全文获取类型
收费全文 | 2561篇 |
免费 | 535篇 |
国内免费 | 493篇 |
专业分类
航空 | 1682篇 |
航天技术 | 648篇 |
综合类 | 538篇 |
航天 | 721篇 |
出版年
2024年 | 7篇 |
2023年 | 25篇 |
2022年 | 58篇 |
2021年 | 78篇 |
2020年 | 68篇 |
2019年 | 53篇 |
2018年 | 73篇 |
2017年 | 67篇 |
2016年 | 50篇 |
2015年 | 86篇 |
2014年 | 146篇 |
2013年 | 142篇 |
2012年 | 166篇 |
2011年 | 161篇 |
2010年 | 195篇 |
2009年 | 196篇 |
2008年 | 167篇 |
2007年 | 142篇 |
2006年 | 123篇 |
2005年 | 104篇 |
2004年 | 69篇 |
2003年 | 79篇 |
2002年 | 75篇 |
2001年 | 94篇 |
2000年 | 105篇 |
1999年 | 154篇 |
1998年 | 119篇 |
1997年 | 103篇 |
1996年 | 119篇 |
1995年 | 81篇 |
1994年 | 101篇 |
1993年 | 70篇 |
1992年 | 61篇 |
1991年 | 50篇 |
1990年 | 56篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有3589条查询结果,搜索用时 15 毫秒
101.
V. Yurchyshyn Q. Hu R.P. Lepping B.J. Lynch J. Krall 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1821-1826
Coronal mass ejections (CMEs) observed near the Sun via LASCO coronographic imaging are the most important solar drivers of geomagnetic storms. ICMEs, their interplanetary, near-Earth counterparts, can be detected in situ, for example, by the Wind and ACE spacecraft. An ICME usually exhibits a complex structure that very often includes a magnetic cloud (MC). They can be commonly modelled as magnetic flux ropes and there is observational evidence to expect that the orientation of a halo CME elongation corresponds to the orientation of the flux rope. In this study, we compare orientations of elongated CME halos and the corresponding MCs, measured by Wind and ACE spacecraft. We characterize the MC structures by using the Grad–Shafranov reconstruction technique and three MC fitting methods to obtain their axis directions. The CME tilt angles and MC fitted axis angles were compared without taking into account handedness of the underlying flux rope field and the polarity of its axial field. We report that for about 64% of CME–MC events, we found a good correspondence between the orientation angles implying that for the majority of interplanetary ejecta their orientations do not change significantly (less than 45 deg rotation) while travelling from the Sun to the near-Earth environment. 相似文献
103.
For the performance issues of satellite transceivers suffering passive intermodulation interference,a novel and effective digital suppression algorithm is presented in this paper.In con trast to analog approaches,digital passive intermodulation (PIM) suppression approaches can be easily reconfigured and therefore are highly attractive for future satellite communication systems.A simplified model of nonlinear distortion from passive microwave devices is established in consid eration of the memory effect.The multiple high-order PIM products falling into the receiving band can be described as a bilinear predictor function.A suppression algorithm based on a bilinear poly nomial decorrelated adaptive filter is proposed for baseband digital signal processing.In consideration of the time-varying characteristics of passive intermodulation,this algorithm can achieve the rapidness of online interference estimation and low complexity with less consumption of resources.Numerical simulation results show that the algorithm can effectively compensate the passive intermodulation interference,and achieve a high signal-to-interference ratio gain. 相似文献
104.
Rui Tu Jinhai Liu Rui Zhang Pengfei Zhang Xiaodong Huang Xiaochun Lu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(2):913-926
This paper proposes a real-time kinematic (RTK) model that uses one common reference satellite for the Galileo system with four frequency observations. In the proposed model, the double-differenced (DD) pseudorange and carrier phase biases among the different frequencies are estimated as unknown parameters to recover the integer features of the DD ambiguities among the different frequencies for ambiguity resolution and precise positioning. Analysis results show that the E5a, E5b, and E5 frequencies have virtually the same performance in terms of the positioning accuracy, observation residuals, and ratio values of ambiguity resolution. However, the E1 frequency performs worse than the E5a, E5b, and E5 frequencies. The RTK results for the combination of multiple frequencies are much better than those for a single-frequency observation, the coordinates’ standard deviation is improved about 20–30%, and the ambiguity fix time is improved about 10%. 相似文献
105.
106.
108.
109.
基于间接法在线能力评估和自主规划技术研究 总被引:1,自引:0,他引:1
针对运载火箭推力故障条件下的自主救援任务,研究了一种基于间接法的在线能力评估和自主规划方法.构建了以入轨点能量最大为最优性能指标的最优控制问题.通过数值方法探讨了在满足轨道倾角和入轨点路径角约束条件下,入轨点速度、远地点和近地点跟入轨高度之间的关系,设计了一种与入轨高度相关的特征量来对入轨能力进行评估.以近地点最高为救... 相似文献
110.