首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 140 毫秒
1.
一年又一年     
上了年纪的人都有相似的感觉,就是年纪越大,时间好像过得越快。小时候,过了元旦盼春节,过了春节盼五一、六一,过了六一盼国庆,过了国庆再盼元旦。时间总是那么漫长,盼望的假期似乎总是姗姗来迟。而如今,似乎一眨眼,一年就过去了。我给这个现象总结了一个理论,叫做相对  相似文献   

2.
酷想大晒台     
哎呀呀,这个世界乱套了!大人变成了小孩,小孩变成了大人。现在,终于轮到各位小酷想家来当家做主了,快来看看他们都有什么出色的表现吧!看到爸妈变成了小孩,我立马学着他们的样子,下达了第一道命令:写作业去!我想他们一定会哭的,因为老师留的作业实在是太多了。新浪YOYO  相似文献   

3.
贝时璋先生与20世纪同行,经历了百年世事沧桑,目睹了世纪科技巨变,体会了人生的无尽乐趣;同时,他也对中国生物物理学的发展做出了杰出贡献,展示了人生的巨大价值.  相似文献   

4.
叙述了生物信息学中途径的研究背景;综述了近几年来相关途径及生物化学数据库及其特点;介绍了有关的途径分析方法.同时对于途径研究应用作了展望.  相似文献   

5.
远程教育培训给生物教学带来新的生机。夯实了专业知识,梳理了生物知识,使我认识到应该如何把握生物课堂教学,提高了课堂教学设计能力,凝聚了生物教师的力量,使老师们学到了很多知识和教学技能,解决了平时教学中的一些难题,提升了生物的教学水平。  相似文献   

6.
蔡崇达  CFP 《生命世界》2006,(6):22-27
中国全面推行计划生育政策,少生了3亿多人,节约了7万亿抚养费,也少了3亿可以负担养老的劳动力。由于老龄化加速,老年抚养比由1964年的6.4%上升为2002年的11.6%,离退休金平均实际递增18.9%。到2050年,中国的抚养比将可能达到70%。老龄化速度,法国用了115年,英国用了80年,美国用了60年,我国用了18年。  相似文献   

7.
综述了近年来乌龙茶品质的研究进展,介绍了乌龙茶的感官品质特征,阐述了乌龙茶的理化品质特征和相关药理作用,分析了影响乌龙茶品质的主要因素,概述了乌龙茶品质研究技术,提出乌龙茶品质下一步的研究重点方向。  相似文献   

8.
禹晓晶 《化石》2007,(3):44-44
自从1953年DNA双螺旋结构发现以后,紧接着对生物大分子的各种新发现层出不穷,生物学可谓就进入了分子生物学的时代,它使人们对生物学的认识提高到了一个新的水平,也开拓了新的领域.当然,分子生物学也使进化论的研究转入了一个更精细的水平,解决了进化论中一些争论的问题,同时也提出了一些新的研究思想和观点.  相似文献   

9.
霉菌吸附重金属离子的研究进展   总被引:1,自引:0,他引:1       下载免费PDF全文
介绍了目前国内外采用霉菌吸附分离废水中重金属离子的研究情况,总结了不同霉菌的吸附能力,讨论了霉菌吸附重金属离子的影响因素、机理以及固定化技术,最后展望了霉菌吸附重金属的发展趋势.  相似文献   

10.
《生命世界》2006,(1):45-47
方精云生态学家。北京大学教授。1959年出生于安徽怀宁。1982年毕业于安徽农学院林学系,1989年获日本大阪市立大学生物学博士学位。现任中国生态学会副理事长及国内外多个学术刊物的副主编或编委。建立了我国陆地植被和土壤碳储量的研究方法,系统研究了我国陆地生态系统的碳储量及其变化,较早地开展了碳循环主要过程的野外观测,构建了中国第一个国家尺度的陆地碳循环模式,为我国陆地碳循环的研究奠定了基础;系统研究了我国大尺度的植被动态及时空变化,揭示了我国植被生产力的变化趋势、空间分异及其对气候变化响应的规律;系统开展了我国植被分布与气候关系的定量研究,提出了基于植被气候关系的我国植被带划分的原则和依据,首次采用统一的调查方法,较系统地研究了我国山地植物多样性的分布规律。  相似文献   

