首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   576篇
  免费   194篇
  国内免费   319篇
测绘学   86篇
大气科学   700篇
地球物理   42篇
地质学   75篇
海洋学   61篇
天文学   4篇
综合类   25篇
自然地理   96篇
  2024年   3篇
  2023年   10篇
  2022年   24篇
  2021年   33篇
  2020年   23篇
  2019年   19篇
  2018年   35篇
  2017年   28篇
  2016年   43篇
  2015年   37篇
  2014年   57篇
  2013年   58篇
  2012年   54篇
  2011年   61篇
  2010年   46篇
  2009年   61篇
  2008年   43篇
  2007年   33篇
  2006年   57篇
  2005年   55篇
  2004年   36篇
  2003年   48篇
  2002年   22篇
  2001年   17篇
  2000年   33篇
  1999年   16篇
  1998年   24篇
  1997年   11篇
  1996年   11篇
  1995年   14篇
  1994年   15篇
  1993年   11篇
  1992年   8篇
  1991年   6篇
  1990年   6篇
  1989年   6篇
  1988年   5篇
  1986年   6篇
  1985年   6篇
  1984年   1篇
  1983年   1篇
  1982年   3篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有1089条查询结果,搜索用时 15 毫秒
21.
北京市春夏季大气气溶胶的单颗粒分析表征   总被引:9,自引:0,他引:9  
采集了北京市2000年春夏季大气气溶胶样品5个,采用扫描电镜X射线能谱技术分析大气气溶胶单颗粒约2500个。研究结果表明,沙尘期间,矿物尘是最主要的颗粒物种类,非沙尘期间,北京市大气气溶胶中主要检出矿物尘和含硫颗粒物。夏季随着颗粒物污染的加重,含硫颗粒物的数目百分数增加。是北京市大气颗粒物污染的重要特征。重点讨论了Ca-S颗粒、K-S颗粒和Ca-K-S颗粒三类典型含硫颗粒物的化学组成和粒径分布特征。数目可观的Ca-K-S颗粒以及其他硫酸盐颗粒的生成与相对湿度和云量等气象条件相关,这些颗粒物可能是云中过程的产物。减少SO2排放,减少含硫颗粒物,对于控制北京市的大气颗粒物浓度水平具有重要意义。  相似文献   
22.
By utilizing observational data from a 325 m tower of the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) on March 19-29, 2001 and August 11-25, 2003, a comprehensive study was conducted on the vertical dynamical and thermodynamic characteristics of the urban lower boundary layer (ULBL) and its relationship with aerosol concentration over Beijing. Firstly, a comparative analysis was made on the gradient data (wind, temperature and humidity), ultrasonic data (atmospheric turbulences) and air-quality observations at different tower heights (47, 120 and 280 m). Secondly, a diagnosis was made to reveal the major features of normalized variances of velocity and temperature, turbulence kinetic energy as well as their relationship with aerosol concentrations. Furthermore, the characteristics of the ULBL vertical structure and the TSP concentration/distribution variations during a sand/dust weather process were also analyzed. The outcome of the study showed that under unstable stratification, the normalized variances of velocity (σu/u*, σv/u*, σw/u*) and temperature (σT/T*) at 47 and 120 m heights fit the Monin-Obukhov similarity (MOS) framework and the fitting formulas were given out accordingly. According to the stratification parameter (z′/L), the stable ULBL could be divided into 2 zones. With z′/L<0.1, it was a weakly stable zone and MOS framework was applicable. The other was a highly stable zone with z′/L>0.1 and the normalized velocity variances tended to increase along with higher stability, but it remained constant for normalized temperature variances. At daytime, the near-surface layer includes two heights of 47 and 120 m, while 280 m has been above it. The ULBL analysis in conjunction with a sand/dust weather process in Beijing in March 2001 indicated that the maximum concentration of Total Suspended Particulates (TSP) at 320 m reached 913.3 μg/m3 and the particles were transported from the upper to lower ULBL, which was apparently related to the development process of a low-level jet and its concomitant strong sinking motion.  相似文献   
23.
