全文获取类型
收费全文 | 359篇 |
免费 | 70篇 |
国内免费 | 41篇 |
专业分类
航空 | 262篇 |
航天技术 | 111篇 |
综合类 | 42篇 |
航天 | 55篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 26篇 |
2014年 | 22篇 |
2013年 | 16篇 |
2012年 | 23篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 19篇 |
2008年 | 18篇 |
2007年 | 25篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有470条查询结果,搜索用时 15 毫秒
371.
《中国航空学报》2021,34(11):254-266
This study aimed to explore the evolution of flow lines and microstructures of M50-steel bearing ring and the anisotropy of its tensile mechanical properties after Multi-Stage Hot Forging (MSHF) and subsequent spheroidizing annealing (MSHFA). To this end, the present study mainly employed stereo microscopy, Optical Metallurgical Microscopy (OMM), Scanning Electron Microscopy (SEM), and Electron Backscatter Diffraction (EBSD) to characterize and analyze the workpiece at each processing stage of MSHF while performing microhardness measurement and uniaxial tensile experiment to test and analyze the mechanical properties of the workpiece. Macro-structure observation showed that the simulation results of flow lines at each stage were consistent with the experimental results. Microscopic observation showed that, after MSHF, deformation gradually became less significant along the outward radial direction of the bearing ring. After MSHFA, the microstructures of the bearing ring became uniform, whereas primary carbides did not dissolve. The mechanical properties were better in the axial direction (AD) than in the radial (RD) and circumferential directions (CD) after MSHF due to the smaller grain width. After MSHFA, the mechanical properties in the ADs and CDs were better than those in the RDs, which was due to the large cross-sectional area of carbides along the flow-line direction. 相似文献
372.
卫星导航定位设备的“生存”环境日益复杂、严峻,各类电子对抗、干扰欺骗十分激烈,人为干扰已成为卫星导航定位安全与对抗的重点。针对传统手段无法有效应对干扰复杂性、全面性、系统性的不足,本文在分析“OODA环”理论和实践转化的基础上,结合复杂环境下“干扰-抗干扰”的整体对抗过程,优化“OODA环”运行,将其与卫星导航定位安全与对抗应用进行耦合,提出基于“环境感知-筛选隔离-检测识别-效能评估-策略规划-对抗反制-回访反馈-再感知”的卫星导航定位安全与对抗不定向循环链路,并对拓展、映射的七个环节及关键技术进行分析、论证。通过引入“循环”和“不定向”两个概念,不仅实现了周期性外循环和部分环节内循环的嵌套迭代和导向性传输的运行机制;而且优化了内循环的自由度,使得各环节互联且独立、循环但不定向,有效增强了卫星导航定位安全与对抗的鲁棒性。本文的设计思路可加快实现循环链路的动态闭环,提高对抗的整体效能,在实践应用和技术论证中具有一定的参考价值。 相似文献
373.
374.
375.
外场金属支架在工作过程中需要进行应力监测,一般采用应变电测法,由于金属支架表面为曲面,可能会给测量带来影响。本文从计算分析和实验验证两个方面,探讨曲面对应变电测法测量结果的影响。最终得出由于金属支架曲率半径较大,应变片尺寸相对较小,曲面对测量产生的误差很小,可忽略,证明使用应变片法对金属支架进行应力监测是可行的。 相似文献
376.
377.
MEMS科氏力振动陀螺具有体积小、质量小、功耗低的优势,在高精度姿态控制、短时智能设备导航等领域具有广泛的应用前景。其中,零偏不稳定性优于0.1(°)/h的高性能MEMS陀螺是该领域的重要研究方向。目前,以环形拓扑结构为代表的科氏力振动陀螺成为该领域的主流技术方案之一。回顾了环形科氏力振动陀螺的发展历程,综述了近几年国内外研究机构围绕该类型陀螺开展的研究热点,总结了该类型陀螺的性能优势与面临的挑战,整理了该类型陀螺潜在的发展方向,为国内外同行开展该类型陀螺结构科学研究,提高MEMS科氏力振动陀螺性能提供了参考和借鉴。 相似文献
378.
在中国传统航天器中,通信系统格式通常各不相同。随着载荷越来越复杂,通信系统的格式往往需要重建,而且由于缺乏灵活性,会产生许多限制。对于SMILE卫星中的紫外极光成像仪(UVI)工程任务, 为与国际对接,提高数据处理的效率,设计实现了基于遥控遥测包应用标准(PUS)的通信与控制系统,根据通信与控制系统的构成及工作原理,PUS业务的选择和实现,对通信功能进行设计,按照PUS标准完成遥测遥控功能,并基于PUS业务提出故障诊断和处理方法。通过对系统进行集成测试,结果表明电控箱通信与控制系统工作稳定,能够完成指令处理、科学数据接收存储、故障诊断以及多种数据包发送,满足任务需求。 相似文献
379.
针对可重构航天器模块超近距离对接场景下特征点消失问题,提出一种可见光/激光的高精度相对位姿测量方法。该方法先通过可见光/激光组合对初始相对横滚角误差进行校零,完成粗校准环节;然后通过激光二维双镜反射法进行精确的相对位姿解算,获得高精度相对位姿数据。仿真结果表明,在现有技术条件下,该方法在模块相对距离在100cm内可不依赖视觉特征点,实现±1.2mm和±0.03°的相对位姿测量精度,为模块航天器对接后续的超近距离高精度位姿控制奠定基础。 相似文献
380.
Katarzyna Pajak Kamil Kowalczyk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1768-1780
In this paper, seasonal sea level variations have been determined at five locations in the Baltic Sea from satellite altimetry for the period 1993–2015. The results were compared to tide gauge water level data. Annual and semi-annual amplitudes have been investigated for both sea level anomalies and tide gauge water level. It was found that the two independent observations of sea level variations along the Polish coast are in good agreement both in terms of their annual and semi-annual amplitudes and their annual and semi-annual phases. The annual cycles in the sea level variations measured by altimetry and tide gauge reach maximum values at approximately the same month (November/December).Moreover, this article shows the differences between the annual and semi-annual amplitudes and phases in the sea level anomalies and water level data within the same time frame. The difference in the annual amplitudes between the satellite altimetry and the tide gauge results is between 0.33?cm and 1.53?cm. The maximum differences in the annual cycle of the sea level changes were found at the Swinoujscie station. The correlations between the original series and the calculated curves were determined, and the relationship between the amplitudes and the phases were investigated. The correlation between the annual variations observed from the two independent observation techniques is 0.92.To analyse the dynamics of the change in sea level, the linear trend was estimated from the satellite altimetry and tide gauge time series both in the original time series of the data and in the time series in which seasonal variations were removed. In addition, we calculated the estimated errors of regression and how many years’ worth of data are needed to obtain an accuracy of 0.1?mm per year. The estimated errors of regression showed that to get an accuracy of 0.1?mm per year, we need 100?years of data. 相似文献