全文获取类型
收费全文 | 1467篇 |
免费 | 322篇 |
国内免费 | 433篇 |
专业分类
航空 | 1069篇 |
航天技术 | 513篇 |
综合类 | 213篇 |
航天 | 427篇 |
出版年
2024年 | 13篇 |
2023年 | 33篇 |
2022年 | 57篇 |
2021年 | 66篇 |
2020年 | 85篇 |
2019年 | 88篇 |
2018年 | 125篇 |
2017年 | 73篇 |
2016年 | 85篇 |
2015年 | 79篇 |
2014年 | 112篇 |
2013年 | 98篇 |
2012年 | 147篇 |
2011年 | 146篇 |
2010年 | 111篇 |
2009年 | 132篇 |
2008年 | 108篇 |
2007年 | 71篇 |
2006年 | 97篇 |
2005年 | 74篇 |
2004年 | 48篇 |
2003年 | 52篇 |
2002年 | 34篇 |
2001年 | 37篇 |
2000年 | 22篇 |
1999年 | 24篇 |
1998年 | 31篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 22篇 |
1991年 | 27篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1984年 | 2篇 |
排序方式: 共有2222条查询结果,搜索用时 343 毫秒
901.
G. Efstathiou R.I. Jedrzejewski 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Application of the cosmic virial theorem to galaxy redshift surveys suggests an open universe - if the dark material is distributed in the same way as galaxies. Here we investigate four redshift surveys. We present new results on the amplitudes of the two- and three-point galaxy correlation functions and we estimate the relative peculiar velocities in the deep redshift survey of Kirshner and co-workers (1983). Next, we review evidence which suggests that dark material is clustered on scales comparable to the optical radii of galaxies. In particular, we use spectroscopic and photometric observations to set constraints on the mass distribution in elliptical galaxies. 相似文献
902.
A novel two-stage extended Kalman filter algorithm for reaction flywheels fault estimation 总被引:2,自引:0,他引:2
《中国航空学报》2016,(2):462-469
This paper investigates the problem of two-stage extended Kalman filter(TSEKF)-based fault estimation for reaction flywheels in satellite attitude control systems(ACSs). Firstly, based on the separate-bias principle, a satellite ACSs with actuator fault is transformed into an augmented nonlinear discrete stochastic model; then, a novel TSEKF is suggested such that it can simultaneously estimate satellite attitude information and actuator faults no matter they are additive or multiplicative; finally, the proposed approach is respectively applied to estimating bias faults and loss of effectiveness for reaction flywheels in satellite ACSs, and simulation results demonstrate the effectiveness of the proposed fault estimation approach. 相似文献
903.
《中国航空学报》2023,36(3):368-381
Formation control of fixed-wing aerial vehicles is an important yet rarely addressed problem because of their complex dynamics and various motion constraints, such as nonholonomic and velocity constraints. The guidance-route-based strategy has been demonstrated to be applicable to fixed-wing aircraft. However, it requires a global coordinator and there exists control lag, due to its own natures. For this reason, this paper presents a fully distributed guidance-route-based formation approach to address the aforementioned issues. First, a hop-count scheme is introduced to achieve distributed implementation, in which each aircraft chooses a neighbor with the minimum hop-count as a reference to generate its guidance route using only local information. Next, the model predictive control algorithm is employed to eliminate the control lag and achieve precise formation shape control. In addition, the stall protection and collision avoidance are also considered. Finally, three numerical simulations demonstrate that our proposed approach can implement precise formation shape control of fixed-wing aircraft in a fully distributed manner. 相似文献
904.
《中国航空学报》2023,36(2):17-28
It is common for aircraft to encounter atmospheric turbulence in flight tests. Turbulence is usually modeled as stochastic process noise in the flight dynamics equations. In this paper, parameter estimation of nonlinear dynamic system with both process and measurement noise was studied, and a practical filter error method was proposed. The linearized Kalman filter of first-order approximation was used for state estimation, in which the filter gain, along with the system parameters and the initial states, constituted the parameter vector to be estimated. The unknown parameters and measurement noise covariance were estimated alternately by a relaxation iteration method, and the sensitivities of observations to unknown parameters were calculated by finite difference approximation. Some practical aspects of the method application were discussed. The proposed filter error method was validated by the flight simulation data of a research aircraft. Then, the method was applied to the flight tests of a subscale aircraft, and the aerodynamic stability and control derivatives were estimated. All the estimation results were compared with the results of the output error method to demonstrate the effectiveness of the approach. It is shown that the filter error method is superior to the output error method for flight tests in atmospheric turbulence. 相似文献
905.
针对雷达窄带回波信号的循环互相关估计多普勒频移问题进行了研究。利用信号循环平稳特性,分析了存在多普勒频移条件下雷达窄带回波信号的循环统计特性,在此基础上提出了基于循环互相关变换的多普勒频移估计算法,该方法能有效地估计多普勒频移参数。最后利用计算机进行了仿真实验,验证了该算法的有效性。 相似文献
906.
本文研完惯性制导系统工具误差的自适应估计问题。运用自适应技术,这是解决制导精度鉴定问题的一个新的尝试,文中对仪表的误差模型给出了动态补偿,并给出了误差系数的递推估计。对模型中随机量的统计特性应用了自适应技术,并对岭回归引入了自适应估计,对滤波过程中模型的辨识及估值中偏倚的补偿,进行了讨论。 相似文献
907.
偏置动量卫星偏航姿态估计与控制研究 总被引:2,自引:1,他引:2
为改善偏置动量卫星无偏航姿态敏感器时用滚动角间接控制偏航姿态的精度,基于降维观测器设计提出了一种采用偏航角估计值直接控制偏航姿态方法。在分析收敛性的基础上,给出了降维观测器的设计,以及直接控制法的系统模型。理论分析和仿真结果表明,该法能大幅提高偏置动量卫星的姿态精度,且易于软件实现,不增加系统硬件配置。 相似文献
908.
909.
910.
关志东 《北京航空航天大学学报》1994,20(2):136-141
本文提出了一种处理钉孔挤压化或或干涉配合强化后元件疲劳寿命的可靠性分析方法,在假设挤压量(干涉量)服从正态分布,以及具有确定强化参数的元件的对数疲劳寿命服从正态分布或疲劳寿命服从威布尔分布的条件下,分别给出了考虑强化参数及其公差影响的强化后元件疲劳寿命的分布函数,从而,可以由几组不同挤压量(干涉量)的元件疲劳寿命推算出元件在任意挤压量(干涉量)及公差要求情况下,其疲劳寿命提高到某一给定值的概率,这 相似文献