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   4234篇
  免费   63篇
  国内免费   519篇
安全科学   138篇
废物处理   226篇
环保管理   376篇
综合类   1166篇
基础理论   1322篇
污染及防治   1055篇
评价与监测   249篇
社会与环境   225篇
灾害及防治   59篇
  2023年   16篇
  2022年   70篇
  2021年   59篇
  2020年   40篇
  2019年   44篇
  2018年   160篇
  2017年   172篇
  2016年   237篇
  2015年   116篇
  2014年   110篇
  2013年   140篇
  2012年   541篇
  2011年   327篇
  2010年   115篇
  2009年   99篇
  2008年   109篇
  2007年   131篇
  2006年   141篇
  2005年   449篇
  2004年   583篇
  2003年   459篇
  2002年   84篇
  2001年   90篇
  2000年   79篇
  1999年   80篇
  1998年   58篇
  1997年   48篇
  1996年   48篇
  1995年   50篇
  1994年   28篇
  1993年   23篇
  1992年   20篇
  1991年   13篇
  1990年   16篇
  1989年   9篇
  1988年   5篇
  1987年   4篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1983年   7篇
  1982年   4篇
  1981年   2篇
  1978年   2篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1966年   2篇
  1961年   1篇
  1957年   1篇
排序方式: 共有4816条查询结果,搜索用时 62 毫秒
241.
Reforestation Strategies Amid Social Instability: Lessons from Afghanistan   总被引:1,自引:0,他引:1  
Foreign and domestic government agencies and other international organizations pursue reforestation programs in rural upper watershed areas of Afghanistan over the past decade to alleviate poverty, combat the insurgency and rehabilitate a depleted forest resource base. Popular programs incorporate cash-for-work to conduct hillside terracing, check dam construction and tree-planting for nut production, fuel wood, timber, dune stabilization, and erosion abatement. Programmatic approaches have varied as a function of accessibility, security and local objectives. Uncertain land tenure and use rights, weak local environmental management capacity, and a focus on agricultural production to meet immediate needs limit interest, nationally and locally. Unreliable security, a lack of high quality tree planting stock, limited technical knowledge and coordination among government agencies, and poor security hamper program expansion. Reforestation success would be most likely where these issues are least acute. The Afghan government should focus on supporting community based natural resource management, developing and disseminating improved conservation tree nursery strategies, and promoting watershed management schemes that incorporate forestry, range management and agronomic production. Reforestation practitioners could benefit from the human and material resources now present as part of the international war effort. Successes and failures encountered in Afghanistan should be considered in order to address similar problems in insecure regions elsewhere when reforestation may help reverse environmental degradation and contribute to broader social stabilization efforts.  相似文献   
242.
The Great Western Development Strategy (GWDS) is a long term national campaign aimed at boosting development of the western area of China and narrowing the economic gap between the western and the eastern parts of China. The Strategic Environmental Assessment (SEA) procedure was employed to assess the environmental challenges brought about by the western development plans. These plans include five key developmental domains (KDDs): water resource exploitation and use, land utilization, energy generation, tourism development, and ecological restoration and conservation. A combination of methods involving matrix assessment, incorporation of expert judgment and trend analysis was employed to analyze and predict the environmental impacts upon eight selected environmental indicators: water resource availability, soil erosion, soil salinization, forest destruction, land desertification, biological diversity, water quality and air quality. Based on the overall results of the assessment, countermeasures for environmental challenges that emerged were raised as key recommendations to ensure ecological security during the implementation of the GWDS. This paper is intended to introduce a consensus-based process for evaluating the complex, long term pressures on the ecological security of large areas, such as western China, that focuses on the use of combined methods applied at the strategic level.  相似文献   
243.
Wildland fire in the South commands considerable attention, given the expanding wildland urban interface (WUI) across the region. Much of this growth is propelled by higher income retirees and others desiring natural amenity residential settings. However, population growth in the WUI increases the likelihood of wildfire fire ignition caused by people, as humans account for 93% of all wildfires fires in the South. Coexisting with newly arrived, affluent WUI populations are working class, poor or otherwise socially vulnerable populations. The latter groups typically experience greater losses from environmental disasters such as wildfire because lower income residents are less likely to have established mitigation programs in place to help absorb loss. We use geographically weighted regression to examine spatial variation in the association between social vulnerability (SOVUL) and wildfire risk. In doing so, we identify “hot spots” or geographical clusters where SOVUL varies positively with wildfire risk across six Southern states—Alabama, Arkansas, Florida, Georgia, Mississippi, and South Carolina. These clusters may or may not be located in the WUI. These hot spots are most prevalent in South Carolina and Florida. Identification of these population clusters can aid wildfire managers in deciding which communities to prioritize for mitigation programming.  相似文献   
244.
To facilitate forest planning and management on National Wildlife Refuges, we synthesized multiple data sources to describe land ownership patterns, land cover, landscape pattern, and changes in forest composition for four ecoregions and their associated refuges of the Upper Midwest. We related observed patterns to ecological processes important for forest conservation and restoration, with specific attention to refuge patterns of importance for forest landbirds of conservation priority. The large amount of public land within the ecoregions (31–80%) suggests that opportunities exist for coarse and meso-scale approaches to conserving and restoring ecological processes affecting the refuges, particularly historical fire regimes. Forests dominate both ecoregions and refuges, but refuge forest patches are generally larger and more aggregated than in associated ecoregions. Broadleaf taxa have increased in dominance in the ecoregions and displaced fire-dependent taxa such as pine (Pinus spp.) and other coniferous species; these changes in forest composition have likely also affected refuge forests. Despite compositional changes, larger forest patches on refuges suggests that they may provide better habitat for area-sensitive forest landbirds of mature, compositionally diverse forests than surrounding lands if management continues to promote increased patch size. We reason that although fine-scale research and monitoring for species of conservation priority is important, broad scale (ecoregional) assessments provide crucial context for effective forest and wildlife management in protected areas.  相似文献   
