全文获取类型
收费全文 | 2052篇 |
免费 | 551篇 |
国内免费 | 282篇 |
专业分类
航空 | 1505篇 |
航天技术 | 446篇 |
综合类 | 299篇 |
航天 | 635篇 |
出版年
2024年 | 11篇 |
2023年 | 25篇 |
2022年 | 95篇 |
2021年 | 118篇 |
2020年 | 106篇 |
2019年 | 97篇 |
2018年 | 130篇 |
2017年 | 102篇 |
2016年 | 91篇 |
2015年 | 98篇 |
2014年 | 160篇 |
2013年 | 161篇 |
2012年 | 137篇 |
2011年 | 153篇 |
2010年 | 188篇 |
2009年 | 172篇 |
2008年 | 186篇 |
2007年 | 111篇 |
2006年 | 130篇 |
2005年 | 121篇 |
2004年 | 66篇 |
2003年 | 56篇 |
2002年 | 39篇 |
2001年 | 56篇 |
2000年 | 34篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 16篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有2885条查询结果,搜索用时 203 毫秒
411.
Jie Jiang Robert H. Cameron Dieter Schmitt Manfred Schüssler 《Space Science Reviews》2013,176(1-4):289-298
To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations. 相似文献
412.
A joint mid-course and terminal course cooperative guidance law for multi-missile salvo attack 总被引:1,自引:0,他引:1
Salvo attacking a surface target by multiple missiles is an effective tactic to enhance the lethality and penetrate the defense system. However, existing cooperative guidance laws in the mid-course or terminal course are not suitable for long- and medium-range missiles or stand-off attacking. Because the initial conditions of cooperative terminal guidance that are generally generated from the mid-course flight may not lead to a successful cooperative terminal guidance without proper mid-course flight adjustment. Meanwhile, cooperative guidance in the mid-course cannot solely guarantee the accuracy of a simultaneous arrival of multiple missiles. Therefore, a joint mid-course and terminal course cooperative guidance law is developed. By building a distinct leader-follower framework, this paper proposes an efficient coordinated Dubins path planning method to synchronize the arrival time of all engaged missiles in the mid-course flight. The planned flight can generate proper initial conditions for cooperative terminal guidance, and also benefit an earliest simultaneous arrival. In the terminal course, an existing cooperative proportional navigation guidance law guides all the engaged missiles to arrive at a target accurately and simultaneously. The integrated guidance law for an intuitive application is summarized. Simulations demonstrate that the proposed method can generate fast and accurate salvo attack. 相似文献
413.
414.
415.
介绍电子产品设计时元器件选用对系统可靠性的影响。结合实际案例,总结并强调在电子产品设计时的元器件选用应从质量等级入手,充分进行降额设计和热设计。阐明合理选用元器件是实现电子产品系统设计高可靠性水平的基础。 相似文献
416.
从安全性角度提出80x86汇编语言程序的编码规则.通过分析航天型号典型案例.依据型号软件的应用特点,从代码结构、指令使用、中断控制、算法设计等角度对安全性编码规则进行分类,提出具体要求.设计了对应规则的检查方法和检查工具,采用静态分析方法,从软件源代码中提取安全性规则的相关元素,判断代码与规则的符合性,实现规则自动检查. 相似文献
417.
Li Jie Zhou Zhou 《中国航空学报》2008,21(1):19-27
To compute transonic flows over a complex 3D aircraft configuration, a viscous/inviscid interaction method is developed by coupling an integral boundary-layer solver with an Eluer solver in a "semi-inverse" manner. For the turbulent boundary-layer, an integral method using Green's lag equation is coupled with the outer inviscid flow. A blowing velocity approach is used to simulate the displacement effects of the boundary layer. To predict the aerodynamic drag, it is developed a numerical technique called far-field method that is based on the momentum theorem, in which the total drag is divided into three component drags, i.e. viscous, induced and wave-formed. Consequently, it can provide more physical insight into the drag sources than the often-used surface integral technique. The drag decomposition can be achieved with help of the second law of thermodynamics, which implies that entropy increases and total pressure decreases only across shock wave along a streamline of an inviscid non-isentropic flow. This method has been applied to the DLR-F4 wing/body configuration showing results in good agreement with the wind tunnel data. 相似文献
418.
419.
420.
某型蒸发式稳定器气动及燃烧特性研究 总被引:3,自引:0,他引:3
为解决亚燃冲压发动机在高速低温来流条件下的可靠点火、火焰稳定和高效燃烧问题,对某型蒸发式火焰稳定器分别进行了冷态流场和燃烧流场的数值研究,并与常规V型火焰稳定器进行了对比分析。研究结果表明:在给定范围内,蒸发式稳定器随来流速度的增大,总压恢复系数和停留时间明显减小,回流区长度、回流率和燃烧效率变化不大;与相同槽宽的常规V型火焰稳定器相比,回流率明显减小,总压恢复系数、回流区长度和停留时间略有减小。蒸发式稳定器后部形成明显的回流区,且基本上不受外部主流流动的干扰,通过单独控制稳定器局部供油,可以使稳定器在最佳油气比下工作,有利于在高速来流条件下可靠工作。 相似文献