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1.
湖北宜昌大坪奥陶纪阿仑尼克期三叶虫生态组合   总被引:6,自引:2,他引:4  
首次对扬子区奥陶纪大湾组的三叶虫相作了初步分析。在详细研究了湖北宜昌大坪大湾组30种三叶虫的地层和岩相分布的基础上,划分出3个生态组合,即:Asaphid-Pseudocalymene组合,Asaphid-Raphiophorid组合和Trinucleid组合,它们依次指示由浅而深的浅外陆棚环境。研究表明这3个组合在大湾组的交替出现应与阿仑尼克期海平面变化密切相关。  相似文献
2.
黑龙江伊春早寒武世西伯利亚型动物群   总被引:5,自引:1,他引:4  
记述黑龙江伊春地区早寒武世含多门类小壳化石的三叶虫为主的动物群,并依据东北北部及其紧邻俄罗斯境内的寒武纪地层及动物群特征,论证了东北北部地区的沉积-生物-构造古地理属于西伯利亚构造域,华北与西伯利亚两大构造域的对接主带应在二连浩特-西拉木伦-长春-延吉-符拉迪沃期斯克一线。  相似文献
3.
Shabaella fengzuensis的蜕壳   总被引:4,自引:1,他引:3  
描述了浙江江山早寒武世三叶虫Shabaella fengzuensis的蜕壳方式,指出Shabaella的蜕壳机制与同时代的Redlichia有别,但与Hunanocephalus,Sinolenus等的蜕壳方式可能接近。  相似文献
4.
峡东地区寒武纪三叶虫Palaeolenus的新材料   总被引:4,自引:2,他引:2  
对采自峡东地区宜昌、秭归等地的Palaeolenus Mansuy,1912的新材料的形态、保存状态、挤压变形以及个体发育等方面的研究,提出Megapalaeolenus Chang,1966的模式种Palaeolenus deprati Mansuy。1912是Palaeolenus Mansuy的模式种Palaeolenus douvillei Mansuy,1912的晚出异名,属名Mega palaeolenus Chang和种名Palaeolenus deprati Mansuy均应予以废弃。文中还对原归于Palaeolenus和Megapalaeolenus的种作较大的归并和修订。  相似文献
5.
The newly examined Lower Cambrian strata in the Laisvall-Storuman area, central Swedish Caledonides, yield diverse and stratigraphically significant phytoplanktic organic-walled microfossils (acritarchs) associated with the olenellid trilobites of Holmia sp. that appear to be at the lowermost horizon ever recorded in the Caledonides. The acritarchs, recovered throughout the Grammajukku Formation, are taxonomically reviewed in the context of regional and global trends of phytoplankton diversity. The assemblages are assigned to acritarch zones Skiagia ornata-Fimbriaglomerella membranacea and Heliosphaeridium dissimilare-Skiagia ciliosa , corresponding to the Schmidtiellus mickwitzi and Holmia kjerulfi trilobite zones. The records of acritarch radiations and appearances of trilobites and other faunas in Baltica, and on a more interregional scale, are biochronologically correlated, revealing tightly coupled evolutionary events among primary producers and consumers. The timing of early diversifications of trilobites in various faunal provinces is discussed and the relative age of the oldest known non-mineralized arthropods from the Zawiszyn Formation in Poland is estimated.  相似文献
6.
We have cloned zebrafish focal adhesion kinase (Fak) and analyzed its subcellular localization. Fak protein is localized at the cortex of notochord cells and at the notochord-somite boundary. During somitogenesis, Fak protein becomes concentrated at the basal region of epithelial cells at intersomitic boundaries. Phosphorylated Fak protein is seen at both the notochord-somite boundary and intersomitic boundaries, consistent with a role for Fak in boundary formation and maintenance. The localization of Fak protein to the basal region of epithelial cells in knypek;trilobite double mutant embryos shows that polarization of Fak distribution in the somite border cells is independent of internal mesenchymal cells. In addition, we show that neither Notch signaling through Suppressor of Hairless (SuH) nor deltaD is necessary for the wild-type segmental pattern of fak mRNA expression in the anterior paraxial mesoderm. However, nonsegmental expression of fak mRNA occurs with ectopic activation of Notch signaling through SuH and also in fused somite and beamter mutant embryos, indicating that there are multiple regulators of fak mRNA expression. Our results suggest that Fak plays a central role in notochord and somite morphogenesis.  相似文献
7.
奥陶纪Darriwilian早、中期的向阳组三叶虫动物群仅分布于滇西东部红河断裂和南定河-澜沧江断裂之间,这一狭长地带代表奥陶纪印支地体的北延部分。  相似文献
8.
Hypermecaspis(三叶虫)的蜕壳   总被引:2,自引:0,他引:2  
在中国,只在浙江江山早奥陶世印渚埠组顶部的Arenig期发现有Hypermecaspis asiata Han一个种。文中的Hypermecaspis采自江山横塘塘及竹余,和江山城北4km公路两侧的印渚埠组顶部。仅有少数标本保存有头盖,大部分只保留有自由颊、胸与尾,极少相对移位,应为原地理葬标本,所发现的Hypermecaspis几乎全为况壳标本。面线起机能作用,面线裂开,头盖与胸部分离,头盖 表  相似文献
9.
The Furongian (upper Cambrian) Leptoplastus Zone marks a time of critical changes in the evolution of olenid trilobites. This zone, unexposed at Andrarum in Skåne, southern Sweden, has been re-excavated and the sequence of faunas and sediments logged in detail. The faunal succession accords with that previously described from borehole cores by Westergård, and the subzones of L. paucisegmentatus, L. raphidophorus, L. crassicornis, L. ovatus, L. angustatus, and L. stenotus have been recognized. In the first two subzones the olenid assemblages are monospecific. At the base of the L. crassicornis Subzone more than one species is present and morphotypes with long genal spines appear for the first time. Faunal turnover is rapid, but the incoming of new species is invariably linked to an abrupt change in sedimentation, or follows an unfossiliferous interval; species either arose or migrated in after a time of environmental perturbation. Particular faunal associations are often confined to discrete sedimentary packages though some species may range through a succession of sedimentary changes. Leptoplastus crassicornis has very long genal spines, adapted for resting on the sea floor; it may have competed with the coeval, and very similar, L. angustatus. Subsequently, L. angustatus is accompanied by the stout-bodied, short-spined L. ovatus, which presumably occupied a different niche within the same environment. Leptoplastus stenotus is convergent on the much earlier L. paucisegmentatus, and likewise is found as a monospecific assemblage, presumably being adapted to a similar niche.  相似文献
10.
Hybridization in the evolution of animal form and life-cycle   总被引:1,自引:0,他引:1  
Examples of animal development that pose problems for Darwinian evolution by 'descent with modification' but are consistent with 'larval transfer' are discussed. Larval transfer claims that genes that prescribe larval forms originated in adults in other taxa, and have been transferred by hybridization. I now suggest that not only larvae but also components of animals have been transferred by hybridization. The ontogeny of some Cambrian metazoans without true larvae is discussed. The probable sequence of acquisition of larvae by hemichordates and echinoderms is presented. I contend (1) that there were no true larvae until after the establishment of classes in the respective phyla, (2) that early animals hybridized to produce chimeras of parts of dissimilar species, (3) that the Cambrian explosion resulted from many such hybridizations, and (4) that modern animal phyla and classes were produced by such early hybridizations, rather than by the gradual accumulation of specific differences.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 585–602.  相似文献
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