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391.
徐萍 《西安航空技术高等专科学校学报》2007,25(6):32-34
以2005年陕西城镇居民消费支出的截面数据为样本,运用扩展线性支出系统对陕西城镇家庭的基本支出、边际消费倾向、需求收入弹性、需求价格弹性、消费结构的变化趋势进行了实证分析。分析显示,不同收入层次家庭的消费水平、消费类别存在明显差异,居民消费结构呈现多层次的新特点。 相似文献
392.
Chen Dong Yuming Fu Guanghui Liu Hong Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Minimizing energy consumption and maximizing crop productivity are major challenges to growing plants in Bioregenerative Life Support System (BLSS) for future long-term space mission. As a primary source of energy, light is one of the most important environmental factors for plant growth. The purpose of this study is to investigate the effects of low light intensity at different stages on growth, pigment composition, photosynthetic efficiency, biological production and antioxidant defence systems of wheat (Triticum aestivum L.) cultivars during ontogenesis. Experiments were divided into 3 intensity-controlled stages according to growth period (a total of 65 days): seedling stage (first 20 days), heading and flowering stage (middle 30 days) and grain filling stage (last 15 days). Initial light condition of the control was 420 μmol m−2 s−1 and the light intensity increased with the growth of wheat plants. The light intensities of group I and II at the first stage and the last stage were adjusted to the half level of the control respectively. For group III, the first and the last stage were both adjusted to half level of the control. During the middle 30 days, all treatments were kept the same intensity. The results indicated that low-light treatment at seedling stage, biomass, nutritional contents, components of inedible biomass and healthy index (including peroxidase (POD) activity, malondialdehyde (MDA) and proline content) of wheat plants have no significant difference to the control. Furthermore, unit kilojoule yield of group I reached 0.591 × 10−3 g/kJ and induced the highest energy efficiency. However, low-light treatment at grain filling stage affected the final production significantly. 相似文献
393.
394.
系统地建立了含湍流的三维低空风切变模型,并综合分析了其对直升机飞行安全的威胁。建立了微下击暴流风场及大气湍流场组合的风切变模型,在不增加计算量的前提下,选取特征点发展直升机飞行动力学模型,有效捕捉了风切变的切变特性,提高了在风场中的动态响应计算精度。模型配备姿态保持功能的控制增稳系统已符合一般直升机的飞行状态,并改善机体响应。根据风速分布的特点,选取不同飞行速度、不同风场位置进行飞行仿真,定性地对比分析状态量变化与风场对应关系,并且以垂向通道为例,从动力学角度分析验证了响应的理论计算表达式。结果表明:湍流主要导致高频姿态角响应,风切变对飞行状态量变化占主导作用,且垂向风是引起威胁的主要因素,据此提出危险风场规避建议。 相似文献
395.
姚姣 《中国民航飞行学院学报》2014,25(5):30-32
针对ATC3000空管自动化系统的运行要求以及飞行管制区现场实际工作的需要,介绍了ATC3000航空地图制作软件的关键技术。文中分析了该软件的结构以及在Windows系统中使用Delphi开发的具体实现技术。 相似文献
396.
基于RISC芯片的32位嵌入式基本系统的研究和设计是当前嵌入式星载计算机研制方面的一个重要课题,着重介绍了该RISC基本系统的设计特点以及所使用的构思新颖的调试方法等两方面的研究情况。 相似文献
397.
398.
Robert H. Nichols Jr. 《Space Science Reviews》2000,92(1-2):113-122
Variations in the abundances of short-lived radionuclides such as 26Al (τ1/2 ≈ 0.74 Ma) and 53Mn (τ1/2 ≈ 3.7 Ma) in meteoritic solids may be used to infer relative formation intervals of these solids in the nebula at precisions
of less than 1 Ma. In a strict chronometric interpretation of the isotopic variations, whereby criteria such as spatial and
temporal isotopic homogeneity and closed system isotopic evolution are met, solid formation occurred in the nebula for at
least several million years. This is longer than some theoretical and astronomical estimates for the duration of the active
nebula. The evidence for live 41Ca (τ1/2 ≈ 0.10 Ma) in meteoritic inclusions further indicates that the onset of solid formation occurred quite early, perhaps within
a few hundred thousand years after the onset of the collapse of the sun's parent molecular cloud. Failure of the chronometric
interpretation may arise for a variety of reasons, including but not limited to, the late, inhomogeneous injection of material
from a nearby stellar source or the local production of short-lived radionuclides by an energetic particle irradiation, e. g., from T Tauri (X-wind) or galactic cosmic ray sources. Although some isotopic evidence exists that the criteria required
for a strict chronometric interpretation are not met by each of the short-lived chronometers, there is no compelling reason
to shorten the interval of solid formation in the nebula to less than 1 Ma.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
399.
研究了风速对电容式湿度传感器最终测量值和响应时间的影响,并分析了产生影响的机理;根据测量数据拟合出了电容式湿度传感器的响应时间和风速之间的函数关系。 相似文献
400.