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   1243篇
  免费   37篇
  国内免费   26篇
测绘学   28篇
大气科学   341篇
地球物理   45篇
地质学   175篇
海洋学   130篇
天文学   3篇
综合类   68篇
自然地理   516篇
  2023年   4篇
  2022年   30篇
  2021年   29篇
  2020年   33篇
  2019年   57篇
  2018年   60篇
  2017年   61篇
  2016年   66篇
  2015年   53篇
  2014年   45篇
  2013年   232篇
  2012年   39篇
  2011年   50篇
  2010年   45篇
  2009年   46篇
  2008年   53篇
  2007年   63篇
  2006年   42篇
  2005年   39篇
  2004年   32篇
  2003年   32篇
  2002年   27篇
  2001年   22篇
  2000年   27篇
  1999年   24篇
  1998年   21篇
  1997年   12篇
  1996年   5篇
  1995年   8篇
  1994年   4篇
  1993年   5篇
  1992年   2篇
  1991年   7篇
  1989年   1篇
  1988年   7篇
  1987年   4篇
  1986年   3篇
  1985年   5篇
  1984年   4篇
  1983年   4篇
  1982年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有1306条查询结果,搜索用时 203 毫秒
971.
Sea angling has been shown to be a high value activity with significant expenditure by individuals on their sport. Deriving estimates of the economic contribution of recreational sea angling is important in a number of related policy contexts, from tourism management and economic development policy, to the sustainable management of inshore fish stocks. This paper reveals some of the challenges in understanding the economic effects associated with recreational sea angling, and provides estimates of the economic value of recreational sea angling in England. The results were derived from research undertaken in England in 2011-13, which was conducted as part a wide ranging government-funded study, Sea Angling 2012, that estimated sea angler catches, spending and activity. Recreational sea angling made a significant contribution to the economy, supporting just over £2 billion of total spending, and 23,600 jobs in England in 2012-13. The implications of these results are discussed in the context of the management of recreational sea angling in England.  相似文献   
972.
This paper reviews the major themes and contributions of this Special Issue in light of a broader social science literature on how to conceptualize small-scale fisheries, the role of the state in facilitating or limiting neoliberalism, and the failure of neoliberal policies to improve conservation. It concludes with a look at ways in which neoliberalism is being undermined by emerging alternatives.  相似文献   
973.
Taxonomic information provides a crucial understanding of the most basic component of biodiversity – which organisms are present in a region or ecosystem. Taxonomy, however, is a discipline in decline, at times perceived as ‘obsolete’ due to technical advances in science, and with fewer trained taxonomists and analysts emerging each year to replace the previous generation as it retires. Simultaneously, increasing focus is turned towards sustainable management of the marine environment using an ecosystem approach, and towards conserving biodiversity, key species, and habitats. Sensitive indicators derived from taxonomic data are instrumental to the successful delivery of these efforts. At the base of the marine food web and closely linked to their immediate environment, plankton are increasingly needed as indicators to support marine policy, inform conservation efforts for higher trophic organisms, and protect human health. Detailed taxonomic data, containing information on the presence/absence and abundance of individual plankton species, are required to underpin the development of sensitive species- and community-level indicators which are necessary to understand subtle changes in marine ecosystems and inform management and conservation efforts. Here the critical importance of plankton taxonomic data is illustrated, and therefore plankton taxonomic expertise, in informing marine policy and conservation and outline challenges, and potential solutions, facing this discipline.  相似文献   
974.
Conflicts over resource are becoming increasingly frequent as human development accelerates and resource limitations become evident. The impact of these conflicts is felt disproportionately by Indigenous Peoples, who despite international recognition that they must be consulted over resource extraction, have not been adequately included in policy development. As creation of effective environmental policy relies on meaningful consultation of all stakeholders, there is now a global outcry surrounding this eroded process. In British Columbia, Canada, a lack of meaningful government consultation has resulted in the approval of large-scale developments (the Site C Hydroelectric Dam and the Pacific Northwest Liquefied Natural Gas terminal) that are directly opposed by multiple stakeholders (First Nations, the academic community, conservation organizations, and other concerned citizens). A key component of the consultation process, trust, is explored here. Specifically, how poor government consultation erodes stakeholder trust in the consultation process. This trust is essential if holistic environmental policy, policy that protects both the environment and the economy, is to be created.  相似文献   
975.
测绘地理信息成果的共享服务和社会化消费是当前行业发展的主流趋势,但受限于相关保密政策,精度较高的地理信息成果当前仅能在政府相关部门内部使用,企业需求与数据供给之间矛盾突出。本文从资源整合入手,提出了线下高精度数据和在线低精度数据结合应用新模式,为规划设计成果的量化分析、三维可视化、在线展示和公众参与提供了一种技术解决思路,可有效提升地理信息成果的利用效率和服务能力。  相似文献   
976.
FWG1幂指数递减开发模型   总被引:15,自引:7,他引:8  
冯文光 《矿物岩石》1999,19(4):66-69
本文提出了FWG1幂指数递减开发模型,提出了开发速度,采出程度等开发指标的数学关系式。分析了参数对FWG1幂指数递减开发模型的影响。当c^1/2t=1时,VD=e^-1为不动点。提出了开发初期FWG1幂指数递减开发模型的确定方法,便于开发初期决策。  相似文献   
977.
文章通过对俄罗斯、蒙古一些已知古道型铀矿床的调研,归纳了该类铀矿床空间定位的构造控制、铀源的近源性、潜水氧化成因、含矿层的单层位性等与勘查工作有关的地质特征,并在分析上述特征的基础上提出我国今后对古河道型砂岩铀矿勘查工作方面的对策和方针。  相似文献   
978.
文章从我国目前农业生产形势及今后发展中将面临的环境和形势变化,分析到:世纪末我国的“粮改”政策有其现必要性和积极作用,但同于其有迅改革市场取向原则的地方,因此,不可能从根本上解决我国粮食生产的方向性和长远发展问题。在跨入新世纪之际,必须在对我国农业面临形势进行正确判断基础上,从转变农业目标增长方式,按照产业化目标指导农业生产;强化农业投资,改善条件,有机兼顾长短目标;加大 业科技力度,确立重点,不  相似文献   
979.
美国的区域政策及其对我国西部开发的启示   总被引:5,自引:0,他引:5  
本文分析了美国区域政策的特点:区域政策的核心是提高受援地区的社会福利;致力于改善落后的投资环境;突出重点,实施增长中心战略;注重培育欠发达地区的自我发展能力;依靠法制化管理,保障援阻工作顺利进行。在此基础上,提出解决我国地区发展不平衡问题的一些措施。  相似文献   
980.
区域发展不平稳是范围内普遍存在的现象,但地区差距过大会影响到一个国家的整体发展和社会的稳定,因此,许多国家十分重视解决地区差距问题,制定相应的区域经济政策,加强对欠发达地区的开发,保进国家经济的协调发展,分析和总结国外区域经济政策的成功经验,对我国西部开发具有一定的启迪和借鉴作用。  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