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   3429篇
  免费   26篇
  国内免费   14篇
航空   1662篇
航天技术   1185篇
综合类   12篇
航天   610篇
  2021年   29篇
  2019年   25篇
  2018年   64篇
  2017年   57篇
  2016年   45篇
  2015年   27篇
  2014年   73篇
  2013年   98篇
  2012年   89篇
  2011年   127篇
  2010年   85篇
  2009年   143篇
  2008年   160篇
  2007年   103篇
  2006年   76篇
  2005年   103篇
  2004年   94篇
  2003年   101篇
  2002年   74篇
  2001年   120篇
  2000年   68篇
  1999年   75篇
  1998年   87篇
  1997年   62篇
  1996年   94篇
  1995年   118篇
  1994年   114篇
  1993年   48篇
  1992年   71篇
  1991年   35篇
  1990年   32篇
  1989年   78篇
  1988年   29篇
  1987年   29篇
  1986年   38篇
  1985年   91篇
  1984年   97篇
  1983年   72篇
  1982年   67篇
  1981年   101篇
  1980年   21篇
  1979年   26篇
  1978年   30篇
  1977年   27篇
  1975年   29篇
  1974年   24篇
  1973年   21篇
  1969年   21篇
  1968年   23篇
  1967年   24篇
排序方式: 共有3469条查询结果,搜索用时 0 毫秒
881.
Beginning in 1995, a team of 3-D engineering visualization experts assembled at the Lockheed Martin Space Systems Company and began to develop innovative virtual prototyping simulation tools for performing ground processing and real-time visualization of design and planning of aerospace missions. At the University of Colorado, a team of 3-D visualization experts also began developing the science of 3-D visualization and immersive visualization at the newly founded British Petroleum (BP) Center for visualization, which began operations in October, 2001. BP acquired ARCO in the year 2000 and awarded the 3-D flexible IVE developed by ARCO (beginning in 1990) to the University of Colorado, CU, the winner in a competition among 6 Universities. CU then hired Dr. G. Dorn, the leader of the ARCO team as Center Director, and the other experts to apply 3-D immersive visualization to aerospace and to other University Research fields, while continuing research on surface interpretation of seismic data and 3-D volumes. This paper recounts further progress and outlines plans in Aerospace applications at Lockheed Martin and CU.  相似文献   
882.
At present the main trends among the most important problems of otorhinolaryngology in space medicine have become defined as vestibulology, audiology and clinical aspects (prophylaxis, diagnosis and treatment of ENT diseases in flight). The principal result of recent vestibular studies has probably been the establishment of an apparent relationship between the resistance of the vestibular system to adequate ground-based stimulation and tolerance to space flight. The findings of the studies formed the basis for the development of a new system of vestibular selection, as well as demonstrated the usefulness of special vestibular training of astronauts by active and passive methods. In audiology certain urgency is acquired by the problem of noise limitation in space cabins and auditory system reliability prediction for preserving a high work capability in crew members. The hemodynamic changes in weightlessness, as well as the possibility for allergic lesions, create conditions for distorted course of the ENT diseases and vaso-motor disorders. The prophylaxis of aspirations also deserves close attention since the possibilities of their onset increase in weightlessness. The rendering of immediate, timely aid will depend not only on the presence of the necessary medical equipment but also on the ability of the crew members to render the appropriate otorhinolaryngological aid.  相似文献   
883.
On management and control of turbulent shear flows   总被引:6,自引:0,他引:6  
Concepts of turbulent flow control have become of growing importance during the last few years, following increased interest in the detailed structural scenario of turbulence—in particular our improved understanding of coherent structures on the one hand (the prerequisite), and a need for improvement of technological processes on the other (the goal). These considerations have mainly been followed by engineers and physicists concerned with problems in aerodynamics. It is our aim to draw the attention of a wider group of engineers to turbulent flow control in order to speed up the transfer of knowledge from aerodynamics to applications in other fields of engineering.

In this paper an attempt is made to compile a major body of the available knowledge on flow control in separated and wall bounded turbulent flows. After a brief introduction of the basics of control theory (Section 2) and of the major flow structures and their stability characteristics (Section 3) free and wall bounded turbulent shear flows are discussed (Sections 4 and 5). This discussion summarizes the main relationships between structure and flow behaviour and shows possibilities of influencing properties of these flows such as increasing mixing or avoiding separation.  相似文献   

884.
The paper describes a mathematical model of drop tests on the landing gear of the Ka-62 helicopter. The model is formulated using the multibody system simulation procedure based on the Lagrange equations of the first kind.  相似文献   
885.
Long-lived, stable jets are observed in a wide variety of systems, from protostars, through Galactic compact objects to active galactic nuclei (AGN). Magnetic fields play a central role in launching, accelerating, and collimating the jets through various media. The termination of jets in molecular clouds or the interstellar medium deposits enormous amounts of mechanical energy and momentum, and their interactions with the external medium, as well, in many cases, as the radiation processes by which they are observed, are intimately connected with the magnetic fields they carry. This review focuses on the properties and structures of magnetic fields in long-lived jets, from their launch from rotating magnetized young stars, black holes, and their accretion discs, to termination and beyond. We compare the results of theory, numerical simulations, and observations of these diverse systems and address similarities and differences between relativistic and non-relativistic jets in protostellar versus AGN systems. On the observational side, we focus primarily on jets driven by AGN because of the strong observational constraints on their magnetic field properties, and we discuss the links between the physics of these jets on all scales.  相似文献   
886.
The tables of vibration modes for a blade obtained by the experimental method of holographic interferometry and systematized according to the number of nodal lines are presented. The graphical dependences of resonant frequencies that allow eliminating the vibration mode miss are presented. The vibration modes for a rectangular plate and a blade are compared. A technique of determining the resonant frequency for a missed harmonics is proposed.  相似文献   
887.
888.
889.
890.
Differential Doppler measurements by a passive array are used to track an unstable continuous wave (CW) source moving in a ballistic trajectory, e.g., a projectile carrying a proximity fuse. The ballistic equations of motion couple frequency measurements at various sections along the track with the track parameters at any arbitrary time, e.g., at impact. A nonlinear weighted leastsquare method is used to estimate the track parameters, and the resulting error covariance matrix is derived. A numerical example demonstrates the relative contributions of various frequency measurements to the estimation accuracy.  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