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   571篇
  免费   39篇
  国内免费   49篇
测绘学   8篇
大气科学   24篇
地球物理   157篇
地质学   84篇
海洋学   218篇
天文学   2篇
综合类   15篇
自然地理   151篇
  2023年   5篇
  2022年   13篇
  2021年   8篇
  2020年   12篇
  2019年   19篇
  2018年   13篇
  2017年   31篇
  2016年   26篇
  2015年   24篇
  2014年   51篇
  2013年   48篇
  2012年   17篇
  2011年   36篇
  2010年   41篇
  2009年   40篇
  2008年   55篇
  2007年   38篇
  2006年   31篇
  2005年   9篇
  2004年   12篇
  2003年   15篇
  2002年   21篇
  2001年   8篇
  2000年   12篇
  1999年   13篇
  1998年   11篇
  1997年   8篇
  1996年   4篇
  1995年   4篇
  1994年   4篇
  1993年   6篇
  1992年   2篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1987年   3篇
  1986年   2篇
  1985年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
排序方式: 共有659条查询结果,搜索用时 31 毫秒
71.
In 1998, in order to combat the degradation of yellow tang populations on the west coast of Hawaii Island, fish replenishment areas (FRAs) were established prohibiting aquarium fishing along more than thirty percent of the coastline. Unlike other marine management approaches in Hawaii, which have largely been controversial, fraught with confusion over regulations, inadequately enforced, and lacking public support, these FRAs have been lauded as a marine conservation success, with wide-ranging support and evidence of rapid replenishment of the yellow tang population. In order to better understand the contextual factors contributing to the success of the West Hawaii FRAs, this research explores the following questions: (1) What factors documented in the literature on marine protected areas (MPAs) have been demonstrated to contribute to or inhibit MPA success internationally; (2) which of these factors do the FRAs of West Hawaii exhibit; and (3) are there additional factors that may have contributed to their wide acceptance and success? Common factors contributing to MPA success are determined through a synthesis of the literature. These include: level of community engagement, socioeconomic characteristics, ecological factors, MPA design, governance, and enforcement. The outcomes of West Hawaii′s FRAs are examined in the context of these factors. While the common factors agreed upon in the literature were key to the success of the FRAs, additional contextual factors such as the unique nature of the aquarium fishery and its social marginalization also played a vital role.  相似文献   
72.
The ecosystem approach to fisheries (EAF) is a holistic paradigm that considers stocks of exploitable species, marine ecosystems and stakeholders. Management agencies must strike a balance between their capacity constraints and the requisites of management measures. Most small-scale sea cucumber fisheries of Pacific Islands have been plundered while others are being opened to commercial exploitation. Data from fishery managers and a regional workshop were used to assess the current problems, institutional constraints and solutions to the management of sea cucumber fisheries in 13 Pacific Island countries (PICs). Technical capacity was often strong for some management actions such as developing marine reserves but weak for others, such as enforcement. Using multi-disciplinary indicators, half of the fisheries were diagnosed by their managers as being overfished or depleted, despite evidence of optimistic bias. Fishery governance varied greatly among the PICs, and co-management frameworks were not typical of any cultural region. Management objectives were prioritised differently among managers but most highly ranked was to protect ecological resilience. The fishery managers proposed different sets of regulatory measures and various management actions, such as surveys to collect socio-economic and fishery-dependent data, support for local governance and strong enforcement – all widely under-practised. Pacific sea cucumber fisheries exemplify how the transition to an EAF by management institutions must involve reorganisation of their technical and human-resource capacities among management tasks. Levies on exports need to be internalised to fund improved management. Management agencies should consider a shift in resources from developing marine reserves, conducting underwater surveys and aquaculture-based restocking to strengthening enforcement capacity, stakeholder involvement and communication with fishers. In concert with these actions, short fishing seasons, shortlists of allowable species and tighter enforcement at export points may serve to turn the tide on boom-and-bust exploitation and safeguard biodiversity.  相似文献   
73.
