全文获取类型
收费全文 | 547篇 |
免费 | 115篇 |
国内免费 | 93篇 |
专业分类
航空 | 424篇 |
航天技术 | 123篇 |
综合类 | 54篇 |
航天 | 154篇 |
出版年
2023年 | 13篇 |
2022年 | 29篇 |
2021年 | 33篇 |
2020年 | 26篇 |
2019年 | 21篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 23篇 |
2012年 | 19篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 21篇 |
2007年 | 31篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 19篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 30篇 |
1998年 | 45篇 |
1997年 | 38篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 25篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 3篇 |
排序方式: 共有755条查询结果,搜索用时 62 毫秒
161.
Valentina Shevtsova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The experiment IVIDIL (Influence of Vibrations on Diffusion in Liquids) is scheduled to be performed in forthcoming fall 2009 onboard the ISS, inside the SODI instrument mounted in the Glovebox on the ESA Columbus module. It is planned to carry out 39 experimental runs with each of them lasting 18 h. The objective of the experiment is threefold. 相似文献
162.
M.B. Krainev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The different types of the data recorded in the experiment of the regular balloon monitoring of cosmic rays (carried out since 1957 by Lebedev Physical Institute, Moscow, Russia, in several locations) are described. So called detailed information (the form of each pulse detected by the ground-based receiver) recorded during the last 12 years is discussed in more details. The use of these data both for getting and correcting the standard results of the experiment and for obtaining some additional information on the cosmic rays in the Earth’s atmosphere is considered. 相似文献
163.
Spectral analysis and self-adjusting mechanism for oscillation phenomenon in hydrogen-oxygen continuously rotating detonation engine 总被引:2,自引:0,他引:2
The continuously rotating detonation engine(CRDE)is a new concept of engines for aircraft and spacecraft.Quasi-stable continuously rotating detonation(CRD)can be observed in an annular combustion chamber,but the sustaining,stabilizing and adjusting mechanisms are not yet clear.To learn more deeply into the CRDE,experimental studies have been carried out to investigate hydrogen-oxygen CRDE.Pressure histories are obtained during each shot,which show that stable CRD waves are generated in the combustor,when feeding pressures are higher than 0.5 MPa for fuel and oxidizer,respectively.Each shot can keep running as long as fresh gas feeding maintains.Close-up of the pressure history shows the repeatability of pressure peaks and indicates the detonation velocity in hydrogen–oxygen CRD,which proves the success of forming a stable CRD in the annular chamber.Spectrum of the pressure history matches the close-up analysis and confirms the CRD.It also shows multi-wave phenomenon and affirms the fact that in this case a single detonation wave is rotating in the annulus.Moreover,oscillation phenomenon is found in pressure peaks and a self-adjusting mechanism is proposed to explain the phenomenon. 相似文献
164.
Prolog is one of the most important candidates to build expert systems and AI-related programs and has potential applications in embedded systems. However, Prolog is not suitable to develop many kinds of components, such as data acquisition and task scheduling, which are also crucial. To make the best use of the advantages and bypass the disadvantages, it is attractive to integrate Prolog with programs developed by other languages. In this paper, an IPC-based method is used to integrate backward chaining inference implemented by Prolog into applications or embedded systems. A Prolog design pattern is derived from the method for reuse, whose principle and definition are provided in detail. Additionally, the design pattern is applied to a target system, which is free software, to verify its feasibility. The detailed implementation of the application is given to clarify the design pattern. The design pattern can be further applied to wide range applications and embedded systems and the method described in this paper can also be adopted for other logic programming languages. 相似文献
165.
