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   993篇
  免费   23篇
  国内免费   22篇
安全科学   48篇
废物处理   42篇
环保管理   186篇
综合类   134篇
基础理论   235篇
环境理论   2篇
污染及防治   248篇
评价与监测   104篇
社会与环境   33篇
灾害及防治   6篇
  2023年   6篇
  2022年   10篇
  2021年   13篇
  2020年   10篇
  2019年   13篇
  2018年   23篇
  2017年   16篇
  2016年   29篇
  2015年   23篇
  2014年   19篇
  2013年   84篇
  2012年   55篇
  2011年   64篇
  2010年   51篇
  2009年   47篇
  2008年   57篇
  2007年   69篇
  2006年   71篇
  2005年   51篇
  2004年   46篇
  2003年   42篇
  2002年   38篇
  2001年   27篇
  2000年   16篇
  1999年   14篇
  1998年   16篇
  1997年   7篇
  1996年   18篇
  1995年   12篇
  1994年   10篇
  1993年   7篇
  1992年   9篇
  1990年   12篇
  1989年   2篇
  1988年   3篇
  1987年   5篇
  1986年   4篇
  1985年   6篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1981年   7篇
  1980年   2篇
  1979年   4篇
  1973年   2篇
  1971年   1篇
  1966年   1篇
  1961年   1篇
  1957年   1篇
  1955年   1篇
排序方式: 共有1038条查询结果,搜索用时 46 毫秒
981.
This paper examines the impact of various social, economic and political changes on the work of the Indian Forest Service, the elite organization concerned with environmental management in India. It is noted that whilst many leading authors criticize this organization, nobody has taken the time to analyse the role of the Indian Forest Service and the way it has responded to the many challenges it has faced in the last 20 years. This paper seeks to rectify this by focusing on three key challenges: (1) due to economic liberalization the actual work that the forest officer is expected to undertake has changed beyond recognition; (2) political manipulation and correspondingly accusations of corruption have increased; (3) social changes and their impact on recruitment into the Indian Forest Service. It is concluded that, despite the many challenges which the Indian Forest Service has faced over the years, it is remarkably resilient and remains the most powerful agent in rural India.  相似文献   
982.
This article addresses the removal of methyl tertiary‐butyl ether (MTBE) from water, using Fenton's Reagent. Although complete mineralization of MTBE by Fenton's Reagent was not achieved, greater than 99 percent destruction of MTBE was realized. This was accomplished at a Fe+2:H2O2 ratio of 1:1 and 1 hour of contact time. In all tests, twice the stoichiometric ratio of H2O2 to MTBE was used. The major by‐products were tertiary‐butyl alcohol, tertiary‐butyl formate, and acetone with traces of 2‐methyl‐1‐propene (isobutylene). While small quantities of O2 evolved, no significant quantity of CO2 gas was detected.  相似文献   
983.
984.
要减少/消除危险物资和产品的生成,世界需要更多的资源.发达国家一直在增加的危险废物生成需要靠强制手段来缩减.当前实行的危险废物再生办法是不可持续的.当今最重要的两种危险废物贸易,一是废船解体业(经常出现在亚洲拆解厂),二是电子垃圾从大多数高度工业化国家出口到发展中国家处理.这每一种活动,都对人类健康和环境有严重影响.  相似文献   
985.
青岛近海PCDD/Fs的沉积通量、毒性当量及来源   总被引:5,自引:0,他引:5  
用高分辨率气相色谱-质谱方法对青岛胶州湾内外表层沉积物、柱状岩心及贻贝样品中的17种毒性多氯代二苯并二 /呋喃(PCDD/Fs)进行了分析和讨论.表层沉积物的SP4-8CDD/Fs含量范围在11.6~369pg/g dw,主要以P4-8CDFs为主.S2,3,7,8-PCDD/Fs含量范围4.1~232.4pg/g dw.在环流作用下沉积物中形成了明显的东-西分布格局.除河口处外,PCDD/F同系物分布基本上相同,即低氯代PCDD/Fs占主导.SP4-8CDD/Fs沉积通量从1951年起逐渐增大,STEQ沉积通量从1980年显著增大.青岛近海PCDD/Fs的来源相对恒定,推测为城市污水污泥和大气沉降.贝肉中S2,3,7,8-PCDD/Fs为2.9~5.1pg/g dw. TEQ的主要来源为2,3,4,7,8-PeCDF(35%)、2,3,7,8-TCDF(30%)、2,3,7,8,-TCDD(30%).  相似文献   
986.
The fisheries of Lake Victoria have undergone a major transformation over the last three decades. The character of the lake has been subject to the influence of many powerful factors including: substantial increases in fishing effort; growing integration into the global fish market; acceleration of anthropogenic activities in the catchment area; demographic change; the influence of adverse shifts in the climate; and introduction of exotic plant and animal species. The task of managing the lake's resources, therefore, has never been more daunting. This article argues that, in most cases, the authorities charged with achieving the goal of sustainable development for the fishery, have failed to address the symptoms—let alone the origins—of the current unsustainable tendencies embedded in the social, economic and political fabric of Lake Victoria's riparian States. It is these factors that directly impinge upon the success of management initiatives for the lake. The article argues that if sustainable development is to be achieved, then stakeholders must act in concert, eliminate unsustainable practices and reprogramme development plans to focus on realistic goals. A possible way forward will be to develop a participatory management system.  相似文献   
987.
