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   38篇
  免费   1篇
  国内免费   2篇
  2018年   1篇
  2014年   1篇
  2013年   6篇
  2012年   1篇
  2010年   1篇
  2009年   1篇
  2008年   2篇
  2006年   1篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  2001年   3篇
  2000年   4篇
  1995年   1篇
  1985年   1篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   4篇
  1978年   4篇
  1977年   2篇
排序方式: 共有41条查询结果,搜索用时 15 毫秒
1.
Hybridization is an important evolutionary factor in the diversification of many plant and animal species. Of particular interest is that historical hybridization resulting in the origin of new species or introgressants has occurred between species now geographically separated by great distances. Here, we report that Senecio massaicus, a tetraploid species native to Morocco and the Canary Islands, contains genetic material of two distinct, geographically separated lineages: a Mediterranean lineage and a mainly southern African lineage. A time-calibrated internal transcribed spacer phylogeny indicates that the hybridization event took place up to 6.18 Ma. Because the southern African lineage has never been recorded from Morocco or the Canary Islands, we hypothesize that it reached this area in the distant past, but never became permanently established. Interestingly, the southern African lineage includes S. inaequidens, a highly invasive species that has recently become widespread throughout Europe and was introduced at the end of the 19th century as a 'wool alien'. Our results suggest that this more recent invasion of Europe by S. inaequidens represents the second arrival of this lineage into the region.  相似文献   
2.
Background: Hybridisation in Senecio/Jacobaea is frequent and of significance in speciation and evolution. Moreover, these genera are model systems for studying the evolution of pyrrolizidine alkaloids (PAs). Hybrids between Jacobaea aquatica and J. vulgaris have been reported from north-western Europe.

Aims: Our aim was to determine whether hybrids between Jacobaea aquatica and J. vulgaris also occurred in Austria, and if these hybrids could be responsible for the presumed increase of J. aquatica-like plants in this part of Europe. Furthermore, we tested if such hybrids showed an altered PA spectrum compared with parental species.

Methods: We used amplified fragment length polymorphisms (AFLPs) to analyse genetic diversity and structure, and gas chromatography–mass spectrometry (GC–MS) to identify PAs.

Results: We were able to identify genetically one hybrid population adjacent to a large J. aquatica population. The AFLP phenotypes of hybrids demonstrated a closer relationship to J. aquatica, suggesting frequent backcrossing. All hybrid individuals contained the same set of PAs as the parental species, but in differing amounts, plus four additional PAs, one of which may be novel.

Conclusions: Although hybridisation in Jacobaea is common, we were able to confirm only one hybrid population in Austria. Therefore, it seems unlikely that hybridisation plays a role in the presumed increase of J. aquatica in this area.  相似文献   
3.
4.
A phylogeny of Packera is presented based on sequence data from the internal transcribed spacer region of nuclear ribosomal DNA of 26 species (28 populations) of Packera and 23 outgroup taxa, including representatives of all three subtribes of the Senecioneae. The results support a Mexican origin for Packera, with its closest relatives found among Old World taxa in the subtribe Senecioninae, such as Senecio jacobaea and Pericallis. Packera species from the west coast of the United States, previously included in the section Bolanderi of Greenman, are part of a basal assemblage including species of Greenman's Mexican section Sanguisorboidei. The rest of Packera separates into two sister groups, one containing species from the Arizona-New Mexico region and the other containing more geographically diverse taxa. Among the outgroups, New World Senecio species are monophyletic and two Tussilaginoid assemblages are strongly supported; the Tephroseroid group (Tephroseris and Sinosenecio) plus Petasites combine with the Luina complex to form a clade of north temperate taxa, and the four Mexican genera (Psacalium, Robinsonecio, Barkleyanthus, and Pittocaulon) form a monophyletic group.  相似文献   
5.
研究了国产菊科千里光族款冬亚族及其相关类群 1 1属 1 5种植物的花粉超薄结构。研究类群的花粉超薄结构可分为 2类 :“千里光型”和“向日葵型”。多榔菊属、大吴风草属和毛冠菊属为“向日葵型”,其余种类均为“千里光型”。根据花粉超薄结构类型 ,结合其它有关方面的研究 ,认为大吴风草属与橐吾属并不近缘 ,而毛冠菊属可能接近于紫菀族。  相似文献   
6.
Rugelia nudicaulis afforded, in addition to known compounds, three new highly oxygenated oplopanone derivatives and a bisabolone derivative. The structures were elucidated by high field 1H NMR spectroscopy. The chemotaxonomic situation is discussed briefly.  相似文献   
7.
大吴风草属、假橐吾属花粉表面纹饰及其分类学意义   总被引:1,自引:0,他引:1  
观察了千里光族款冬亚族中大吴风草属,假橐吾属及其相关类群5属共8种植物在扫描电镜下的花粉性状,所有种类的花粉外壁均为刺状纹饰,但在刺的长短,刺部是否膨大、刺基膨大上的纹饰以及刺基之间的纹饰等方面存在差别,大吴风草的花粉外壁性状不同于橐吾属,从而不支持它与后者有较近亲缘关系的观点它与花粉超薄结构同为“向日葵型”的多榔菊属的花粉外壁性状也不相同,假橐吾属不同于橐吾属和垂头菊属的花粉外壁性状,研究结果支持本单种属的成立。  相似文献   
8.
The genus Psednotrichia (Asteraceae–Senecioneae) is endemic to Angola and currently consists of two annual species, P. xyridopsis (O. Hoffm.) Anderb. & P. O. Karis, and P. newtonii (O. Hoffm.) Anderb. & P. O. Karis. A perennial member of the genus was collected on a recent field trip to Angola, and is here described as P. perennis N. G. Bergh & B. Nord., sp. nov. A key to the three species is provided.  相似文献   
9.
10.
The genus Lopholaena contains several eremophilane derivatives. The structures of four new furanoeremophilanes and one eremophilone derivative were elucidated using spectroscopic methods. The chemical relationship of Lopholaena to other genera is discussed.  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