The spatial/temporal variation information of atmospheric dynamic-chemical processes at observation site points of the "canopy" boundary of Beijing urban building ensemble and over urban area "surface", as well as the seasonal correlation structure of the gaseous and particulate states of urban atmospheric pollution (UAP) and its seasonal conversion feature at observation points are investigated, using the comprehensive observation data of the Beijing City Air Pollution Observation Experiment (BECAPEX) in winter and summer 2003 with a "point-surface" combined research approach. By using "one dimension spatial empirical orthogonal function (EOF)" principal component analysis (PCA) mode, the seasonal change of gaseous and particulate states of atmospheric aerosols and the association feature of pollutant species under the background of the complicated structure of urban boundary layer (UBL) are analyzed. The comprehensive analyses of the principal components of particle concentrations,gaseous pollutant species, and meteorological conditions reveal the seasonal changes of the complex constituent and structure features of the gaseous and particulate states of UAP to further trace the impact feature of urban aerosol pollution surface sources and the seasonal difference of the component structure of UAP. Research results suggest that in the temporal evolution of the gaseous and particulate states of winter/summer UAP, NOx, CO, and SO2 showed an "in-phase" evolution feature, however, O3 showed an "inverse-phase" relation with other species,all possessing distinctive dependent feature. On the whole, summer concentrations of gaseous pollutants CO, SO2, and NOx were obviously lower than winter ones, especially, the reduction in CO concentration was most distinctive, and ones in SO2 and NOx were next. However, the summer O3 concentration was more than twice winter one. Winter/summer differences in PM10and PM2.5 particle concentrations were relatively not obvious, which indicates that responses of PM10 and PM2.5 particle concentrations to the difference of winter/summer heating period emission sources are far less distinctive than those of NOx, SO2, and CO. The correlation feature of winter/summer gaseous and particulate states depicts that both PM10 and PM2.5 particles were significantly correlated with NOx, and their correlations with NOx are more significant than those with other pollutants. Through PCA, it is found that there was a distinctive difference in the principal component combination structure of winter/summer PM10 and PM2.5 particles: SO2 and NOx dominated in the principal component of winter PM10 and PM2.5 particles; while CO and NOx played the major role in the principal component of summer PM10 and PM2.5 particles. For winter/summer PM10 and PM2.5 particles, there might exist the gaseous and particulate states correlation structures of different "combinations" of such dependent pollutant species. Research results also uncover that the interaction processes of gaseous and particulate states were also related with the vertical structure of UBL, that is to say, the low value layer of UBL O3 concentration was associated with the collocation of atmospheric vertical structures of the low level inversion,inverse humidity, and small wind, which depicts summer boundary layer atmospheric character, i.e.the compound impact of the dependent factor "combination" of wind, temperature, and humidity elements and their collocation structure on the variations of different gaseous pollutant concentrations. Such a depth structure of the extremely low value of O3 concentration in the UBL accords with its "inverse-phase" relation with other gaseous pollutant species. The PCA of meteorological factors associated with PM10 and PM2.5 concentrations also reveals the sensitivity of PM10 and PM2.5 concentration to the combinatory feature of local meteorological conditions.  相似文献   
24.
针对区域大气污染物排放量与空气质量在时空分布上存在不完全协同、匹配的现象,论文选择SO2、NOX、PM2.5、CO和VOCs作为大气污染物指标,选择气溶胶光学厚度(Aerosol Optical Depth, AOD)表征颗粒物环境空气质量,以武汉市为例,综合应用耦合模型和空间错位指数模型研究2类指标之间的空间非协同耦合规律。主要结论如下:① 武汉市大气污染物排放量与颗粒物空气质量具有不同空间分布特征,大气污染物排放量呈现由城市中心城区向远城区递减的趋势,其中SO2、PM2.5和VOCs的排放具有明显的中心聚集现象,而NOX和CO聚集现象不显著,且与道路分布明显相关;AOD分布具有明显的空间差异性,总体上呈由西北向东南依次递减的趋势。② 武汉市大气污染物排放与颗粒物空气质量的空间非协同耦合规律:越靠近城市中心城区,空间协同耦合现象越显著,空间错位现象越弱;越远离主城区,空间非协同耦合现象越显著,空间错位现象越显著;SO2排放量与AOD在武汉市远城区的空间错位指数均大于0.7,且耦合度指数小于0.3,呈现较强的非协同耦合特征,NOX、VOCs、PM2.5的排放量与AOD在武汉中心城区的空间错位指数均小于0.5,且耦合度指数大于0.5,协同耦合现象较为显著。③ 基于时空非协同耦合分析城市大气环境污染治理建议:针对污染物与AOD空间错位不显著的城市中心城区,以本地减排治理为主;针对污染物与AOD空间错位显著的远城区,应在污染溯源分析的基础上进行区域协调综合治理。  相似文献   
25.
基于FY3A/MERSI资料分析广东省气溶胶光学厚度分布   总被引:3,自引:3,他引:0  
邓玉娇  胡猛  林楚勇  曹静 《气象》2016,42(1):61-66
利用国产极轨气象卫星FY3A的MERSI AOD产品分析2010—2013年广东省气溶胶光学厚度的分布规律。结果表明:MERSI AOD产品与地面太阳光度计实测数据的相关系数为0.72,其平均绝对值误差为0.12,均方根误差为0.15,数据精度可满足研究需要;从AOD的空间分布看,珠三角西翼东翼山区五市,其中佛山市、东莞市、中山市为广东省AOD均值最高的地区,梅州市、河源市为广东省AOD均值最低的地区;从AOD的时间分布看,2010—2013年间,AOD呈现先升高后降低的趋势,2011年为拐点,与此同时,AOD还表现出明显的季节变化特征,春季为AOD高值期,夏季、秋季次之,冬季最低。  相似文献   
26.