11.
Research on the influence of sea level variations on the benthic faunas have been carried out in the Upper Ordovician of Sardinia. Study of the depositional facies and sequence analysis of the upper part (Lower Ashgill) of the Portixeddu Formation led to the identification of the sedimentary environments. Cystoids and crinoids are associated to bryozoans and brachiopods in most levels. The numerical analysis of associations and megaguilds shows that crinoids and cystoids have a higher frequency in the proximal and median facies of the upper offshore. The columnal association characterized by Conspectocrinus celticus and the coronoid Mespilocystites tregarvanicus has been discovered in the upper part of the formation. This material and complementary samples from Upper Ordovician of Sardinia and Kabylia (Algeria) bring additional data on the systematic and show the wide distribution of this fauna outside of the Ibero-armorican domain. The distribution of this echinoderm association supports a palaeogeographical position of the Ibero-armorican domain and Sardinia within the north gondwanan margin during the Lower Palaeozoic.  相似文献   

12.
The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.  相似文献   

13.
A phylogenetic analysis of the interrelationships of the barbets (Capitonidae) and the toucans (Aves: Ramphastidae, Superfamily Ramphastoidea) is presented. Thirty-two morphological characters from the literature and independent osteological observations were analysed. Character polarity was determined by outgroup comparison to the Picidae, Indicatoridae, Galbulidae, Bucconidae and Coraciiformes. Four alternative phylogenetic hypotheses were compared: (1) the overall most parsimonious morphological phylogeny, (2) the most parsimonious morphological phylogeny in which the capitonids and ramphastids were hypothesized as monophyletic sister groups, and (3) and (4) the most parsimonious hypotheses for the evolution of the morphological characters within two proposed DNA-DNA hybridization phylogenies of the ramphastoids. The analysis focused on the higher level relationships of ramphastids and capitonids and interrelationships among capitonid genera. Two cladistic analyses were performed using 26 phylogenetically informative characters, and the PAUP and CONTREE computer alogorithms. The most parsimonious morphological phylogeny required fewer character changes and had a lower consistency index than any of the alternative hypotheses but congruence between the most parsimonious phylogeny and the second, revised DNA-DNA hybridization hypothesis was very high. Based on these results the monophyly of the Capitonidae is rejected. The ramphastids and the Neotropical capitonids form a well corroborated clade within the pantropical ramphastoid radiation. Neither the African, Asian nor New World capitonids is monophyletic. The genus Trachyphonus is the sister group to all other capitonids and ramphastids. The sister group to the ramphastids is the genus Semnornis. The interrelationships of the Old World capitonids excluding Trachyphonus are not completely resolved by these morphological data but one of the alternative phylogenetic resolutions is presented as a preliminary hypothesis. The clades in this resolved phylogeny are diagnosed and the palaeontology and biogeography of the ramphastoids arc-reviewed in light of this new evidence. A phylogenetic classification is proposed in which the Capitonidae is rejected and the capitonids and ramphastids are placed in seven subfamilies of the Ramphastidae.  相似文献   

