首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   945篇
  免费   203篇
  国内免费   186篇
航空   655篇
航天技术   240篇
综合类   136篇
航天   303篇
  2024年   2篇
  2023年   12篇
  2022年   32篇
  2021年   29篇
  2020年   37篇
  2019年   32篇
  2018年   29篇
  2017年   20篇
  2016年   18篇
  2015年   28篇
  2014年   56篇
  2013年   56篇
  2012年   57篇
  2011年   86篇
  2010年   87篇
  2009年   76篇
  2008年   66篇
  2007年   61篇
  2006年   54篇
  2005年   47篇
  2004年   38篇
  2003年   30篇
  2002年   45篇
  2001年   35篇
  2000年   27篇
  1999年   41篇
  1998年   46篇
  1997年   36篇
  1996年   28篇
  1995年   18篇
  1994年   21篇
  1993年   20篇
  1992年   11篇
  1991年   11篇
  1990年   13篇
  1989年   10篇
  1988年   8篇
  1987年   5篇
  1986年   3篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
排序方式: 共有1334条查询结果,搜索用时 31 毫秒
781.
双CPU环境下飞行控制软件的设计   总被引:2,自引:1,他引:1  
宋征宇 《宇航学报》1997,18(3):86-90
本文介绍运载火箭飞行控制软件在双CPU冗余硬件配置下的可靠性设计和可靠性指标分配的方法。文中提到的部分技术经过了实验的检验,证明是可行的  相似文献   
782.
长盛不衰 百年犹荣--一个颇具盛名的标准化团体ASTM   总被引:1,自引:0,他引:1  
回顾了ASTM的建立过程,该机构目前已有30000多个国内外会员,131个技术委员会,每年都出版标准年鉴,标准被世界各国广泛采用,与美国国防部标准化部门及其他标准化机构有广泛的联系,活动经费主要依靠出售标准和提供标准化服务的收入。  相似文献   
783.
文章利用MAX2620构造宽带可调VCO并用ADS建模进行参数优化,在此基础上与MB15E03频率合成芯片构造锁相环,并利用ADS对暂态响应和相位噪声性能进行分析,在仿真分析的基础上建立实际的锁相环电路。  相似文献   
784.
In this paper, we report the statistical analysis of flare events observed by NoRH during 1992–2005 and NoRP during 1994–2005. We give the power law indices for the frequency distribution of peak brightness temperature which is 1.87 ± 0.05 for 17 GHz observation and is 1.64 ± 0.04 for 34 GHz observation. We also present the frequency variation of power law indices for peak flux and total energy of flare for NoRP observation, which is mono-increasing from 1 to 17 GHz.  相似文献   
785.
以发动机缸体水套为例着重论述了热芯盒模具在使用中存在的问题,并针对这些问题提出了解决方案,为以后的设计积累经验。  相似文献   
786.
To solve the problem of robust servo performance of Flight Environment Testbed(FET)of Altitude Ground Test Facilities(AGTF) over the whole operational envelope, a two-degree-offreedom μ synthesis method based on Linear Parameter Varying(LPV) schematic is proposed, and meanwhile a new structure frame of μ synthesis control on two degrees of freedom with double integral and weighting functions is presented, which constitutes a core support part of the paper. Aimed at the problem of reference command's rapid change, one freedom feed forward is adopted, while another freedom output feedback is used to meet good servo tracking as well as disturbance and noise rejection; furthermore, to overcome the overshoot problem and acquire dynamic tuning,the integral is introduced in inner loop, and another integral controller is used in outer loop in order to guarantee steady errors; additionally, two performance weighting functions are designed to achieve robust specialty and control energy limit considering the uncertainties in system. As the schedule parameters change over large flight envelope, the stability of closed-loop LPV system is proved using Lyapunov inequalities. The simulation results show that the relative tracking errors of temperature and pressure are less than 0.5% with LPV μ synthesis controller. Meanwhile, compared with non-LPV μ synthesis controller in large uncertainty range, the proposed approach in this research can ensure robust servo performance of FET over the whole operational envelope.  相似文献   
787.
本文介绍了使用PLC对两台车进行全自动控制的程序设计过程,重点 利用表格法驱动行车的方案和具体实现方法。  相似文献   
788.
A new form of the probabilistically strongest neighbor filter (PSNF) algorithm taking into account the number of validated measurements is proposed. The probabilistic nature of the strongest neighbor (SN) measurement in a cluttered environment is shown to be varied with respect to the number of validated measurements. Incorporating the number of validated measurements into design of the PSNF produces a consistent and cost effective data association method. Simulation studies show that the new filter is less sensitive to the unknown spatial clutter density and is more reliable for practical target tracking in nonhomogeneous clutter than the existing PSNF. It has similar performances to the probabilistic data association filter amplitude information (PDAF-AI) with much less computational complexities.  相似文献   
789.
With the increase of complexity of electromagnetic environment and continuous appearance of advanced system radars, signals received by radar reconnaissance receivers become even more intensive and complex. There- fore, traditional radar sorting methods based on neural network algorithms and support vector machine (SVM) cannot process them effectively. Aiming at solving this problem, a novel radar signal sorting method based on the cloud model theory and the geometric covering algorithm is proposed. By applying the geometric covering algo- rithm to divide input signals into different covering domains based on their distribution characteristics, the method can overcome a typical problem that it is easy for traditional sorting algorithms to fall into the local extrema due to the use of complex nonlinear equation to describe input signals. The method uses the cloud model to describe the membership degree between signals to be sorted and their covering domains, thus it avoids the disadvantage that traditional sorting methods based on hard clustering cannot deinterleave the signal samples with overlapped param- eters. Experimental results show that the presented method can effectively sort advanced system radar signals with overlapped parameters in complex electromagnetic environment.  相似文献   
790.
For maritime radiation source target tracking in particular electronic counter measures(ECM)environment,there exists two main problems which can deteriorate the tracking performance of traditional approaches.The frst problem is the poor observability of the radiation source.The second one is the measurement uncertainty which includes the uncertainty of the target appearing/disappearing and the detection uncertainty(false and missed detections).A novel approach is proposed in this paper for tracking maritime radiation source in the presence of measurement uncertainty.To solve the poor observability of maritime radiation source target,using the radiation source motion restriction,the observer altitude information is incorporated into the bearings-only tracking(BOT)method to obtain the unique target localization.Then the two uncertainties in the ECM environment are modeled by the random fnite set(RFS)theory and the Bernoulli fltering method with the observer altitude is adopted to solve the tracking problem of maritime radiation source in such context.Simulation experiments verify the validity of the proposed approach for tracking maritime radiation source,and also demonstrate the superiority of the method compared with the traditional integrated probabilistic data association(IPDA)method.The tracking performance under different conditions,particularly those involving different duration of radiation source opening and switching-off,indicates that the method to solve our problem is robust and effective.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号