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第五章宪全规范化引言术语“完全规范化”将被用来描述一个不包含冗余数据的表的集合。在绝大数情况下一个很好规范化的表(每一个函数决定是一个候选的行标识符)也是完全规范化的,但也存在着需要进一步规范化的一些情况。5.1隐含的传递依赖图5.1表示了一个“订货”的坏的规范化表的二个很好规范化的形式。形式A是无懈可击的,但形式B却具有某些不满意的特征。首先,在形式B中的属性组在逻辑上没有形式A合理。在直觉上,形式A似乎更合理一些,因为存在着仅包含顾客属性的一个表,而另一个表使订货与顾客相联系。在形式B中,两个表都… 相似文献
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华蘅芳造氢气球辨 总被引:1,自引:0,他引:1
姜老(指姜长英教授)的《清末天津的氢气球》一文(载《航空史研究》1996年第4期)提到孙筱槎、姚石荃和卢木斋合造气球,特别是卢木斋的一些情况。今先将我所见资料中关于卢木斋的事迹一谈: 卢靖(1855~1948),字勉之,号木斋,沔阳人。清末民初数学家。著《割圆术辑要》11卷、《万象一原演式》9卷和《火器真诀释例》1册,都有印本行世。1983年,天津师范大学因该校数学系李兆华老师(现为教授、系主任)之介,于天津古旧书店购得《迭微分补草》稿本1册和《九章代数草》稿本2册,都有卢靖自序。今依李兆华文章《卢靖两稿本数学书跋》(载《数学史研究文集》第一辑,1990年8月出版,李迪主编)转录如下,并稍加按语注释。 相似文献
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康刚华 《航空精密制造技术》1993,(1)
导电胶是机载雷达平板缝阵天线胶接的关键材料。本文论述了导电胶研制中解决的几个主要问题;给出了导电胶的主要性能指标及其应用效果。结果表明:本导电胶在-55~+100℃温度范围内具有优良的耐老化性能,较高的强度和韧性,还具有工艺简单、使用方便、成本低等优点。所胶接的平板天线完全满足《×××飞机成品附件环境技术要求》中振动功能和振动强度的要求,这种导电胶适用于胶接,特别适用于机载环境下导电零部件的胶接。 相似文献
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顾玲 《西安航空技术高等专科学校学报》2014,(4):8-12,77
大明宫为唐朝"三大内"(太极宫、大明宫、兴庆宫)中规模最大、气势最恢弘、使用最长久的一组宫殿群,见证了唐朝的兴衰,大明宫的建筑及曾存在其间的音乐、舞蹈、书画等都是大唐文化的精髓,如果说都城长安是唐王朝的政治文化中心的话,那么,大明宫可以说是唐王朝政治文化高度集聚的中心点。大明宫体现了唐文化气势恢宏、博大开放、兼容并蓄、自由洒脱等特点,该遗址外显和内隐的历史文化遗产对我们今人来说具有丰富的历史、文化、经济及教育价值,对其进行合理的开发意义匪浅。 相似文献
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袁森坡 《中国民航学院学报》1994,(4)
对于清代前期的统一,我们既要看到它的深远影响,也应指出其严重失误。诸如排斥汉族将帅参与边疆事务,在边疆某些地区滥施淫威,对蒙古及黄教政策的消极影响,虚边政策的危害,闭关自守政策的恶果等等,结果很快从“盛世”坠入“衰世”,内忧外患,纷至沓来,到清末时已是不可救药了。 相似文献
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石风 《西安航空技术高等专科学校学报》2014,(4):42-45
清代小学研究发达,丛书收录小学著作的数量非常可观。综合性丛书收录小学著作,自《四库全书》以后,较明代有了较大发展。专科丛书在《说文》学著作和音韵学著作的汇辑上最为突出。此外,由于清代辑佚学的兴盛,辑佚类丛书中收录小学著作的数量也比较多。清代丛书汇集小学著作,对清代以来的语言学及语言学史研究,是重要的文献基础,具有很高的学术价值。 相似文献
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曲洪波 《沈阳航空工业学院学报》2010,27(6):65-67
银冈书院是清代辽宁地区重要的教育与学术文化机构,它由清初流人郝浴建立,由清初到近代,经历了200余年的发展,成为清代辽宁地区最负盛名的传统书院。银冈书院以传统文化教育为主要内容,主张关注社会发展,讲求经世致用,为地方培育了大量社会需求的人才,促进了辽宁地区学术文化的发展。 相似文献
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Energetic particles constitute an important component of the heliospheric plasma environment. They range from solar energetic particles in the inner heliosphere to the anomalous cosmic rays accelerated at the interface of the heliosphere with the local interstellar medium. Although stochastic acceleration by fluctuating electric fields and processes associated with magnetic reconnection may account for some of the particle populations, the majority are accelerated by the variety of shock waves present in the solar wind. This review focuses on “gradual” solar energetic particle (SEP) events including their energetic storm particle (ESP) phase, which is observed if and when an associated shock wave passes Earth. Gradual SEP events are the intense long-duration events responsible for most space weather disturbances of Earth’s magnetosphere and upper atmosphere. The major characteristics of gradual SEP events are first described including their association with shocks and coronal mass ejections (CMEs), their ion composition, and their energy spectra. In the context of acceleration mechanisms in general, the acceleration mechanism responsible for SEP events, diffusive shock acceleration, is then described in some detail including its predictions for a planar stationary shock, shock modification by the energetic particles, and wave excitation by the accelerating ions. Finally, some complexities of shock acceleration are addressed, which affect the predictive ability of the theory. These include the role of temporal and spatial variations, the distinction between the plasma and wave compression ratios at the shock, the injection of thermal plasma at the shock into the process of shock acceleration, and the nonlinear evolution of ion-excited waves in the vicinity of the shock. 相似文献
