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   434篇
  免费   25篇
  国内免费   64篇
安全科学   68篇
废物处理   2篇
环保管理   50篇
综合类   225篇
基础理论   79篇
污染及防治   19篇
评价与监测   11篇
社会与环境   64篇
灾害及防治   5篇
  2024年   3篇
  2023年   8篇
  2022年   20篇
  2021年   14篇
  2020年   14篇
  2019年   12篇
  2018年   21篇
  2017年   17篇
  2016年   18篇
  2015年   15篇
  2014年   13篇
  2013年   33篇
  2012年   26篇
  2011年   25篇
  2010年   28篇
  2009年   27篇
  2008年   36篇
  2007年   24篇
  2006年   24篇
  2005年   13篇
  2004年   19篇
  2003年   18篇
  2002年   9篇
  2001年   14篇
  2000年   15篇
  1999年   9篇
  1998年   4篇
  1997年   4篇
  1996年   3篇
  1995年   1篇
  1994年   9篇
  1993年   1篇
  1992年   2篇
  1991年   6篇
  1990年   5篇
  1989年   1篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   2篇
  1976年   1篇
  1973年   1篇
排序方式: 共有523条查询结果,搜索用时 203 毫秒
351.
In order to analyse potential influences of soda industryeffluents on the ecological integrity of Traunsee (TS) weinvestigated the fish community of the lake in comparison witha reference lake (Hallstättersee HS) and used a reconstructionfrom the (older) literature concerning the original speciescomposition of Traunsee. Published `Index of Biotic Integrity(IBI)' metrics were considered to be of limited value due tothe relatively low species number in the oligotrophic, Alpinelake. Therefore we included, in addition to speciescomposition, studies on egg distribution, larval fishdensities, life-history parameters (i.e. growth, maturity,fecundity, age and size composition), stress levels and heavymetal content of the dominant whitefish (Coregonuslavaretus), as well as overall fish density and biomass (usinghydroacoustics) to assess the ecological status of the fishcommunity. Two of the original 18 species have disappearedfrom the lake, presumably in connection with the introductionof non-native eel (Anguilla anguilla) and theconstruction of a power plant in the outflow. Silt from grindedlimestone together with highly alkaline pore waters is emittedvia industrial wastewater from Sodaworks and covers part of thelake bottom. We observed that eggs of whitefish were spawnedmainly in the main inflowing river and close to the shore, thusavoiding the silty areas and making the anticipated damage tothe reproductive potential of whitefish neglectable. This wascorroborated by larval surveys done weekly on both lakes fromJanuary to May, which showed halve the density of whitefishlarvae in TS compared to HS. Estimates of potentially spawningfish from hydroacoustic surveys resulted in a ratio of 1(TS) :3 (HS). Analysis of whitefish revealed that they are growingfaster in TS and have higher fecundity leading to somecompensation of lower abundance. High levels of fishing in TSmight have led to this pattern and to depressed yields asindicated by the age composition. Level of oxidative stress andheavy metal content were not discernible from the referencelake. Therefore we concluded that negative impacts on theecological status of the fish community resulted from fisheriesmismanagement and a power plant situated in the outflow of thelake, considered to have damaged spawning places for somespecies, but not from soda industry effluents.  相似文献   
352.
Competition between individuals permeates people's lives as they strive for limited resources, services, and status. However, research on competition and competitiveness in organizations is limited despite its relevance to relational dynamics (e.g., rivalry), individual differences (e.g., traits and gender), social factors (e.g., competitive climate), and organizational outcomes (e.g., work performance and unethical behavior). In this article, we propose a multilevel model of competition and competitiveness that includes the individual, the group, and the situation. By providing a holistic overview of research across a broad array of disciplines, we organize the field and create a usable framework to advance knowledge of competition and competitiveness. In doing so, we identify what we know, what we still need to discover, and provide direction for future research. The article closes with an assessment of methods and measures used in studying competition. In conclusion, this review establishes a multilevel and integrative structure that incorporates individual and team competitiveness with competitive situations that prompt competitive processes and important organizational outcomes.  相似文献   
353.
