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   465篇
  免费   2篇
  国内免费   1篇
安全科学   2篇
废物处理   11篇
环保管理   15篇
综合类   268篇
基础理论   49篇
污染及防治   80篇
评价与监测   33篇
社会与环境   10篇
  2017年   5篇
  2016年   6篇
  2014年   7篇
  2013年   18篇
  2012年   12篇
  2011年   11篇
  2010年   8篇
  2009年   8篇
  2008年   23篇
  2007年   13篇
  2006年   8篇
  2005年   8篇
  2004年   11篇
  2003年   9篇
  2002年   8篇
  2001年   7篇
  2000年   5篇
  1999年   5篇
  1997年   6篇
  1994年   7篇
  1992年   5篇
  1991年   5篇
  1990年   6篇
  1989年   6篇
  1988年   8篇
  1987年   6篇
  1985年   5篇
  1979年   5篇
  1978年   7篇
  1976年   7篇
  1969年   4篇
  1968年   11篇
  1967年   9篇
  1966年   6篇
  1965年   6篇
  1964年   7篇
  1963年   6篇
  1962年   5篇
  1961年   6篇
  1960年   4篇
  1958年   4篇
  1956年   8篇
  1955年   4篇
  1954年   8篇
  1952年   4篇
  1943年   5篇
  1924年   4篇
  1918年   4篇
  1917年   4篇
  1913年   5篇
排序方式: 共有468条查询结果,搜索用时 14 毫秒
181.
Meeting lateness is pervasive and potentially highly consequential for individuals, groups, and organizations. In Study 1, we first examined base rates of lateness to meetings in an employee sample and found that meeting lateness is negatively related to both meeting satisfaction and effectiveness. We then conducted 2 lab studies to better understand the nature of this negative relationship between meeting lateness and meeting outcomes. In Study 2, we manipulated meeting lateness using a confederate and showed that participants' anticipated meeting satisfaction and effectiveness were significantly lower when meetings started late. In Study 3, participants holding actual group meetings were randomly and blindly assigned to either a 10 min late, 5 min late, or a control condition (n = 16 groups in each condition). We found significant differences concerning participants' perceived meeting satisfaction and meeting effectiveness, as well as objective group performance outcomes (number, quality, and feasibility of ideas produced in the meeting). We also identified differences in negative socioemotional group interaction behaviors depending on meeting lateness. In concert, our findings establish meeting lateness as an important organizational phenomenon and provide important conceptual and empirical implications for meeting research and practice.  相似文献   
182.

Goal and Scope

Several studies show that the concentration of metals in mosses depends not only on metal deposition but also on factors such as moss species, canopy drip, precipitation, altitude, distance to the sea and the analytical technique used. However, contrasting results have been reported and the interpretation of the spatial variability of the metal accumulation in mosses remains difficult. In the presented study existing monitoring data from the European Heavy Metals in Mosses Surveys together with surface data on precipitation, elevation and land use are statistically analysed to assess factors other than emissions that have an influence on the metal accumulation in the mosses.

Main Features

Inference statistics and Spearman correlation analysis were applied to examine the association of the metal accumulation and the distance of the monitoring sites to the sea as well as the altitude. Whether or not significant differences of the metal loads in the mosses exist at national borders was examined with help of the U-test after Mann and Whitney. In order to identify and rank the factors that are assumed to have an influence on the metal uptake of the mosses Classification and Regression Trees (CART) were applied.

Results

No clear tendency could be derived from the results of the inference statistical calculations and the correlation analyses with regard to the distance of the monitoring site to the sea and the altitude. According to the results of the CART-analyses mainly the moss species, potential emission sources around the monitoring sites, canopy drip and precipitation have an effect on the metal bioaccumulation. Assuming that each participating country followed strictly the manual for sampling and sample preparation the results of the inference statistical calculations furthermore suggest that in most cases different techniques for digestion and analysis bias the measurements significantly.

Discussion

For the first time a national monitoring data base consisting of measurement data and metadata as well as surface information on precipitation, land use and elevation was applied to examine influence factors on the metal bioaccumulation in mosses. The respective results mirror existing knowledge from other national studies to a large extend, although further analyses are necessary to affirm the findings. These analyses should include data from other national monitoring programmes and should additionally be carried out with other decision tree algorithms than CART.

Conclusions

The local variability in the metal concentration in mosses can be uncovered in terms of predictors or underlying hidden causes by using CART. Ideally, such an approach should be applied across the whole of Europe. This will only be feasible if all participating countries provide additional information about site characteristics as currently is done in for example the German moss surveys.

Recommendations

The UNECE Metals in Mosses Survey experimental protocol should be improved in order to reduce the observed influences, to enhance standardisation, and to strengthen the quality control. This implies the integration of sampling site describing metadata into the assessment. Furthermore, basis research is needed to test the hypothesis concerning moss species-specific accumulation of depositions.

Perspectives

Provided that the presented results hold true in further analyses correction factors should be applied on the moss data in order to get the depicted spatial patterns and temporal trends of metal bioaccumulation unbiased. Such factors should be calculated for natural landscape units or ecoregions that are homogeneous with regard to climate, vegetation and altitude.  相似文献   
183.
Experiments were carried out in order to obtain information on the uptake characteristics of metals in the algal and fungal components of lichens. The uptake of 115Cd, 65Zn, 64Cu, 140La, 187W and 76As in the alga Scenedesmus pannonicus, subsp. Berlin and the fungus Aureobasidium pullulans was determined at pH 7 and 5 respectively, in 4 h experiments varying with respect to temperature and Ca2+ solution concentrations. Furthermore, the effects of pre-rinsing the cell suspensions on metal uptake were investigated.Pre-rinsing resulted in decreased uptake of W and As by algae and in increased uptake of all elements measured by fungi, which may be attributed to combined effects of starvation and changing densities.For algae, the uptake rates of As, W, Zn and Cd were markedly increased at the highest temperature employed. For Cu and La hardly any effects of temperature were observed, indicating the absence of metabolically controlled uptake. For fungi, but for As no relation of uptake with temperature could be determined.The presence of Ca2+ ions in the solution applied hardly affected the uptake of As but resulted in increased uptake of W by both the algae and the fungi. The effects of Ca2+ on the uptake of Cu and La were relatively small, probably due to specific binding sites in the cell walls for Cu and to the supercalcium status of the La-ion.The presence of Ca2+ caused decreased uptake of Cd2+ and Zn2+ by algae, but hardly affected the uptake of Zn2+ by fungi.The results indicate component-specific uptake and accumulation behaviour in intact lichens.  相似文献   
184.
The endotoxic principle of lipopolysaccharides (LPS) is localized in their lipid A component. Biological effects of LPS on, for instance, body temperature, blood pressure, and blood picture, are also induced by free lipid A. In contrast to the great variability of the 0-specific chains, the chemical structure of lipid A is much more constant. It is common for Salmonella and similar for other genera of the Enterobacteriaceae. Recently, a number of lipid A's have been recognized that exhibited distinct structural features compared with Enterobacteriaceae. These lipid A's were found to be also distinct with regard to some of their biological properties.  相似文献   
185.
Ohne Zusammenfassung Hintergrundinformation Umweltbundesamt (2007). Abschlussbericht des Forschungsprojektes „Charakterisierung endokrin vermittelter Wirkungen in Fischen: Relevante Parameter für die Entwicklung einer neuen OECD-Testmethode und in der Anwendung in der gesetzlichen Umweltrisikobewertung“ im Auftrag des Umweltbundesamtes (F?rderkennzeichen 206 67 470). Online erh?ltlich unter  相似文献   
186.
187.
188.
189.
190.
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