全文获取类型
收费全文 | 271篇 |
免费 | 53篇 |
国内免费 | 56篇 |
专业分类
航空 | 214篇 |
航天技术 | 82篇 |
综合类 | 28篇 |
航天 | 56篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 18篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 24篇 |
2015年 | 9篇 |
2014年 | 21篇 |
2013年 | 23篇 |
2012年 | 14篇 |
2011年 | 28篇 |
2010年 | 22篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有380条查询结果,搜索用时 15 毫秒
1.
丁羟弹性体的交联密度 总被引:6,自引:1,他引:6
简要介绍了丁羟弹性体交联密度的表征参数、实验方法及其在丁羟推进剂研究中的实际应用。 相似文献
2.
对离散事件动态系统(DEDS)的仿真过程建立了包含中断事件集和驱动事件集的广义半马尔可夫过程(GSMP)模型,对参数的无穷小扰动所引起的系统状态转移时刻进行了扰动分析,最后,讨论了扰动分析所需要的可变换条件和样本性能函数的关系,并提出值得进一步研究的问题。 相似文献
3.
吕川 《北京航空航天大学学报》1992,(1):112-119
70年代初,Miele A等人提出SGRA方法用于优化飞行轨迹计算。但方法存在时间加权系数难于确定、长时间的飞行轨迹计算积分精度不易控制及要计算数字微分等不足。对此提出一改进梯度方法,并计算了某型战斗机从亚音速三维转弯升高到超音速的最短时间飞行轨迹。结果表明,本方法稳定有效,为解决飞机最快机动轨迹的优,乜提供了一种行之有效的手段。 相似文献
4.
5.
《中国航空学报》2016,(6):1762-1773
L-band digital aeronautical communication system 1 (L-DACS1) is a promising candi-date data-link for future air-ground communication, but it is severely interfered by the pulse pairs (PPs) generated by distance measure equipment. A novel PP mitigation approach is proposed in this paper. Firstly, a deformed PP detection (DPPD) method that combines a filter bank, correlation detection, and rescanning is proposed to detect the deformed PPs (DPPs) which are caused by mul-tiple filters in the receiver. Secondly, a finite impulse response (FIR) model is used to approximate the overall characteristic of filters, and then the waveform of DPP can be acquired by the original waveform of PP and the FIR model. Finally, sparse representation is used to estimate the position and amplitude of each DPP, and then reconstruct each DPP. The reconstructed DPPs will be sub-tracted from the contaminated signal to mitigate interference. Numerical experiments show that the bit error rate performance of our approach is about 5 dB better than that of recent works and is closer to interference-free environment. 相似文献
6.
《中国航空学报》2020,33(12):3176-3188
Numerical simulation and theoretical analysis were conducted to study the hysteresis inside scramjet isolator during the reciprocating process of back pressure variation. It is revealed that only a regular reflection is theoretically possible for two leading shocks when the inflow Mach number is greater than 2.0, and no hysteresis can occur in the transition between shock reflection types. Nevertheless, wall suction, gas injection, and background waves cause non-uniformity of the incoming flow and would make hysteresis possible. Besides the classical hysteresis in the transition between shock reflection, new kinds of hysteresis were found in both the deflection angle of separated boundary layer and the location of the shock train. Moreover, the occurrence of hysteresis in the deflection angle of the separated boundary layer is accompanied with the shock reflection hysteresis. In the case with background waves or gas injection, hysteresis in the starting position of leading shock was observed too. As back pressure decreases, the leading shock does not follow the same path as that as the back pressure increases, and it is anchored at the location where the background shock or the injection interacts with the leading shock. It is inferred that, if two strong adverse pressure gradient regions move towards and interact with each other, hysteresis will take place when they start to separate. 相似文献
7.
Mehdi Eshagh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The geoid can be used to validate the satellite gravity gradiometry data. Validation of such data is important prior to their downward continuation because of amplification of the data errors through this process. In this paper, the second-order radial derivative of Abel–Poisson’s formula is modified stochastically to reduce the effect of the far-zone geoid and generate the second-order radial derivative of geopotential at 250 km level. The numerical studies over Fennoscandia show that this method yields the gradients with an error of 10 mE and when the long wavelength of geoid is removed from the estimator and restored after the computations (remove–compute–restore) the error will be in 1 mE level. We name this method semi-stochastic modification. The best case scenario is found when the degree of modification of the integral formula is 200 and the long wavelength geoid to degree 100 is removed and restored. In this case the geoid should have a resolution of 15′ × 15′ and the integration should be performed over a cap size of 3°. 相似文献
8.
介绍了Fibonacci搜索方法应用于发动机性能优化中的原理,建立带两个出口面积、气流马赫数可变的引射器的涡喷发动机的总体性能计算模型,应用Fibonacci搜索方法在优化参数区间内对该发动机进行了最大推力、最低油耗、最低涡轮前温度模式的寻优.举例说明了Fibonacci搜索方法应用的具体过程.给出了不同高度、马赫数下的寻优结果.结果表明:最优目标性能满足的约束边界与飞行高度、马赫数密切相关.不同的飞行高度、马赫数对应了不同的最优控制策略.但不论飞行任务如何,根据该方法进行的优化控制所获得的目标性能是最佳的.该优化方法不仅适用于该类涡喷发动机,也为其他类型航空发动机的优化控制打下一定的基础. 相似文献
9.
10.
为了研究高主流湍流度下二次流密度比对涡轮导叶全气膜冷却特性的影响,使用热色液晶测量了在主流湍流度为15%,二次流密度比为1.0和1.5下三维涡轮导叶的气膜冷却效率和换热系数。二次流与主流质量流量比为7.0%和12.5%。结果表明:二次流密度比增大可以降低冷气射流的动量,小流量比工况下,在叶片前缘和压力面前半段,动量较低的二次流在高主流湍流度的影响下更易耗散,增大二次流密度比使冷却效率明显降低;大流量比工况下,二次流动量降低使气膜孔后区域冷气贴附性增强,气膜冷却效率和冷气覆盖效果均得到提升。小流量比工况下,二次流密度比增大对叶片表面换热的影响较小;大流量比工况下,二次流密度比增大使吸力面中弦区域和压力面后半段的平均换热系数比分别降低15%和25%。 相似文献