首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
We present data on the chemical composition of hoarfrost, rime, and snow grains that accumulated during an eighteen-day long temperature inversion event in Salt Lake City, Utah in December 1985 and January 1986. Chemical analyses show that the precipitation formed during this inversion event was acidic (as low as pH 3.85) and had nitrate and sulfate contents up to 1680 and 1290 μeq · L?1, respectively. Ammonia, nitrate, and sulfate deposition of 361, 615, and 792 μeq · m?2, respectively, occurred in a six-day period due to the accumulation of snow grains during this inversion.  相似文献   

2.
In coastral and mountainous environments, fog and cloud droplets are frequently deposited onto terrestrial surfaces; this deposition pathway may account for a large fraction of both moisture and chemical loading. Stratus cloudwater was collected for chemical analyses at Henninger Flats (870 m MSL), a site in the foothills of the San Gabriel Mountains, 25 km northeast of downtown Los Angeles. Concurrent samples of intercepted cloudwater were manually removed, drop-by-drop, from needles on various species of pine trees upon which it had deposited. Samples were analyzed for pH, major cations, and anions. Solute concentrations were substantially higher in samples removed from pine needles compared to the suspended cloudwater. For example, cloudwater concentrations for nitrate and sulfate were measured between 0.25 and 4.5 meq L?1 while deposited samples were 0.4 to 90 meq L?1. This solute enhancement was due to evaporation following droplet deposition and to nutrient leaching. Nutrient leaching was indicated by (a) a disproportionate increase in the concentrations of cations such as K and Mg (a factor of 2 to 15 enrichment relative to sulfate), and (b) reductions in the leachate acidity and ammonium relative to the incident droplets. A relationship was observed between the enhancement of Na, Ca, and nitrate in pine needle leachate. This suggests that reactions at the foliar surfaces are occurring which involve gaseous HNO3 and accumulated soil dust and sea-salt particles.  相似文献   

3.
Infestation by the gypsy moth (Lymantria dispar) can alter biogeochemical conditions in affected catchments. Stream-water concentration data obtained over the period of 1980–1993 for White Oak Run, a stream in Shenandoah National Park, Va., indicate that change in catchment acid-base status is associated with forest defoliation by the moth larva. Stream-water concentration changes following defoliation included increasing concentrations of strong-acid anions, base-cations, and hydrogen ion, as well as decreasing concentrations of acid-neutralization capacity (ANC) and sulfate. The largest change was in the concentration of nitrate; annual discharge-weighted mean concentrations increased from predefoliation levels consistently less than 5 μeq L?1 to postdefoliation levels greater than 50 μeq L?1. An intensification of acidification was indicated by record-high hydrogen ion concentrations and record-low ANC concentrations. The long-term biogeochemical implications of the infestation are uncertain due to the nonlinearity of the observed responses and unknown patterns of recovery and recurrence.  相似文献   

4.
Contaminants in Arctic Snow Collected over Northwest Alaskan Sea Ice   总被引：1，自引：0，他引：1  
Snow cores were collected over sea ice from four northwest Alaskan Arctic estuaries that represented the annual snowfallfrom the 1995–1996 season. Dissolved trace metals, major cationsand anions, total mercury, and organochlorine compounds weredetermined and compared to concentrations in previous arctic studies. Traces (<4 nanograms per liter, ng L-1) of cis- and trans-chlordane, dimethyl 2,3,5,6-tetrachloroterephthalate, dieldrin, endosulfan II, andPCBs were detected in some samples, with endosulfan I consistently present. High chlorpyrifos concentrations (70–80 ng L-1) also were estimated at three sites. The snow washighly enriched in sulfates (69–394 mg L-1), with highproportions of nonsea salt sulfates at three of five sites (9 of 15 samples), thus indicating possible contamination throughlong-distance transport and deposition of sulfate-rich atmospheric aerosols. Mercury, cadmium, chromium, molybdenum, and uranium were typically higher in the marine snow (n = 15) in relation to snow from arctic terrestrial studies, whereas cations associated with terrigenous sources, such as aluminum,frequently were lower over the sea ice. One Kasegaluk Lagoon site (Chukchi Sea) had especially high concentrations of totalmercury (mean = 214 ng L-1, standard deviation = 5 ng L-1), but no methyl mercury was detected above the method detection limit (0.036 ng L-1) at any of the sites. Elevated concentrations of sulfate, mercury, and certain heavymetals might indicate mechanisms of contaminant loss from the arctic atmosphere over marine water not previously reported overland areas. Scavenging by snow, fog, or riming processes and thehigh content of deposited halides might facilitate the loss of such contaminants from the atmosphere. Both the mercury and chlorpyrifos concentrations merit further investigation in view of their toxicity to aquatic organisms at low concentrations.  相似文献   

