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   531篇
  免费   3篇
  国内免费   4篇
安全科学   13篇
废物处理   42篇
环保管理   64篇
综合类   59篇
基础理论   106篇
环境理论   1篇
污染及防治   183篇
评价与监测   41篇
社会与环境   26篇
灾害及防治   3篇
  2023年   7篇
  2022年   22篇
  2021年   13篇
  2020年   10篇
  2019年   11篇
  2018年   17篇
  2017年   15篇
  2016年   26篇
  2015年   15篇
  2014年   23篇
  2013年   54篇
  2012年   27篇
  2011年   48篇
  2010年   22篇
  2009年   18篇
  2008年   38篇
  2007年   35篇
  2006年   33篇
  2005年   23篇
  2004年   13篇
  2003年   18篇
  2002年   16篇
  2001年   2篇
  2000年   5篇
  1999年   3篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   2篇
  1994年   4篇
  1993年   3篇
  1990年   3篇
  1989年   3篇
  1986年   3篇
  1985年   1篇
  1971年   1篇
排序方式: 共有538条查询结果,搜索用时 31 毫秒
301.
Current brief aims to introduce the concept of safety in European industrial sectors, particularly in mechanics and machinery industry. It also highlights the importance to ensure an even level of machinery safety along the European Union, setting up the appropriate frame and procedures to keep it under control. An overview over market surveillance activities for machinery (regulations, main actors and their roles) first at Community level, and secondly an approach to one of the Member States is also introduced.  相似文献   
302.
303.
304.
Transparency and reproducibility remain challenges for sustainability assessment, particularly in developing world contexts where formal scientific information is often limited. We posit that even in such contexts, sustainability assessment can be productive and informative if the underlying assumptions about sustainability are made transparent. Thus, the process of assessment can be as instructive as the results, if not more so. In this article, we describe and discuss how we combined multicriteria decision analysis and system analysis as a unified approach to sustainability assessment. This approach is transparent, practical, flexible, and reproducible; it also facilitates the development of recommendations for enhancing sustainability. We illustrate the approach with examples from a recent environmental sustainability assessment of irrigated commercial maize production in Sinaloa, Mexico.  相似文献   
305.
306.
Petroleum hydrocarbons are considered one of the main organic chemicals found in water bodies. In the present study, the median lethal concentration (LC50) was estimated for mullet Mugil liza after acute exposure to petroleum water-soluble fraction (PWSF). Furthermore, histopathological studies and micronuclei frequency were also performed in order to observe deleterious effects of medium-term exposition to PWSF. Mullets (25?±?2.3 g) were exposed to chronic concentrations (1.7, 3.5 and 7 % of PWSF), plus the control group, for 14 and 7 days of clearance time. Throughout the experimental period (1, 4, 14 and 21 days), blood samples were collected for analysis of micronucleus (MN) and liver and gills for histopathological study. For these procedures, seven fish were sampled per concentration tested. The LC50-96 h was estimated at 37.5 % of the PWSF. The time required for MN induction was 96 h of exposure. The time of clearance was sufficient to achieve a MN frequency similar to that of the control group. Histopathological studies showed severe changes in the gill and liver tissues. The most relevant histopathology in the gills was telangiectasia. Hepatic histopathology such as cholestasis, dilated sinusoids and inflammatory infiltrates were commonly described. The MN test and histological study effectively detected damages caused by medium-term exposition to the PWSF, and despite the toxicity, a few days without exposure can minimize PWSF genotoxicity in juveniles of M. liza.  相似文献   
307.
Derivatization of cyprodinil with different reagents and solvents has been evaluated to improve the GC/MS characterization of this fungicide. After assessing some preliminary acylation and silylation reactions, derivatization with anhydrous heptafluorobutyric anhydride (HFBA) was selected as the best derivatization option for cyprodinil. The HFBA-cyprodinil derivative was clearly identified and characterized by GC/MS (ion-trap). The spectrum of the HFBA derivative of cyprodinil was characterized by the base peak, 252 m/z ion, and two other ions with relative abundances of 5% (224 m/z ion) and 4% (420 m/z molecular ion). Conversion rates in the range of 83–92% were obtained when 0.1–1 μg cyprodinil were derivatized in vial without solvent at 25ºC temperature for 120 min, with 5 μL HFBA and 5 μL pyridine. Simultaneous extraction-derivatization of cyprodinil in supercritical carbon dioxide was only achieved when no modifier was present, but conversion/recovery rates obtained in the replicate experiments carried out with 15 mL supercritical carbon dioxide at 50°C and 200 atm (n = 5), 300 atm (n = 7), and 400 atm (n = 5) were no reproducible (RSD > 50%) and ranged between 10% and 45% (related to the signal obtained for derivatization in vial).  相似文献   
308.
Cohort life table experiments were conducted on M. macrocopa using copper at three nominal concentrations (as CuSO4, 0.1, 0.2 and 0.4 mg L? 1, in addition to controls) for different periods of exposure (3 to 24 h). Age-specific survivorship of M. macrocopa decreased in relation to age of the cohort, concentration and duration of exposure to copper. Age-specific life expectancy curves also decreased with increasing age of the cohort. However, at low copper levels and shorter exposure time, there was an increase in life expectancy when the cohort was about 10 day old. Fecundity (m x ) was nearly regular in controls; however, at higher copper levels and longer duration of exposure, the offspring production was more oscillating. The offspring production completely ceased when continuously exposed to CuSO4 at 0.4 mg L? 1. Most of the measured demography variables significantly decreased with increasing concentration of Cu in the medium. The average lifespan and life expectancy at birth varied 2.9 to 9.6 and 2.4 to 9.1 days, respectively. Gross reproductive rate (GRR) varied from 31 to 89 offspring female? 1 lifespan? 1, while the survival-weighted net reproductive rates were nearly one-third of the GRR. Generation time of M. macrocopa varied from 5 to 7 days while the rate of population increase ranged from 0.36 to 0.84 per day. The results are discussed in relation to the sensitivity of M. macrocopa to copper toxicity and the necessity of amending the national water quality criteria in Mexico.  相似文献   
309.
ABSTRACT

