全文获取类型
收费全文 | 2971篇 |
免费 | 1703篇 |
国内免费 | 418篇 |
专业分类
航空 | 3769篇 |
航天技术 | 225篇 |
综合类 | 202篇 |
航天 | 896篇 |
出版年
2024年 | 18篇 |
2023年 | 30篇 |
2022年 | 135篇 |
2021年 | 176篇 |
2020年 | 134篇 |
2019年 | 127篇 |
2018年 | 100篇 |
2017年 | 148篇 |
2016年 | 199篇 |
2015年 | 145篇 |
2014年 | 196篇 |
2013年 | 206篇 |
2012年 | 231篇 |
2011年 | 242篇 |
2010年 | 196篇 |
2009年 | 206篇 |
2008年 | 177篇 |
2007年 | 189篇 |
2006年 | 186篇 |
2005年 | 225篇 |
2004年 | 167篇 |
2003年 | 203篇 |
2002年 | 181篇 |
2001年 | 139篇 |
2000年 | 124篇 |
1999年 | 140篇 |
1998年 | 116篇 |
1997年 | 124篇 |
1996年 | 96篇 |
1995年 | 94篇 |
1994年 | 70篇 |
1993年 | 70篇 |
1992年 | 69篇 |
1991年 | 52篇 |
1990年 | 51篇 |
1989年 | 59篇 |
1988年 | 52篇 |
1987年 | 18篇 |
1986年 | 1篇 |
排序方式: 共有5092条查询结果,搜索用时 15 毫秒
141.
142.
For the problem that the plume flow field structure of a multi engine parallel rocket is complicated and the bottom thermal environment is extremely harsh, which may cause the failure of the engine structural components, the plume flow field and thermal environment at different altitudes are studied through numerical simulation. The result is compared with the measured results in flight which shows that when the rocket is flying at a low altitude, the plume of the engines do not interfere with each other. As the flight altitude increases, the plumes gradually expand and begin to interfere with each other, and finally there is an obvious backflow at the bottom of the rocket. The maximum heat flux at the moment of take off is basically the same as the measured value in flight. Before the backflow occurs, the heat flux mainly consists of radiant heat, the convective heat flow increases as the flight altitude grows, but it is also much smaller than the peak heat flow at takeoff. The result has certain guiding significance for the optimal design of engine structure thermal protection. 相似文献
143.
《中国航空学报》2020,33(4):1288-1298
The degradation of components in complex mechatronic systems involves multiple physical processes which will cause coupling interactions among nodes in the system. The interaction of nodes may be carried out not only by physical connections but also by the environment which cannot be described by single network using the traditional methods. In order to give out a unified model to quantitatively describe the coupling degradation spreading by both physical connections and environment, a novel Energy-Flow-Field Network (EFFN) and a coupling degradation model based on EFFN are proposed in this paper. The EFFN is driven by energy flow and the state transition of spatially related nodes is triggered by the dissipation energy. An application is conducted on aviation actuation system in which the degradation spreading by fluid-thermal-solid interaction is considered. The degradation path and the most probable fault reason can be obtained by combining the state transition and energy output of nodes, which is consistent with the given scenario. 相似文献
144.
针对某型发动机自动调节器自动检测异常的故障现象,对产生发动机自动调节器自动检测异常的原因进行了深入地研究分析,并提出了针对性的预防措施。 相似文献
145.
通过对深圳航空公司CFM56-7B发动机水洗方法改进前后的发动机进厂大修数据进行比较,主要分析HPT导向器报废率的变化,说明改进的发动机水洗方式对于延长发动机在翼时间、降低HPT导向器报废率、节约大修成本起到良好促进作用。 相似文献
146.
147.
Aiming at the high fuel consumption and use-cost of truck-mounted concrete pump , an energy-saving matching strategy of pumping system is presented and the experimental study is conducted.Since pumping system occupies most resources of engine , the matching strategy between engine and main pump is analyzed to meet the load demand and reduce the engine rational speed drop.The testing method is established to measure the fuel consumption of engine under various working conditions , and the experimental data are analyzed to find the law of the fuel consumption of engine.The system performance can be improved by adjusting the system input value.Finally , the energy-saving matching strategy is established to reduce the fuel consumption of truck for unit workload , which provides a new approach for the energy-saving of truck-mounted concrete pump. 相似文献
148.
针对某新型靶机出现的发动机空中停车故障,对测控站记录数据进行分析,发现了转速采集系统和ECU控制系统存在的缺陷,并提出了解决措施。 相似文献
149.
150.
介绍了PW4000发动机2.5放气系统的构成、工作原理及常见故障,针对一起机械连接失效导致的喘振故障进行分析并寻找故障根源,为故障判断和该型发动机的工程管理提供了参考。 相似文献