5.
A statistically significant decrease in sulfate was observed in high elevation Cascade lakes during 1983 through 1988. The total decrease averaged 2.2 μeq L?1 in two slow-flush lakes and 4.2 μeq L?1 in three fast-flush lakes for 1983–1985 vs 1986–1988, respectively. Coincident with these changes in sulfate concentrations were a sharp decrease of SO2 emissions from the ASARCO smelter (100 km SE of the lakes), from 87 to 70 kt yr?1 during 1983–1984 to 12 in 1985, the year of its closure, and a gradual change in SO2 emissions from Mt. St. Helens, from 39 to 27 during 1983–1984 to 5 in 1988. The sharpest decreases occurred in non-marine sulfate in fast-flush lakes from 1984 to 1985 (about 2 μeq L?1) and in slow-flush lakes from 1985 to 1986 (1 μeq L?1, which point to the ASARCO closure as the sole cause. However, some of the more gradual decline in non-marine sulfate observed during 1983 through the 1988 sampling periods may have been due to a slow washout of sulfate enriched ash from the 1980 Mt. St. Helens' eruption. Sulfate concentrations in precipitation also declined significantly by about 2 μeq L?1, but changes in volume-weighted sulfate content were not significant. Lake alkalinity did not show a consistent increase in response to decreased sulfate. This was probably due to either watershed neutralization of acidic deposition or the greater variability in alkalinity measurements caused by small changes in acidic deposition making it difficult to detect changes.  相似文献   

6.
To assess the influence of acidic deposition on the forest ecosystem, it is necessary to evaluate the gross amount of acidic deposition. In this paper, we discuss the variation of sulfate (SO4 2?) and nitrate (NO3 ?) loads as well as related concentration from 1991 to 1999 in the Hinoki (Chamaecyparis obtusa) plantation in Kochi, southwest Japan. The annual precipitation varied significantly from 1,700 to 3,900 mm during the study period. The annual sulfate concentration of rainfall was about 15 µmol L?1, including about 80% non sea salt sulfate, while the annual nitrate concentration of rainfall was increased. The sulfate and nitrate concentrations of the through fall and the nitrate concentration of the stem flow were equal to or slightly higher than those of rainfall. However, the sulfate concentration of the stem flow was higher than that of rainfall, 21 to 55 µmol L?1. The sulfate and nitrate loads of rainfall were measured to be 27 to 46 and 14 to 43 mmol m?2 y?1, respectively. The sulfate and nitrate loads of the through fall were the same or slightly higher than those of rainfall. In contrast, the sulfate and nitrate loads of the stem flow were less than those of rainfall. Combined sulfate loads of the through fall and the stem flow reached about 1.5 times that of the sulfate load of rainfall.  相似文献   

7.
The Massachusetts Acid Rain Monitoring project surveyed 80.5% of the state's 5294 named water bodies between 1983 and 1985. PH and acid neutralizing capacity (ANC) were measured monthly the first 14 mo and semi-annually afterwards. Sample collection and analysis were performed by volunteers. The majority of surface waters in Massachusetts were found to be sensitive to possible long term acidification, with 63% exhibiting ANC less than 200 μeq L?1 and 22% with ANC less than 40 μeq L?1. Seasonal patterns in ANC were observed, the median ANC being 384 μeq L?1 in summer/fall and 134 μeq L?1 in winter/spring. Geographical differences were also found across the state: the streams and lakes with lowest pH and ANC were located in the southeastern and north-central parts of the state, while the most alkaline surface waters were found in the western-most part of the state, which is the only area of the state with significant limestone deposits.  相似文献   

