全文获取类型
收费全文 | 4324篇 |
免费 | 890篇 |
国内免费 | 1019篇 |
专业分类
航空 | 4627篇 |
航天技术 | 463篇 |
综合类 | 711篇 |
航天 | 432篇 |
出版年
2024年 | 12篇 |
2023年 | 62篇 |
2022年 | 163篇 |
2021年 | 184篇 |
2020年 | 180篇 |
2019年 | 190篇 |
2018年 | 172篇 |
2017年 | 200篇 |
2016年 | 229篇 |
2015年 | 242篇 |
2014年 | 273篇 |
2013年 | 236篇 |
2012年 | 296篇 |
2011年 | 352篇 |
2010年 | 262篇 |
2009年 | 279篇 |
2008年 | 233篇 |
2007年 | 237篇 |
2006年 | 199篇 |
2005年 | 192篇 |
2004年 | 143篇 |
2003年 | 152篇 |
2002年 | 163篇 |
2001年 | 134篇 |
2000年 | 168篇 |
1999年 | 127篇 |
1998年 | 115篇 |
1997年 | 124篇 |
1996年 | 161篇 |
1995年 | 111篇 |
1994年 | 124篇 |
1993年 | 105篇 |
1992年 | 86篇 |
1991年 | 78篇 |
1990年 | 79篇 |
1989年 | 71篇 |
1988年 | 85篇 |
1987年 | 11篇 |
1986年 | 3篇 |
排序方式: 共有6233条查询结果,搜索用时 29 毫秒
1.
《中国航空学报》2020,33(11):2907-2920
This paper investigates a time-varying anti-disturbance formation problem for a group of quadrotor aircrafts with time-varying uncertainties and a directed interaction topology. A novel Finite-Time Convergent Extended State Observer (FTCESO) based fully-distributed formation control scheme is proposed to enhance the disturbance rejection and the formation tracking performances for networked quadrotors. By adopting the hierarchical control strategy, the multi-quadrotor system is separated into two subsystems: the outer-loop cooperative subsystem and the inner-loop attitude subsystem. In the outer-loop subsystem, with the estimation of disturbing forces and uncertain dynamics from FTCESOs, an adaptive consensus theory based cooperative controller is exploited to ensure the multiple quadrotors form and maintain a time-varying pattern relying only on the positions of the neighboring aircrafts. In the inner-loop subsystem, the desired attitude generated by the cooperative control law is stably tracked under a FTCESO-based attitude controller in a finite time. Based on a detailed algorithm to specify the cooperative control protocol, the feasibility condition to achieve the time-varying anti-disturbance formation tracking is derived and the rigorous analysis of the whole closed-loop multi-quadrotor system is given. Some numerical examples are conducted to intuitively demonstrate the effectiveness and the improvements of the proposed control framework. 相似文献
2.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2551-2558
The whistler-mode chorus waves are one of the most important plasma waves in the Earth’s magnetosphere. Generally, the amplitude of whistler-mode chorus waves prefers to strengthen when the energetic fluxes of anisotropic electrons increase outside the plasmapause. This characteristic is commonly associated with the geomagnetic storms or substorms. However, the relationship between the solar wind dynamic pressure (Psw) and the long-time variation of chorus waves during the quiet period of the geomagnetic activity still needs more detailed investigations. In this paper, based on MMS observations, we present a chorus event just observed in the inner side of magnetopause without obvious geomagnetic storms or substroms. Interestingly, during this time interval, some Psw fluctuations were recorded. Both the amplitudes and frequencies of chorus waves changed as a response to the variation in Psw. It proved that the enhancement of Psw increases the energetic electrons fluxes, which provides free energies for the chorus amplification. Furthermore, the wave growth rates calculated using linear theory increases and the central frequency of the chorus waves shifts to a higher frequency when the Psw enhancement is greater, which are also consistent well with the observations. The results provide a direct evidence that the Psw play an important role in the long-time variation of whistler-mode chorus waves inside the magnetopause. 相似文献
3.
《中国航空学报》2020,33(3):879-892
Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine (LPT) cascade. All of the measurements were conducted in both the presence and absence of incoming wakes, and numerical analysis was performed to elucidate the flow mechanism. With increasing Reynolds number, the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers, leading to a lower blade loading near the leading edge and suppression of the Pressure Side (PS) leg of the horseshoe vortex. However, the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side (SS) separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers. Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000. In contrast, at the high Reynolds number of 100,000, the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes, and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade. 相似文献
4.
陈伟 《沈阳航空工业学院学报》2002,19(1):21-23
本文分析了在塑料熔体充满型腔的过程中,流动阻力及能量损失产生的形式和物理原因,进而讨论了对塑料制件成型及凝固过程中的影响。并提出降低影响的措施。 相似文献
5.
6.
ADI方法求解完全跨声速非定常小扰动方程 总被引:1,自引:1,他引:0
本文修改了Whitlow的ADI格式,以便求解另一变形的完全跨声速小扰动方程。本文给出的NACA64A006和NACA0012翼型的非定常跨声速流动的计算结果与其它数值结果和实验结果的比较表明本文格式是合理的且便于实际应用的。 相似文献
7.
A numerical procedure for the calculation of the transonic dip of airfoils in the time domain is presented. A viscous-inviscid aerodynamic interaction method is taken to calculate the unsteady aerodynamic loads. In the present case the integral boundary layer equations are coupled with the Transonic Small Disturbance (TSD) Potential Equation. The coupling between structural motion and aerodynamic loads is carried out using State Space equation. It is solved by State Transition Matrix technique. Results are presented for NACA 64A010 and NLR 7301 airfoils with structural data from Isogai and DLR, respectively. Comparisons show good agreement with other numerical results. Certain deviations of experimental data taken from literature need more insight in the detailed test conditions. 相似文献
8.
9.
10.