全文获取类型
收费全文 | 528篇 |
免费 | 81篇 |
国内免费 | 155篇 |
专业分类
安全科学 | 127篇 |
废物处理 | 21篇 |
环保管理 | 32篇 |
综合类 | 377篇 |
基础理论 | 81篇 |
污染及防治 | 67篇 |
评价与监测 | 19篇 |
社会与环境 | 14篇 |
灾害及防治 | 26篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 34篇 |
2020年 | 33篇 |
2019年 | 34篇 |
2018年 | 23篇 |
2017年 | 21篇 |
2016年 | 22篇 |
2015年 | 30篇 |
2014年 | 24篇 |
2013年 | 36篇 |
2012年 | 44篇 |
2011年 | 46篇 |
2010年 | 36篇 |
2009年 | 39篇 |
2008年 | 22篇 |
2007年 | 46篇 |
2006年 | 39篇 |
2005年 | 49篇 |
2004年 | 16篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 15 毫秒
721.
Pius Lee Youhua Tang Daiwen Kang Jeff McQueen Marina Tsidulko Ho-Chun Huang Sarah Lu Mary Hart Hsin-Mu Lin Shaocai Yu Geoff DiMego Ivanka Stajner Paula Davidson 《Environmental Fluid Mechanics》2009,9(1):23-42
Discrepancies in grid structure, dynamics and physics packages in the offline coupled NWS/NCEP NAM meteorological model with
the U.S. Environmental Protection Agency Community Multiscale Air Quality (CMAQ) model can give rise to inconsistencies. This
study investigates the use of three vertical mixing schemes to drive chemistry tracers in the National Air Quality Forecast
Capability (NAQFC). The three schemes evaluated in this study represent various degrees of coupling to improve the commonality
in turbulence parameterization between the meteorological and chemistry models. The methods tested include: (1) using NAM
predicted TKE-based planetary boundary height, h, as the prime parameter to derive CMAQ vertical diffusivity; (2) using the NAM mixed layer depth to determine h and then proceeding as in (1); and (3) using NAM predicted vertical diffusivity directly to parameterize turbulence mixing
within CMAQ. A two week period with elevated surface O3 concentrations during the summer 2006 has been selected to test these schemes in a sensitivity study. The study results are
verified and evaluated using the EPA AIRNow monitoring network and other ozonesonde data. The third method is preferred a
priori as it represents the tightest coupling option studied in this work for turbulent mixing processes between the meteorological
and air quality models. It was found to accurately reproduce the upper bounds of turbulent mixing and provide the best agreement
between predicted h and ozonesonde observed relative humidity profile inferred h for sites investigated in this study. However, this did not translate into the best agreement in surface O3 concentrations. Overall verification results during the test period of two weeks in August 2006, did not show superiority
of this method over the other 2 methods in all regions of the continental U.S. Further efforts in model improvement for the
parameterizations of turbulent mixing and other surface O3 forecast related processes are warranted. 相似文献
722.
Sensitivity of air quality model prediction to parameterization of vertical eddy diffusivity 总被引:1,自引:0,他引:1
This paper investigates the effects of vertical eddy diffusivities derived from the 3 different planetary boundary layer (PBL)
schemes on predictions of chemical components in the troposphere of East Asia. Three PBL schemes were incorporated into a
regional air quality model (RAQM) to represent vertical mixing process and sensitivity simulations were conducted with the
three schemes while other options are identical. At altitudes <2km, all schemes exhibit similar skill for predicting SO2 and O3, but more difference in the predicted NOx concentration. The Gayno–Seaman scheme produces the smallest vertical eddy diffusivity (Kz) among all schemes, leading to
higher SO2 and NOx concentrations near the surface than that from the other 2 schemes. However, the effect of vertical mixing on O3 concentration is complex and varies spatially due to chemistry. The Gayno–Seaman scheme predicts lower O3 concentrations than the other two schemes in the parts of northern China (generally VOC-limited) and higher ones in most
parts of southern China (NOx-limited). The Byun and Dennis scheme produces the largest mixing depth in the daytime, which bring more NOx into upper levels, and the mixing depth predicted by the Gayno–Seaman scheme is the smallest, leading to higher NOx and lower O3 concentrations near the surface over intensive emission regions. 相似文献
723.
724.