8.
Since snow crystals provide information on the processes leading to their formation and growth, their observation gives insight to the microphysics of cloud and precipitation. The capture of supercooled cloud droplets by snow crystals (riming) forms an important link between precipitation and cloudwater and thus plays an important role in wet deposition. In the project ‘Winter Precipitation at Mount Rigi’ ice crystals are collected at two stations at different elevations. The shape, size and degree of riming of each crystal are analyzed for more than 10000 crystals. Differences in the degree of riming of the crystals between the higher and the lower station are discussed. With the aid of Doppler radar data the location of snow crystal origin is estimated. Furthermore a relationship between the degree of riming of snow crystals and the vertical Doppler velocities is established.  相似文献   

9.
The role clouds play as processors of atmospheric aerosols and trace gases was studied along the slope of Mt. Rigi in central Switzerland. Upon cloud formation many aerosols and trace gases are efficiently scavenged by cloud drops. The cloud drops can enhance removal of pollutants from the atmosphere by transferring them to snow or rain which falls rapidly to the ground. This often occurs through a process known as riming, where falling ice crystals capture cloud drops. When ice crystals are grown primarily via water vapor deposition, without significant capture of cloud drops, however, the cloud drops isolate atmospheric pollutants from the precipitation process, thereby inhibiting their deposition. Increased riming results in increased precipitation ion concentrations. The extent of ice crystal riming at times exhibits spatial inhomogeneities with greater riming apparent near the mountain summit. Variations in cloud chemistry with drop size indicate that bulk cloudwater composition is not an accurate predictor for the composition of cloud drops captured by the ice crystals.  相似文献   

10.
Rain and snow were collected in plastic beakers either manually or with a Wong sampler during 58 precipitation events in 1974 at Yonkers, New York approximately 24 km north of the center of New York City. Determinations were made of total dissolved ionic species, free H ions, total H ions, sulfate, nitrate, chloride, and fluoride. Conductivity measurements ranged from 6.8 to 162 gmhos, pH from 3.4 to 4.9, total acidity from 36 to 557 μeq 1?1 sulfate from less than 1 to 20 mg 1?1, nitrate from less than 1 to 14 mg 1?1, and chloride from less than 1 to 7 mg 1?1. All fluoride concentrations were less than 0.1 mg 1?1. The results indicate that precipitation at this suburban location adjacent to New York City is consistently acidic and contains concentrations of sulfate, nitrate, and chloride which are similar to values found for other locations in the northeastern United States. Positive correlations were found between nitrate and sulfate concentrations and acidity suggesting that the atmospheric contaminants, SO2, and NO2 are causally-related to the occurrence of acidic precipitation. Further research will be necessary to clarify the relative influence of natural and man-made sources of N and S compounds and the contributions of gaseous and particulate contaminants in the atmosphere to the acidity of precipitation at this location.  相似文献   

