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排序方式: 共有123条查询结果,搜索用时 12 毫秒
71.
J. Rudolph R. S. Anderson K. V. Czapiewski E. Czuba D. Ernst T. Gillespie L. Huang C. Rigby A. E. Thompson 《Journal of Atmospheric Chemistry》2003,44(1):39-55
A technique was developed that allows the determination of the stable carbon isotope ratio of isoprene in air. The method was used for a limited number of ambient measurements as well as laboratory studies of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis), including the light and temperature dependence. The mean stable carbon isotope ratio ( 13C) of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis) for all our measurements is –27.7 ± 2.0 (standard deviation for 23 data points). Our results indicate a small dependence of the stable carbon isotope ratios on leaf temperature and photosynthetic photon flux density (PPFD). The light dependence is 0.0026 ± 0.0012/( mol of photons m–2 s–1) for the studied range from 400 to 1700 mol of photons m–2 s–1. The temperature dependence is 0.16 ± 0.09/K. On average, the emitted isoprene is 2.6 ± 0.9 lighter than the leaf carbon. An uncertainty analysis of the possibility to use stable carbon isotope ratio measurements of isoprene for estimates of its mean photochemical age suggests that meaningful results can be obtained. This is supported by the results of a small number of measurements of the stable carbon isotope composition of ambient isoprene at different locations. The results range from approximately –29 to –16. They are consistent with vegetation emissions of isoprene that is slightly depleted in 13C relative to the plant material and enrichment of 13C in the atmosphere due to isotope fractionation associated with the reaction with OH-radicals. The stable carbon isotope ratio of ambient isoprene at locations directly influenced by isoprene emissions is very close to the values we found in our emission studies, whereas at sites located remote from isoprene emitting vegetation we find substantial enrichment of 13C. This suggests that stable carbon isotope ratio measurements will be a valuable, quantitative method to determine the extent of photochemical processing of isoprene in ambient air. 相似文献
72.
应用查表法模拟区域对流层O3、Nox分布和演化的研究 总被引:2,自引:0,他引:2
应用STEM-II气相光化学模式探讨了影响对流层O3、NOx气相光化学转化率的各物理、化学因子。表明在我国多数地区光化学污染物特征(NMHC/NOx较高)下,光辐射强度、温度、初始O3浓度和NOx浓度是影响O3、NOx气相光化学转化率的主要因子。将以上因子分档组合,计算并建立了各种情况下O3、NOx气相光化学转化率的查算表,并将之用于模拟区域O3、NOx的演化和分布。结果表明,与光化学模式直接耦合计算法相比,该方法既能显著缩短计算时间,又能基本反映大气化学反应的非线性过程,并与直接耦合法符合得较好。 相似文献
73.
74.
M.?E.?Cope G.?D.?HessEmail author S.?Lee K.?J.?Tory M.?Burgers P.?Dewundege M.?Johnson 《Boundary-Layer Meteorology》2005,116(2):363-384
Physical parameterisations of turbulent transfer processes in the atmospheric boundary layer, such as the stability parameterisations
developed by Joost Businger, and recent advances in computing capabilities, have been important factors leading to the emergence
of operational, numerical air quality forecasting systems. The present paper investigates the performance of the Australian
Air Quality Forecasting System (AAQFS) in forecasting the peak 1 h ozone for the current or next day. These 24/36 h forecasts
are generated for the Sydney and Melbourne regions and issued twice daily. Quantitative evidence is presented of the potential
for the AAQFS to provide accurate numerical air quality forecasts. A second goal is to provide an initial benchmark for investigating
the limits of predictability for air quality in the Sydney and Melbourne regions by looking at the dependence of the forecasts
on the domain spatial scale (while maintaining the same model grid resolution), the starting time and length of the forecast
(0000 UTC starts are 36-h forecasts and 1200 UTC starts are 24-h forecasts), and the sophistication of the photochemical mechanism
(simple chemistry, Generic Reaction Set (GRS) and complex chemistry, Carbon Bond IV (CBIV)). The probability of detection
by the forecast model is much better than persistence, showing considerable skill. The normalised bias, in general, decreases
going from regional scale to sub-regional scale and becomes negative at the station scale. In Melbourne the gross error increases
as the domain spatial scale decreases, but in Sydney there is a dip in the error at the sub-regional scale due to a sampling
artifact. Better results are obtained at the smaller domain scales for 1200 UTC forecasts in Sydney. These are attributed
to the shorter forecast period and secondarily to greater model spin-up effects at 0000 UTC. In Melbourne the results are
ambiguous. Similar conclusions are derived from scatter plots of forecasts versus observations. Dividing the scatter plots
into four sections by plotting vertical and horizontal lines (at 60 ppb) forms contingency tables for categorical forecasting.
