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A field study was conducted at a mountain-top site in northwestern Colorado. Supercooled cloud water, collected as a function of droplet size, was analyzed for anions, cations and trace elements. Enrichment factors (EF) of SO
4
2–
, K+, Na+ and Cl– relative to crustal and marine reference elements (Al and Na) were calculated to determine whether chemical fractionation of the aerosol occurs during cloud droplet formation. The largest EF's for all ions were found for droplets less than 10–15 µm diameter. Ratios of the small to large droplet mean EF's ranged from 1 to 2, for SO
4
2–
relative to both Al and Na+, to 10 to 12 for Na+, Cl– and K+, relative to Al. EF's of K+ and Cl– in the bulk cloud water were in crustal and marine proportions, respectively. It was concluded that although bulk could chemistry may indicate a lack of enrichment of a species, this may not be true throughout the droplet size distribution. The higher enrichments in small droplets is likely a result of their formation on small aerosol particles whereas the large droplets form on the largest aerosol particles. This may suppress EF's in precipitation relative to the total aerosol. 相似文献
95.
Randolph D. Borys Edward E. Hindman Paul J. DeMott 《Journal of Atmospheric Chemistry》1988,7(3):213-239
The relationships between the physical and chemical properties of mixed-phase clouds were investigated at Storm Peak Laboratory (3220m MSL) located near the continental divide in northwestern Colorado. Interstitial aerosol particles, cloud droplets and snow crystals were concurrently collected when the laboratory was enveloped by a precipitating cloud. All samples were analyzed for trace elements, soluble anions, electrical conductivity and acidity.The results show average trace constituent concentration ratios of cloud water to snow water range from 0.4 to 26. All but six of the 32 elements and ions measured had ratios greater than one. This result suggests a chemical species dependency of in-cloud aerosol particle scavenging processes. Evidence of a decrease of in-cloud aerosol particle scavenging efficiency by snow due to increases in aerosol concentration is also presented.Differences between the chemical composition of cloud water and snow water are manifested most strongly when snow crystals grow by vapor deposition. In-cloud scavenging efficiencies by snow crystals for most aerosol particle chemical species are dependent on the growth of the snow crystals by accretion of cloud droplets. This chemical fractionation of the atmospheric aerosol by snow crystal formation and growth should be most active where narrow, continental cloud droplet size distributions and low liquid water contents are prevalent, enhancing the probability of snow crystal growth by diffusion. 相似文献
96.
Charles A. Brock Lawrence F. Radke Jamie H. Lyons Peter V. Hobbs 《Journal of Atmospheric Chemistry》1989,9(1-3):129-148
Airborne observations during August 1985 over Greenland and the North American Arctic revealed that dense, discrete haze layers were common above 850 mb. No such hazes were found near the surface in areas remote from local sources of particles. The haze layers aloft were characterized by large light-scattering coefficients due to dry particles (maximum value 1.24 × 10–4m–1) and relatively high total particle concentrations (maximum value 3100 cm–3). Sulfate was the dominant ionic component of the aerosol (0.06 – 1.9 g m–3); carbon soot was also present. Evidence for relatively fresh aerosols, accompanied by NO2 and O3 depletion, was found near, but not within, the haze layers. The hazes probably derived from anthropogenic sources and/or biomass burning at midlatitudes.It is hypothesized that the scavenging of particles by stratus clouds plays an important role in reducing the frequency and intensity of hazes at the surface in the Arctic in summer. Since the detection of haze layers aloft through measurements of column-integrated parameters from the surface (e.g., by lidar) cannot be carried out reliably when clouds are present, such measurements have likely underestimated the occurrence of haze layers in the Arctic, particularly in summer. 相似文献
97.
2001年7月山西中部一次罕见暴雨过程的诊断分析 总被引:4,自引:6,他引:4
利用常规探空和地面实测资料以及GMS-5红外卫星云图资料,对发生在2001年7月26~27日山西省晋中市的一次区域性暴雨进行了天气学诊断和准地转Q矢量、湿Q矢量诊断及对比分析,结果表明:(1)此次暴雨发生在稳定的大尺度环流背景下,低涡切变线是其主要影响系统;东移发展的地面强冷锋是造成此次暴雨的天气尺度系统;而冷锋云系中新生、发展的中-β尺度暴雨云团是造成这次暴雨的直接系统。能量场在地面表现为Ω型。(2)Q矢量锋生函数表现出典型的准地转特征,而湿Q矢量锋生函数则具有明显的中尺度特征,且与降水量有滞后6 h的正相关关系,其强中心的出现是未来6 h强降水预报的重要指标。(3)对湿Q矢量的分解表明,Qx*和Qy*在强度、层次以及出现的时间上存在明显差异,这可能是由于对于暴雨这种伴有强烈垂直上升运动的天气现象来说,其经向上热量和动量的交换较纬向上的要大得多;暴雨出现在Qy*正、负值的交汇处。 相似文献
98.
99.
利用江苏省1960—2000年13个测站逐日降水资料,分析了41 a来江苏省年、季、月雨日的时空特征和雨日的气候变化。结果表明,江苏省的年雨日已经明显减少,平均每10 a雨日减少10.4 d。各季的雨日都呈负趋势,平均每10 a季雨日减少2.6 d。而秋季雨日减少最明显也最多。雨日长期趋势变化有明显的空间变化。江苏省的年雨日东部比西部减少的多,东部雨日每10 a减少14.6 d。月雨日也呈减少趋势,尤以4月、9月明显。雨日的长期趋势变化与降水量的长期趋势变化并不完全一致,这种不一致表现在长期趋势变化的强度上、范围上。总的来说,雨日的负趋势变化要强于降水量,负趋势的范围也要比降水量来得广一些。 相似文献
100.
Frank Drewnick Johannes Schneider Silke S. Hings Nele Hock Kevin Noone Admir Targino Silke Weimer Stephan Borrmann 《Journal of Atmospheric Chemistry》2007,56(1):1-20
The Aerodyne aerosol mass spectrometer (Q-AMS) was coupled with a counterflow virtual impactor (CVI) for the first time to measure cloud droplet residuals of warm tropospheric clouds on Mt. Åreskutan in central Sweden in July 2003. Operating the CVI in different operational modes generated mass concentration and species-resolved mass distribution data for non-refractory species of the ambient, interstitial, and residual aerosol. The ambient aerosol measurements revealed that the aerosol at the site was mainly influenced by long-range transport and regional photochemical generation of nitrate and organic aerosol components. Four different major air masses were identified for the time interval of the experiment. While two air masses that approached the site from northeastern Europe via Finland showed very similar aerosol composition, the other two air masses from polar regions and the British Islands had a significantly different composition. During cloud events the larger aerosol particles were found to be activated into cloud droplets. On a mass basis the activation cut-off diameter was approximately 150 nm for nitrate and organics dominated particles and 200 nm for sulfate dominated particles. Generally nitrate and organics were found to be activated into cloud droplets with higher efficiency than sulfate. While a significant fraction of the nitrate in ambient particles was organic nitrates or nitrogen-containing organic species, the nitrate found in the cloud droplet residuals was mainly ammonium nitrate. After passage of clouds the ambient aerosol size distribution had shifted to smaller particle sizes due to the predominantly activation of larger aerosol particles without a significant change in the relative composition of the ambient aerosol. 相似文献