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981.
Athanassiadis Georgios A. Rao S. Trivikrama Ku Jia-Yeong Clark Richard D. 《Environmental Fluid Mechanics》2002,2(4):339-357
Accurate determination of the planetary boundary layer (PBL) height (i.e., mixing height (MH)) is critical to properly simulating pollutant levels with the grid-based photochemical models. In this study, the daytime mixing heights based on the parcel and bulk Richardson number methods are compared with those obtained directly from a numerical mesoscale meteorological model in an effort to evaluate the uncertainties in the estimation of the PBL evolution. Mixing heights are estimated from hourly outputs of meteorological variables of the Penn State/NCAR Mesoscale Model Version 3.3 (MM5V3) with two PBL schemes (Blackadar and Gayno-Seaman) during July 1999 over Philadelphia, PA. An analysis of the diurnal variation in the urban PBL and its influence on ground-level ozone (O3) levels is presented in this paper. The results indicate that on average, the MHs determined from the bulk Richardson number were larger than those estimated from the parcel method. The MHs from the MM5V3 output were much smaller than those derived from the parcel and bulk Richardson number methods, especially for the Gayno-Seaman scheme that is based on turbulent kinetic energy. The MH and ground-level O3 concentration have been found to be twice as much on episode days than on non-episode days. The average hourly MH growth rate and O3 tendency (i.e. rate of change in O3) were largest during the morning hours (0700 to 1000 eastern standard time (EST)), suggesting that vertical mixing contributes significantly to the accumulation of ground-level O3 in urban areas in the morning hours. 相似文献
982.
大气中存在的卤代甲烷对臭氧层具有极强的破坏作用并参与其它气候现象,其动态变化对臭氧的恢复和地球生态系统有重要影响。文章概述了全球变化下卤代甲烷源汇的研究情况并简单探索其进一步的研究方向。几种卤代甲烷中,溴代甲烷源汇最复杂且对臭氧具有最强的破坏力,因此研究较多。已证明CH3Br的来源有:海洋、土壤、生物燃烧、陆地植物和沼泽地的释放等;CH3Br的汇包括:光化学分解、被土壤和植物吸收、在海洋中的化学和生物降解等。但事实上是已知汇远远大于已知源,且各个源汇的通量在不同研究中结果差异较大,归其原因是卤代甲烷释放与吸收机制的不确定性。虽然近几年的研究也应用了稳定同位素示踪技术,但卤代甲烷各源汇的具体贡献并不清楚。今后卤代甲烷源汇的研究重点应放在与气体产生机制最密切的地下部分即“地下生态学”对其通量的影响,而同位素技术的改进及其在痕量气体研究中的应用也将是未来的重点方向。 相似文献
983.
Gardar Johannesson Noel Cressie Hsin-Cheng Huang 《Environmental and Ecological Statistics》2007,14(1):5-25
Data from remote-sensing platforms play an important role in monitoring environmental processes, such as the distribution
of stratospheric ozone. Remote-sense data are typically spatial, temporal, and massive. Existing prediction methods such as
kriging are computationally infeasible. The multi-resolution spatial model (MRSM) captures nonstationary spatial dependence
and produces fast optimal estimates using a change-of-resolution Kalman filter. However, past data can provide valuable information
about the current status of the process being investigated. In this article, we incorporate the temporal dependence into the
process by developing a dynamic MRSM. An application of the dynamic MRSM to a month of daily total column ozone data is presented,
and on a given day the results of posterior inference are compared to those for the spatial-only MRSM. It is apparent that
there are advantages to using the dynamic MRSM in regions where data are missing, such as when a whole swath of satellite
data is missing. 相似文献
984.
985.
Deepak Pudasainee Balkrishna Sapkota Manohar Lal Shrestha Akikazu Kaga Akira Kondo Yoshio Inoue 《Atmospheric environment (Oxford, England : 1994)》2006,40(40):8081-8087
This paper summarizes the results of a yearlong continuous measurements of gaseous pollutants, NO, NO2, NOx and O3 in the ambient air at Kathmandu valley. Measured concentration of the pollutants in study area is a function of time. NO, NO2 and O3 peak occurred in succession in presence of sunlight. At the time of maximum O3 concentration most of the NOx are utilized. The diurnal cycle of ground level ozone concentrations, revealed mid-day peak with lower nocturnal concentrations and inverse relationship exists between O3 and NOx, which are evidences of photochemical O3 formation. The observed ground level ozone during monsoon is slight lower than the pre-monsoon value. Further, lack of rainfall and higher temperature, solar radiation in the pre-monsoon have given rise to the gradual build up of ozone and it is lowest during winter. Ground level ozone concentrations measured during bandha (general strike) and weekend are 19% and 13% higher than those measured during weekdays. The most effective ozone abatement strategy for Kathmandu Valley may be control of NOx emissions. 相似文献
986.