The management of marine ecosystems requires adequate knowledge of both environmental and human dimensions, as well as their interrelationships. In this study, the aquaculture and fisheries activities are analyzed in one of most important fishing regions in Europe, Galicia (NW Spain). In particular, the intensity and characteristics of the fishing dependency are evaluated in terms of income and employment. Thus, nine marine economic activities for nine Maritime Zones have been defined, considering the social and economic relevance of the provided ecosystem services to these communities. This paper highlights the entire Galician coast as fishing-dependent, independently of the urbanization level. Furthermore, the contribution of different fishery segments to the income and employment of these coastal communities is reviewed, including fluctuations on whether the activity is small or large-scale. Finally, this study establishes a strong relationship among the marine activities, which generate most employment, and the regulatory framework of the Regional Government. Therefore, the conclusions are relevant to design and implement policies that affect Galicia׳s Region and all its related marine ecosystems.  相似文献   
74.
Governance failures associated with top-down management have spawned a myriad of institutional arrangements to engage resource users in decision-making through co-management. Although co-management can take many forms and may not always lead to positive outcomes, it has emerged as a promising governance option available to meet social and ecological goals. Recent research on co-management of small-scale fisheries has used comparative approaches to test factors associated with social and ecological success. Less is known however, about how co-management institutional arrangements emerge and persist in the face of socioeconomic and environmental change. Here, we examine the emergence of co-management governance using a case study from coral reef fisheries in the Hawaiian Islands. We used a mixed methods approach, combining a robust policy analysis and a set of key respondent interviews to trace the evolution of this co-management arrangement. Our research uncovers a set of linked drivers and social responses, which together comprise the emergence phase for the evolution of co-management in this case study. Drivers include resource depletion and conflict, and social responses comprise self-organization, consensus building, and collective action. We share insights on key factors that affect these phases of emergence, drawing on empirical findings from our policy review and key respondent interviews. We conclude by describing ways that our findings can directly inform policy and planning in practice, including the importance of documenting the ‘creation story’ that spawned the new institutional arrangement, ensuring that enabling conditions are present, the complexity of defining community, the connection between process legitimacy and outcomes, and understanding the costs and timelines associated with co-management governance transitions.  相似文献   
75.
Studies on the coral reefs of the South China Sea (SCS) was the theme of the 6th Session of the 3rd Conference on Earth System Science (CESS) in Shanghai, 2014. This session discussed the most recent study developments on the SCS coral reefs, including coral reefs’ responses to global changes, coral reefs’ records on past climatic variations, and the activities about constructions and oil gas explorations in the coral reefs areas of the SCS. Disturbed by intensive anthropogenic activities and global climate warming, coral reefs in the SCS have declined dramatically, reflecting the up to 80% decrease of living coral cover and many areas having less than 20% of living coral cover. Geochemical data of SCS coral skeletons clearly show that since the Industry Revolution, the pollution situation of the SCS have dramatically increased and the seawater pH values have been continuously lowering, i.e. oceanic acidification. All these environmental phenomenon are further stressing the healthy development of the coral reef ecosystem in the SCS. Meanwhile, the poor coral reef ecosystems in the SCS are facing more anthropogenic disturbances such as coastal developments and engineering constructions. Obviously, the SCS coral reefs will be faced with more environmental challenges in the coming future. We therefore suggest that the policy makers should realize the extreme importance and the fragile of the coral reef ecosystems, and scientifically and with great cautions design construction project when in coral reef areas. We initiated the concept of “green engineering” for future developments in coral reef areas. Coral reefs are widely spreading in the whole SCS, and most of them developed since Miocene. Variations in coral reef structures provide good future oil-gas exploration. Because the SCS coral reefs have a long-developing history and a wide spatial distribution, they provide great potential in recording past environmental changes.  相似文献   
76.
DETERMINANTS OF STRUCTURE IN AQUATIC NON-PELAGIC PROTOZOAN COMMUNITIES   总被引:2,自引:0,他引:2  
Although microbes have traditionally been used as models for testing ecological theory, research on the organization of these communities has largely been isolated from other areas of community ecology. Early studies indicated that microbial populations can form dynamic, interacting assemblages. Observations of distributional patterns suggest that certain deterministic forces regulate community structure. It appears that protozoans are tolerant of a wide range of environmental conditions although evidence for this is largely based on gross environmental analyses. Laboratory studies have suggested the importance of negative and positive biotic interactions in determining community membership, but little field evidence for this exists. The importance of transport processes in controlling community composition is being increasingly recognized. All three types of processes likely act to regulate the colonization and successional dynamics of these communities. A simple model is presented to promote the devel  相似文献   
77.
