全文获取类型
收费全文 | 514篇 |
免费 | 65篇 |
国内免费 | 354篇 |
专业分类
安全科学 | 47篇 |
废物处理 | 37篇 |
环保管理 | 90篇 |
综合类 | 500篇 |
基础理论 | 127篇 |
污染及防治 | 78篇 |
评价与监测 | 40篇 |
社会与环境 | 14篇 |
出版年
2024年 | 6篇 |
2023年 | 15篇 |
2022年 | 19篇 |
2021年 | 42篇 |
2020年 | 25篇 |
2019年 | 31篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 40篇 |
2013年 | 68篇 |
2012年 | 46篇 |
2011年 | 51篇 |
2010年 | 42篇 |
2009年 | 28篇 |
2008年 | 40篇 |
2007年 | 52篇 |
2006年 | 44篇 |
2005年 | 33篇 |
2004年 | 40篇 |
2003年 | 37篇 |
2002年 | 18篇 |
2001年 | 20篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有933条查询结果,搜索用时 109 毫秒
191.
Sophie Pierce Keith E. Schilling 《Journal of the American Water Resources Association》2023,59(5):913-928
Nutrient export from the agricultural Midwest threatens the Gulf of Mexico and new conservation practices are needed to reduce the loss of nutrient from subsurface tile drainage systems. Oxbows are natural waterbodies formed when a river cuts off a meander loop and water quality benefits of reconstructed oxbows are being increasingly recognized. In this study, we monitored four reconstructed oxbow sites (two tile-fed, two non-tile) over a 2-year period in north-central Iowa and assessed their capacity for NO3-N and dissolved reactive phosphorus (DRP) reductions. Water flow and quality monitoring of tiles, shallow groundwater, oxbow and receiving streams documented that the oxbows were dominated by tile drainage inputs. NO3-N concentrations were highest in the drainage tiles flowing into the tile-fed oxbows (mean 8–10 mg/L) and much lower in floodplain groundwater (<1–2 mg/L). Annual NO3-N loads into the tile-fed oxbows were substantially larger than input loads into the non-tiled oxbows. For the two tile-fed oxbows, the 2-year NO3-N retention efficiencies were very similar (0.76–0.77) and on a monthly basis, greater retention efficiencies were measured in summer and fall. DRP concentrations and loads into the tile-fed oxbows were too low to allow for meaningful estimates of retention. Reconstructing oxbows to receive tile drainage water should be considered a sustainable conservation practice for tile drainage treatment in agricultural areas. 相似文献
192.
ABSTRACT: Levels of nitrate and other inorganic contaminants in the drinking water of 453 Nebraska communities in 1986 were compared with health data for counties in which these communities were located. Data used included death rates per 100,000 population from heart disease, cancer, cerebrovascular disease, pneumonia and chronic lung disease, plus the rate of birth defects. Water samples from 42 communities exceeded the 0.01 mg/liter state and federal standards for selenium while 19 exceeded the 10 mg/liter NO3-N standard. Statistical analysis using Pearson's correlation coefficient method showed no significant relationship between nitrate or selenium and any of the health effects studied. Only barium, fluoride, and chromium were weakly but significantly (P<0.05) correlated to one or more of the health effects. Approximately one-third of the water samples high in NO3-N also had high levels of selenium. In some communities, the presence of nitrate also signaled the presence of barium, chromium, or arsenic. Results appear to indicate no immediate health risks related to levels of nitrate, selenium, or other inorganic contaminants in Nebraska drinking water. However, this type of statistical analysis cannot be interpreted as proving or disproving a cause and effect relationship. 相似文献
193.
Geng Bing Zhu Yanfang Jin Zhaohui Li Tielong Kang Haiyan Wang Shuaima 《Frontiers of Environmental Science & Engineering in China》2007,1(3):357-361
Catalytic reduction of nitrate in groundwater by sodium formate over the catalyst was investigated. Pd-Cu/γ-Al2O3 catalyst was prepared by impregnation and characterized by brunauer-emmett-teller (BET), inductive coupled plasma (ICP),
X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). It was found that total
nitrogen was effectively removed from the nitrate solution (100 mg/L) and the removal efficiency was 87%. The catalytic activity
was affected by pH, catalyst amount used, concentration of sodium formate, and initial concentration of nitrate. As sodium
formate was used as reductant, precise control in the initial pH was needed. Excessively high or low initial pH (7.0 or 3.0)
reduced catalytic activity. At initial pH of 4.5, catalytic activity was enhanced by reducing the amount of catalyst, while
concentrations of sodium formate increased with a considerable decrease in N2 selectivity. In which case, catalytic reduction followed the first order kinetics.