14.
The present study describes the fetal regions ethmoidalis and orbitotemporalis of the cranium of Galea musteloides and Kerodon rupestris and compares them with Galea spixii and Cavia porcellus . The fetal crania of these representatives of the Caviinae were serially sectioned and 3D plate reconstructions were built. For a broader scope, serially sectioned heads of the caviomorph taxa Hydrochaeris hydrochaeris and Dasyprocta leporina were also examined. The ethmoidal and orbitotemporal regions of the cranium provides characters that are pertinent to the discussion of systematics of the Caviinae. Nine cranial characters were identified as being significant and discussed phylogenetically. Taking the monophyly of the Cavioidea as given, two characters are autapomorphic for the genus Galea: the reduction of the crista semicircularis and the lacrimale forming the 'arco antorbitario' (Kraglievich 1930). Cavia is the sister group of Galea; synapomorphic characters are the extent of the processus palatinus medialis of the praemaxillare and the presence lamina pterygoidea of the alisphenoid. There were no apomorphic characters of the structural complexes examined that could support the Caviinae. The reduced and nonperforated alisphenoid is an autapomorphic feature of the Caviidae. The division of the nasoturbinale is evidence for a sistergroup relationship of the Hydrochaeridae and the Caviidae. Autapomorphic characters for the Cavioidea include the ventrolateral opening of the organon vomeronasale and the lateral prolongation of the lacrimale.  相似文献   

15.
Foliar sclereids in the Magnoliaceae   总被引:4,自引:0,他引:4  
The foliar sclereids in 136 species representing 11 of the 12 genera of Magnoliaceae were studied and compared. Sclereids occur in four different cell assemblages within the leaf: diffuse idioblasts, mesophyll, dermal system, and the vein sheath including terminal elements. Tropical members tend to have the most highly sclerified leaves. In species of Manglietia the leaves have sclerified spongy mesophyll and either sclerified epidermis or hypodermis. In Talauma , sclerification affects the vein sheath and terminal cells of veinlets, with a specialized thick marginal vein in the Asian taxa but not in the American ones. Liriodendron and the magnolias native to the north temperate zone have only minimal sclerification, which usually is confined to the vein sheath of the midrib and the main lateral veins, and as idioblastic sclereids in the petiole and the midrib near the base of the blade. The two largest genera Magnolia and Michelia are heterogeneous and include species which vary as to their combinations of sclerified elements among the four possible types.  相似文献   

16.
In the mutualistic symbioses between legumes and rhizobia, actinorhizal plants and Frankia, Parasponia sp. and rhizobia, and cycads and cyanobacteria, the N2-fixing microsymbionts exist in specialized structures (nodules or cyanobacterial zones) within the roots of their host plants. Despite the phylogenetic diversity among both the hosts and the microsymbionts of these symbioses, certain developmental and physiological imperatives must be met for successful mutualisms. In this review, phylogenetic and ecological aspects of the four symbioses are first addressed, and then the symbioses are contrasted and compared in regard to infection and symbio-organ development, supply of carbon to the microsymbionts, regulation of O2 flux to the microsymbionts, and transfer of fixed-N to the hosts. Although similarities exist in the genetics, development, and functioning of the symbioses, it is evident that there is great diversity in many aspects of these root-based N2-fixing symbioses. Each symbiosis can be admired for the elegant means by which the host plant and microsymbiont integrate to form the mutualistic relationships so important to the functioning of the biosphere.  相似文献   

17.
Recent stratigraphic studies in southern Tibet provide new information about the timing of the initial collision between the India and Eurasia continental blocks. The stratigraphic and paleontological evidence document dramatic changes in sedimentary facies and microfauna content across the Cretaceous-Paleogene (K/Pg) boundary. In the Zhongba and Gamba areas in southern Tibet, the K/Pg boundary is marked by a major disconformity, separating platform carbonates from overlying terrigenous conglomerates and sandstones. The stratigraphy of the boundary sequences has recently been improved with the recognition of three foraminiferal assemblages. They are: Maastrichtian Orbitoides-Omphalocyclus , Danian Rotalia-Smoutina-Lockhartia and Thanetian Miscellanea-Daviesina microfaunal assemblages. The K/Pg boundary at the Gamba area is placed between the Orbitoides-Omphalocyclus and Rotalia-Smoutina-Lockhartia faunas. In Tingri, Cretaceous Globotruncana and tertiary Globigerina-Globorotalia microfauna demark the position of the K/Pg boundary. The occurrence of terrigenous sandstones and boulder-size conglomerates in the early Paleocene is compelling evidence for tectonic uplift and emergence of the southern margin of the Lhasa block and of the northern margin of the Indian plate. Therefore, supported by biostratigraphic evidence, we argue that the uplift is caused by the onset of continental collision during the earliest Danian. Progressing plate collision resulted in deformation and fragmentation of the Paleocene carbonate platform and deposition of limestone breccias, which we consider as further evidence for tectonic compression as a result of early continental collision during the Thanetian, earlier than indicated by previous studies in the Himalayas. It is the change in the sedimentary facies and depositional environment that provides the earliest evidence and dating of the initiation of the collision process. From studies of sedimentary strata in southern Tibet, the collision of the India and Lhasa continental blocks was initiated at ~K/Pg boundary time (~65Ma). If that is the case, than the major lithofacies changes at the K/Pg boundary observed in the western Tethys, mostly referred to as intrinsic to the eustatic sea level change, has been driven by continental convergence and collision of the Indian and Eurasian plates.  相似文献   