ABSTRACT: Turfgrass systems are one of the most intensively managed land uses in the United States. Establishment and maintenance of high quality turfgrass usually implies substantial inputs of water, nutrients, and pesticides. The focus of this work was to quantify the concentration and loading of a typically maintained municipal turfgrass environment on surface water. Water quantity and quality data were collected from a golf course in Austin, Texas, and analyzed for a 13‐month period from March 20, 1998, to April 30, 1999. Twenty‐two precipitation events totaling 722 mm, produced an estimated 98 mm of runoff. Nutrient analysis of surface runoff exiting the course exhibited a statistically significant (p < 0.05) increase in median nitrate plus nitrite nitrogen (NO3+NO2‐N) concentration compared to runoff entering the course, a statistically significant decrease in ammonia nitrogen (NH4‐N), but no difference in orthophosphate (PO4‐P). During the 13‐month period, storm runoff contributed an estimated 2.3 kg/ha of NO3+NO2‐N and 0.33 kg/ha of PO4‐P to the stream. Storm flow accounted for the attenuation of 0.12 kg/ha of NH4‐N. Baseflow nutrient analysis showed a statistically significant increase in median NO3+NO2‐N, a significant reduction in NH4‐N, and no change in PO4‐P. Estimated NO3+NO2‐N mass in the baseflow was calculated as 4.7 kg/ha. PO4‐P losses were estimated at 0.06 kg/ha, while 0.8 kg/ha of NH4‐N were attenuated in baseflow over the study period. Even though nutrient concentrations exiting the system rarely exceeded nutrient screening levels, this turfgrass environment did contribute increased NO3+NO2‐N and PO4‐P loads to the stream. This emphasizes the need for parallel studies where management intensity, soil, and climate differ from this study and for golf course managers to utilize an integrated management program to protect water quality while maintaining healthy turfgrass systems.  相似文献   
988.
Monitoring the population trends of multiple animal species at a landscape scale is prohibitively expensive. However, advances in survey design, statistical methods, and the ability to estimate species presence on the basis of detection-nondetection data have greatly increased the feasibility of species-level monitoring. For example, recent advances in monitoring make use of detection-nondetection data that are relatively inexpensive to acquire, historical survey data, and new techniques in genetic evaluation. The ability to use indirect measures of presence for some species greatly increases monitoring efficiency and reduces survey costs. After adjusting for false absences, the proportion of sample units in a landscape where a species is detected (occupancy) is a logical state variable to monitor. Occupancy monitoring can be based on real-time observation of a species at a survey site or on evidence that the species was at the survey location sometime in the recent past. Temporal and spatial patterns in occupancy data are related to changes in animal abundance and provide insights into the probability of a species' persistence. However, even with the efficiencies gained when occupancy is the monitored state variable, the task of species-level monitoring remains daunting due to the large number of species. We propose that a small number of species be monitored on the basis of specific management objectives, their functional role in an ecosystem, their sensitivity to environmental changes likely to occur in the area, or their conservation importance.  相似文献   
989.
990.
Nepstad DC  Tohver IM  Ray D  Moutinho P  Cardinot G 《Ecology》2007,88(9):2259-2269
Severe drought episodes such as those associated with El Ni?o Southern Oscillation (ENSO) events influence large areas of tropical forest and may become more frequent in the future. One of the most important forest responses to severe drought is tree mortality, which alters forest structure, composition, carbon content, and flammability, and which varies widely. This study tests the hypothesis that tree mortality increases abruptly during drought episodes when plant-available soil water (PAW) declines below a critical minimum threshold. It also examines the effect of tree size, plant life form (palm, liana, tree) and potential canopy position (understory, midcanopy, overstory) on drought-induced plant mortality. A severe, four-year drought episode was simulated by excluding 60% of incoming throughfall during each wet season using plastic panels installed in the understory of a 1-ha forest treatment plot, while a 1-ha control plot received normal rainfall. After 3.2 years, the treatment resulted in a 38% increase in mortality rates across all stems >2 cm dbh. Mortality rates increased 4.5-fold among large trees (>30 cm dbh) and twofold among medium trees (10-30 cm dbh) in response to the treatment, whereas the smallest stems were less responsive. Recruitment rates did not compensate for the elevated mortality of larger-diameter stems in the treatment plot. Overall, lianas proved more susceptible to drought-induced mortality than trees or palms, and potential overstory tree species were more vulnerable than midcanopy and understory species. Large stems contributed to 90% of the pretreatment live aboveground biomass in both plots. Large-tree mortality resulting from the treatment generated 3.4 times more dead biomass than the control plot. The dramatic mortality response suggests significant, adverse impacts on the global carbon cycle if climatic changes follow current trends.  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