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   1541篇
  免费   141篇
  国内免费   228篇
测绘学   43篇
大气科学   100篇
地球物理   220篇
地质学   270篇
海洋学   430篇
天文学   7篇
综合类   86篇
自然地理   754篇
  2024年   13篇
  2023年   25篇
  2022年   69篇
  2021年   101篇
  2020年   71篇
  2019年   82篇
  2018年   65篇
  2017年   59篇
  2016年   82篇
  2015年   73篇
  2014年   104篇
  2013年   82篇
  2012年   72篇
  2011年   87篇
  2010年   70篇
  2009年   104篇
  2008年   70篇
  2007年   85篇
  2006年   99篇
  2005年   114篇
  2004年   54篇
  2003年   69篇
  2002年   37篇
  2001年   47篇
  2000年   54篇
  1999年   30篇
  1998年   17篇
  1997年   24篇
  1996年   10篇
  1995年   9篇
  1994年   8篇
  1993年   6篇
  1992年   4篇
  1991年   5篇
  1990年   2篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
排序方式: 共有1910条查询结果,搜索用时 15 毫秒
101.
燕乃玲  虞孝感 《湖泊科学》2004,16(Z1):143-152
生态功能区划是我国正在开展的一项关于资源与环境管理的重大基础性工作.生态功能区划的理论和方法是当前生态学、环境科学、地理学等学科面临的一项新的热点课题.本文首先讨论了生态功能区划的概念,从认识区划看,生态功能区划属于生态系统区域划分的范畴,从实践的角度,则强调人文活动对生态系统可持续能力产生的影响,指出自然生态区不是生态功能区,生态功能区须反映人类的利用和价值判断.生态功能区划,不单是以自然要素或自然系统的"地带性分异"为基础,更是以生态系统的等级结构和尺度原则为基础,用生态系统完整性的评价测量人类活动对生态系统的影响,将生态功能区划的科学基础落在"基于生态系统的管理"平台上.文章提出了基于流域的我国生态功能区划的初步思想,讨论了区划的原则和方法,建立了生态系统完整性评价和功能区划分的指标体系.其基本内容是,认识并按照生态系统的自然边界划分生态系统单元;进行生态系统完整性评价;在此基础上划分不同的生态功能区,确定主导生态功能.  相似文献   
102.
王嵩  孙才志  范斐 《地理科学》2018,38(3):342-350
建立海洋生态与海洋经济的共生演化Logistic模型,通过压力-状态-影响-响应(PSIR)模型对Logistic模型中的基本指数进行求解,进一步计算海洋生态与海洋经济之间的共生系数,结果表明:天津和上海两市发展模式已摆脱资源索取模式,其海洋经济生态共生模式的探讨意义较小;其余沿海九省中,河北、江苏、广西和海南4省处于反向共生水平,辽宁和山东两省呈现并生模式,浙江和广东呈现出生态受益的偏利共生模式,福建则呈现出经济受害的偏利共生模式。根据沿海各省市海洋经济生态共生模式,提出相关的政策建议,以期对沿海省市今后的经济和生态发展模式提供理论依据。  相似文献   
103.
The ecosystem is important because it is the life sustaining system for human survival.Three ecosystem characteristics are:regional particularities,ecosystem complexity and conventional cultural particularities.This paper develops a remote sensing based dynamic model to assess grassland ecosystem service values involving multidisciplinary knowledge.The ecological value of grassland ecosystems is focused on using a remote sensing technique in the model,and setting up the framework for a dynamic assessing model.The grassland ecological services condition and value in 1985 is used as the benchmark.The dynamic model has two adjusting indicators:biomass and price index.The biomass is simulated using the CASA(Carnegie-Ames-Stanford Approach) model.The price index was obtained from statistics data published by the statistical bureau.Results show that the grassland ecosystem value in Gansu Province was 28.36 billion Chinese Yuan in 1985,140.37 billion in 1999 and 130.86 billion in 2002.  相似文献   
104.
