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   1649篇
  免费   361篇
  国内免费   208篇
测绘学   12篇
大气科学   94篇
地球物理   389篇
地质学   464篇
海洋学   1154篇
天文学   1篇
综合类   52篇
自然地理   52篇
  2024年   9篇
  2023年   31篇
  2022年   58篇
  2021年   55篇
  2020年   62篇
  2019年   68篇
  2018年   63篇
  2017年   173篇
  2016年   83篇
  2015年   89篇
  2014年   157篇
  2013年   97篇
  2012年   69篇
  2011年   119篇
  2010年   112篇
  2009年   114篇
  2008年   115篇
  2007年   98篇
  2006年   71篇
  2005年   48篇
  2004年   43篇
  2003年   52篇
  2002年   96篇
  2001年   33篇
  2000年   34篇
  1999年   42篇
  1998年   45篇
  1997年   22篇
  1996年   26篇
  1995年   19篇
  1994年   11篇
  1993年   28篇
  1992年   8篇
  1991年   19篇
  1990年   10篇
  1989年   7篇
  1988年   5篇
  1987年   1篇
  1986年   3篇
  1985年   7篇
  1984年   6篇
  1983年   7篇
  1982年   2篇
  1978年   1篇
排序方式: 共有2218条查询结果,搜索用时 0 毫秒
951.
海洋调查船是了解认知与开发利用海洋的关键基础设施。欧洲海洋调查船运作组织(ERVO)推动这一关键基础设施协同的努力颇具代表性。它面对欧洲海洋调查船多元化且无权威主体的境地,通过会员制构建协同平台,明晰了业务主导、可持续发展的协作目标;它通过年会聚焦海洋调查船及相关仪器装备,交流运行管理,研讨技术创新、改造更新以及与海洋调查船相关的共性话题,以促进欧洲海洋调查船和相关装备具有最佳的运行成效;它与相关海洋调查与研究组织机构联动,跻身于欧洲海洋调查船发展战略层,推动欧洲海洋调查船在项目层面组队共享。文章解析了欧洲海洋调查船运作组织的背景和运作模式,同时针对我国海洋调查船协作多头发力缺乏合纵连横的状况,提议发起中国海洋调查船协同论坛,组建联合工作组做好长期务实的基础性工作,筹划中国及关系国调查船协调计划,以建立我国海洋调查船协同机制并逐步跻身国际海洋调查船战略协同层。  相似文献   
952.
文章针对海洋渔业由于过度捕捞造成渔业资源枯竭的问题,提出了一种基于海洋遥感(ORS)、全球定位系统(GPS)和海洋地理信息系统(MGIS)等高新技术的海洋捕捞与海水养殖监管系统设计方案,可以远程自动对海洋渔业区域的水质多参数信息和养殖环境视频信息进行综合采集、传输及监控,也可以自动采集传输渔船RFID身份识别信息、渔船AIS自动识别信息、渔船GPS定位信息和捕捞生产视频信息等,并通过海洋精细渔业专家系统ES进行渔业养殖监控、渔业环境资源监测评估、渔船船数和功率数控制和海洋捕捞生产渔情监测等。该系统可以实现海洋渔业精细化捕捞和海洋渔业精细化养殖,促进海洋渔业可持续发展。  相似文献   
953.
A bioenergetic model of marine phase, wild Atlantic salmon was constructed to investigate the potential effects on post-smolt growth of predicted changes in oceanic conditions. Short-term estimates of growth in weight were similar to measurements in captivity and simulated growth varied with water temperature and swimming speed as expected. Longer-term estimates of growth in length were less than that achieved by wild salmon, particularly with constant swimming assumed. The model was sensitive to parameters relating to maximum daily food consumption, respiration and the relationships between body energy content, length and weight. Some of the sensitive parameters were based on substantive information on Atlantic salmon and their realistic ranges are likely to be much narrower than those tested. However, other parameter values were based on scant data, farmed Atlantic salmon or other salmonid species, and are therefore less certain and indicate where future empirical research should be focussed.  相似文献   
954.
This study examines the roles of innovation-support organizations in their acquisition and diffusion of technological ideas, solutions, and know-how throughout the marine science and technology innovation system. The research is based on a set of case studies that involved semi-structured interviews with directors and managers in three innovation-support organizations: Maritime Innovation (MI), the Interdisciplinary Centre for the Development of Ocean Mapping (ICDOM), and the Marine Biotechnology Research Centre (MBRC). Each of these organizations contributes not only to the development of the marine science and technology industry, but also to research and technology transfer in some of the key areas boasting the highest potential for technological commercialization and applications in the coastal region of Quebec. Central to this analysis is to show how these organizations operate and co-ordinate their activities, and how they formulate their technological and other standard services for the support of business development.  相似文献   
955.
This paper provides an overview of the small-scale fisheries sector in countries within the Benguela Current Large Marine Ecosystem (BCLME), one of the most productive large marine ecosystems in the world. The study revealed that Angola, Namibia and South Africa have very different legal and policy frameworks, show different levels of compliance with international and regional agreements to protect the livelihoods and food security of small-scale fishers, as well as of integration of fisheries into food security objectives. Angolan law recognises and protects small-scale fishers through legal and institutional mechanisms. In Namibia, this sector of fishers is not legally recognised, while in South Africa traditional fishers have been largely excluded from the new fisheries management framework. Trends in national and regional fish consumption and in the extent of export orientation in fisheries are explored, as well as the potential threats to small-scale producers and food security in the region posed by ongoing drives to incorporate fisheries in the World Trade Organisation (WTO) agreements.  相似文献   
956.