姚青  刘敬乐  韩素芹  樊文雁 《气象》2016,42(4):443-449
利用天津城区2009-2014年春节期间大气气溶胶观测资料和相关气象资料,重点分析2013和2014年春节期间气溶胶污染特征,探求燃放烟花爆竹以及气象条件对春节期间大气气溶胶的影响。结果表明,受燃放烟花爆竹影响,春节期间PM_(2.5)质量浓度最高值均发生在除夕夜间;持续雾霾天气条件下燃放烟花爆竹,造成2013年除夕夜间PM_(2.5)质量浓度峰值达到1240μg·m~(-3),是近年来最严重的一次;2014年春节期间烟花爆竹燃放量有所减少,加之空气扩散条件较为有利,PM_(2.5)质量浓度显著低于2013年;不同天气条件下,气溶胶数浓度谱分布特征存在明显差异,燃放烟花爆竹期间气溶胶数浓度水平与严重雾-霾天气相当。  相似文献   
27.
针对HJ-1卫星CCD数据,利用改进的暗像元法反演气溶胶光学厚度(AOD),再利用反演的AOD对其进行大气校正。将反演的气溶胶与地基太阳光度计数据进行对比验证,发现当反演的AOD值大于0.2时,反演值与地基观测值的相关系数为0.964,符合MODIS业务化反演AOD的精度要求。再将反演得到的气溶胶带入6S辐射传输模型中,对HJ-1卫星CCD数据进行大气校正实验。结果表明,该方法能有效提高HJ-1卫星CCD数据大气校正的精度,更好地复原地物的真实光谱信息。  相似文献   
28.
刘小力  王琪洁  张勇  梁忠壮 《测绘科学》2016,41(4):55-60,82
针对使用6S模型中标准气溶胶模型进行大气辐射校正时结果较差的问题,该文提出使用实测气溶胶模型代替其进行计算。利用AERONET数据产品分析了香河、榆中等部分站点的气溶胶成分及其区域性分布特点,证明了中国气溶胶的成分具有明显的区域特性;并对6S模型中标准气溶胶模型与香河地基观测气溶胶光学参数进行比较,结果表明,两者具有较大的差异;最后使用不同的气溶胶模型校正Landsat5TM影像,结果表明,采用实测气溶胶数据进行大气辐射校正结果较优。  相似文献   
29.
Spatiotemporal characteristics and anthropogenic signals of aerosol optical thickness (AOT) distributions over Korea are investigated in this study using AOT time-series data from the Moderate Resolution Imaging Spectroradiometer (MODIS). AOT observations, a quantitative measure of the atmospheric quality, had significant geographical variations during the study period (2000–2010). Comparing metro cities or counties with similar populations, western regions showed higher AOT values than eastern regions. Particular matter with a diameter < 10 µm (PM10), including aeolian dust or yellow dust, is the primary component of atmospheric aerosols, and their transport into the region has shown a strong seasonal pattern with its peak from March to April and lows from July to September. These seasonal dust patterns, however, did not correspond well to temporal AOT records, which typically reached the maximum level in June nationwide. Rather, widespread regional fire events and humidity showed significant correlations with AOT time-series. This correlation rapidly increased as the range of fire occurrence was extended to the west as far as 115°E. The relative humidity also had a significant correlation with AOT during the month of June. In addition to urban emission of anthropogenic aerosols, regional biomass burning and secondary growth of hygroscopic aerosols are considered important contributors to the degradation of the atmospheric environment during the non-Asian Dust season over the Korean Peninsula.  相似文献   
30.
利用重建的华南区域黑碳气溶胶(Black Carbon, BC)浓度资料,分析其与南海夏季风在年际尺度上的关系。结果表明,华南区域BC浓度与南海夏季风的关系在2000年前后有明显的突变,由显著负相关变为显著正相关,即由高BC浓度弱季风变为高BC浓度强季风。通过合成对比分析,发现1988—1999年(第一时间段)的华南BC主要气候效应是间接辐射强迫作用:华南BC使云粒子半径减小,抑制华南区域春季降水,增加了云的生命期,从而使到达地面的短波辐射减少,表面和低层大气降温。负温度异常激发了异常反气旋,在南海区域即有东风异常。到夏季,东风异常减弱了季风强度,同时抑制了南海地区的降水。2000—2010年(第二时间段)的华南BC主要气候效应是直接辐射强迫作用:春季高BC浓度通过直接气候效应,增暖大气,加强降水,但是雨日减少,从而使到达地面的短波辐射增多,表面和低层大气增温。正温度异常激发了异常气旋,在南海区域即有西风异常一直维持到夏季,增大了季风强度,同时增强了南海地区的降水。  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