全文获取类型
收费全文 | 242篇 |
免费 | 45篇 |
国内免费 | 21篇 |
专业分类
航空 | 147篇 |
航天技术 | 88篇 |
综合类 | 19篇 |
航天 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 11篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 21篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 7篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
排序方式: 共有308条查询结果,搜索用时 734 毫秒
301.
《中国航空学报》2022,35(11):401-415
The aeroengine casing ring forgings have complex cross-section shapes, when the conventional ultrasonic or phased array is applied to detect such curved surfaces, the inspection images always have low resolution and even artifacts due to the distortion of the wave beam. In this article, taking a type of aeroengine casing ring forging as an example, the Total Focusing Method (TFM) algorithms for curved surfaces are investigated. First, the Acoustic Field Threshold Segmentation (AFTS) algorithm is proposed to reduce background noise and data calculation. Furthermore, the Vector Coherence Factor (VCF) is adopted to improve the lateral resolution of the TFM imaging. Finally, a series of 0.8 mm diameter Side-Drilled Holes (SDHs) are machined below convex and concave surfaces of the specimen. The quantitative comparison of the detection images using the conventional TFM, AFTS-TFM, VCF-TFM, and AFTS-VCF-TFM is implemented in terms of data volume, imaging Signal-to-Noise Ratio (SNR), and defect echo width. The results show that compared with conventional TFM, the data volume of AFTS-VCF-TFM algorithm for convex and concave is decreased by 32.39% and 73.40%, respectively. Moreover, the average SNR of the AFTS-VCF-TFM is gained up to 40.0 dB, while the average 6 dB-drop echo width of defects is reduced to 0.74 mm. 相似文献
302.
303.
李真 《民用飞机设计与研究》2013,(Z2)
介绍了角元法、切割法和板元法三种飞机结构型材压损的计算方法。采用切割法和板元法对某型飞机机身长桁压损试验件进行了计算,结果表明切割法和板元法均为偏保守的计算方法,切割法偏保守4%以上,板元法偏保守11%以上。切割法的计算结果更接近试验结果,为提高机体结构效率,减轻结构重量,建议采用切割法进行工程计算。 相似文献
304.
目前对引射过程的分析模型还比较简单并且不准确。为提高引射分析模型精度,从引射过程的物理机制出发,以速度差异导致的质量交换作为一、二次流掺混过程的控制因素,以一次流动量覆盖整个法向截面时的参数剖面计算引射效果,建立了引射过程分析方法,并采用数值模拟和试验结果对方法进行了验证。结果表明:一、二次流掺混过程的计算模型能反映横截面上参数的变化趋势;当一次流处于过膨胀状态和轻度欠膨胀状态时,本方法计算的引射系数偏差在4.56%以内;当一次流处于严重欠膨胀状态时,在利用特征线法对截面静压进行校正以后,偏差在6%以内;以上精度均优于传统的Fabri模型。本方法还能准确地获得引射系统的临界背压,因此更适用于RBCC发动机这种有背压的应用场景。 相似文献
305.
This study proposed a force and shape collaborative control method that combined method of influence coefficients(MIC) and the elitist nondominated sorting genetic algorithm(NSGA-II) to reduce the shape deviation caused by manufacturing errors, gravity deformation,and fixturing errors and improve the shape accuracy of the assembled large composite fuselage panel. This study used a multi-point flexible assembly system driven by hexapod parallel robots. The proposed method simultaneously considers... 相似文献
306.
《中国航空学报》2022,35(9):1-18
As an indispensable component of the emerging 6G networks, Space-Air-Ground Integrated Networks (SAGINs) are envisioned to provide ubiquitous network connectivity and services by integrating satellite networks, aerial networks, and terrestrial networks. In 6G SAGINs, a wide variety of network services with the features of diverse requirements, complex mobility, and multi-dimensional resources will pose great challenges to service provisioning, which urges the development of service-oriented SAGINs. In this paper, we conduct a comprehensive review of 6G SAGINs from a new perspective of service-oriented network. First, we present the requirements of service-oriented networks, and then propose a service-oriented SAGINs management architecture. Two categories of critical technologies are presented and discussed, i.e., heterogeneous resource orchestration technologies and the cloud-edge synergy technologies, which facilitate the interoperability of different network segments and cooperatively orchestrate heterogeneous resources across different domains, according to the service features and requirements. In addition, the potential future research directions are also presented and discussed. 相似文献
307.
308.