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1.
This study investigated the influence of climatic variables on the spatio-temporal variation of vegetation growth using normalized difference vegetation index (NDVI) data and climate data from 2000 to 2013 in the Northeast China Transect. Partial correlation and linear regression methods were applied to quantify the response of the growing season NDVI to climatic variables. Gradient analysis was used to investigate how the response changes across the precipitation gradient over the transect. The results show that, at the spatial scale, NDVI increases with precipitation in grassland, and the spatial sensitivity is 0.001/mm. At the temporal scale, grassland NDVI is less correlated with precipitation in wet areas where precipitation exceeds a threshold of 250 mm. The temporal sensitivity of grassland NDVI to precipitation is 0.0003–0.0006/mm. Positive correlations between NDVI and temperature dominate in forest areas, and forest NDVI is sensitive to temperature by 0.06–0.12/°C.  相似文献   

2.
Based on measured stream nitrogen concentrations at outlets of 12 small sub‐areas (1·3–54·7 km2) in a largely forested catchment during the base flow period, we investigated the influences of discharges and different catchment characteristics on stream nitrogen concentration. Our field surveys were carried out during the 11‐month's period from April 2001 to February 2002 and the correlations between nitrogen concentrations and catchment characteristics were studied. The results showed that the vegetation cover was strongly correlated to total nitrogen (TN) and nitrate + nitrite ? nitrogen (NOx‐N) concentrations. That is, the TN and NOx‐N concentrations had positive correlations with mean normalized difference vegetation cover index (NDVI) of each sub‐area during dormant seasons (mean NDVI < 0 · 70) and had negative correlations during the growing season (mean NDVI ≥ 0 . 70). The significance of catchment characteristics to TN and NOx‐N concentrations was ranked as vegetation cover > soil > topography > land use, and the best models can account for 55–64% of the variance of TN and NOx‐N concentrations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
In this study, the vegetation dynamics and their correlations with climate variability in northern China were evaluated based on the normalized difference vegetation index (NDVI) and meteorological datasets from 1982 to 2006. The NDVI showed that vegetation cover had a tiny increasing trend for whole study area in the past 25 years. However, the interannual changes of NDVI were different in each season. The part of spring and autumn NDVI values increased significantly, while the summer NDVI increased no significantly. And the interannual variations of the NDVI showed obvious spatial differentiations. The annual max NDVI increased were mainly distributed in most areas of grassland and farmland, whereas the annual max NDVI decreased were mainly distributed in forest areas. The annual NDVI and temperature had more important relationships. Thus, as compared to precipitation, the correlation between NDVI with temperature was stronger than the precipitation in northern China. NDVI and climatic variables were different in each season. The NDVI trends exhibited a close correspondence to climatological variations in region and season. In Addition, human activities also had profound effect to the NDVI trends in some regions. All these findings will make humans know more about the knowledge of the natural forces that influence vegetation change and supply a scientific basic resource to for the environmental management in northern China.  相似文献   

4.
Normalized Difference Vegetation Index (NDVI) is widely recognized as a good indicator of vegetation productivity. Diagnosing the NDVI trend and understanding climatic factors influences on NDVI can predict the productivity changes under different climatic scenarios. This paper examined NDVI dynamic and its response to climate factors during a 10 year period (1998–2008) in Inner Mongolia. The main findings are as follows: (1) The NDVI multi-scale characters can be revealed well by wavelet transform, and the average NDVI and the NDVI amplitude show a gradually decreased trend from northeast to southwest in Inner Mongolia during the past 10 years, furthermore, this trend is consistent with the heat and water distribution caused by latitude difference in north–south direction and Asia monsoon effect in east–west direction. (2) The relation between NDVI and temperature is the most close, followed by precipitation, sunshine hours and relative humidity. Different vegetation cover types show different strengths in correlation between NDVI and climate variables with the correlation values decreasing from forest, meadow steppe to desert steppe in whole. (3) The precipitation and temperature have the same change cycle, both nearly 290 days in the 20 selected stations. The NDVI has the same change cycle with the precipitation and temperature or either 10 days earlier or later than precipitation and temperature, which supports the significant correlation between NDVI and its climatic factors from a new perspective. The nearly 290 days change cycle implies that the vegetation growth cycle is nearly 10 months and there are no obvious differences change cycles in different vegetations. (4) Vegetation dynamic is significantly correlated to the temperature and precipitation at the time scale of 10, 20, 40, 80, 160, and 320-day, respectively, and the S3 scale (i.e., the time scale of 80-day), nearly 3 months (one season), is most significant and suitable for evaluating the vegetation dynamic to climatic factors.  相似文献   

