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   117篇
  免费   6篇
  国内免费   3篇
测绘学   3篇
大气科学   5篇
地球物理   36篇
地质学   5篇
海洋学   71篇
综合类   3篇
自然地理   3篇
  2023年   2篇
  2022年   3篇
  2021年   1篇
  2020年   2篇
  2019年   3篇
  2018年   1篇
  2017年   19篇
  2016年   6篇
  2015年   5篇
  2014年   10篇
  2013年   1篇
  2012年   3篇
  2011年   8篇
  2010年   8篇
  2009年   10篇
  2008年   9篇
  2007年   4篇
  2006年   9篇
  2005年   3篇
  2004年   3篇
  2002年   1篇
  1999年   2篇
  1998年   6篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1984年   1篇
排序方式: 共有126条查询结果,搜索用时 15 毫秒
71.
The relationship between organic enrichment and macrobenthic colonization patterns was investigated during an 8-month period in Diplodus sargus (white seabream) production ponds. A stratified sampling design was applied and each pond was divided into three zones: water entrance (WE); central (C); and automatic feeder zones (AF). Generally, the number of species and Shannon–Wiener diversity increased from the WE to the AF zone. Abundance did not present a clear trend. The recently developed marine biotic index (AMBI) was applied and showed to be sufficiently robust to discriminate, within a relatively small area, differences in macrobenthic communities due to organic enrichment. Nevertheless, caution is advised when applying this index or others based on ecological group’s assignment, as the classification of a certain area may differ when allocating a certain species to an unsuitable group. This is particularly evident when common species are involved.  相似文献   
72.
Over the past years the export of agricultural and fishery products from developing countries has substantially increased to markets within the OECD. Retailers and importers are expanding their international operations to meet consumer demands for year-round delivery of products. Moreover, consumers have become increasingly concerned about the safety of food, including those derived from aquatic resources [FAO/NACA/WHO Joint Study Group, 1999. Report food safety issues associated with products from aquaculture. WHO Technical Report Series No 883: VII, pp. 1-55]. Governments and leading businesses are responding by imposing new safety regulations and standards to the international food system (e.g. HACCP, EUREP-GAP), product liability and labeling [Reilly, A., Howgate, P., K?ferstein, F., 1997. Safety hazards and the application of HACCP in aquaculture. In: Proceedings of the Second International Conference on Fish Inspection and Quality Control: A Global Focus, Arlington, VA, 19-24 May 1996. Technomic Publishing, Lancaster, PA, pp. 353-373]. Initial concerns for imports of aquacultural products from developing to industrialized countries focussed on bacterial contamination [Buras, N. 1993. Microbial safety of produce from wastewater-fed aquaculture. In: Pullin, R.V.C., Rosenthal, H., MacLean, J.L.(Eds.), Proceedings of ICLARM Conferences, vol. 31, pp. 285-295]. Today, if trade opportunities are to be maintained, these countries must adapt to a full array of regulations and standards. This paper describes four scenarios in aquaculture and fishing product trade between developing countries and countries in the European Union.  相似文献   
73.
Macroalgae has numerous commercial uses and the potential to create large carbon sinks. The study reviewed the legal context, including environmental and social aspects, for the setting up of a seaweed farm in the UK. A lease is required to use the seabed and a Marine Licence is required from the national regulator. There is no need for new legislation, however, the existing guidance should be updated. There is a major need to clarify what level of assessment is required as part of the marine licensing process. The environmental and social considerations to licensing were also reviewed. Changes to the hydrodynamics and sediment transport are expected in and around the farm. These may lead to changes in seabed siltation and light levels. The addition of hard substrate (from the anchors) and a macroalgae canopy lead to attraction of benthic animals, fish, marine mammals and birds. These, in addition to potential changes in organic matter and nutrients reaching the seabed from exudate and detritus, could create changes in existing benthic communities on the seafloor. No reason for major population-level impacts were seen. However, numerous knowledge gaps where identified. Scale appears to be an important consideration. A small farm on its own is unlikely to have a large effect on the marine environment. However, a very large farm, or multiple small farms next to each other could have a more notable effect. Knowledge gaps were identified and recommendations were provided that can assist the development of the UK macroalgae farming industry.  相似文献   
74.
As a result of aquaculture activities Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded the European Wadden Sea. Using a variable noncoding mitochondrial marker, we show that the invaded range is the result of two independent invasions. Haplotype frequencies point towards two separate groups, one in the southern and the other in the northern Wadden Sea. We found virtually no genetic differentiation throughout the southern range and the putative source from British Columbia, Canada, suggesting that the Southern region can be considered as a closed population. In the North, mismatch distributions, haplotype ordination and isolation-by-distance analysis suggest a stronger, persistent impact of aquaculture on invasive populations. Due to the ongoing supply of new genetic material from hatchery production the northern invasive populations can therefore be considered as an open population highlighting the importance of aquaculture practice on the genetics of this keystone invader in the Wadden Sea.  相似文献   
75.
