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   291篇
  免费   26篇
  国内免费   24篇
测绘学   11篇
大气科学   8篇
地球物理   65篇
地质学   81篇
海洋学   148篇
综合类   8篇
自然地理   20篇
  2023年   4篇
  2022年   7篇
  2021年   6篇
  2020年   5篇
  2019年   11篇
  2018年   4篇
  2017年   20篇
  2016年   11篇
  2015年   12篇
  2014年   18篇
  2013年   18篇
  2012年   17篇
  2011年   20篇
  2010年   15篇
  2009年   20篇
  2008年   21篇
  2007年   13篇
  2006年   21篇
  2005年   11篇
  2004年   9篇
  2003年   8篇
  2002年   6篇
  2001年   2篇
  2000年   5篇
  1999年   12篇
  1998年   9篇
  1997年   7篇
  1996年   4篇
  1995年   3篇
  1994年   7篇
  1993年   1篇
  1992年   3篇
  1990年   1篇
  1989年   2篇
  1985年   2篇
  1984年   3篇
  1981年   3篇
排序方式: 共有341条查询结果,搜索用时 0 毫秒
1.
This article provides a historical account of Chinese public policy on fisheries subsidies, and a discussion of problems and limitations resulting from the World Trade Organization (WTO) Doha Round fisheries subsidies negotiation. By analyzing subsidization trends and applying a proportional assessment of subsidized areas, the article tracks the evolvement of Chinese fishery policy objective and priorities. Chinese fishery is not historically significantly subsidized in light of its relatively market-oriented structure and a sustained momentum in reducing marine capture capacity. However, due to the commitment to encouraging qualitative growth and to satisfying a rising domestic demand for fish, the government seeks for adequate policy space to employ fuel, distant water fisheries, infrastructure and various ‘green light’ subsidies. Whether or not such a claim can be accepted as a developmental right not an exception remains to be answered by the revision of current negotiation draft.  相似文献   
2.
This paper uses an input–output model to quantify the socioeconomic impact of fishing and aquaculture on Galicia, one of Spain's most important maritime regions. Results indicate that the carryover effects of these production activities are important for Galicia's economy because they contribute not only to job creation but also to possibilities for obtaining income in other economic sectors. These sectors’ combined production in 2013 was almost a million euros, and that production was estimated to account for nearly 2% of the regional economy's value added and for more than 17,000 full-time jobs. Together these contributions amounted to some €1.7 billion in production and €975 million in value added to other Galician economic activities. At the same time, fishing and aquaculture were responsible for creating the equivalent of more than 14,000 full-time jobs in other economic activities.  相似文献   
3.
于2011年3月、5月、8月和10月对大连沿海10个排污口及部分排污口的邻近水域分别采集水样, 对样本进行细菌总数3M试纸计数、2216E培养基和TCBS培养基培养并菌落计数, 对不同菌株进行16S rRNA基因克隆测序, 鉴定种属, 对细菌时间、空间的动态分布与群落结构及细菌分布与生态因子的相关性进行了分析。结果表明, 不同的排污口之间细菌总数差别很大, 数量在(1.6—500.0)×104cfu/mL之间; 排污口与其邻近水域差异明显, 排污口、邻近5m、100m和500m距离的细菌总数全年平均分别为77.94×104、 34.00×104、 4.520×104和0.448×104 cfu/mL。不同季节之间, 远距离水样季节性差异较大, 而排污口间季节性差异相对较小。在群落构成上, 假交替单胞菌属、肠杆菌科、假单胞菌属、弧菌属和希瓦氏菌属为优势菌属, 检出率较高, 数量较大。细菌分布与多种生态因子具有不同程度的相关。  相似文献   
4.
Experiments using cages at four shore levels were carried out to determine the part played by the feeding of the gastropods Neothais scalaris and Lepsiella scobina on the zonation of three species of intertidal barnacles: Chamaesipho brunnea, C. columna, and Epopella plicata. The lower limit of the two larger barnacle species was determined by predation, but C. columna was affected only in the absence of the other two barnacles.  相似文献   
5.