5.
卫星遥感数据评估黄土高原陆面干湿程度研究   总被引:1,自引:1,他引:0       下载免费PDF全文
康悦  文军  张堂堂  田辉  陈昊 《地球物理学报》2014,57(8):2473-2483
卫星遥感数据具有估算时空尺度上地表参量的优势,在陆地环境状况评估和监测等方面有很大的应用潜力.本文利用美国地球观测系统卫星搭载中等分辨率成像光谱仪(EOS/MODIS)在黄土高原2002-2010年期间获取的每16天归一化植被指数(NDVI)和每日地表温度(LST)数据,分析了黄土高原地区LST-NDVI空间的基本特征.结果发现:当研究区域足够大且遥感数据时间序列足够长时,LST-NDVI空间中(NDVI,LST)散点并非呈三角形或梯形分布.为了能够利用EOS/MODIS的NDVI和LST数据正确地评估陆面的干湿状况,本文给出了利用数据集合法确定LST-NDVI空间中干边和湿边的数值,即在LST-NDVI空间中,利用NDVI等值区间内LST最大值和最小值的集合代表干边和湿边的数值,并进一步证明了在LST-NDVI空间中干边和湿边数值并非呈线性关系.在分析LST-NDVI空间特征的基础上,通过构建地表温度-植被干旱指数(TVDI),探讨其在评估黄土高原地区陆面的干湿状况的应用潜力.结果表明:由TVDI距平表征的陆面的干湿程度与局地降水距平有很好的关联性,二者在时空分布上有较好的对应关系.在我国陇东黄土高原塬区,TDVI数值与地面观测的表层土壤湿度有很好的相关性,相关系数在0.67以上,并通过显著性为1%的检验.由此说明:如果合理选取干边和湿边的数值,TDVI可应用于区域陆面干湿程度的客观评估.  相似文献   

6.
目的:探讨基于MRI测量小腿软组织厚度对评估原发性下肢淋巴水肿(PLEL)分期的价值。方法:回顾性收集确诊为PLEL患者90例的临床及MR影像资料,所有患者均行双侧下肢MR检查。采用短时反转恢复序列(STIR)序列测量双侧小腿软组织总厚度(T)、肌骨厚度(M)和皮下软组织厚度(S),分别计算双侧小腿T及S的差值(DT、DS)。参考2020年国际淋巴协会及淋巴外科下肢淋巴水肿的临床分期标准将患者分为Ⅰ、Ⅱ、Ⅲ 期。使用单因素方差分析比较不同临床分期之间的小腿软组织厚度,使用Spearman相关分析小腿软组织厚度与临床分期的相关性,使用ROC曲线确定小腿软组织厚度对临床分期的鉴别效能。结果:3期之间T、S、DT及DS差异均有统计学意义,而M不存在统计学差异;各分期间两两比较,T、S、DT及DS在Ⅰ期与Ⅱ期及Ⅰ期与 Ⅲ 期之间比较均具有统计学差异,而在Ⅱ期与 Ⅲ 期比较无统计学差异。DT(r=0.750)与DS(r=0.772)与临床分期的相关性明显大于T(r=0.669)及S(r=0.734),DS与临床分期相关性最高;M与临床分期无明显相关关系。ROC曲线显示各参数鉴别Ⅰ期与Ⅱ期的AUC值大于鉴别Ⅱ期与 Ⅲ 期的AUC值,所有参数中DS(AUC=0.945)鉴别Ⅰ期与Ⅱ期的曲线下面积(AUC)最高。结论:MRI小腿软组织厚度测量可以作为单侧PLEL临床分期的定量辅助方法,对于单侧PLEL患者,我们推荐DS作为鉴别Ⅰ期与Ⅱ期淋巴水肿的最佳厚度指标。   相似文献   

