全文获取类型
收费全文 | 1368篇 |
免费 | 328篇 |
国内免费 | 277篇 |
专业分类
航空 | 912篇 |
航天技术 | 352篇 |
综合类 | 308篇 |
航天 | 401篇 |
出版年
2024年 | 6篇 |
2023年 | 14篇 |
2022年 | 29篇 |
2021年 | 44篇 |
2020年 | 26篇 |
2019年 | 21篇 |
2018年 | 27篇 |
2017年 | 32篇 |
2016年 | 31篇 |
2015年 | 56篇 |
2014年 | 84篇 |
2013年 | 83篇 |
2012年 | 104篇 |
2011年 | 91篇 |
2010年 | 109篇 |
2009年 | 105篇 |
2008年 | 99篇 |
2007年 | 82篇 |
2006年 | 71篇 |
2005年 | 61篇 |
2004年 | 42篇 |
2003年 | 41篇 |
2002年 | 45篇 |
2001年 | 64篇 |
2000年 | 58篇 |
1999年 | 92篇 |
1998年 | 61篇 |
1997年 | 60篇 |
1996年 | 63篇 |
1995年 | 44篇 |
1994年 | 53篇 |
1993年 | 33篇 |
1992年 | 30篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有1973条查询结果,搜索用时 15 毫秒
461.
462.
为解决目前面向林火持续侦察多无人机(UAV)协同控制实用性与自主性不足的问题,基于蔓延速度诱导元胞自动机(SVICA)林火蔓延算法、无人机与传感器建模,构建了较为真实的三维多无人机火场侦察仿真环境与侦察效能指标,提出了一种面向林火持续侦察的多无人机双层分布式控制架构,在行动层基于强化学习训练的人工神经网络(ANN),实现了有风条件下无人机自主火场环绕与地形跟随功能,在策略层设计通过时域均匀分布算法进行各无人机空速的离散自主调节,最终达到多无人机林火持续侦察时域分布的均匀性与即时性目的。通过一系列数值仿真实验,验证了所提出的无人机分布控制策略在无人机损失和补充突发情况下的自适应性。基于无人机数量与侦察效能指标关系的实验与研究,定义了无人机出动阈值并验证了无人机长时间出动回收策略。最终实验结果表明,针对林火持续侦察任务,所提出的多无人机分布式控制方法具备一定的有效性与实用性。 相似文献
463.
空域拥挤风险管理时间决策模型与方法 总被引:1,自引:0,他引:1
针对目前日益严重的空域拥挤现象,缺乏有效的空域拥挤风险管理机制,造成拥挤难以应对等问题,建立了空域拥挤风险预测模型、空域拥挤风险解决模型和风险损失成本模型。采用风险预测模型和解决模型预测可能产生空域拥挤的时段、提出不同时段的实施流量管理策略,基于风险损失成本模型给出了不同时段调整拥挤的运行成本,通过比较运行成本和空域拥挤风险管理决策方法确定出解决空域拥挤的最佳时间点。采用实际运行数据进行验证,结果表明:所建立的空域拥挤预测模型、空域拥挤风险解决模型、风险损失成本模型和空域拥挤风险管理时间决策方法能有效地预测未来空域发生拥挤的时段,迅速找到运行成本最小的调整拥挤的时间点,为空中交通流量动态管理提供了新途径。 相似文献
464.
Jian Huang Weidong Hu Mounir Ghogho Qin Xin Xiaoyong Du Weiwei Guo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The increase in space debris can seriously threaten regular activities in the Low Earth Orbit (LEO) environment. Therefore, it is necessary to develop robust, efficient and reliable techniques to understand the potential motions of the LEO debris. In this paper, we propose a novel signal processing approach to detect and estimate the motions of LEO space debris that is based on a fence-type space surveillance radar system. Because of the sparse distribution of the orbiting debris through the fence in our observations, we formulate the signal detection and the motion parameter estimation as a sparse signal reconstruction problem with respect to an over-complete dictionary. Moreover, we propose a new scheme to reduce the size of the original over-complete dictionary without the loss of the important information. This new scheme is based on a careful analysis of the relations between the acceleration and the directions of arrival for the corresponding LEO space debris. Our simulation results show that the proposed approach can achieve extremely good performance in terms of the accuracy for detection and estimation. Furthermore, our simulation results demonstrate the robustness of the approach in scenarios with a low Signal-to-Noise Ratio (SNR) and the super-resolution properties. We hope our signal processing approach can stimulate further work on monitoring LEO space debris. 相似文献
465.
Kaichang Di Wenmin Hu Yiliang Liu Man Peng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012,50(12):1615-1628
Topographic information is of fundamental importance for various scientific investigations in lunar and planetary exploration. To provide high-precision, seamless mapping capability, it is critical to co-register image and altimetry data, the two major data sources for topographic modeling. This paper presents a method for co-registration of Chang’E-1 (CE-1) stereo images and laser altimeter (LAM) data with crossover adjustment and refinement of the image sensor model. The crossover adjustment is tested in a larger area (0–60°N, 50–0°W); the image refinement and co-registration with LAM data are tested in an area (46.2–50.0°N, 31.8–28.8°W) within the larger area. Experimental results demonstrate that this co-registration reduces the mean differences of inconsistency from more than 200 m to just 3.21 m in the Z direction of object space. In image space, the mean errors of homologous points both in the column and row directions are reduced to below 0.1 pixel. This indicates that the proposed crossover adjustment of LAM data and refinement of the CE-1 stereo image model can effectively improve co-registration of the two data sets. 相似文献
466.
Zongjie Hao Dunhai Li Yanhui Li Zhicong Wang Yuan Xiao Gaohong Wang Yongding Liu Chunxiang Hu Qifang Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Some phytoplankton can be regarded as possible candidates in the establishment of Controlled Ecological Life Support System (CELSS) for some intrinsic characteristics, the first characteristic is that they should grow rapidly, secondly, they should be able to endure some stress factors and develop some corresponding adaptive strategies; also it is very important that they could provide food rich in nutritious protein and vitamins for the crew; the last but not the least is they can also fulfill the other main functions of CELSS, including supplying oxygen, removing carbon dioxide and recycling the metabolic waste. According to these characteristics, Nostoc sphaeroides, a potential healthy food in China, was selected as the potential producer in CELSS. It was found that the oxygen average evolution rate of this algae is about 150 μmol O2 mg−1 h−1, and the size of them are ranged from 2 to 20 mm. Also it can be cultured with high population density, which indicated that the potential productivity of Nostoc sphaeroides is higher than other algae in limited volume. We measured the nutrient contents of the cyanobacterium and concluded it was a good food for the crew. Based on above advantages, Nostoc sphaeroides was assumed to a suitable phytoplankton for the establishment of Controlled Ecological Life Support System. We plan to develop suitable bioreactor with the cyanobacterium for supplying oxygen and food in future space missions. 相似文献
467.
468.
Airborne Distributed Coherent Aperture Radar(ADCAR) is one of the most promising next-generation radars to significantly improve target detection and discrimination abilities. However, time and phase synchronization among unit radars should be done before an ADCAR is intended to cohere on a potential target. To address this problem, a time and phase synchronization technique using clutter observations is proposed in this paper. Clutter returns from different azimuths and elevations on the surfac... 相似文献
469.
470.
胡行康 《航空标准化与质量》1999,(6):9
概述了治理汽车排放污染的技术法规、汽车排放控制技术和车用燃油三大要素的内容和作用,以及它们相互依存的关系。最后提出了对我国治理汽车排放污染的4 点建议。 相似文献