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   336篇
  免费   4篇
  国内免费   7篇
安全科学   12篇
废物处理   9篇
环保管理   63篇
综合类   64篇
基础理论   75篇
环境理论   1篇
污染及防治   82篇
评价与监测   22篇
社会与环境   15篇
灾害及防治   4篇
  2023年   1篇
  2022年   4篇
  2021年   1篇
  2020年   3篇
  2019年   3篇
  2018年   8篇
  2017年   11篇
  2016年   17篇
  2015年   12篇
  2014年   13篇
  2013年   31篇
  2012年   13篇
  2011年   23篇
  2010年   13篇
  2009年   15篇
  2008年   11篇
  2007年   19篇
  2006年   12篇
  2005年   19篇
  2004年   21篇
  2003年   16篇
  2002年   10篇
  2001年   9篇
  2000年   4篇
  1999年   4篇
  1998年   4篇
  1997年   1篇
  1996年   2篇
  1995年   3篇
  1994年   2篇
  1993年   4篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1989年   4篇
  1988年   5篇
  1986年   1篇
  1985年   1篇
  1984年   4篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1978年   2篇
  1977年   4篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
  1969年   1篇
  1958年   1篇
排序方式: 共有347条查询结果,搜索用时 31 毫秒
91.
The Little Miami River (LMR) basin, dominated by agriculture, contains two geologically-distinct regions; a glaciated northern till plain with soils three times more permeable than a southern, pre-Wisconsinan drift plain. The influences of two landscape measures, percent row crop cover (%RCC, computed at three spatial scales), and soil permeability (PERM), on baseflow nutrient concentrations were modeled using linear regressions. Quarterly water samples collected for four years were analyzed for nitrate-N (NN), Kjeldahl-N (KN), total-N (TN), and total-P (TP). In till plain streams (n = 17), NN concentrations were 8.5-times greater than drift plain streams (n = 18), but KN and TP were 20–40% lower at comparable %RCC. These differences resulted in TN/TP molar ratios >80 in till plain streams, but <6 in drift plain streams. For till plain steams regression models based on %RCC accounted for 79% of the variance in NN concentrations but only 27% in drift plain streams. However, regressions on %RCC accounted for 68–75% of the KN and TP concentration variance in the drift plain streams but essentially none in the till plain. Catchment PERM influenced the regional NN/KN ratios which were 10-fold higher in the drift plain streams. For both till and drift streams the catchment scale %RCC gave the best predictions of NN, a water soluble anion, but the smaller spatial scales produced better models for insoluble nutrient species (e.g., KN and TP). Published literature on Ohio streams indicates that these inter-regional differences in nutrient ratios have potential implications for aquatic biota in the receiving streams.  相似文献   
92.
93.
94.
In this paper, the occupational accidents and their effects on people are modeled. The basis of energy flow/barrier analysis is used to define an accident as the impact of a hazardous agent on a target, as a result of failure of control and protective barriers. This definition is enhanced to include serial and parallel barriers and to distinguish energy barriers from target barriers. The barrier attributes are defined and used to create a quantitative scenario-building model. The probability and severity of various accidents are estimated, by studying barrier reliability and efficiency. This approach is used to develop and simulate accident scenarios and to calculate their consequences. This model can be used in complex systems for analyzing the risk and estimating the importance of barriers.  相似文献   
95.
Hydrocephalus-stenosis of the acqueduct of Sylvius sequence (HSAS) is characterized by hydrocephalus, macrocephaly, adducted thumbs, spasticity, agenesis of the corpus callosum and mental retardation. X-linked hydrocephalus is known to be due to mutations in the gene coding for the neural cell adhesion molecule L1 (L1-CAM) and diagnosis is made by identification of a mutation in the L1-CAM gene. Prenatal diagnosis of HSAS is usually suggested on ultrasound examination showing hydrocephalus in a male fetus associated with bilateral adducted thumbs. Mutation screening of the L1-CAM gene is indicated when neuropathological examination shows hypoplasia of the corticospinal tract associated with aqueductal stenosis. We report here two cases of HSAS diagnosed within the same family by ultrasound examination in the first trimester of pregnancy when bilateral adducted thumbs were the only early ultrasound marker. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
96.
