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   8553篇
  免费   21篇
  国内免费   27篇
航空   3876篇
航天技术   3092篇
综合类   34篇
航天   1599篇
  2021年   84篇
  2019年   62篇
  2018年   183篇
  2017年   119篇
  2016年   125篇
  2015年   58篇
  2014年   208篇
  2013年   254篇
  2012年   243篇
  2011年   364篇
  2010年   262篇
  2009年   398篇
  2008年   460篇
  2007年   271篇
  2006年   204篇
  2005年   227篇
  2004年   215篇
  2003年   266篇
  2002年   182篇
  2001年   279篇
  2000年   160篇
  1999年   200篇
  1998年   236篇
  1997年   143篇
  1996年   207篇
  1995年   243篇
  1994年   247篇
  1993年   155篇
  1992年   193篇
  1991年   77篇
  1990年   75篇
  1989年   187篇
  1988年   77篇
  1987年   83篇
  1986年   86篇
  1985年   248篇
  1984年   195篇
  1983年   156篇
  1982年   175篇
  1981年   261篇
  1980年   71篇
  1979年   77篇
  1978年   67篇
  1977年   51篇
  1975年   58篇
  1974年   45篇
  1973年   41篇
  1972年   43篇
  1971年   42篇
  1970年   45篇
排序方式: 共有8601条查询结果,搜索用时 0 毫秒
851.
From an investigation of the activity of six glucocorticoid dependent liver enzymes, the existence of chronic, transient, stress-induced hypercorticosteronaemia during flight is probable. This hypercorticosteronaemia arises from weightlessness and induces gluconeogenesis. Weightlessness also caused substantial increases in liver glycogen level. The increased lipolytic activity and that of lipoprotein lipase in several groups of animals could be interpreted as enhancement of fat mobilization and utilization under the influence of stress. As this latter enhancement was also found in ground-based controls, it may have been due to the stress of handling rather than to space flight per se.  相似文献   
852.
Constructed in 1986, the Biosphere 2 Test Module has been used since the end of that year for closed ecological systems experiments. It is the largest closed ecological facility ever built, with a sealed variable volume of some 480 cubic meters. It is built with a skin of steel spaceframes with double-laminated glass panels admitting about 65 percent Photosynthetically Active Radiation (PAR). The floor is of welded steel and there is an underground atmospheric connection via an air duct to a variable volume chamber ("lung") permitting expansion and contraction of the Test Module's air volume caused by changes in temperature and barometric pressure, which causes a slight positive pressure from inside the closed system to the outside thereby insuring that the very small leakage rate is outward. Several series of closed ecological system investigations have been carried out in this facility. One series of experiments investigated the dynamics of higher plants and associated soils with the atmosphere under varying light and temperature conditions. Another series of experiments included one human in the closed system for three, five and twenty-one days. During these experiments the Test Module had subsystems which completely recycled its water and atmosphere; all the human dietary needs were produced within the facility, and all wastes were recycled using a marsh plant/microbe system. Other experiments have examined the capability of individual component systems used, such as the soil bed reactors, to eliminate experimentally introduced trace gases. Analytic systems developed for these experiments include continuous monitors of eleven atmospheric gases in addition to the complete gas chromatography mass spectrometry (GCMS) examinations of potable, waste system and irrigation water quality.  相似文献   
853.
Ariel VI observations of Cygnus X-2 have revealed a rather flat spectrum between 0.1 and 1.5 keV with variable emission at low energy. Of the two conflicting interpretations of this object in terms of i) a distant high-luminosity (Lx 1038 ergs s−1) binary and ii) a nearby low-luminosity (Lx 1035 ergs s−1) degenerate dwarf system, our measurements support the latter.  相似文献   
854.
This paper presents the pointing vector and angular rate relationshipsfor various optical elements as well as techniques developed forestablishing comprehensive analytical models of precision electroopticalstabilization systems. Since the performance of such systemsmay be critically dependent on the disturbance environment and theintegrity of the associated mechanism, these factors are also examinedin detail.  相似文献   
855.
The derivation of parametric equations for a limiting surface in the space of internal forces and moments that act in the rod cross-sections, using the basic concepts of plasticity theory and conventional hypotheses of the rod theory, is presented. The plastic properties of rod material are described by the Mises criterion. A case of small displacements and strains under static simple loading is considered. The results of solving a number of problems of constructing limiting curves in the planes of internal forces and moments are given.  相似文献   
856.
Guell A 《Acta Astronautica》1995,35(4-5):271-280
The article presents the current status of lower body negative pressure (LBNP) as a countermeasure for preventing orthostatic intolerance after space flight or bed rest. Devices discussed include the Chibis vacuum suit, the Anthrorack device, a collapsible device, and an inflatable device. Two bed rest studies examined the effect of LBNP and exercise on orthostatic tolerance; plasma volume; vasopressin, plasma renin activity, and catecholamines; and side effects.  相似文献   
857.
858.
A problem of transverse bending of elastic isotropic parallelogram plates under the action of uniformly distributed load is considered. The plate sides are either pivoted or rigidly restrained. To determine the value of maximum plate deflection, it is proposed that an interpolation technique with respect to form factor be used; and as a geometrical argument, an inner-outer conformal radius ratio can be applied instead of the form factor.  相似文献   
859.
The finite-difference method acceptable for on-board computers is applied to analyze the thermo-stressed state for the thermal-barrier coating of a perforated turbine blade and its wall at transient and stationary conditions of air-breathing jet engine operation during a flight.  相似文献   
860.
The paper presents the results of calculating nonstatitionary heat exchange between a heattransfer agent (water) and a gadolinium working element of the thermomagnetic engine with the use of ANSYS 13.0 certified software. Recommendations for designing the thermomagnetic engine working elements are given based on the analysis of calculation results.  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