全文获取类型
收费全文 | 680篇 |
免费 | 141篇 |
国内免费 | 154篇 |
专业分类
航空 | 528篇 |
航天技术 | 199篇 |
综合类 | 59篇 |
航天 | 189篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 23篇 |
2021年 | 41篇 |
2020年 | 50篇 |
2019年 | 50篇 |
2018年 | 37篇 |
2017年 | 68篇 |
2016年 | 49篇 |
2015年 | 46篇 |
2014年 | 68篇 |
2013年 | 34篇 |
2012年 | 61篇 |
2011年 | 42篇 |
2010年 | 39篇 |
2009年 | 41篇 |
2008年 | 52篇 |
2007年 | 43篇 |
2006年 | 30篇 |
2005年 | 20篇 |
2004年 | 27篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 1篇 |
排序方式: 共有975条查询结果,搜索用时 562 毫秒
41.
42.
43.
44.
This paper studies the proximate satellite interception guidance strategies where both the interceptor and target can perform orbital maneuvers with magnitude limited thrusts. This problem is regarded as a pursuit-evasion game since satellites in both sides will try their best to capture or escape. In this game, the distance of these two players is small enough so that the highly nonlinear earth-centered gravitational dynamics can be reduced to the linear Clohessy-Wiltshire (CW) equations. The system is then simplified by introducing the zero effort miss variables. Saddle solution is formulated for the pursuit-evasion game and time-to-go is estimated similarly as that for the exo-atmospheric interception. Then a vector guidance is derived to ensure that the interception can be achieved in the optimal time. The proposed guidance law is validated by numerical simulations. 相似文献
45.
Reliability-based trajectory optimization using nonintrusive polynomial chaos for Mars entry mission 总被引:1,自引:0,他引:1
Yuechen Huang Haiyang Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(11):2854-2869
This paper presents the reliability-based sequential optimization (RBSO) method to settle the trajectory optimization problem with parametric uncertainties in entry dynamics for Mars entry mission. First, the deterministic entry trajectory optimization model is reviewed, and then the reliability-based optimization model is formulated. In addition, the modified sequential optimization method, in which the nonintrusive polynomial chaos expansion (PCE) method and the most probable point (MPP) searching method are employed, is proposed to solve the reliability-based optimization problem efficiently. The nonintrusive PCE method contributes to the transformation between the stochastic optimization (SO) and the deterministic optimization (DO) and to the approximation of trajectory solution efficiently. The MPP method, which is used for assessing the reliability of constraints satisfaction only up to the necessary level, is employed to further improve the computational efficiency. The cycle including SO, reliability assessment and constraints update is repeated in the RBSO until the reliability requirements of constraints satisfaction are satisfied. Finally, the RBSO is compared with the traditional DO and the traditional sequential optimization based on Monte Carlo (MC) simulation in a specific Mars entry mission to demonstrate the effectiveness and the efficiency of the proposed method. 相似文献
为了描述人体肩部骨骼系统的运动特征,将肩胛骨与胸廓的相对运动关系定义为类似于圆柱-平面副的运动约束,建立了肩部骨骼系统的空间混联机构模型。首先定义了肩部复合体各关节的类型,并完成了肩带部分和整个肩部机构的自由度分析。然后通过定义附着于各骨骼上的局部坐标系,以齐次坐标变换矩阵和矢量法建立机构的运动分析方程,求得其关节位置的闭合解。最后为了验证该模型,以获得自肩部运动实验的骨骼姿态数据反向驱动该机构模型,从而得到肩胛骨姿态的计算结果,并与测量结果进行对比。结果表明:该机构模型能够反映肩部骨骼的运动约束关系。同时,该模型可以通过缩放处理从而用于适应不同个体的骨骼几何特征。 相似文献