《组织行为杂志》2017,38(1):124-151
The Workplace Intergenerational Climate Scale (WICS) is designed to measure employees' attitudes and perceptions about workers of different ages in the workplace. In Study 1, an initial 18‐item measure was developed, reflecting five subscales: Intergenerational Contact, Workplace Intergenerational Retention, Positive Intergenerational Affect, Workplace Generational Inclusiveness, and Lack of Generational Stereotypes. Scores on the five WICS subscales were linked to workplace mentoring, opinions about older workers, and job satisfaction. In Study 2, the WICS items and subscales were further refined, and subscale relationships with similar constructs were explored via structural equation modeling. In Study 3, a more occupationally diverse sample was used to support criterion, incremental, discriminant, and external validity. Evidence supports the use of the WICS as a valid and reliable multidimensional measure of an organization's intergenerational climate. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
354.
The purpose of this article is to gather results of studies on the relationship between median frequency (MF) and mean power frequency (MPF) and the level of muscle contraction, and to use those results to discuss the differences in the trends according to factors related to measurement technique and subject. Twenty-one studies with 63 cases for upper limb muscles and nine studies with 31 cases for lower limb muscles were analysed. Most results showed an increase in parameters with an increased level of muscle contraction, only some studies showed a decrease. The influence on parameters of the level of muscle contraction and factors such as subjects, type of contraction, muscle length and electrodes was analysed for each muscle. It was concluded that when analysing the influence of different factors on MF and MPF, because those factors interact they should be considered together, not separately.  相似文献   
355.
Effective leadership requires a leader claiming as well as team members granting the leadership position. Contingent reward and participative leadership may both facilitate this mutual process. However, these behaviors differ in the degree to which they require a leader to have status and be prototypical. Their effectiveness might thus depend on the status‐related characteristics of the leader. In this respect, we propose that younger leaders, by deviating from the leader prototype in terms of age, lack a natural status cue, which will determine the effectiveness of these two leadership behaviors in shaping turnover. Two pilot studies (N = 113 and 121 individuals) confirm that younger leaders are perceived as less prototypical and to have lower status than older leaders. Examining 83 work teams, we show that leader age differently moderates the effects of contingent reward and participative leadership on time‐lagged team turnover. For younger (compared with older) leaders, contingent reward was effective as illustrated by decreased voluntary turnover and increased involuntary turnover, whereas participative leadership, which was associated with increased voluntary turnover and decreased involuntary turnover, was ineffective. These findings point to the importance of incorporating natural status cues of leaders for understanding the effectiveness of different leadership behaviors. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
356.
为量化研究管制区域内飞机架次的时空变化对管制员疲劳的影响,设计相应测试方案进行试验研究。有针对性地选取20名在职管制员分别在大、小夜班的班前和班后进行试验,采集完成不同流量等级下雷达模拟机任务过程中的管制员的脑电(EEG)信号数据,从数据中提取疲劳指标值,运用SPSS20.0软件统计分析指标值,根据管制员的岗龄将其分成2组进行比较,线性拟合班前班后的管制员疲劳指标值。结果表明:岗龄≥10年的管制员疲劳指标值及其波动性明显低于岗龄<10年的管制员;班前管制员疲劳指标值随管制架次的增加中后期呈下降趋势;班后管制员的疲劳指标值随管制架次的增加而增长,随时间呈3次曲线变化。  相似文献   
357.
安徽省乔木林固碳能力研究   总被引:6,自引:0,他引:6  
以安徽省第六次森林资源连续清查结果为依据,对安徽省不同类型乔木林固碳能力进行了研究。结果表明,不同林种乔木固碳能力依次为:用材林(薪炭林(特种用途林(防护林;不同发育阶段乔木林固碳能力依次为:幼龄林(中龄林(近成熟林(成熟林(过成熟林;不同优势树种组乔木林固碳能力依次为:针叶林(阔叶林(针阔混交林;不同优势树种乔木林固碳能力依次是:杉木林(马尾松林(杨树林;同时,得出相同龄组但不同优势树种或相同优势树种但不同龄组的乔木林固碳能力也不同,其中杉木的幼龄林固碳能力最大,达到19.75 t/(hm^2.a)。  相似文献   
358.
