全文获取类型
收费全文 | 571篇 |
免费 | 187篇 |
国内免费 | 82篇 |
专业分类
航空 | 345篇 |
航天技术 | 150篇 |
综合类 | 101篇 |
航天 | 244篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 24篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 17篇 |
2016年 | 15篇 |
2015年 | 28篇 |
2014年 | 43篇 |
2013年 | 45篇 |
2012年 | 38篇 |
2011年 | 39篇 |
2010年 | 38篇 |
2009年 | 43篇 |
2008年 | 40篇 |
2007年 | 27篇 |
2006年 | 41篇 |
2005年 | 30篇 |
2004年 | 6篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有840条查询结果,搜索用时 15 毫秒
161.
4内、中框轴线垂直度的调整一般来说,内中框轴相互垂直度的精度主要取决于中框架安装内框轴承的上下两孔的轴线与中框轴安装端面的平行度、与上、下孔、左、右止口的同轴度,即取决于中框架的加工精度,对于高精度的要求(1″),受加工机床精度的局限,不能满足精度要... 相似文献
162.
闫吉 《西安航空技术高等专科学校学报》2009,27(4)
"流行书风"的形成与当时书法艺术家主体的完全独立、书法理论界的思想解放、创作主体对创作的个性化与原创性追求,以及以国家级的展览为代表的展厅文化的推波助澜息惠相关.只要其"根植传统、张扬个性"的宗旨不变,在当前乃至今后一个较长的时期,它将一如既往地继续"流行". 相似文献
163.
Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods. 相似文献
164.
针对飞行器进入火星大气时气体辐射加热对防热设计带来不确定性,在简述火星探测和气体辐射研究的发展历程的基础上,对火星进入气体辐射加热研究的进展进行综述。首先,针对火星大气环境描述了气体辐射加热的概念和问题由来。其次,重点综述了近年来火星进入气体辐射加热基础模型的数值和试验研究进展,其中包括:热化学非平衡气体动力学、气体辐射特性和辐射传输的计算模型与方法等数值研究;地面测试设备、试验技术和模拟火星大气环境的气体辐射测量与验证等试验研究。再次,综述了流动辐射耦合和后体气体辐射加热等火星进入器设计方面开展的研究。最后,对未来火星进入气体辐射加热研究进行了展望,提出了研究建议。 相似文献
165.
166.
Gang Li Shuren Guo Jing Lv Kanglian Zhao Zehua He 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(5):1701-1708
Short Message Communication (SMC) is a featured service of BeiDou Navigation Satellite System (BDS). After its successful deployment in 2003, Regional Short Message Communication (RSMC) service has been continuously serving China and its neighboring countries and regions, especially in life safety scenarios. In this paper, the architecture of the Global Short Message Communication (GSMC) system is proposed based on the medium earth orbit (MEO) constellation and the crosslinks of the global BeiDou navigation system (BDS-3). Three subtypes of GSMC service, i.e. positioning report, emergency search and rescue (SAR) and regular SMC are designed in accordance with the technical characteristic of integration of navigation and communication in BDS-3, which supports future wide applications of GSMC. The performance of the designed GSMC system is analyzed by numerical calculations. As BDS-3 was officially announced completion on July 31, 2020, GSMC has been providing initial service. First test results of the in orbit GSMC payloads are also presented in the paper to verify the designed capabilities. Preliminary results also show that the requirements of Global Maritime Distress and Safety System (GMDSS) can also be fulfilled. 相似文献
167.
168.
Meteor Phenomena and Bodies 总被引:12,自引:0,他引:12
Zdeněk Ceplecha JiřÍ Borovička W. Graham Elford Douglas O. ReVelle Robert L. Hawkes VladimÍr Porubčan Miloš Šimek 《Space Science Reviews》1998,84(3-4):327-471
Meteoroids can be observed at collision with the Earth's atmosphere as meteors. Different methods of observing meteors are
presented: besides the traditional counts of individual events, exact methods yield also data on the geometry of the atmospheric
trajectory; on the dynamics and ablation of the body in the atmosphere; on radiation; on the spectral distribution of radiation;
on ionization; on accompanying sounds; and also data on orbits. Theoretical models of meteoroid interaction with the atmosphere
are given and applied to observational data. Attention is paid to radar observations; to spectroscopic observations; to experiments
with artificial meteors and to different types of meteor sounds. The proposed composition and structure of meteoroids as well
as their orbits link them to meteorites, asteroids and comets. Meteor streams can be observed as meteor showers and storms.
The rate of influx of meteoroids of different sizes onto Earth is presented and potential hazards discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
169.
170.