全文获取类型
收费全文 | 623篇 |
免费 | 102篇 |
国内免费 | 138篇 |
专业分类
航空 | 388篇 |
航天技术 | 200篇 |
综合类 | 109篇 |
航天 | 166篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 28篇 |
2013年 | 40篇 |
2012年 | 46篇 |
2011年 | 50篇 |
2010年 | 42篇 |
2009年 | 49篇 |
2008年 | 44篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 25篇 |
1995年 | 14篇 |
1994年 | 27篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有863条查询结果,搜索用时 859 毫秒
531.
介绍了利用极大似然法辨识飞机极曲线的基本原理。通过仿真研究及对实测飞行试验数据的处理,表明该方法能够辨识出光滑的非线性飞机极曲线,算法具有良好的收敛性及结果的唯一性,并且可方便地推广应用于工程中其它类型的非线性曲线辨识问题。 相似文献
532.
533.
是哪一方秘境的澄怀之水在低唱浅吟?是哪一刻光阴的微妙斑斓在亘古的石上漫过?该是第一缕初春的气息化开的那一芽绿吧,也定是入冬最销骨的那阵寒霜激活了那一枚红,当清晨的风舞动原野的时候,当黄昏跃动的光点亮烂漫花海的时候,我以为,我似乎就看见了大自然那颗最柔曼少女的心——她的圣洁与温馨,[编按] 相似文献
534.
535.
利用计算流体力学的仿真软件FLUENT对鱼雷发射箱内流场变化情况进行仿真计算,通过仿真计算分析发射箱内的压强分布规律及其对易碎裂盖体的影响。仿真结果表明,后盖在助推器射流直接冲击下会受到极不均匀的压强作用,可能使后盖中心破裂而不碎;前盖受后盖反射的射流影响而开盖。研究结果对发射箱的碎裂开盖方案设计有一定的指导意义。 相似文献
536.
Weiping Jiang Liansheng Deng Zhao Li Xiaohui Zhou Hongfei Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Higher-order ionospheric (HOI) effects are one of the principal technique-specific error sources in precise global positioning system (GPS) analysis. These effects also influence the non-linear characteristics of GPS coordinate time series. In this paper, we investigate these effects on coordinate time series in terms of seasonal variations and noise amplitudes. Both power spectral techniques and maximum likelihood estimators (MLE) are used to evaluate these effects quantitatively and qualitatively. Our results show an overall improvement for the analysis of global sites if HOI effects are considered. We note that the noise spectral index that is used for the determination of the optimal noise models in our analysis ranged between −1 and 0 both with and without HOI corrections, implying that the coloured noise cannot be removed by these corrections. However, the corrections were found to have improved noise properties for global sites. After the corrections were applied, the noise amplitudes at most sites decreased, among which the white noise amplitudes decreased remarkably. The white noise amplitudes of up to 81.8% of the selected sites decreased in the up component, and the flicker noise of 67.5% of the sites decreased in the north component. Stacked periodogram results show that, no matter whether the HOI effects are considered or not, a common fundamental period of 1.04 cycles per year (cpy), together with the expected annual and semi-annual signals, can explain all peaks of the north and up components well. For the east component, however, reasonable results can be obtained only based on HOI corrections. HOI corrections are useful for better detecting the periodic signals in GPS coordinate time series. Moreover, the corrections contributed partly to the seasonal variations of the selected sites, especially for the up component. Statistically, HOI corrections reduced more than 50% and more than 65% of the annual and semi-annual amplitudes respectively at the selected sites. 相似文献
537.
538.
Identification Method for RLG Random Errors Based on Allan Variance and Equivalent Theorem 总被引:1,自引:0,他引:1
An identification method using Allan variance and equivalent theorem is proposed to identify non-stationary sensor errors mixed out of different simple noises. This method firstly derives the discrete Allan variances of all component noises inherent in noise sources in terms of their different equations; then the variances are used to estimate the parameters of all component noise models; finally, the original errors are represented by the sum of the non-stationary component noise model and the equivalent model mixed out of the stationary and critically stationary component noises. Results of two examples for identification confirm the superiority of this approach regardless of the errors being stationary or not. The comparison of results of real ring laser gyro (RLG) errors processed by various methods shows that the proposed approach is more suited to depict the original noises than common ones. 相似文献
539.
空间拦截非线性控制问题的高精度计算 总被引:2,自引:0,他引:2
在空间拦截非线性控制问题数学模型的基础上,采用动力系统的一种高精度计算方法-时程精细分法,对非线性空间拦截问题进行了研究,其主要步骤为,首先将非线性控制问题线性化,使其满足精细积分算法的要求,进而根据线性化的方程,建立一套处理非线性问题的精细迭代算法,该算法不仅具有很高的计算精度,还具有很好的数值稳定一。 相似文献
540.