全文获取类型
收费全文 | 642篇 |
免费 | 148篇 |
国内免费 | 95篇 |
专业分类
航空 | 401篇 |
航天技术 | 150篇 |
综合类 | 129篇 |
航天 | 205篇 |
出版年
2023年 | 9篇 |
2022年 | 29篇 |
2021年 | 23篇 |
2020年 | 20篇 |
2019年 | 22篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 31篇 |
2015年 | 40篇 |
2014年 | 31篇 |
2013年 | 46篇 |
2012年 | 41篇 |
2011年 | 49篇 |
2010年 | 45篇 |
2009年 | 48篇 |
2008年 | 32篇 |
2007年 | 30篇 |
2006年 | 22篇 |
2005年 | 31篇 |
2004年 | 19篇 |
2003年 | 19篇 |
2002年 | 14篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 18篇 |
1996年 | 26篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1965年 | 2篇 |
排序方式: 共有885条查询结果,搜索用时 312 毫秒
521.
采用火星大气物理化学模型,求解带辐射源项的三维热化学非平衡N S方程,对探路者号火星探测器进入过程中的高温流场和热环境进行了数值模拟,分析了气体辐射与非平衡流场耦合效应对流场和热流的影响。结果表明:1)探路者号火星探测器流场热化学非平衡效应显著,CO 2 气体发生大规模离解,高度低至 28.5 km 仍存在热力学非平衡效应;2)热力学与化学非平衡效应的影响均与表面催化特性相关,完全催化热流要高于完全非催化热流50%以上;3)高温流场中的CO组分会产生较强的气体辐射加热,辐射热流与对流热流的比值为15%~45%,靠近肩部区域比值最大;4)气体辐射对非平衡流场的冷却效应使激波脱体距离减小;与非耦合方法相比,采用耦合方法得到的辐射热流降低约12%~25%。 相似文献
522.
523.
524.
An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted.The dynamic process of air-throttling ignition was explored systematically.The influences of throttling parameters,i.e.,throttling mass rate and duration,were investigated.When the throttling mass rate was 45% of the inflow mass rate,ambient ethylene could be ignited reliably.The delay time from ignition to throttling was about 45–55 ms.There was a threshold of throttling duration under a certain throttling mass rate.It was shorter than 100 ms when the throttling mass rate was 45%.While a 45%throttling mass rate would make the shock train propagate upstream to the isolator entry in about10–15 ms,four lower throttling mass rates were tested,including 30%,25%,20%,and 10%.All of these throttling mass rates could ignite ethylene.However,combustion performances varied with them.A higher throttling mass rate made more ethylene combust and produced higher wall pressure.Through these experiments,some aspects of the relationships between ignition,flame stabilization,combustion efficiency,and air-throttling parameters were brought to light.These results could also be a benchmark for CFD validation. 相似文献
525.
《模拟电子技术》课程是电子技术专业的一门核心主干课程,主要培养学生常用电子元器件的识别与检测,电子电路的分析、制作与测试等职业能力。通过对学生职业能力的培养,有力促进了教学模式、教学内容、教学方法、教学手段等诸多方面的改革,承载了职业院校的人才培养目标,取得了比较明显的教学成效。 相似文献
526.
Pressure sensing and schlieren imaging with high resolution and sensitivity are applied to the study of the interaction of single-pulse laser energy with bow shock at Mach 5. An Nd:YAG laser operated at 1.06 lm, 100 mJ pulse energy is used to break down the hypersonic flow in a shock tunnel. Three-dimensional Navier–Stokes equations are solved with an upwind scheme to simulate the interaction. The pressure at the stagnation point on the blunt body is measured and calculated to examine the pressure variation during the interaction. Schlieren imaging is used in conjunction with the calculated density gradients to examine the process of the interaction. The results show that the experimental pressure at the stagnation point on the blunt body and schlieren imaging fit well with the simulation. The pressure at the stagnation point on the blunt body will increase when the transmission shock approaches the blunt body and decrease with the formation of the rarefied wave. Bow shock is deformed during the interaction. Quasi-stationary waves are formed by high rate laser energy deposition to control the bow shock. The pressure and temperature at the stagnation point on the blunt body and the wave drag are reduced to 50%, 75% and 81% respectively according to the simulation. Schlieren imaging has provided important information for the investigation of the mechanism of the interaction. 相似文献
527.
528.
529.
530.