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   464篇
  免费   7篇
  国内免费   2篇
大气科学   23篇
地球物理   14篇
地质学   8篇
海洋学   418篇
综合类   2篇
自然地理   8篇
  2023年   1篇
  2022年   3篇
  2021年   3篇
  2020年   5篇
  2019年   3篇
  2018年   1篇
  2017年   57篇
  2016年   25篇
  2015年   29篇
  2014年   39篇
  2013年   9篇
  2012年   44篇
  2011年   25篇
  2010年   51篇
  2009年   28篇
  2008年   33篇
  2007年   30篇
  2006年   29篇
  2004年   4篇
  2003年   7篇
  2002年   4篇
  2001年   2篇
  2000年   5篇
  1999年   3篇
  1998年   4篇
  1997年   1篇
  1996年   1篇
  1994年   1篇
  1985年   8篇
  1984年   4篇
  1983年   4篇
  1982年   10篇
排序方式: 共有473条查询结果,搜索用时 46 毫秒
31.
This study investigates whether there has been a decline in fish stocks of a coral reef in Thailand, and if so, whether that decline is due to small-scale fishing. The research methods used included fish sampling by UVC, interviews and questionnaires with key informants and artisanal fishers. The results confirmed that there has been a decline in piscivores and carnivores (though not herbivores), and the main perceived threat came not from artisanal but from commercial fishing. Recommendations are to replace the largely unrestricted fishery with a more regulated regime backed by effective enforcement.  相似文献   
32.
This paper reviews the available information (observer programs, estimates, statutes, regulations) for bycatch of marine mammals, sea turtles, and seabirds in fisheries of the United States. Goals of the review were to evaluate the state of knowledge of bycatch and the role of existing protective legislation in shaping bycatch management for different taxa. Pressing issues are identified, as well as knowledge gaps and policy limitations that hinder multi-species bycatch reduction. The USA has made important progress toward reducing bycatch in its fisheries, but the efficacy of its management has been limited somewhat by a focus on taxon- and fishery-specific regulation and the lack of consistent mandate across taxa for taking a cumulative perspective on bycatch. Applying consistent criteria across taxa for setting bycatch limits (e.g., extending the approach used for marine mammals to sea turtles and seabirds) would be the first step in a multi-species approach to bycatch reduction. A population-based multi-species multi-gear approach to bycatch would help identify priority areas where resources are needed most and can be used most effectively.  相似文献   
33.
Small-scale marine fisheries policy in Vietnam   总被引:1,自引:0,他引:1  
Vietnam's marine fisheries are considered to be small scale and are concentrated in coastal near-shore waters. This has resulted in heavy pressure on near-shore fisheries resources. Near-shore fisheries are considered by fishers and the government to be over-exploited, causing hardship for many coastal communities. This paper reviews and analyzes changes in policy towards small-scale fisheries in Vietnam over the last two decades. The primary issues facing the small-scale fisheries in Vietnam are to restructure the near-shore fisheries and to address over-capacity. Recommended actions include improved fisheries statistics, resources for provincial fisheries staff, and a coordinated and integrated approach involving a mixed strategy of resource management; resource restoration; economic and community development; and new governance arrangements.  相似文献   
34.
We aim to show how some of the important interdisciplinary fixes or solutions to diverse problems observed in fisheries can complement each other. This can be achieved through methodical allocation of the rights pertaining to fisheries and simultaneous implementation of policy instruments to correct for market failures and equity concerns. We emphasize via a roadmap that there are some general principles that should be invoked when choosing between alternative structures of rights. Our examples from Sweden provide evidence of the flexibility of fishing rights and how they can be adapted to integrate fixes from different disciplines into practical fisheries management.  相似文献   
35.
Community-based coastal resource management (CBCRM) is a major conservation and fisheries management strategy in the tropics. In this study, the performance of 16 CBCRM programs in the Philippines was assessed using a meta-analysis of eight indicators that represented the perceptions of local resource users. Overall, the CBCRM programs in the Philippines were perceived to have a significant positive impact. However, the performance of each of the indicators was mixed. Although the CBCRM programs were perceived to be effective in empowering the local fishing communities, their perceived impact on improving the state of the local fisheries resources remained limited. This highlights the importance of incorporating ecological and socio-economic considerations in setting fisheries management regimes.  相似文献   
36.
In order to evaluate the health status of fish inhabiting Port Phillip Bay, Australia, southern sand flathead (Platycephalus hassensis, N = 133) were collected at six stations throughout the Bay. Fish had a similar serum sorbitol dehydrogenase (SDH) activity level (p = 0.12), indicating that they were not experiencing hepatocellular injuries. Ethoxyresorufin-O-deethylase (EROD) activity was generally lower in the non-urbanized and non-industrialized southern part of the Bay. The highest EROD activity was observed in Hobson Bay, the closest station from Melbourne city. Naphthalene-type biliary metabolites were also highest in Hobson Bay with intermediate levels found in Corio Bay where refineries are present. An opposite trend was observed with the pyrene-type bile metabolites, the highest levels being observed in Corio Bay while intermediate levels were found in Hobson Bay. The ratio of naphthalene-type to benzo(a)pyrene (B(a)P)-type metabolites indicate that relatively to other sites sampled in Port Phillip Bay, Corio Bay is subjected to enriched petroleum hydrocarbons of pyrolytic origin. Temporal trends indicate that the availability of xenobiotics to fish remained unchanged over the 1990s.  相似文献   
37.