11.
Gillett  R. W.  Ayers  G. P.  Selleck  P. W.  Tuti  MHW  Harjanto  H. 《Water, air, and soil pollution》2000,120(3-4):205-215
Gas mixing ratios of SO2, NO2 and HNO3 and nitrate and sulfate concentrations in rainwater have beenmeasured at six sites in Indonesia. The sites, Jakarta, Serang,Cilegon, Merak and Bogor, in Java, and Bukit Koto Tabang inSumatra, provide a range of pollution regimes in Indonesia.Jakarta and Bogor are heavily polluted sites in Java, whereasBukit Koto Tabang is a clean air station in a relativelyunpopulated area on the west coast of equatorial Sumatra. At thesesites rainwater was collected daily and gas samples weeklyduring 1996. The other three sites Serang, Cilegon and Merakrepresent smaller regional towns in west Java. At these sitesrainwater samples were collected weekly from June 1991 untilJune 1992.The results show that Jakarta has the highest volume-weightedmean sulfate concentrations in rainwater while the lowest weremeasured at Bukit Koto Tabang. Volume-weighted mean nitrateconcentration was about 24 μeq L-1 at Jakarta and Bogor,significantly higher than the 0.8 μeq L-1 measured atBukit Koto Tabang.Sulfur dioxide mixing ratios ranged from 4–7 ppbv in Jakarta toan average of 1.3 ppbv at Bukit Koto Tabang. Nitrogen dioxidemixing ratio was highest in Jakarta averaging 28 ppbv comparedwith the background mixing ratio of 1.2 ppbv at Bukit KotoTabang. Using dry deposition velocities estimated during aseparate study in the similar conditions of Malaysia enabled drydeposition estimates of SO2, HNO3 and NO2.Results of estimated total acidic S and N deposition (wet anddry) were greater than 250 meq m-2 yr-1 at the Jakartaand Bogor sites compared with about 23 meq m-2 yr-1 atBukit Koto Tabang. At Jakarta and Bogor dry deposition accountedfor more than 50% of the total deposition estimates compared with about 20% at Bukit Koto Tabang. Such deposition rates arehigh when compared to critical loads estimated for Indonesia bythe RAINS-Asia model. In this model, critical loads in western Java and equatorial western Sumatra fall into one of twoclasses: 50–100 and 20–50 meq m-2 yr-1. Thus acidic deposition flux at Jakarta and Bogor wasfound to be above the predicted critical loads even for the moreacid insensitive soils.  相似文献   

12.
The processes of lake acidification and lake restoration frequently involve major changes in DIC and DIN, both of which may potentially limit algal growth. We evaluate nutrient limitation of benthic algal biomass and species abundances during summers 1987 and 1989, before and after the liming of Lake Earnest (NE Pennsylvania) in November 1988. Limestone addition caused immediate increases in pH from 4.7 to 7.2. Alkalinity was ?34 μeq L?1 in summer 1987, but rose to 620 μeq L?1 in summer 1989, whereas DIN declined from 10.7 μmol L?1 to 1.1 μmol L?1 The algae were sampled after 45 to 46 d from clay flower pot substrates diffusing combinations of N, P and C. Algal biomass was strongly C-limited in 1987, but NP-limited in 1989. Mougeotia sp., which comprised >99% of total algal biovolume prior to liming, declined to < 1% of the community on control substrates, while Oedogonium sp. increased to 43% of total biovolume in 1989. The stimulation of chlorophyll-a accrual with C-enrichment during 1987 was consistent with the later increase in chlorophyll-a on control substrates following liming. Species enhanced by the diffused nutrients, however, generally differed from those which dominated the natural community.  相似文献   

13.
Steam chemistry was investigated from May 1991 through April 1992 for 13 Japanese forested watersheds and from May 1990 through August 1994 for two of these watersheds. Nine watersheds were treated over different periods (1983–1991) with different amounts of N (nitrogen) fertilizer as urea and ammonium salts. Total N additions ranged from 20 to 375 kg ha-1. There were no distinct seasonal differences in stream NO3 - concentrations in either the treated or untreated watersheds, but concentrations tended to be somewhat higher during periods of high discharge. The annual average NO3 - concentrations in streams had a significant, positive (p < 0.001, r = 0.84) relationship to the total amount of N applied from 1985–1991. The application of 330 kg N ha-1 raised annual average stream NO3 - concentration to about 300 μeq L-1 compared to less than 160 μeq L-1 in untreated watersheds. The concentrations of K+, Ca2+, and Mg2+ in stream water also increased in those watersheds with high rates of N fertilizer as a result of nitrification that increased the generation of the mobile nitrate anion. The lack of seasonality in stream NO3 - concentrations and the large rates of N loss with N addition both suggest that these watersheds were ‘nitrogen saturated’  相似文献   

