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   480篇
  免费   50篇
  国内免费   151篇
安全科学   20篇
废物处理   3篇
环保管理   119篇
综合类   311篇
基础理论   92篇
污染及防治   34篇
评价与监测   53篇
社会与环境   29篇
灾害及防治   20篇
  2024年   1篇
  2023年   19篇
  2022年   17篇
  2021年   27篇
  2020年   21篇
  2019年   16篇
  2018年   11篇
  2017年   14篇
  2016年   19篇
  2015年   34篇
  2014年   32篇
  2013年   40篇
  2012年   29篇
  2011年   22篇
  2010年   31篇
  2009年   24篇
  2008年   24篇
  2007年   45篇
  2006年   26篇
  2005年   22篇
  2004年   21篇
  2003年   10篇
  2002年   13篇
  2001年   23篇
  2000年   17篇
  1999年   7篇
  1998年   10篇
  1997年   10篇
  1996年   14篇
  1995年   9篇
  1994年   11篇
  1993年   4篇
  1992年   13篇
  1991年   8篇
  1990年   6篇
  1989年   6篇
  1988年   2篇
  1987年   3篇
  1986年   5篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1980年   1篇
  1979年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
  1969年   1篇
排序方式: 共有681条查询结果,搜索用时 281 毫秒
271.
The long-term (40 yr) observation results of phosphates–phosphorus concentration and its runoff in the Lithuanian fourth largest river Nevezis are analysed. Amounts and peculiarities of background runoff, agricultural runoff, andpoint source pollution from towns were studied for various periods. It has been determined that phosphates enter into the river Nevezis mainly from towns (76.5%), from agricultureonly up to 16%, and the background runoff for 7.5%.Considerable agricultural influence was observed in 1979–1991,when the phosphate runoff increased to 22 kg P km-2 a-1 and formed in 1984 33% of the entire runoff. A relation of the phosphates runoff from agriculture, for the entire study period, was obtained with the number of animals in the river's basin. Since 1990, when the number of animals started to decrease, the runoff of phosphates decreased too. Now the phosphatesrunoff from agriculture formed only 2% of the entire runoff. Water in the river Nevezis is heavily polluted with phosphate,according to the EU general classification of the water quality of rivers, although the Lithuanian pollution norms for effluentsdischarging to surface water are not exceeded. Norms for effluents discharging in the rivers from point-sources pollution should be made stricter and the highest permitted ratiobetween the phosphorus load in the river and its waterdischarge should be established.  相似文献   
272.
This study investigated the effects of multiple cognitive tasks on human performance. Twenty-four students at North Carolina A&;T State University participated in the study. The primary task was auditory signal change perception and the secondary task was a computational task. Results showed that participants' performance in a single task was statistically significantly different from their performance in combined tasks: (a) algebra problems (algebra problem primary and auditory perception secondary); (b) auditory perception tasks (auditory perception primary and algebra problems secondary); and (c) mean false-alarm score in auditory perception (auditory detection primary and algebra problems secondary). Using signal detection theory (SDT), participants' performance measured in terms of sensitivity was calculated as ?0.54 for combined tasks (algebra problems the primary task) and ?0.53 auditory perceptions the primary task. During auditory perception tasks alone, SDT was found to be 2.51. Performance was 83% in a single task compared to 17% when combined tasks.  相似文献   
273.
At present,continuous observation data for atmospheric nitrous oxide(N_2O) concentrations are still lacking,especially in east Antarctica.In this paper,nitrous oxide background concentrations were measured at Zhongshan Station(69°22′25″S,76°22′14″E),east Antarctica during the period of 2008–2012,and their interannual and seasonal characteristics were analyzed and discussed.The mean N_2O concentration was 321.9 n L/L with the range of 320.5–324.8 n L/L during the five years,and it has been increasing at a rate of 0.29% year-1.Atmospheric N_2O concentrations showed a strong seasonal fluctuation during these five years.The concentrations appeared to follow a downtrend from spring to autumn,and then increased in winter.Generally the highest concentrations occurred in spring.This trend was very similar to that observed at other global observation sites.The overall N_2O concentration at the selected global sites showed an increasing annual trend,and the mean N_2O concentration in the Northern Hemisphere was slightly higher than that in the Southern Hemisphere.Our result could be representative of atmospheric N_2O background levels at the global scale.This study provided valuable data for atmospheric N_2O concentrations in east Antarctica,which is important to study on the relationships between N2 O emissions and climate change.  相似文献   
274.
