全文获取类型
收费全文 | 6406篇 |
免费 | 1006篇 |
国内免费 | 1294篇 |
专业分类
航空 | 3687篇 |
航天技术 | 1848篇 |
综合类 | 1193篇 |
航天 | 1978篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 95篇 |
2021年 | 77篇 |
2020年 | 146篇 |
2019年 | 63篇 |
2018年 | 81篇 |
2017年 | 74篇 |
2016年 | 77篇 |
2015年 | 187篇 |
2014年 | 348篇 |
2013年 | 370篇 |
2012年 | 397篇 |
2011年 | 427篇 |
2010年 | 523篇 |
2009年 | 533篇 |
2008年 | 480篇 |
2007年 | 448篇 |
2006年 | 379篇 |
2005年 | 320篇 |
2004年 | 219篇 |
2003年 | 175篇 |
2002年 | 172篇 |
2001年 | 233篇 |
2000年 | 252篇 |
1999年 | 347篇 |
1998年 | 331篇 |
1997年 | 263篇 |
1996年 | 272篇 |
1995年 | 201篇 |
1994年 | 208篇 |
1993年 | 196篇 |
1992年 | 173篇 |
1991年 | 139篇 |
1990年 | 125篇 |
1989年 | 103篇 |
1988年 | 76篇 |
1987年 | 66篇 |
1986年 | 35篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1965年 | 3篇 |
排序方式: 共有8706条查询结果,搜索用时 15 毫秒
1.
2.
Yongliao Zou Yan Zhu Yunfei Bai Lianguo Wang Yingzhuo Jia Weihua Shen Yu Fan Yang Liu Chi Wang Aibing Zhang Guobin Yu Jihong Dong Rong Shu Zhiping He Tielong Zhang Aimin Du Mingyi Fan Jianfeng Yang Yongqing Peng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):812-823
This paper describes the scientific objectives and payloads of Tianwen-1, China’s first exploration mission to Mars. An orbiter, carrying a lander and a rover, lifted-off in July 2020 for a journey to Mars where it should arrive in February 2021. A suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of Mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. The mission will also investigate Mars climate history. It is expected that Tianwen-1 will contribute significantly to advance our scientific knowledge of Mars. 相似文献
3.
本文利用LabVIEW软件所设计的三轴光纤陀螺的动态性能测试软件平台可以完成对转台的姿态控制,实现对转台速度角度的设置;同时完成对运动模拟转台及三轴光纤陀螺的参数采集、存储、处理。通过相关数据处理,实现对相关测试数据及评估结果的直观显示。 相似文献
4.
可靠性设计优化(RBDO)在航空航天等领域已经被广泛应用,具有显著提高可靠性的效果;然而它包含两个迭代循环-总体优化循环和可靠性分析循环,双循环求解方法效率低下甚至难以承受。本文提出一种可以提高可靠性设计优化求解效率的方法-球空间设计法,该方法可以方便地表达搜索区域,最大可能失效点可以从极值点处精确获取;同时,该方法可以将总体优化以及可靠性分析同步进行。本文所提出的球空间法的有效性将通过2个算例进行测试,测试结果表明该方法不仅精度与同类方法持平,求解效率有明显提升,它将会对提高航空航天装备如卫星、火箭、飞行器等产品的可靠性提供更为有效的方法和技术支持。 相似文献
5.
复合材料的耐撞性受到了广泛重视,而波纹梁因其优异的抗屈曲构型被广泛应用于飞机翼梁和直升机底板等经常发生碰撞的结构中。进行了复合材料波纹梁的屈曲分析,研究了高度对波纹梁破坏模式的影响。建立复合材料波纹梁的连续损伤单波模型,层内基于Hashin判据建立含损伤因子的损伤刚度矩阵,层间根据二次名义应力准则和B-K准则模拟损伤演化,并通过典型复合材料波纹梁压溃试验验证了所建立模型的正确性。基于单波分析模型,通过施加周期性边界条件和反对称边界条件,研究了多波结构的吸能特性。 相似文献
6.
