全文获取类型
收费全文 | 158篇 |
免费 | 34篇 |
国内免费 | 18篇 |
专业分类
航空 | 115篇 |
航天技术 | 51篇 |
综合类 | 24篇 |
航天 | 20篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 17篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 14篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1984年 | 3篇 |
排序方式: 共有210条查询结果,搜索用时 17 毫秒
1.
《中国航空学报》2020,33(4):1192-1205
Over the last few decades, the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient. To this end, two kinds of brush-labyrinth seals for the bristle pack element installed upstream of the labyrinth teeth named BSU and installed downstream of the labyrinth teeth called BSD were used to investigate the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals. Using the numerical model combining the porous medium model and the whirling rotor method, the rotordynamic characteristics of the BSU and BSD at various operating conditions including four kinds of pressure ratios, five kinds of inlet preswirl speeds and four kinds of rotor spinning speeds were conducted. The obtained results show that the effects of operating conditions on rotordynamic coefficients for the different seal configurations are different. The direct stiffness, cross-coupled stiffness and direct damping of the BSU are lower than those of the BSD. The rotordynamic coefficients of the BSU are more insensitive to the operating conditions variation. From the perspective of the seal stability, the BSU is a better brush-labyrinth seal configuration at high pressure ratio, high positive preswirl or high rotor spinning speed conditions. While in the case of low pressure ratio, low positive preswirl or low rotor spinning speed conditions, the BSD is a better choice. 相似文献
2.
S.V. Chalov H.J. Fahr 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this paper we start from the most recently observed fact that the solar wind plasma after passage over the termination shock is still supersonic with a Mach number of about 2. To explain this unexpected phenomenon and to predict the evolution of properties of the downstream plasma flow we here consider a two-fluid proton plasma with pick-up protons as a separate suprathermal, second proton fluid. We then formulate a self-consistent system of hydrodynamical conservation equations coupling the two fluids by dynamical and thermodynamical coupling terms and taking into account the effects of newly incorporated protons due to charge exchange with the H-atoms in the heliosheath. This then allows us to predict that in the most probable case the solar wind protons will become subsonic over a distance of about 30 AU downstream of the shock. As we can also show, it may, however, happen that the plasma mixture later again reconverts to a supersonic signature and has to undergo a second shock before meeting the heliopause. 相似文献
3.
新型的多孔材料以其重量轻、强度高备受航天工程设计人员的亲睐,尤其是作为隔热材料使用,可以说是航天工程热防护系统的热门材料.多孔介质在辐射热传递方面具有吸收发射和散射的功能,这些功能在其接受外来热流的作用下,于内部达到热能量平衡,求解这一平衡方程就可以求出辐射热流在材料中的分布.由于求解这一方程的困难,许多学者对材料特性... 相似文献
4.
5.
李美容 《长沙航空职业技术学院学报》2007,7(3):83-86
新闻报料具有扩大新闻源、丰富新闻内容、增强新闻地方化色彩、强化媒体舆论监督作用等积极作用,但也弱化了新闻的真实性原则、媒体社会功能与社会责任感,应从建立科学规范的报料核实体制,加强通讯员队伍与新闻线人的建设与培养,加强对媒体及媒体市场的管理等方面来规范新闻报料。 相似文献
6.
S. W. Kahler 《Space Science Reviews》2007,129(4):359-390
Electrons with near-relativistic (E≳30 keV, NrR) and relativistic (E≳0.3 MeV) energies are often observed as discrete events in the inner heliosphere following solar transient activity. Several
acceleration mechanisms have been proposed for the production of those electrons. One candidate is acceleration at MHD shocks
driven by coronal mass ejections (CMEs) with speeds ≳1000 km s−1. Many NrR electron events are temporally associated only with flares while others are associated with flares as well as with
CMEs or with radio type II shock waves. Since CME onsets and associated flares are roughly simultaneous, distinguishing the
sources of electron events is a serious challenge. On a phenomenological basis two classes of solar electron events were known
several decades ago, but recent observations have presented a more complex picture. We review early and recent observational
results to deduce different electron event classes and their viable acceleration mechanisms, defined broadly as shocks versus
flares. The NrR and relativistic electrons are treated separately. Topics covered are: solar electron injection delays from
flare impulsive phases; comparisons of electron intensities and spectra with flares, CMEs and accompanying solar energetic
proton (SEP) events; multiple spacecraft observations; two-phase electron events; coronal flares; shock-associated (SA) events;
electron spectral invariance; and solar electron intensity size distributions. This evidence suggests that CME-driven shocks
are statistically the dominant acceleration mechanism of relativistic events, but most NrR electron events result from flares.
Determining the solar origin of a given NrR or relativistic electron event remains a difficult proposition, and suggestions
for future work are given. 相似文献
7.
In this paper we review the possible mechanisms for production of non-thermal electrons which are responsible for the observed
non-thermal radiation in clusters of galaxies. Our primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering,
that produce hard X-ray emission. We first give a brief review of acceleration mechanisms and point out that in most astrophysical
situations, and in particular for the intracluster medium, shocks, turbulence and plasma waves play a crucial role. We also
outline how the effects of the turbulence can be accounted for. Using a generic model for turbulence and acceleration, we
then consider two scenarios for production of non-thermal radiation. The first is motivated by the possibility that hard X-ray
emission is due to non-thermal Bremsstrahlung by nonrelativistic particles and attempts to produce non-thermal tails by accelerating
the electrons from the background plasma with an initial Maxwellian distribution. For acceleration rates smaller than the
Coulomb energy loss rate, the effect of energising the plasma is to primarily heat the plasma with little sign of a distinct
non-thermal tail. Such tails are discernible only for acceleration rates comparable or larger than the Coulomb loss rate.
However, these tails are accompanied by significant heating and they are present for a short time of <106 years, which is also the time that the tail will be thermalised. A longer period of acceleration at such rates will result
in a runaway situation with most particles being accelerated to very high energies. These more exact treatments confirm the
difficulty with this model, first pointed out by Petrosian (Astrophys. J. 557:560, 2001). Such non-thermal tails, even if possible, can only explain the hard X-ray but not the radio emission which needs GeV or
higher energy electrons. For these and for production of hard X-rays by the inverse Compton model, we need the second scenario
where there is injection and subsequent acceleration of relativistic electrons. It is shown that a steady state situation,
for example arising from secondary electrons produced from cosmic ray proton scattering by background protons, will most likely
lead to flatter than required electron spectra or it requires a short escape time of the electrons from the cluster. An episodic
injection of relativistic electrons, presumably from galaxies or AGN, and/or episodic generation of turbulence and shocks
by mergers can result in an electron spectrum consistent with observations but for only a short period of less than one billion
years. 相似文献
8.
阐述了硬质合金材料的电火花线切割加工特点.通过采用限位棒、恒张力装置提高电极丝的空间稳定性,并在前两次切割采用复合工作液最后精修采用煤油作为工作介质对硬质合金YG8进行了多次切割.试验结果表明,多次切割的加工表面粗糙度达到1μm以下;与采用复合工作液精修后的加工表面相比,煤油精修后的加工表面微裂纹和微孔洞均明显减少,获得较好的加工表面质量. 相似文献
9.
基于航空发动机叶片的全报废数据,建立了发动机叶片报废率威布尔分布模型,并运用中位秩的方法对威布尔模型的参数进行了求解。为验证所建立模型的有效性,运用某航空公司CFM56-7B航空发动机报废率数据对模型进行了验证,取得了较好的效果。所建立的报废率模型能够为航空发动机的送修目标确定、维修工作范围制定等提供理论的支持。 相似文献
10.