Evolution and distribution of medullary bone: evidence from a new Early Cretaceous enantiornithine bird     

Min Wang  Jingmai K O&#x;Connor  Alida M Bailleul  Zhiheng Li 《国家科学评论(英文版)》2020,7(6):1068

Living birds are unique among vertebrates in the formation of a female-specific bone tissue called medullary bone (MB) that is strictly associated with reproductive activity. MB is a rapidly mobilized source of calcium and phosphorus for the production of eggshell. Among living taxa, its skeletal distribution can be highly extensive such that it even exists in the ribs of some species. Due to its ephemeral nature, MB is rarely fossilized and so little is understood with regard to the origin of MB and its skeletal distribution in early taxa. Here we describe a new Early Cretaceous enantiornithine bird, Mirusavis parvus, gen. et. sp. nov., indicating that skeleton-wide distribution of MB appeared early in avian evolution. We suggest that this represents the plesiomorphic condition for the Aves and that the distribution of MB observed among extant neornithines is a product of increased pneumatization in this lineage and natural selection for more efficient distribution of MB.  相似文献   

植物自花授粉的类型及其适应性进化     

杨期和  杨和生  李姣清 《嘉应学院学报》2011,29(8):55-64

综述了植物自花授粉的方式和类型,分析了自花授粉的生态适应性、可能的进化趋势及其影响因素.自花授粉是指两性花中雌雄蕊之间的授粉,通常也包括同株异花间的授粉.植物按授粉方式可分为自花授粉植物、异花授粉植物和常异花授粉植物3类.在自然界很少有绝对自花授粉的植物,都存在一定频率的异交,根据其自交发生的时间,可将自交分为3种方式:优先自交、竞争自交和滞后自交.自交进化的假说主要集中在两个方面,即繁殖保障和自动选择优势,并已得到广泛的数据支持.分子生物学和生态学相结合的研究方法将进一步揭示植物自花授粉的形成与进化机制.  相似文献   

影响非洲菊离体繁殖的若干因子   总被引：1，自引：0，他引：1  

ZHOU Heng  HUANG Ke 《铜仁职业技术学院学报》2007,(3)

本文从不同的激素种类、不同的培养基类型等方面探讨了上述诸因子对非洲菊离体繁殖的影响,比较深入地研究了非洲菊离体繁殖中各因子对芽诱导、增殖及生根的一系列作用机理。此外,还对试管的苗驯化、移栽作了探讨。结果表明,细胞分裂素和生长素的组合诱导芽及芽的增殖效果最好;而培养基以B5诱导芽效果最好;培养基中低浓度的无机盐有利于生根。通过对比试验,以腐殖土∶沙∶壤土=1∶1∶1的混合基质移栽效果最好。  相似文献   

旅游开发视野下的少数民族文化重构     

周治勇 《安顺学院学报》2011,(4):120-123

民族旅游的开发导致了少数民族文化的过度理性化、商品化以及少数民族文化分化等问题。同时,民族旅游的开发重塑了少数民族地区人民的民族意识、民族文化价值得以重新估量、少数民族地区人民的生活水平得到较大改善、传统手工艺得以重生与传承。在旅游开发过程中,少数民族文化变迁经历了解构再到重构的过程,实现了少数民族文化的再生产。  相似文献   

‘Real Pictures of Current Events’     

Christoph Raetzsch 《Media History》2015,21(3):294-312

Objectivity has been regarded as a central ideal of American journalism in the early twentieth century. The concurrent emergence of photography in the press is rarely associated with this development. The article explores the photographic legacy of journalistic objectivity by discussing a crucial phase in the development of reproduction media for images, the transition from wood engravings to halftones. The former was the dominant mode of ‘illustrated journalism’, the latter became the dominant mode of reproducing photojournalism in print in the twentieth century. The halftone process introduced an equivalence between photographs and their reproductions, obliterating the mediation that had taken place in a code of reproduction that was almost imperceptible. In the contested adoption of the halftone process, it is argued, a shifting valuation of photographs can be observed that prefigures the formulation of objectivity as a transparent code of mediation in journalism.  相似文献   

How stable is the stratification of higher education in England and Scotland?     

