全文获取类型
收费全文 | 181篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 1篇 |
地球物理 | 76篇 |
地质学 | 50篇 |
海洋学 | 29篇 |
天文学 | 12篇 |
自然地理 | 4篇 |
出版年
2023年 | 1篇 |
2014年 | 1篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2008年 | 22篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有182条查询结果,搜索用时 734 毫秒
23.
24.
25.
26.
Are Taxonomic Distinctness measures compliant to other ecological indicators in assessing ecological status? 总被引:1,自引:0,他引:1
Salas F Patrício J Marcos C Pardal MA Pérez-Ruzafa A Marques JC 《Marine pollution bulletin》2006,52(7):817-829
Assessing the ecological status, a concept implemented in the European Water Framework Directive [EC, 2000. Directive of the European Parliament and of the Council 2000/60/EC establishing a framework for community action in the field of water policy PE-CONS 3639/1/00, p. 72], requires the application of methods capable of distinguishing different levels of ecological quality. The Average Taxonomic Distinctness has been used as tool in this context, and we tested the robustness of Taxonomic Distinctness measures applying it in different scenarios (estuarine eutrophication, organic pollution, and re-colonisation after physical disturbance), analysing simultaneously its compliance to other types of ecological indicators. Results show that, in most of the case studies, only Total Taxonomic Distinctness was relatively satisfactory in discriminating between disturbed situations. Other Taxonomic Distinctness measures have not proved to be more sensitive than other ecological indicators (Shannon-Wiener, Margalef, and Eco-Exergy indices). Therefore, this approach does not seem to be particularly helpful in assessing systems' ecological status with regard to the WFD implementation. 相似文献
27.
Bycatch mortality in net fisheries was the major reason for the decline of the endangered smalltooth sawfish, Pristis pectinata, in the United States. These fisheries have been reduced or eliminated in some states including Florida--where most smalltooth sawfish are currently found in the United States. To determine whether other factors are still affecting this species, we obtained non-net fishery entanglement, injury, and mortality data by soliciting information from anyone who may have encountered this species. Smalltooth sawfish were damaged by marine pollution (e.g., polyvinyl chloride pipe, monofilament line, non-monofilament line) and injured by humans. Examples of injuries caused directly by humans include removal of rostra, shooting an individual with a powerhead, and shooting another with arrows. Many people are aware that the smalltooth sawfish is protected by state and federal laws, but some are still not aware of (or willing to accept) this status. The impacts of marine pollution and injuries directly caused by humans on this endangered species can be ameliorated by incorporating fisher education into the conservation and management processes. 相似文献
28.
Total mercury (Hg) and methylmercury (MeHg) were analyzed in near surface sediments (0-2 cm) and biota (zooplankton, macro-invertebrates, finfish) collected from Narragansett Bay (Rhode Island/Massachusetts, USA) and adjacent embayments and tidal rivers. Spatial patterns in sediment contamination were governed by the high affinity of Hg for total organic carbon (TOC). Sediment MeHg and percent MeHg were also inversely related to summer bottom water dissolved oxygen (DO) concentrations, presumably due to the increased activity of methylating bacteria. For biota, Hg accumulation was influenced by inter-specific habitat preferences and trophic structure, and sediments with high TOC and percent silt-clay composition limited mercury bioavailability. Moreover, hypoxic bottom water limited Hg bioaccumulation, which is possibly mediated by a reduction in biotic foraging, and thus, dietary uptake of mercury. Finally, most biota demonstrated a significant positive relationship between tissue and TOC-normalized sediment Hg, but relationships were much weaker or absent for sediment MeHg. These results have important implications for the utility of estuarine biota as subjects for mercury monitoring programs. 相似文献
29.
Phytoplankton community compositions within near-shore coastal and estuarine waters of Louisiana were characterized by group diversity, evenness, relative abundance and biovolume. Sixty-six taxa were identified in addition to eight potentially harmful algal genera including Gymnodinium sp. Phytoplankton group diversity was lowest at Vermillion Bay in February 2008, but otherwise ranged between 2.16 and 3.40. Phytoplankton evenness was also lowest at Vermillion Bay in February 2008, but otherwise ranged between 0.54 and 0.77. Dissolved oxygen increased with increased biovolume (R2 = 0.85, p < 0.001) and biovolume decreased with increased light attenuation (R2 = 0.34, p = 0.007), which supported the importance of light in regulating oxygen dynamics. Diatoms were dominant in relative abundance and biovolume at almost all stations and all cruises. Brunt-V?is?l? frequency was used as a measure of water column stratification and was negatively correlated (p = 0.02) to diatom relative percent total abundance. 相似文献
30.
Dauvin JC 《Marine pollution bulletin》2012,64(3):463-471
The English Channel is part of the "Greater North Sea" sub-region in the Marine Strategy Framework Directive. However, the Channel is characterized by hydrologic, oceanographic and biogeographic features that support its division into two main entities: the western basin and the eastern basin. This paper summarizes the Channel's main natural features and principal human activities to examine the similarities and differences between both basins. The differences between the basins support an ecosystem-based management approach at the combined basin scale, rather than the present approach of separating the France and UK sides. 相似文献