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   660篇
  免费   17篇
  国内免费   2篇
测绘学   2篇
大气科学   35篇
地球物理   14篇
地质学   50篇
海洋学   420篇
综合类   4篇
自然地理   154篇
  2023年   5篇
  2022年   7篇
  2021年   9篇
  2020年   8篇
  2019年   9篇
  2018年   7篇
  2017年   72篇
  2016年   40篇
  2015年   33篇
  2014年   46篇
  2013年   48篇
  2012年   55篇
  2011年   31篇
  2010年   56篇
  2009年   35篇
  2008年   38篇
  2007年   35篇
  2006年   35篇
  2005年   8篇
  2004年   10篇
  2003年   12篇
  2002年   12篇
  2001年   5篇
  2000年   6篇
  1999年   7篇
  1998年   5篇
  1997年   3篇
  1996年   1篇
  1995年   1篇
  1994年   3篇
  1987年   3篇
  1985年   9篇
  1984年   7篇
  1983年   6篇
  1982年   12篇
排序方式: 共有679条查询结果,搜索用时 46 毫秒
601.
The status and prospects of fisheries in northeastern Asia are reviewed in conjunction with climate change and social issues. This region has the biggest yield, consumption, and international trade of fisheries products in the world. Due to increasing industrialization and greenhouse gas emissions, higher rates of warming have occurred. The impacts of climate change on fisheries could be detrimental because the main fishery products are small pelagic fish whose biomass fluctuations are sensitive to climate changes. Improvements in the economies of the nations in this region offset the demand for fish products in human diets, and employment in fisheries. It is recommended that fisheries management plans consider both changes in climate and in social systems. Stocks which migrate between national jurisdictions are in need of particular attention.  相似文献   
602.
Exploited fish and shellfish stocks in European marine waters underlie the Common Fisheries Policy (CFP). The next round of reform of the CFP is due for completion in 2012. The exploitation at maximum sustainable yield (MSY) may be confirmed as the common environmental objective for good environment status (GES) of exploited fish and shellfish stocks of the reformed CFP and the Marine Strategy Framework Directive (MSFD). The foreseen time horizon to achieve or maintain GES by 2020 appears inconsistent with the World Summit on Sustainable Development UN agreement in 2002, which stipulates that maintenance or restoring of stocks to produce MSY be realized by 2015. The MSFD requires instead that by 2015 the national programmes of measures be designed in order to become operational the following year (2016).  相似文献   
603.
Commercial fisheries are heavily dependent upon the combustion of fossil fuels and as such contribute to increased atmospheric concentrations of greenhouse gases and the concomitant impact on the world's climate. The fuel use and greenhouse gas intensity of a fishery is a function of several variables. One that has not been previously investigated is the role of fisheries management. Using historical gear-specific fuel use and landings data, we employ scenarios to examine the potential impact that recent changes in the management of the New England fishery for Atlantic herring (Clupea harengus) may have on fishery-related fuel use and greenhouse gas emissions. Specifically, we consider the direct effect of the seasonal ban of midwater trawling in favor of purse seine and fixed gears within Atlantic herring fishing Area 1A. We also evaluate the indirect effect of reductions to the Area 1A total allowable catch of Atlantic herring on the regional supply of bait and the resulting potential need to import bait herring from Canada. Our results indicate that because of the five-fold lower fuel intensity of purse seining, relative to midwater trawling (21 L/ton versus 108-118 L/ton), the seasonal ban on midwater trawling has the potential to markedly reduce overall fuel use and greenhouse gas emissions associated with the herring fishery. These results indicate that management decisions can strongly influence energy demands and resulting greenhouse gas emissions of fisheries. We urge those involved with fisheries management to take this into account when developing policy and management measures.  相似文献   
604.
There is increasing concern over the consequences of global warming for the food security and livelihoods of the world's 36 million fisherfolk and the nearly 1.5 billion consumers who rely on fish for more than 20% of their dietary animal protein. With mounting evidence of the impacts of climate variability and change on aquatic ecosystems, the resulting impacts on fisheries livelihoods are likely to be significant, but remain a neglected area in climate adaptation policy. Drawing upon our research and the available literature, and using a livelihoods framework, this paper synthesizes the pathways through which climate variability and change impact fisherfolk livelihoods at the household and community level. We identify current and potential adaptation strategies and explore the wider implications for local livelihoods, fisheries management and climate policies. Responses to climate change can be anticipatory or reactive and should include: (1) management approaches and policies that build the livelihood asset base, reducing vulnerability to multiple stressors, including climate change; (2) an understanding of current response mechanisms to climate variability and other shocks in order to inform planned adaptation; (3) a recognition of the opportunities that climate change could bring to the sector; (4) adaptive strategies designed with a multi-sector perspective; and (5) a recognition of fisheries potential contribution to mitigation efforts.  相似文献   
605.
