided for concrete structures below chemical equipments built as a barrier against ecologically harmful substances (petrol tanks). The intersectional aspect of further qualifications of the technique is emphasized.  相似文献   
5.
Layered structures are ubiquitous, from one-atom thick layers in two-dimensional materials, to nanoscale lipid bi-layers, and to micro and millimeter thick layers in composites. The mechanical behavior of layered structures heavily depends on the interfacial properties and is of great interest in engineering practice. In this work, we give an analytical solution of the bending rigidity of bilayered structures as a function of the interfacial shear strength. Our results show that while the critical bending stiffness when the interface starts to slide plastically is proportional to the interfacial shear strength, there is a strong nonlinearity between the rigidity and the applied bending after interfacial plastic shearing. We further give semi-analytical solutions to the bending of bilayers when both interfacial shearing and pre-existing crack are present in the interface of rectangular and circular bilayers. The analytical solutions are validated by using finite element simulations. Our analysis suggests that interfacial shearing resistance, interfacial stiffness and preexisting cracks dramatically influence the bending rigidity of bilayers. The results can be utilized to understand the significant stiffness difference in typical biostructures and novel materials, and may also be used for non-destructive detection of interfacial crack in composites when stiffness can be probed through vibration techniques.  相似文献   
6.
The thermal effects of an interface crack between two dissimilar half-spaces is considered. The interface cracks are partially or fully insulated, and spaced in a periodic array. Using the complex variable technique, the temperature and fluxes are found in closed form, and the interactions between heat flows due to nearby cracks are determined.  相似文献   
7.
In this paper interfacial edge crack problems are considered by the application of the finite element method. The stress intensity factors are accurately determined from the ratio of crack-tip-stress value between the target given unknown and reference problems. The reference problem is chosen to produce the singular stress fields proportional to those of the given unknown problem. Here the original proportional method is improved through utilizing very refined meshes and post-processing technique of linear extrapolation. The results for a double-edge interface crack in a bonded strip are newly obtained and compared with those of a single-edge interface crack for different forms of combination of material. It is found that the stress intensity factors should be compared in the three different zones of relative crack lengths. Different from the case of a cracked homogeneous strip, the results for the double edge interface cracks are found to possibly be bigger than those for a single edge interface crack under the same relative crack length.  相似文献   
8.
单轴荷载下饱水岩石静态和动态抗压强度的细观力学分析   总被引:1,自引:0,他引:1  
王斌  李夕兵 《爆炸与冲击》2012,32(4):423-431
由于单轴荷载下饱水岩石的动态力学特性与静态力学特性存在很大差异,从宏观上进行力学分析 存在局限性。根据岩石受压全应力应变曲线的细观机制,分析了静态及动态单轴荷载条件下孔隙水影响饱水 岩石裂纹扩展的情况。在静态单轴压缩条件下,初始裂隙受压使自由水产生孔隙水压力,自由水对翼裂纹有 向外挤压的应力,促进裂纹扩展。在动态单轴压缩条件下,自由水会产生粘结力,抑制裂纹扩展。根据翼裂纹 受压扩展原理,推导出饱水单轴条件下动态抗压强度、静态抗压强度的计算公式,在相同断裂韧度下,饱水岩 石静态抗压强度风干岩石静态抗压强度饱水岩石动态抗压强度。对自然风干和饱水砂岩进行单轴静态、 动态压缩实验,结果与理论模型的结果相符。  相似文献   
9.
SH波入射时半空间界面裂纹与圆形衬砌的相互作用   总被引:1,自引:0,他引:1  
利用复变函数和Green函数法研究了双相介质半空间界面裂纹及界面附近圆形衬砌对SH 波的 散射与动应力集中问题。首先,采用映像思想构造满足自由边界条件的散射波表达式,进而求解所需的 Green函数;其次,采用裂纹切割技术构造裂纹,并根据连续性条件建立了求解该问题的无穷代数方程组; 最后,给出了不同入射波数时界面裂纹与衬砌的相互作用。结果表明,裂纹的存在显著放大了衬砌界面的动 应力集中。  相似文献   
10.
L.W. Li 《Applied Surface Science》2009,255(18):7841-7845
The effect of humidity on subcritical crack growth of indentation crack in lead zirconate titanate (PZT) ferroelectric ceramics under various sustained electric field has been investigated. The results showed that subcritical crack growth of indentation crack could occur in humid air of 60%RH without electric field but did not in air with RH ≤ 30%. The subcritical crack growth could occur in vacuum under a sustained electric field of E/EC = 0.14. The incubation time decreased and the amount of the subcritical crack growth increased with increasing the humidity under the sustained field. The threshold electric field for subcritical crack growth decreased with increasing the humidity.  相似文献   
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