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   1518篇
  免费   145篇
  国内免费   254篇
安全科学   23篇
废物处理   10篇
环保管理   193篇
综合类   819篇
基础理论   518篇
污染及防治   57篇
评价与监测   74篇
社会与环境   213篇
灾害及防治   10篇
  2024年   7篇
  2023年   22篇
  2022年   57篇
  2021年   53篇
  2020年   52篇
  2019年   46篇
  2018年   53篇
  2017年   72篇
  2016年   62篇
  2015年   73篇
  2014年   73篇
  2013年   105篇
  2012年   86篇
  2011年   128篇
  2010年   107篇
  2009年   91篇
  2008年   70篇
  2007年   109篇
  2006年   121篇
  2005年   87篇
  2004年   80篇
  2003年   71篇
  2002年   42篇
  2001年   41篇
  2000年   34篇
  1999年   28篇
  1998年   28篇
  1997年   18篇
  1996年   23篇
  1995年   17篇
  1994年   14篇
  1993年   15篇
  1992年   6篇
  1991年   6篇
  1990年   7篇
  1989年   1篇
  1988年   4篇
  1987年   1篇
  1986年   2篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
排序方式: 共有1917条查询结果,搜索用时 31 毫秒
951.
Cities are areas of increased diversity of species in the taiga zone. The aboriginal fraction of Karelian flora is a stable natural system whose main characteristics are preserved in the urban flora. The adventive fraction, which is a dynamic component of the flora, has not been completely formed in the cities, as well as in eastern Fennoscandia as a whole. It has become substantially richer during the past 20–25 years. Cities of the taiga zone may serve as objects for monitoring the anthropogenic processes of flora transformation in the North.  相似文献   
952.
The development of a sampling design for optimisingsampling site locations collected from a coastalmarine environment has been the purpose of the presentwork; application of statistical analysis and spatialautocorrelation methods have been carried out. Thedataset included data collected from 34 sampling sitesspaced out in the Strait of Lesbos, Greece, arrangedin a 1×1 NM grid. The coastal shallow ecosystem wassubdivided into three zones, an inner one (7stations), a middle one (16 stations) and an offshorezone (11 stations). The standard error of thechlorophyll-a concentrations in each zone hasbeen used as the criterion for the sampling designoptimisation, resulting into reallocation of thesampling sites into the three zones. The positions ofthe reallocated stations have been assessed byestimation of the spatial heterogeneity and anisotropyof chlorophyll-a concentrations usingvariograms. Study of the variance of the initialdataset of the inner zone taking into account spatialheterogeneity, revealed two different sub-areas andtherefore, the number of the inner stations has beenreassessed. The proposed methodology eliminates thenumber of sampling sites and maximises the informationof spatial data from marine ecosystems. It isdescribed as a step-by-step procedure and could bewidely applied in sampling design concerning coastalpollution problems.  相似文献   
953.
“A skyscraper is as natural as a bird’s nest” –Alan Watts For millennia, people have altered freshwater ecosystems directly through water development and indirectly by global change and surrounding land-use activities. In these altered ecosystems, human impacts can be subtle and are sometimes overlooked by the people who manage them. This article provides two case studies near Boulder, Colorado that demonstrate how perceptions regarding these ecosystems affect their management. These examples are typical of lakes and streams along the Front Range of Colorado that are simultaneously natural and social in origin. Although natural, many of the region’s freshwater ecosystems are affected by ongoing ecologic, hydrologic, chemical, and geomorphic modifications produced by human activity. People and nature are both active participants in the production of these freshwater ecosystems. The concept of “hybridity,” borrowed from geographers and social scientists, is useful for describing landscapes of natural and social origin. Hybrid freshwater ecosystems are features of the humanized landscape and are derived from deliberate cultural activities, nonhuman physical and biological processes, and incidental anthropogenic disturbance. Our perceptions of “natural” freshwater ecosystems and what definitions we use to describe them influences our view of hybrid systems and, in turn, affects management decisions regarding them. This work stresses the importance of understanding the underlying societal forces and cultural values responsible for the creation of hybrid freshwater ecosystems as a central step in their conservation and management.  相似文献   
954.
包头地区的生态环境建设   总被引:1,自引:0,他引:1  
内蒙古包头地区属于季风尾闾区,干旱少雨,生态环境十分脆弱.近几十年来,由于多种因素的影响,本区生态环境退化现象严重,因此积极探索本区生态环境建设途径,有效遏制生态环境退化,改善区域生产、生活条件的意义非常重大.在大量实地考察和资料研究的基础上,指出了本区生态环境建设中存在的主要问题,并提出了搞好生态环境建设的对策建议.  相似文献   
955.
Theuplandreferstoanyplacewhoserelativealtitudeismorethan 2 0 0meters.Itmaynotonlyincludelowmountains,mediummountains,highmountainsandsky highmountains,butalsotablelands,plateaus,hills,valleysandbasinsthatlieamongthem .Itisindeedacomplexecosystemcomprisingnat…  相似文献   
956.
程鹏  袁长顺  张新法 《灾害学》2004,19(1):81-86
通过对“两山一湖“区域生态系统的分析,认识到影响该区域生态不稳定的主要因素是人类活动对野生动植物栖息地的破坏、毁林垦种、外来物种入侵、森林火灾等;提出了保护森林资源、调整土地利用结构、实行退耕还林、推广水流域综合治理、加强物种保护、预防松材线虫病和森林火灾、建立以森林为主体的生态安全保障体系.  相似文献   
957.
Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha–1 year–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing 15N labelled ammonium nitrate (+35 kg N ha–1 year–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of 15N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.  相似文献   
958.
从生态学角度分析了滇池富营养化形成的原因,认为滇池富营养化是滇池流域各子生态系统受到破坏所造成的结果。提出治理滇池应该用生态学的原理和方法分别修复受到破坏的各子生态系统,恢复各子生态系统的合理结构、高效功能和协调关系,并把各子生态系统整合为一个整体协调、自我维持、自我演替的滇池流域生态系统,才能最终实现滇池富营养化治理。  相似文献   
959.
蔡正帮 《四川环境》1995,14(4):26-31
本文阐述了生态环境与社会经济之间的关系,探讨了保护环境、资源对发展经济的作用。  相似文献   
960.
生态保护的基础是生态监测与生态调查,生态保护的关键则是生态系统健康评价,生态系统健康评价因素有组织、结构、活力、恢复力、系统对相邻系统的影响、投入、对人类健康的影响等,其类型有健康、较健康、亚健康、不健康、患病五级;其相应的生态恢复为生态预防、自然恢复、生态修复、生态重建;其相应的生态工程有建立自然保护区、封育、补播与放流、人工林、人工草场、人工湿地等。  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