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   725篇
  免费   9篇
  国内免费   6篇
安全科学   33篇
废物处理   20篇
环保管理   173篇
综合类   66篇
基础理论   214篇
环境理论   1篇
污染及防治   113篇
评价与监测   60篇
社会与环境   48篇
灾害及防治   12篇
  2022年   4篇
  2021年   3篇
  2020年   7篇
  2019年   8篇
  2018年   19篇
  2017年   13篇
  2016年   24篇
  2015年   12篇
  2014年   18篇
  2013年   37篇
  2012年   24篇
  2011年   44篇
  2010年   23篇
  2009年   37篇
  2008年   35篇
  2007年   32篇
  2006年   31篇
  2005年   27篇
  2004年   20篇
  2003年   21篇
  2002年   28篇
  2001年   17篇
  2000年   23篇
  1999年   14篇
  1998年   13篇
  1997年   9篇
  1996年   14篇
  1995年   18篇
  1994年   16篇
  1993年   13篇
  1992年   9篇
  1991年   7篇
  1990年   10篇
  1989年   6篇
  1988年   11篇
  1987年   7篇
  1985年   11篇
  1984年   9篇
  1983年   14篇
  1982年   8篇
  1981年   5篇
  1980年   4篇
  1979年   8篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1972年   4篇
  1968年   2篇
  1967年   2篇
排序方式: 共有740条查询结果,搜索用时 31 毫秒
581.
Engines in boats and ships using total loss lubrication deposit a significant proportion of their lubricant and fuel directly into the water. Their impact on the Australian coastline and marine ecosystems is of great concern. The purpose of this study was to document the velocity and concentration field characteristics of a submerged swirling water jet emanating from a propeller in order to provide information on its fundamental characteristics. The properties of the jet were examined far enough downstream to be relevant to the eventual modelling of the mixing problem. Measurements of the velocity and concentration field were performed in a turbulent jet generated by a model boat propeller (0.02 m diameter) within a 0.4 m-wide and 0.15 m-deep flume, operating at 1,500 and 3,000 rpm in a weak co-flow of 0.04 m/s. The measurements were carried out in the Zone of Established Flow up to 50 propeller diameters downstream of the propeller. Results pertaining to radial distribution, self-similarity, standard deviation growth, maximum value decay and integral fluxes of velocity and concentration fitted with empirical correlations. Furthermore, propeller-induced mixing and pollutant source concentration from a two-stroke engine were estimated.  相似文献   
582.
2006年的粮食既已颗粒归仓,现在是盘库和规划未来的时候了。2006年,全球共收获了19亿6700万吨粮食,比估计的消费量20亿4000万吨约少7300万吨。短缺几近4%,创下历史记录。更清醒地看,近7年中的6年里,世界粮食生产一直不敷使用。结果,世界库存的谷物降到只够消费57天,是34年来的最低水平。而上次达到这么低的水平时,小麦和稻谷的价格翻了一番。  相似文献   
583.
In the initial phase of a complex emergency, an immediate population size assessment method, based on area sampling, is vital to provide relief workers with a rapid population estimate in refugee camps. In the past decade, the method has been progressively improved; six examples are presented in this paper and questions raised about its statistical validity as well as important issues for further research. There are two stages. The first is to map the camp by registering all of its co-ordinates. In the second stage, the total camp population is estimated by counting the population living in a limited number of square blocks of known surface area, and by extrapolating average population calculated per block to the total camp surface. In six camps selected in Asia and Africa, between 1992 and 1994, population figures were estimated within one to two days. After measuring all external limits, surfaces were calculated and ranged between 121,300 and 2,770,000 square metres. In five camps, the mean average population per square was obtained using blocks 25 by 25 meters (625 m2), and for another camp with blocks 100 by 100 m2. In three camps, different population density zones were defined. Total camp populations obtained were 16,800 to 113,600. Although this method is a valuable public health tool in emergency situations, it has several limitations. Issues related to population density and number and size of blocks to be selected require further research for the method to be better validated.  相似文献   
584.
One of the biggest environmental concerns caused by coal-fired power plants is the emission of mercury (Hg), which is toxic metal. To control the emission of Hg from coal-derived flue gas, it is important to understand the behavior and speciation of Hg as well as the interaction between Hg and solid materials in the flue gas stream. In this study, atomic-scale theoretical investigations using density functional theory (DFT) were carried out in conjunction with laboratory-scale experimental studies to investigate the adsorption behavior of Hg on hematite (α-Fe2O3). According to the DFT simulation, the adsorption energy calculation proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of ?0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The projected density of states (PDOS) analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. In summary, α-Fe2O3 has the ability to adsorb and oxidize Hg, and this reactivity is enhanced in the presence of Cl. For the laboratory-scale experiments, three types of α-Fe2O3 nanoparticles were prepared using the precursors Fe(NO3)3, Fe(ClO4)3, and FeCl3, respectively. The particle shapes varied from diamond to irregular stepped and subrounded, and particle size ranged from 20 to 500 nm depending on the precursor used. The nanoparticles had the highest surface area (84.5 m2/g) due to their highly stepped surface morphology. Packed-bed reactor Hg exposure experiments resulted in this nanoparticles adsorbing more than 300 μg Hg/g. The Hg LIII-edge extended X-ray absorption fine structure spectroscopy also indicated that HgCl2 physisorbed onto the α-Fe2O3 nanoparticles.