Medicinal plants and fungi play important roles in the health of Maliseet people of northern Maine, USA. A critical aspect of exercising choice in health care for this community is the ability to locate and have access to these plants. Habitat suitability modeling is a form of geospatial technology that can enhance health sovereignty by identifying locations in which populations of medicinal plants can be conserved or established. However, use of this technology within indigenous communities has been limited. Focusing on the medicinal plant muskrat root, Acorus americanus (Raf.) Raf., we generate a habitat suitability model for eastern Aroostook County, Maine (1,055,653.659 ha) that also takes community needs into consideration. Drawing on participatory ethnographic data as well as environmental characteristics, our model combines ecological and sociocultural parameters to identify previously unknown populations of A. americanus that are accessible to tribal elders. Our model successfully predicted 95% of A. americanus locations in our field validation data set of ∼71,000 ha. Results suggest that approximately 0.6% of our study area contains suitable habitat to plant muskrat root that could also meet tribal members' gathering needs for the future. Increasing the number of potential collection sites gives communities options for gathering, thereby enhancing health sovereignty. Broadly, our work suggests that, when done in partnership with communities, different forms of geospatial technology can be beneficial tools for efforts to promote health sovereignty.  相似文献   
78.
Sediment disturbance patterns in the coastal area off the Tagus Estuary (Portugal) have been assessed using a set of combined techniques. The potential sources of disturbance in the area include chronic contamination of the fine sediments originating from the estuary, a local input from a long-sea sewage outfall and occasional high runoff episodes following torrential rain. The Sediment Quality Triad approach, combining environmental chemistry (namely organic contaminants), macrofaunal benthic communities and laboratory sediment toxicity assays, was performed on sediment samples from 20 sites. The samples were collected before the outfall commenced operation and four years after commissioning, in order to evaluate the relative magnitudes of the three potential sources of disturbance. The sediment contamination created by the estuary was identified as the most important cause of reduced sediment quality, as disturbance in all three components of the Sediment Quality Triad were only found in a site located near the estuary.  相似文献   
79.
Closely related scleractinian coral species that exhibited similar survival patterns under relatively normal field conditions responded very differently to the occurrence of an environmental disturbance. The two species studied were Porites cylindrica and Porites rus which occur in the same reef zones in shallow reef flats. Transplants of both species were evenly distributed and attached to three different types of substrate: live coral colonies of P. cylindrica, dead coral colonies (also of P. cylindrica), and epoxy coated metal grids that were raised above the sandy substrate. With the onset of above-normal water temperatures due to the El Ni?o episode of 1998, P. cylindrica transplants immediately showed signs of bleaching stress and tissue necrosis, followed by algal overgrowth and mortality soon afterwards. In contrast, transplants of P. rus bleached more slowly and suffered less mortality, with a few actually showing signs of recovery at the end of the experimental period which covered a total of 14 weeks. These differences in responses could be attributed to properties of the symbiotic zooxanthellae, of the host coral tissue itself, or both. Over-all, survival was good on the metal grids (average of 35%), and on the live coral (average of 22%). It was poor on the dead coral (average of 6%). The metal grids as well as live coral tissue apparently provided a favorable substrate for the attached coral fragments, even for those of a different species. Under the conditions of this particular study, attachment of live coral fragments on already dead colonies for the purpose of increasing live coral cover on the reef did not yield favorable results. This is an area that requires further investigation.  相似文献   
80.
A 3000 km2 multibeam survey was carried out on the eastern Anaximander Mountains (Mts), (Eastern Mediterranean). The objective was to obtain detailed bathymetry of known mud volcanoes and identify new sites of active mud volcanism in the area. N-NW of the Amsterdam Mud-Volcano (MV) several mounds and cone-like morphological irregularities with a height of few tens of meters to about one hundred meters were detected and considered as potential MVs on the basis of their distinctive backscattered character. A group of two mounds was selected, the northern mound was sampled, documented as active, and named accordingly Athina MV. These new findings strongly support the presence of extensive active mud volcanism in the Anaximander Mountains especially in the area north of the Amsterdam MV.GEM  相似文献   
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