Translated from Acta Scientiae Circumstantiae, 2006, 26(4): 567–571 [译自: 环境科学学报] 相似文献
194.
为研究中国典型湿地沉积物硝酸盐异化还原成铵过程(Dissimilatory nitrate reduction to ammonium,DNRA)的群落组成,针对DNRA过程的功能基因nrfA进行高通量测序.选取中国典型湿地岸边带的表层沉积物8个样点,质控后每个样品得到60000条序列,在相似度≥90%得到279个OTUs进行生态学分析.由基因丰度值显示:8个湿地沉积物的丰度为(6.69±0.28)×10~7~(8.44±0.48)×10~8 copies g~(-1).多样性分析(OTUs水平)结果表明:本研究的湿地沉积物样点中,南方湿地沉积物样点的多样性要高于北方样点.对代表OTUs进行分类,共定义到8个门(Phylum),23个属(Genus).其中相对丰度最高的3个属为Anaeromyxobacter(24.71%)、Anaerolinea(9.70%)和Dokdonella(7.94%),表明三者在群落组成中占主导地位.PCoA分析(OTUs水平)表明南北方地区差异是导致中国湿地沉积物中DNRA菌群结构不同的最主要影响因素.结合沉积物理化因子分析,DNRA细菌的丰度与碳氮比、年平均降水量及年平均温度呈显著正相关.本研究在一定程度上揭示了中国典型湿地沉积物DNRA细菌的群落组成、多样性及其与环境因子的关系. 相似文献
195.
Adsorption-desorption behavior of acetochlor to soils in the presence of some environmental substances 总被引:5,自引:0,他引:5
IntroductionAlthoughtheherbicideacetochlor [2 chloro N (ethoxymethyl) N (2 ethyl 6 methylphenyl)acetamide]hasbeenusedfortenyearsinChina,limitedinformationhasbeencollectedtodetermineitsfateandtransportintheenvironment.Formulationsaregenerallysoldasemulsifiabl… 相似文献
196.
197.
在湛江市典型区域采集了14个蔬菜品种的28个样品,分析了样品中硝酸盐和亚硝酸盐的含量,对其污染状况及食用安全性进行了评价.结果表明:叶菜类硝酸盐含量普遍较高,有8个样品超标,根茎类和瓜果类硝酸盐含量均没有超标,而所有样品亚硝酸盐含量均较低.根据WHO/FAO规定的硝酸盐日允许摄入量换算得到的标准进行评价,青瓜、莲藕、葫芦瓜、花菜、包菜等品种食用较为安全,而萝卜、瓢瓜和生菜、大白菜等蔬菜经盐溃或煮熟后也可放心食用;但菜心、芥菜、通心菜、小白菜和油麦菜等蔬菜属于严重污染,食用可能会对人体健康带来风险. 相似文献
198.
玉米/空心菜间作降低土壤及蔬菜中硝酸盐含量的研究 总被引:16,自引:2,他引:16
菜地中过量的施用氮肥使土壤剖面中累积了大量的硝酸盐,会增加地下水的硝酸盐污染的风险.选择了深根系的玉米和浅根系的空心菜间作来验证深根系作物和浅根系作物问作将降低土壤剖面硝酸盐累积的假说.结果表明,间作有降低蔬菜地上部硝酸盐浓度和土壤剖面硝酸盐残留量的趋势;与单作种植相比,间作玉米的产量有显著增加,间作空心菜的产量没有显著降低;与单作玉米和空心菜相比,问作五米的根系表层分布较多,间作空心菜的根长密度有所降低.这为降低土壤剖面及蔬菜中的硝酸盐累积提供了新的途径。 相似文献
199.
Nitrate levels and the age of groundwater from the Upper Devonian sandstone aquifer in Fife,Scotland
The tritium concentrations in 13 groundwater samples from boreholes throughout the Upper Devonian sandstone aquifer of Fife have been measured. Due to atmospheric variations in tritium concentrations over the last century, this radioactive tracer can be used as a groundwater age indicator. In this study, the groundwater tritium concentrations have allowed for the area to be divided into three zones, and the variable chemistry of the groundwater samples, including the problem of recent elevated nitrate levels in the Fife Aquifer, has been interpreted in terms of their relative ages. 相似文献
200.