7.
This study explores the potential for predicting the spatial variation in subsurface water level change with crop growth stage from satellite data in Thabua Irrigation Project, situated in the northern central region of Thailand. The relationship between subsurface water level change from pumping water to irrigate rice in the dry season and the age of the rice was analysed. The spatial model of subsurface water level change was developed from the classification using greenness or (normalized difference vegetation index NDVI) derived from Landsat 5 Thematic Mapper data. The NDVI of 52 rice fields was employed to assess its relationship to the age of the rice. It was found that NDVI and rice age have a good correlation (R2 = 0·73). The low NDVI values (−0·059 to 0·082) in these fields were related to the young rice stage (0–30 days). NDVI and subsurface water level change were also correlated in this study and found to have a high correlation (Water level change (m day−1) = 0·3442 × NDVI − 0·0372; R2 = 0·96). From this model, the water level change caused by rice at different growth stages was derived. This was used to show the spatial variation of water level change in the project during the 1998–99 dry‐season cropping. This simple method of using NDVI relationships with water level change and crop growth stages proves to be useful in determining the areas prone to excessive lowering of the subsurface water level during the dry season. This could assist in the appropriate planning of the use of subsurface water resources in dry‐season cropping. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

8.
The temporal evolution of vegetation activity on various land cover classes in the Spanish Pyrenees was analyzed. Two time series of the normalized difference vegetation index (NDVI) were used, corresponding to March (early spring) and August (the end of summer). The series were generated from Landsat TM and Landsat ETM+ images for the period 1984–2007. An increase in the NDVI in March was found for vegetated areas, and the opposite trend was found in both March and August for degraded areas (badlands and erosion risk areas). The rise in minimum temperature and the time variation of the cloud cover during the study period appears to be the most important factors explaining increased NDVI in the vegetated areas. In degraded areas, no climatic or topographic variable was associated with the negative NDVI trend, which may be related to erosion processes taking place in these regions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
近年来随着人类的活动日益加剧,水体富营养化问题已经严重威胁到湖泊生态安全。为了快速并准确地获取藻华爆发的范围,本文提出浮游藻类指数线性拟合模型(FAI linear fitting model, FAI-L)。在以往的研究中,NDVI(normalized difference vegetation index)已经广泛应用于藻华的识别中,且采用坡度计算获取NDVI阈值的方法也得到验证,相对于NDVI,FAI对环境条件的改变敏感度较低,且由于FAI增加了短红外波段,能够有效地降低部分大气和薄云的影响,对藻华的识别有较高的精度,但是FAI识别藻华的阈值如何确定的问题没有有效的解决办法。本文通过建立NDVI与FAI的线性拟合方程,利用NDVI阈值确定FAI阈值,能够有效地解决FAI阈值确定问题。通过Landsat8和Sentinel-2的提取结果显示:(1)FAI-L相对于NDVI提取结果在精度上有较大提升。采用该方法对于Landsat8影像的藻华提取精度为97.16%,相对于NDVI的提取精度(91.72%)提高了5.44%。(2)以Sentinel-2数据为基础探究FAI-L的适用性情...  相似文献   

10.
Study on NDVI-T_s space by combining LAI and evapotranspiration   总被引:1,自引:1,他引:1  
Vegetation index and land surface temperature (Ts) are important parameters for land surface process modeling. The remotely sensed data in visible/near infrared and thermal infrared wavelengths have proven to be well suited to monitoring vegetation status, soil surface moisture conditions, drought and crop yield. More useful information can be created by integrated analyses of these two kinds of data, which will help us to study main principles of the temporal and spatial variations of land su…  相似文献   

