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   2461篇
  免费   29篇
  国内免费   12篇
航空   979篇
航天技术   908篇
综合类   12篇
航天   603篇
  2022年   13篇
  2021年   27篇
  2019年   24篇
  2018年   73篇
  2017年   61篇
  2016年   49篇
  2015年   20篇
  2014年   78篇
  2013年   92篇
  2012年   71篇
  2011年   137篇
  2010年   102篇
  2009年   145篇
  2008年   148篇
  2007年   77篇
  2006年   63篇
  2005年   76篇
  2004年   78篇
  2003年   81篇
  2002年   56篇
  2001年   75篇
  2000年   39篇
  1999年   47篇
  1998年   52篇
  1997年   49篇
  1996年   41篇
  1995年   56篇
  1994年   34篇
  1993年   38篇
  1992年   50篇
  1991年   13篇
  1990年   16篇
  1989年   41篇
  1988年   19篇
  1987年   16篇
  1986年   13篇
  1985年   60篇
  1984年   51篇
  1983年   41篇
  1982年   41篇
  1981年   56篇
  1980年   34篇
  1979年   16篇
  1978年   17篇
  1977年   9篇
  1976年   16篇
  1975年   15篇
  1974年   12篇
  1971年   7篇
  1969年   7篇
排序方式: 共有2502条查询结果,搜索用时 15 毫秒
291.
This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.  相似文献   
292.
293.
This paper shows the possibilities of the optical scanning imager for investigation of the structure of the auroral, SAR and tropical arcs and in this way to study the particle precipitation, neutral winds across the magnetic equator, drifts, electric fields and the current systems in the ionosphere.  相似文献   
294.
295.
A problem of optimization of cutting parameters with respect to the criteria of maximum efficiency and maximum tool resistance is formulated. To solve the problem, a method is developed and applied for determining the Pareto-optimal values of machining conditions in milling the present-day GTE monoimpeller blade passages with a circular milling cutter.  相似文献   
296.
The results of experimental investigations of gasodynamic characteristics of a combustion chamber model in the integrated power plant (IPP) with an asymmetric air intake are presented. The influence of an angle of air supply into the chamber model on hydraulic losses and the flow structure is shown at different air flowrates, relative values of the minimal flow section area of the feeding air intake pipes, under changes of the flowrate of gas simulating gas generation products and geometric model parameters. A technique for measuring the concentration of carbon dioxide simulating IPP gas generation products in the combustion chamber air flow and the results of experimental investigations of a mixture formation process in the combustion chamber model are described.  相似文献   
297.
The paper presents an improved technique and the results of strength analysis for the aircraft structural elements with a structural defect like an arbitrary shape delamination.  相似文献   
298.
299.
Vegetable cultivation plays a crucial role in dietary supplements and psychosocial benefits of the crew during manned space flight. Here we developed a ground-based prototype of horn-type sequential vegetable production facility, named Horn-type Producer (HTP), which was capable of simulating the microgravity effect and the continuous cultivation of leaf–vegetables on root modules. The growth chamber of the facility had a volume of 0.12 m3, characterized by a three-stage space expansion with plant growth. The planting surface of 0.154 m2 was comprised of six ring-shaped root modules with a fibrous ion-exchange resin substrate. Root modules were fastened to a central porous tube supplying water, and moved forward with plant growth. The total illuminated crop area of 0.567 m2 was provided by a combination of red and white light emitting diodes on the internal surfaces. In tests with a 24-h photoperiod, the productivity of the HTP at 0.3 kW for lettuce achieved 254.3 g eatable biomass per week. Long-term operation of the HTP did not alter vegetable nutrition composition to any great extent. Furthermore, the efficiency of the HTP, based on the Q-criterion, was 7 × 10−4 g2 m−3 J−1. These results show that the HTP exhibited high productivity, stable quality, and good efficiency in the process of planting lettuce, indicative of an interesting design for space vegetable production.  相似文献   
300.
Searches for primordial black holes are reviewed.  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