全文获取类型
收费全文 | 871篇 |
免费 | 192篇 |
国内免费 | 234篇 |
专业分类
航空 | 914篇 |
航天技术 | 120篇 |
综合类 | 164篇 |
航天 | 99篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 32篇 |
2021年 | 42篇 |
2020年 | 48篇 |
2019年 | 52篇 |
2018年 | 38篇 |
2017年 | 37篇 |
2016年 | 58篇 |
2015年 | 55篇 |
2014年 | 56篇 |
2013年 | 46篇 |
2012年 | 53篇 |
2011年 | 69篇 |
2010年 | 49篇 |
2009年 | 70篇 |
2008年 | 58篇 |
2007年 | 52篇 |
2006年 | 35篇 |
2005年 | 28篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 35篇 |
2001年 | 12篇 |
2000年 | 21篇 |
1999年 | 29篇 |
1998年 | 29篇 |
1997年 | 22篇 |
1996年 | 26篇 |
1995年 | 19篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 23篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 1篇 |
排序方式: 共有1297条查询结果,搜索用时 62 毫秒
991.
992.
《中国航空学报》2021,34(5):47-64
The friction is the considerable boundary condition in bulk metal forming. In this paper, the ring compression test was used to evaluate the friction coefficient and factor in Coulomb friction model and Tresca friction model for the plastic deformation of aluminum alloy AA5052. The micro-macro analysis method combining surface morphology and micro-texture was used to explore the friction behaviors in AA5052 cold forming process. In general, the magnitude (μ or m) of friction changes before and after a deformation threshold during ring compression. The maximum change rate of the magnitude (μ or m) before and after the deformation threshold is close to 18.5% under the present experimental conditions, and the change rate decreases with increasing loading speed. The lubrication using MoS2 is better than that using oil at lower speeds (0.15 mm/s, 1.5 mm/s), but the lubrications for MoS2 and oil are similar at higher speeds (15 mm/s). The surface roughness, three-dimensional topography, and surface texture of compressed ring have a sudden change around the deformation threshold, which deviate from the previous evolution trend. The increased friction after deformation threshold also promotes the formation of sufficient shear strain layer in the subsurface plane of the compressed ring, and then it hinders the formation of the typical deformation textures with β-oriented line and promotes the appearance of shear textures such as , and textures. 相似文献
993.
对原始的k-ω-γ转捩模式和"层流+转捩准则"模型进行了改进,在2种方法中分别增加了横流模态时间尺度和横流转捩准则用于预测横流失稳诱导转捩。通过对网格预处理可并行计算获得边界层外缘信息以及边界层内横流速度。采用不同雷诺数条件下的0°攻角尖锥以及HIFiRE-5外形对2种方法预测高超声速边界层转捩的性能进行了比较分析。研究结果表明,2种方法均能正确反映高超声速边界层转捩起始位置和转捩区长度随雷诺数的变化趋势,但不能捕捉转捩区热流峰值;"层流+转捩准则"模型计算得到的传热系数在全湍流区较k-ω-γ转捩模式偏高。对于同时存在流向不稳定和横流不稳定的HIFiRE-5外形,改进的k-ω-γ转捩模式和改进的"层流+转捩准则"模型相比于原始的模型均能更加准确地预测中心线两侧横流失稳诱导形成的转捩;对于中心线附近因速度剖面拐点引起的边界层转捩,"层流+转捩准则"模型由于与边界层厚度相关,预测得到的转捩位置较试验结果靠前,k-ω-γ转捩模式与试验结果吻合很好。 相似文献
994.
BLI效应下整流罩设计对翼型气动特性的影响 总被引:1,自引:0,他引:1
边界层吸入(BLI)效应对飞行器气动特性的影响比较显著,而整流罩的设计会进一步影响BLI效应下的翼型气动特性。为了揭示BLI效应下整流罩的主要设计参数对翼型气动特性的影响及其原因,本文采用计算流体力学(CFD)和Morris敏感度分析相结合的方法对该问题进行了详细研究,得到了整流罩主要设计参数对翼型气动特性的敏感度排序和耦合影响程度排序;对敏感度较高和耦合影响较大的参数进行了流动分析。结果表明:在巡航和起飞2种状态下,对气动系数影响相对较大的设计参数是整流罩最大厚度和进气边界弦向位置,整流罩最大厚度对翼型气动特性影响的主要原因是整流罩背风面会发生局部分离,且其还会改变阻力-流量系数曲线的趋势;整流罩最大厚度和进气边界弦向位置对翼型气动特性的耦合影响作用较强。 相似文献
995.
