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排序方式: 共有838条查询结果,搜索用时 203 毫秒
381.
长期以来,拉萨机场规定进出港航空器在泽当以西严禁对头起降(09号跑道起飞,27号跑道落地),在正常的情况下,这样做有其必要性与合理性:
1.拉萨机场进近航路周围地形复杂,山高均在5000米左右,进离港航空器沿雅鲁藏布江河谷飞行,没有回旋避让的余地; 相似文献
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Zhong Lingwei Liu Yu Li Juan Gu Zuo Jiang Haocheng Wang Haixing Tang Haibin 《中国航空学报》2010,23(1):15-21
Charge exchange(CEX) ions could inflict severe damages on the ion thruster optical system. This article is aimed at investigating the characteristics of the CEX ions and their influences upon the optical system by means of particle-in- cell(PIC) ion simulation and Monte Carlo collision(MCC) methods. The results from numerical simulation indicate that despite the fact that CEX ions appear in the entire beamlet region near the ion optical system, the ones that present themselves downstream of the accelerator grid have good reason for attracting more attention. As their trajectories are significantly affected by the local electric field, a great number of CEX ions are accelerated toward grids resulting in sputtering erosion. When the influences of the CEX ions are considered in the numerical simulation, there could hardly be observed augments in the screen grid current, but the accelerator grid current increases from zero to 1. 4% of the beamlet current. It can be understood from the numerical simulation that the CEX ions formed in the region far downstream of the accelerator grid should be blamed for the erosion on the downstream surface of the accelerator grid. 相似文献
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Optimal guidance based on receding horizon control for low-thrust transfer to libration point orbits
Haijun Peng Qiang Gao Zhigang Wu Wanxie Zhong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper addresses the design and computation of a guidance law for a transfer mission from an orbit near the Earth to a halo orbit around the libration point L2 in the Sun–Earth system. The guidance law, which is designed based on receding horizon control and compensates for launch velocity errors that are introduced by inaccuracies of the launch vehicle, is solved using the generating function method. During the design of the closed-loop guidance law, the entire transfer mission, which is considered a nonlinear optimal control problem, is evaluated to obtain a nominal reference trajectory. Using the launch velocity errors and the uncertainty of the model, a spacecraft controlled by the proposed guidance law tracks the reference trajectory. Furthermore, the original Riccati differential equation in the receding horizon control algorithm is replaced by an equivalent convenient form of the Riccati differential equation that is based on the generating function. The high-efficiency solution of the equivalent equation avoids the online direct integration of the original Riccati differential equation, which significantly increases the computational efficiency for the receding horizon control problem. Numerical simulations using a nonlinear bicircular four-body model demonstrate the capabilities of the proposed receding horizon guidance law for the transfer mission. In addition, the generating function method improves the computational efficiency by at least one order of magnitude over the backward sweep method in solving the receding horizon control problem. 相似文献
388.
Long term dynamics and optimal control of nano-satellite deorbit using a short electrodynamic tether 总被引:1,自引:0,他引:1
R. Zhong Z.H. Zhu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper studies the long term dynamics and optimal control of a nano-satellite deorbit by a short electrodynamic tether. The long term deorbit process is discretized into intervals and within each interval a two-phase optimal control law is proposed to achieve libration stability and fast deorbit simultaneously. The first-phase formulates an open-loop fast-deorbit control trajectory by a simplified model that assumes the slow-varying orbital elements of electrodynamic tethered system as constant and ignores perturbation forces other than the electrodynamic force. The second phase tracks the optimal trajectory derived in the first phase by a finite receding horizon control method while considering a full dynamic model of electrodynamic tether system. Both optimal control problems are solved by direct collocation method base on the Hermite–Simpson discretization schemes with coincident nodes. The resulting piecewise nonlinear programing problems in the sequential intervals reduces the problem size and improve the computational efficiency, which enable an on-orbit control application. Numerical results for deorbit control of a short electrodynamic tethered nano-satellite system in both equatorial and highly inclined orbits demonstrate the efficiency of the proposed control method. An optimal balance between the libration stability and a fast deorbit of satellite with minimum control efforts is achieved. 相似文献
389.
便携式相控阵探伤仪在复合材料检测中的应用 总被引:1,自引:0,他引:1
相控阵探伤仪能够通过图像的形式直观地显示缺陷,并通过线性B扫描图或扇形图显示一定区域范围内的缺陷,有利于对缺陷的评判. 相似文献
390.
Talso C P Chui Inseob Hahn Konstantin Penanen Fang Zhong Donald Strayer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(1):99-106
We discuss how superconductivity and superfluidity can be applied to solve the challenges in the exploration of the Moon and Mars. High sensitivity instruments using phenomena of superconductivity and superfluidity can potentially make significant contributions to the fields of navigation, automation, habitation, and resource location. Using the quantum nature of superconductivity, lightweight and very sensitive diagnostic tools can be made to monitor the health of astronauts. Moreover, the Moon and Mars offer a unique environment for scientific exploration. We also discuss how powerful superconducting instruments may enable scientists to seek answers to several profound questions about nature. These answers will not only deepen our appreciation of the universe, they may also open the door to paradigm-shifting technologies. 相似文献