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排序方式: 共有419条查询结果,搜索用时 15 毫秒
41.
从系统论角度认识绿色经济的发展   总被引:1,自引:1,他引:1  
系统探讨了绿色经济发展的整体性要求和层次性特征以及从简单到复杂的演进过程 ,并分析了元素、结构、环境要素对绿色经济系统功能及其演进的影响。指出发展绿色经济其实质是实现社会 经济 生态复合大系统的可持续发展以及社会、经济和生态三大效益总和的最大化。  相似文献   
42.
PCR systems were designed to amplify the entire 5 external transcribed spacer (ETS) region of the 18S rRNA gene of all the diploid species of Aegilops and several other taxa closely related to domesticated wheat. Phylogenetic analysis was performed on the complete ETS sequences using the neighbor-joining, maximum parsimony, and maximum likelihood methods. Among the individual taxa studied, speciation in Secale is very recent. In the case of the A genome diploids, the results support the theory that the A genomes of wheat have experienced reticulate evolution owing to introgression. The B and G genomes of tetraploid domesticated wheats form a clade with Ae. speltoides in which the B genome diverged first and the G genome more recently. It was demonstrated that the complete ETS sequences of the Triticeae yield coherent phylogenetic information. The ETS is a useful tool for studying the phylogeny of closely related species.  相似文献   
43.
Sample populations of 157 Cannabis accessions of diverse geographic origin were surveyed for allozyme variation at 17 gene loci. The frequencies of 52 alleles were subjected to principal components analysis. A scatter plot revealed two major groups of accessions. The sativa gene pool includes fiber/seed landraces from Europe, Asia Minor, and Central Asia, and ruderal populations from Eastern Europe. The indica gene pool includes fiber/seed landraces from eastern Asia, narrow-leafleted drug strains from southern Asia, Africa, and Latin America, wide-leafleted drug strains from Afghanistan and Pakistan, and feral populations from India and Nepal. A third putative gene pool includes ruderal populations from Central Asia. None of the previous taxonomic concepts that were tested adequately circumscribe the sativa and indica gene pools. A polytypic concept of Cannabis is proposed, which recognizes three species, C. sativa, C. indica and C. ruderalis, and seven putative taxa.  相似文献   
44.
基于信息熵的县域土地利用结构变化与分布研究   总被引:3,自引:0,他引:3  
蔡进  刘秀华  丁恩俊 《安徽农业科学》2007,35(21):6539-6541
信息熵是对系统的不确定性(无序性)的一种量度,其演变在一定程度上可以反映区域各类土地利用类型的动态演变规律,也可以反映区域土地的分布。根据信息熵原理研究了重庆市荣昌县土地利用结构变化及分布,并与重庆市进行了比较。结果表明,从时间变化看,荣昌县土地利用结构信息熵在1996~2005年一直处于上升状态,1996年土地利用结构信息熵最低,为1.306 5,2005年达到最大值1.450 8,正处于"凸"型非线性增加态势;从空间变化看,信息熵的大小与经济发展水平密切相关,信息熵大,经济发展较好。荣昌县土地利用信息熵比重庆市水平低,且二者变化趋势差别很大,重庆市信息熵波动较大。  相似文献   
45.
华南野猪的核型及其与家猪的进化关系   总被引:8,自引:0,他引:8  
 本文报道了分布于云南西双版纳热带丛林的华南野猪(Sus scrofa chirodentus)的染色体组型、G-带、C-带和核仁形成区(NOR)。其结果显示,华南野猪的染色体数目2n=38。与过去报道的欧洲野猪和中亚及远东地区的亚洲野猪各亚种(2n=36)比较,少1对近中着丝粒染色体,而多2对端着丝粒染色体。染色体数目、形态和G-带带型均与过去报道的家猪相同;C-带1号、13—18号染色体着丝粒区结构异染色质显示深染,其余双臂染色体(2—12号和X)着丝粒区均浅染;核仁形成区(NOR)亦定位于8号和10号染色体的次缢痕处,惟8号染色体有的细胞仅出现一个具有活性的NOR。本研究结果表明,华南野猪与欧洲和中亚、远东地区野猪亚种的核型有着明显的差异,而与家猪完全一致。这揭示了华南野猪与家猪在起源和进化方面存在着极为密切的亲缘关系。根据核型进化理论,华南野猪很可能是现代家猪的原始祖先之一。  相似文献   
46.
