全文获取类型
收费全文 | 3669篇 |
免费 | 443篇 |
国内免费 | 259篇 |
专业分类
航空 | 2330篇 |
航天技术 | 657篇 |
综合类 | 326篇 |
航天 | 1058篇 |
出版年
2024年 | 26篇 |
2023年 | 70篇 |
2022年 | 114篇 |
2021年 | 91篇 |
2020年 | 84篇 |
2019年 | 113篇 |
2018年 | 106篇 |
2017年 | 81篇 |
2016年 | 97篇 |
2015年 | 83篇 |
2014年 | 127篇 |
2013年 | 100篇 |
2012年 | 97篇 |
2011年 | 103篇 |
2010年 | 108篇 |
2009年 | 115篇 |
2008年 | 107篇 |
2007年 | 139篇 |
2006年 | 152篇 |
2005年 | 133篇 |
2004年 | 84篇 |
2003年 | 116篇 |
2002年 | 86篇 |
2001年 | 99篇 |
2000年 | 99篇 |
1999年 | 75篇 |
1998年 | 87篇 |
1997年 | 110篇 |
1996年 | 112篇 |
1995年 | 117篇 |
1994年 | 152篇 |
1993年 | 54篇 |
1992年 | 80篇 |
1991年 | 110篇 |
1990年 | 92篇 |
1989年 | 61篇 |
1988年 | 102篇 |
1987年 | 120篇 |
1986年 | 31篇 |
1985年 | 113篇 |
1984年 | 100篇 |
1983年 | 114篇 |
1982年 | 72篇 |
1981年 | 42篇 |
1980年 | 34篇 |
1979年 | 19篇 |
1978年 | 5篇 |
1977年 | 12篇 |
1960年 | 6篇 |
1959年 | 8篇 |
排序方式: 共有4371条查询结果,搜索用时 828 毫秒
231.
An experimental investigation into pre-swirl effectiveness and receiver hole discharge coefficient characteristics for a high radius injection pre-swirl cooling systems was carried out on a physically representative experimental rig with a 450 mm diameter rotor.The receiver holes and pre-swirl nozzle were located at a radius of 181 mm and 180 mm respectively.The experimental work was mainly conducted at 5 000~12 000 r/min,4 bar absolute pressure and 1.132 kg/s air supply.The maximum air supply temperature was 190 ℃.Pressure and temperature distributions in the pre-swirl system were examined with an emphasis on the velocity effectiveness of the pre-swirl system as a whole and on the discharge coefficients of the rotating 'receiver holes' in the rotor.The results showed that the velocity effectiveness increased with increasing swirl ratio resulting in reduced blade cooling flow temperature.Different seal flow configurations caused very different effectiveness at different speeds,but outflow through the inner and outer seals always gave the highest effectiveness compared other configurations.Increasing the seal flow rate reduced the effectiveness.For the coefficient of discharge,except for the low speed range,it increased with increase in swirl ratio for most speeds. 相似文献
232.
The role of AVDR in linear cascade testing 总被引:1,自引:0,他引:1
Linear cascade testing plays an important role in the research and development of turbomachinery and is widely used over the world.The ideal cascade model of a turbomachinery blade row is two-dimensional.In actual linear cascade testing, the flow through the test section converges due to the development of the boundary layer and secondary flow along the sidewall surfaces of the test section.Axial velocity density ratio(AVDR) is adopted to account for the deviation of the tested cascade flow from the ideal 2D model.Among numerous published cascade works, the influence of AVDR on cascade performance is seen to be complicated with many affecting factors, such as those related to cascade/blade geometry and flow conditions.Also, controlling AVDR is limited by the facility capability.Furthermore, real blade-to-blade flow in turbomachines is usually associated with AVDR greater than unity due to limited span of blades between the hub and shroud such that cascade testing without reducing AVDR could be favored sometimes.All these facets add complexity and diversification to the matter.The current paper reviews previous studies and results on AVDR.Consolidated understanding on the role of AVDR and recommendations on how to deal with it in linear cascade testing are provided. 相似文献
233.
234.
<正>司库管理是企业在战略层面管控资金的管理模式。司库体系的建设能够提升企业资金管理水平,加强企业对金融资源的管控能力和战略决策支持能力。本文以H集团为分析实例,通过论证H集团进行司库管理体系建设的必要性和提出需要解决的问题,从企业组织架构和管理模式、制度及流程优化、信息化建设等方面阐述司库管理体系建设方案,为企业司库体系建设提供思路。 相似文献
235.
月面软着陆探测器地面力学试验方法研究 总被引:1,自引:1,他引:0
月面软着陆探测器的主要任务是携带有效载荷实现在月球表面的安全着陆,其经历的主要过程包括发射段、地月转移段、近月制动段、环月段、着陆段和月面工作段。软着陆探测器面临的月球环境比近地轨道卫星复杂得多。为提高软着陆探测器系统的可靠性,必须进行充分的地面试验,验证软着陆探测器的设计合理性。文章分析了月球软着陆探测器在各飞行过程中面临的力学环境,分析了力学环境对探测器系统的影响及作用效果,提出软着陆探测器需完成的地面力学试验项目,设计相应的试验方法,并给出确定试验量级的基本原则。 相似文献
236.
Rain.L 《中国航天(英文版)》2008,(1)
THE FOURTH BEIDOU NAVIGATION EXPERIMENTAL SATELLITE LAUNCHED The fourth Beidou experimental navigation satellite was launched into snace aton a LM-3A launch vehicle at Xichang Satellite Launch Center on February 3 at 00:28(Beijing Time).24 minutes later,the satellite separated from the launch vehicle and 相似文献
237.
Rain.L 《中国航天(英文版)》2008,(2)
FY-3A,the first satellite of China's new generation of polar-orbiting meteorological satellites,was launched into space atop a modified LM-4C launch vehicle.The satellite separated from the rocket 19 minutes after the takeoff.Flying at an altitude of 807km with an inclination of 98.8 degrees,the satellite circles in polar orbit 14 times everyday,covering the whole globe twice a day. FY-3A has a design lifetime of three years.Weighing 2295kg,the three-axis stabilized satellite is equipped with 11 remote s... 相似文献
238.
239.
设计出了一种简单可靠的钩针式的马尾织布机自动分尾装置,在介绍了该装置的机械结构和工作原理的基础上,采用蒙特卡洛法模拟法对关键的结构参数进行了优化设计,大大缩短了设计和试验周期;该装置已成功用于生产,提高了生产效率。 相似文献
240.