全文获取类型
收费全文 | 206篇 |
免费 | 25篇 |
国内免费 | 113篇 |
专业分类
航空 | 161篇 |
航天技术 | 72篇 |
综合类 | 25篇 |
航天 | 86篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 3篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 16篇 |
2012年 | 19篇 |
2011年 | 15篇 |
2010年 | 23篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 234 毫秒
301.
跨声速叶栅抽吸流、激波以及分离流相干效应 总被引:3,自引:3,他引:0
以某高负荷、跨声速压气机叶栅为研究对象,应用数值模拟手段探讨通过抽吸控制激波从而控制附面层发展的可行方法。研究结果表明:随着抽吸量的增加吸力面马赫数峰值提高,激波损失增加,同时使得吸力面马赫数峰值点位置后移,附面层分离减弱,分离的减弱所导致的总压恢复系数增加量要远大于激波强度增加所导致的总压恢复系数减小量;抽吸对叶栅性能改善存在一个最佳抽吸量1.2%;在保证叶栅静压压升不变的前提下,相对于未抽吸条件1.2%抽吸使得叶栅总压恢复系数提高10%,扩散因子降低18%,落后角减小5°;通道激波后实施附面层小流量抽吸不能有效改善附面层内部流动参数,当实现前缘入射斜激波投射点位于通道激波上游时,叶表附面层流动得到较大改善。 相似文献
302.
光学头罩超声速绕流流场光学传输效应风洞试验研究 总被引:3,自引:0,他引:3
在Ma=3连续超声速风洞中,开展了光学头罩绕流流场光学传输效应的风洞模拟试验方法研究,进行了现场振动测量与隔离,研制了专用试验装置,采用哈特曼传感器和剪切干涉仪两种手段进行了光学传输效应的试验测量。试验中,针对试验装置各部分的不同组合状态,进行了大量的测试,研究了试验装置有效性以及试验数据重复性,着重分析了探测光束的PV值与RMS值。结果表明:导流板可明显抑制风洞洞壁边界层干扰,试验装置与方法可行,对于连续式风洞中模型绕流流场光学传输效应测试有一定参考价值。 相似文献
303.
Plume aerodynamic effects of cushion engine in lunar landing 总被引:1,自引:0,他引:1
During the second period of China "Tanyue" Project, the explorer will softland on the moon. The cushion engines are used to decelerate the explorer and reduce the impact on the lunar ground. It is necessary to study its plume effects on the explorer component. The self-developed PWS (Plume WorkStation) software based on direct simulation Monte Carlo (DSMC) method is used to simulate the plume effects of two 150 N engines. Due to the complex structure of the explorer, PWS uses a decoupling method to treat the boundary mesh, which mainly interacts with simulation particles, and has no relation with the computational grids. After the analytical expressions of plane surfaces and curved surfaces of each boundary block are given, the particle position within or without the boundary blocks can be easily determined. Finally the 3D plume field of two 150 N engines is simulated. The pressure, temperature and velocity distributions of plume field are clearly presented by three characteristic slices. The aerodynamic effects on the explorer bottom, the landfall legs and antenna are separately shown. The compression influence on the plume flow of four landfall legs can be observed. 相似文献
304.
分析了矩形及国影节流孔的流量特性。介绍了伺服阀制造过程中所需各种流量测试时的油路连接和流量关系式,并对差压式流量计的特点及在伺服阀制造工艺中的实际应用作了叙述。 相似文献
305.
Gerhard Drolshagen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(7):1123-1131
When the impact risk from meteoroids and orbital debris is assessed the main concern is usually structural damage. With their high impact velocities of typically 10–20 km/s millimeter or centimeter sized objects can puncture pressure vessels and other walls or lead to destruction of complete subsystems or even whole spacecraft. Fortunately chances of collisions with such larger objects are small (at least at present). However, particles in the size range 1–100 μm are far more abundant than larger objects and every orbiting spacecraft will encounter them with certainty. Every solar cell (8 cm2 area) of the Hubble Space Telescope encountered on average 12 impacts during its 8.25 years of space exposure. Most were from micron sized particles. 相似文献
306.
《中国航空学报》2016,(6):1618-1625
A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing (VCA) model is briefly reviewed, which is based on the equivalent plastic zone concept. In this method, the retardation phenomenon is explained by the crack closure level variation, which is derived from the interactions between forward and reverse plastic zones ahead of the crack tip. As a comparison, the Forman equation in conjunction with the Willenborg model is also reviewed. The retardation phenomenon is described by directly modifying the stress intensity factor. It is known that the large plastic zone created by the overload can decelerate the fatigue crack growth rate until the crack grows beyond this region. A relationship between the plastic zone and the modified stress intensity factor is developed, which is a mathematical fitting equation instead of physical-based formulation. The experimental data in aluminum alloys are used to val-idate these two models. Overall, good agreement is observed between the model predictions and the testing data. It is noted that the approach based on modified VCA model can give more accurate prediction curves than the Willenborg model. 相似文献
307.
宋福铁 《郑州航空工业管理学院学报(管理科学版)》2006,24(4):61-64
采用多元Granger因果测试模型和1980~2003年的相关数据实证检验我国国债的宏观经济效应。实证结果表明,我国国债融资实际上并未对宏观经济产生显著影响。这主要是因为我国利用国债融资的时间较短,国债的宏观经济效应尚未显现;利用国债融资的多为基础设施项目,周期较长,真正发挥效应尚需一段时间;尤其是国债资金管理不到位,使得国债融资未对实体经济作出积极贡献。因此,政府当务之急是完善国债投资管理和审批体制,增加国债资金运用的透明度,加大对国债资金管理和使用的监督和检查力度,提高国债项目的投资效益。 相似文献
308.
奥运会对北京经济的挤出效应 总被引:16,自引:0,他引:16
阎为民 《郑州航空工业管理学院学报(管理科学版)》2004,22(1):27-29
举办2008年奥运会,是发展北京经济强有力的助推器,对北京经济具有巨大的提升作用.然而,奥运对北京经济同时也具有不利的影响--挤出效应.文章具体分析了奥运对北京经济的挤出效应,以便更好的利用这次机遇促进北京经济的进一步发展. 相似文献
309.
310.