In a prior study on the haplomes of wheat using the 5S rRNA gene we assigned the long A1 and short A1 unit classes to the A haplome in the diploid T. monococcum. The short A1 unit class is absent in the tetraploids T. turgidum and T. timopheevii and in the hexaploid T. aestivum, although present in the hexaploid T. zhukovskyi. Both T. turgidum and T. aestivum contained a different 5S DNA unit class labeled the short A2.The purpose of this paper was to study the short A2 units in the two diploid species to shed light on the theory that the A haplome donor of T. turgidum and T. aestivum was T. urartu. Fifty eight clones were obtained from 12 accessions, sequenced and analyzed. As expected T. baeoticum, which is often classified as a subspecies of T. monococcum, contained the long A1 and the short A1 5S DNA units. Unexpectedly, T. urartu had the long A1 and the short G1 unit classes instead and other units not found so far in Triticum. These findings support the hypothesis that the donor of the A genome in T. zhukovskyi was T. monococcum, as identified by the short A1 units. However, the short A1 units are absent in T. timopheevii, also a carrier of the A genome. The short G1 units found in T. urartu also identify it as a possible donor of the G genome to T. timopheevii. The short G1 units were also found in T. aestivum in our prior study. The long G1 unit class was not found in T. urartu but reported from T. timopheevii and T. zhukovskyi. The implications of these and related findings on the evolution of wheats are discussed.  相似文献   
47.
Sequence variation of nuclear internal transcribed spacer regions of ribosomal DNA (ITS1, 5.8S rRNA and ITS2) from Chinese vegetable mustards (AB-genome) and its putative parents Brassica rapa (the A-genome) and Brassica nigra (the B-genome) were used to investigate the molecular phylogeny and the probable evolutional pattern of this amphidiploid species that uniquely formed in China. Totally, 16 accessions of Chinese vegetable mustard those covering nearly all the diverse variations were included in this study, and together with three accessions of B. rapa and one accession of B. nigra. The results disclosed two strongly supported clades, one containing four accessions of vegetable mustard which have closer relationship with B-genome species “B.nigra” lineage and the other containing 12 accessions of B. juncea and three A-genome accessions. This classification was in disagreement with the evidence from chloroplast DNA, mitochondrial DNA, nuclear DNA restriction fragment length polymorphism (RFLP), which suggested that B. juncea was closely related to the A-genome type. For the incongruence, we speculated that the B. juncea crops derived from Chinese have evolved through different recombined events of the diploid morphutypes and evolved unidirectional concerted evolution. The traditional phenotypic classification of B. juncea was not wholly supported by ITS results, and hence the phylogenetic relationships among these subspecies need to be reconsidered on molecular level.  相似文献   
48.
通过对广场历史发展的研究,分析了4个广场的案例,得出了隐喻的5个不同时期的演变:民主政治的隐喻、帝王君权的隐喻、宗教神权的隐喻、人文精神的隐喻、历史文脉的隐喻.认为历史延续性和社会适应性是城市广场隐喻演变的两大特性.  相似文献   
49.
运用群体生育型特征与演化的观点,分析了冀、鲁、豫夏玉米区玉米杂交种群体生育型演化进程至端的第Ⅳ演化阶段群体生育型基本特征与演化特征及其演进趋向,结果表明,第Ⅳ演化阶段群体生育型基本特征表现为株型紧凑或半紧凑,穗位叶适中,雄穗分枝较少,抗倒性和抗斑性优良,籽粒长,出籽率高;其演化特征主要由穗粒结构与第一叶面积、生育日数决定,其穗长演化将趋于稳态,穗行数、穗粗、百粒重、行粒数与第一叶面积、株高将呈现较明显的持续演进态势,其中生育日数、行粒数和株高将分别向早熟、多粒和高棵方向回归。第Ⅳ演化阶段群体生育型演进临近转型期。  相似文献   
50.
杂草的形成   总被引:1,自引:0,他引:1  
杂草的形成是自然选择和人工选择共同作用的结果,其形成机制与杂交,特别是渗入杂交(inerogressire hybridization)有着极为密切的关系。无融合生殖(apomixis)、染色体加倍或减少也都是杂草形成的重要方式。 本文还从自然和人工选择讨论了杂草不同生活习性的形成,并分析了一年生、二年生和多年生杂草对环境的适应和环境对杂草的选择;自花传粉对杂草后代生存和繁衍的重要性;杂草中种子大小的选择意义化及人工选择所产生的拟态种(mimicus)对环境适应的特点。 最后,还讨论了受人工干扰生境的变化和杂草在这变化环境中的变异情况。  相似文献   
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