全文获取类型
收费全文 | 340篇 |
免费 | 99篇 |
国内免费 | 48篇 |
专业分类
航空 | 300篇 |
航天技术 | 89篇 |
综合类 | 31篇 |
航天 | 67篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 19篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 20篇 |
2013年 | 19篇 |
2012年 | 21篇 |
2011年 | 28篇 |
2010年 | 20篇 |
2009年 | 26篇 |
2008年 | 22篇 |
2007年 | 28篇 |
2006年 | 25篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 15篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有487条查询结果,搜索用时 15 毫秒
451.
四轴端刀无干涉刀位点计算 总被引:3,自引:0,他引:3
针对四坐标端刀加工,提出一种新的干涉检测和排除方法.该方法基于曲面的多面体模型,用解析法判断刀具与曲面是否干涉,并给出排除干涉的计算公式.最后给出四轴端刀无干涉刀位点计算的算法,实例表明该方法稳定高效. 相似文献
452.
风洞实验中经常遇到利用多台仪器测量同一物理量的问题,而各子系统之间的一致性是影响测试准确度的重要因素。就子系统之间的误差对测压实验结果的影响进行了分析并介绍了统校方法。结果表明:子系统本身不确定度比较高,一般不低于0.1%,而多个子系统的分散度相对比较差。因此,利用多套子系统同时测量某一物理量时,有必要进行系统统校;经过统校并作适当处理后,系统的准确度明显提高,实验结果也更趋合理。 相似文献
453.
T. Miyachi M. Fujii N. Hasebe G. Kuraza K. Mori O. Okudaira N. Yamashita S. Sasaki T. Iwai K. Nogami H. Matsumoto H. Ohashi H. Shibata S. Minami S. Takechi T. Onishi E. Grün R. Srama N. Okada 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(7):1147-1151
The detector characteristics of a pentagonal element were studied by colliding it with hypervelocity micro-particles. A charge-sensitive amplifier was developed for the element of its capacitance ∼10 nF. The output amplitudes were expressed as a linear function of the momentum at collision. Empirical formulas obtained from on-ground experiments could be used for the calibration of the detector. The pentagonal element was potential to measure the momentum during collision from the output amplitude. A set of electrodes on the surface was used to confirm the measurement of the coordinates at collision. A possible application of this pentagonal element on a real-time dust detector was discussed. 相似文献
454.
C^4ISR系统评估环境的构建对C^4ISR系统效能评估至关重要。本文深入分析了C^4ISR系统特点和评估需求,提出了效能评估思路,设计了基于HLA的评估环境基本构架和C^4ISR系统模型体系结构,该研究对C^4ISR系统鉴定具有重要现实意义。 相似文献
455.
Swantje Hauschild Svantje Tauber Beatrice Lauber Cora S. Thiel Liliana E. Layer Oliver Ullrich 《Acta Astronautica》2014
Dating back to the Apollo and Skylab missions, it has been reported that astronauts suffered from bacterial and viral infections during space flight or after returning to Earth. Blood analyses revealed strongly reduced capability of human lymphocytes to become active upon mitogenic stimulation. Since then, a large number of in vitro studies on human immune cells have been conducted in space, in parabolic flights, and in ground-based facilities. It became obvious that microgravity affects cell morphology and important cellular functions. Observed changes include cell proliferation, the cytoskeleton, signal transduction and gene expression. This review gives an overview of the current knowledge of T cell regulation under altered gravity conditions obtained by in vitro studies with special emphasis on the cell culture conditions used. We propose that future in vitro experiments should follow rigorous standardized cell culture conditions, which allows better comparison of the results obtained in different flight- and ground-based experiment platforms. 相似文献
456.
Sensing snow height and surface temperature variations in Greenland from GPS reflected signals 总被引:1,自引:0,他引:1
Shuanggen Jin Nasser Najibi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The in situ measurements of snow surface temperature (SST) and snow height (SH) are very difficult with high costs, particularly in Greenland Ice Sheet (GrIS). Since the snow depth variations coupling with surface temperature are related to GPS multipath, it is possible to estimate the snow depth and surface air temperature variations by incorporating GPS-Reflectometry (GPS-R). In this paper, the reflected signals from ground GPS receivers are used to sense the SST and SH variations based on the thermophysical behavior and variations of snow layer from April to June 2010 at SMM1 site and from March to December 2010 at MARG site in Greenland. The results show that the mean daily changes in the ionospheric geometrical-free linear combination (GPS-L4) of dual-frequency GPS signals are related to daily SST and SH variations. The nonparametric bootstrapping model in direct (forward) and inverse models are developed and applied to estimate the SST and SH variations. The mean biases of SST and SH estimates are 0.18 °C and 0.23 m at SMM1 site, respectively, and 3.8 °C and 0.13 m at MARG site, respectively. 相似文献
457.
月球表面没有磁场的保护,粒子辐射是人类在月球活动的重要风险要素。概述了月球的辐射环境以及辐射来源,并介绍了月球探测的现状,特别提及了近年来几个较为典型的月球辐射探测实例及其探测结果;介绍了我国“嫦娥4号”上搭载的月表中子与辐射剂量探测仪(Lunar Lander Neutron&Dosimetry,LND)的科学目标及其技术指标。LND的科学目标主要包括:载人登月辐射剂量的测量、月球南极艾特肯盆地水含量的测量、艾特肯盆地FeO含量的测量,以及为日球层科学的研究提供依据。 相似文献
458.
459.
460.
一体化的指挥与控制系统(C4ISR)作为网络中心站的核心,在2003年的伊拉克战争中初步展示了其作战能力。信息安全是保证信息获取、信息传输、信息处理和信息使用等多个环节畅通无阻的有力保障。本文综合论述了美军在C4ISR信息安全方面的政策、网络防御及技术应用。 相似文献