全文获取类型
收费全文 | 440篇 |
免费 | 111篇 |
国内免费 | 137篇 |
专业分类
航空 | 423篇 |
航天技术 | 94篇 |
综合类 | 76篇 |
航天 | 95篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 31篇 |
2021年 | 36篇 |
2020年 | 37篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 33篇 |
2015年 | 30篇 |
2014年 | 41篇 |
2013年 | 30篇 |
2012年 | 31篇 |
2011年 | 32篇 |
2010年 | 34篇 |
2009年 | 27篇 |
2008年 | 21篇 |
2007年 | 17篇 |
2006年 | 19篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
排序方式: 共有688条查询结果,搜索用时 187 毫秒
1.
Arman Seuylemezian Manuela Buonanno Lisa Guan David J. Brenner David Welch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):496-503
This work aims to investigate far-UVC light at 222 nm as a new microbial reduction tool for planetary protection purposes which could potentially be integrated into the spacecraft assembly process. The major advantage of far-UVC (222 nm) compared to traditional germicidal UVC (254 nm) is the potential for application throughout the spacecraft assembly process in the presence of humans without adverse health effects due to the limited penetration of far-UVC light into biological materials. Testing the efficacy of 222-nm light at inactivating hardy bacterial cells and spores isolated from spacecraft and associated surfaces is a necessary step to evaluate this technology. We assessed survival of Bacillus pumilus SAFR-032 and Acinetobacter radioresistens 50v1 exposed to 222-nm light on proxy spacecraft surfaces simulated by drying the bacteria on aluminum coupons. The survival fraction of both bacteria followed a single stage decay function up to 60 mJ/cm2, revealing similar susceptibility of both species to 222-nm light, which was independent of the exposure rate. Irradiation with far-UVC light at 222 nm is an effective method to decontaminate the proxy spacecraft materials tested in this study. 相似文献
2.
论述纵向耦合振动(POGO)蓄压器的变频降幅特性,指出其主要影响因素是蓄压器容积及连接管路的液阻,根据输送管路的特定频率,选择适当的蓄压器容积,使其固有频率与特定管路的压力脉动频率相一致,可以获得预期的变频降幅效果。给出了蓄压器的变频降幅试验研究结果,可为POGO蓄压器的设计,研制,使得提供参考。 相似文献
3.
4.
5.
6.
Jessica M. Sunshine Michael F. A’Hearn Olivier Groussin Lucy A. McFadden Kenneth P. Klaasen Peter H. Schultz Carey M. Lisse 《Space Science Reviews》2005,117(1-2):269-295
The science payload on the Deep Impact mission includes a 1.05–4.8 μm infrared spectrometer with a spectral resolution ranging
from R∼200–900. The Deep Impact IR spectrometer was designed to optimize, within engineering and cost constraints, observations
of the dust, gas, and nucleus of 9P/Tempel 1. The wavelength range includes absorption and emission features from ices, silicates,
organics, and many gases that are known to be, or anticipated to be, present on comets. The expected data will provide measurements
at previously unseen spatial resolution before, during, and after our cratering experiment at the comet 9P/Tempel 1. This
article explores the unique aspects of the Deep Impact IR spectrometer experiment, presents a range of expectations for spectral
data of 9P/Tempel 1, and summarizes the specific science objectives at each phase of the mission. 相似文献
7.
THERESEARCHOFINCREASINGLIFTANDREDUCINGDRAGFORWING-TIPSAILSChenMingyan,QiMengbu(NanjingUniversityofAeronauticsandAstronautics,... 相似文献
8.
针对复合壳阻尼结构的拓扑减振优化问题,以约束阻尼层的有限单元为设计变量,采用体积比、模态频率和振型为优化约束条件,构建以多模态权重系数的结构模态损耗因子数值关系为优化目标函数的拓扑减振优化模型。为了拓展优化目标灵敏度具有不局限于某一变密度法插值模型的形式,推导了数值表达式的一般函数式。动力学优化中优化目标灵敏度正、负数集共存,使得非凸性的目标函数设计变量出现负值或优化函数寻优于局部极值点。为此,推导出复合壳阻尼结构的全域灵敏度改进优化准则法迭代格,以确保每次迭代域均为全域设计变量集。结合有限单元法编程实现了复合壳阻尼结构改进准则法,并对复合壳结构进行拓扑减振优化分析。结果表明:在敷设体积减为全覆盖的50%时,复合壳结构的模态损耗因子增减偏差为10%,具有提升减振的轻量化设计目的;各阶目标函数和拓扑构型所需的迭代次数少,中间密度区域较小,多阶优于单阶模态优化函数,易于获得全域寻优的有效减振。 相似文献
9.
This paper presents a brief review of activities in laminar flow control being performed at the Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (TsAGI). These efforts are focused on the improvement of the existing laminar flow control methods and on the development of new ones. The investigations have demonstrated the effectiveness of aircraft surface laminarization applications with the aim of friction drag reduction. The opportunity of considerable delaying of laminar-turbulent transition due to special wing profile geometry and using boundary layer suction and surface cooling has been verified at sub- and supersonic speeds through various wind tunnel testing at TsAGI and during flying laboratory experiments at the Flight Research Institute (LII). The investigations on using hybrid laminar flow control systems for friction drag reduction were also carried out. New techniques of laminar flow control were proposed, in particular, the method of local heating of the wing leading edge, boundary layer laminarization by means of receptivity control, and electrohydrodynamic methods of boundary layer stability control. 相似文献
10.
针对铆接工作过程中振动和噪声过大影响工作人员身体健康以及装配质量等严峻问题,介绍了阻尼减振降噪技术,探讨了铆接过程中阻尼减振降噪的可行性技术,并简要的介绍了国内外在这一方面的研究成果。最后,认为利用建模仿真模拟来优化阻尼结构的设计和开发以及确定阻尼敷设的最优位置等。并总结出如何设计阻尼器以及设计一款合适的阻尼器所必需具备的几个特性。 相似文献