全文获取类型
收费全文 | 1356篇 |
免费 | 352篇 |
国内免费 | 251篇 |
专业分类
航空 | 1380篇 |
航天技术 | 182篇 |
综合类 | 205篇 |
航天 | 192篇 |
出版年
2024年 | 6篇 |
2023年 | 34篇 |
2022年 | 99篇 |
2021年 | 107篇 |
2020年 | 119篇 |
2019年 | 113篇 |
2018年 | 87篇 |
2017年 | 103篇 |
2016年 | 100篇 |
2015年 | 84篇 |
2014年 | 102篇 |
2013年 | 92篇 |
2012年 | 97篇 |
2011年 | 81篇 |
2010年 | 75篇 |
2009年 | 71篇 |
2008年 | 65篇 |
2007年 | 56篇 |
2006年 | 48篇 |
2005年 | 63篇 |
2004年 | 34篇 |
2003年 | 29篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 25篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 28篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1959条查询结果,搜索用时 15 毫秒
121.
捕风一号卫星是中国首次实现基于星载导航卫星反射信号测量(global navigation satellite system-reflection,GNSS-R)技术的气象卫星,采用新型L波段海面风场信息探测技术,在风场测量、海面飓风风速反演等方面为国家气象、防灾减灾等行业提供服务.从系统设计角度介绍了捕风一号卫星的总... 相似文献
122.
123.
人们在日常或某些特殊条件下常会面临方向和大小发生迅速变化的加速度环境,已有研究发现加速度环境会影响心血管系统生理、病理特征。利用计算机模拟方法详细研究了向前加速度环境下人体颈动脉内的血流动力学参数变化规律。结果表明:加速度会对颈动脉内压力、压力梯度、壁面剪切应力等与血管生理、病理现象密切相关的血流动力学参数产生显著影响。研究结果为加速度环境下颈动脉生理、病理研究提供了一定的理论依据,也为航空航天领域加速度环境下人员防护提供参考。 相似文献
124.
为了分析不同直径圆球诱导振荡燃烧的规律,并揭示圆球大小在振荡燃烧现象中所发挥的深层次作用,本文采用二维轴对称Euler方程和基元反应模型,对不同直径的圆球在H2/air预混气体中诱导振荡燃烧的现象开展数值模拟研究。研究发现,振荡频率并不是简单地随直径增大而逐渐从高频向低频连续过渡,而是存在两次突变,形成了超高频、高频以及低频三种振荡燃烧模态。在两种模态间过渡时,振荡达到稳定状态前,会存在一段双频耦合的振荡阶段。三种不同振荡燃烧模态的产生是受到了不同振荡机制的作用,而两种模态间过渡时的双频耦合现象则是两种机制相互竞争的结果。 相似文献
125.
126.
《中国航空学报》2021,34(10):81-90
In this paper, the flow field characteristics of Oblique Detonation Waves (ODWs) induced by a finite wedge under argon dilution are studied by solving the Euler equations with a detailed chemical model of hydrogen and air. First, the effects of the expansion waves, argon concentration, geometric parameters, and Mach number on the ODW are discussed. The results show that the changes of these parameters may make the oblique detonation not be initiated. Then, the ODW initiation criterion of the finite wedge is summarized, as the characteristic length of the induction zone LC and the characteristic length of the oblique wedge LW meet the condition LC/LW < 1, the initiation of the ODW occurs; otherwise, it does not occur. What’s more, the Constant Volume Combustion (CVC) theory is applied to study the characteristic length of induction zone. It is found that CVC theory is more suitable for the “smooth transition” type of ODW flow field, the theoretical and numerical characteristic length in induction regions are in good agreement. This work is of great significance for the design of oblique detonation engines for hypersonic vehicles. 相似文献
127.
《中国航空学报》2020,33(4):1260-1271
In the design process of advanced aero-engines, it is necessary to carry out an effective analysis method between structural features and mechanical characteristics for a better structural optimization. Based on the structural composition and functions of aero-engines, the concept and contents of structural efficiency can reflect the relation between structural features and mechanical characteristics. In order to achieve the integrated design of structural and mechanical characteristics, one quantitative analysis method called Structural Efficiency Assessment Method (SEAM) was put forward. The structural efficiency coefficient was obtained by synthesizing the parameters to quantitatively evaluate the aero-engine structure design level. Parameterization method to evaluate structural design quality was realized. After analyzing the structural features of an actual dual-rotor system in typical high bypass ratio turbofan engines, the mechanical characteristics and structural efficiency coefficient were calculated. Structural efficiency coefficient of high-pressure rotor (0.43) is higher than that of low-pressure rotor (0.29), which directly shows the performance of the former is better, there is room for improvement in structural design of the low-pressure rotor. Thus the direction of structural optimization was pointed out. The applications of SEAM shows that the method is operational and effective in the evaluation and improvement of structural design. 相似文献
128.
基于直接蒙特卡洛(DSMC)算法、浸入式有限元算法(IFE)、粒子云及蒙特卡洛碰撞(PIC-MCC)算法以及Ammosov-Delone-Krainov(ADK)隧穿电离模型建立了碳纳米管阵列推力器工质气体和CNT场电离过程的三维仿真模型。利用文献中的实验数据对本文仿真模型的有效性进行了验证,结果表明本文仿真模型与实验结果基本一致。针对碳纳米管阵列推力器的放电特性进行了研究,并重点分析了离子与原子碰撞过程对碳纳米管阵列推力器放电特性的影响。结果表明CNT可以极大地增强局部电场,稳态时场增强因子约为1308;与原子的碰撞使得离子在CNT附近更加集中,降低了局部电场,进而降低了其场增强能力。 相似文献
129.
Experimental investigation of large amplitude yaw-roll coupled oscillations was conducted in a low-speed wind tunnel using an aircraft configuration model. A special test rig was designed and constructed to provide different coupled motions from low to high angles of attack.A parameter ‘‘coupling ratio" was introduced to indicate the extent of yaw-roll coupling. At each pitch angle, seven coupling ratios were designed to study the yaw-roll coupling effects on the lateraldirectional aerodynamic characteristics systematically. At high angles of attack, the damping characteristics of yawing and rolling moments drastically varied with coupling ratios. In the coupled motions with the rotation taking place about the wind axis, the lateral-directional aerodynamic moments exhibited unsteady characteristics and were different from the ‘‘quasi-steady" results of the rotary balance tests. The calculated results of the traditional aerodynamic derivative method were also compared with the experimental data. At low and very high angles of attack, the aerodynamic derivative method was applicative. However, within a wide range of angles of attack, the calculated results of aerodynamic derivative method were inconsistent with the experimental data, due to the drastic changes of damping characteristics of lateral-directional aerodynamic moments with yaw-roll coupling ratios. 相似文献
130.
针对如何在时频域降低干扰噪声对椭圆球面波函数(Prolate Spheroidal Wave Functions,PSWFs)信号时频域分布特性的影响,引入精细滤波,提出了 1种新的椭圆球面波信号时频域滤波方法。仿真结果表明,所提方法在时频域以能量峰值点为基准,构造以距离为依据的滤波算子调节参数,能够有效抑制噪声对 PSWFs信号时频域分布特 性的影响,提高信号局部区域的能量聚集性。 相似文献