245.
European bison, the largest mammal in Europe, after being exterminated in the wild and then restored during the 20th century is still listed by the International Union for Conservation of Nature (IUCN Red List of Threatened Species) as a species vulnerable to extinction. However, the increasing number of European bison, through creation of new and expansion of existing populations strongly increases the risk of human-bison conflict in the near future. We analyzed the depredation of farm crops by bison and the factors influencing the level of damage in the vicinity of two forest areas inhabited by bison in northeastern Poland. Between 2000 and 2010, the total cost of compensation was 196,200. The level of damage and amount of compensation was increasing from year to year in both forests and correlated with the number of bison. The majority of damage (57?% of cases) was recorded in winter (December-March). Snow depth and temperature did not influence the frequency of damage. The incidences of damage increased with decreasing distance from the woodland patches, therefore, 69?% of cases in Bia?owie?a Forest, and 80?% in Knyszyn Forest were recorded closer than 0.5?km from nearest woodland patch. The majority of the crops damaged by bison were cereals (61?%) but also hay (20?%) and rape (13?%). When compared to the availability of crops, bison strongly selected rape and rye in both regions. This study is the first addressing the increasing problem of human-bison conflict in re-introduced populations and analyzing long-term data on crop depredation. Such situations probably occur in the majority of growing and expanding bison populations, however, it has not yet to be monitored and is rather neglected in post-Soviet countries.  相似文献   
246.
浊漳河山西省潞城市境内干流段及南源段河道生态环境目前最突出的问题在于水质恶化、水量减少以及生物多样性衰退。本文从水质、水量、生物状况三个要素出发,通过建立浊漳河潞城市境内河段的水生态健康评价体系,对浊漳南源及干流段进行了生态健康诊断。结果显示,浊漳干流段生态健康总指数36.74,呈生态病态状;南源段生态健康总指数60.03,呈基本健康状态。据此,浊漳河潞城境内段目前的核心问题是生态恢复问题,应当针对其存在的问题选择适当的生态修复模式,采取相应的生态环境管理方法,把生态系统的恢复和重建作为其流域治理的最终目标。  相似文献   
247.
Strandberg M  Damgaard C  Degn HJ  Bak J  Nielsen KE 《Ambio》2012,41(4):393-401
We report observations of disappearance of Erica tetralix in wet heathland, which is unlikely to be caused by competition, as E. tetralix is dying before its place is taken up by other species. To investigate the causes, we used both old and new data. Results showed that presence of Molinia caerulea and Calluna vulgaris were substantial in the former E. tetralix dominated areas. Measurements of the C/N ratio in the morlayer were between 21 and 26 under the E. tetralix stands. As the expected C/N ratio in a healthy nutrient poor ecosystem like the E. tetralix wet heathland is around 30, this indicates that the ratio is probably decreasing and, correspondingly, the probability of nitrogen leaching from the ecosystem is increasing. The morlayer pH was extremely low—between 3.03 and 3.78. This represents a pH decline since the 1960s, where pH values generally were above 4. This supports the hypothesis that the decrease in morlayer pH is the major factor explaining the disappearance of E. tetralix and that measures to increase pH should be considered as part of the recommendations for relevant future management.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-012-0251-z) contains supplementary material, which is available to authorized users.  相似文献   
248.
We quantified horizontal transport patterns and the net exchange of nutrients between shallow regions and the open sea in the Baltic proper. A coupled biogeochemical-physical circulation model was used for transient simulations 1961-2100. The model was driven by regional downscaling of the IPCC climate change scenario A1B from two global General Circulation Models in combination with two nutrient load scenarios. Modeled nutrient transports followed mainly the large-scale internal water circulation and showed only small circulation changes in the future projections. The internal nutrient cycling and exchanges between shallow and deeper waters became intensified, and the internal removal of phosphorus became weaker in the warmer future climate. These effects counteracted the impact from nutrient load reductions according to the Baltic Sea Action Plan. The net effect of climate change and nutrient reductions was an increased net import of dissolved inorganic phosphorus to shallow areas in the Baltic proper.  相似文献   
249.

Purpose  

Prevalence of organic pollutants or their natural analogs in soil is often assumed to lead to adaptation in the bacterial community, which results in enhanced bioremediation if the soil is later contaminated. In this study, the effects of soil type and contamination history on diesel oil degradation and bacterial adaptation were studied.  相似文献   
250.

Introduction  

High concentrations of hexabromocyclododecane (HBCD) sometimes recorded in free-range hens' eggs are thought to be due to soil ingestion. Of the three stereoisomers of HBCD (α-, β-, and γ-HBCD), γ-HBCD is the main component in the commercial mixture, as well as in environmental matrices, whereas the isomer profile is α-dominated in biota. In fish and in mammals, this shift is thought to be due to a rapid elimination of γ-HBCD and to its bioisomerization to the more persistent α-HBCD. The aim of the current controlled study was to better understand the fate of ingested HBCD in laying hens. The isomer profile in soil being γ-dominated, excretion kinetics of γ-HBCD into egg yolk, and accumulation in liver and in abdominal fat were investigated.  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