14.
不同钠吸附比的咸水结冰融水入渗后滨海盐土的水盐分布   总被引：2，自引：2，他引：0  
在室内利用相同矿化度(10 g·L-1)、不同钠吸附比(5、10 和30)的咸水进行咸水结冰融水模拟试验、结冰融水入渗和咸水直接入渗的土柱试验, 以淡水处理为对照, 分析不同钠吸附比咸水结冰融水入渗下滨海盐土水盐分布特征。结果表明: 咸水冰融化过程中, 融出水的矿化度和钠吸附比均呈由高到低的变化趋势。咸水结冰融水入渗速度和入渗深度均快于和深于淡水。咸水钠吸附比越小, 结冰融水入渗速率越快、深度越深。水盐分布也表现为低钠吸附比咸水结冰处理的表层土壤含水量较低, 水分向深层迁移, 这种水分分布也使盐分向深层运移, 表现为表层土壤含盐量低, 深层土壤含盐量大。土层含水量低钠吸附比咸水处理高于高钠吸附比处理, 10~45 cm 土层则表现出相反的趋势; 表层土含盐量低钠吸附比处理高于高钠吸附比处理, 且咸水处理下土壤脱盐的深度大于淡水处理。钠吸附比5 的咸水结冰处理, 0~10 cm 土壤平均含水量和含盐量分别为30.3%和1.1 g·kg-1, 显著低于其他处理。为比较咸水结冰灌溉和咸水直接灌溉的效果, 室内利用含盐量为10 g·L-1、钠吸附比10 的咸水进行直接入渗的土柱(土壤含盐量为21.3 g·kg-1)模拟试验, 结果表明: 与咸水直接入渗处理相比, 咸水结冰融水处理盐分淋洗效果更好, 该处理0~25 cm土层平均土壤含盐量为2.9 g·kg-1, 显著低于咸水直接入渗的10.6 g·kg-1。  相似文献   

15.
Observations are presented on ion concentration in winter deposits to coniferous and deciduous trees at an elevated site (860 m). Such sites, with persistent snow and ice cover and considerable deposition of atmospheric pollutants, are common in Eastern Canada and the North-Eastern U.S. Spot samples at a given sampling date and samples of total deposits accumulated over extended periods of time were taken during the winters of 1986–87 and 1987–88. Samples were analyzed for pH and the major anion and cations. Results of spot samples were similar between different sampling times (and years) for deposits on balsam fir but variable for those on branches and twigs of deciduous trees (birch, choke cherry). The chemistries of snow on the ground and snow on trees not in contact with foliage or branches were found not to be significantly different statistically (p<0.05). However, significant differences exist between concentrations of nutrient ions in snow and ice with and without contact with biological elements of coniferous and deciduous trees. This indicates occurrence of nutrient leaching during winter conditions, leading to possibly non-negligent nutrient stress for K? and Mg?. Based on spot and cumulative samples for balsam fir, and correcting for possible contributions from dry deposition, the contribution from leaching in winter deposits on balsam fir foliage has been estimated at 26, 14 and 9 μeq L?1, for K+, Ca++ and Mg++, respectively. With approximate estimates of stand characteristics and precipitation loading at the sampling sites, these figures represent 90/c, 1% and 8%, respectively, of the estimated annual growth component of the stand for K+, Ca++ and Mg++ This indicates the possibility of non-negligible nutrient stress for K+ and Mg+ during winter conditions at the given site.  相似文献   

16.
The method of single point, single application liming has been studied as a means of mitigating anthropogenic acid in trout streams in Virginia. Three critically acid sensitive streams were dosed with a total of five applications of limestone sand and monitored before, during and after the treatments to assess changes in water chemistry and biota. Limestone treatments of 8 to 50 tons (particle sizes 150–1000 μm), with the amounts based on sulfate deposition loading and existent stream water chemistry, were used to restore ‘lost’ acid neutralizing capacity (ANC). Contact time between the limestone bed in the stream bottom and the water was the limiting factor affecting the degree of treatment with bed length primarily controlled by the gradient of the stream at the dosing site. A single site application was able to restore approximately 2/3 of the ANC. Exponential fits of limestone consumption data were used to predict that treaments of similar streams would last from two five years before reliming was necessary. Both total and monomeric aluminum levels were reduced up to 50%, and aquatic biota increased below the treatment sites. Post-liming average values for the three streams were pH 6.66, 82.7 μeq L?1 ANC and 2.63 mg L?1 Ca. The average ANC improvement suggests that some 88% of the native trout streams in Virginia, which average 29 μeq L?1 ANC reduction from acid deposition, could be temporarily restored using single application liming.  相似文献   