These plots show the increase in missed forecasts due to underprediction and the decrease in the number of extreme events
detected as the spatial scale decreases. A comparison of the highly condensed GRS photochemical mechanism with the comprehensive
CBIV mechanism indicates that, in general, GRS performs well for predicting ozone in urban situations provided that the background
concentrations are appropriately specified. The potential to improve the forecasts at the smaller spatial scales, particularly
for extreme events at high ozone concentrations, may require moving to a more complex mechanism as computer resources become
available.
This paper is dedicated to Joost Businger, who had strong ties with the atmospheric boundary-layer community in Australia
over the past 40 years. It was while visiting CSIRO in Aspendale, Victoria, in 1965–1966 that Joost determined the stability
dependence of the Monin-Obukhov surface-layer profiles. He immediately walked over to Arch Dyer’s office to show Arch his
results. Arch carefully examined them, and then opened his desk drawer and pulled out his own plots of the stability dependence
that he and Bruce Hicks had obtained. They showed the same curves, and thus the Businger-Dyer-Hicks stability functions were
born. Arch and Bruce at the time were struggling with how to handle the internal politics; they needed Bill Swinbank’s approval,
as Assistant Divisional Chief, before they could submit their results for publication. Bill had his own very strong ideas
that conflicted with observations. Joost’s independent confirmation of their results provided a way forward (Bruce Hicks,
personal communication, 2003). Joost has contributed significantly, either directly or indirectly, to experimental field programs
both within Australia and overseas and to the development of parameterisations of turbulent transfer processes in the boundary
layer. 相似文献
75.
Yang?ZhangEmail author Christian?H.?Bischof Richard?C.?Easter Po-Ting?Wu 《Journal of Atmospheric Chemistry》2005,51(1):1-41
Photochemical indicators for determination of O3–NOx–ROG sensitivity and their sensitivity to model parameters are studied for a variety of polluted conditions using a comprehensive mixed-phase chemistry box model and the novel automatic differentiation ADIFOR tool. The main chemical reaction pathways in all phases, interfacial mass transfer processes, and ambient physical parameters that affect the indicators are identified and analyzed. Condensed mixed-phase chemical mechanisms are derived from the sensitivity analysis.Our results show that cloud chemistry has a significant impact on the indicators and their sensitivities, particularly on those involving H2O2, HNO3, HCHO, and NOz. Caution should be taken when applying the established threshold values of indicators in regions with large cloud coverage. Among the commonly used indicators, NOy and O3/NOy are relatively insensitive to most model parameters, whereas indicators involving H2O2, HNO3, HCHO, and NOz are highly sensitive to changes in initial species concentrations, reaction rate constants, equilibrium constants, temperature, relative humidity, cloud droplet size, and cloud water content. 相似文献
76.
The formation of products following the hydroxyl radical initiated photo-oxidations of n-and isopropyl acetates has been studied. Mixtures of synthetic air containing a few ppm of nitrous acid, nitric oxide, nitrogen dioxide and one of the propyl acetates were irradiated with sunlamps in a Teflon bag smog chamber. The decay of reactants and the formation of products was monitored by chemiluminescent analysis or by gas chromatography. The major primary products from the photo-oxidation of n-propyl acetate are acetaldehyde and propionaldehyde while from isopropyl acetate they are acetone and methyl nitrate. It was not possible to analyse for formaldehyde, an expected primary product in these systems. The nature and distribution of products indicate that a significant fraction of primary products arise from decomposition reactions of the alkoxy-type radicals generated following the initial attack of hydroxyl radicals on the esters. The derived reaction stoichiometries (molecules of NO oxidised per molecule of ester reacted) are also consistent with the proposed mechanisms. 相似文献
77.
