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   2466篇
  免费   481篇
  国内免费   472篇
航空   2015篇
航天技术   529篇
综合类   353篇
航天   522篇
  2024年   6篇
  2023年   35篇
  2022年   81篇
  2021年   97篇
  2020年   124篇
  2019年   122篇
  2018年   126篇
  2017年   121篇
  2016年   135篇
  2015年   138篇
  2014年   184篇
  2013年   143篇
  2012年   174篇
  2011年   202篇
  2010年   168篇
  2009年   158篇
  2008年   130篇
  2007年   161篇
  2006年   144篇
  2005年   101篇
  2004年   96篇
  2003年   80篇
  2002年   82篇
  2001年   70篇
  2000年   53篇
  1999年   54篇
  1998年   59篇
  1997年   46篇
  1996年   50篇
  1995年   38篇
  1994年   42篇
  1993年   28篇
  1992年   39篇
  1991年   44篇
  1990年   31篇
  1989年   33篇
  1988年   12篇
  1987年   9篇
  1986年   2篇
  1984年   1篇
排序方式: 共有3419条查询结果,搜索用时 15 毫秒
71.
首先在小弹塑性范围内用应变的奇次四项式相当精确地拟合一般硬化材料的拉伸曲线;再在体积不变条件下用弹性位移场的已知模态和一待定幅值构成弹塑性位移场;最后用势能原理确定该幅值而得到封闭解。  相似文献   
72.
In this paper, an improved Kalpana-1 infrared (IR) based rainfall estimation algorithm, specific to Indian summer monsoon region is presented. This algorithm comprises of two parts: (i) development of Kalpana-1 IR based rainfall estimation algorithm with improvement for orographic warm rain underestimation generally suffered by IR based rainfall estimation methods and (ii) cooling index to take care of the growth and decay of clouds and thereby improving the precipitation estimation.  相似文献   
73.
《中国航空学报》2020,33(6):1625-1641
The Tilt Quad Rotor (TQR) has complex dynamics characteristics, especially in conversion mode. It is difficult to build the dynamic model of the TQR and the environmental factors have a great influence on it. To solve the problem of control in conversion mode of TQR, this paper carries out the design of the controller based on improved Active Disturbance Rejection Control (ADRC). According to the characteristics of flight in conversion mode, Tracking Differentiator (TD) with explicit model is used to solve the problem of multiple integrals when the system is high-order system. Extended State Observer (ESO) with Radial Basis Function (RBF) neural network is used to estimate and compensate for internal and external uncertainties, and the adaptive sliding mode control in Nonlinear State Error Feedback (NLSEF) is used to improve the response speed of the controller and reduce the parameters which should be tuned. Through the flight control simulation of the TQR, the validity and rationality of the control system are verified.  相似文献   
74.
作为对二战后美国社会矛盾激化、社会动荡的回应,在对社会学家关于社会冲突的种种观点反思与发展的基础上,科塞建立了功能冲突论。科塞的功能冲突论由冲突正功能的发挥条件、冲突正功能的具体内容、社会安全阀制度等内容组成。功能冲突论启示我们,在我国构建和谐社会的过程中,要正视、分析社会矛盾、社会冲突,构建社会安全阀制度,消除社会冲突产生的社会土壤。  相似文献   
75.
根据波音AMM手册要求,在更换波音737NG飞机上的大气数据系统传感器后,需通过试车测试其自动加温功能。本文研究了波音737NG飞机大气数据系统探头自动加温的工作原理,并提出避免试车的解决方案。  相似文献   
76.
This paper studies an auroral event using data from three spacecraft of the Cluster mission, one inside and two at the poleward edge of the bottom of the Auroral Acceleration Region (AAR). The study reveals the three-dimensional profile of the region’s poleward boundary, showing spatial segmentation of the electric potential structures and their decay in time. It also depicts localized magnetic field variations and field-aligned currents that appear to have remained stable for at least 80?s. Such observations became possible due to the fortuitous motion of the three spacecraft nearly parallel to each other and tangential to the AAR edge, so that the differences and variations can be seen when the spacecraft enter and exit the segmentations, hence revealing their position with respect to the AAR.  相似文献   
77.
We present a data correction algorithm for real-time data processing for the NM64 galactic cosmic ray neutron monitor at the Royal Meteorological Institute (RMI) in Dourbes, Belgium. The correction is based on three main tests: a continuity test, tube ratios test and a derivative test. The continuity test works as a high pass filter with a threshold based on the entire recorded dataset. Additionally, it monitors whether the logging takes place at regular intervals (continuously). The ratios test identifies noisy sections and the final derivative test criterion will identify single or double spikes by testing them against the median increase of the intensities. Using these criteria, all data from the cosmic ray station at Dourbes is corrected in real time. Test results have been compared with data from verified neutron monitor stations with a similar geomagnetic cutoff rigidity.  相似文献   
78.
Vegetable oil can be used as a base oil in minimal quantity of lubrication(MQL). This study compared the performances of MQL grinding by using castor oil, soybean oil, rapeseed oil, corn oil, sunflower oil, peanut oil, and palm oil as base oils. A K-P36 numerical-control precision surface grinder was used to perform plain grinding on a workpiece material with a high-temperature nickel base alloy. A YDM–III 99 three-dimensional dynamometer was used to measure grinding force,and a clip-type thermocouple was used to determine grinding temperature. The grinding force, grinding temperature, and energy ratio coefficient of MQL grinding were compared among the seven vegetable oil types. Results revealed that(1) castor oil-based MQL grinding yields the lowest grinding force but exhibits the highest grinding temperature and energy ratio coefficient;(2) palm oil-based MQL grinding generates the second lowest grinding force but shows the lowest grinding temperature and energy ratio coefficient;(3) MQL grinding based on the five other vegetable oils produces similar grinding forces, grinding temperatures, and energy ratio coefficients, with values ranging between those of castor oil and palm oil;(4) viscosity significantly influences grinding force and grinding temperature to a greater extent than fatty acid varieties and contents in vegetable oils;(5) although more viscous vegetable oil exhibits greater lubrication and significantly lower grinding force than less viscous vegetable oil, high viscosity reduces the heat exchange capability of vegetable oil and thus yields a high grinding temperature;(6) saturated fatty acid is a more efficient lubricant than unsaturated fatty acid; and(7) a short carbon chain transfers heat more effectively than a long carbon chain. Palm oil is the optimum base oil of MQL grinding, and this base oil yields 26.98 N tangential grinding force,87.10 N normal grinding force, 119.6 °C grinding temperature, and 42.7% energy ratio coefficient.  相似文献   
79.
从品质因数的原始定义出发,分别计算出简单RLC串、并联电路的品质因数,得到两个结论,并将其推广,提出了两种简单的计算品质因数的方法,最后通过求解一个实际的LC并联谐振电路的品质因数得到验证。  相似文献   
80.
该文介绍了将机轮导轨的冷压装改为热压装工艺,从而降低了生产成本,提高了产品装配质量。  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