利用454高通量测序技术对宁波沿海10个陆源排污口20个站位的放线菌的时空分布及5个工业排污口的放线菌的种类作了整体分析。成功鉴定出了83个属,84个种。研究结果显示:放线菌在陆源排污口的分布呈现季节性分布,从3月份到10月份,放线菌数量呈现先升高后下降的变化,5月份和8月份数量居高,在3月份和10月份偏低;在综合排污口(S4,S6,S8和S9)检测频次较高,在工业排污口(S1,S3,S5,S7和S10)检测频次居中,在市政排污口(S2)检出频次最低。不同类型的排污口,氨氮浓度的排出量不同,放线菌的种类和数量也不同。在5个工业排污口中,S7和S10检出的共同菌最多;在S7独自检出短双歧杆菌(Bifidobacterium breve)、长双歧杆菌(B.longum)和两岐双岐杆菌(B.bifidum),表明存在粪源污染物;在S5检出皱孢链霉菌(Streptomyces scabrisporus)和硫藤黄链霉菌(S.thioluteus),显示有石油降解物和重金属的污染。总体上看,放线菌数量在距排污口外50m处略高于排污口处。排放指标越相似,菌的种类越接近。  相似文献   
6.
A case study was carried out in 2000 in the shallow coastal area of the Northern Adriatic Sea (Gulf of Trieste) where untreated domestic sewage and industrial wastes are discharged at rate of 5500 m3·day?1. The sewage plume above the outfall was followed using faecal coliforms (FC) and overturning length scale (lT). The latter was rejected as a marker as the discharge conditions prohibit following the turbulence of sewage water. Intermittent sewage discharge is reflected in the minimal effect of eutrophication. Increase of phytoplankton biomass is thus only minor compared with the unpolluted area regardless of elevated concentrations of sewage‐derived nutrients (confirmed by correlation coefficients between FC and NH4+, TP, PO43?: 0.78, 0.71 and 0.67, respectively). Deteriorated trophic status, determined by the TRIX index, was observed only in the surface layer (average TRIX: 5.67). High FC content well above the regulation limit (up to 2.6 × 105 FC·100 ml?1) represents, therefore, the major negative impact of the improperly treated waste for the risk to human health.  相似文献   
7.
Survey and Geographic Information System (GIS) data analysis describes the relative influence of biophysical and human variables on site choices made by marine farmers in New Zealand. Community conflicts have grown in importance in determining farm location and different government planning strategies leave distinct signature patterns. Recent legislation empowers local governments to choose among three strategies for future regional aquaculture development. This paper suggests each strategy could result in different spatial outcomes. Simulation modelling of the type described here can provide a better understanding of farmer responses to management approaches and the range of futures that could result from planning choices made today.  相似文献   
8.
The European Blue Growth strategy aims to expand the new maritime sectors of aquaculture, energy, biotechnology, coastal tourism and mineral mining. Growth of these sectors will increases pressure on the seas, particularly on those areas that are densely used by traditional sectors such as fisheries and transport. This has triggered interest in developing multiuse of space and multiuse platforms at sea. This paper assesses the feasibility of offshore mussel production project in wind farms by design and ex-ante evaluation of a mussel aquaculture system in the North Sea. A system for mussel cultivation in the Dutch Borssele offshore wind farm was designed, producing both mussel seed and consumption-sized mussels with semi-submerged longlines. Based on the economic model and the risk assessment, this paper concludes that mussel aquaculture is an appealing commercial model for increased returns in offshore wind farms. The economic models shows that the internal rate of return and net present value are positive and based on the sensitivity analysis, it can be concluded that these results are robust.  相似文献   
9.
10.
Robyn Heaslip   《Marine Policy》2008,32(6):988-996
British Columbia's current approach to monitoring salmon aquaculture waste is disconnected from political and legal trends towards the recognition of Aboriginal rights in Canada. Drawing on insights from collaborative monitoring in northern Canada and interviews with 23 Kwakwaka’wakw clam-diggers and cultural specialists (2006–2007), preliminary directions for integrating First Nations’ values, knowledge and stewardship practices into marine environmental monitoring are identified. Kwakwaka’wakw monitoring practices include the use of qualitative individual, community and population scale indicators and the integration of traditional knowledge as baseline data about the healthy conditions of traditional food resources.  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