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   112篇
  免费   2篇
  国内免费   1篇
现状及发展   3篇
综合类   32篇
自然研究   80篇
  2024年   1篇
  2023年   1篇
  2021年   3篇
  2020年   1篇
  2019年   4篇
  2018年   4篇
  2017年   4篇
  2016年   5篇
  2015年   6篇
  2014年   3篇
  2013年   2篇
  2012年   62篇
  2011年   2篇
  2009年   1篇
  2008年   1篇
  2007年   1篇
  2006年   1篇
  2005年   2篇
  2004年   1篇
  2003年   2篇
  2002年   2篇
  2001年   2篇
  2000年   1篇
  1999年   1篇
  1997年   2篇
排序方式: 共有115条查询结果,搜索用时 15 毫秒
1.
The most prominent cooling event of the Earth surface during Cenozoic in the long-term transition from a non-glaciated planet, or “green-house world”, to a polar, glaciated planet, or “ice-house world”, is the Earliest Oligocene Glacial Maximum (EOGM) above the Eocene/Oligocene boundary at about 33.7 Ma. Planktonic and benthic foraminiferal oxygen and carbon isotopes, carbonate content, and coarse fraction, along with high-resolution color reflectance and magnetic susceptibility records during 35-30 Ma, from deep-water Sites 1262 and 1265, Ocean Drilling Program (ODP) Leg 208 in South Atlantic, reveal the global cooling event occurring in both surface and deep oceans. The results show that the earliest Oligocene δ^18O values during 33.5-33.1 Ma represent the magnitude of continental ice sheets on east Antarctica and indicate the large decrease in both surface and deep water temperatures of worldwideoceans. The δ^13C records show the large excursion during the period of EOGM event and indicate some types of shift in global carbon reservoir, probably demonstrating the sudden increase in organic carbon burial rates and the changes in the distribution and timing of production. At the same time, lithologic composition, carbonate content, color reflectance, and coarse fraction brought about significant changes close to the Eocene/Oligocene boundary, reflecting the abrupt deepening in the carbonate compensation depth (CCD). Changes in carbonate content were revealed from the color reflectance identify periodicities associated with eccentricity of the Earth‘s orbit (100 and 400 ka), further indicating orbitally forced global climate variations in the Early Oligocene.  相似文献   
2.
《Journal of Natural History》2012,46(11):1597-1615
Over 8000 amphipods were examined from coastal (primarily intertidal) and anchialine pool habitats of Ascension Is. Twenty-seven species, of which 14 are undescribed, were identified. Comparison of species from Ascension with amphipods found in possible source areas suggests that most colonization of the island by these animals has been via the Benguela Current. Possible western Atlantic faunal contributions are significantly lower than for other marine taxa that have been studied at Ascension, all of which are generally characterized by having dispersive larval stages. The high proportion of apparently endemic species, which exceeds that described for amphipods of other oceanic islands, is probably due to both the island's isolation and incomplete faunal surveys in possible source areas. Amphipod species diversity is low, a probable consequence of the size, isolation, youth and low habitat variability of Ascension Is. Consistent with other Atlantic islands that have been studied, nestlers predominate (56% of the species), with tubicolous species (33%) of secondary importance and inquilines (11%) making only a minor contribution. Three species occur in the anchialine pool habitat. Rather unexpectedly, caprellid amphipods are absent.  相似文献   
3.
ABSTRACT

This study is primarily directed to the most poorly known species of the genus Trichomycterus, comprising five nominal species (T. florensis, T. immaculatus, T. nigricans, T. paquequerensis and T. santaeritae) endemic to south-eastern Brazil. One of them, T. nigricans, is the type species of the genus, involved in taxonomic problems for over 150 years. A detailed historical review, accompanied by examination of type specimens and recent collections, revealed that the correct type locality of T. nigricans is in the vicinity of Rio de Janeiro, not Santa Catarina as commonly appears in the literature; specimens previously misidentified as T. nigricans from Santa Catarina belong to a possibly undescribed species of the genus Cambeva; T. paquequerensis is a synonym of T. immaculatus, and T. florensis is a synonym of T. santaeritae; and the hypothesis that T. santaeritae is closely related to the Amazon Sarcoglanidinae is refuted. The three valid species are redescribed. These species are members of a clade also including T. caipora that is highly supported by molecular data, diagnosed by a pronounced posterior maxillary process and caudal fin emarginate at least in larger specimens. A subclade comprising T. caipora, T. nigricans and T. santaeritae is diagnosed by a long maxilla and a bifid anterior extremity of hypobranchial 3.  相似文献   
4.