水产养殖业在我国渔业产业结构中占据重要地位,在促进我国渔业经济发展中发挥着重要作用。当前渔业正处于由要素驱动向创新驱动转型的新旧动能转换时期,这也对水产养殖业的转型升级提出了更高要求。文章根据产业演化路径及其运行机理,从资源、技术、市场、制度4个方面构建指标体系,采用1998—2019年的指标数据,通过灰色关联分析和岭回归分析,探索影响产业演化的因素,探讨不同影响因素对水产养殖业演化发展的影响程度,以期为促进中国水产养殖产业的发展,增强水产养殖业的竞争力提供理论支撑。结果表明,城镇居民人均水产品消费量对中国水产养殖产业演化影响程度最大,GDP及单位面积产量的影响显著,水产技术推广经费支出影响最小。基于此,为促进我国水产养殖业的转型升级提出做好水产品消费需求引领与管理、拓展国内国际消费市场;增加科技投入,发展养殖技术;加大资源保护力度,推进绿色发展;着力解决养殖水产品质量安全问题等相应对策建议。  相似文献   
76.
Work migration is increasing in Norway, particularly in the production sector of the aquaculture industry. This sector is growing rapidly and manual labor needed in the industry is consistently being sought through Eastern European networks and temp-agencies. This article looks at the island community of Frøya, in Sør Trøndelag in Norway, where around 20% of the population is of foreign descent, and where stakeholders in the production line experience a lack of upward mobility due to their lack of Norwegian language skills, and the insecure nature of their employment status. The capacity of the island community to adapt to a 3-fold increase in aquaculture production will depend on this segment of society as well being able to adjust, and on their inclusiveness in society. Based on a stakeholder driven workshop looking at the perceptions of a set of foreign workers in the aquaculture industry,segmented labor market theory was applied to the experience of the workers. The priority issues of the migrant population of Frøya involved in the aquaculture industry was also explained, and their wish for upward mobility and job security, as well as inclusiveness in society elaborated upon. This upward mobility, however, would lead to the bottom segment of the labor market on Frøya – the aquaculture production line – to have to be filled with another lower segment group of workers.  相似文献   
77.
提出一种关于同质溶液混合的浓度或溶液量任意项求解的线性图解法,并阐明其在水产养殖的换水水质控制和盐度调节方面的应用。  相似文献   
78.
Fish resources are critical to the food security of many nations. Similar to most contemporary food systems, many fisheries and aquaculture resource supply chains are heavily dependent on fossil fuels. Energy price increases and volatility may hence undermine food security in some contexts. Here, we explore the relationships between energy price changes, fish resource supply chain viability, seafood availability and food security outcomes – both for producers and consumers of fish resources. We begin by characterizing the energy intensities of fish resource supply chains, which are shown to be highly variable. We subsequently assess the comparative magnitude and distribution of potential food security impacts of energy price increases for nation states by scoring and ranking countries against a set of vulnerability criteria including metrics of national exposure, sensitivity and adaptive capacity. Considerable variability in the vulnerability of populations and high levels of exposure for already food-insecure populations are apparent. Developed countries are likely to be most exposed to the effects of energy price increases due to their high rates of fleet motorization and preference for energy-intensive seafood products. However, heavy reliance on seafood as a source of food and income, as well as limited national adaptive capacity, translates into greater overall vulnerability in developing countries. At the level of individual producers, a variety of adaptation options are available that may serve to reduce vulnerability to energy price changes and hence contribute to increased food security for producers and consumers, but uptake capacity depends on numerous situational factors.  相似文献   
79.
We have investigated the impact of a large mussel farm on the benthic environment using a battery of benthic indicators of environmental quality (including biochemical, microbial and meiofaunal parameters). These were analysed through a multi-control sampling strategy over one year. The differences across the seasons are typically higher than those between the impacted and the control stations. No effects are seen in terms of the sediment oxygen penetration and the downward fluxes (as the total mass, organic and phytopigment fluxes). The indicators based on the biochemical compositions of the sediment organic matter and the microbial parameters also show no evidence of the eutrophication process, except as a slight increase in the bacterial density in the sediments beneath the long-lines of the farm during the period of highest mussel stocks. Finally, no effects are observed in terms of the benthic faunal indicators, as the meiofaunal abundance, the community structure and the taxa richness are all indistinguishable between the farm sediments and the controls. These results show that mussel farming in the investigated system is eco-sustainable and does not significantly alter the coastal marine ecosystem, both in terms of the functioning and the trophic state. The battery of indicators selected in this study represents a useful tool for the monitoring of the potential ecological impact of mussel farms, towards guaranteeing the sustainable development of aquacultures in shallow coastal environments.  相似文献   
80.
Remote sensing data have been proposed as a potential tool for monitoring environmental treaties. However, to date, satellite images have been used primarily for visualization, but not for systematic monitoring of treaty compliance. In this paper, we present a methodology to operationalize the use of satellite imagery to assess the impact of the Ramsar Convention on Wetlands. The approach uses time series analysis of landscape pattern metrics to assess land cover conditions before and after designation of Ramsar status to monitor compliance with the Convention. We apply the methodology to two case studies in Vietnam and evaluate the success of Ramsar using four metrics: (1) total mangrove extent; (2) mangrove fragmentation; (3) mangrove density; and (4) aquaculture extent. Results indicate that the Ramsar Convention did not slow the development of aquaculture in the region, but total mangrove extent has remained relatively constant, primarily due to replanting efforts. Yet despite these restoration efforts, the mangroves have become fragmented and survival rates for replanting efforts are low. The methodology is cost effective and especially useful to evaluate Ramsar sites that rely mainly on self-reporting methods and where third parties are not actively involved in the monitoring process. Finally, the case study presented in this paper demonstrates that with the appropriate satellite record, in situ measurements and field observations, remote sensing is a promising technology that can help monitor compliance with international environmental agreements.  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