“一带一路”区域可持续发展生态环境遥感监测   总被引:1,自引:1,他引:1  
2013年9月和10月,习近平主席在出访中亚和东南亚国家期间,先后提出了共建"丝绸之路经济带"和"21世纪海上丝绸之路"(简称"一带一路")的重大倡议。要全面保护"一带一路"区域生态环境,实现2030年可持续发展目标,是一个具有挑战性的问题。遥感技术对生态环境监测与评价发挥着十分重要的作用。本研究利用多尺度、多源遥感数据,对2015年"一带一路"区域的生态环境状况进行监测和分析,旨在提供可持续发展目标生态环境遥感监测的本底。本文选取了几个重要的生态环境方面开展监测与分析,主要包括宏观生态系统结构和植被状况、太阳能资源分布、水资源平衡、主要生态环境限制因素对经济走廊建设的影响、主要城市生态环境质量等。监测区域覆盖亚洲、非洲、欧洲和大洋洲的陆上区域。研究结果为生态环境评价与保护提供了有效的决策依据,有助于"一带一路"建设积极推进。  相似文献   
105.
荒漠生态系统是地球上最大的陆地生态系统,全球四分之一的人口生活在这一区域。清晰地定义荒漠生态系统生态质量,制定反映生态质量优劣的关键监测指标,集成"星–空–地"一体化监测技术、构建综合评价模型可为干旱区生态质量监测、促进区域可持续发展提供技术支撑。荒漠生态质量是指一定时空范围内荒漠生态系统要素、结构和功能的综合特征。该研究通过集成卫星、无人机和地面传感器网络的"星–空–地"一体化监测技术,在区域和站点两个尺度上对荒漠生态系统的生态要素、生物多样性和生态功能进行连续监测,通过标准化生态质量指标数值、厘定其阈值范围,构造判断矩阵建立生态质量综合评价模型,评价荒漠生态系统质量状况。本论文阐明了构建荒漠生态质量动态综合监测技术规范与评价方法的概念框架,为实现我国荒漠生态系统生态质量综合监测、科学诊断和定量评估提供理论基础。  相似文献   
106.
Various waterborne anthropogenic contaminants disrupt the endocrine systems of wildlife and humans, targeting reproductive pathways, among others. Very little is known, however, regarding the occurrence of endocrine disruptive activity in South African freshwater ecosystems, and coastal ecosystems have not been studied in this regard. In a first attempt to investigate endocrine disruptive activity in South African coastal waters, surface water samples collected from harbours, river mouths and estuaries in three metropolitan municipalities, eThekwini (which includes Durban), Nelson Mandela (specifically Port Elizabeth Harbour) and City of Cape Town, were screened for (anti) oestrogenicity and (anti)androgenicity using recombinant yeast bioassays. Moreover, levels of the female hormone 17β-(o)estradiol (E2) were determined in all samples, as well as a selection of hydrocarbons in the eThekwini samples. A high proportion of samples collected from eThekwini were oestrogenic, whereas none from Port Elizabeth Harbour and only a single river mouth sampled in the City of Cape Town were oestrogenic. E2 was detected in all the samples tested, but at higher concentrations at the eThekwini and City of Cape Town localities than Port Elizabeth Harbour. In addition, the recombinant yeast assays revealed that anti-androgenicity was widespread, being detected in the majority of samples screened apart from those representing Port Elizabeth Harbour. Conversely, no anti-oestrogenic or androgenic activity was detected. Anti-androgenicity did not associate with hydrocarbon loads, providing evidence that other anti-androgens were responsible for the observed activity. The present data suggest potential reproductive disruption in marine and estuarine fauna inhabiting the eThekwini and City of Cape Town regions.  相似文献   
107.
