首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   67篇
  免费   6篇
  国内免费   7篇
  2020年   4篇
  2019年   1篇
  2018年   1篇
  2017年   1篇
  2016年   4篇
  2015年   4篇
  2013年   4篇
  2012年   1篇
  2011年   3篇
  2010年   4篇
  2009年   1篇
  2008年   6篇
  2007年   4篇
  2006年   4篇
  2005年   4篇
  2004年   2篇
  2003年   6篇
  2002年   3篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1990年   4篇
  1987年   1篇
  1985年   1篇
排序方式: 共有80条查询结果,搜索用时 62 毫秒
1.
2.
The genus Apalis is a member of the African forest warblers clade of the Cisticolidae. In view of its morphological diversity, it was suggested that this genus needs a taxonomic revaluation. For this, we sequenced a nuclear intron (myoglobin intron 2) and two mitochondrial protein‐coding genes (ND2 and ND3). The 2016 bp of sequence data obtained were aligned and subjected to parsimony, maximum likelihood and Bayesian inference. All three genes strongly reject the monophyly of Apalis but support the placing of all apalises within a broader clade of forest cisticolids which also includes Urolais. Within this forest clade, a subclade is defined which includes the genera Urolais, Schistolais and a well‐supported clade comprising three afromontane species, the Black‐collared Apalis Apalis pulchra, the Ruwenzori Apalis Apalis ruwenzorii and the African Tailorbird Artisornis. This subclade is sister to other members of Apalis, including the type species of the genus the Bar‐throated Apalis Apalis thoracica. A new generic name, Oreolais, is suggested for the Black‐collared and Ruwenzori Apalises.  相似文献   
3.
Hodotermopsiphila gen. nov. is described to include four termitophilous species: H. maruyamai sp. nov. (Yaku‐shima, Japan), H. nitens sp. nov. (Yaku‐shima, Japan), H. longisetosa sp. nov. (Taiwan), and H. sugayai sp. nov. (Taiwan and northern Laos). These species are associated with the damp‐wood termite, Hodotermopsis sjostedti Holmgren, 1911. Hodotermopsiphila species share possible apomorphic character states with three termitophilous species, Hodotermophilus gloriosus, Yakuus iwatai, and Termophidoholus formosanus, which are also associated with H. sjostedti.  相似文献   
4.
The small phytoplankton genus Triparma belongs to the class Bolidophyceae and contains two distinct forms: silicified species and naked flagellated species (formerly Bolidomonas). Recent studies showed that four silicified species/strains (Triparma laevis f. inornata, T. laevis f. longispina, T. strigata, and T. aff. verrucosa) belong to a single clade that is paraphyletic, because it also contains an unclassified flagellated strain, and is sister to a flagellated species, T. eleuthera. In this study, we isolated and characterized two new strains of silicified species to test the phylogenetic unity of silicified bolidophytes. The isolates were identified as T. retinervis strains because they possessed fine areolation on the cell wall. 18S rDNA and rbcL phylogenetic analyses demonstrated that T. retinervis formed a new silicified clade that is sister to the flagellated species T. pacifica. This reveals that there are at least two distinct clades including both silicified and flagellated Triparma species.  相似文献   
5.
The occurrence of villi (outgrowths, projections) on the bases of the basalmost downy barbulcs of breast-feathers is documented with scanning electron microscopy. The presence of these structures is thought to constitute a synapomorphic character for Passeriformes, Trochilidac, Capitonidac, Indicatoridae, Ramphastidae, and Picidae, which once more casts suspicion on the monophylv of Wetmore's order Piciformes.  相似文献   
6.
