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   5823篇
  免费   15篇
  国内免费   31篇
航空   2652篇
航天技术   2192篇
综合类   26篇
航天   999篇
  2021年   56篇
  2019年   44篇
  2018年   126篇
  2017年   83篇
  2016年   73篇
  2015年   26篇
  2014年   126篇
  2013年   170篇
  2012年   161篇
  2011年   234篇
  2010年   151篇
  2009年   263篇
  2008年   315篇
  2007年   177篇
  2006年   152篇
  2005年   185篇
  2004年   179篇
  2003年   198篇
  2002年   123篇
  2001年   184篇
  2000年   136篇
  1999年   144篇
  1998年   158篇
  1997年   126篇
  1996年   155篇
  1995年   197篇
  1994年   181篇
  1993年   94篇
  1992年   147篇
  1991年   50篇
  1990年   51篇
  1989年   127篇
  1988年   40篇
  1987年   40篇
  1986年   58篇
  1985年   179篇
  1984年   138篇
  1983年   105篇
  1982年   133篇
  1981年   164篇
  1980年   46篇
  1979年   30篇
  1978年   37篇
  1977年   36篇
  1976年   29篇
  1975年   26篇
  1974年   34篇
  1973年   25篇
  1970年   27篇
  1969年   25篇
排序方式: 共有5869条查询结果,搜索用时 349 毫秒
271.
272.
The problem and features of measuring the speed and the direction angle of the wind vector relative to the longitudinal helicopter axis during parking, starting and takeoff-landing modes by onboard means are considered. The construction principles, information processing algorithms and advantages of onboard system for measuring the wind vector parameters based on ion-beacon and aerometric measuring channels, are disclosed.  相似文献   
273.
We consider the stability of stationary motions of a model of a spacecraft as a system of coaxial bodies with small asymmetry caused by the shift of the axes of dynamic symmetry of bodies relative to the axis of rotation. We determine the stationary motions of the system; their stability is studied with respect to both the projections of angular velocity and the position of the axis of rotation. The sufficient conditions for the stability of these stationary motions are obtained by constructing a Lyapunov function, and the necessary conditions are obtained by analyzing the corresponding linearized equations of perturbed motion.  相似文献   
274.
A methodology of creating a loading imitation model of a single-rotor helicopter with artificial neural network algorithms is considered. Stages of creation, the structure, and an algorithm of searching for an optimal neural networks configuration of loading imitation model are presented.  相似文献   
275.
By using a Doppler Weather Radar (DWR) at Shriharikota (13.66°N & 80.23°E), an Artificial Neural Network (ANN) based technique is proposed to improve the accuracy of rain intensity estimation. Three spectral moments of a Doppler spectra are utilized as an input data to an ANN. Rain intensity, as measured by the tipping bucket rain gauges around the DWR station, are considered as a target values for the given inputs. Rain intensity as estimated by the developed ANN model is validated by the rain gauges measurements. With the help of a developed technique, reasonable improvement in the estimation of rain intensity is observed. By using the developed technique, root mean square error and bias are reduced in the range of 34–18% and 17–3% respectively, compared to ZR approach.  相似文献   
276.
277.
The dried, fleshy stems of Cistanche deserticola (Orobanchaceae) are popular tonics in Traditional Chinese Medicine (TCM) to treat the inability of kidney in expelling extra fluid in the body, causing fluid retention, and reform reproductive system. However, the wild plants of C. deserticola have become endangered due to habitat downsizing and over-harvesting for its medicinal usages. The present research was carried out for the following purposes: (1) promoting the space-breeding research; (2) providing molecular evidence for agricultural selective breeding; and (3) protecting this endangered herbal medicine and conserving its genetic resources.  相似文献   
278.
We considered the influence of temperature on the nitric oxide emission under combustion of the near-stoichiometric mixtures with and without water feed. We revealed the advantage of the method of fuel-water-air mixture combustion over that of the leaned mixture combustion.  相似文献   
279.
A technique for calculating the energy parameters of shock waves at electrical discharge in water is presented for the transition region of discharge channel expansion using as the base the predetermined characteristics of discharge circuit. The technique is based on the solution of energy transport equation that is similar in form to that of radiative transfer. The validity of the presented approach was experimentally verified.  相似文献   
280.
Aerodynamic characteristics of two-dimensional smart flap under the ground effect have been assessed by a numerical simulation. In this process, a pressure-based implicit procedure to solve Navier–Stokes equations on a nonorthogonal mesh with collocated finite volume formulation is used. The boundedness criteria for this procedure are determined from the Normalized Variable Diagram (NVD) scheme. The procedure incorporates the kε eddy–viscosity turbulence model. Cantilever beam with uniformly varying load with roller support at the free end is considered for the configuration of the smart flap. The method is first validated against experimental data. Then, the algorithm is applied for turbulent aerodynamic flows around airfoil with smart and conventional flaps for different attack angle, flap angle and ground clearance where the results of two flaps are compared. The comparisons show that the quality of the solution is considerable.  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