David Raffe  Linda Croxford 《British Journal of Sociology of Education》2015,36(2):313-335

This paper asks whether the institutional hierarchies defined by ‘golden triangle’, other Russell Group, other pre-1992 and post-1992 universities in England, and by ancient, old and new universities in Scotland, have become weaker since the 1990s. Using indicators constructed from Universities and Colleges Admissions Service data for 1996–2010, the article finds a stable hierarchical relationship among the sectors within each country, with some indicators showing a slight widening of status differences between sectors towards the end of the period. The main exception was a slight ‘upgrading’ of new (post-1992) universities in Scotland early in the period. There was little change in the association of institutional sector with social class, but in England the association with private secondary schools became slightly stronger and the association with ethnicity weakened.  相似文献   

足球的仿猎原理     

路云亭 《成都体育学院学报》2021,(2):39-45

足球属于实体球类游戏,正因如此,其与狩猎的关系更为紧密。从竞技内涵的角度看,足球与其他球类项目一样,是一种对远古狩猎行为的一种纪念方式。英文"sport"一词本就含有狩猎之意,足球的狩猎基因散落在足球游戏肌体中,足球的狩猎寓意还涉及人与动物多元性关系。足球在英格兰并未遭到彻底禁绝,因为它承载了岛国国民的思维特性,延续了日耳曼人的行事风格,还继承了罗马帝国时代的生活风尚。狩猎精神对球类项目皆有贯通作用,足球之于球员,兼有三重角色,分别为猎具、伴侣与猎物。足球与狩猎的关系呈现出了复合性特质,足球一直有一种简单、自然、便捷的快乐感,足球由此而缔造出一种新的文化载体,并在现实中重新生发出一种新的自然观、人生观与生态观。  相似文献   

文化再生产论——布迪厄理论在民俗体育文化开发中的运用     

何妍  ;夏成龙 《山西师大体育学院学报》2014,(3):35-38

运用文献资料调研与逻辑分析法,分析布迪厄的文化再生产理论用以诠释后申遗时代我国民俗体育文化在开发中的运作过程以及策略活动。研究认为：生存心态是民俗体育文化再生产的基本动力,权力正当化是民俗体育文化再生产的运作逻辑方式,而象征性实践则构成了民俗体育文化再生产的本质意涵。  相似文献   

动物繁殖学实验教学改革与创新人才培养探讨     

任春环  李运生 《科教文汇》2014,(21):51-53

动物繁殖学实验是动物科学专业重要的基础课程,对培养学生的创新精神和实践能力起着十分重要的作用。通过对动物繁殖学实验内容的调整,将实验内容划分为两大模块：室内实验4个,室外实验3个。实验包括验证性实验、综合性实验、设计性实验和开放性实验,重点突出综合实验。实验重视设计性及创新性,引入多媒体辅助教学,并建立全面灵活的考核体系。通过这些改革措施,提高了学生的实验兴趣、增强了学生在实验中的主动性,培养了学生的创新能力。  相似文献   

Dress rehearsal: a Bourdieusian analysis of body work in career portfolio programs     

Ross Collin 《British Journal of Sociology of Education》2011,32(5):785-804

This article examines how career portfolio programs at two secondary schools establish corporeal regimes. Both programs require students to compose portfolios that plot their trajectories through school and into paid work. Prior to graduation, students defend their portfolios before panels of educators and businesspeople. Employing the Bourdieusian concepts of capital and habitus, this article investigates how these programs set up systems that value certain kinds of bodies. Further, it examines how students negotiate these systems and display different kinds of bodies in different kinds of ways. Ultimately, it is argued these disparate bodily performances are read by authorities as indicators of the types of paths students are travelling or should travel into the future.  相似文献