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We describe the properties of high velocity events in the corona and upper transition region and propose that they are the same phenomenon as the well studied explosive events seen in the lower transition region around T=105 K. Furthermore, we discuss how the SOHO spectrometers, CDS and SUMER, may be used to check this conjecture. Magnetic reconnection has been considered a strong candidate for the physical mechanism causing explosive events. We present a phenomenological model showing how some of the observed properties of explosive events may be explained by reconnection occurring in small magnetic loops. 相似文献
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元朝在中国历史上是一个非常重要的朝代,它的疆域之大超过任何一个朝代。可在中国各个朝代中元朝无论在经济、文化等各方面都不突出,但在发展对外贸易。文化交流等却别开生面,由此进入比汉唐更为繁荣的中外文化交流的极盛时代。论述了元朝对外关系在开放意识、文化交流、对外贸易等方面对中国和世界的影响,以及对我们今天如何处理对外关系方面的反思。 相似文献
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采用喷射成形工艺制备大尺寸(?300mm)GH738合金锭坯,对锭坯进行热等静压,热等静压后进行不同温度的热挤压,利用XRD、SEM、TEM、EBSD和相分析方法,研究热等静压和热挤压对喷射成形 GH738合金锭坯显微缺陷、碳氮化物、γ/γ′相演变的影响。结果表明:热等静压对沉积坯中的显微疏松具有焊合作用;热挤压过程中GH738 合金再结晶组织主要受形变温度和应力-应变状态影响;热等静压态合金中碳氮化物主要沿晶界连续分布,热挤压后碳氮化物转变为沿挤压方向条带状分布;不同热工艺条件下合金γ′相的组成结构、质量分数及形貌尺寸分布主要受合金经历的温度场以及冷却条件影响。 相似文献
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Solar energetic particle (SEP) events reaching rigidities >1 GV are observed at 1?AU as ground-level events (GLEs). They are considered to be extreme cases of gradual SEP events, produced by shocks driven by wide and fast CMEs that are usually associated with long-duration (>1 hour) soft X-ray (SXR) flares. However, some large gradual SEP events, including GLEs, are associated with flares of short-duration (<1 hour) timescales comparable to those of flares seen with impulsive, low-energy SEP events with enhanced charge states, heavy-element abundances, and e/p ratios. The association of some GLEs with short-duration SXR events challenges us to understand the GLE event-to-event variation with SXR durations and whether it truly reflects the nature of the particle acceleration processes or simply the characteristics of the solar regions from which large, fast CMEs arise. We examine statistically the associated flare, active region (AR), and CME characteristics of ~40?GLEs observed since 1976 to determine how the GLE e/p and Fe/O ratios, each measured in two energy ranges, depend on those characteristics. The abundance ratios trend weakly to lower, more coronal, and less scattered values with increasing flare timescales, thermal and nonthermal peak fluxes, and measures of source AR sizes. These results and the wide range of solar longitude connections for GLEs with high abundance ratios argue against a significant role for flare effects in the GLEs. We suggest that GLE SEPs are accelerated predominately in CME-driven shocks and that a coupling of flare size and timescales with CME properties could explain the SEP abundance correlations with flare properties. 相似文献