全文获取类型
收费全文 | 2042篇 |
免费 | 327篇 |
国内免费 | 531篇 |
专业分类
航空 | 2106篇 |
航天技术 | 232篇 |
综合类 | 395篇 |
航天 | 167篇 |
出版年
2024年 | 7篇 |
2023年 | 38篇 |
2022年 | 74篇 |
2021年 | 110篇 |
2020年 | 110篇 |
2019年 | 130篇 |
2018年 | 106篇 |
2017年 | 151篇 |
2016年 | 167篇 |
2015年 | 137篇 |
2014年 | 150篇 |
2013年 | 129篇 |
2012年 | 172篇 |
2011年 | 173篇 |
2010年 | 143篇 |
2009年 | 123篇 |
2008年 | 116篇 |
2007年 | 115篇 |
2006年 | 87篇 |
2005年 | 77篇 |
2004年 | 68篇 |
2003年 | 65篇 |
2002年 | 50篇 |
2001年 | 45篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 31篇 |
1997年 | 24篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 32篇 |
1993年 | 30篇 |
1992年 | 35篇 |
1991年 | 19篇 |
1990年 | 24篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 4篇 |
1986年 | 2篇 |
排序方式: 共有2900条查询结果,搜索用时 265 毫秒
991.
某涡喷发动机压气机气动失稳过程的非线性分析 总被引:6,自引:1,他引:5
对某涡喷发动机压气机的气动失稳过程进行了相关积分分析。对节流过程中压气机静压信号进行延时嵌入重构,发现失稳过程中重构相空间的吸引子结构发生了显著变化;应用相关积分值作为压气机内部流动状况变化的评价指标,发现节流过程中压气机第1级端部的流动最先发生不稳定,随后第2级先于第3,4级发生不稳定征兆;1,2级的失速类型为渐进型失速,3,4级为突变型失速;第3级叶根最先发生不稳定,且发展较快,最终导致全叶高失速;低通滤波可以提高相关积分方法检测失速征兆的时效性。分析表明,非线性的相关积分分析方法是进行压气机气动失稳过程研究的有效手段。 相似文献
992.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(1):312-325
Spacecraft relative motion with inter-craft electromagnetic force has distinct advantages, and its invariant shapes that are convenient for formation keeping ensure some potential significant applications. However, the electromagnetic actuators affect both the relative trajectory and attitude motion, complicating related researches on issues of invariant shape design and formation control. In this paper, the formation keeping problem for an invariant three-craft triangular electromagnetic formation is investigated on the basis of a 6-DOF full nonlinear dynamic model. Moreover, a combined control scheme consisting of feed-forward and feed-back control components is proposed to handle the high nonlinearity, strong coupling, model uncertainties and external disturbances. The feed-forward component is obtained through desired invariant shape design which is complicated by the coupling and superposition effects of any two distinct magnetic dipoles, and the feed-back component is developed with a combination of linear feed-back controller by the LQR method and active disturbance rejection by the extended state observer. Finally, the numerical simulation is presented to verify the feasibility and validity of the proposed 6-DOF combined control scheme. 相似文献
993.
994.
《中国航空学报》2020,33(7):1991-2001
This paper presents a novel optimal Motion Cueing Algorithm (MCA) to control the rotations of a Human Centrifuge (HC) and achieve the best simulation of a SpaceCraft (SC) motion. Relations of the specific forces sensed by astronauts of the SC and the HC have been derived and linearized. A Linear Quadratic Regulator (LQR) controller is implemented for the problem which tends to minimize the error between the two sensed specific forces as well as control input in a cost function. It results in control inputs of the HC to generate its sensed specific force as close as possible to the one in the SC. The algorithm is implemented for both linearized and nonlinear portions of a US space shuttle mission trajectory as a verification using MATLAB. In longitudinal direction, the proposed MCA, works well when the acceleration is less than 2g in which the tracking error does not exceed 12%. In lateral direction the tracking is much better even in nonlinear region since the error remains less than 7% for tilting up to 50°. Finally, the effect of weight matrixes in the LQR cost function on overall weight and power of the HC motion system is discussed. 相似文献
995.
《中国航空学报》2020,33(7):2055-2069
It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications. However, the current studies take too much time to achieve this goal. Therefore, this paper presents an efficient feedrate optimization method for constant peak cutting force in five-axis flank milling process. The solution method of the instantaneous undeformed chip thickness (IUCT) is proposed using least squares theory with the cutter entry angle and feedrate as variables. Based on this method, an explicit analytical expression of the peak cutting force for each cutting point is established. Furthermore, a feedrate scheduling method is developed to quickly solve the appropriate feedrate under constant peak cutting force. To verify the proposed IUCT model, the fitting IUCT is compared with the accuracy data at different feedrates. Additionally, some experiments of five-axis flank milling are conducted to demonstrate the effectiveness of the peak force model and the feedrate scheduling method. And the surface roughness before and after feedrate scheduling is detected. The results show that the proposed feedrate scheduling method can quickly adjust the feedrate and ensure constant peak force during machining. At the same time, the surface quality is kept at a high level. 相似文献
996.
997.
998.
999.
1000.