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   1188篇
  免费   4篇
  国内免费   4篇
航空   525篇
航天技术   375篇
综合类   2篇
航天   294篇
  2022年   6篇
  2021年   24篇
  2019年   11篇
  2018年   49篇
  2017年   36篇
  2016年   33篇
  2015年   18篇
  2014年   49篇
  2013年   67篇
  2012年   59篇
  2011年   55篇
  2010年   51篇
  2009年   76篇
  2008年   88篇
  2007年   43篇
  2006年   25篇
  2005年   37篇
  2004年   26篇
  2003年   28篇
  2002年   20篇
  2001年   37篇
  2000年   21篇
  1999年   12篇
  1998年   27篇
  1997年   11篇
  1996年   21篇
  1995年   18篇
  1994年   27篇
  1993年   11篇
  1992年   16篇
  1991年   4篇
  1989年   14篇
  1988年   7篇
  1987年   9篇
  1986年   3篇
  1985年   26篇
  1984年   18篇
  1983年   10篇
  1982年   11篇
  1981年   16篇
  1980年   5篇
  1979年   5篇
  1978年   5篇
  1976年   4篇
  1975年   6篇
  1974年   8篇
  1972年   8篇
  1968年   6篇
  1967年   5篇
  1966年   5篇
排序方式: 共有1196条查询结果,搜索用时 62 毫秒
1.
The simplest version of the method of detecting the single molecular scattering field based on the polarization measurements of the twilight sky background by all-sky cameras has been considered. The method can be used during transitive twilight (with solar zenith angles of 94°–98°), when effective single scattering occurs in the upper stratosphere and lower mesosphere. The long-term measurements conducted using this method in the Moscow region and Apatity make it possible to determine the temperature of these atmospheric layers and estimate the contribution and properties of multiple scattering during the transitive twilight.  相似文献   
2.
The paper presents the research results of the effect of a capacitor energy storage device configuration on the specific characteristics of advanced modern propulsion systems based on the ablative pulsed plasma thrusters (APPT). These thrusters are designed to perform specific tasks within the small spacecrafts with the onboard power capacity up to 200 W.  相似文献   
3.
4.
Plants have evolved under the influence of UV-B radiation and have acquired systems for monitoring it and investing appropriate resources for protection against it, i.e., filters, quenchers of radicals and reactive oxygen species, and repair systems. An hypothesis for how plants monitor radiation has been presented.  相似文献   
5.
6.
The problem of target motion analysis (TMA) has been the subject of an important literature. However, present methods use data estimated by a short time analysis (azimuths, Dopplers, etc.). For far sources, the nonstationarities of the array processing outputs, induced by the sources motion, may be simply modeled. This model leads one to consider directly a spatio-temporal TMA. Then new (spatio-temporal) data can be estimated. These estimates correspond to a long time analysis. Further, note that they are estimated independently of the (classical) bearings. In this general framework, the concept of source trajectory replaces the classical instantaneous bearings. Corresponding TMA algorithms are then studied. Then the study of statistical performance is carefully studied  相似文献   
7.
The results of the experimental studies of damping characteristics of a composite torsion bar in the helicopter main rotor hingeless hub are presented. A variant of their improvement is considered.  相似文献   
8.
The application of the quadrature method [1] to analyzing the shells of revolution under symmetrical loading relative to the zero meridian is considered. The method can be treated as a generalization of the method presented in [2] to solve the Volterra integral equation of the second kind.  相似文献   
9.
Microbial processes in frozen food   总被引:2,自引:0,他引:2  
Deep freezing of food and storage at −19°C is a standard conservation procedure in food technology. The lower limit of growth of bacteria in food is from about −5°C to about −8°C, whereas the reproduction limit of yeasts is 2 to 3°C lower. Storage temperatures above −10°C should therefore not be used. At −18°C, a commonly used storage temperature, no growth of microorganisms will occur. The microorganisms mainly found at the lower growth limit are Pseudomonas sp. and basidiomycete yeasts. The reduction in the number of microorganisms due to freezing, storage, and thawing is not of practical importance. Microbial enzymes, in particular lipases and proteases, are still active at −18°C. Therefore, the quality of raw products and good hygiene at the production site are most important.  相似文献   
10.
We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z  0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations.  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