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排序方式: 共有351条查询结果,搜索用时 15 毫秒
1.
运用灰色系统的理论及方法,将疲劳应力与寿命的相互制约关系看成一个灰色系统,将疲劳试验的应力水平均匀分成数级,并找出与之对应的安全寿命的白化值。通过对安全寿命值数列的一次累加,生成一个光滑离散函数。据此建立灰色系统模型,并求解灰色系统的微分方程 。通过残差模型的修正,提高模型精度,再运用灰色系统模型的还原模型,可计算出任一应力水平下的安全寿命值。为机床主轴的安全寿命计算提供了新的途径,具有较大的推广应用价值。 相似文献
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目的在切削力、重力和顶尖顶紧力的作用下, 横置的细长轴很容易弯曲甚至失稳, 因此, 车削细长轴时有必要改善细长轴的受力问题. 方法采用反向进给车削, 配合以最佳的刀具几何参数、切削用量、拉紧装置和轴套式跟刀架等一系列有效措施. 结果提高了细长轴的刚性, 达到了加工要求. 结论本方法操作简单, 加工精度高, 有可取之处. 相似文献
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Sophie Ramananarivo Ramiro Godoy-Diana Benjamin Thiria 《Journal of the Royal Society Interface》2013,10(88)
Swimmers in nature use body undulations to generate propulsive and manoeuvring forces. The anguilliform kinematics is driven by muscular actions all along the body, involving a complex temporal and spatial coordination of all the local actuations. Such swimming kinematics can be reproduced artificially, in a simpler way, by using the elasticity of the body passively. Here, we present experiments on self-propelled elastic swimmers at a free surface in the inertial regime. By addressing the fluid–structure interaction problem of anguilliform swimming, we show that our artificial swimmers are well described by coupling a beam theory with the potential flow model of Lighthill. In particular, we show that the propagative nature of the elastic wave producing the propulsive force is strongly dependent on the dissipation of energy along the body of the swimmer. 相似文献
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The paper describes an experimental method for determining the residual lifetime of wheelset axles which was developed and proved. The procedure includes all necessary steps: crack initiation from an artificially generated surface defect, monitoring of crack growth, and specification of the end-of-test criterion. The crack propagation tests described in this paper were carried out on a complete wheelset that was installed on a full-scale wheel-rail roller test rig using a measured load spectrum. During both the test planning and test implementation phases, considerable attention was paid to the complex processes involved in crack propagation in wheelset axles. In addition to axle material and design issues, important factors that have to be taken into account include sequence effects, the reliability of load cycle omission strategies to reduce the overall duration of testing, static stresses introduced by press-fitting procedures and residual stresses caused by manufacturing processes, and crack closure effects. The results obtained indicate that the method produces reliable results that are of practical relevance. Examples were also presented that indicated how far experimentally determined residual axle lifetimes could still differ from lifetimes calculated using current fracture mechanics modelling techniques. 相似文献
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As well known, an interaction effect arises, on crack propagation, when a specimen or a component is subjected to variable amplitude fatigue loading. Depending on the applied load sequence, a certain amount of retardation or acceleration can then be observed, on the fatigue crack growth rate, with respect to the constant amplitude case. In the case of structural ductile materials, the interaction phenomenon is mainly addressed by the local plasticity at the crack tip and can be explained, from a global point of view, by adopting the crack closure concept. In the present research, load interaction effects in a medium strength steel for railway axles are experimentally analyzed by companion and full-scale specimens. The experimental outcomes show a significant retardation with respect to a simple no-interaction approach and the Strip-Yield model offers good, yet conservative, estimates of crack advance. The consequences of crack growth retardation on the inspection periodicity of railway axles are then discussed. 相似文献
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细长柱的二阶效应在结构设计中容易被忽略。该文通过对“虚柱法”理论的阐述,总结出细长柱可根据“虚柱法”来计算二阶效应:由于细长柱的二阶效应与构件侧向荷载无关,故只需要输入构件轴向压力来得到二阶效应的刚度,并叠加单元力学属性的刚度。就可以得到考虑二阶效应的细长柱内力计算方法。最后通过sap2000算例得到验证。 相似文献
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Passive energy dissipation devices have been used around the world to mitigate the response of structures under dynamic excitations, such as wind or seismic loading. The use of tuned mass dampers (TMD) in tall and slender buildings to reduce unwanted responses has proved to be very effective. The main purpose of this work is to study the structural behavior of a 115‐m‐height slender monument fitted with TMDs subjected to simulated wind and seismic loading. Turbulent wind forces were calculated based on samples of turbulent wind speed simulated with an auto regressive and moving average (ARMA) model. Ground motions compatible with a seismic site spectrum were also simulated. An optimization approach is suggested to determine the parameters of the TMDs that reduce the structural response to the maximum. The effectiveness of the TMDs for reducing the structural response of the monument is discussed in detail, and the use of optimally tuned TMDs is emphasized. 相似文献