11.
This paper discusses the preliminary results of a study on the vegetation pattern and its relationship with meteorological parameters in and around Istanbul. The study covers an area of over 6800 km2 consisting of urban and suburban centers, and uses the visible and near-infrared bands of Landsat. The spatial variation of the Normalized Difference Vegetation Index (NDVI) and meteorological parameters such as sensible heat flux, momentum flux, relative humidity, moist static energy, rainfall rate and temperature have been investigated based on observations in ten stations in the European (Thracian) and Anatolian parts of Istanbul. NDVI values have been evaluated from the Landsat data for a single day, viz. 24 October 1986, using ERDAS in ten different classes. The simultaneous spatial variations of sensible heat and momentum fluxes have been computed from the wind and temperature profiles using the Monin-Obukhov similarity theory. The static energy variations are based on the surface meteorological observations. There is very good correlation between NDVI and rainfall rate. Good correlation also exists between: NDVI and relative humidity; NDVI, sensible heat flux and relative humidity; NDVI, momentum flux and emissivity; and NDVI, sensible heat flux and emissivity. The study suggests that the momentum flux has only marginal impact on NDVI. Due to rapid urbanization, the coastal belt is characterized by reduced NDVI compared to the interior areas, suggesting that thermodynamic discontinuities considerably influence the vegetation pattern. This study is useful for the investigation of small-scale circulation models, especially in urban and suburban areas where differential heating leads to the formation of heat islands. In the long run, such studies on a global scale are vital to gain accurate, timely information on the distribution of vegetation on the earth’s surface. This may lead to an understanding of how changes in land cover affect phenomena as diverse as the atmospheric CO2 concentrations, the hydrological cycle and the energy balance at the surface-atmosphere interface.  相似文献   

12.
Abstract

This work deals with the problem of the use of remote sensing data derived from NOAA/AVHRR observations for monitoring the West African Sahel climatic variability. NDVI is widely used in hydrological and climatological research, and in the study of global climatic changes. The relationships between NDVI and climatic parameters are not well established yet and are the focus of many studies. The relationships between NDVI and rainfall were studied at a 10-day time step in the Nakambe River basin in Burkina Faso in the Sahelo-Sudanian area over the years 1982–1999. Good correlations were found in the annual evolution of these two variables. The statistical analysis shows a significant relationship between NDVI and the sum of the annual rainfall with determination coefficients greater than 0.80. At the spatial scale of 0.5° × 0.5°, the determination coefficient ranges from 0.91 to 0.96. It was also found that the NDVI is a good indicator of the determination of the beginning and the end of the rainy season. It gives reasonably good results in comparison with the other methods commonly used in the study region.  相似文献   

13.
目的:探讨CT淋巴管造影对淋巴管肌瘤病乳糜胸的诊断价值。方法:回顾性分析2009至2014年我院38例临床或病理证实的LAM患者及172例非LAM乳糜胸患者的临床及影像学资料,所有患者均接受淋巴管造影(DLG)及淋巴管造影后CT检查,由2名医师对CT淋巴管造影(CTL)显示乳糜胸的发生部位、分布类型及胸导管梗阻情况进行分析。结果:CTL显示36例LAM合并乳糜胸。单侧积液23例(右侧11例,左侧12例),双侧积液13例;脏层胸膜型3例,壁层胸膜型7例,混合型4例,未显示型22例。172例非LAM乳糜胸(原发性乳糜胸118例,继发性乳糜胸54例)。118例原发性乳糜胸中,右侧积液26例,左侧积液27例,双侧积液65例;脏层型60例,壁层型15例,混合型23例,未显示型20例。54例继发性乳糜胸中,右侧积液13例,左侧积液3例,双侧积液38例;脏层型43例,壁层型2例,混合型6例,未显示型3例。LAM乳糜胸与原发性乳糜胸的发生部位不存在差异,LAM乳糜胸与继发性乳糜胸的发生部位存在差异。LAM乳糜胸的发生侧别几乎没有差别,继发性乳糜胸常见为双侧。LAM乳糜胸与原发性乳糜胸和继发性乳糜胸在胸膜类型上存在差异,LAM乳糜胸以未显示型最常见,而原发性和继发性乳糜胸以脏层型最常见。结论:CTL可显示LAM乳糜胸的发生类型,提示胸导管梗阻或者腹腔淋巴管压力增高可能是LAM乳糜胸的致病原因,为临床手术治疗LAM乳糜胸提供影像学依据。   相似文献   