北京秋冬季近地层PM2.5质量浓度垂直分布特征 总被引:25,自引:4,他引:21
选取秋冬两季各14 d对北京地区近地层ρ(PM2.5)垂直分布进行监测,获得ρ(PM2.5)垂直廓线;结合同步测得的气象数据,就气象因素对垂直分布的影响进行了分析;最终拟合了ρ(PM2.5)垂直廓线方程.研究表明:秋冬两季ρ(PM2.5)的垂直分布随高度增加而呈对数递减的规律;风速随高度的变化遵循对数规律;发生逆温时,大气层结稳定,垂直方向上的湍流受到抑制,风速与PM2.5逐时质量浓度在垂直方向的分布呈较好的线性关系,ρ(PM2.5)随高度改变呈显著的对数相关关系;而在非逆温的情况下,PM2.5逐时质量浓度垂直分布与风速线性相关的概率较小,质量浓度的垂直分布与高度的对数关系不显著. 相似文献
725.
即时合成层状双氢氧化物法去除阴离子染料刚果红 总被引:5,自引:2,他引:3
利用层状双氢氧化物(LDH)合成原理,提出了即时合成LDH处理染料废水的方法,并对其可行性进行了实验研究.该方法的基本原理是由于Mg2+,Al3+水解共沉淀形成LDH,阴离子染料优先进入LDH结构层间平衡结构电荷,从而使阴离子染料以LDH沉淀的形式被去除.探讨了反应时间,pH,n(Mg2+):n(Al3+)及温度对染料去除率的影响.结果表明,在常温下,最佳pH为9.0,反应时间为2 h,n(Mg2+):n(Al3+)为2:1,对刚果红染料的去除率可达100%,效果十分显著. 相似文献
726.
Spatial and temporal distribution of atmospheric mercury species over the Adriatic Sea 总被引:2,自引:0,他引:2
Field measurements of atmospheric mercury and related species were carried out during an intensive cruise campaign performed
over the Adriatic sea from October 26th to November 12th, 2004 on board the R/V Urania. Hg0 ranged between 0.8 and 3.3 ng/m3 with an average of 1.6 ± 0.4 ng/m3 over the entire period. Hg(II) concentrations ranged from 0.1 to 62.8 pg/m3 with an average of 6.7 ± 11.7 pg/m3 whereas Hg-p levels were in a range of 0.04 and 51 pg/m3 with an average of 4.5 ± 8 pg/m3. Higher Hg0 and Hg-p concentrations were observed in the Gulf of Venice and Gulf of Trieste due primarily to air masses transported from
the mainland reflecting the contribution from anthropogenic sources. In contrast, higher Hg(II) concentrations observed during
the first period of the cruise campaign were likely due to the occurrence of photo-oxidants production which are the main
players of the gas phase oxidation of to Hg(II)(g). These findings have been confirmed by the backward trajectories analysis of air masses crossing the studied area during
selected days. 相似文献
727.
Four networks of wind data are used to construct the first systematic estimates of the horizontal diffusivity from observations
of submeso motions on scales often unresolved in numerical models. Currently, the horizontal diffusivity in numerical models
is specified mainly for numerical reasons without observational support. The data analysis in this study emphasizes the stable
boundary layer although results are briefly presented for the unstable boundary layer. The horizontal diffusivity is estimated
from the horizontal gradient and the observed flux. Horizontal gradients of scalars are generally difficult to directly estimate
from observations with sufficient accuracy for much of the data. As an alternative, simulated particles with conservative
properties are introduced into the observed wind field in order to estimate the horizontal diffusivity for submeso motions.
The sensitivity of the horizontal diffusivity to details of the method is examined. The horizontal diffusivity increases with
the range of time and space scales that are included in the evaluation. The horizontal diffusivity is much larger with significant
topography and may increase with wind speed, depending on the site location. The coarse station spacing or the small domain
size is found to be a major limitation to the analysis. 相似文献
728.
碾压混凝土层面抗剪强度的细观数值研究 总被引:5,自引:4,他引:1
碾压混凝土 (RCC)层面抗剪强度关系到碾压混凝土坝的安全。笔者采用随机骨料模型模拟碾压混凝土的细观结构 ,利用有限元方法数值模拟碾压混凝土试件的细观损伤断裂和抗剪强度 ,将所得数值结果与混凝土重力坝设计规范参考值比较 ,结果较为吻合。同时对直剪试验尺寸效应进行研究 ,并给出提高层面抗剪能力的措施。 相似文献
729.
主要介绍了90°推制大口径弯头设计及成形的工艺过程、变形特点,分析了推制大口径弯头成形过程中金属的流动规律以及弯头内外弧壁厚与设计强度的关系。 相似文献
730.
选取国外有代表性的新一代空气质量模式系统(HPDM、PPSP、AMS)和我国目前广泛采用的模式(称为EIA模式)进行对比研究,研究表明,理论上HPDM总体上比PPSP、AMS和EIA模式更为合理,物理框架上更为完善. 相似文献