全文获取类型
收费全文 | 11482篇 |
免费 | 9662篇 |
国内免费 | 1854篇 |
专业分类
航空 | 18781篇 |
航天技术 | 1329篇 |
综合类 | 400篇 |
航天 | 2488篇 |
出版年
2024年 | 121篇 |
2023年 | 249篇 |
2022年 | 442篇 |
2021年 | 474篇 |
2020年 | 601篇 |
2019年 | 1238篇 |
2018年 | 1424篇 |
2017年 | 1364篇 |
2016年 | 1363篇 |
2015年 | 1326篇 |
2014年 | 1159篇 |
2013年 | 1186篇 |
2012年 | 1137篇 |
2011年 | 1118篇 |
2010年 | 1104篇 |
2009年 | 1123篇 |
2008年 | 987篇 |
2007年 | 857篇 |
2006年 | 674篇 |
2005年 | 481篇 |
2004年 | 426篇 |
2003年 | 371篇 |
2002年 | 397篇 |
2001年 | 327篇 |
2000年 | 284篇 |
1999年 | 305篇 |
1998年 | 253篇 |
1997年 | 213篇 |
1996年 | 168篇 |
1995年 | 141篇 |
1994年 | 147篇 |
1993年 | 198篇 |
1992年 | 138篇 |
1991年 | 313篇 |
1990年 | 264篇 |
1989年 | 295篇 |
1988年 | 207篇 |
1987年 | 82篇 |
1986年 | 32篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1972年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
11.
本文针对当前各种计算机高级语言运算精度的不足,用PASCAL语言实现了高精度的加、减、乘、除算术四则运算。以满足教学、科研的实际需要。 相似文献
12.
T. J. Ponman A. M. Read 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):361-364
Using data from the Wide Field Camera EUV all-sky survey, we have established upper limits to the EUV flux from a sample of 30 bright, nearby, non-active spiral galaxies. These galaxies were chosen to be those most likely to be detected in the EUV on the basis of (i) low interstellar absorption within our own galaxy, (ii) brightness in other wavebands, (iii) high star formation activity, and (iv) proximity. The derived EUV upper limits are restrictive, and establish for the first time that the EUV flux escaping from galaxies does not constitute a major component of their bolometric luminosity, and in particular that it cannot be the sink for the energy injected into the interstellar medium by supernova explosions, as had been suggested following the failure to detect this power in the X-ray band. 相似文献
13.
参考类似机型的经验是我国目前民用飞机研制的主要途径之一。为了更好地借鉴国内外类似机型的经验,本文提出了一种基于信息熵的类似机型确定方法,该方法应用信息熵理论,直接通过类似机型数据所蕴含的客观信息计算各属性的权重,消除了依靠人为指定权重的主观因素影响。在此基础上,给出了包含有不精确信息属性的相似度的计算方法,最后应用支线飞机实例进行了验证,表明该方法具有较高的客观有效性。 相似文献
14.
The authors present a new scientific space mission consisting of a satellite carrying a receiving- only SAR which receives the signal transmitted by the ENVISAT-1 SAR. The integration of ENVISAT-1 SAR and bistatic radar data offers an improved potentiality of surface classification, three-dimensional observation, and the opportunity of advanced scientific experiments in the field of bistatic scattering. The small satellite nominal orbit and the attitude manoeuvres are designed in order to maintain an adequate overlap between the two radar swaths along the whole orbit, taking into account the ENVISAT-1 attitude and pointing. A preliminary satellite design (2-year lifetime) is then performed to evaluate the orbit decay and to determine the appropriate orbit manoeuvres (every 4 days) to control the satellites relative phase. The numerical simulation shows that a spacecraft of about 584kg is able to meet the mission requirements. 相似文献
15.
In extension to common applications such as groundtrack displays and antenna steering, the SGP4 orbit model is proposed for operational orbit determination in small satellite missions. SGP4 is an analytical orbit model for Low-Earth orbiting satellites that is widely used for the propagation of NORAD twoline elements. Twoline elements may hence be generated completely independent of NORAD. Their use as exclusive source of orbital information simplifies the operations concept and reduces mission costs through the extensive use of existing low-cost mission support software. Due to small computer resource requirements of 8–10kByte, the SGP4 model may also be applied for onboard orbit computations making use of e.g. a 80186 processor, thus ensuring full compatibility of ground-based and onboard operations. The proposed approach is particularly suited in combination with a space-borne GPS receiver, were the C/A-code navigation solutions are treated as measurements that are adjusted in a least-squares sense using the SGP4 model. As consequence, inherent drawbacks of the pure navigation solutions such as data gaps and scatter as well as limited velocity accuracy are avoided, while the operational navigation activities are kept at a minimum. The feasibility of the concept is illustrated based on real GPS navigation data from the TOPEX/Poseidon and the MIR space station with an inherent data quality of 50–100 m. It is shown that 3 hours of data within a 4 day period are sufficient to keep the position error within 4 km, that is considered sufficient for most applications. 相似文献
16.
管辉 《华北航天工业学院学报》2005,15(2):23-25
本文从集合住宅的发展谈起,简单提出几点设计新概念,重点对住宅户型设计中的功能空间进行探讨和分析。 相似文献
17.
18.
无人机自由编队飞行的补偿模糊神经网络控制 总被引:1,自引:0,他引:1
为了克服当前提出的无人机编队飞行的不足,提出一种新的无人机编队飞行概念——自由编队飞行,制定了相关的避让规则,用补偿模糊神经网络进行训练,实现自由编队飞行的补偿模糊神经网络控制。仿真显示,编队飞行的飞机能按照规则自主改变航路进行避让,表明了该方法的有效性。 相似文献
19.
结合 TMS32 0 C80的编程结构 ,利用神经网络的权并行性和神经元并行性 ,提出了BP算法的并行实现方法 ,并解决了存储器访问冲突、数据双缓冲传输、PP细粒度并行和死锁等问题。结果表明 ,该并行 BP算法十分有效。 相似文献
20.