14.
This paper focuses on interpreting the different spatial relationships between NDVI and T s, a triangular or a trapezoid, and on analyzing transformation conditions, the physical and ecological meanings of the vegetation index-surface temperature space as well. Further, we use the Temperature-Vegetation Dryness Index (TVDI) to explain the existent meaning of a triangular space after NDVI reaches its saturated state by employing the relationships between NDVI, LAI and evapotranspiration. The specific relations between NDVI and T s are useful for describing, validating and updating land surface models.  相似文献   

15.
Vegetation index is a simple, effective and experiential measurement of terrestrial vegetation activity, and plays a very important role in qualitative and quantitative remote sensing. Aiming at shortages of current vegetation indices, and starting from the analysis of vegetation spectral characteristics, we put forward a new vegetation index, the three-band gradient difference vegetation index (TGDVI), and established algorithms to inverse crown cover fraction and leaf area index (LAI) from it. Theoretical analysis and model simulation show that TGDVI has high saturation point and the ability to remove the influence of background to some degree, and the explicit functional relation with crown cover fraction and LAI can be established. Moreover, study shows that TGDVI also has the ability to partly remove the influence of thin cloud. Experiment in the Shunyi District, Beijing, China shows that reasonable result can be reached using the vegetation index to retrieve LAI. We also theoretically analyzed the  相似文献   

16.
The distributions of dimethylsulfide (DMS) and its precursor, dimethylsulfoniopropionate (DMSP), were examined in the surface microlayer and corresponding subsurface water of the Yellow Sea, China, in April 2006. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were 5.42 (1.78–12.75), 9.22 (2.85–19.73) and 17.50 (4.33–36.09) nmol L−1 in the subsurface water, and those in the surface microlayer were 4.92 (1.69–10.66), 17.08 (3.13–38.82) and 22.54 (4.85–47.24) nmol L−1, respectively. The enrichment factor (EF) of DMS in the microlayer ranged from 0.47 to 2.24 with a mean of 0.98. In contrast, DMSPd and DMSPp appeared to be enriched in the microlayer with average EFs of 1.98 and 1.39, respectively. A close correlation of integrated DMS, DMSPp and chlorophyll a concentrations for compiled data from all stations in the microlayer and the subsurface water indicated that phytoplankton biomass might play an important role in controlling the distributions of biogenic sulfurs in the study area. Moreover, a statistically significant relationship was found between the microlayer concentrations of DMS, DMSP and chlorophyll a and their subsurface water concentrations, suggesting a close linkage between these two water compartments. Interestingly, we observed higher biological production rates and consumption rates of DMS in the microlayer relative to the subsurface water. Furthermore, the DMS production rates were closely correlated both with DMSPd and chlorophyll a concentrations. Our study showed that the major sink of DMS in microlayer was escape into the atmosphere, which greatly exceeded its bacterial consumption. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 6.41 μmol m−2 d−1 during spring.  相似文献   

17.
Jing Fu  Jun Niu  Bellie Sivakumar 《水文研究》2018,32(12):1814-1827
Vegetation cover plays an important role in linking the atmosphere, water, and land and is deemed as a key indicator in the terrestrial ecological system. Therefore, it is of great importance to monitor vegetation dynamics and understand the mechanisms of vegetation change, including that driven by climate change. This study examines (a) the evolution of vegetation dynamics over the Heihe River Basin in the typical arid zone in north‐western China using nonparametric Mann–Kendall test and Thiel Sen's slope; (b) the relationships between remotely sensed vegetation indices (normalized difference vegetation index [NDVI] and enhanced vegetation index [EVI]) and hydroclimatic variables based on correlation analysis; and (c) the prediction of vegetation anomalies using a multiple linear regression model. For the analysis, the Moderate Resolution Imaging Spectroradiometer NDVI/EVI product and the gridded daily meteorological data at a spatial resolution of 0.125° over the period 2001–2010 are considered. The results indicate that vegetation cover improved over a large proportion during 2001–2010, with a significant trend towards warm and wet, characterized by an increase in average annual temperature and precipitation by 0.042 °C/year and 5.8 mm/year, respectively. We test the feasibility of NDVI and EVI in quantifying the responses of vegetation anomaly to climate change and develop a statistical model to predict vegetation dynamics in the basin. The NDVI‐based model is found to be more reliable than the EVI‐based model, partly due to the vegetation characteristics and geomorphologic properties of the study region. The proposed model performs well when there is no lag time between meteorological factors and vegetation indices for grassland and cropland, whereas 1‐month lead time prediction is found to be best for forest. The soil water content is introduced as an extra explanatory variable, which effectively improves the prediction accuracy for different land use types. In general, the predictive ability of the proposed model is stable and satisfactory, and the model can provide useful early warning information for regional water resources management under changing climate.  相似文献   