成都市黑碳气溶胶污染特征及与气象因子的关系   总被引:1,自引:0,他引:1       下载免费PDF全文
孙欢欢  倪长健  崔蕾 《环境工程》2016,34(6):119-124
为系统了解成都市黑碳气溶胶(BC)的污染特征,利用四川省环境监测站提供的成都市人民南路四段2013年9月至2014年7月逐时BC监测数据,对其浓度进行了统计分析。结果表明:1)BC小时平均浓度变化范围较大,介于0.01~57.83μg/m3,浓度中值(5.17μg/m3)小于平均值(7.32μg/m3),即BC小时浓度具有偏态分布特征。2)BC日均浓度变化范围为2~28.2μg/m3,其浓度日变化在四季均呈明显的单谷型,谷值出现在16:00时附近,表现为从凌晨到10:00时变化较平稳,10:00—16:00时浓度急剧下降,16:00到夜间浓度急剧上升;浓度季变化呈现出冬高夏低,春秋平稳的基本特征。3)秋、冬、春、夏四季BC本底浓度值分别为2.49,5.05,2.89,2.43μg/m3。4)BC质量浓度与PM2.5和PM10变化趋势一致,BC浓度相对颗粒物浓度变化较快,在0.01水平上与PM2.5和PM10均呈显著正相关,相关系数分别为0.657、0.638,与温度、降水和风速均呈负相关,相关系数分别为-0.334,-0.338,-0.202。  相似文献   
275.
We examine issues to consider when reframing conservation science and practice in the context of global change. New framings of the links between ecosystems and society are emerging that are changing peoples’ values and expectations of nature, resulting in plural perspectives on conservation. Reframing conservation for global change can thus be regarded as a stage in the evolving relationship between people and nature rather than some recent trend. New models of how conservation links with transformative adaptation include how decision contexts for conservation can be reframed and integrated with an adaptation pathways approach to create new options for global‐change‐ready conservation. New relationships for conservation science and governance include coproduction of knowledge that supports social learning. New processes for implementing adaptation for conservation outcomes include deliberate practices used to develop new strategies, shift world views, work with conflict, address power and intergenerational equity in decisions, and build consciousness and creativity that empower agents to act. We argue that reframing conservation for global change requires scientists and practitioners to implement approaches unconstrained by discipline and sectoral boundaries, geopolitical polarities, or technical problematization. We consider a stronger focus on inclusive creation of knowledge and the interaction of this knowledge with societal values and rules is likely to result in conservation science and practice that meets the challenges of a postnormal world.  相似文献   
276.
In the actual work environment, a specific objective noise, like machine and industrial noises, shows impulsive fluctuation form. Furthermore, it often occurs that a specific noise is partially or completely contaminated by background noise. In that case, the fluctuation wave form of the specific noise has to be estimated moment by moment in order to evaluate and/or improve the work environment. In this study, a digital filter for estimating an impulsively fluctuating specific noise is proposed. More specifically, after introducing a generalized time series regressive model of the specific noise, a method for estimating the impulsive noise based on an observation contaminated by the background noise is theoretically derived. Furthermore, the proposed method is applied to the actual task of estimating an industrial impact noise.  相似文献   
277.
