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441.
《中国航空学报》2021,34(3):50-60
The dynamic performance of a nozzle-flapper servo valve can be affected by several factors such as the disturbance of the input signal, the motion of the armature assembly and the oscillation of the jet force. As the part of vibrating at high frequency, the armature assembly plays a vital role during the operation of the servo valve. In order to accurately predict the transient response of the armature assembly during the vibration, a mathematical model of armature assembly is established based on the distributed parameters method (DPM) and Hamilton principle. The new mathematical model is composed of three main parts, the modal eigenfunction, modal mechanical response expressions of the spring tube and the motion equation of the other armature assembly. After programing, the purpose of using the DPM to predict the dynamic response of different positions located on the armature assembly is achieved. For verifying the validity of the mathematical model, the finite element method (FEM) and classic model (CM) of armature assembly are applicated by commercial software under the same condition. The comparison results prove that the DPM can effectively predict the axial and tangential deflection of the armature assembly different positions which the CM can’t duing to its over-simplification. A certain error is generated when predicting the axial deformation at different heights by DPM, which is caused by an approximate method to simulate the torsion of the spring tube. The comparison results of the spring tube deflection at different vibration frequencies shows that the adaptability of DPM is significantly higher than the classic model, which verify the model is more adaptable for predicting the dynamic response of the armature assembly. 相似文献
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基于云微物理参数的飞机积冰多因子预测方法 总被引:1,自引:0,他引:1
基于气象探测信息,准确进行飞机积冰预测并及时开启防/除冰系统是保障飞机飞行安全的重要方法。提出了一种多因子积冰预测方法,当已知飞机所在飞行云层类型、飞行高度、速度、气温、气压和露点温度时,使用提出的方法可计算得到飞行高度上的相对湿度、比湿、0℃高度上的气压、液态含水量等气象参数,用所建立的多因子积冰强度判别式可对飞机积冰的可能性及积冰强度进行预测。将方法应用于飞机积冰案例中,与美国国家大气科学中心提出的RAOB积冰预报方法进行了对比。分析结果表明,提出的方法准确有效,可为飞机积冰预测提供技术支持。 相似文献
446.
天线反射器型面精度是衡量、评价天线质量的重要指标之一,天线型面精度的高低将直接影响天线的电性能指标。大型环形可展开天线型面精度测试,目前多采用高精度工业数字化摄影测量技术进行,在使用高精度数字化摄影测量系统对大型环形可展开天线开展型面测试过程中,系统测量精度主要受摄影基准选用、测量距离、测量靶标大小、测量角度、测量拍照数量、相机参数等多项工艺参数影响。就如何使用数字化摄影测量系统对大型环形可展开天线开展高精度型面测试方法开展研究,通过对高精度长基准尺的设计及布局研究,以及对摄影测量系统最优匹配工艺参数研究及验证,得到一种针对大型环形可展开天线开展高精度型面测试的方法。试验证明,该方法可靠有效,能够满足大型环形可展开天线开展型面高精度测试的测量需求。 相似文献
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超声速流中三波结构的参数优化研究 总被引:1,自引:1,他引:1
对三波结构的参数进行了探讨,给出了在反射激波和主激波后一些气动力变量的比值存在极值,文中称这种结构为优化结构,当给定气流的马赫数时,理论上就可确定优化三波结构的入射激波强度和存在区域,这可为一些超声速气动装置的设计提供参考依据。 相似文献
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449.
J.S. Ojo P.A. Owolawi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Millimeter and microwave system design at higher frequencies require as input a 1-min rain-rate cumulative distribution function for estimating the level of degradation that can be encountered at such frequency bands. Owing to the lack of 1-min rain-rate data in South Africa and the availability of 5-min and hourly rainfall data, we have used rain-rate conversion models and the refined Moupfouma model to convert the available data into 1-min rain-rate statistics. The attenuation caused by these rain rates was predicted using the International Telecommunication Union (ITU) recommendations model. The Kriging interpolation method was used to draw contour maps over different percentages of time for spatial interpolation of rain-rate values into a regular grid in order to obtain a highly consistent and predictable inter-gauge rain-rate variation over South Africa. The present results will be useful for system designers of modern broadband wireless access (BWA) and high-density cell-based Ku/Ka, Q/V band satellite systems, over the desired area of coverage in order to determine the appropriate effective isotropically radiated power (EIRP) and receiver characteristics of this region. 相似文献
450.
This paper describes a longitudinal parameter identification procedure for a small unmanned aerial vehicle(UAV)through modified particle swam optimization(PSO).The procedure is demonstrated using a small UAV equipped with only an micro-electro-mechanical systems(MEMS)inertial measuring element and a global positioning system(GPS)receiver to provide test information.A small UAV longitudinal parameter mathematical model is derived and the modified method is proposed based on PSO with selective particle regeneration(SRPSO).Once modified PSO is applied to the mathematical model,the simulation results show that the mathematical model is correct,and aerodynamic parameters and coefficients of the propeller can be identified accurately.Results are compared with those of PSO and SRPSO and the comparison shows that the proposed method is more robust and faster than the other methods for the longitudinal parameter identification of the small UAV.Some parameter identification results are affected slightly by noise,but the identification results are very good overall.Eventually,experimental validation is employed to test the proposed method,which demonstrates the usefulness of this method. 相似文献