18.
The age of past lava flows is crucial information for evaluating the hazards and risks posed by effusive volcanoes, but traditional dating methods are expensive and time‐consuming. This study proposes an alternative statistical dating method based on remote sensing observations of tropical volcanoes by exploiting the relationship between lava flow age and vegetation cover. First, the factors controlling vegetation density on lava flows, represented by the normalized difference vegetation index (NDVI), were investigated. These factors were then integrated into pixel‐based multi‐variable regression models of lava flow age to derive lava flow age maps. The method was tested at a pixel scale on three tropical African volcanoes with considerable recent effusive activity: Nyamuragira (Democratic Republic of Congo), Mt Cameroon (Cameroon) and Karthala (the Comoros). Due to different climatic and topographic conditions, the parameters of the spatial modeling are volcano‐specific. Validation suggests that the obtained statistical models are robust and can thus be applied for estimating the age of unmodified undated lava flow surfaces for these volcanoes. When the models are applied to fully vegetated lava flows, the results should be interpreted with caution due to the saturation of NDVI. In order to improve the accuracy of the models, when available, spatial data on temperature and precipitation should be included to directly represent climatic variation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

19.
溶解性有机质(DOM)在流域水环境中广泛存在,参与各种生物地球化学循环过程。快速的城镇化过程和人类活动显著改变了流域水体DOM含量和特性,从分子层面上解析DOM在流域尺度上的时空分异特征对流域水质管控具有重要的理论和应用价值。以长三角地区樟溪流域为研究对象,依据土地利用和人类活动强度布设采样点,于2022年7月采集水样。结果表明,樟溪流域水体溶解性有机物主要的分子式元素组成为CHO、CHON、CHOS,其中木质素/富羧酸脂环分子类有机物相对占比最高。在子流域空间分布上,人类活动强的子流域CHON、CHONS类型化合物含量更高。选取采样点距城镇距离、距源头距离以及土地利用类型所占采样点缓冲区的比例来表征人类活动的影响。结果表明,流域内DOM杂原子受人类活动强度影响,距源头的距离与水体DOM分子中氮原子的强度加权平均值(Nwa)和CHON化合物百分呈显著正相关,与碳、氢原子和荷质比的强度加权平均值(Cwa、Hwa、m/zwa)呈显著负相关。CHON分子的相对丰度与林地面积比例呈显著负相关,与农业用地比例呈显著正相关。比较具有典型土地利用类型的水体DOM:典型农田、城镇土地利用类型DOM含有更多独特的CHON分子式,农田DOM在木质素/富羧酸脂环分子区域出现CHON分子式的富集,城镇DOM在脂肪类和木质素/富羧酸脂环分子区域均出现了CHON分子式富集。研究表明在城郊流域中,人类活动显著改变了水体DOM的分子特征,增加了分子多样性,促进了特定分子式的富集。  相似文献   

20.
植被覆盖状况影响中国地表气温变化的观测事实   总被引:3,自引:0,他引:3       下载免费PDF全文
利用NOAA/AVHRR归一化植被指数(NDVI)及观测气温与再分析地表气温的差值(Observation Minus Reanalysis, OMR)分析了植被覆盖状况对中国地表气温变化的影响.结果表明,地表气温OMR趋势值与NDVI在空间上呈现出显著的负相关关系,植被覆盖状况差(NDVI小于0.1)的区域地表升温较为显著,气温OMR趋势值超过0.2℃/10a,而植被覆盖度高(NDVI大于0.5)的区域气温OMR趋势值则变化不大,甚至出现降温.气温OMR趋势值对植被的季节变化还有着敏感的响应.不同区域植被覆盖状况的差异可能导致中国地表气温变化对全球变暖的响应不同,预测中国未来气候变化需要考虑植被覆盖状况及其动态变化的影响.  相似文献   

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