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   517篇
  免费   10篇
  国内免费   4篇
安全科学   28篇
废物处理   26篇
环保管理   66篇
综合类   45篇
基础理论   125篇
污染及防治   162篇
评价与监测   39篇
社会与环境   30篇
灾害及防治   10篇
  2023年   7篇
  2022年   10篇
  2021年   10篇
  2020年   8篇
  2019年   10篇
  2018年   12篇
  2017年   13篇
  2016年   17篇
  2015年   15篇
  2014年   16篇
  2013年   47篇
  2012年   25篇
  2011年   43篇
  2010年   29篇
  2009年   30篇
  2008年   28篇
  2007年   33篇
  2006年   34篇
  2005年   33篇
  2004年   19篇
  2003年   14篇
  2002年   17篇
  2001年   4篇
  2000年   3篇
  1999年   6篇
  1998年   4篇
  1997年   6篇
  1996年   4篇
  1995年   6篇
  1994年   6篇
  1993年   3篇
  1992年   4篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1985年   2篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1974年   1篇
  1964年   1篇
排序方式: 共有531条查询结果,搜索用时 0 毫秒
81.
Data are reported from a postal questionnaire completed by 747 residents of two urban local authority areas within which there were sites of brownfield land with significant levels of contamination. Respondents rated their perceptions of the extent to which their neighbourhood and own home were relatively vulnerable to contamination, their concern about possible effects of contamination, their satisfaction with their council in terms of consultation with residents on housing and development issues, and their trust in their council with respect to contaminated land risks. Satisfaction with, and trust in, the council was generally low in both areas, and especially so among those who perceived themselves to be more vulnerable to contamination. Nonetheless, dissatisfaction was less marked in the area where the local authority, according to background information, had pursued a more open and proactive style of risk communication and consultation with residents. The main predictors of trust, across both areas, were perceptions that the council was openly prepared to tell residents what they knew, and that the council had residents' interests at heart. Implications are discussed for the impact of different modes of risk communication on trust.  相似文献   
82.
ORSANCO and the six Ohio River main stem states have been working to align states' fish consumption advisories (FCAs) to enhance the value of advice issued to the public. To achieve this goal, ORSANCO worked closely with a panel consisting of state and USEPA representatives. The result of this effort is the Ohio River Fish Consumption Advisory Protocol (ORFCAP). The ORFCAP represents a single set of variables agreed upon by the panel that allows for a standardized protocol to create advisory thresholds to which states can defer to issue consumption advice for the Ohio River. The ORFCAP identifies ORSANCO as a clearinghouse for data which will be distributed to the panel for decision making. Other components include identifying primary contaminants of concern (PCBs and mercury) and dividing the river into four reporting units. The protocol was developed to issue FCAs for the protection of sensitive populations using five advisory groupings for PCBs and four for mercury. Specific variables used in the calculation of advisory thresholds such as health protection values, cooking reductions, average meal sizes, etc., were selected by the panel. Lastly, the protocol calls for FCA decisions to be based on analysis of the most recent 10?years of data for each species in each reporting unit to determine size class needs and advisory groupings. Upon pending implementation of the protocol by the main stem states, these decisions will be made annually through a series of discussions involving ORSANCO, the panel, and other appropriate state personnel.  相似文献   
83.
Calculations of large-scale displacement distances were made to evaluate the combined effect of small-scale movement pattern of a Collembola, Protaphorura armata. The effect of presence of food and conspecific density on turning angle, step length and activity/motility was investigated. Calculations of net square displacement were made both by assuming correlated random walk (CRW) and by resampling data to account for correlation structures in movement patterns that violate the assumptions of CRW.  相似文献   
84.
ABSTRACT

Pig production systems in China are shifting from small to industrial scale. Significant variation in housing ammonia (NH3) emissions can exist due to differences in diet, housing design, and management practices. However, there is a knowledge gap regarding the impacts of farm-scale in China, which may be critical in identifying hotspots and mitigation targets. Here, continuous in-situ NH3 concentration measurements were made at pig farms of different scales for sows and fattening pigs over periods of 3–6 days during two different seasons (summer vs. winter). For the sow farms, NH3 emission rates were greater at the small farm (summer: 0.52 g pig?1 hr?1; winter: 0.21 g pig?1 hr?1) than at the large farm (summer: 0.34 g pig?1 hr?1; winter: 0.12 g pig?1 hr?1). For the fattening pig farms, NH3 emission rates were greater at the large farm (summer: 0.22 g pig?1 hr?1; winter: 0.16 g pig?1 hr?1) than at the small farm (summer: 0.19 g pig?1 hr?1; winter: 0.07 g pig?1 hr?1). Regardless of farm scale, the NH3 emission rates measured in summer were greater than those in winter; the NH3 emission rates were greater in the daytime than at the nighttime; a positive relationship (R2 = 0.06–0.68) was established between temperature and NH3 emission rate, whereas a negative relationship (R2 = 0.10–0.47) was found between relative humidity and NH3 emission rate. The effect of farm-scale on indoor NH3 concentration could mostly be explained by the differences in ventilation rates between farms. The diurnal variation in NH3 concentration could be partly explained by ventilation rate (R2 = 0.48–0.78) in the small traditional farms and by emission rate (R2 = 0.26–0.85) in the large industrial farms, except for the large fattening pig farm in summer. Overall, mitigation of NH3 emissions from sow farms should be a top priority in the North China Plain.

