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   1025篇
  免费   75篇
  国内免费   99篇
测绘学   93篇
大气科学   34篇
地球物理   43篇
地质学   355篇
海洋学   464篇
天文学   12篇
综合类   71篇
自然地理   127篇
  2023年   7篇
  2022年   25篇
  2021年   27篇
  2020年   37篇
  2019年   30篇
  2018年   20篇
  2017年   72篇
  2016年   53篇
  2015年   45篇
  2014年   70篇
  2013年   47篇
  2012年   71篇
  2011年   58篇
  2010年   82篇
  2009年   56篇
  2008年   60篇
  2007年   60篇
  2006年   54篇
  2005年   20篇
  2004年   40篇
  2003年   27篇
  2002年   23篇
  2001年   15篇
  2000年   17篇
  1999年   17篇
  1998年   24篇
  1997年   19篇
  1996年   20篇
  1995年   12篇
  1994年   14篇
  1993年   10篇
  1992年   8篇
  1991年   6篇
  1990年   6篇
  1989年   10篇
  1988年   2篇
  1987年   1篇
  1985年   9篇
  1984年   5篇
  1983年   4篇
  1982年   13篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有1199条查询结果,搜索用时 203 毫秒
351.
Worldwide demand for energy is growing and predicted to increase by up to three times by 2050. Renewable energy will play a vital role in meeting this demand whilst maintaining global climate change targets. Around the British Isles, development of wind farms has entered Round three, with large, high capacity wind parks being planned to enhance energy security and achieve 2020 renewable energy targets. Such developments place additional pressure on existing sea space and may result in conflicts with other marine activities and users. Co-location of certain activities, marine protected areas, aquaculture and commercial fishing in particular, has therefore been proposed as an option to ease demands on space. Using the UK guided by EU and regional policy, as a case study, following the criteria-based planning system, co-location is legally feasible. Crucially, co-location options will depend on site specific characteristics and site management plans. The biology, ecology and hydrology of the site as well as consideration of important commercial and economic factors will be determining factors of success. For marine protected areas compatibility with conservation objectives for the site will be fundamental. Where possible, it is suggested that activities suitable for co-location will develop in tandem with renewable energy projects. The importance of developing joint projects in this manner is particularly true for aquaculture projects to ensure tenure security and commercial viability. Adaptive management will be a basis for evolution of the concept and practice of co-location. Pilot projects and continued monitoring will be essential in shaping the future of co-location of activities. As the Marine Management Organisation continues the development of marine plans for the English inshore and offshore waters, a study into potential solutions for resolving sea use conflicts is timely. This paper therefore provides a concise overview of the current regulation affecting co-location of key marine activities within wind farm zones and provides suggestions on how co-location projects can be adopted and taken forward, using the UK as a case study.  相似文献   
352.
This study examined the perceptions of fishers from two fishing communities with differing use histories and involvement in the long-standing (16 yr) multiple use Mafia Island marine protected area (MIMP), Tanzania. A randomly distributed questionnaire indicated that 94% of fishers believed that without the MIMP, there would be overfishing, dynamite use, destroyed habitats, and few fish. Fishers were more positive about core zones (no-take fishery closures) than general use zones (areas allowing selective fishing) as a consequence of increases in fishing pressure. Those that reported increased catches and sizes of fish since the creation of the MIMP were more likely to agree with present zone locations and more positive in general about fisheries and conservation planning. Most thought that fish size and gear restrictions were preferable to permanent closures. Perceptions differed among communities and gear users. Community and gear type explained 46% of the variance in responses about the perception that fisheries and conservation are compatible goals. Somewhat surprisingly, these effects were more important than catch increases or involvement in MIMP-related activities. The differences in perception between communities may be partly attributed to different fishing histories. Multiple-use zoning provides a means to identify and resolve conflicts and achieve what are likely universal objectives for fisheries sustainability and conservation.  相似文献   
353.
The use of self-governance as a fisheries management tool is increasing in New Zealand and elsewhere. Researchers argue that in theory self-governance can lead to improved outcomes, but evaluating actual benefits is difficult because of the need to distinguish self-governance impacts from other influences on fisheries performance. An indicator system was developed in this paper to evaluate the contribution of selfgovernance to the performance of the Bluff Oyster fishery (OYU5), which is also managed under New Zealand's Quota Management System. There is evidence that self-governance makes a positive contribution to economic efficiency, institutional effectiveness and resource preservation in the Bluff Oyster fishery.  相似文献   
354.
The Galapagos Islands are a prime example of a place where fishery management policies have been established without first understanding the behavior of fishermen. Since the creation of the Galapagos Marine Reserve in 1998, there has not been a single study in the archipelago that investigates fishing behavior and the factors affecting this behavior. This paper addresses this gap in the literature by describing and analyzing the decisions of the fishing fleet for the red spiny lobster fishery. It focuses on factors that affect the short-term decisions regarding both participation and intensity of participation in the lobster fishery. This paper finds that the fishing fleet in the Galapagos Islands behaves as profit maximizing firms, because they consider all the benefits and costs that affect both their participation decision as well as their decision about how frequently to be active after they have decided to participate. The results also show that there is a large latent effort in the lobster fisheries that could threaten the sustainability of any initiatives aimed at increasing catchability, prices, or markets. It is expected that this analysis will be valuable to policy makers when designing or improving the management plans for Galapagos fisheries.  相似文献   
355.