横流不稳定性转捩预测模型 总被引:1,自引:0,他引:1
由于Langtry和Menter提出的γ-Reθt边界层转捩模型只能预测流向的边界层转捩现象,因此继续改进该转捩模型使其具有横流不稳定性转捩的预测能力显得非常必要。通过对经典Falkner-Skan-Cooke (FSC)三维边界层相似解的理论分析和数值求解,结合Thwaites压力梯度因子与当地后掠角构建的函数关系来求解复杂构型的当地Hartree压力梯度因子βH以及形状因子H12,采用由试验数据标定的C1准则关系式获得横流转捩位移厚度雷诺数,从而建立能够对复杂构型进行横流不稳定性转捩预测的转捩判据。应用所建模型对30°前缘后掠角的ONERA-M6机翼和变前缘后掠角的DLR-F5机翼以及标准6:1椭球标模进行了横流不稳定转捩数值模拟,计算结果显示转捩位置均与试验数据吻合较好,证明了该模型的合理性和实用性。 相似文献
996.
997.
《中国航空学报》2021,34(12):251-264
Electrochemical Discharge Machining (ECDM) is potentially applicable for the fabrication of film-cooling holes. However, It is extremely difficult for the holes to achieve higher precision and machining quality owing to the working liquid diminish in the lateral machining gap. In this study, a non-metallic backing layer was proposed to overcome the diminish of working liquid, and the electrochemical reaming, as a post-processing method for ECDM, was used to further improve the machining accuracy and quality of the holes. First, the three-dimensional morphology of the melted pit of a paraffin backing layer was scanned to obtain the geometric parameters. Then, simulation analysis and experimental verification of auxiliary flushing by using the non-metallic backing layer were performed. The machining performance of the holes machined with electrochemical reaming based on non-metallic backing layer was confirmed by the observations of the surface topography of the hole wall and orifice, measurement of the orifice precision, and analysis of the element composition on the surface of the orifice wall. Finally, an optimum combination of machining parameters for electrochemical reaming is obtained through a process parameter optimization experiment. 相似文献
998.
《中国航空学报》2021,34(11):94-105
This paper reports an experimental study on the supersonic jet surface flow structure visualization and shear stress field measurement issuing from a rectangular nozzle with extended shelf. The evolution of the near-field surface flow structures with an increased Nozzle Pressure Ratio (NPR) is successfully captured by the surface oil flow, infrared detection technology, and the Shear-Sensitive Liquid Crystal Coating (SSLCC) technique. Results reveal that under smaller NPR, the wall flow structure is similar to that of a jet without the extended shelf i.e., clean jets, and this is caused by insufficient effect on the boundary layer. However, at higher amplitudes of NPR, there exists a significant effect of the boundary layer, as a near triangular separation forms on the trailing edge of the Mach stem due to the adverse pressure gradient, which is visualized for the very first time in this paper. Furthermore, the vector field of shear stress is measured quantitatively by SSLCC technique. Results shows that the magnitude of shear stress heightened with NPR increasing, and the directions of shear stress changes across the shock wave and expansion fans. In addition, surface streamlines measured by SSLCC is significantly consistent with the streamlines visualized using the oil flow technique. 相似文献
999.
1000.
《中国航空学报》2021,34(4):124-131
Via material erosion in wire electrical discharge machining (WEDM), recast layers form on the surfaces of workpiece. In addition, ultra fine Wire-EDM can be usually cut once. To reduce the thickness of the recast layer as much as possible, the wire electrical discharge-electrochemical machining (WEDCM) method was proposed, which is based on the micro conductivity of the dielectric and microelectrolytic characteristics by adjusting the no-load rate of the pulse in the machining process. Furthermore, a state discrimination and servo control system based on discharge current was designed. The experiment results of different no-load rates show that the electrolytic effects increase as the no-load rate increases, and the main machining process is spark discharge erosion with a no-load rate in the range of 10% to 80%. At 90% no-load rate, the amount of recast layer formation in the forward direction of the wire electrode is almost the same as that of electrolytic dissolution, and it can be practically processed without a recast layer. Compared with 10% no-load rate, the kerf width only increases by 7.5%. 相似文献