17.
From 1986–1989, a team of scientists measured atmospheric concentrations and fluxes in precipitation and throughfall, and modeled dry and cloudwater deposition in a spruce-fir forest of the Great Smoky Mountains National Park which is located in the Southern Appalachian Region of the United States. The work was part of the Integrated Forest Study (IFS) conducted at 12 forests in N. America and Europe. The spruce-fir forest at 1740 m consistently received the highest total deposition rates (～2200, 1200, and 700 eq ha?1 yr?1 for SO4 2?, NO3 ?, and NH4 +). During the summers of 1989 and 1990 we used multiple samplers to measure hydrologie, SO4 2?, and NO3 ? fluxes in rain and throughfall events beneath spruce forests above (1940 m) and below (1720 m) cloud base. Throughfall was used to estimate total deposition using relationships determined during the IFS. Although the SO4 2? fluxes increased with elevation by a factor of ～2 due to higher cloudwater interception at 1940 m, the NO3 ? fluxes decreased with elevation by ～30%. To investigate further, we began year round measurements of fluxes of all major ions in throughfall below spruce-fir forests at 1740 m and at 1920 m in 1993–1994. The fluxes of most ions showed a 10–50% increase with elevation due to the ～70 cm yr?1 cloudwater input at 1920 m. However, total inorganic nitrogen exhibited a 40% lower flux in throughfall at 1920 m than at 1740 m suggesting either higher dry deposition to trees at 1740 m or much higher canopy uptake of nitrogen by trees at 1920 m. Differential canopy absorption of N by trees at different elevations would have significant consequences for the use of throughfall N fluxes to estimate deposition. We used artificial trees to understand the foliar interactions of N.  相似文献   

18.
Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H+, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L?1 of H+ and sulfate-S, μmol L?1 Al, μeq L?1 total base cations and μmol L?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed.  相似文献   

19.
Cloud water deposition to canopies of Cryptomeria japonica at Mt.Rokko, Kobe, Japan, was estimated from throughfall measurements and fog water collections carried out during a full year. Annual cloud frequency was 11.5–15.5% and liquid water content (LWC) was 0.059 g/m3. Since cloud water deposition on to forest canopies was significantly correlated with the amount of fog water collected, the former parameter could be quantitatively derived from throughfall measurements. Annual cloud water deposition on to Cryptomeria canopies was 1420–2860 mm (Av. 2140 mm), corresponding to 90–180% (Av. 122%) of annual rainfall. The rate of deposition was higher at the mountain ridge and the forest edge than at the mountain side and the forest interior. Annual deposition of SO4 2?, NO3 ?, H+ and NH4 + from cloud water was estimated as 204, 153, 2.5 and 58 kg/ha, respectively, equivalent to 5.8–11.7 times the corresponding deposition via rain. The values are equal to, or exceed, the maximum deposition reported for Appalachian forests in the eastern United States. Multiple regression analyses indicate that cloud water deposition on to Cryptomeria canopies was significantly correlated with the following three parameters: cloud frequency, LWC, and wind speed. Thus, these three factors apparently control cloud water deposition on to forest canopies.  相似文献   

20.
A water quality survey has been performed on selected lakes and streams in southwest China. The purpose of the study was to measure the concentrations of acidic deposition and surface water chemistry in a region of severe air pollution, forest decline, and relatively sensitive geology to acidic deposition. We show that, although there are some high elevation lakes of low acid neutralizing capacity (ANC<150μeq L?1, acidification of lakes has not occurred in southwest China due to production of base cations in soil and dry deposition of dust that serves to neutralize acidic deposition. Water chemistry is buffered by high base cation concentrations (Ca2+, Mg2+, Na+, and K+ greater than 300μeq L?1, and pH values are always greater than 6.5.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号