To determine background values of the 252 chemical compounds listed in Dutch legislation, a survey was designed with the aim of estimating percentiles of the cumulative frequency distributions and areal fractions exceeding the former, legislative reference values. Sampling locations were selected by probability sampling, so that in estimating the target quantities no model assumptions on the spatial variation were required, and valid estimates could be obtained by design-based inference. Strata in random sampling were formed by overlaying an aggregated soil map and land use map. For most of the heavy metals the areal fraction with concentrations in the topsoil (0-10 cm) exceeding the reference value was smaller than the allowable maximum of 5%. For these compounds a background value was determined smaller than the reference value. Exceptions were V, Co, Ba and Cu, for which a background value was defined (slightly) larger than the reference value.  相似文献   
278.
Values are the fundamental reasons why people engage in conservation behaviors. Recent research has called for a more refined approach to studying values in a way that accounts for the concept of eudaimonia. However, the empirical properties for a eudaimonic value scale have not been tested given that previous investigations have remained at the theoretical level. Drawing from an on-site survey of visitors to Denali National Park and Preserve, Alaska, we used a latent profile analysis to better understand the expression of multiple values of nature. Specifically, we segmented respondents by their value orientations with a particular focus on evaluating eudaimonic and hedonic values, alongside the established dimensions of altruistic, biospheric, and egoistic values. We identified 4 distinct subgroups defined by value orientations and validated these subgroups based on measures of conservation behavior and sociodemographic characteristics (e.g., age). These results indicated campaign messaging should harness a combination of eudaimonic, biospheric, and altruistic values to propel individual behavior. We also observed that hedonic and egoistic values defined how people related to nature and played a role, albeit less pronounced, in motivating them to take action. Our study is one of the first efforts to operationalize eudaimonia in a conservation context; thus, we have opened a new avenue for protected-area managers to align their strategies with the underlying values of stakeholders.  相似文献   
279.
ABSTRACT: The hedonic valuation method was used to quantify the impact of floodplain location on housing values in Fargo‐Moor‐head. Being located in the 100‐year floodplain lowered the home values by $8,990, and such homes were worth $10,241 less than similar homes located outside the floodplain before the major flood event of 1997. Required flood insurance premiums for these homes were determined to account for approximately 81 percent of this price depreciation. In contrast, homes in the 500‐year floodplain were worth $3,100 more than similar homes not in the floodplain. It was concluded that more disclosure is needed regarding the location of the 500‐year floodplain, and that the hedonic valuation method can be used to calculate the economic gains and losses associated with flood mitigation projects or floodplain remapping efforts that result in the reclassification of the legal floodplain status of individual homes.  相似文献   
280.
Measures aimed at conservation or restoration of ecosystems are often seen as net‐cost projects by governments and businesses because they are based on incomplete and often faulty cost‐benefit analyses. After screening over 200 studies, we examined the costs (94 studies) and benefits (225 studies) of ecosystem restoration projects that had sufficient reliable data in 9 different biomes ranging from coral reefs to tropical forests. Costs included capital investment and maintenance of the restoration project, and benefits were based on the monetary value of the total bundle of ecosystem services provided by the restored ecosystem. Assuming restoration is always imperfect and benefits attain only 75% of the maximum value of the reference systems over 20 years, we calculated the net present value at the social discount rates of 2% and 8%. We also conducted 2 threshold cum sensitivity analyses. Benefit‐cost ratios ranged from about 0.05:1 (coral reefs and coastal systems, worst‐case scenario) to as much as 35:1 (grasslands, best‐case scenario). Our results provide only partial estimates of benefits at one point in time and reflect the lower limit of the welfare benefits of ecosystem restoration because both scarcity of and demand for ecosystem services is increasing and new benefits of natural ecosystems and biological diversity are being discovered. Nonetheless, when accounting for even the incomplete range of known benefits through the use of static estimates that fail to capture rising values, the majority of the restoration projects we analyzed provided net benefits and should be considered not only as profitable but also as high‐yielding investments. Beneficios de Invertir en la Restauración de Ecosistemas  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