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   733篇
  免费   169篇
  国内免费   162篇
测绘学   34篇
大气科学   45篇
地球物理   197篇
地质学   340篇
海洋学   167篇
天文学   1篇
综合类   66篇
自然地理   214篇
  2024年   2篇
  2023年   15篇
  2022年   37篇
  2021年   43篇
  2020年   37篇
  2019年   33篇
  2018年   26篇
  2017年   44篇
  2016年   50篇
  2015年   27篇
  2014年   68篇
  2013年   47篇
  2012年   50篇
  2011年   42篇
  2010年   47篇
  2009年   43篇
  2008年   70篇
  2007年   45篇
  2006年   69篇
  2005年   38篇
  2004年   30篇
  2003年   42篇
  2002年   17篇
  2001年   30篇
  2000年   19篇
  1999年   20篇
  1998年   11篇
  1997年   13篇
  1996年   7篇
  1995年   13篇
  1994年   8篇
  1993年   10篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1986年   1篇
  1981年   1篇
排序方式: 共有1064条查询结果,搜索用时 93 毫秒
31.
基于生态工程的海岸带全球变化适应性防护策略   总被引:2,自引:0,他引:2  
在全球变化导致的海平面上升和灾害性气候等压力下,我国海岸带风暴潮、海岸侵蚀、地面沉降等灾害发生频率和强度正在增加,对海岸防护体系的需求日益提高。传统海岸防护工程维护成本高,更新困难,而且可能造成地面沉降、水质恶化、生态退化、渔业资源衰退等后果。基于生态工程的海岸防护提供了抵御海岸带灾害的新理念。修复和重建沙滩、红树林、沼泽湿地、珊瑚礁等海岸带生态系统,可以起到消浪、蓄积泥沙、抬升地面的作用,有效应对全球变化引发的灾害风险,形成更可持续的海岸防护体系。通过分析不同海岸防护技术的优势和限制,认为以生态工程为核心理念构建和管理我国海岸防护体系,才能起到保障社会经济发展和维持生态健康的最佳效果。  相似文献   
32.
In this short discussion, we consider societal responses to the (impending) ‘death of nature’ associated with the epoch now dubbed the Anthropocene. We forward the case for a geographical perspective that engages with psychological and psychoanalytic analyses to better understand responses and coping mechanisms, such as societal death anxiety.  相似文献   
33.
During thermal remediation the increase in subsurface temperature can lead to bubble formation and mobilization. In order to investigate the effect of gas formation on resulting aqueous concentrations, a 2D finite difference flow and mass transport model was developed which incorporates a macroscopic invasion percolation (MIP) model to simulate bubble expansion and movement. The model was used to simulate three soil scenarios with different permeabilities and entry pressures at various operating temperatures and groundwater velocities. It was observed that discrete bubble formation occurred in all three soils, upward mobility being limited by lower temperatures and higher entry pressures. Bubble mobilization resulted in a different aqueous mass distribution than if no discrete gas formation was modeled, especially at higher temperatures. This was a result of bubbles moving upwards to cooler areas, then collapsing, and contaminating previously clean zones. The cooling effect also led to possible non-aqueous phase liquid (NAPL) formation which was not predicted using a model without discrete bubble formation.  相似文献   
34.
甘肃内陆河流域生态功能及保护对策   总被引:2,自引:0,他引:2  
从阐述张掖生态功能的重要意义入手,阐明了祁连山森林、湿地、人工绿洲成板块结构镶嵌分布,组成了强大的生态屏障,阻止了沙漠化的进程。针对张掖生态安全屏障保护存在的主要问题和甘肃祁连山国家自然保护区及张掖黑河湿地国家自然保护区建设现状,提出了祁连山自然保护区生态保护与管理及湿地国家级自然保护区生态恢复与综合治理的具体措施,为甘肃内陆河流域生态安全屏障建设提供参考依据。  相似文献   
35.
南泥湾湿地生态变迁研究   总被引:2,自引:0,他引:2  
南泥湾是我国陕北的一片重要湿地,曾为中国革命的生存和发展提供了重要保障,在抗战时期垦殖而至今未被科学认知。根据史料记载以及人物传记,基于南泥湾湿地的科学认定,分析了南泥湾湿地的生态变迁,明确提出恢复南泥湾湿地,为陕北的好江南建设提供一定的科学支撑,为南泥湾湿地的恢复与部分重建提供前期基础。理想完美的南泥湾生态系统应当是湿地、森林、农田、草地的综合体,应当是陕北黄土高原的一块绿洲。  相似文献   
36.
淮北煤矿塌陷区湿地生态环境营建及旅游产品开发   总被引:2,自引:0,他引:2  
煤矿塌陷区生态环境治理一直是一个关系国计民生的难题。近年来,淮北市对煤矿塌陷区形成的大面积湿地进行大力整治,经过近20年努力,建成我国第一个煤矿塌陷区国家级城市湿地公园,将昔日荒凉的废弃地变成了生态旅游天堂。对淮北煤矿塌陷区生态环境营建进行分析总结,对其生态旅游产品开发提出了建议。  相似文献   
37.
The declining health of marine ecosystems around the world is evidence that current piecemeal governance is inadequate to successfully support healthy coastal and ocean ecosystems and sustain human uses of the ocean. One proposed solution to this problem is ecosystem-based marine spatial planning (MSP), which is a process that informs the spatial distribution of activities in the ocean so that existing and emerging uses can be maintained, use conflicts reduced, and ecosystem health and services protected and sustained for future generations. Because a key goal of ecosystem-based MSP is to maintain the delivery of ecosystem services that humans want and need, it must be based on ecological principles that articulate the scientifically recognized attributes of healthy, functioning ecosystems. These principles should be incorporated into a decision-making framework with clearly defined targets for these ecological attributes. This paper identifies ecological principles for MSP based on a synthesis of previously suggested and/or operationalized principles, along with recommendations generated by a group of twenty ecologists and marine scientists with diverse backgrounds and perspectives on MSP. The proposed four main ecological principles to guide MSP—maintaining or restoring: native species diversity, habitat diversity and heterogeneity, key species, and connectivity—and two additional guidelines, the need to account for context and uncertainty, must be explicitly taken into account in the planning process. When applied in concert with social, economic, and governance principles, these ecological principles can inform the designation and siting of ocean uses and the management of activities in the ocean to maintain or restore healthy ecosystems, allow delivery of marine ecosystem services, and ensure sustainable economic and social benefits.  相似文献   
38.
基于资源等价分析法的海洋溢油生态损害评估模型及应用   总被引:1,自引:1,他引:0  
李京梅  王晓玲 《海洋科学》2012,36(5):98-102
采用资源等价分析法构建溢油海洋生态损害评估的模型,重新对2002年渤海塔斯曼溢油事件的潮间带生物损害进行定量评估,得出补偿修复工程的规模从而估算出针对潮间带受损资源的赔偿额度。资源等价分析法的研究与应用填补了国内在该类方法研究领域的空白,进一步完善了中国溢油生态损害评估方面的研究,为各类溢油损害计算提供参考和补偿依据。  相似文献   
39.
Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for 4 months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analyzing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes.  相似文献   
40.
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