全文获取类型
收费全文 | 30篇 |
免费 | 13篇 |
国内免费 | 14篇 |
专业分类
大气科学 | 1篇 |
地球物理 | 4篇 |
地质学 | 44篇 |
海洋学 | 2篇 |
综合类 | 3篇 |
自然地理 | 3篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 5篇 |
2006年 | 1篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有57条查询结果,搜索用时 31 毫秒
1.
2.
Kenneth H. Dunton Jonathan L. Goodall Susan V. Schonberg Jacqueline M. Grebmeier David R. Maidment 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3462
Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m−2 and <50 mg m−2, respectively). One notable exception is an area of relatively high biomass (50–100 g m−2) and chlorophyll (80 mg m−2) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves. 相似文献
3.
Susanne I. Schmidt Hans J. Hahn Gerald D. Watson Robert J. Woodbury Thomas J. Hatton 《洁净——土壤、空气、水》2004,32(2):131-137
Groundwater bores act as traps. Net samplers are regularly used for sampling this type of trap for fauna. To enable direct comparisons of faunal communities in groundwater bores and stream sediments, stream sediment tubes were built similar to groundwater bores and were sampled with net samplers for fauna. These stream sediment tubes consisted of a tube anchored in the stream sediment, also called interstitial space. To test the efficacy of this trap method in stream sediments, it was compared to another type of trap, Hahn's trap. Faunal communities sampled by a net in the stream sediment tubes did not differ hugely from fauna in Hahn's trap samples. Physical and chemical factors of sampled water in both the stream sediment tubes, the surrounding interstitial sediments and the second type of traps, Hahn's traps, showed that water in both the tubes and Hahn's traps was closely related to interstitial water. The net sampler is inexpensive and easy to handle. It is suggested that sampling stream tubes with nets may be an appropriate method for long‐term monitoring studies. 相似文献
4.
The morphology of the horn-core structure and section shape of the Bos galerianus type specimen, as well as the general anatomy of the frontal and occipital areas of the skull, suggest that the skull is better attributed to the Indian genus Hemibos. This finding contributes to our understanding of faunal dispersal patterns into Europe at the Early–Middle Pleistocene transition. 相似文献
5.
CHEN Ailin FENG Hongzhen ZHU Maoyan MA Dongsheng LI Ming Department of Earth Science Nanjing University Nanjing Jiangsu E-mail: feng.h@jlonline.com Nanjing Institute of Geology Palaeontology Chinese Academy of Sciences Nanjing Jiangsu Chenjiang Fauna National Geological Park Chengjiang Yunnan Wang Si''en Xie Guanglian 《《地质学报》英文版》2003,77(3):281-287
The genus and species Yuyuanozoon magnificissimi gen. et sp. nov., a new fossil vetulicolian, is reported from the Early Cambrian Chengjiang Fauna in Yunnan of China. It has a bipartite body plan and five pairs of chain-formed gill sacs, showing the general characteristics of Ventulicolia. However, the exclusive "atrial cavity" and external gill observed indicate that the new form is different from those previously described as vetulicolians, probably representing a lineage developed within deuterostomes and more primitive than urochordates. 相似文献
6.
主要评述了近年来泥河湾盆地磁性地层学的研究进展,包括建立泥河湾组的磁性地层年代格架、厘定泥河湾动物群的时代和确定华北地区早期人类活动年代序列.研究表明:第一,泥河湾组河湖相沉积序列记录了高斯正极性时末期以来的地磁极性特征(松山和布容极性时),即沉积时代始于约2.6Ma.早期人类至少在1.66~0.78Ma期间的大约90万年的时间内长期持续地占据高纬度的泥河湾盆地.泥河湾动物群(包括广义和狭义)的时代为2.0~0.8 Ma.第二,华北地区早期人类已经能够适应东亚高纬度地区冬季风增强、夏季风减弱和干旱化趋势增强的复杂环境变化,尤其能适应中更新世气候转型前后中国北方多变而且不稳定气候条件和生态环境.因此,气候和生态环境的多变性与不稳定性是促进人类进化的重要因素.第三,早期人类走出非洲以后,可能沿不同的路径并以较快的速度扩散到东亚地区.向南越过印度尼西亚的赤道地区,向北至少扩散到40°N的泥河湾盆地. 相似文献
7.
Sabine K.J. Cochrane Stanislav G. Denisenko Paul E. Renaud Christopher S. Emblow William G. Ambrose Jr. Ingrid H. Ellingsen Jofrid Skarhamar 《Journal of Sea Research》2009,61(4):222-233
Benthic faunal assemblages were analysed from 47 stations in the central and southern parts of the Barents Sea, together with sedimentary and water column parameters, daily ice records and modelled integrated primary productivity. Sampling spanned areas influenced by Atlantic Water (AW) to those lying under Arctic Water (ArW), and included stations with mixed water masses. Ice cover suppressed water column productivity in the northern areas. Three main faunal groups were identified, based on similarity of numerical faunal composition. The northern and southern faunal groups were separated by the northernmost penetration of AW in the bottom water and the third group, the Hopen group, was influenced by modified bank water. Faunal abundances were significantly higher within the southern faunal group relative to the northern group, but the numbers of taxa present were similar. The particularly rich fauna of the Hopen group reflected sediment heterogeneity and tight pelagic–benthic coupling. These results suggest that a retreat and thinning of the ice cover in the Barents Sea likely will result in the northern parts of the Barents Sea becoming more Atlantic in character, with a higher productivity at the sea floor. 相似文献
8.
9.
The fluvio-lacustrine sequences in the Nihewan Basin of North China (known as the Nihewan Formation) are rich sources of Early Pleistocene Paleolithic sites and mammalian fossils (known as the Nihewan Fauna sensu lato), which offer an excellent opportunity to investigate the evolution of early humans and land mammals in East Asia. Also abundant mammalian fossils provide clues about the general environmental and climatic setting of early humans. Among the Nihewan Fauna (sensu lato), the Daodi Fauna is one of the most complete and oldest in the eastern Nihewan Basin: seven mammalian fossil-bearing layers in the Nihewan Formation have been described. Except for a biostratigraphy, however, precise age control on the Daodi Fauna has remained unavailable. Here we report a new magnetostratigraphic record that stringently constrains its age. The seven fossil-rich layers span an age range of ca 2.5–1.8 Ma between the Gauss–Matuyama boundary and the termination of the Olduvai polarity subchron. Combining our new and recently published paleomagnetic data, we further establish a Pleistocene magnetochronology of the fauna and Paleolithic sites in the Nihewan Basin. Age ranges of about 2.5–0.5 Ma for the faunas and 1.7–0.3 Ma for the Paleolithic sites are deduced, which span most of the Pleistocene. The chronological framework and calculated proportions of mammals that were adapted to different environments indicate that mixed settings of dominant grasslands and subordinate forests continued at least from 2.5 to 0.5 Ma for early human occupation in the basin, similar to the mixed open savannah and woodland habitats of early humans in Africa. The Nihewan hominins consistently adopted a simple Oldowan-like technology (i.e., Mode 1 core and flake technologies) from at least ca 1.7 to 0.3 Ma. A more advanced Acheulean technology (Mode 2) has not been found in the Nihewan Basin, although it started to emerge in the Bose Basin of South China at ca 0.8 Ma. This implies that multiple groups of hominins distinguished by differential stone-tool-making capabilities may have coexisted in China after 0.8 Ma. 相似文献
10.