为解决南大西洋至几内亚湾海域的海浪组成成分、传播特性及来源这3个该海域一直需要解决的问题,建立SWAN (Simulating WAves Nearshore)双层嵌套海浪模型对南大西洋至几内亚湾冬季海浪时空分布进行模拟分析,结果表明:南大西洋海浪有效波高呈高纬度区(30°S以南)向低纬度区(30°S以北)递减的趋势 ,高纬度区海浪传播方向与风场关系密切,低纬度区则与风场差异明显;南大西洋涌浪波高与混合浪波高分布高度相关,涌浪在混合浪中所占比例较大,尤其在风速较小的低纬度海域更为显著;南大西洋中部至几内亚湾存在相对固定的S-SW涌浪系统,其能量在二维海浪谱上分布集中,空间方向上分布范围较窄;模拟时段内几内亚湾呈明显的涌浪主导状态,通过对有效波高最大时刻的一次涌浪过程溯源发现,影响几内亚湾的涌浪可追溯至约6.5天前南大西洋咆哮西风带海域的强风浪。  相似文献   
5.
《Journal of Natural History》2012,46(8):1289-1302
Most soil fauna in tropical rainforests require a pre-existing shelter for at least part of their life cycles. Among termites and ants, the most frequently encountered taxa, the availability of appropriate nesting sites is a major factor controlling the multiplication of colonies. Work carried out in five forests in southern Cameroon indicates that termitaries of Cubitermes subarquatus, whether active or abandoned, provide shelter for large numbers of invasive invertebrates, particularly ants and other termite species, and may be a determining factor in the patchy distribution of many taxa. Dissections of 90 termitaries (65 active, 25 abandoned) produced a great diversity of invasive fauna, including 354 ant colonies representing 75 species in 31 genera. Ants occurred in all abandoned termitaries but 6·1% of active termitaries had no ants present. Nevertheless, in total active termitaries sheltered more ant colonies (273) than did abandoned ones (81). Every termitary examined also sheltered founding pairs or incipient colonies of alien termites, but active C. subarquatus termitaries yielded fewer mature colonies of alien termites (56·9%) than did abandoned ones (84%).  相似文献   
6.
7.
To date, the family Pudeoniscidae includes six species and three genera, Pudeoniscus, Brasiloniscus and Iansaoniscus, with distributions restricted to Brazil. Here, we redefine the family Pudeoniscidae based on the discovery of a new genus and two new species, Oxossioniscus pataxo sp. nov. and Oxossioniscus akoko sp. nov., from the Brazilian Atlantic forest in the state of Bahia, and on the examination of Pudeoniscus birabeni and Pudeoniscus obscurus. Moreover, P. obscurus is re-described and new records are provided for P. birabeni.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:A0123730-C623-49CE-8665-AE17FDDF994A.  相似文献   

8.
《Journal of Natural History》2012,46(30):2759-2794
New data on the warm temperate and tropical east Atlantic Bathyporeia species are presented. Four new species are described: Bathyporeia cunctator sp. nov. from South Africa, B. chevreuxi sp. nov. from Senegal, B. gladiura sp. nov. from South Africa, and B. griffithsi sp. nov. from Namibia. Bathyporeia cunctator sp. nov. and B. chevreuxi sp. nov. are very closely related to the west European B. tenuipes Meinert, 1877 and the Mediterranean B. lindstromi Stebbing, 1906 Stebbing, T. R. R. 1906. Amphipoda 1: Gammaridea.. Das Tierreich, 21: 1806.  [Google Scholar]; these four cryptic species forming the complex tenuipes. Bathyporeia griffithsi sp. nov. and B. gladiura sp. nov. are highly distinctive new species. The morphotype “sunnivae” of Bathyporeia guilliamsoniana is recorded for the first time outside the Mediterranean Sea, in the Canary Islands. An identification key to all known Bathyporeia species is given.  相似文献   
9.
《Journal of Natural History》2012,46(31-32):2039-2047
We describe a species of the exclusively Neotropical dorylomorph ant genus Leptanilloides (Leptanilloidinae), Leptanilloides atlantica sp. nov., based on workers collected in the Atlantic Forest, São Paulo, south-eastern Brazil. The 11 species of Leptanilloides described are known from relatively high altitudes in western America (from the Andes foothills in Bolivia to Sierra Morena in Mexico). The discovery of a Leptanilloides species in south-eastern Brazil represents a significant range extension for the genus; this new species shares characters with Leptanilloides biconstricta (Bolivia), Leptanilloides femoralis (Venezuela) and Leptanilloides gracilis (Mexico) and may be distinguished based on a combination of traits. The hypogaeic habits of Leptanilloidinae combined with inefficient collecting techniques may explain the paucity of information and of specimens of this group in most museum collections as well as its present apparent disjunct distribution. We compare Leptanilloides distribution to that of other organisms that show similar disjunct patterns in the Andes and montane sites in the Brazilian Atlantic Forest. http://www.zoobank.org/urn:lsid:zoobank.org:pub:E7E334AA-58C0-455D-A0A6-724D29226DD0  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