7.
为提高微机电系统(MEMS)加速度计的标定效率并降低对高精度转台的依赖,提出一种基于改进果蝇优化算法(IFOA)的MEMS加速度计无转台标定方法。首先,根据模观测标定法原理将加速度计标定问题转化为非线性函数优化问题。然后,针对经典果蝇优化算法存在的只能搜索正参数及搜索步长固定的不足,对味道浓度判定值及搜索步长进行改进,使改进后的算法具有全局参数搜索及可变步长2种性能,并利用Rosenbrock函数进行测试,结果表明,IFOA相比于经典果蝇优化算法具有全局参数寻优范围及更高的寻优精度。最后,将IFOA应用于求解加速度计待标定参数的非线性函数优化问题,并将结果与牛顿迭代法和粒子群优化(PSO)算法进行对比。仿真结果表明:IFOA在求解精度方面比牛顿迭代法提高了1~3个数量级;在运行稳定性方面比牛顿迭代法和PSO算法分别提高了30%和34%,在运行时间方面分别减小了15.2%和43.6%;在加速度计无转台标定方面具有良好的应用价值。 相似文献
8.
Qi Li Guanyi Ma Weijun Lu Qingtao Wan Jiangtao Fan Xiaolan Wang Jinghua Li Changhua Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(6):1387-1397
This paper presents a method of deriving the instrumental differential code biases (DCBs) of GPS satellites and dual frequency receivers. Considering that the total electron content (TEC) varies smoothly over a small area, one ionospheric pierce point (IPP) and four more nearby IPPs were selected to build an equation with a convolution algorithm. In addition, unknown DCB parameters were arranged into a set of equations with GPS observations in a day unit by assuming that DCBs do not vary within a day. Then, the DCBs of satellites and receivers were determined by solving the equation set with the least-squares fitting technique. The performance of this method is examined by applying it to 361?days in 2014 using the observation data from 1311 GPS Earth Observation Network (GEONET) receivers. The result was crosswise-compared with the DCB estimated by the mesh method and the IONEX products from the Center for Orbit Determination in Europe (CODE). The DCB values derived by this method agree with those of the mesh method and the CODE products, with biases of 0.091?ns and 0.321?ns, respectively. The convolution method's accuracy and stability were quite good and showed improvements over the mesh method. 相似文献
9.
Jin Wang Xiaoming Zhou Lei Qiao Wanlin Gong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(5):1254-1259
An upgrade of Wuhan Ionospheric Backscattering Sounding System (WIOBSS) was developed in 2015. Based on the Universal Serial Bus (USB), and a high performance FPGA, the newly designed WIOBSS has a completely digital structure, which makes it portable and flexible. Two identical WIOBSSs, which were situated at Mile (24.31°N, 103.39°E) and Puer (22.74°N, 101.05°E) respectively, were used to investigate the ionospheric irregularities. The comparisons of group distance, Doppler shift and width between Mile-Puer and Puer-Mile VHF ionospheric propagation paths indicate that the reciprocity of the irregularities is satisfied at midlatitude region. The WIOBSS is robust in the detection of ionospheric irregularities. 相似文献
10.
The uncertainty of the mechanism motion error is mostly caused by the manufacturing process,so the motion error cannot be effectively predicted at the design phase.The problems of manufacturing complexity and the relationship between design and manufacturing are analyzed,and the influence of dimensional tolerance and fit tolerance on the motion accuracy of the system is considered in the design process.Then based on the Monte Carlo simulation,an optimal design model of planar linkage mechanism is set up.A typical offset slider-crank mechanism is used as an illustrative example to carry out the optimal design.Compared with the result of typical robustness design,the similar variation characteristics of the mean value and the standard deviation can be found,so the proposed method is effective.The method is furthermore applied in the optimization of the schemes with different fit tolerances and the prediction of motion errors in the design phase is achieved.A set of quantitative evaluation system for mechanism optimal design is provided.Finally,a basic strategy is presented to balance the motion precision and manufacturing cost. 相似文献