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排序方式: 共有136条查询结果,搜索用时 109 毫秒
131.
132.
针对火星探测器着陆巡视器减速伞筒盖结构在轨运行耐温度交变、辐照等空间环境和再入过程耐温度冲击性能需求,重点开展了筒盖复合材料耐温匹配性、力学性能、耐空间环境性能以及制件成型工艺研究。结果表明,选用J-168-1胶黏剂、J-245胶黏剂及T300/QY8911复合材料制备的试件通过各项性能试验考核,均能满足筒盖结构的设计指标要求。筒盖产品力学性能稳定,成型工艺可行性良好,最高瞬时使用温度可达200℃,经历空间环境模拟后力学性能保持率均在80%以上,耐高温、耐空间环境性良好。产品已成功装星发射,并在着陆巡视器落火阶段成功弹出分离,圆满完成使命。 相似文献
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134.
阵列碳纤维复合材料管是由碳纤维增强复合材料(CFRP)薄壁圆筒壳阵列排布后粘接制备而成,兼具碳纤维复合材料和蜂窝结构的优异性能,是一种新型的可应用于深空探测反射面板的理想材料结构。由于材料和制备方面的特殊性,在阵列碳纤维复合材料管加工过程中会由于磨削力过大导致多种加工损伤,为其高效低损伤加工带来了挑战。本文开展CFRP薄壁圆筒壳磨削加工正交试验,系统研究磨削深度、切出角度、主轴转速、进给率对磨削力的影响规律和影响程度。研究结果表明:工艺参数对水平面合力的影响程度依次为进给率、磨削深度、切出角度、主轴转速,对轴向力的影响程度依次为切出角度、主轴转速、进给率、磨削深度。研究对阵列碳纤维复合材料管高效低损伤加工工艺的制订具有参考意义。 相似文献
135.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1418-1435
Land use and cover change (LUCC) is one of the key variables dominating land–atmosphere interactions and strongly affects the Earth’s eco-environments by altering surface properties. Numerous studies have been carried out to assess the impact of LUCC. However, the Earth is a large, open and complex system characterized by complex interactions between its eco-environments and drivers. This study aimed to summarize previous studies of the impact of LUCC on the Earth’s eco-environments and discuss the progress and limitations in suggesting future directions. Previous studies have confirmed that LUCC has a wide range of impacts on the Earth’s eco-environments, which are represented by the alternation of climate (temperature, precipitation, wind, and humidity), hydrology (soil moisture, runoff, and evapotranspiration), ecology and environmental (air, water, and soil) pollution. Physically, the impacts were mainly attributed to the disturbance of the surface radiation budget and matter conservation caused by LUCC. Although great achievements have been made, several challenges remain because of the unavoidable uncertainties in data sources and methodologies and the complexity of eco-environmental evolution. Therefore, data assimilation, physical-based investigations, contribution isolation, and full-process analysis are required to overcome these challenges in future research. The results of this study helped to capture the impact of LUCC and its physical mechanisms, which provide useful clues for future research and support the relative land use management for sustainable development. 相似文献
136.
《中国航空学报》2022,35(8):280-294
Electrolyte jet machining (EJM) is a promising method for shaping titanium alloys due to its lack of tool wear, thermal and residual stress, and cracks and burrs. Recently, macro-EJM has attracted increasing attention for its high efficiency in machining wide grooves or planes. However, macro-EJM generates large amounts of electrolytic products, thereby increasing the difficulty of rapid product removal with a standard tool and reducing the surface quality. Therefore, for enhanced product transport, a novel tool with a back inclined end face was proposed for macro-EJM of TC4 titanium alloy. For comparison, also proposed were ones with a standard flat end face, a front inclined end face, and both front and back inclined end faces. The flow field distributions of all proposed tools were simulated numerically, and experiments were also conducted to validate the simulation results. The results show that one with a 5° back inclined end face can decrease the low-velocity flow zone in the machining area and increase the high-velocity flow zone at the back end of tool, thereby promoting rapid product removal. A relatively smooth bright-white groove surface was obtained. The same tool also resulted in the highest machining depth and material removal rate among the tested ones. In addition, rapid product removal was beneficial to the subsequent processing. Because of its rapid product removal, the machining depth and material removal rate during deep groove machining using the tool with a 5° back inclined end face were respectively 7% and 14% higher than those produced using a standard one. Moreover, the lowest bottom height difference of 0.027 mm can be obtained when the step-over value was 8.2 mm, and a plane with a depth of 0.285 mm and a bottom height difference of 0.03 mm was fabricated using the tool with a 5° back inclined end face. 相似文献