全文获取类型
收费全文 | 226篇 |
免费 | 57篇 |
国内免费 | 56篇 |
专业分类
航空 | 229篇 |
航天技术 | 41篇 |
综合类 | 46篇 |
航天 | 23篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 13篇 |
2013年 | 15篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 12篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 31 毫秒
201.
《中国航空学报》2020,33(10):2499-2509
Common, unsteady aerodynamic modeling methods usually use wind tunnel test data from forced vibration tests to predict stable hysteresis loop. However, these methods ignore the initial unstable process of entering the hysteresis loop that exists in the actual maneuvering process of the aircraft. Here, an excitation input suitable for nonlinear system identification is introduced to model unsteady aerodynamic forces with any motion in the amplitude and frequency ranges based on the Least Squares Support Vector Machines (LS-SVMs). In the selection of the input form, avoiding the use of reduced frequency as a parameter makes the model more universal. After model training is completed, the method is applied to predict the lift coefficient, drag coefficient and pitching moment coefficient of the RAE2822 airfoil, in sine and sweep motions under the conditions of plunging and pitching at Mach number 0.8. The predicted results of the initial unstable process and the final stable process are in close agreement with the Computational Fluid Dynamics (CFD) data, demonstrating the feasibility of the model for nonlinear unsteady aerodynamics modeling and the effectiveness of the input design approach. 相似文献
202.
A. Taori V. Kamalakar A. Jayaraman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O2 emission monitoring. The deduced mesospheric OH and O2 temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5 months periodicity) oscillation in both OH and O2 data. 相似文献
203.
K.J. Badcock S. TimmeS. Marques H. KhodaparastM. Prandina J.E. MottersheadA. Swift A. Da RonchM.A. Woodgate 《Progress in Aerospace Sciences》2011,47(5):392-423
In this paper the use of eigenvalue stability analysis of very large dimension aeroelastic numerical models arising from the exploitation of computational fluid dynamics is reviewed. A formulation based on a block reduction of the system Jacobian proves powerful to allow various numerical algorithms to be exploited, including frequency domain solvers, reconstruction of a term describing the fluid-structure interaction from the sparse data which incurs the main computational cost, and sampling to place the expensive samples where they are most needed. The stability formulation also allows non-deterministic analysis to be carried out very efficiently through the use of an approximate Newton solver. Finally, the system eigenvectors are exploited to produce nonlinear and parameterised reduced order models for computing limit cycle responses. The performance of the methods is illustrated with results from a number of academic and large dimension aircraft test cases. 相似文献
204.
205.
Debasish Roy Biswajit Sahu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(3):1039-1048
Within a quantum hydrodynamic model and using the reductive perturbation technique, the nonlinear ion-acoustic wave (IAW) excitations due to a moving charged object in an electron-pair-ion quantum plasma are studied both analytically and numerically. In such quantum plasmas we have derived forced Korteweg-de Vries (fKdV) type equation for finite amplitude nonlinear IAWs. The effect of relevant plasma parameters on solitonic excitations is investigated. Numerical simulation shows the generation of advancing solitons ahead of the forcing term traveling at a faster rate with trailing wakes behind the forcing disturbance. It is found that propagation characteristics of nonlinear excitations are significantly affected by quantum parameter. Additionally, we have pursued our analysis by extending it to account for arbitrary amplitude IA solitons, and derived a system of nonlinear differential equations which are analyzed numerically to study the dynamics. Nonlinear analysis predicts the existence of periodic and quasiperiodic nature of the nonlinear system and reveals that the transition from quasiperiodic to periodic behavior occurs due to the variation of quantum diffraction. 相似文献
206.
We analyze here how solar neutrino experiments could detect time fluctuations of the solar neutrino flux due to magnetohydrodynamics
(MHD) perturbations of the solar plasma. We state that if such time fluctuations are detected, this would provide a unique
signature of the Resonant Spin-Flavor Precession (RSFP) mechanism as a solution to the Solar Neutrino Problem.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
207.
线化插值权残法求解强非线性振动问题 总被引:1,自引:0,他引:1
本文用线性化法,插值函数法和权残法相结合的方法求解了几类保守系统强非线性振动问题,其精度比已有的新的改进的L-P法还更好些。 相似文献
208.
A.V. Kartushinsky A.Y. Sidorenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
AVHRR MCSST data for the periods 1982–2000 (mean weekly data) were used to calculate mean gradient fields in the ocean for different periods of time. Three-month averaged sea surface temperature gradients (SSTG) and their mean seasonal variations have been studied for 25 points in the large-scale oceanic fronts zones. Major oceanic fronts in the Atlantic and Pacific have been identified and compared in literature. In the North Atlantic and Pacific, the areas under study were the North Polar Front and Subpolar Fronts. In the South Atlantic and Pacific we studied the region of the Antarctic Circumpolar Current (ACC) and the fronts formed by this current, known as the South Polar Front, and the Subantarctic Front. SSTG were also calculated for El Niño (Southeast Pacific) and Benguela Current (Southeast Atlantic). 相似文献
209.
航空自动控制系统中的延时及其补偿 总被引:1,自引:1,他引:0
总结了作者40年来在各种不同的航空自动控制系统研制过程中,所出现的各类延时,给出了造成各种延时的原因,综述了延时对自动系统的控制精度、稳定性及操纵性的严重影响,并提出对延时所致后果的补偿方法。 相似文献
210.
针对静不稳定电传飞机作动器速率限制环节引起的Ⅱ型驾驶员诱发振荡(PIO)严重威胁飞机飞行安全的问题,研究了考虑作动器速率限制因素的人机闭环系统稳定域。引入增广状态变量分离速率限制环节,建立了人机闭环系统饱和非线性模型。为得到尽可能大的人机闭环系统稳定域估计,首先将稳定域求解问题转化为凸优化问题,再通过Schur补引理将其转化为线性矩阵不等式的求解问题,最终得到了人机闭环系统椭球体稳定域估计的一般算法。时域仿真研究表明:所估计的稳定域略微保守但不冒进,静不稳定电传飞机的Ⅱ型PIO是一种发散很快的振荡而非极限环振荡,驾驶员操纵增益以及作动器速率限制值是影响稳定域的重要因素。稳定域法物理意义清晰、结果直观,可用于非线性人机闭环系统稳定性的评估。 相似文献