全文获取类型
收费全文 | 64篇 |
免费 | 5篇 |
国内免费 | 8篇 |
专业分类
航空 | 33篇 |
航天技术 | 33篇 |
综合类 | 1篇 |
航天 | 10篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 6篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1990年 | 1篇 |
排序方式: 共有77条查询结果,搜索用时 15 毫秒
31.
现有ΔLOD(Delta Length-Of-Day,日长变化)预报模式在进行周期项与残差项拟合分离时,通常没有考虑LS(Least Squares,最小二乘)拟合序列的端部效应,预报精度难以取得较大提高。针对端部效应现象,首先采用时间序列分析模型在ΔLOD序列两端进行数据延拓,构成一个新序列,然后用新序列求得LS外推模型系数,再结合LS外推模型和NN(Neural Network,神经网络)对原始ΔLOD序列进行预测。算例表明,在ΔLOD序列两端增加延拓数据,能有效改善LS拟合序列的端部效应;端部效应改善的LS+NN模型的预报精度明显优于常规LS+NN模型,精度最大提高了17.86%。该方法不仅适用于LS+NN模型,也适用于LS外推模型与其他模型的组合。 相似文献
32.
基于Unscented卡尔曼滤波器的卫星自主天文导航研究 总被引:13,自引:1,他引:13
针对星光折射间接敏感地平的卫星自主天文导航方法,建立了带摄动项的状态方程和以星光视高度为观测量的量测方程。由于该状态方程和量测方程都是严重非线性的,利用推广的卡尔曼滤波器进行导航时精度较低。Unscented卡尔曼滤波是一种针对非线性系统的估计新方法。本文提出将Unscented卡尔曼滤波用于自主天文导航。计算机仿真结果显示Unscented卡尔曼滤波的估计精度远优于推广的卡尔曼滤波。 相似文献
33.
Hsien Shang Frank H. Shu Typhoon Lee Alfred E. Glassgold 《Space Science Reviews》2000,92(1-2):153-176
We discuss the interaction between the magnetosphere of a young star and its surrounding accretion disk. We consider how an
X-wind can be driven magnetocentrifugally from the inner edge of the disk where accreting gas is diverted onto stellar field
lines either to flow onto the Sun or to be flung outwards with the wind. The X-wind satisfies many observational tests concerning
optical jets, Herbig-Haro objects, and molecular outflows. Connections may exist between primitive solar system materials
and X-winds. Chondrules and calcium-aluminum-rich inclusions (CAIs) experienced short melting events uncharacteristic of the
asteroid belt where meteorites originate. The inner edge of the solar nebula has the shortest orbital timescale available
to the system, a few days. Protosolar flares introduce another timescale, tens of minutes to hours. CAIs may form when solids
are lifted from shaded portions of the disk close to the Sun and are exposed to its intense light for a day or so before they
are flung by the X-wind to much larger distances. Chondrules were melted, perhaps many times, by flares at larger distances
from the Sun before being launched and annealed, but not remelted, in the X-wind. Aerodynamic sorting explains the narrow
range of sizes with which CAIs and chondrules are found in chondritic meteorites. Flare-generated cosmic-rays may induce spallation
reactions that produce some of the short-lived radioactivities associated with primitive solar system rocks.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
34.
Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPS-denied environments.Starlight refraction compensates for the significant along-track position error that occurs from only using gravity gradients and benefits from integration in terms of improved accuracy in radial and cross-track position estimates.The between-epoch differencing of gravity gradients is employed to eliminate slowly varying measurement biases and noise near the orbit revolution frequency.The refraction angle measurements are directly used and its Jacobian matrix derived from an implicit observation equation.An information fusion filter based on a sequential extended Kalman filter is developed for the orbit determination.Truth-model simulations are used to test the performance of the algorithm,and the effects of differencing intervals and orbital heights are analyzed.A semi-simulation study using actual gravity gradient data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) combined with simulated starlight refraction measurements is further conducted,and a three-dimensional position accuracy of better than 100 m is achieved. 相似文献
35.
36.
高精度星光折射间接敏感地平的自主导航方法,目前被国内外尤为关注。本文通过对星光折射导航观测对象———导航星捕获的研究,采用了改进的三角匹配算法并结合恒星星表,确定出导航观测星星光方向,同时依据对飞行器在轨观测星的几何关系推导,利用Unscented卡尔曼滤波算法确定航天器的在轨位置和速度。该方法能比较真实地模拟飞行器实际在轨的导航情况。仿真表明,真实星表导航精度大于人造星场;通过比较导航系统捕获20,40,60,80颗折射星的4种情况,可知捕获到的导航星的数量越多,导航精度也随之提高。 相似文献
37.
针对单平台观测条件下目标运动特性反演问题,提出了基于序列图像的目标空间位置重建及运动参数估计模型和方法。为抑制大气折射对位置重建精度的影响,提出将大气视为球面分层,并划分若干层,采用反向追踪策略,从成像系统的入射光线出发,逆向计算出光线在每一层大气中的传输路径,根据追踪路径与目标发射面的交点确定目标空间位置。为减少发射面等先验参数误差的影响,以目标加速度参数一致性作为优化准则,采用迭代估计,在先验误差范围内搜索最优发射面,修正重建误差。通过以上过程反演得到目标运动轨迹以及运动参数,在先验误差范围内,反演的位置误差在200 m以下,速度误差在60 m/s以下。 相似文献
38.
大气折射对电视制导导弹定位精度的影响分析 总被引:1,自引:1,他引:0
为了提高电视制导导弹的定位精度,有必要研究大气折射效应的影响。基于大气折射率模型,采用高精度的4阶Runge-Kutta光线追迹方法,以定位误差和俯角误差为大气折射效应的评价标准,建立了电视制导导弹大气折射误差模型,并通过探空仪实测大气参数验证了模型的有效性以及精度测试验证了算法的可靠性。基于该模型,仿真分析了不同发射高度和俯角对定位精度的影响规律。研究结果发现:高海拔时,基于三段模型的大气折射误差要小于其他模型;相同高度下导弹发射的视在俯角扩大10倍,由大气折射造成的定位误差和俯角误差将分别缩小1 000倍和10倍;5 km高度、视在俯角为30°时的定位误差已减小到2 m以内。研究结果表明,该方法可以辅助电视制导导弹的设计,对提高其精确打击能力具有重要意义。 相似文献
39.
预报高空目标对流层折射的新公式 总被引:2,自引:0,他引:2
对于高空目标,本文得到预测射线弯曲角和大气折射引起的距离误差的新公式,它们可以用于1°以上仰角的折射预报,精度高且使用简便. 相似文献
40.
With the improvement of the accuracy of the inertial system, the influence of the disturbing gravity field on the accuracy of long-range rocket has become increasingly prominent. However, in actual engineering, there are problems of low accuracy and being time-consuming for disturbing gravity field compensation. In view of this, this paper proposes a set of online comprehensive solutions combining disturbing gravity reconstruction and stellar correction. According to the pre-launch binding param... 相似文献