Safety at sea is a serious issue for the commercial fishing industry; it ranks highly in all assessments of occupational dangers including risk-taking, injuries, and fatalities. This paper examines the impact of fisheries management on safety at sea and the use of fishermen's input in the safety regulatory and management process. Using case study techniques of analysis, 22 boatowners, captains and crew all with a minimum of 10 years experience in the commercial fishing industry and from a common New England port (New Bedford) are interviewed. Findings strongly suggest that regulations that have been primarily designed to reduce pressure on fish stocks may also result in increased pressure on fishermen and decreased safety at sea. Attitudes about the role of the New England Fisheries Management Council and improvements to the safety regulatory and management process particularly with regard to the increased participation by fishermen are also examined.  相似文献   
606.
Fabrizio Eva 《GeoJournal》1999,48(2):101-107
The nineties will go down in Italian history as the decade of great political change. By way of emphasising this change, the media and politicians use the expressions `Prima Repubblica' and `Seconda Repubblica' (first and second republics), adopting the terminology used by the French for their `republics'. During the so-called First Republic (1948–1994), the centrist Christian Democrat Party represented the moderate political force in every government. However, the corruption trials of 1992–1993, which involved many of this party's members, led to its collapse at the ballot box. In northern Italy, a consequence of the demise of the Christian Democrats was the resounding success of the Lega Nord at the local government elections of 1993 and the general election of 1994. The Lega Nord based, and continues to base, its success on the use of ethno-nationalist slogans and catchcries. Italy has an ancient tradition – dating at least from the fall of the Roman Empire – of political and linguistic splintering. Given today's situation, this factor may have impacts at the level of the structure of the state: federalism, special statutes for regions and/or provinces, the decentralization of the state, and so on. For the first time for perhaps more than a century, in this new period of uncertain political change, Italians are increasingly viewing territory and its characteristics as politically relevant. Justifications for `national' cohesion are being rediscovered, or invented, at the local level, transforming it into political claims. Italians have begun to talk about relationships with territories and neighbouring groups from a different perspective. At present, traditional political parties and politicians are too slow and insufficiently focused in their response to the rising call for autonomy and decision-making authority at the local level. This factor has provided the time and space for isolationist and culturally self-reliant localist ideologies to propagate. It is impossible to say how long this period of transition will last and what its outcomes will be. The three main choices now facing Italians would be appear to be:(1) reclaim the nationalist sentiment of a united state (abandoned after the Fascist era);(2) provide the space (ideological and territorial) for the numerous localist nationalisms;(3) construct a real and flexible `localist' democracy for Italy as a whole.  相似文献   
607.
为促进我国海洋养殖业的可持续发展,文章基于我国海水养殖产量的统计数据,选取19个影响因子,利用地理探测器方法实证分析我国海水养殖产量和主要海水养殖品种产量的影响因素,并提出发展建议。研究结果表明:我国鱼类海水养殖产量主要分布在广东和福建,甲壳类海水养殖产量主要分布在广东,贝类海水养殖产量主要分布在山东和福建,藻类海水养殖产量主要分布在福建;我国海水养殖产量的主要影响因素为市场需求、技术推广和设备,鱼类和甲壳类海水养殖产量的共同主要影响因素为技术推广、科技创新和经济,贝类和藻类海水养殖产量的共同主要影响因素为市场需求和技术推广;相关沿海地区应高度重视科学技术的作用,提高海水养殖产品的附加值和竞争力,并进一步开发利用其生态价值。  相似文献   
608.
The past decade has witnessed a decline in UK fish consumption, concomitent with an increase in fish imports and a dramatic shift in consumer preferences towards frozen fish. The marketing problems that these trends have caused the fish industry were investigated in a recent report commissioned by MAFF, the conclusions of which are appraised in this article. The author finds particular fault with the report's emphasis on fresh fish and the implications of this for intra-industry cooperation.  相似文献   
609.
610.
Most approaches to neighborhood activism among homeowners explain it in terms of a single social variable, such as class or race or gender. This article argues that, by focusing on one social category, these approaches fail to examine the range of variables that influence homeowner activism. The paper argues that, instead of understanding homeowner activism as a politics of class or race or gender, it should be understood as a politics of space. Such an approach allows us to understand how social variables interrelate in homeowners’ political project and provides a more effective explanation for why this agenda is translated into action.  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