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   1987篇
  免费   177篇
  国内免费   164篇
测绘学   40篇
大气科学   312篇
地球物理   340篇
地质学   648篇
海洋学   355篇
天文学   4篇
综合类   67篇
自然地理   562篇
  2024年   6篇
  2023年   29篇
  2022年   89篇
  2021年   81篇
  2020年   83篇
  2019年   93篇
  2018年   56篇
  2017年   126篇
  2016年   91篇
  2015年   98篇
  2014年   122篇
  2013年   132篇
  2012年   61篇
  2011年   96篇
  2010年   72篇
  2009年   137篇
  2008年   125篇
  2007年   101篇
  2006年   98篇
  2005年   75篇
  2004年   69篇
  2003年   46篇
  2002年   64篇
  2001年   39篇
  2000年   52篇
  1999年   47篇
  1998年   41篇
  1997年   31篇
  1996年   34篇
  1995年   36篇
  1994年   15篇
  1993年   20篇
  1992年   15篇
  1991年   13篇
  1990年   7篇
  1989年   9篇
  1988年   4篇
  1987年   4篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1980年   1篇
  1976年   1篇
排序方式: 共有2328条查询结果,搜索用时 415 毫秒
181.
杨宇  任亚文 《地理研究》2023,42(1):1-16
全球能源治理是当前能源话语权塑造的重要形式,其本质是能源利益主体间围绕多元能源议题而构建的关系网络。在以往相关研究中,各能源组织的架构、功能、绩效以及所产生的复杂影响占据了主要内容,而对于全球能源治理的整体结构以及内部关系却未能有进一步探索。本研究认为,能源组织与实际贸易存在交互关系,将二者相结合来进一步呈现和解释全球能源治理架构是有必要的。基于此,本研究以2019年为时间节点,收集主要能源组织的属性数据与各国之间的石油和天然气贸易数据,将国家间在能源治理组织的常态化合作关系与实际发生的能源贸易关系作为分析基础;并利用社会网络分析方法构建全球能源治理网络,探析其基本结构以及出现的“边界重构”现象。研究发现:(1)能源组织网络与能源贸易网络存在显著的结构性差异,在两种网络对比中,美国与俄罗斯均占据主导地位。(2)中国已经成为能源贸易大国,但在全球能源组织合作中不具优势,与传统能源利益集团之间缺乏正式的治理合作。(3)全球能源治理体系呈现出典型的“核心-边缘”结构,主要被划分为欧盟以及亚太-北美“社区”,其中OECD(经济合作与发展组织)国家占据“核心”地位;而以单一能源输出为主导功能的出...  相似文献   
182.
Water Flows Toward Power: Socioecological Degradation of Lake Urmia,Iran   总被引:1,自引:0,他引:1  
Water is an invaluable resource, and equitable access to it is a fundamental human right. Disenfranchised groups often lose access to water resources because their interests are not well represented by decision makers. Excluding these groups from resource management policy often results in myopic decisions that contribute to further ecosystem damage. We describe the ecological degradation of Lake Urmia in Iran, which has recently experienced increased salinity and declining water quantity. The lake is a UNESCO Biosphere Reserve and Ramsar site, and supports unique biodiversity in the region. The lake's decline is driven by the destruction of Zagros forests and the government's water policies, which diverted water to more politically connected agricultural land users, increasing social inequity and prompting more deforestation. The most straightforward restoration solution is to discontinue the diversions and allow critical inflows to recharge Lake Urmia, preserving the lake and wetlands for migratory birds, tourists, and local communities.  相似文献   
183.
哈拉湖岩芯XRF扫描元素统计分析及其环境意义   总被引:3,自引:0,他引:3  
青藏高原东北缘高山湖泊哈拉湖是位于季风与西风影响的交汇带的封闭深水湖泊,是区域环境和气候变化的良好记录载体。目前对该湖的研究还较少,缺乏对沉积物中元素环境意义的系统认识。通过高分辨率XRF岩芯扫描,用相关、聚类和因子分析的方法对哈拉湖沉积岩芯地球化学元素进行分析。结果显示Ti、K、Si、Al、Fe、Mn等元素变化一致,相关性高,归为同一类,即径流输入的陆源碎屑组分,反映了流域水文状况如径流量的变化。Sr、Zr元素相关性高,为赋存在粗颗粒沉积物中的元素,根据哈拉湖实际,应为冬季湖泊冰面风力搬运,反映了湖区冬季风力强度的变化。Ca元素既与径流输入元素总体变化一致,也与Sr、Zr元素显著相关,且在第一和第二主成分(径流和风力)上的载荷相当,表明哈拉湖沉积物中的碳酸盐既有粗颗粒的外源碎屑,也有湖泊自生的组分,这在利用碳酸盐进行地球化学研究时应重视,注意去除外源碎屑碳酸盐的影响。可溶元素S和Cl可能反映了入湖水量与蒸发对比情况,与湖泊盐度有关。  相似文献   
184.
从汉石桥湿地自然保护区自身特点出发,通过分析受众类型、设计原则、展示形式、内容等方面,对解说系统、展示系统和环境教育活动三方面进行设计,最终形成汉石桥湿地自然保护区的环境教育体系。  相似文献   
185.
