全文获取类型
收费全文 | 321篇 |
免费 | 141篇 |
国内免费 | 24篇 |
专业分类
航空 | 270篇 |
航天技术 | 120篇 |
综合类 | 17篇 |
航天 | 79篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 18篇 |
2012年 | 19篇 |
2011年 | 23篇 |
2010年 | 25篇 |
2009年 | 25篇 |
2008年 | 13篇 |
2007年 | 44篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 15 毫秒
431.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013,52(2):262-271
In this paper we review the lunar laser ranging conducted by the laser altimeter (LALT) on board the KAGUYA lunar explorer (2007–2009). Five aspects of LALT measurements are described: (1) General operational history, (2) Laser shot and data statistics, (3) Revisions to LALT topographic data, (4) Variations in laser output energy, and (5) Peak height analysis of laser echo pulses. LALT was able to range to the lunar surface despite some troubles with respect to laser output energy in the middle of the KAGUYA mission. The time series topographic data set was revised (Ver. 2) by incorporating new lunar gravity model based on KAGUYA and other historical lunar satellite’s orbit data, along with other improvements, for example by incorporating the accurate position of the laser collimator on board the KAGUYA; however, more than half of the acquired range data could not be converted properly due to problems with orbit accuracy during the extended phase of the mission. The spherical harmonic coefficients and the basic lunar figure parameters derived from LALT_LGT_TS agree very well with LRO-LOLA and the Chang’E-1 LAM model. It is possible that partial failure to the laser diode was responsible for the gradual degradation of laser power (0.835 mJ per million shots) and the rapid decrease that occurred over April 9–14, 2008. The laser power also proved to be extremely sensitive to the temperature of the laser oscillator. The peak height ratio – that is peak height telemetry data divided by calculated ratio – is about 19% on average using the mean slope and albedo data from LALT and Spectral Profiler on KAGUYA space craft, respectively, which suggests the performance of peak height measurement is more than 1/5 for more than 70 km altitude, if compared with calculated one. The peak height ratio may be better if we take the effect of small scale topography within a footprint into account. 相似文献
432.
433.
介绍了一个由工业控制机和智能测量仪器组成的自动化检定系统,采用定角测时法,利用高精度光学棱体和激光测角技术,实现了对高精度低速回转台的自动化检定。阐述了自动化检定系统的组成、转速检定原理、软件设计和数据处理方法,并给出了实际应用的结果。 相似文献
434.
Wendong Meng Haifeng Zhang Peicheng Huang Jie Wang Zhongping Zhang Ying Liao Yang Ye Wei Hu Yuanming Wang Wanzhen Chen Fumin Yang Ivan Prochazka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
High-precision time synchronization between satellites and ground stations plays the vital role in satellite navigation system. Laser time transfer (LTT) technology is widely recognized as the highest accuracy way to achieve time synchronization derived from satellite laser ranging (SLR) technology. Onboard LTT payload has been designed and developed by Shanghai Astronomical Observatory, and successfully applied to Chinese Beidou navigation satellites. By using the SLR system, with strictly controlling laser firing time and developing LTT data processing system on ground, the high precise onboard laser time transfer experiment has been first performed for satellite navigation system in the world. The clock difference and relative frequency difference between the ground hydrogen maser and space rubidium clocks have been obtained, with the precision of approximately 300 ps and relative frequency stability of 10E−14. This article describes the development of onboard LTT payload, introduces the principle, system composition, applications and LTT measuring results for Chinese satellite navigation system. 相似文献
435.
D.A. Liedahl A. Rubenchik S.B. Libby S. Nikolaev C.R. Phipps 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Among the approaches to the proposed mitigation and remediation of the space debris problem is the de-orbiting of objects in low Earth orbit through irradiation by ground-based high-intensity pulsed lasers. Laser ablation of a thin surface layer causes target recoil, resulting in the depletion of orbital angular momentum and accelerated atmospheric re-entry. However, both the magnitude and direction of the recoil are shape dependent, a feature of the laser-based remediation concept that has received little attention. Since the development of a predictive capability is desirable, we have investigated the dynamical response to ablation of objects comprising a variety of shapes. We derive and demonstrate a simple analytical technique for calculating the ablation-driven transfer of linear momentum, emphasizing cases for which the recoil is not exclusively parallel to the incident beam. For the purposes of comparison and contrast, we examine one case of momentum transfer in the low-intensity regime, where photon pressure is the dominant momentum transfer mechanism, showing that shape and orientation effects influence the target response in a similar, but not identical, manner. We address the related problem of target spin and, by way of a few simple examples, show how ablation can alter the spin state of a target, which often has a pronounced effect on the recoil dynamics. 相似文献
436.
激光自动跟踪空间坐标测量系统的发展(一) 总被引:3,自引:0,他引:3
介绍了近十年来国外在激光跟踪空间坐标动态测量方面的研究成果,它集多种现代先进技术于一体,目前多应用于机器人领域,但应用的前景非常广阔,代表了计量学新的发展方向。下面将介绍球坐标法,三角法,多边法等多种测量方法,讨论单站,多站(双站、三站和四站)的测量原理及系统结构,还分析了各系统可能或已经达到到的精度及优缺点。 相似文献
437.
Hong Wang Yaowu Shi Shuili Gong 《航空制造技术》2004,(Z1):48-50
探讨了激光深熔焊过程中焊接熔池流体流动的各种驱动力,分析了熔池流动热边界层和固液界面粘性边界层的作用,研究了激光小孔出口的等离子体焰流对熔池Marangoni流的影响. 相似文献
438.
介绍容错设计思想在由多路激光干涉仪构成的柔性坐标测量系统中的应用。由于采用了硬件冗余、软件冗余等技术,不但使该测量系统具有自我标定的能力,而且可恢复因测量过程中“丢光”现象而造成的干涉仪丢失的测量数据。并用三路单轴跟踪系统实现了二维坐标测量。 相似文献
439.
440.
激光二维切割工艺的优化 总被引:1,自引:0,他引:1
主要阐述了如何选取合适的激光二维切割加工工艺参数,如:激光器工作气体、激光器功率大小、光斑模式情况、辅助气体、激光焦点离工件的距离、加工板材性质及厚度、二维CAD/CAM控制系统等,以便达到最佳的切割质量及最少的气体消耗。 相似文献