全文获取类型
收费全文 | 5024篇 |
免费 | 1228篇 |
国内免费 | 1003篇 |
专业分类
航空 | 3591篇 |
航天技术 | 1220篇 |
综合类 | 697篇 |
航天 | 1747篇 |
出版年
2024年 | 21篇 |
2023年 | 67篇 |
2022年 | 170篇 |
2021年 | 206篇 |
2020年 | 233篇 |
2019年 | 170篇 |
2018年 | 205篇 |
2017年 | 215篇 |
2016年 | 196篇 |
2015年 | 236篇 |
2014年 | 335篇 |
2013年 | 343篇 |
2012年 | 377篇 |
2011年 | 407篇 |
2010年 | 394篇 |
2009年 | 403篇 |
2008年 | 393篇 |
2007年 | 312篇 |
2006年 | 270篇 |
2005年 | 220篇 |
2004年 | 167篇 |
2003年 | 165篇 |
2002年 | 184篇 |
2001年 | 168篇 |
2000年 | 158篇 |
1999年 | 184篇 |
1998年 | 201篇 |
1997年 | 146篇 |
1996年 | 124篇 |
1995年 | 93篇 |
1994年 | 86篇 |
1993年 | 88篇 |
1992年 | 69篇 |
1991年 | 61篇 |
1990年 | 44篇 |
1989年 | 35篇 |
1988年 | 44篇 |
1987年 | 29篇 |
1986年 | 14篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有7255条查询结果,搜索用时 46 毫秒
921.
王武宏 《北京航空航天大学学报》1998,24(6):714-717
复杂可修系统可信度建模对保证效能的定量分析至关重要.本文在考虑不同维修状况的基础上,着重对不同任务剖面内相应任务阶段中武器装备可信度进行了深入的定量分析和综合,进而构造出武器装备的可信度矩阵,用于武器装备的效能分析;文中以某地面车辆为例,进一步论证了武器装备可信度矩阵的工程含义,旨在为合理确定一大类武器装备的效能和可信度指标提供理论依据. 相似文献
922.
923.
A formal approach using SysML for capturing functional requirements in avionics domain 总被引:1,自引:0,他引:1
In this work, a Model-Based Systems Engineering approach based on SysML is proposed. This approach is used for the capture and the definition of functional requirements in avionics domain. The motivation of this work is triple: guide the capture of functional requirements, validate these functional requirements through functional simulation, and verify efficiently the consistency of these functional requirements. The proposed approach is decomposed into several steps that are detailed to go from conceptual model of avionics domain to a formal functional model that can be simulated in its operating context. To achieve this work, a subset of SysML has been used as an intermediate modelling language to ensure progressive transformation that can be understood and agreed by system stakeholders. Formal concepts are introduced to ensure theoretical consistency of the approach. In addition, transformation rules are defined and the mappings between concepts of ARP4754A civil aircraft guidelines and SysML are formalized through meta-model. The resulting formalization enables engineers to perform functional simulation of the top-level functional architecture extracted from operational scenarios. Finally, the approach has been tested on an industrial avionics system called the Onboard Maintenance System. 相似文献
924.
925.
载人航天器具有系统规模大、技术难度高、单件小批量、无法通过多次飞行持续完善设计、可靠性要求高等特点。当前载人航天器研制中仍存在着参数化和模型化程度不高、基于模型的系统综合仿真验证不足、研制各环节缺乏数字化集成等问题,传统基于文本的系统工程方法已无法满足研制需求,亟需采用基于模型的系统工程方法。本文针对载人航天器的研制现状和应用需求,提出了面向载人航天器全生命周期的模型体系,定义了需求模型、功能模型、产品模型、工程模型、制造模型、实做模型等六类模型,提出了基于模型的研制流程,包含系统设计闭环验证、产品设计闭环验证、实做产品闭环验证3个验证环节,并深入探索了各研制环节中不同模型间的传递与关联关系。以某型号载人航天器为应用基础,系统地验证了提出的方法。 相似文献
926.
927.
928.
929.
930.
S. Guo X. LiuW. Ai Y. TangJ. Zhu X. WangM. Wei L. QinY. Yang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):736-741
Based on a formerly developed ground-based prototype of space plant-growing facility, the development of its improved prototype has been finished, so as to make its operating principle better adapt to the space microgravity environment. According to the developing experience of its first generation prototype and detailed demonstration and design of technique plan, its blueprint design and machining of related components, whole facility installment, debugging and trial operations were all done gradually. Its growing chamber contains a volume of about 0.5 m3 and a growing area of approximate 0.5 m2; the atmospheric environmental parameters in the growing chamber and water content in the growing media were controlled totally and effectively; lighting source is a combination of both red and blue light emitting diodes (LED). The following demonstrating results showed that the entire system design of the prototype is reasonable and its operating principle can nearly meet the requirements of space microgravity environment. Therefore, our plant-growing technique in space was advanced further, which laid an important foundation for next development of the space plant-growing facility and plant-cultivating experimental research in space microgravity condition. 相似文献