最近吴征镒等发表的被子植物“多系_多期_多域”的“八纲”新分类系统,是以该系 统作者自己人为截取早白垩世时间横断面并认为在这个横断面上存在8条主传代线为基础建 立的。“八纲系统”在祖先式样及其起源时间和地点方面缺乏证据,各主传代线相互之间及 其与被子植物共同祖先的关系也基本没有说明。由于没有接受植物系统发育重建研究中共同 遵守的共同祖先原理,而且混淆使用了“单系”和“多系”的概念,可以认为“八纲 系统”是人为性很强的被子植物分类系统。  相似文献   
7.
Mathematical consequences of the genealogical species concept   总被引:16,自引:0,他引:16  
A genealogical species is defined as a basal group of organisms whose members are all more closely related to each other than they are to any organisms outside the group ("exclusivity"), and which contains no exclusive group within it. In practice, a pair of species is so defined when phylogenies of alleles from a sample of loci shows them to be reciprocally monophyletic at all or some specified fraction of the loci. We investigate the length of time it takes to attain this status when an ancestral population divides into two descendant populations of equal size with no gene exchange, and when genetic drift and mutation are the only evolutionary forces operating. The number of loci used has a substantial effect on the probability of observing reciprocal monophyly at different times after population separation, with very long times needed to observe complete reciprocal monophyly for a large number of loci. In contrast, the number of alleles sampled per locus has a relatively small effect on the probability of reciprocal monophyly. Because a single mitochondrial or chloroplast locus becomes reciprocally monophyletic much faster than does a single nuclear locus, it is not advisable to use mitochondrial and chloroplast DNA to recognize genealogical species for long periods after population divergence. Using a weaker criterion of assigning genealogical species status when more than 50% of sampled nuclear loci show reciprocal monophyly, genealogical species status depends much less on the number of sampled loci, and is attained at roughly 4-7 N generations after populations are isolated, where N is the historically effective population size of each descendant. If genealogical species status is defined as more than 95% of sampled nuclear loci showing reciprocal monophyly, this status is attained after roughly 9-12 N generations.  相似文献   
8.
A variety of research projects focus on genetic variation among and within maternal lineages as encompassed by mitochondrial DNA (mtDNA). While mtDNA often differs substantially between species, large differences may also be found within species. The evaluation of such divergent lineages, for example in intraspecific contact zones (hybrid zones), commonly involves sequencing numerous individuals. Large‐scale sequencing is both expensive and labour‐intensive. Based on sequences from 15 individuals, we devised a simple and quick polymerase chain reaction assay for identification of divergent mtDNA lineages in a secondary contact zone of the side‐blotched lizard (Uta stansburiana). The application uses lineage‐selective primers to amplify a lineage‐diagnostic product, and is based on each group of mtDNA haplotypes being a monophyletic assemblage of haplotypes sharing the same maternal ancestry, deeply divergent from the other group. The assay was tested on a larger sample (n = 147) of specimens from the contact zone, confirming its usefulness in quick and reliable identification of mtDNA lineages. This approach can be modified for other species, provided diagnostic lineage variation is available, and may also be performed in simple laboratory settings while conducting fieldwork.  相似文献   
9.
Ernst Haeckel, who first introduced the term ‘monophyly’ into the biological literature, has in the past been appealed to in adjudication of the modern use of that concept. A contextual analysis of his writings reveals an inconsistent use of the term ‘monophyly’ by Haeckel. Morphological phylogeny was decoupled in Haeckel’s thinking from the evolutionary history of taxa. Monophyly could mean the derivation of one taxon from another, ancestral one, where these taxa could be species or of supraspecific rank. Monophyly could also mean the phylogenetic differentiation of a diversity of organismal ‘forms’ (morphologies) from a common primitive ‘form’ (morphological stage). And finally, monophyly, as also polyphyly, could apply to the origin of specific anatomical structures, in which case the monophyly/polyphyly of anatomical structures needed not to correlate with the monophyly/polyphyly of the taxon characterized by these structures. With respect to the issue of the unity and reality of monophyletic taxa, Haeckel’s writings again are indeterminate as is his stance on the monophyletic origin of life.  相似文献   
10.
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