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961.
De-icing technology has become an increasingly important subject in numerous applications in recent years. However, the direct numerical modeling and simulation the physical process of thermo-mechanical deicing is limited. This work is focusing on developing a numerical model and tool to direct simulate the de-icing process in the framework of the coupled thermo-mechanical peridynamics theory. Here, we adopted the fully coupled thermo-mechanical bond-based peridynamics (TM-BB-PD) method for modeling and simulation of de-icing. Within the framework of TM-BB-PD, the ice consti-tutive model is established by considering the influence of the temperature difference between two material points, and a modified failure criteria is proposed, which takes into account temperature effect to predict the damage of quasi-brittle ice material. Moreover, thermal boundary condition is used to simulate the thermal load in the de-icing process. By comparing with the experimental results and the previous reportedfinite element modeling, our numerical model shows good agreement with the pre-vious predictions. Based on the numerical results, we find that the developed method can not only predict crack initiation and propagation in the ice, but also predict the temperature distribution and heat conduction during the de-icing process. Furthermore, the influence of the temperature for the ice crack growth pattern is discussed accordingly. In conclusion, the coupled thermal-mechanical peridynamics formulation with modified failure criterion is capable of providing a modeling tool for engineering ap-plications of de-icing technology. 相似文献
962.
Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance. One special ballistic performance is the embedding effect, which can achieve a delayed high-explosive reaction on the target surface. This embedding effect includes a rebound phase that is significantly different from the traditional penetration process. To better study embedment behavior, this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration. Specifically, we conducted a series of low-velocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy. We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations. The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure, but then it increased significantly-that is, the fluctuation of penetration resistance was affected by the irregular nose shape. Moreover, we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations. The combination of these phenomena revealed the embed-ment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance. The embedment was achieved primarily by the target material filled in the groove structure. Therefore, preventing the shear failure that occurred on the filling material was key to achieving this embedding effect. 相似文献
963.
测试了C/SiC复合材料在高温空气下的压缩、弯曲和拉伸性能,利用扫描电子显微镜分析复合材料在室温与高温条件下的断口微观形貌。结果表明:从室温升温到1 000 ℃测试温度时,C/SiC复合材料的压缩强度由247 MPa降低至78 MPa,性能降低68%;弯曲强度由480 MPa降低至277 MPa,性能降低42%;拉伸强度由247 MPa降低至152 MPa,性能降低38%。高温氧化导致界面退化,损伤材料基体与碳纤维结构,加剧了纤维断裂程度,改变了纤维与基体的结合状态,纤维增韧机制逐渐消失,导致复合材料性能下降。 相似文献
964.
针对多阶段武器装备组合规划中的选择难、规划难问题,提出基于多目标优化算法以及强化学习技术的混合优化方法。在各个阶段以装备组合效能最大和成本最小为准则,构建单阶段多目标优化模型,并设计基于非支配排序遗传算法的求解算法以生成各阶段的Pareto解,在此基础上建立多阶段的组合优化模型。通过强化学习的Q-Learning方法,在各阶段的Pareto解中采用探索或者利用两种模式,生成各阶段的装备组合,并指导下一阶段的装备选型,从而生成整个周期内的规划方案。通过对比实验分析,验证了所提模型和算法的有效性,能够为多阶段武器装备组合规划提供辅助决策。 相似文献
965.
966.
针对重大突发事件人员应急疏散难题,提出了基于情景应对的应急决策方法.将重大突发事件相关关键属性表示为一系列情景,对情景进行定性与定量相结合的描述.以疏散时间作为决策收益的判断标准,引入交通流量算法并考虑安全距离,建立数学模型.通过计算机仿真应急疏散算例,求解决策的最优解,验证了方法的有效性. 相似文献
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968.
969.
970.
给出了无尾舵布局超空泡航行体在纵垂面内的受力分析及运动方程,建立了变深度机动最优轨迹问题的数学模型。针对空泡扩张与收缩带来的延时效应,提出改进的延时型高斯伪谱法,利用所有高斯节点的运动状态插值获得整个运动过程的状态量,由此得到各个时刻的实时超空泡航行微分方程。通过计算各节点处运动方程约束,对其变深度机动轨迹进行数值求解,得到相应的优化弹道结果及控制策略。对给定布局方案的超空泡航行体下潜机动最优弹道问题进行求解,计算结果表明,采用空化器偏转控制策略,无尾舵布局超空泡航行体可满足运动稳定性与机动性要求,所提出的延时型高斯伪谱法能够处理超空泡航行弹道优化中的延时效应,具有较好的快速收敛性。 相似文献