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   23588篇
  免费   251篇
  国内免费   383篇
安全科学   619篇
废物处理   1003篇
环保管理   3124篇
综合类   3806篇
基础理论   6213篇
环境理论   7篇
污染及防治   6068篇
评价与监测   1556篇
社会与环境   1676篇
灾害及防治   150篇
  2022年   240篇
  2021年   235篇
  2020年   177篇
  2019年   251篇
  2018年   360篇
  2017年   382篇
  2016年   564篇
  2015年   396篇
  2014年   612篇
  2013年   1898篇
  2012年   722篇
  2011年   992篇
  2010年   832篇
  2009年   849篇
  2008年   1042篇
  2007年   1053篇
  2006年   949篇
  2005年   764篇
  2004年   832篇
  2003年   752篇
  2002年   713篇
  2001年   973篇
  2000年   645篇
  1999年   382篇
  1998年   314篇
  1997年   291篇
  1996年   324篇
  1995年   349篇
  1994年   342篇
  1993年   290篇
  1992年   317篇
  1991年   292篇
  1990年   322篇
  1989年   297篇
  1988年   246篇
  1987年   237篇
  1986年   198篇
  1985年   224篇
  1984年   246篇
  1983年   231篇
  1982年   231篇
  1981年   231篇
  1980年   171篇
  1979年   190篇
  1978年   160篇
  1977年   149篇
  1975年   142篇
  1974年   146篇
  1973年   149篇
  1972年   176篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
171.
This paper considers the evolution of attempts to control and manage air pollution, principally but not exclusively focussing upon the challenge of managing air pollution in urban environments. The development and implementation of a range of air pollution control measures are considered. Initially the measures implemented primarily addressed point sources, a small number of fuel types and a limited number of pollutants. The adequacy of such a source-control approach is assessed within the context of a changing and challenging air pollution climate. An assessment of air quality management in the United Kingdom over a 50-year timeframe exemplifies the range of issues and challenges in contemporary air quality management. The need for new approaches is explored and the development and implementation of an effects-based, risk management system for air quality regulation is evaluated.  相似文献   
172.
173.
174.
微生物絮凝剂改善城市污水厂浓缩污泥脱水性能的研究   总被引:7,自引:2,他引:5  
采用酱油曲霉(Aspergillus sojae)产生的微生物絮凝剂(MBF)作为污泥絮凝脱水剂,对城市污水处理厂浓缩污泥进行调理,确定该絮凝剂对浓缩污泥脱水的处理工艺参数为:微生物絮凝液最佳投加体积为6%~8%(体积比),发挥絮凝作用的最适污泥温度为28~32℃,最适pH为6~7。经微生物絮凝剂调理的污泥在3 000 r/min离心9 min,污泥脱水率高达82.7%,滤饼含水率降低至77.3%,污泥脱水后体积减至原来的1/5左右。  相似文献   
175.
The paper describes results obtained in the development of a previous research. We study here, in fast firing, the sintering behaviour and measure some properties of tiles containing a mixture of 60 wt% of paper mill sludge and 40 wt% of glass cullet. The behaviour of this material is compared to those displayed by materials obtained by the same mixture added with 10, 20 and 30 wt% of a natural red clay. In parallel, the same properties are measured also on a reference blend, which is presently used to produce commercial tiles. We show that powders containing 60 wt% of paper sludge and 40 wt% of glass cullet to which 30 wt% of clay is added give rise to materials that display a stable sintering process and have good hardness and strength and therefore could be used for the industrial production of tiles.  相似文献   
176.
177.
Changes in the autotrophic pico- (0.2–2 μm), nano- (2–20 μm), and microplankton (>20 μm) biomass (chlorophyll a) and primary production were measured in the estuarine and coastal waters off Cochin, southwest coast of India during the onset and establishment of a monsoon. During this period, the estuary was dominated by nutrient-rich freshwater, whereas the coastal waters were characterized with higher salinity values (>30 psu) and less nutrients. The average surface chlorophyll a concentrations and primary production rates were higher in the estuary (average 13.7 mg m???3 and 432 mgC m???3 day???1) as compared to the coastal waters (5.3 mg m???3 and 224 mgC m???3 day???1). The nanoplankton community formed the major fraction of chlorophyll a and primary production, both in the estuary (average 85 ± SD 8.3% and 81.2 ± SD 3.2%) and the coastal waters (average 73.2 ± SD 17.2% and 81.9 ± 15.7%). Nanoplankton had the maximum photosynthetic efficiency in the coastal waters (average 4.8 ± SD 3.9 mgC mgChl a m???3 h???1), whereas in the estuary, the microplankton had higher photosynthetic efficiency (average 7.4 ± 7 mgC mgChl a m???3 h???1). The heavy cloud cover and increased water column turbidity not only limit the growth of large-sized phytoplankton in the Cochin estuary and coastal waters but also support the proliferation of nanoplankton community during the monsoon season, even though large variation in nanoplankton chlorophyll a and production exists between these two areas.  相似文献   
178.
The purpose of this study is to determine the impact of leachate recirculation on the degradation of municipal solid wastes (bioreactor concept). The study was carried out using columns containing approximately 50 kg of waste, in order to follow waste degradation over a limited time. Three types of waste were studied: fresh waste of standard composition, fresh waste of fermentable composition and some 8-yr-old waste extracted from a site in France. Measurement of the global parameters, such as chemical oxygen demand (COD), volatile acidity, alkalinity, leachate conductivity, methane potential of the wastes and biogas production monitoring (volume of CO2 and CH4 produced), were carried out. The quantity of oxydizable matter and biogas production was increased by the leachate recirculation, and the duration of the first degradation phases was reduced in all cases. Chloride, ammonium and organic pollution accumulation was observed according to the duration of recirculation. After 400 days of degradation, waste stabilization seemed to be reached for all of the recirculated columns (COD<300 mg/L O2, and methane potential reached).  相似文献   
179.
Several lysimeter scenarios and approaches exist to study the fate of agro-chemicals or contaminants from deposition in soil columns. In many systems just transport and leaching of the parent compound is followed, in some systems the leaching and transport of the metabolites is investigated as well. In more sophisticated lysimeter systems the volatilization and also the mineralization of the applied chemicals can be additionally monitored. Depending on the lysimeter system used and on the fact whether the applied chemicals are 14C-labeled or not, different results and various interpretations of the results might be achieved. Different lysimeter systems are described in this paper and a real dataset of a specific lysimeter experiment was transferred and evaluated in a virtual approach in the different lysimeter systems in order to show the advantages and disadvantages of the various systems.  相似文献   
180.
MULTI INCREMENT® and discrete sampling strategies were used to estimate the average concentration and the three‐dimensional distribution of TCE in a 3,300‐m3 zone composed of two decision units (e.g., area of concern, population, exposure unit). Authors of this article and a private contractor (Stanley Consultants Inc.), respectively, implemented these two sampling strategies independently. Compared to discrete sampling, the MULTI INCREMENT sampling strategy identified more locations where percent‐level concentrations of TCE have migrated, is more economical, and provided greater data quality. © 2008 Wiley Periodicals, Inc.  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