Implications: Atomic-scale theoretical simulations proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of ?0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The PDOS analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. Following laboratory-scale experiment of Hg sorption also shows that HgCl2 physisorbs onto α-Fe2O3 nanoparticles which have highly stepped structure.  相似文献   
585.
Regional Environmental Change - The published online version contains mistake. Anna Maria Jönsson was inadvertently omitted in the author group section. Correct author group section is shown...  相似文献   
586.
Data from 25 sites were used to evaluate associations between macroinvertebrate assemblages on large woody debris (snags) and environmental variables in the lower San Joaquin and Sacramento River drainages in California as part of the U.S. Geological Survey's National Water Quality Assessment Program. Samples were collected from 1993 to 1995 in the San Joaquin River drainage and in 1996 and 1997 in the Sacramento River drainage. Macroinvertebrate taxa were aggregated to the family (or higher) level of taxonomic organization, resulting in 39 taxa for analyses. Only the 31 most common taxa were used for two-way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA). TWINSPAN analysis defined four groups of snag samples on the basis of macroinvertebrate assemblages. Analysis of variance identified differences in environmental and biotic characteristics among the groups. These results combined with the results of CCA indicated that mean dominant substrate type, gradient, specific conductance, water temperature, percentage of the basin in agricultural land use, percentage of the basin in combined agricultural and urban land uses, and elevation were important factors in explaining assemblage structure. Macroinvertebrate assemblages on snags may be useful in family level bioassessments of environmental conditions in valley floor habitats.  相似文献   
587.
Tidal streams are ecologically important components of lotic network, and we identify dissolved oxygen (DO) depletion as a potentially important stressor in freshwater tidal streams of northern New Zealand. Other studies have examined temporal DO variability within rivers and we build on this by examining variability between streams as a basis for regional-scale predictors of risk for DO stress. Diel DO variability in these streams was driven by: (1) photosynthesis by aquatic plants and community respiration which produced DO maxima in the afternoon and minima early morning (range, 0.6-4.7 g/m(3)) as a product of the solar cycle and (2) tidal variability as a product of the lunar cycle, including saline intrusions with variable DO concentrations plus a small residual effect on freshwater DO for low-velocity streams. The lowest DO concentrations were observed during March (early autumn) when water temperatures and macrophyte biomass were high. Spatial comparisons indicated that low-gradient tidal streams were at greater risk of DO depletions harmful to aquatic life. Tidal influence was stronger in low-gradient streams, which typically drain more developed catchments, have lower reaeration potential and offer conditions more suitable for aquatic plant proliferation. Combined, these characteristics supported a simple method based on the extent of low-gradient channel for identifying coastal streams at risk of DO depletion. High-risk streams can then be targeted for riparian planting, nutrient limits and water allocation controls to reduce potential ecological stress.  相似文献   
588.
Ambient air quality has been an important issue for humans and the environment for hundreds of years. More recently, definitive links have been identified between pollutants and adverse effects on human health and on environmental sustainability. Of particular concern since the last quarter of the twentieth century has been the presence of toxic 'heavy metals' in ambient air. In order to measure the concentrations of pollutants, including 'heavy metals', in ambient air, to assess human and environmental exposure, comply with developing legislation, and assess newly introduced abatement strategies, the UK government established nationwide air quality measurement networks in the late 1970s. The nationwide measurement of 'heavy metals' in ambient air began in the late 1970s, and in 1980 was developed into several national networks, aimed at different metals and different emissions sources. These networks were rationalised into the current UK Heavy Metals Monitoring Network in 2003. The data produced by the current scientific operator of the Network, the National Physical Laboratory (NPL), in 2005, marked 25 years of ambient 'heavy metals' measurement in the UK at a nationwide level. This paper celebrates this milestone and provides a novel and critical examination of Network operations, measured concentration levels, and trends, over the last quarter of a century.  相似文献   
589.
590.
This paper presents the local institutional and organizational development insights from a five-year ongoing interdisciplinary research project focused on advancing the implementation of sustainable urban water management. While it is broadly acknowledged that the inertia associated with administrative systems is possibly the most significant obstacle to advancing sustainable urban water management, contemporary research still largely prioritizes investigations at the technological level. This research is explicitly concerned with critically informing the design of methodologies for mobilizing and overcoming the administrative inertia of traditional urban water management practice. The results of fourteen in-depth case studies of local government organizations across Metropolitan Sydney primarily reveal that (i) the political institutionalization of environmental concern and (ii) the commitment to local leadership and organizational learning are key corporate attributes for enabling sustainable management. A typology of five organizational development phases has been proposed as both a heuristic and capacity benchmarking tool for urban water strategists, policy makers, and decision makers that are focused on improving the level of local implementation of sustainable urban water management activity. While this investigation has focused on local government, these findings do provide guideposts for assessing the development needs of future capacity building programs across a range of different institutional contexts.  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