Implications: The present study firstly examined the farm-scale effect of ammonia emissions in the North China Plain. Of all farms, the sow farm was identified as the greatest source of ammonia emission. Regardless of farm scale, ammonia emission rates were observed to be higher in summer. Ammonia concentrations were mostly higher in the large industrial farms partly due to lower ventilation rates than in the small traditional farms.  相似文献   
85.
Fetal surgery has become a clinical reality, with interventions for twin-to-twin transfusion syndrome (TTTS) and spina bifida demonstrated to improve outcome. Fetal imaging is evolving, with the use of 3D ultrasound and fetal MRI becoming more common in clinical practise. Medical imaging analysis is also changing, with technology being developed to assist surgeons by creating 3D virtual models that improve understanding of complex anatomy, and prove powerful tools in surgical planning and intraoperative guidance. We introduce the concept of computer-assisted surgical planning, and present the results of a systematic review of image reconstruction for fetal surgical planning that identified six articles using such technology. Indications from other specialities suggest a benefit of surgical planning and guidance to improve outcomes. There is therefore an urgent need to develop fetal-specific technology in order to improve fetal surgical outcome. © 2015 The Authors. Prenatal Diagnosis published by John Wiley & Sons Ltd.  相似文献   
86.
87.
ABSTRACT

At a variety of Canadian monitoring sites, carbonaceous compounds were estimated to account for an average of 50% of fine particle mass. These estimates were determined by subtracting the total fine particle mass associated with inorganic compounds from the total fine mass determined gravimetrically. This approach, which yields an upper limit estimate of the total amount of carbon-related mass was necessary since particulate carbon was not measured in the Canadian National Air Pollution Surveillance (NAPS) network. In this paper, total carbon estimates are evaluated against organic and elemental carbon measurements at locations in the Greater Vancouver area and Toronto. In addition, particle nitrate measurements at seven Canadian locations are used to determine the importance of nitrate relative to total mass and to examine the sampling artifacts due to the loss of particle nitrate from Teflon filters used in the NAPS di-chotomous samplers.

Measurements of organic and elemental carbon indicated that the total carbon estimation approach provides representative estimates of the average contribution by carbonaceous material to the total fine and coarse mass. The average total carbon among all Vancouver area measurements (N = 225) was 4.28 μg m-3, while the estimated value was 4.34 μg m-3. There was a larger discrepancy between Toronto total carbon measurements (12.1 μg m-3) and estimates (8.8 μg m-3), which is attributed in part to sampling of particles above 10 mm in diameter. However, the R2 relating the measurements and estimates was about 0.71 for both areas. Linear regression slopes of 0.98 for Vancouver and 0.78 for Toronto (nonsignificant intercepts) indicate little bias in the Vancouver estimates, but a tendency for underestimation as the observed total carbon concentration increased in Toronto.

Annually, nitrate was responsible for 17% and 12% of the fine mass in the Vancouver area and Ontario, respectively. In contrast, at two rural locations in southern Quebec and Nova Scotia, only 6% of fine mass was associated with nitrate. Due to filter losses, nitrate concentrations determined through the NAPS dichot sampling were much lower than actual concentrations (0.44 μg m-3 vs. 2.63 μg m-3). As a result of these losses (attributed mostly to loss during laboratory storage), previous total carbon estimates for the Canadian NAPS sites were likely to have been overestimated on average by about 10%.  相似文献   
88.
Hypoxia has occurred intermittently over the Holocene in the Baltic Sea, but the recent expansion from less than 10 000 km2 before 1950 to >60 000 km2 since 2000 is mainly caused by enhanced nutrient inputs from land and atmosphere. With worsening hypoxia, the role of sediments changes from nitrogen removal to nitrogen release as ammonium. At present, denitrification in the water column and sediments is equally important. Phosphorus is currently buried in sediments mainly in organic form, with an additional contribution of reduced Fe-phosphate minerals in the deep anoxic basins. Upon the transition to oxic conditions, a significant proportion of the organic phosphorus will be remineralized, with the phosphorus then being bound to iron oxides. This iron-oxide bound phosphorus is readily released to the water column upon the onset of hypoxia again. Important ecosystems services carried out by the benthic fauna, including biogeochemical feedback-loops and biomass production, are also lost with hypoxia. The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan.  相似文献   
89.
Monitored natural attenuation (MNA) has recently emerged as a viable groundwater remediation technology in the United States. Area 6 at Dover Air Force Base (Dover, DE) was chosen as a test site to examine the potential for MNA of tetrachloroethene (PCE) and trichloroethene (TCE) in groundwater and aquifer sediments. A "lines of evidence" approach was used to document the occurrence of natural attenuation. Chlorinated hydrocarbon and biogeochemical data were used to develop a site-specific conceptual model where both anaerobic and aerobic biological processes are responsible for the destruction of PCE, TCE, and daughter metabolites. An examination of groundwater biogeochemical data showed a region of depleted dissolved oxygen with elevated dissolved methane and hydrogen concentrations. Reductive dechlorination likely dominated in the anaerobic portion of the aquifer where PCE and TCE levels were observed to decrease with a simultaneous increase in cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC), ethene, and dissolved chloride. Near the anaerobic/ aerobic interface, concentrations of cis-DCE and VC decreased to below detection limits, presumably due to aerobic biotransformation processes. Therefore, the contaminant and daughter product plumes present at the site appear to have been naturally atteuated by a combination of active anaerobic and aerobic biotransformation processes.  相似文献   
90.
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