全文获取类型
收费全文 | 5307篇 |
免费 | 1545篇 |
国内免费 | 968篇 |
专业分类
航空 | 5285篇 |
航天技术 | 472篇 |
综合类 | 679篇 |
航天 | 1384篇 |
出版年
2024年 | 10篇 |
2023年 | 63篇 |
2022年 | 194篇 |
2021年 | 212篇 |
2020年 | 208篇 |
2019年 | 192篇 |
2018年 | 177篇 |
2017年 | 216篇 |
2016年 | 245篇 |
2015年 | 262篇 |
2014年 | 300篇 |
2013年 | 266篇 |
2012年 | 339篇 |
2011年 | 386篇 |
2010年 | 311篇 |
2009年 | 336篇 |
2008年 | 310篇 |
2007年 | 317篇 |
2006年 | 280篇 |
2005年 | 283篇 |
2004年 | 222篇 |
2003年 | 216篇 |
2002年 | 216篇 |
2001年 | 185篇 |
2000年 | 211篇 |
1999年 | 202篇 |
1998年 | 174篇 |
1997年 | 203篇 |
1996年 | 226篇 |
1995年 | 154篇 |
1994年 | 175篇 |
1993年 | 154篇 |
1992年 | 139篇 |
1991年 | 100篇 |
1990年 | 104篇 |
1989年 | 99篇 |
1988年 | 108篇 |
1987年 | 23篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有7820条查询结果,搜索用时 328 毫秒
1.
《中国航空学报》2020,33(3):879-892
Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine (LPT) cascade. All of the measurements were conducted in both the presence and absence of incoming wakes, and numerical analysis was performed to elucidate the flow mechanism. With increasing Reynolds number, the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers, leading to a lower blade loading near the leading edge and suppression of the Pressure Side (PS) leg of the horseshoe vortex. However, the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side (SS) separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers. Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000. In contrast, at the high Reynolds number of 100,000, the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes, and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade. 相似文献
2.
陈伟 《沈阳航空工业学院学报》2002,19(1):21-23
本文分析了在塑料熔体充满型腔的过程中,流动阻力及能量损失产生的形式和物理原因,进而讨论了对塑料制件成型及凝固过程中的影响。并提出降低影响的措施。 相似文献
3.
4.
ADI方法求解完全跨声速非定常小扰动方程 总被引:1,自引:1,他引:0
本文修改了Whitlow的ADI格式,以便求解另一变形的完全跨声速小扰动方程。本文给出的NACA64A006和NACA0012翼型的非定常跨声速流动的计算结果与其它数值结果和实验结果的比较表明本文格式是合理的且便于实际应用的。 相似文献
5.
Steven D. Howe 《Space Policy》2001,17(4):275-283
The potential benefits to humankind of space exploration are tremendous. Space is not only the final frontier but is also the next marketplace. The orbital space above Earth offers tremendous opportunities for both strategic assets and commercial development. The critical obstacle retarding the use of the space around the Earth is the lack of low cost access to orbit. Further out, the next giant leap for mankind will be the human exploration of Mars. Almost certainly within the next 30 years, a human crew will brave the isolation, the radiation, and the lack of gravity to walk on and explore the Red planet. Both of these missions will change the outlook and perspective of every human being on the planet. However, these missions are expensive and extremely difficult. Chemical propulsion has demonstrated an inability to achieve orbit cheaply and is a very high-risk option to accomplish the Mars mission. An alternative solution is to develop a high performance propulsion system. Nuclear propulsion has the potential to be such a system. The question will be whether humanity is willing to take on the challenge. 相似文献
6.
介绍自行研制的VKM—5型立式捏合机的构造及工作原理,详述了该机采用液压传动和气动元件进行位置检测以及气、电、液安全联锁的特点,并说明与卧式捏合机对比试验情况。 相似文献
7.
A Novel Onboard-gateway-based Mechanism to Improve TCP Performance in Aeronautical Satellite Networks 总被引:1,自引:1,他引:0
GU Ming ZHANG Jun 《中国航空学报》2007,20(3):260-265
The IP-based networks on aircraft serve to support Internet services via satellites. However, in aeronautical satellite hybrid net- works,the TCP protocol performance often deteriorates due to improper decreases and slow recovery of the congestion window. This paper proposes a window size determination and notification mechanism, onboard-gateway-based mechanism (OGBM), which is based on the onboard gateway in the networks on aircraft. A cross-layer approach is adopted by the onboard gateway to obtain the satellite link bandwidth information. And then, by the gateway, through changing the receiver’s advertised window field in ACK packets, TCP sources are notified of the window size of each TCP source calculated on the ground of bandwidth delay product and flow numbers. The mechanism is able to avoid improper changes of TCP window and serve multiple users. Simulation results show that the mechanism with the fairness index close to 1 improves TCP performance in aeronautical satellite networks. 相似文献
8.
9.
10.
根据工作实践研究了固体发动机切线照相无损检测中黑度分布、散射线防治、象质计使用、检测概率计算、脱粘临界值确定等技术问题. 相似文献