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931.
932.
In this paper, a novel algorithm is presented for direction of arrival(DOA) estimation and array self-calibration in the presence of unknown mutual coupling. In order to highlight the relationship between the array output and mutual coupling coefficients, we present a novel model of the array output with the unknown mutual coupling coefficients. Based on this model, we use the space alternating generalized expectation-maximization(SAGE) algorithm to jointly estimate the DOA parameters and the mutual coupling coefficients. Unlike many existing counterparts, our method requires neither calibration sources nor initial calibration information. At the same time,our proposed method inherits the characteristics of good convergence and high estimation precision of the SAGE algorithm. By numerical experiments we demonstrate that our proposed method outperforms the existing method for DOA estimation and mutual coupling calibration. 相似文献
933.
周烨斐刘艳涛 《民用飞机设计与研究》2014,(3):88-91
对比航电传统系统架构,分析了综合模块化航电系统(Integrated Modular Avionics,简称IMA)架构的优点;针对IMA系统功能的高集成度带来的资源分配难度和安全性要求,提出了IMA系统分区和资源分配策略,并给出了具体方法,对民用飞机IMA系统设计具有一定的指导意义和实用价值。 相似文献
934.
The terminal guidance problem for an unpowered lifting reentry vehicle against a sta- tionary target is considered. In addition to attacking the target with high accuracy, the vehicle is also expected to achieve a desired impact angle. In this paper, a sliding mode control (SMC)-based guidance law is developed to satisfy the terminal angle constraint. Firstly, a specific sliding mode function is designed, and the terminal requirements can be achieved by enforcing both the sliding mode function and its derivative to zero at the end of the flight. Then, a backstepping approach is used to ensure the finite-time reaching phase of the sliding mode and the analytic expression of the control effort can be obtained. The trajectories generated by this method only depend on the initial and terminal conditions of the terminal phase and the instantaneous states of the vehicle. In order to test the performance of the proposed guidance law in practical application, numerical simulations are carried out by taking all the aerodynamic parameters into consideration. The effec- tiveness of the proposed guidance law is verified by the simulation results in various scenarios. 相似文献
935.
This paper presents a two-level geometric calibration method for the permanent magnet (PM) spherical actuator to improve its motion control accuracy. The proposed actuator is com- posed of a stator with circumferential coils and a rotor with multiple PM poles. Due to the assembly and fabrication errors, the real geometric parameters of the actuator will deviate from their design values. Hence, the identification of such errors is critical for the motion control tasks. A two-level geometric calibration approach is proposed to identify such errors. In the first level, the calibration model is formulated based on the differential form of the kinematic equation, which is to identify the geometric errors in the spherical joint. In the second level, the calibration model is formulated based on the differential form of torque formula, which is to calibrate the geometric parameters of the magnetization axes of PM poles and coils axes. To demonstrate the robustness and availability of the calibration algorithm, simulations are conducted. The results have shown that the proposed two-level calibration method can effectively compensate the geometric parameter errors and improve the positioning accuracy of the spherical actuator. 相似文献
936.
Almost all work on model-based diagnosis (MBD) potentially presumes faults are per- sistent and does not take intermittent faults (IFs) into account. Therefore, it is common for diag- nosis systems to misjudge IFs as permanent faults (PFs), which are the major cause of the problems of false alarms, cannot duplication and no fault found in aircraft avionics. To address this problem, a new fault model which includes PFs and IFs is presented based on discrete event systems (DESs). Thereafter, an approach is given to discriminate between PFs and IFs by diagnosing the current fault. In this paper, the regulations of (PFs and IFs) fault evolution through fault and reset events along the traces of system are studied, and then label propagation function is modified to account for PFs and the dynamic behavior of IFs and diagnosability of PFs and IFs are defined. Finally, illustrative examples are presented to demonstrate the proposed approach, and the analysis results show the fault types can be discriminated within bounded delay if the system is diagnosable. 相似文献
937.
代晓青%曾竟成%刘钧 《宇航材料工艺》2007,37(4):31-33
用DSC研究了RFI工艺用环氧树脂的固化过程,研究表明:该固化反应较复杂,其反应动力学方程为dα/dt=2.27×10^4exp(-4764.65/T)(1-α)^0.861.为RFI用环氧树脂固化工艺的确定提供了理论依据. 相似文献
938.
939.
940.
Investigation on the Thermal Conductivity of 3-Dimensional and 4-Directional Braided Composites 总被引:4,自引:0,他引:4
Liu Zhenguo Zhang Haiguo Lu Zixing Li Diansen 《中国航空学报》2007,20(4):327-331
It is vital to choose a factual and reasonable micro-structural model of braided composites for improving the calculating precision of thermal property of 3-D braided composites by finite element method (FEM). On the basis of new microstructure model of braided composites proposed recently, the model of FEM calculation for thermal conductivity of 3-dimennsional and 4-directional braided composites is set up in this paper. The curves of coefficient of effective thermal conductivity versus fiber volume ratio and interior braiding angle are obtained. Furthermore, comparing the results of FEM with the available experimental data,the reasonability and veracity of calculation are confirmed at the same time. 相似文献