Accurate fuel injection control of aircraft engine can optimize the energy efficiency of UAV power system while meeting the propeller speed requirement. Traditional injection control method such as open-loop calibration causes instability of fuel supply which brings the risk of power loss of UAV. Considering that the closed-loop control of AFR can ensure a stable fuel feeding, this paper proposes an AFR control based fuel supply strategy in order to improve the efficiency of fuel-powered UAV while obtaining the required engine speed. According to the optimum fuel injection results, we implement fuzzy-PID method to control the set AFR in different situations. Through simulation and experiment studies, the results indicate that, to begin with, the calibrated mathematical model of the aircraft engine is effective. Next, this fuel supply strategy based on AFR control can normally realize the engine speed regulation, and the applied control algorithm can eliminate the overshoot of AFR throughout all the working progress. What is more,the fuel supply strategy can averagely shorten the response time of the engine speed by about two seconds. In addition, compared with the open-loop calibration, in this work the power efficiency is improved by 9% to 33%. Last but not the least, the endurance can be improved by 30 min with a normal engine speed. This paper can be a reference for the optimization of UAV aircraft engine. 相似文献
166.
《中国航空学报》2020,33(6):1774-1787
The main objective of the turboprop engine control system is to ensure propeller absorbed power at a constant propeller speed by controlling fuel flow and blade angle. Since each input variable affects the selected output variables, there exist strong interactions between different control loops of a Two-Spool TurboProp Engine (TSTPE). Inverted decoupling is used to decouple the interactions and decompose the TSTPE into two independent single-input single-output systems. The multi-variable PI controller and two single-variable PI controllers are designed for the TSTPE with actuator dynamics based on Linear Matrix Inequality (LMI), respectively, which is derived from static output feedback and pole placement condition. The step responses show that due to the difference in the response times of the selected output variables, it is difficult to design an appropriate multi-variable PI controller. The designed single-variable PI controllers are tested on the TSTPE integrated model to illustrate the effectiveness of the proposed method, that is, the interactions are first decoupled and then the controllers are designed, and the resulting simulated responses show that compared with the controller designed without actuator dynamics, the gas-generator shaft speed and power turbine shaft speed can better track their respective commands under the action of the controller designed with actuator dynamics. 相似文献
167.
《中国航空学报》2020,33(7):1953-1968
The vibration caused blade High Cycle Fatigue (HCF) is seriously affects the safety operation of turbomachinery especially for aero-engine. Thus, it is crucial important to identify the blade vibration parameters and then evaluate the dynamic stress amplitude. Blade Tip Timing (BTT) method is one of the promising method to solve these problems. While, it need a high resolution Once Per Revolution (OPR) signal which is difficult to get for the aero-engine. Here, a Coupled Vibration Analysis (CVA) method for identifying blade vibration parameters by a none OPR BTT is proposed. The method assumes that every real blade has its own vibration performance at a given speed. Whereby, it can take any blade as the reference blade, and the other blades using the reference blade as the OPR for vibration displacement calculating and further parameter identifying. The proposed method is validated by numerical model. Also, experimental studies are carried out on a straight blade and a twisted three dimensional blade test rig as well as a large industrial axial compressor respectively. The results show that the proposed method can accurately identify the blade synchronous vibration parameters and quantitatively evaluate the mistuning in bladed disks, which lays a foundation for the reliability improvement of aero-engine. 相似文献
168.
169.
170.
齿轮箱是船舶动力传动系统的主要振源之一,为了研究船舶齿轮箱振动性能及优化措施,进而实现船舶的低噪声化,以本单位自主研发的船用齿轮箱为例,通过台架试验和振动频谱分析结合的方法分析齿轮箱振动的主要影响因素,对振动性能关键影响因素进行优化改进。本文结合振动频谱分析结果对齿轮箱从齿轮修形设计和液压供油系统改进两个方面进行了优化,并对采取优化措施后的齿轮箱进行振动试验验证和振动频谱分析。结果表明:齿轮修形和液压供油系统改进两项优化措施可以切实有效的改善齿轮箱的振动性能。在文中的齿轮箱案例中,齿轮修形后齿轮啮合频率处振动峰值下降40.2%,总振级下降1.85dB,进一步采取液压供油系统改进措施后,齿轮箱总振级下降9.99dB。齿轮修形和液压供油系统改进对船用齿轮箱振动性能提升具有工程应用价值。 相似文献