This paper examines the sustainability of United States fisheries managed under the Magnuson-Stevens Fishery Conservation and Management Act, the law that provides the framework for federal fisheries management. Sustainability across a broad suite of criteria, including health of the fished stock, bycatch, and effects on the habitat and ecosystem, was measured against the Monterey Bay Aquarium׳s Seafood Watch criteria for ecological sustainability. Seafood Watch ratings and numerical scores for U.S. federally managed fisheries were analyzed to elucidate strengths and weaknesses among federally-managed fisheries. Of U.S. federally managed fisheries assessed by Seafood Watch, only 2% are rated “Avoid”, and strong ratings for stock health for nearly all fisheries indicate that the Magnuson-Stevens Act is fundamentally succeeding at maintaining or rebuilding the abundance of targeted stocks. The majority (79%) of U.S. fisheries earn the intermediate rating of “Good Alternative”, and 19% earn the top rating of “Best Choice”. Given that U.S. fisheries management is considered among the strongest in the world, this analysis assesses why the majority of U.S. fisheries are not rated “Best Choice”. Fisheries for all variety of species, and using a wide range of fishing methods, can merit “Best Choice” status. However, the majority of U.S. fisheries do not achieve this rating due primarily to bycatch concerns. By improving performance with regard to bycatch, most “Good Alternative” U.S. federal fisheries could reach “Best Choice” status and reap rewards in the marketplace for that recognition. Findings suggest that current science-based management should be maintained in the Magnuson-Stevens Act reauthorization, managers should adopt best practices based on fisheries that are already performing well in the U.S., and more specific federal bycatch mitigation requirements should be implemented.  相似文献   
38.
Achieving a balance between fishing capacity and fishing opportunities is one of the major challenges in European fisheries. One way to achieve this is to introduce individual tradable quotas or similar management measures. In several mackerel and herring fisheries in the Northeast Atlantic, such systems have already been introduced on a national basis and the long term economic gains of this have been acknowledged. This paper takes this a step further and investigates the potential economic gains from introducing individual tradable quotas between countries. Overall, the results show that the gross cash flow can be improved by 21% by allowing the mackerel and herring quotas to be traded internationally in the Northeast Atlantic. This rent gain arises mainly from increased productivity by allowing tradability between areas and fleets. The analysis also shows that the Danish pelagic fleet will gain from increasing its share of mackerel and herring quotas, whereas the Irish fleets are incentivised to sell quota, if individual quotas are allowed to be traded among countries. This result is in line with the qualitative analyses that show that Irish fishermen targeting herring in the Celtic Sea are negatively oriented towards international individual tradable quotas, whereas the Danish pelagic fishermen have strong preferences for international individual tradable quotas.  相似文献   
39.
While the economic and environmental benefits of fisheries management are well accepted, the costs of effective management in low value fisheries, including the research necessary to underpin such management, may be considerable relative to the total economic benefits they may generate. Co-management is often seen as a panacea in low value fisheries. Increasing fisher participation increases legitimacy of management decision in the absence of detailed scientific input. However, where only a small number of operators exist, the potential benefits of co-management are negated by the high transaction cost to the individual fishers engaging in the management process. From an economic perspective, sole ownership has been identified as the management structure which can best achieve biological and economic sustainability. Moving low value fisheries with a small number of participants to a corporate-cooperative management model may come close to achieving these sole ownership benefits, with lower transaction costs. In this paper we look at the applicability of different management models with industry involvement to low value fisheries with a small number of participants. We provide an illustration as to how a fishery could be transitioned to a corporate-cooperative management model that captures the key benefits of sole management at a low cost and is consistent with societal objectives.  相似文献   
40.
Following the decision in 2007 by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to include European eel Anguilla anguilla on its Appendix II, and the 2010 ban of all eel exports by EU member states, a shift has occurred to tropical Asian eel species to meet the demand from East Asia. Here the focus is on the role Indonesia played in fulfilling this demand using official export figures, reports in the Indonesian media and government documents. Despite Indonesia first putting in place restrictions on the export of eel in 1974 the export has increased exponentially over the last 25 years. Prior to the EU ban it exported ~1.4 million kg/year. With the infrastructure in place, and close trade links to East Asia, and helped by government encouragement, Indonesia was in an excellent position to step in where the EU posed restrictions. Exports increased to 3.2 million kg/year (2007–2009), to 4.0 million kg/year (2010–2012), and to 6.1 million kg (2013). The interest in eel trade in Indonesia increased in parallel with the exports. From 2010 onwards the searches for the Indonesian equivalent of eel (“ikan sidat”) became frequent enough for it to be picked up by Google Trends. Indonesia is home to five species of eel, and while it is unclear in what quantities each is traded, Indonesian media reports suggest that the majority comprises A. bicolar and A. marmorata. More stringent management schemes, possibly including CITES-listing, and better monitoring are needed to ensure that international trade is not an impediment to the conservation of tropical eels.  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