Sinnhuber B.-M. Müller R. Langer J. Bovensmann H. Eyring V. Klein U. Trentmann J. Burrows J. P. Künzi K. F. 《Journal of Atmospheric Chemistry》1999,34(3):281-290
In this study measurements of mid-stratospheric Arctic ozone are compared with model simulations. The measurements obtained at Spitsbergen (79°N, 12°E) by ground based millimeter-wave radiometry exhibit large day to day variabilities as well as periods with low ozone. To interpret these measurements, calculations were made using the new photochemical box-trajectory model BRAPHO, with air parcel trajectories calculated from analyzed wind fields. Using a relatively simple approach, the model reproduces the observed ozone variability well, including inter-annual variations. The explanation for the observed ozone behavior is that at these altitudes ozone is determined by what we call dynamically controlled photochemistry. This means that the photochemical evolution of the ozone volume mixing ratio is mainly controlled by the atmospheric dynamics, in particular the solar zenith angle the air parcel has experienced. 相似文献
78.
利用LLA-C光化学反应机制,在NOX保持高值不变时,模拟分布范围很广的8种初始[NMHC]/[NOx](109/109)(1.0、3.0、7.1、14.3、28.6、57.2、100.0、200.0)条件下臭氧体积分数的变化。模拟结果表明,当[NMHC]/[NOx]≥15.0时,臭氧生成量对NMHC的改变不大敏感而主要依赖于NOx的大小。但是,当非甲烷烃与氮氧化物的比北较低(<7.0)时,臭氧生成量紧密地依赖于非甲烷烃体积分数。进一步的验证工作还有待于加强。 相似文献
79.
Ying Yu Qian Zhao Haolin Bao Qing Mou Zeming Shi Youliang Chen Ying Gao 《Geostandards and Geoanalytical Research》2020,44(3):617-627
With increasing use of bismuth in industry, a better understanding of its environmental behaviour is required, including an improved knowledge of its background concentration range in (non‐saline) freshwaters. However, the poor analytical sensitivity of previous methods may lead to inaccurate measurement results for Bi3+ in environmental samples. In this work, cobalt ion‐assisted photochemical vapour generation (PVG) was developed for the detection of trace Bi with inductively coupled plasma‐mass spectrometry (ICP‐MS) measurement. The volatile species of Bi was found to be (CH3)3Bi generated under UV irradiation in the presence of formic acid, acetic acid and Co2+. The major parameters potentially influencing the detection of Bi were investigated. Under optimised conditions, the limit of detection (3s, n = 11) of the proposed method was 0.3 ng l?1. The analytical sensitivity was enhanced about 70‐fold for Bi3+ compared with that using classic pneumatic nebulisation of ICP‐MS. Furthermore, the proposed method showed better analytical sensitivity and anti‐interference ability towards co‐existing ions compared with ferric ion‐assisted PVG systems. The accuracy of the proposed method was evaluated by analysis of environmental water samples and certified reference materials with satisfactory results. 相似文献
80.
北京市夏季臭氧特征及臭氧污染日成因分析 总被引:1,自引:0,他引:1
为研究北京市夏季臭氧特征及污染成因,于2017年7月15日至2017年8月10日期间,在北京市城区进行气象要素、臭氧(O3)、氮氧化物(NOx)和一氧化碳(CO)的连续观测,并选取7d(2017年7月20日、30日和8月1日、4~7日)密集采集大气样品进行挥发性有机化合物(VOCs)和含氧挥发性有机化合物(OVOCs)的分析。结果表明,观测期间北京市夏季O3污染严重,臭氧污染日以东南风为主,一般伴随着高温、低湿、低压和高前体物(VOCs、CO和NOx)浓度,占总观测天数的51.8%。密集采样日中臭氧污染日的成因与副热带高压或均压场下的弱高压系统有关。此外,来自河北、内蒙古中部和蒙古国东部途经保定和张家口等地的气流为北京夏季臭氧污染日的形成提供了部分外源,日平均贡献量为16%~37%,最大贡献量为53%,显示区域传输对臭氧污染日形成有重要影响。敏感性试验发现O3的生成主要受VOCs控制,特别是人为源VOCs。以上结果表明,控制北京本地VOCs的人为排放和周边空气质量将有助于降低北京城区的O3浓度。 相似文献