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1.
将电力工程项目发生延迟的各个风险因素通过BN模型进行了量化,结果显示,天气状况恶劣、项目时间计划过紧、技术工种能力低、缺乏先进设备仪器和供应商不能按时供货这5种风险因素会直接对项目的延迟产生影响;供应商不能按时供货、技术工种能力低、项目计划安排不当3种风险因素对项目的延迟十分敏感.项目经理应该重点控制这些敏感因素.  相似文献   
2.
以洛阳黄土为源土的室内配制氯盐渍土为研究对象,通过自制的单轴抗拉仪,进行了氯盐渍土抗拉特性试验,研究了干密度、初始含水率、含盐量对氯盐渍土抗拉强度的影响.试验结果表明,在相同含盐量和干密度下,抗拉强度与含水率呈对数关系;试样的抗拉强度随着干密度的增加而增加;在含水率小于15%时,破坏拉应力随着含盐量的增加,先减小后增大,拐点为8%;在含水率大于15%时,随着含盐量的增加,抗拉强度减小,而拉应变恰好相反;相同含盐量下,随着含水率的增加,破坏拉应力减小,破坏拉应变增大.  相似文献   
3.
    
Acrylic bone cement is used to fixate hip replacement implants into the bone. Creep and fatigue failure of the cement promote failure of the implant. For the purpose of implant testing, we derived a finite element algorithm that simulates creep and damage accumulation in acrylic bone cement. The simulation combines a Maxwell creep model, with a 3-D continuum damage mechanics approach modeling anisotropic damage accumulation. The technical details of the simulation are described. In a first application tensile fatigue tests on tubular cement specimens are simulated. The creep elongation and fatigue life of the specimens, as predicted by the simulations, are successfully correlated to the experimental results. In a second application, the simulation is used to predict creep and fatigue failure of the cement mantle around two hip implants with different clinical outcomes. It is shown how the simulation is able to predict the locations of cement damage around the implants, and the amounts of implant migration attributable to creep.  相似文献   
4.
    
An experimental method based on laser triangulation was used to measure the 3-D profile of fracture surface of concrete. The projective-covering method was established to determine the fractal characteristics of fracture surface. Based on the experiment, the influence of composition of concrete on the fractal dimension, including water–binder ratio, maximum aggregate size and aggregate type, was investigated. The variation of fractal dimension with the material composition was also analysed to make further understanding of fracture mechanism of concrete.  相似文献   
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Fluid dynamics of a family of two-dimensional flat plates and rectangular prisms (aspect ratio of 0.27, 0.5 and 1.0) with moving surface boundary-layer control (MSBC) was carried out employing three complementary approaches: (i) extensive wind tunnel test program; (ii) finite element-based numerical integration of the complete Navier–Stokes equations; and (iii) flow visualization. A comparison between the drag of rectangular prisms of varying aspect ratios with sharp and rounded corners reveal substantial drag reduction, even in absence of the MSBC. It suggests fundamentally different fluid mechanical processes involved. The surface pressure distribution, resultant forces, streamline patterns and wake characteristics suggest significant increase in the wake pressure, with associated decrease in the drag, in presence of the MSBC. Results show increase in the Strouhal number indicating effective decrease in the bluffness. Both the numerical and flow visualization results show narrowing of the wake with increasing momentum injection and eventual suppression of the vortex shedding. In case of the flat plate, classical quasi-steady analysis suggests significant improvement against galloping type of instability. Implications of the present study to alleviate flow-induced instabilities such as vortex resonance and galloping are apparent.  相似文献   
7.
    
This study reports some preliminary observations of microcracks in hardened high performance cement paste (i.e., cement paste of low water:binder ratio). Specimens were examined at high magnifications and at relative humidities ranging from 0 to 100% in an environmental scanning electron microscope (ESEM). Direct microcracks were observed in samples that had not been dried, indicating that microcracks are probably an intrinsic feature of high performance concrete. It was further observed that the microcracks widened upon drying and closed again upon rewetting. Some practical consequences of these findings are discussed briefly.  相似文献   
8.
    
《Composites》1991,22(3):181-190
Stress-controlled fatigue tests have been carried out on pultruded 60 vol % ECR-glass/polyester rods. Damage evolution was monitored continuously using stiffness decay and replication techniques. When the cyclic stresses corresponded to those within the linear portion of the monotonic stress/strain curve, fatigue damage accumulated linearly, whereas damage developed non-linearly at higher stresses. Using continuum damage mechanics, a strain energy model was developed to predict life, and then verified with the experimental results. The constants for the strain energy model were related to the slope of the S/N curve and stress-axis intercept at a half-cycle, according to a Basquin-type relationship.  相似文献   
9.
    
《Composites Part B》2007,38(5-6):509-522
Recent world events such as bombings in London, Madrid and Istanbul have highlighted the susceptibility of many civilian structures to terrorist attack. Explosives directed towards vulnerable structures may cause considerable damage and loss of life. As a result, there is now a desire to increase the blast resistance of many types of existing structures. This has led to experimental and finite element (FE) research in retrofitting concrete and masonry structures with fibre reinforced polymer (FRP) composites for blast protection. This paper presents a review of the publicly available literature and highlights areas where research is lacking.  相似文献   
10.
橡胶材料具有密度低、线弹性变形能力强、耐久性好、耗能大等优点,其衍生物与土体制成的混合物被广泛应用于岩土工程和交通工程领域。为研究橡胶颗粒与砂土混合物这种新型路基填料在循环列车荷载作用下的动力参数特性,进行室内固结不排水动三轴试验,分析了橡胶颗粒含量、围压以及加载频率等因素对橡胶颗粒-砂混合物动剪切模量、阻尼比等特性的影响,研究结果表明:应变一定时,混合物的动剪切模量随着橡胶颗粒含量的增加而减小,随着围压的增大而增大,随着加载频率的增加而轻微减小;基于Hardin-Drnevich双曲线模型对动剪切模量试验结果进行拟合,得出最大动剪切模量,发现最大动剪切模量随着橡胶颗粒含量的增加而减小。应变一定时,混合物的阻尼比随着橡胶颗粒含量的增大而增大,随着围压的增大而减小,加载频率对阻尼比的影响较小;基于试验结果,建立了橡胶颗粒-砂混合物阻尼比与剪切应变的关系式。最后,基于柔性橡胶颗粒与刚性砂土颗粒的微观接触特性,分析了橡胶颗粒对混合物动剪切模量以及阻尼比的影响机理。综合研究结果得出:橡胶颗粒含量不宜超过20%,此时橡胶颗粒-砂混合物作为新型路基填料的动剪切模量可以满足要求,阻尼比较大,具有良好的减震耗能效果。  相似文献   
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