The environmental agency in the metropolitan area of Mexico City has launched a program to introduce more energy-efficient modes of transport, one of which is the use of alternative and less polluting fuels. With that perspective in mind, a liquefied petroleum gas (LPG) fleet of vehicles is exempt of the mandatory "one day without a car" program if the emission of pollutants is below the standard authorized for that specific purpose. Today, about 28,000 light-duty vehicles and heavy-duty trucks circulate in the area, most of them as aftermarket converted vehicles. In this work, we evaluated regulated exhaust emission and other parameters on 134 representative vehicles of that fleet. From the data obtained, an estimate of emission factors and their contribution to the global emission in the metropolitan area is provided. It is concluded that more than 95% of the in-use vehicles using LPG presented regulated emissions which exceeded in one or more the environmental regulations values required for certification. The poor maintenance of the vehicles and the type of conversion kit installed could be the culprits of the results obtained.  相似文献   
310.
ABSTRACT

An estimation of hydrocarbon emissions caused by the consumption of liquefied petroleum gas (LPG) in the Metropolitan Area of Mexico City (MAMC) is presented. On the basis of experimental measurements at all points of handling, during the distribution process, and during the consumption of LPG in industrial devices and domestic appliances, an estimated 76,414 tons/year are released to the air. The most important contribution is found during the domestic consumption of LPG (70%); this makes the control initiatives available to the consumer. By developing a control program of LPG losses, a 77% reduction in emission is expected in a 5-yr period.

The calculated amounts of LPG emissions when correlated with the consumption of LPG, combined with information from air samples from the MAMC, do not point to LPG emissions as the most important factor contributing to tropospheric ozone in the air in Mexico City.  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