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   17篇
  免费   1篇
测绘学   1篇
地球物理   2篇
地质学   3篇
自然地理   12篇
  2016年   1篇
  2012年   3篇
  2009年   1篇
  2005年   1篇
  2001年   1篇
  1999年   1篇
  1998年   1篇
  1996年   1篇
  1993年   1篇
  1989年   2篇
  1987年   2篇
  1984年   1篇
  1976年   2篇
排序方式: 共有18条查询结果,搜索用时 640 毫秒
1.
2.
3.
The Turiec Basin (TB) of Slovakia formed in the Miocene when the West Carpathians escaped from the Alpine region. The 1,250-m-thick sedimentary Neogene fill of the basin preserved fossil leaves as well as endemic bivalves, gastropods, and ostracodes. The paleolimnologic changes recorded in the TB infill were derived from the most abundant fossils, the ostracodes. Five contemporaneous ostracode assemblages within the Late Miocene lacustrine system were distinguished through statistical analysis. These assemblages have low species similarity, between 2.1 and 24.1%, and are recognized by shape differences among the Candoninae. The ostracode assemblages, mollusca fossils, and Sr-isotope ratios suggest a low-salinity environment at the beginning of the Late Miocene, during a brief connection with the Central Paratethys. When the connection ceased, the basin became an isolated freshwater lake, with five zones differentiated ecologically and bathymetrically using the ostracode assemblages. Taxonomic comparison of the faunas of the TB and the freshwater to brackish Neogene basins of Europe demonstrates the endemic character of the TB ostracode fauna. The biologic characteristics of the ostracode families, along with the geology of the lake basin, suggest that the longevity of the Late Miocene lake probably exceeded 1 Ma.  相似文献   
4.
Life and depositional environments in the sublittoral zone of Lake Pannon, a large, brackish Paratethyan lake from the Late Miocene, were reconstructed from fossils and facies of the Szák Formation. This formation is exposed in several, roughly coeval (9.4–8.9 Ma) outcrops, located along strike of the paleo-shelf-break in northwestern Hungary. The silty argillaceous marl of the formation was deposited below storm wave base, at 20–30 to 80–90 m water depth. The abundance of benthic organisms indicates that the bottom water was usually well oxygenated. Interstitial dysoxia, however, may have occurred immediately below the sediment–water interface, as evidenced by occasional preservation of trace fossils such as Diplocraterion. The fauna comprised endemic mollusks, including brackish cockles of the subfamily Lymnocardiinae, dreissenid mussels (Congeria), and highly adapted, uniquely large-sized deep-water pulmonate snails (planorbids and lymnaeids). Ostracods were dominated by endemic species and, in some cases, endemic genera of candonids, leptocytherids, cypridids, and loxoconchids. Fish remnants include a sciaenid otolith and the oldest skeletal occurrence of Perca in Europe. The phytoplankton comprised exclusively endemic coccolithophorids, mostly endemic dinoflagellates (prevailingly Spiniferites), and cosmopolitan green algae. The Late Miocene fauna and flora of Lake Pannon were in many ways similar to the modern Caspian biota, and in particular cases can be regarded as its precursor.  相似文献   
5.
Human disturbance of wildlife is an under‐recognised and under‐regulated problem. This article discusses traditional approaches to conservation management in protecting wildlife from disturbance in the context of the New Zealand coastal environment and threatened birds. Limitations and challenges are identified and alternative actions proposed. The key problems are deficiencies in regulation of species disturbance, lack of definition of thresholds of harm that contemplate rarity and conservation status, insufficient comprehensive wildlife conservation planning and the need for innovative planning methods that address species mobility, permeable boundaries and environmental dynamism. Regulatory controls including enforcing setbacks/approach distances through either extended species protection or 'mobile habitat' protection are recommended.  相似文献   
6.
Summary: Soluble carbohydrate and starch were examined in shoots of Ceratophyllum demersum, Elodea canadensis, Myriophyllum exalbescens, Potamogeton foliosus and P. zosteriformis in Shoal Lake (Manitoba–Ontario) during the 1985 season. A wide range of variation was found for the same species on any given day among different sampling stations at the same depth. Correlations of each of total soluble carbohydrate and starch with water depth were inconsistent on any given day, although inverse correlations were more common. In M. exalbescens, roots consistently contained more soluble carbohydrate than shoots. The soluble carbohydrate fraction of all species contained glucose, fructose and sucrose. However C. demersum also contained significant and relatively constant proportions of melibiose, raffinose and stachyose. Starch content decreased during the season in C. demersum but increased in P. foliosus and P. zosteriformis shoots. E. canadensis and M. exalbescens showed no significant seasonal trends. Starch comprised 30 … 85 % of the total nonstructural carbohydrate in the 5 species. Seasonal carbohydrate and starch concentrations were not significantly correlated with each other in any of the macrophytes examined. The proportion of starch relative to the total nonstructural carbohydrate increased during the season in P. foliosus and P. zosteriformis.  相似文献   
7.
8.
Fifty-two ostracod taxa were identified from two sediment cores collected from the early Badenian ?idlochovice stratotype. Ostracod assemblages were analyzed with a focus on taxonomy, paleoecology, distribution of taxa along the sediment cores, quantification of valve/carapace ratios, and species richness by Simpson??s Reciprocal Index. The changes in ostracod assemblages identified in these cores reflect a shallowing of the marine water-depth from circalittoral/epibathyal to shallow infralittoral, and an increase in the sedimentation rate upwards through time. A comparison of all Badenian ostracod assemblages in the Carpathian Foredeep indicates a high proportion of deep-water ostracod species in ?idlochovice and its surroundings, suggesting that the deepest part of the Carpathian Foredeep was probably situated in this part of the Czech Republic.  相似文献   
9.
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