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   22篇
  免费   0篇
  国内免费   2篇
  24篇
  2018年   1篇
  2014年   1篇
  2012年   1篇
  2011年   2篇
  2009年   1篇
  2008年   2篇
  2005年   1篇
  2001年   1篇
  1998年   1篇
  1994年   1篇
  1993年   1篇
  1990年   2篇
  1985年   1篇
  1984年   2篇
  1982年   1篇
  1981年   5篇
排序方式: 共有24条查询结果,搜索用时 15 毫秒
11.
The Obon sections in the central Iberian ranges, thestratigraphy of which is well established, have a rich microfauna of Foraminifera from Upper Domerian and Toarcian. It is partly original (4 new species are described, and 4 are left as open nomenclature).The plentifulness of the material has allowed thestructures of some of the populations to be shown up, some of the forms to be grouped up into spectrums and precisions brought in about the notion of the Lenticulina genus and its systematics.A part of the Iberian species is also to be found in the rest of Western Europe and Morocco. The Poitou species created by J.M. Payard (1947) are the objects of critical comparison. The later appearance of the marly-calcareous facies in Poitou may explain the differences in stratigraphic repartition fairly constantly observed.  相似文献   
12.
We tested the applicability of two available Water Framework Directive (WFD) compliant phytoplankton indices on three large peri-alpine lakes to analyze their suitability for trophic classification. We show that the indices vary in their final resulting Ecological Quality Ratios (EQRs) and are only appropriate to roughly distinguish lakes of different water quality according to OECD criteria (OECD, 1982). Annual mean TP concentration in Lake Geneva was 0.03 mg l?1 in 2006 (Lazzarotto &; Rapin, 2007), which marks mesotrophic conditions. According to the tested indices, the lake is of ‘good’ (0.60–0.80) quality after the German WFD method (PSI) and of ‘moderate’ quality according to the Austrian WFD method (BI). We prove that the way how to derive the per annum value of the metric ‘Brettum Index’ (BI) in the Austrian WFD method significantly influences the resulting index and the scatter of long-term data. We focused on improvement strategies for this index in terms of calculation and sampling frequency. Contrary to the tested bin, the modified index presents no significant differences between four and six sampling dates per year. In order to improve the significance of the available indices, we propose to modify the way of per annum index calculation for the Austrian WFD method as well as to focus on species composition to achieve a high relative proportion of indicator species. A phytoplankton index alone may not be sensitive enough to track the changes that occur within a lake. The results confirm the need to take into account other biological elements such as fish, macrophytes, attached diatoms and macrozoobenthos as suggested by the WFD.  相似文献   
13.
14.
We recently discovered several populations of the red alga Rhodospora sordida Geitler in samples from seep walls in Tennessee. This species is thought to be an extremely rare alga. It was reported previously only from seep walls in Europe. The last published reports of the alga were made in the mid‐1970s. A culture of the alga was made from one other site in North America (a rock wall in Arkansas) in 1977, but no publication accompanied that find. Since discovering the alga in summer 2004, we found a second population in a seep wall in northeast Ohio. We suspect that this species has a broader distribution than previously thought and has been overlooked or misidentified in past studies.  相似文献   
15.
Richard Lund  Wendy Lund 《Geobios》1984,17(2):237-244
Four new species of coelacanths (Actinistia) from the Namurian E2b marine Bear Gulch Limestone of Montana are described, and a fifth species, originally described as an actinopterygian, is redescribed. Two new suborders are diagnosed. The taxonomy is: Suborder Coelacanthocdei, family Rhabdodermatidae, Caridosuctor populosum nov. sp., suborder Hadronectoroidei nov., family Hadronectoridae nov., Hadronector donbairdi nov. sp., Polyosteorhynchus simplex nov. sp. and Allenypterus montanusMelton. Lochmocercus aciculiodontus nov. sp. is incertae sedis.  相似文献   
16.
A biostratigraphic sequence based upon dinosaureggshells during the lower and upper Rognacian (upper Cretaceous) in the Aix-en-Provence sedimentary basin (Bouches-du-Rhône, France) has been studied from a morphometric and microstructural viewpoint. Stratigraphic control of eggshell fragment sampling made it possible to follow their evolution throughout the Rognacian. Our results differ from those of certain authors who have worked in this region in that no tendancy toward abnormal eggshell thinness appears at the end of the Cretaceous which could be linked to the problem of dinosaur extinction. Furthermore, we observed no significant increase in the number of bi- or multistratified eggshells («ovum-in-ovo) in the deposits. The microstructural study shows the presence mainly of normal egg-shells belonging to at least three morphotypes.  相似文献   
17.
A fin spine previously described as ‘Myriacanthus paradoxus’ Agassiz from the Lower Lias (Lower Jurassic) of Lyme Regis, is allocated to the new genus and species Recurvacanthus uniserialis. The spine is unusual in possessing a single median row of four large, hook-like, downturned denticles on the distal part of the posterior wall. It is concluded that the unique specimen should be classified with the myriacanthoid chimaeriform holocephalans since it possesses a tubercular ornament on the lateral walls.  相似文献   
18.
本文记载了中国大风子科植物6族、12属、40种5变种。讨论了本科在中国的地理分布,其区系地理特征以下列5方面最为明显:1.华南至华西南几乎集中了所有的国产种类;2.特有现象明显;3.具有明显的热带区系性质;4.北纬35°可能是本科在东亚乃至北半球的北界;5.分布类型多样。同时建立了一个新族和一个新变种,报道了2个中国新记录种和一个大陆新记录种。并对其它一些种类进行了讨论。  相似文献   
19.
陆兆华  朱有昌 《植物研究》1994,14(4):359-360
本文发表了老鹳草属二新变种,一新组合变种,即复花鼠掌老鹳草Gerauium sibiricum L.var.multiflorum Z.H.Lu;白河块根老鹳草Geranium dahuricum DC.var.baiheense Z.H.Lu et Y.C.Zhu和伏毛绒背老鹳草Geranium vlassovianum Fisch.ex DC.var.hattai(Nakai)Z.H.Lu。  相似文献   
20.
微生物群落在调节全球气候、人类健康和工业生物技术应用中扮演着重要角色。定量表征微生物群落多样性是认识微生物群落基本特征、动态变化和功能的前提。本文介绍了常用的α多样性指数,包括物种数目、Shannon-Weaver指数、Simpson多样性指数和Hill多样性指数;并介绍了其他多样性评估方法及其原理,包括能够评价样本对微生物群落各物种覆盖程度的稀释性曲线和Good’s coverage指数,以及能估算群落多样性的Chao1、ACE指数和基于物种丰度分布曲线的模型方法;并以最大规模的生物技术应用——污水处理厂为例,介绍了这些方法在认识微生物群落多样性中的应用。现有研究表明:所检测到的城市污水处理厂中微生物群落的物种数目和Shannon-Weaver指数随检测方法解析通量(样本大小)的增加而增大;但现有方法仍无法反映城市污水处理厂微生物群落的真实多样性。基于特定的物种丰度分布曲线对DNA样本数据进行模拟和重建,结果表明对群落物种数目的评估存在较大的不确定性;Shannon-Weaver指数,特别是Simpson多样性指数等受低丰度物种影响较小,可以准确计算,是评价和比较微生物群落分类学多样性的好手段。改进模型拟合方法和加大取样深度能提高微生物群落物种数目的评估精度。此外,认识微生物群落其他方面的多样性如系统发育多样性和功能多样性,也对认识微生物生态特征具有重要意义。  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