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591.
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Aimed at low accuracy of attitude determination because of using low-cost components which may result in non-linearity in integrated attitude determination systems, a novel attitude determination algorithm using vector observations and gyro measurements is presented. The various features of the unscented Kalman filter (UKF) and optimal-REQUEST (quaternion estimator) algorithms are introduced for attitude determination. An interlaced filtering method is presented for the attitude determination of nano-spacecraft by setting the quaternion as the attitude representation, using the UKF and optimal-REQUEST to estimate the gyro drifts and the quaternion, respectively. The optimal-REQUEST and UKF are not isolated from each other. When the optimal-REQUEST algorithm estimates the attitude quaternion, the gyro drifts are estimated by the UKF algorithm synchronously by using the estimated attitude quaternion. Furthermore, the speed of attitude determination is improved by setting the state dimension to three. Experimental results show that the presented method has higher performance in attitude determination compared to the UKF algorithm and the traditional interlaced filtering method and can estimate the gyro drifts quickly. 相似文献
593.
E. Nielsen H. Zou D. A. Gurnett D. L. Kirchner D. D. Morgan R. Huff R. Orosei A. Safaeinili J. J. Plaut G. Picardi 《Space Science Reviews》2006,126(1-4):373-388
The Martian ionosphere has for the first time been probed by a low frequency topside radio wave sounder experiment (MARSIS)
(Gurnett et al., 2005). The density profiles in the Martian ionosphere have for the first time been observed for solar zenith angles less
than 48 degrees. The sounder spectrograms typically have a single trace of echoes, which are controlled by reflections from
the ionosphere in the direction of nadir. With the local density at the spacecraft derived from the sounder measurements and
using the lamination technique the spectrograms are inverted to electron density profiles. The measurements yield electron
density profiles from the sub-solar region to past the terminator. The maximum density varies in time with the solar rotation
period, indicating control of the densities by solar ionizing radiation. Electron density increases associated with solar
flares were observed. The maximum electron density varies with solar zenith angle as predicted by theory. The altitude profile
of electron densities between the maximum density and about 170m altitude is well approximated by a classic Chapman layer.
The neutral scale height is close to 10 to 13 km. At altitudes above 180 km the densities deviate from and are larger than
inferred by the Chapman layer. At altitudes above the exobase the density decrease was approximated by an exponential function
with scale heights between 24 and 65 km. The densities in the top side ionosphere above the exobase tends to be larger than
the densities extrapolated from the Chapman layer fitted to the measurements at lower altitudes, implying more efficient upward
diffusion above the collision dominated photo equilibrium region. 相似文献
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Fei-yan Hou Rui-fang Dong Run-ai Quan Yu Zhang Yun Bai Tao Liu Shou-gang Zhang Tong-yi Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We proposed a fiber-based quantum clock synchronization protocol by employing the dispersion cancellation feature of the frequency anti-correlated entangled source under the quantum interference measurement. It is shown that, the accuracy of the synchronization is mainly dependent on the bandwidth of the frequency entangled biphoton spectrum and on the temperature variation induced fluctuations in both the reference fiber coiling and the fiber link. With this proposal, synchronization between two clocks at a distance of ten kilometers can be implemented with an accuracy below a picosecond. 相似文献
598.
<正>作为材料科学与工程领域的专家,您主持研究的许多成果达到了国内领先、国际先进水平,请您介绍一下您所从事的研究工作及取得的研究成果和进展。邹炳锁:我们开展的工作主要是半导体的光电行为,探索其在能 相似文献
599.
针对基于加速模型参数不变、基于统计方法及基于试验观察3种常见的失效机理一致性检验方法进行研究,发现3种方法均需要加速试验数据来对失效机理一致性进行检验,不能事先为加速试验提供理论指导;提出了一种基于灰色理论的失效机理一致性检验方法,该方法可用预试验数据进行失效机理一致性检验,为加速试验制定最高应力台阶提供理论指导;结合某型光电编码器预试验数据对该方法进行实例验证,得出175℃附近为失效机理变化点,并与基于统计的方法进行对比;最后,对产品进行失效机理分析,利用扫描电镜分析(SEM,Scanning Electron Microscope)结果验证该方法的正确性. 相似文献
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