海洋生态修复是遏制海洋生态系统退化的重要途径,受到全球越来越多学者的关注。本研究以科学引文索引(Science Citation Index Expanded,SCIE)数据库为数据源,采用文献计量统计分析方法,结合VOSviewer知识图谱可视化分析软件,定量分析了1980—2019年国际上在海洋生态修复领域发表的相关文献,梳理了近40年来该领域研究的发展脉络、前沿热点和未来方向。结果表明,近40年间,海洋生态修复领域的发文数量随时间呈上升趋势,尤其2000年后增长速度加快,以北美洲、大洋洲、欧洲国家居多,其中美国占绝对领先地位。海洋生态修复领域涉及的学科主要有环境科学、生态学、海洋及淡水生物学等,Journal of Coastal Research、Restoration Ecology、Ecological Engineering和Estuarine,Coastal and Shelf Science是该领域的主要发文期刊。当前海洋生态修复研究热点主要包括植被恢复、海洋生物种群恢复、滨海湿地修复与生物地球化学、气候变化与生态系统管理等主题,其中关于缓解和适应气候变化、生态系统的自然恢复途径、生态系统服务功能提升等方面的研究愈来愈受到关注,是未来一段时间内海洋生态修复领域的研究热点。随着我国《国民经济和社会发展第十四个五年规划》拉开序幕以及海洋生态文明建设不断深化,我国海洋生态修复研究将驶入快车道,建议在应对气候变化的海洋生态修复、区域性海洋生态系统修复规划、海洋生态退化机理与修复关键技术、适应性管理等方面加强研究和探索。  相似文献   
108.
There is currently a critical knowledge gap in how eutrophication and climate variables separately and interactively impact the dynamics of marine ecosystems. Based on long-term monitoring data we quantified the separate and combined impacts of nutrient loading, temperature, salinity, and wind conditions on zooplankton, zoobenthos and fish inhabiting a brackish water ecosystem in the Gulf of Riga. Changes in zoobenthos communities and herring stock were largely explained by climate variables. Zooplankton species were related to both eutrophication and climate variables, and models combining all environmental variables explained additional variation in zooplankton data compared to the separate models of climate and eutrophication. This suggests that zoobenthos communities and herring stock are largely driven by weather conditions, whereas the combined effect of weather and nutrient loads are likely the cause for dynamic zooplankton communities in the Gulf of Riga.  相似文献   
109.
利用实地调研结果,结合相关文献资料,采用市场价值法、影子工程法、旅行费用法等评估方法,对溱湖湿地生态系统的物质生产、涵养水源和调蓄洪水、提供动植物栖息地、调节气候、降解污染物和科考旅游等6个效益最为突出的生态系统服务功能经济价值指标进行评估。研究表明:溱湖湿地生态系统的总价值为1.15×109元,其中直接使用价值为7.708×108元,间接使用价值为3.62×108元,非使用价值为0.18×108元。其中科考旅游价值所占比重最大,为40.84%,调节气候价值次之,而生物多样性保护价值仅占1.45%。对溱湖湿地生态系统服务功能及服务价值的探讨,可正确认识该生态系统的生态经济价值,为合理开发利用提供决策参考,确保其资源的可持续利用。  相似文献   
110.
Global environmental change leads to degradation of tropical forests in many countries. In response to this pressure, programs for payments for ecosystem services (PES) are developing and organizations are emerging which manage forests in order to supply ecosystem services, rather than only harvest timber. Typically such services are carbon sequestration, biodiversity conservation, pollination, and watershed protection. Public or private actors interested to invest in or donate money for the provisioning of such services are faced with the problem of choosing the appropriate organization supplying ecosystem services. The goal of this paper was to develop an assessment framework based on the balanced scorecard concept including drivers, impact, performance and context variables. Results of a survey of international market actors were used to determine assessment criteria and their weights. Putting the focus of this paper on drivers and impacts, we assessed Latin American organizations that “sell” ecosystem services from tropical forests in terms of their general management, marketing, forest management, client and stakeholder satisfaction, and forest ecosystem status. We found that supplying organizations vary widely with respect to their achievements in these areas. However, the variance of assessment results is influenced even more by the variance in weights the international market actors allocate to the assessment criteria. The insights of this study can contribute to the continuous improvement of management processes in supplying organizations and can support investors and donors in their decision-making with respect to organization supplying ecosystem services.  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