全文获取类型
收费全文 | 1479篇 |
免费 | 293篇 |
国内免费 | 405篇 |
专业分类
航空 | 1550篇 |
航天技术 | 202篇 |
综合类 | 263篇 |
航天 | 162篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 52篇 |
2021年 | 71篇 |
2020年 | 66篇 |
2019年 | 89篇 |
2018年 | 78篇 |
2017年 | 78篇 |
2016年 | 109篇 |
2015年 | 108篇 |
2014年 | 88篇 |
2013年 | 87篇 |
2012年 | 99篇 |
2011年 | 114篇 |
2010年 | 96篇 |
2009年 | 115篇 |
2008年 | 88篇 |
2007年 | 84篇 |
2006年 | 73篇 |
2005年 | 54篇 |
2004年 | 53篇 |
2003年 | 52篇 |
2002年 | 46篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 39篇 |
1998年 | 38篇 |
1997年 | 33篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 31篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 1篇 |
排序方式: 共有2177条查询结果,搜索用时 31 毫秒
931.
932.
何允祥 《长沙航空职业技术学院学报》2011,11(4):39-42
以某型飞机在使用过程中频繁出现进气道铆钉松动、蒙皮裂纹、铆钉裂纹等故障为研究对象,运用飞机气动弹性力学理论进行了分析研究,找出故障发生的原因,提出在进气道蒙皮上加装阻尼层的新方法。验证表明,该方法能有效地弥补设计缺陷、延迟金属材料老化及预防性修理机体结构裂纹。 相似文献
933.
As boundary layer transition plays an important role in aerodynamic drag prediction,the proposal and study of transition prediction methods simulating the complex flow phenomena are prerequisite for aerodynamic design. In this paper, with the application of the linear stability theory based on amplification factor transport transition equations on the two-equation shear stress transport(SST) eddy-viscosity model, a new method, the SST-N TS-N CF model, is yielded. The new amplification factor transport equation for the crossflow instability induced transition is proposed to add to the N TS equation proposed by Coder, which simulates Tollmien–Schlichting wave transition. The turbulent kinetic energy equation is modified by introducing a new source term that simulates the transition process without the intermittency factor equation. Finally, coupled with these two amplification factor transport equations and SST turbulence model, a four-equation transition turbulence model is built. Comparisons between predictions using the new model and wind-tunnel experiments of NACA64(2)A015, NLF(2)-0415 and ONERA-D infinite swept wing and ONERAM6 swept wing validate the predictive quality of the new SST-N_(TS)-N_(CF) model. 相似文献
934.
We present a preliminary analysis of two quiet Sun transition region areas observed with the SOHO/SUMER spectrometer, using
lines from oxygen, nitrogen and silicon. The average quiet Sun physical parameters are studied as a function of line intensity.
Systematic variations of line position and width with increasing intensity are found. A large number of small-scale active
points have been observed, and preliminary analysis of the physical properties and dynamics of these active features is presented.
A jet-like structure, found in an active point, is also investigated and its velocity along the line of sight determined.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
935.
P. Lemaire 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,39(12):1876-1881
The two XUV–EUV spectrometers on SOHO have collected a large amount of data in the 6000–106 K solar plasma temperature range. These data have allowed us to greatly enhance our knowledge of the processes acting in the solar atmosphere, from the chromosphere to the corona. Some results on the quiet Sun structure (network, quiet Sun versus coronal hole), on the dynamics (velocities, waves, transient events), and the main characteristics of the quiet Sun atmosphere are presented and discussed. 相似文献
936.
C.P. Escoubet J. Berchem J.M. Bosqued K.J. Trattner M.G.G.T. Taylor F. Pitout C. Vallat H. Laakso A. Masson M. Dunlop H. Reme I. Dandouras A. Fazakerley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(10):1528-1536
Double cusps have been observed on a few occasions by polar orbiting spacecraft and ground-based observatories. The four Cluster spacecraft observed two distinct regions, showing characteristics of a double cusp, during a mid-altitude cusp pass on 7 August 2004. The Wind spacecraft detected a southward turning of the Interplanetary Magnetic Field (IMF) at the beginning of the cusp crossings and IMF–Bz stayed negative throughout. Cluster 4 observed a high energy step in the ion precipitation around 1 keV on the equatorward side of the cusp and a dense ion population in the cusp centre. Cluster 1, entering the cusp around 1 min later, observed only a partial ion dispersion with a low energy cutoff reaching 100 eV, together with the dense ion population in the cusp centre. About 9 min later, Cluster 3 entered the cusp and observed full ion dispersion from a few keV down to around 50 eV, together with the dense ion population in the centre of the cusp. The ion flow was directed poleward and eastward in the step/dispersion, whereas in the centre of the cusp the flow was directed poleward and westward. In addition the altitude of the source region of ion injection in the step/dispersion was found 50% larger than in the cusp centre. This event could be explained by the onset of dayside reconnection when the IMF turned southward. The step would be the first signature of component reconnection near the subsolar point, and the injection in the centre of the cusp a result of anti-parallel reconnection in the northern dusk side of the cusp. A three-dimensional magnetohydrodynamic (MHD) simulation is used to display the topology of the magnetic field and locate the sources of the ions during the event. 相似文献
937.
Magneto-gravity Waves Trapped in the Lower Solar Corona 总被引:1,自引:0,他引:1
Yu-Qing Lou 《Space Science Reviews》1999,87(1-2):261-264
The possibility of trapped magneto-gravity waves in the lower solar corona with an open magnetic field is discussed. Intensity
variations and/or Doppler shifts of relevant UV, EUV and x-ray spectral lines in the chromosphere, transition region and lower
corona may reveal the existence of such low-frequency modes (with periods longer than ∼ 1.5 hour). The spectrum may be either
discrete or continuous depending on the reflection property of the narrow transition region. These modes can be utilized to
probe the dynamics of the upper chromosphere, transition region and lower corona; they may also play an important role in
coronal heating.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
938.
半节点二次样条是C1类连续的,其二阶导函数是阶梯函数,在半节点处产生跳跃。鉴于此,本文利用最小二乘法,获得了一种半节点二次插值样条边界条件确定方法,该方法可以保证二次插值样条在半节点处二阶导数的变化最小,这相当于保证了曲率的变化最小。为了适应四维数据插值的需要,给出了三元二次插值样条的定义及基样条表示,提出了一种边界条件,证明了其存在唯一性。最后把二次插值样条边界条件确定方法推广到三元二次插值样条上去,获得了三元二次插值样条边界条件的确定方法。该方法的意义是,可以直接从插值条件获得边界条件,从而克服了多元样条边界条件难以确定的困难 相似文献
939.
有迎角的再入旋转钝锥由于周向烧蚀滞后将产生滚转力矩。在烧蚀滞后滚转力矩的计算方法中。本文主要介绍滞后引射率和粗糙度对壁面磨擦系数联合影响的一种快速计算方法。给出计算结果与实验数据的比较,分析烧蚀滞后滚转力矩的模数随飞行参数的变化。 相似文献
940.