Effectively reducing cumulative impacts on marine ecosystems requires co-evolution between science, policy and practice. Here, long-term social–ecological changes in the Baltic Sea are described, illustrating how the process of making the ecosystem approach operational in a large marine ecosystem can be stimulated. The existing multi-level governance institutions are specifically set up for dealing with individual sectors, but do not adequately support an operational application of the ecosystem approach. The review of ecosystem services in relation to regime shifts and resilience of the Baltic Sea sub-basins, and their driving forces, points to a number of challenges. There is however a movement towards a new governance regime. Bottom-up pilot initiatives can lead to a diffusion of innovation within the existing governance framework. Top-down, enabling EU legislation, can help stimulating innovations and re-organizing governance structures at drainage basin level to the Baltic Sea catchment as a whole. Experimentation and innovation at local to the regional levels is critical for a transition to ecosystem-based management. Establishing science-based learning platforms at sub-basin scales could facilitate this process.  相似文献   
957.
Marine social-ecological systems are complex, inter-connected, and highly dynamic, in particular when forced with global changes. However, their human social components are often treated separately from their biophysical components, and by different scientific disciplines. To help bridge these gaps, and to explore conceptual, comparative, and governance issues relating to marine social-ecological systems and global change, an international symposium was held on “Coping with global change in marine social-ecological systems”. This short paper provides an introduction to this topic, and briefly describes nine papers which arose from this symposium and which comprise this special issue of Marine Policy. It is concluded that good progress is being made towards studying marine social and ecological systems as coupled systems, but that many issues remain to challenge natural scientists, social scientists, and humanists to work together. These include incorporating multi-stakeholder participation, the need for a long-term perspective, and development of flexible livelihood and governance strategies.  相似文献   
958.
The U.S. Navy, whose sonars kill marine mammals, provides approximately 50% of the funds for marine mammal research worldwide. We examined six reviews of research on the effects of anthropogenic sound on marine mammals, as well as the primary papers cited in the reviews. These reviews cite references showing noise has no effect on marine mammals at an increasing frequency as their funding moves from a conservation organization to independent to partial U.S. military sources. Primary papers are 2.3 times more likely to be cited in the reviews as concluding no effect of noise if the research was militarily-funded than if not. Thus, conflict of interest may have led to a misrepresentation of the effects of noise on marine mammals in both the primary and secondary literature, and thus misinform public policy decisions.  相似文献   
959.
The earliest comprehensive plankton sampling programme in the Southern Ocean was undertaken during the early part of last century by Discovery Investigations to gain a greater scientific understanding of whale stocks and their summer feeding grounds. An initial survey was carried out around South Georgia during December 1926 and January 1927 to describe the distribution of plankton during the summer, and to serve as a baseline against which to compare future surveys. We have reanalysed phytoplankton and zooplankton data from this survey and elucidated patterns of community distribution and compared them with our recent understanding of the ecosystem based on contemporary data. Analysis of Discovery data identified five groups of stations with characteristic phytoplankton communities which were almost entirely consistent with the original analysis conducted by [Hardy A.C., Gunther, E.R., 1935. The plankton of the South Georgia whaling grounds and adjacent waters 1926-1927. Discovery Report 11, 1-456]. Major groupings were located at the western end of the island and over the northern shelf where Corethron spp. were dominant, and to the south and east where a more diverse flora included high abundances of Nitzschia seriata. Major zooplankton-station groupings were located over the inner shelf which was characterised by a high abundance of Drepanopus forcipatus and in oceanic water >500 m deep that were dominated by Foraminifera, Oithona spp., Ctenocalanus vanus, and Calanoides acutus. Stations along the middle and outer shelf regions to the north and west, were characterised by low overall abundance. There was some evidence that groupings of stations to the north of the island originated in different water masses on either side of the Southern Antarctic Circumpolar Current Front, the major frontal system in the deep ocean close to South Georgia. However, transect lines during 1926/1927 did not extend far enough offshore to sample this frontal region adequately. Interannual variability of zooplankton abundance was assessed from stations which were sampled repeatedly during seven recent British Antarctic Survey cruises (1995-2005) to the region and following taxonomic harmonization and numerical standardization (ind. m−3), a subset of 45 taxonomic categories of zooplankton (species and higher taxa) from 1926/1927, were compared with similar data obtained during the BAS cruises using a linear model. Initially comparisons were restricted to BAS stations that lay within 40 km of Discovery stations although a comparison was also made using all available data. Despite low abundance values in 1926/1927, in neither comparison did Discovery data differ significantly from BAS data. Calculation of the percentage similarity index across cruises did not reveal any systematic differences in species composition between 1926 and 1927 and the present. In the light of ocean warming trends, the existence of more subtle changes in species composition is not ruled out, but an absence of finely resolved time-series data make this impossible to determine.  相似文献   
960.
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