Predator–prey relationships provide an excellent opportunity to study coevolved adaptations. Decades of theoretical and empirical research have illuminated the various behavioral adaptations exhibited by prey animals to avoid detection and capture, and recent work has begun to characterize physiological adaptations, such as immune reactions, metabolic changes, and hormonal responses to predators or their cues. A 2-year study quantified the activity budgets and antipredator responses of adult Belding’s ground squirrels (Spermophilus beldingi) living in three different California habitats and likely experiencing different predation pressures. At one of these sites, which is visually closed and predators and escape burrows are difficult to see, animals responding to alarm calls remain alert longer and show more exaggerated responses than adults living in two populations that likely experience less intense predation pressure. They also spend more time alert and less time foraging than adults at the other two sites. A 4-year study using noninvasive fecal sampling of cortisol metabolites revealed that S. beldingi living in the closed site also have lower corticoid levels than adults at the other two sites. The lower corticoids likely reflect that predation risk at this closed site is predictable, and might allow animals to mount large acute cortisol responses, facilitating escape from predators and enhanced vigilance while also promoting glucose storage for the approaching hibernation. Collectively, these data demonstrate that local environments and perceived predation risk influence not only foraging, vigilance, and antipredator behaviors, but adrenal functioning as well, which may be especially important for obligate hibernators that face competing demands on glucose storage and mobilization.  相似文献   
359.
新疆中部天山雪岭云杉种群动态初步研究   总被引:2,自引:0,他引:2  
王婷  任海保  马克平 《生态环境》2006,15(3):564-571
雪岭云杉PiceaschrenkianaFisch.etMey在中部天山林区内分布于海拔1500m~2700m之间,形成一个垂直分布带。作者采用样方法进行调查,沿海拔梯度每隔100m选取两块样地(20m×20m),在海拔1500~2700m的雪岭云杉林内共选样地26块来调查中部天山雪岭云杉种群的年龄结构、密度和生物量动态。在所选样地内,调查所有雪岭云杉树木(h≥2m)的胸径并按5cm分成不同的径级,每一径级至少选取两棵树,每棵树在不同方向上钻取两个树芯,建立年龄-胸径方程推算样地内所有雪岭云杉树(h≥2m)的年龄;调查样地内所有幼苗(h<50cm)和幼树(50cm≤h<200cm)的高度并根据主干上轮枝数查数一定数目幼苗幼树的年龄,建立年龄-高度方程并推算样地内所有幼苗幼树的年龄。研究结果表明中部天山雪岭云杉种群的胸径、年龄结构和种群密度都呈倒-J型分布,种群生物量呈钟型分布,存活曲线基本介于DeeveyⅡ和DeeveyⅢ型之间。以上研究结果表明中部天山的雪岭云杉种群处于不断更新和稳定发展的时期。  相似文献   
360.
The manipulation of the sex ratio and age structure in many managed ungulate populations calls for a better understanding of their potential consequences on females’ condition and behavior during rut. During 1996–2002, we manipulated the male age structure and male percentage (nine treatments during 7 years) within an experimental herd of semidomestic reindeer (Rangifer tarandus) and investigated their influence on both the body mass change and the behavior of females during rut. On average, the females lost body mass (−0.95±SE 0.18 kg) during rut, which we contend to reflect somatic costs. The females’ losses increased as the percentage of male decreased, but this was certainly ascribed to one treatment with high male percentage (27.7%) as compared to the others (ranging from 3.9 to 12.2%). Female losses were highest for treatments including both young and adult males as compared to only adult or only young males, and higher for treatments including only young compared to only adult males. This is supported by (1) the higher female harassment frequency when females are exposed to only young or a mixture of young and adult males as compared to only adults, (2) the higher female harassment frequency by young males as compared to adults in the mixed treatments, and (3) the reduced females’ feeding activity in treatments including both young and adult males. We conclude that the male age structure during rut will influence the females’ behavior and mass change and may have implications for females’ life history and for population dynamics.  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