Marine and coastal policy in the UK has faced a number of significant changes in recent years, most notably the passing of the Marine and Coastal Access Act in 2009. These changes have brought significant challenges and opportunities for all those involved in the management and use of the UK's marine and coastal environment. This new era of marine policy inspired the UK's first Marine and Coastal Policy forum held in June 2011. In this introductory paper the global context of marine policy changes and the themes which emerged from the forum, forming the basis of the articles in this special issue, are outlined. It is concluded that there is a high level of engagement, capacity and willingness of key stakeholders to work collaboratively to address the environmental, social and economic complexities of managing the marine and coastal environment. It is both evident and encouraging that progress is being made and the many challenges faced in this new era give rise to a number of opportunities to develop new ideas and effective mechanisms for finding solutions.  相似文献   
356.
Mitigating the environmental impact of commercial fishing, by avoiding, minimizing and compensating for adverse effects, is core business for fisheries management authorities globally. The complex interplay of ecological, economic, and social considerations has often resulted in bycatch management being reactive, confrontational and costly. In many cases it has been difficult to demonstrate success and to establish whether bycatch management has been efficient or effective. This article proposes standards for bycatch management following reviews of literature, international agreements and Australian domestic fishery management policies, and consideration by many technical experts and several stakeholder representatives. The standards have been developed using Australian Commonwealth fisheries – and the international fisheries agreements to which Australia is party – as a baseline, but should be applicable to both domestic and regional/international governance systems. The proposed standards involve quantifying fisheries bycatch, agreeing on operational objectives, assessing the effects of fishing on bycatch populations, establishing the cost-effectiveness of mitigation measures, and evaluating performance. The standards encourage domestic management measures that are consistent with the guidance and requirements of international agreements and regional fisheries management organisations. The importance of engaging stakeholders throughout the process is recognised. The standards provide a framework for measuring performance and a checklist of actions for managing bycatch at a fishery level. They have the potential to facilitate the development of more strategic and effective approaches to bycatch management, with defined goals, monitoring systems, and adaptive decision-making. This review of past bycatch management, including the application of the proposed standards to the mitigation of shark bycatch in an Australian longline fishery, demonstrates that the proposed standards are operationally feasible but that they have not always been applied. Specifically, monitoring the performance of bycatch management measures has not always followed their implementation.  相似文献   
357.
358.
Currently there is a strong interest in Cuba in improving the performance of the fisheries sector with respect to social, biological, and economic outcomes. Many important fishery resources appear to be overexploited, and previous fishery regulations have had mixed success in restoring fishery stocks. The current fishing pressure could also have adverse impacts on other valuable ecosystem services that support economic activities such as dive tourism and recreational fishing. A new State policy to expand cooperative enterprises to non-agricultural sectors provides an opportunity for fishery cooperatives to be created for the first time since the early years of the Cuban Revolution. This paper explores the potential ecological, social, and economic benefits of adopting fishery cooperatives as a co-management scheme for Cuba's marine fisheries. It concludes that well-designed fishery cooperatives can offer substantial benefits to the management of the fishery sector. Based on an analysis of the relative success of fishing cooperatives worldwide, guidelines are provided for the design of fishery cooperatives in Cuba.  相似文献   
359.
The new protocol signed in July 2012 by the European Union and Mauritania under the existing Fisheries Partnership Agreement did not produce the expected results. The main component of this protocol consisted of the access rights for 300,000 t/yr of small pelagics. During the first five months after the signature of the protocol, no EU pelagic trawlers used the opportunities created by the protocol. Only after the formal approval of the protocol by the European Council in December 2013, some eastern EU member states started sending their pelagic trawlers back to Mauritania. This resulted in a utilisation of the protocol of 54% for the whole of 2013. Although the EU repeatedly stated that the €70 million/yr paid under the protocol provided good value for money, this assertion was hard to maintain considering the limited utilisation of the agreement. The paper analyses why the EU concluded an agreement with Mauritania that was not wanted by their industry and that was therefore only partially used in the end. It describes the decision making process inside the EU; the different parties involved and their different objectives. It is concluded that the EU decision making process suffers from a lack of transparency and that the combination of a business agreement with development aid resulted in an agreement which did not attain either of the stated objectives. It is proposed that in future the two aspects are clearly separated, and that the development component is extended to other countries in West Africa, including those that have no fish to sell to the EU.  相似文献   
360.
The need for alternative strategies to assist in the monitoring and sustainable management of many commercially important fish stocks is widely recognized. In recent years, greater utilization of fishers’ knowledge has been advocated as a potentially valuable source of ecological data in the assessment and management process. In this study changes in the distribution and relative abundance of common megrim Lepidorhombus whiffiagonis in the North Sea were investigated by comparing three data sources: fishers’ knowledge collected through a structured questionnaire; a vessel’s haul-by-haul catch data from the personal diaries of a single skipper over a 10-year time-series, and catch rates from fishery-independent surveys (IBTS Q1 and Q3). Trends in the distribution and relative abundance of megrim were broadly comparable between the three data sources. The results of the study indicate that, in the northern North Sea, fishers’ knowledge and catch data can provide valid data sources which can contribute to the assessment and management process. A structured approach consisting of a formal agreement, full transparency and commitment between all stakeholders is needed to provide and utilize the necessary data required to provide the most effective and inclusive approach to resource management.  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