The ecosystem approach to fisheries (EAF) is a holistic paradigm that considers stocks of exploitable species, marine ecosystems and stakeholders. Management agencies must strike a balance between their capacity constraints and the requisites of management measures. Most small-scale sea cucumber fisheries of Pacific Islands have been plundered while others are being opened to commercial exploitation. Data from fishery managers and a regional workshop were used to assess the current problems, institutional constraints and solutions to the management of sea cucumber fisheries in 13 Pacific Island countries (PICs). Technical capacity was often strong for some management actions such as developing marine reserves but weak for others, such as enforcement. Using multi-disciplinary indicators, half of the fisheries were diagnosed by their managers as being overfished or depleted, despite evidence of optimistic bias. Fishery governance varied greatly among the PICs, and co-management frameworks were not typical of any cultural region. Management objectives were prioritised differently among managers but most highly ranked was to protect ecological resilience. The fishery managers proposed different sets of regulatory measures and various management actions, such as surveys to collect socio-economic and fishery-dependent data, support for local governance and strong enforcement – all widely under-practised. Pacific sea cucumber fisheries exemplify how the transition to an EAF by management institutions must involve reorganisation of their technical and human-resource capacities among management tasks. Levies on exports need to be internalised to fund improved management. Management agencies should consider a shift in resources from developing marine reserves, conducting underwater surveys and aquaculture-based restocking to strengthening enforcement capacity, stakeholder involvement and communication with fishers. In concert with these actions, short fishing seasons, shortlists of allowable species and tighter enforcement at export points may serve to turn the tide on boom-and-bust exploitation and safeguard biodiversity.  相似文献   
186.
For nearly a decade, governments have been discussing the need to improve efforts to conserve and sustainably use marine biodiversity in areas beyond national jurisdiction (ABNJ). Support for a new international agreement under the United Nations Convention on the Law of the Sea (UNCLOS) – an Implementing Agreement – on the conservation and sustainable use of marine biodiversity in ABNJ has been growing. In June 2012, at the United Nations Conference on Sustainable Development held in Rio de Janeiro, Brazil, States agreed to take a decision on the development of an international instrument under UNCLOS before the end of the 69th session of the United Nations General Assembly (UNGA), which runs from September 2014 to August 2015. In follow-up to this commitment, it was agreed to consider the “scope, parameters and feasibility” of this instrument. To inform these international discussions, this article highlights some potential options for the content of a new UNCLOS Implementing Agreement. It first reviews the history of UN discussions, and then elaborates on options to address key elements identified as priorities for States in 2011: marine genetic resources, including the sharing of benefits, area-based management tools, including marine protected areas, environmental impact assessments, capacity-building and the transfer of marine technology. It addresses cross-cutting issues such as the governing principles, institutional structure as well as on other critical points such as High Seas fishing and flag State responsibilities. The article concludes with suggestions on possible next steps in order to succeed in the negotiations for an agreement.  相似文献   
187.
This introduction explains the context and structure of a block of articles developed as part of the governance work packages of the FP7 project: “Options for Delivering Ecosystem-based Marine management” (ODEMM).  相似文献   
188.
United Nations discussions on the governance of marine areas beyond national jurisdiction have questioned, but not yet reached a decision, on whether existing institutional agreements and structures are sufficient to meet global commitments to protect marine biodiversity, or if additional mechanisms may be required. This paper considers two very different efforts to protect marine biodiversity in these areas: (1) in the North-East Atlantic through the efforts of OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic; and (2) in the central Atlantic, through the efforts of the Sargasso Sea Alliance led by the Bermuda government. In each case, action has been strongly supported by non-governmental organisations and subsequent progress has hinged upon on-going dedicated efforts of “champion” governments to bring other States on board. This paper outlines the difficulties that they have faced, and consequently why they have been time-consuming, and are not yet completed. The paper then considers 10 common recommendations that can be drawn from the experiences of these two distinct initiatives, and their relevance to on-going UN deliberations.  相似文献   
189.
This study integrated environmental variables together with high spectral resolution WorldView-2 imagery to detect and map Thaumastocoris peregrinus damage in Eucalypt plantation forests in KwaZulu-Natal, South Africa. The WorldView-2 bands, vegetation indices and environmental variables were entered separately into PLS regression models to predict T. peregrinus damage. The datasets were then integrated to test the collective strength in predicting T. peregrinus damage. Important variables were identified by variable importance (VIP) scores and were re-entered into a PLS regression model. The VIP model was then extrapolated to map the severity of damage and predicted T. peregrinus damage with an R2 value of 0.71 and a RMSE of 3.26% on an independent test dataset. The red edge and near-infrared bands of the WorldView-2 sensor together with the temperature dataset were identified as important variables in predicting T. peregrinus damage. The results indicate the potential of integrating WorldView-2 data and environmental variables to improve the mapping and monitoring of insect outbreaks in plantation forests. The result is critical for plantation health monitoring using a new sensor which contains important vegetation wavelengths.  相似文献   
190.
Weather conditions that influence natural resource-based tourist destinations are likely to be affected by climate change, but our understanding of how businesses and destinations manage for present and future conditions is limited. In this study we report on the relationships between weather and tourism activities in the Queenstown-Lake Wanaka region, South Island, New Zealand. Key stakeholder interviews and a workshop form the empirical basis of this paper. Coping range application ideas derived from ecological management literature are used to develop a framework to understand and inform thinking and strategies around how tourism businesses and destinations are currently responding to the weather and perhaps could in future respond to climate change. Results show that within a destination individual businesses have widely varying relationships with the weather, with each type of activity operating within its own coping range to particular environmental gradients, for example temperature. Coping, which can be observed outside the ‘ideal’ range of a particular environmental gradient, requires business adjustments so as to cope with increasingly marginal conditions, up to a Critical Stop Point – the ultimate threshold. The data suggest that increased need for adjustments impacts on business viability, and more planned adaptation measures would be necessary to increase viability under increasingly detrimental climatic conditions. Discussion at a destination level workshop indicates that at and beyond thresholds, keystone industry and destination level strategic adaptation planning is required to ensure the viability of the destination as a whole.  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