Increasing atmospheric CO2 is both leading to climate change and providing a potential fertilisation effect on plant growth. However, southern Australia has also experienced a significant decline in rainfall over the last 30 years, resulting in increased vegetative water stress. To better understand the dynamics and responses of Australian forest ecosystems to drought and elevated CO2, the magnitude and trend in water use efficiency (WUE) of forests, and their response to drought and elevated CO2 from 1982 to 2014 were analysed, using the best available model estimates constrained by observed fluxes from simulations with fixed and time-varying CO2. The ratio of gross primary productivity (GPP) to evapotranspiration (ET) (WUEe) was used to identify the ecosystem scale WUE, while the ratio of GPP to transpiration (Tr) (WUEc) was used as a measure of canopy scale WUE. WUE increased significantly in northern Australia (p < 0.001) for woody savannas (WSA), whereas there was a slight decline in the WUE of evergreen broadleaf forests (EBF) in the southeast and southwest of Australia. The lag of WUEc to drought was consistent and relatively short and stable between biomes (≤3 months), but notably varied for WUEe, with a long time-lag (mean of 10 months). The dissimilar responses of WUEe and WUEc to climate change for different geographical areas result from the different proportion of Tr in ET. CO2 fertilization and a wetter climate enhanced WUE in northern Australia, whereas drought offset the CO2 fertilization effect in southern Australia.  相似文献   
97.
98.
99.
Water is an essential element for humankind, animals, and plants. It is also an important element of the aquatic environment (the natural habitat of multiple species), where its quality plays a determining role in their protection and conservation. Unfortunately, the water quality of natural environments has worsened in the last decades. In sub-Saharan Africa and particularly in Bénin, in contrast to river discharges, monitoring the quality of surface water is a very rare activity. Thus, knowledge about physical and chemical properties as a basis for evaluation of the state of the environment and protection measures needed is almost absent. This article presents the results of the first structured, regular monitoring campaign on surface waters in the whole basin of the Ouémé River in Bénin Republic. With 510 km, the Ouémé River’s water quality fluctuates from upstream (Taneka Koko mountains in the north) to downstream (gauging station Bonou in the south) sources. This is due to soil erosion, lack of water treatment plants, and the use of significant quantities of fertilizer in the cotton zone. The present research was initiated to study the resource degradation of this area through chemical and physical water analysis. The monitoring of water quality has been followed for 5 years on twenty physicochemical parameters, from samples taken at four gauging stations on the main channel of the Ouémé River. Means and standard deviations of water analysis results were compared to both the recommendations of the World Health Organization (WHO) and the Maximum Permissible Concentrations (MPC) for drinking water (WHO 1987). Thus, high values were observed for physical parameters, i.e., color and turbidity had peaks of 697.5 uC and 129 FTU at Bétérou station in the wet season, although certain parameters, such as total hardness, present low values compared to the recommended standards. Moreover, excluding the concentrations of NO2 and NH4 + with values above the MPC, nutrient concentrations posed no direct risk for human consumption. However, together with phosphate concentrations (which are up to ten times higher than permissible ecological thresholds), they can cause eutrophication of the aquatic ecosystem. Due to the current flow regime, which has very low discharge rates in the dry season and torrential rainfall and high sediment loads in the wet season, the risk of eutrophication, i.e., excessive concentrations of ammonium and phosphates, is present throughout the year. Accumulation of ammonium and the distribution of nitrate and nitrites in the river water suggest that nitrification is impeded due to a lack of oxygen in both dry and wet seasons. Finally, the investigations show that the risk of water pollution exists and it is necessary to take measures of sanitation and water treatment to prevent the further degradation of water along the Ouémé River.  相似文献   
100.
Peat bog harvesting is an important industry in many countries, including Canada. To harvest peat, bogs are drained and drainage water is evacuated towards neighboring rivers, estuaries or coastal waters. High suspended sediment concentrations (SSC) were found in the drainage water at one particular site during the 2001–2002 spring seasons in New Brunswick (Canada). The main objective of this study was to verify this observation at other sites, compare SSC levels leaving harvested peat bogs with those leaving an unharvested bog, and to determine if high SSC events happen only in Spring or all year round. Suspended sediment concentrations were monitored downstream of three harvested peat bogs and an unharvested reference bog located in New Brunswick during the ice free seasons of 2003–2004. On average, SSC at the harvested sites exceeded 25 mg/l, which is the recommended daily maximum concentration, 72% of the time, while the same concentration was exceeded 30% of the time at the unharvested sites. SSC were found to be significantly higher at harvested sites than at the reference sites for all seasons. The highest SSC medians were recorded in the Fall but SSC was elevated in all seasons. High SSC levels in receiving waters may be caused by field ditching activities and insufficient sediment controls. Findings suggest the NB Peat Harvesting 25 mg/l SSC guideline should be reviewed.  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