全文获取类型
收费全文 | 662篇 |
免费 | 64篇 |
国内免费 | 193篇 |
专业分类
航空 | 299篇 |
航天技术 | 293篇 |
综合类 | 65篇 |
航天 | 262篇 |
出版年
2023年 | 12篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 35篇 |
2019年 | 49篇 |
2018年 | 68篇 |
2017年 | 33篇 |
2016年 | 25篇 |
2015年 | 39篇 |
2014年 | 72篇 |
2013年 | 51篇 |
2012年 | 54篇 |
2011年 | 46篇 |
2010年 | 44篇 |
2009年 | 45篇 |
2008年 | 49篇 |
2007年 | 40篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 16篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 37篇 |
1999年 | 21篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
排序方式: 共有919条查询结果,搜索用时 281 毫秒
841.
842.
文章介绍了碰撞程序和碎片程序,并进行了评价。前一个程序说明了碎片撞击的破裂特性;后一个程序给出了当一个空间物体进入碎片云时的撞击概率。 相似文献
843.
We have conducted a series of low-velocity impact experiments to understand the dispersion properties of fragments newly created by low-velocity impacts possible in space, especially in geostationary Earth orbit. The test results are utilized to establish a mathematical prediction model to be used in debris generation and propagation codes. Since the expected collision velocity between catalogued objects in geostationary Earth orbit shows a peak at a few hundreds meters per second, these impact experiments were conducted at a velocity range lower than 300m/s. As a typical structure of satellites in geostationary Earth orbit, thin aluminum honeycomb sandwich panels with carbon fiber reinforced plastics face sheets were prepared, while the projectile was a stainless steel ball of 9mm diameter. The data collected through these impact experiments have been re-analyzed based on the method used in the National Aeronautics and Space Administration (NASA) standard breakup model 1998 revision. The results indicate that the NASA standard breakup model derived from hypervelocity impacts could be applied to low-velocity collision possible in geostationary Earth orbit with some modifications. 相似文献
844.
Tethers are being proposed for a growing number of space applications. However, they may be particularly vulnerable to orbital debris and meteoroid impacts. In order to provide useful reference data for tether systems design, detailed analytical and numerical computations were carried out to assess the average impact rate of artificial debris and meteoroids. The specific geometric properties of tethers as debris targets, when compared to typical satellites, are discussed, and the results obtained are presented in tabular form, as a function of debris size and tether diameter.The computations were carried out for six circular orbits, spanning three altitudes (600, 800 and 1000km) and two inclinations (30° and 50°). Tether diameters in between 1mm and 2cm and debris larger than 0.1mm were considered in the analysis. The collision risk of tethers with spacecraft and upper stages in orbit was estimated as well.In the debris interval and orbital regimes considered, artificial debris represent the dominant contributor to the impact rate. At 600km and in the 0.1–10mm size range, the meteoroid and orbital debris impact rates are still comparable; however, at higher altitudes and in the 1–10cm size range, meteoroids contribute 20–30 times less to the collision probability.The results obtained confirm that for single-strand tethers in low Earth orbit the probability to be severed by orbital debris and meteoroid impacts is quite significant, making necessary the adoption of innovative designs for long duration missions. 相似文献
846.
介绍NASA为预示空间碎片环境未来发展趋势所建立的空间模型(包括通用模型和专用模型)及其适用范围。通用模型包括ORDEM96、BUMPERII、EVOLVE、CHAIN和DAS;专用模型包括NASA碎片模型、弹道限制方程和轨道计算模型等。这些模型不仅可用于评估当前的碎片环境,而且还可评估载人与无人航天器在轨运行时的碎片碰撞风险。 相似文献
847.
848.
刘宇 《北京航空航天大学学报》1998,24(6):629-632
采用全隐格式的矢通量分裂算法,在通用曲线坐标系内求解三维无因次抛物化强守恒型N-S(Navier-Stokes)方程.所建立的计算程序,可计算较为复杂边界的三维流场,如求解亚、跨、超音速共存的流场,分区模拟内外流共存流动及其混合剪切尾流.给出了一轴对称亚跨超音速喷管内流场的计算结果,包括计算网格,流矢分布,压力、温度和马赫数等值线分布.也给出了一喷管内外流及其混合尾流的计算结果,包括计算网格,流矢分布,无因次压力、密度和温度等值线分布. 相似文献
849.
850.
定子磁场定向控制的异步电机无速度传感器低成本控制系统 总被引:2,自引:0,他引:2
开发了基于高性价比DSPMC56F8013的低成本异步电机控制平台,研究了一种基于定子磁场定向的异步电机无速度传感器控制算法。该算法结构简单,易于实现,对电机参数依赖性小。文中提出定子磁链校正因子,用于补偿低速运行时由于一阶低通滤波器的使用而造成的定子磁链观测误差。新颖的转速调节器,保证电机在动态过程中以最大转矩运行。系统仿真和原理样机的试验结果表明,整个控制系统具有良好的动态和稳态性能。 相似文献