18.
Many recent developments in European marine and estuarine science have been against the demands of European Union legislation. The implementation of certain statutes, the role of scientists and the nature of the data required are discussed using examples from the UK, the Netherlands and Portugal. This includes the implementation of the EU Directives on Urban Waste-water Treatment, the control of Nitrates, the designation of Species and Habitats, the control of Dangerous Substances, the statutory requirement for Environmental Impact Assessments and the recently proposed Water Framework Directive. For these, the integration of physical, chemical and biological monitoring and investigation is discussed in relation to the science dictated by the legislative and administrative requirements. Each of these Directives requires the development of generic guidelines and protocols for implementation and the use of national enabling legislation. This indicates that, in several cases, the science should concentrate on monitoring and assessment in a well-structured and quality-controlled manner. The paper concludes by summarising developments based on similarities in the implementation of present and proposed Directives across Europe.  相似文献   

19.
Chronic exposure to excessive levels of nutrients is postulated to affect the function of several organs and tissues and to contribute to the development of the many complications associated with obesity and the metabolic syndrome, including type 2 diabetes. To study the mechanisms by which excessive levels of glucose and fatty acids affect the pancreatic beta-cell and the secretion of insulin, we have established a chronic nutrient infusion model in the rat. The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin) for 72 hr. This model offers several advantages, including the possibility to finely modulate the target levels of circulating glucose and fatty acids; the option to co-infuse pharmacological compounds; and the relatively short time frame as opposed to dietary models. It can be used to examine the mechanisms of nutrient-induced dysfunction in a variety of organs and to test the effectiveness of drugs in this context.  相似文献   

20.
During the Miocene time, the Atlas-pelagian block, which is limited northward by the atlasic-alpin chain of North Africa-Sicily, southward by the Gafsa-Jeffara-Azizia fault and eastward by the Malta escarpment, resulted from the extension-compression regime, mainly controlled by the subduction-collision processes. This regime induced the opening of many Miocene microbasins, which have been infilled by silicoclastic materials showing lateral and vertical facies variations and several hiatus associated to tectonic and stratigraphic unconformities. Excepting the very local transgressive regimes, such as those of Langhian and Messinian periods, most of the Miocene deposits took place on internal platforms, especially at the NE part of the country. The fluviodeltaic and alluvial sediments are, in fact, lateral equivalents which infilled the valley and depression enclosed systems towards the SW. In this context (rapid facies variations in time and space, superposition of tectonic and eustatic unconformities, climatic variations, rare or absent stratigraphic markers…), some controversies remain as regards the correlation and dating of these series. This work consists of a study of the lateral and vertical facies and thickness variations, coupled to the identification of the main unconformities. It is also a study of significance of the main sedimentological mechanisms and an inventory of the different palynological and paleontological content of the sediments. The aim of this work is to propose a new vision on the Miocene deposits in Tunisia along a NE-SW axis. Then, using these data, we have correlated the different lithological formations, discuss their age and, finally, proposed paleogeographical drafts for them.  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