全文获取类型
收费全文 | 739篇 |
免费 | 27篇 |
国内免费 | 251篇 |
专业分类
安全科学 | 34篇 |
废物处理 | 19篇 |
环保管理 | 89篇 |
综合类 | 465篇 |
基础理论 | 119篇 |
污染及防治 | 214篇 |
评价与监测 | 58篇 |
社会与环境 | 17篇 |
灾害及防治 | 2篇 |
出版年
2024年 | 1篇 |
2023年 | 16篇 |
2022年 | 30篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 24篇 |
2016年 | 42篇 |
2015年 | 56篇 |
2014年 | 52篇 |
2013年 | 61篇 |
2012年 | 65篇 |
2011年 | 68篇 |
2010年 | 56篇 |
2009年 | 70篇 |
2008年 | 64篇 |
2007年 | 66篇 |
2006年 | 47篇 |
2005年 | 25篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 30篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有1017条查询结果,搜索用时 290 毫秒
841.
842.
Lichen Diversity and Lichen Transplants as Monitors of Air Pollution in a Rural Area of Central Italy 总被引:1,自引:0,他引:1
The results of a biomonitoring study carried out in the Municipality of Colle di Val d'Elsa (central Italy), using the diversity of epiphytic lichens and the accumulation of selected elements in thalli of the lichen Evernia prunastri transplanted in two urban sites are reported. The results indicate that the survey area suffers from different types of pollution. The main air pollutants are NO
X
and Pb. Vehicular traffic and domestic heating are the main sources of the former, and traffic and a crystal factory of the latter. Furthermore, most study area is eutrophicated due to diffuse agricultural activities and the presence of pig and sheep stockfarms. 相似文献
843.
Christina N. Kranz Richard A. McLaughlin Aziz Amoozegar Joshua L. Heitman 《Journal of the American Water Resources Association》2023,59(5):1115-1127
There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity (Ks) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m3/m3, and the sandy loam was further tested at high (0.55 m3/m3) and low (0.4 m3/m3) porosities. The Ks and water retention data were then used to model infiltration with HYDRUS-1D. With increasing compost amendment rate, Ks and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve Ks rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant-available, and unavailable water) depended on texture, with only the highest compost rates increasing plant-available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted. 相似文献
844.
利用2014—2018年连云港地区的监测资料,分析了O3的月变化特征,得出O3与NO2、CO呈负相关关系,并给出了相对合理的解释。 相似文献
845.
Urine source separation (NoMix technology) is a promising innovation in wastewater management. To improve and further develop NoMix technology, it has been implemented in four Swiss households and at our research institute (Eawag). We conducted measurements during one year on frequency of toilet usage (in households 5.2/person/day for weekdays, and 6.3/person/day for weekends), flushing behavior (30–85% small flushes), and recovered urine. We calculate the amount of urine effectively recovered per voiding in NoMix toilets (138 ml/flush in households; 309 ml/flush in women's toilets at Eawag), and waterfree urinals (225 ml/usage). We estimate urine recovery in the households to be maximally 70–75% of the expected quantity, leaving room for technical and behavioral improvements. Based on sampling of N and P concentrations, we suspect nitrogen losses in the extended urine piping system. For households and workplaces, the daily and weekly flushing pattern is recorded. Our results are in accordance with literature data from a shorter period but with more people. These results represent a good dimensioning basis for future urine source separation applications. An example of extrapolation to an entire watershed is presented. The flushing pattern corresponds well with the typical nitrogen loading of a treatment plant. 相似文献
846.
847.
Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of
SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil
aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa
(Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant
changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred
after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated
C and N sequestration rates were 0.4 Mg C ha−1 year−1 and 0.04 Mg N ha−1 year−1 following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and
alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only
in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2–0.25 mm) and aggregate stability (mean
weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was
a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa
soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion
of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and
the smallest in the 0.25–0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in
aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual
crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil
structure. 相似文献
848.
Wetland ecosystems are profoundly affected by altered nutrient and sediment loads received from anthropogenic activity in
their surrounding watersheds. Our objective was to compare a gradient of agricultural and urban land cover history during
the period from 1949 to 1997, with plant and soil nutrient concentrations in, and sediment deposition to, riparian wetlands
in a rapidly urbanizing landscape. We observed that recent agricultural land cover was associated with increases in Nitrogen
(N) and Phosphorus (P) concentrations in a native wetland plant species. Conversely, recent urban land cover appeared to alter
receiving wetland environmental conditions by increasing the relative availability of P versus N, as reflected in an invasive,
but not a native, plant species. In addition, increases in surface soil Fe content suggests recent inputs of terrestrial sediments
associated specifically with increasing urban land cover. The observed correlation between urban land cover and riparian wetland
plant tissue and surface soil nutrient concentrations and sediment deposition, suggest that urbanization specifically enhances
the suitability of riparian wetland habitats for the invasive species Japanese stiltgrass [Microstegium vimenium (Trinius) A. Camus]. 相似文献
849.
Ebrayi KN Pathak H Kalra N Bhatia A Jain N 《Environmental monitoring and assessment》2007,131(1-3):451-465
Nitrogen is the most widely used fertilizer nutrient, and it is a universally deficient nutrient too, which often severely
restricts the growth and yield of crops. To improve N fertilizer management, soil–plant system models can be applied to simulate
adequate N supply for both, optimal crop growth and minimal N losses. The likely impact of climate change on the cereal production
is of paramount importance in the planning strategies to meet the future growing needs on sustainable grounds. In this scenario
models are the effective tools to foresee the probable impacts and for choosing appropriate land use options. The study reported
in this thesis, employs field experiments and use of simulation tools to understand the dynamics of soil N balance and relate
growth and yield of rice under varying nitrogen inputs. The InfoCrop model was used in this study, which was calibrated with
the historic data sets, and subsequently validated with the field experiment conducted at IARI Farm, New Delhi. Simulated
results matched well with the observed values in terms of growth and yield of rice and seasonal nitrogen uptake. The components
of soil nitrogen balance differed among varying nitrogen level treatments, which was also captured by use of InfoCrop. The
model was then taken to climate change impact analysis. The results clearly revealed that when temperature increased, the
soil N losses, like denitrification, volatilization, N2O emission increased, whereas grain and biomass yields decreased. The
further scope of the study is to validate the study in contrasting agroenvironments. 相似文献
850.
Gas purging processes in pipeline safety maintenance were studied using the Computational Fluid Dynamics (CFD) methods. A new model (model 1) closer to actual working conditions and another two-side injection model were investigated. The simulation results showed that the relative purging efficiency of model 1 decreases compared to the ideal model (model 0), and two-sided injection model increases the efficiency relative to the single sided purging model. In addition, the models with different intake methods, outlet positions, outlet sizes and outlet pressures were simulated. If the outlet is opened after delaying some time, purging efficiency is improved. Furthermore if “relay purging” method is adopted, the efficiency is increased by 18% with two gas inlets and by 11% with a single inlet. The outlet position affects the average velocity in the last purging time. If the outlet diameter is equal or larger than that of the inlet, the purging efficiency is much higher. 相似文献