Wang Qingeng Han Zhiwei Wang Tijian Higano Yoshiro 《Environmental science and pollution research international》2007,14(1):69-75
Background and Aim An accurate estimation of biogenic emissions of VOC (volatile organic compounds) is necessary for better understanding a series
of current environmental problems such as summertime smong and global climate change. However, very limited studies have been
reported on such emissions in China. The aim of this paper is to present an estimate of biogenic VOC emissions during summertime
in China, and discuss its uncertainties and potential areas for further investigations.
Materials and Methods This study was mainly based on field data and related research available so far in China and abroad, including distributions
of land use and vegetations, biomass densities and emission potentials. VOC were grouped into isoprene, monoterpenes and other
VOC (OVOC). Emission potentials of forests were determined for 22 genera or species, and then assigned to 33 forest ecosystems.
The NCEP/NCAR reanalysis database was used as standard environmental conditions. A typical summertime of July 1999 was chosen
for detailed calculations.
Results and Discussion The biogenic VOC emissions in China in July were estimated to be 2.3×1012gC, with 42% as isoprene, 19% as monoterpenes and 39% as OVOC. About 77.3% of the emissions are generated-from forests and
woodlands. The averaged emission intensity was 4.11 mgC m−2 hr−1 for forests and 1.12 mgC m−2 hr−1 for all types of vegetations in China during the summertime. The uncertainty in the results arose from both the data and
the assumptions used in the extrapolations. Generally, uncertainty in the field measurements is relatively small. A large
part of the uncertainty mainly comes from the taxonomic method to assign emission potentials to unmeasured species, while
the ARGR method serves to estimate leaf biomass and the emission algorithms to describe light and temperature dependence.
Conclusions This study describes a picture of the biogenic VOC emissions during summertime in China. Due to the uneven spatial and temporal
distributions, biogenic VOC emissions may play an important role in the tropospheric chemistry during summertime.
Recommendations and Perspectives Further investigations are needed to reduce uncertainties involved in the related factors such as emission potentials, leaf
biomass, species distribution as well as the mechanisms of the emission activities. Besides ground measurements, attention
should also be placed on other techniques such as remotesensing and dynamic modeling. These new approaches, combined with
ground measurements as basic database for calibration and evaluation, can hopefully provide more comprehensive information
in the research of this field.
Submission Editor: Prof. Dr. Gerhard Lammel (lammel@recetox.muni.cz) 相似文献
987.
988.
989.
选取臭氧(O3)污染高发的7月为夏季典型月,采用自动观测设备,从前体物VOCs的浓度水平及O3生成潜势(OFP),前体物、气象因素与O3相关性等多方面研究了衡水市O3污染影响因素,并剖析了一次典型的O3污染过程,以期为衡水市夏季O3污染防治提供科学参考。研究结果表明:衡水市VOCs主要组分浓度占比为烷烃 > 烯烃 > 芳香烃 > 乙炔,主要组分对总OFP的贡献为烯烃 > 芳香烃 > 烷烃 > 乙炔;O3与前体物VOCs、NO2存在负相关性,与温度存在正相关性;相对湿度低于48%时,O3和相对湿度呈负相关性,相对湿度高于48%时,O3和相对湿度呈正相关性;气团中VOCs化学组成稳定性较低,平均VOCs最大增量反应活性(MIR)较低,为4.855gO3/gVOCs;衡水市7月2—4日重度污染过程受本地生成和区域传输叠加影响。 相似文献
990.
Condensed atmospheric photooxidation mechanisms for isoprene 总被引:1,自引:0,他引:1
William P.L. Carter 《Atmospheric environment (Oxford, England : 1994)》1996,30(24):4275-4290
Two condensed mechanisms for the atmospheric reactions of isoprene, which differ in the number of species used to represent isoprene's reactive products, have been developed for use in ambient air quality modehng. They are based on a detailed isoprene mechanism that has recently been developed and extensively evaluated against environmental chamber data. The new condensed mechanisms give very close predictions to those of the detailed mechanism for ozone, OH radicals, nitric acid, H2O2, formaldehyde, total PANS, and for incremental effects of isoprene on ozone formation in one day simulations. The effects of the condensations become somewhat greater in multi-day simulations, particularly in cases where NO3 reactions are important at nighttime, but the ozone predictions are still very close. On the other hand, the SAPRC-90, RADM-2, and Carbon Bond IV isoprene mechanisms give quite different predictions of these quantities. It is recommended that the new mechanisms replace those currently used in airshed simulations where isoprene emissions are important. 相似文献