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   309篇
  免费   44篇
  国内免费   64篇
测绘学   22篇
大气科学   54篇
地球物理   70篇
地质学   161篇
海洋学   23篇
天文学   19篇
综合类   34篇
自然地理   34篇
  2023年   4篇
  2022年   11篇
  2021年   17篇
  2020年   15篇
  2019年   13篇
  2018年   25篇
  2017年   29篇
  2016年   21篇
  2015年   15篇
  2014年   29篇
  2013年   20篇
  2012年   14篇
  2011年   10篇
  2010年   18篇
  2009年   19篇
  2008年   14篇
  2007年   12篇
  2006年   12篇
  2005年   8篇
  2004年   6篇
  2003年   11篇
  2002年   5篇
  2001年   4篇
  2000年   7篇
  1999年   9篇
  1998年   15篇
  1997年   9篇
  1996年   9篇
  1995年   8篇
  1994年   4篇
  1993年   6篇
  1992年   4篇
  1991年   4篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1974年   1篇
  1958年   1篇
排序方式: 共有417条查询结果,搜索用时 15 毫秒
101.
I.IntroductionTheEuropeanscientistshavelongagorecognizedtheimportantvalueofthesystematiclandscapestudyandapplieditsuccessfullytoanumberoflocalandnationalplanningpolicies.TheWorkingGroupofLandscapeEcoplanningwhichwasestablishedbyIALE(InternationalAssoc…  相似文献   
102.
煤矸石—水相互作用的溶解动力学及其环境地球化学效应研究党志(中国科学院地球化学研究所,贵阳550002)关键词水—岩作用煤矸石地球化学动力学采煤矿区复垦环境效应收稿日期:1997-3-10作者简介:党志男1962年生博士生环境地球化学煤矸石以其量多、...  相似文献   
103.
应用地理信息系统理论、技术和方法,针对煤炭生产管理中的地质测量问题,研究开发了煤矿地质测量信息系统(CMGIS)。在分析CMGIS系统目标的基础上,确立了符合煤炭生产管理实际需要的系统硬件配置和逻辑结构,着重论述了CMGIS的软件组成及系统功能。CMGIS较其它应用系统具有较强的图形功能,能较好地解决煤矿地质测量成图问题。  相似文献   
104.
台风暴雨中尺度系统与结构的数值研究   总被引:7,自引:3,他引:7  
首先对8407,8411和8504号台风进行了数值模拟,并详细分析了模式输出的带通流场,发现;在湿台风引起的大范围暴雨区,低怪有强辐合,高怪有的大尺度辐散,而在干台风产生的弱降水区,高层则无中尺度辐散气流。其次,对引起暴雨突然增幅的8407号台风进行了对比试验,表明:台风大尺度环境场是产生台风暴雨中尺度系统的源,而凝结潜热释放和地形效应则是形成和影响这些中尺度系统中和中尺度的结构和重要因素。  相似文献   
105.
在通讯技术、计算机、现代光学等各个方面都要用到Walsh变换,又如:为了减少图象处理中的复杂性和压缩图象传输中图象所占的频带,就要借助干Walsh变换。在快速Walsh变换中,往往先考虑Walsh—Hadamard变换;然后经过置换,可以转化为Walsh—Kaczmarz变换、Walsh—Paley变换。根据这些变换阵之间的关系式,我们研究了并矢矩阵的性质,以及变换阵的约化(reduction)算子D(m)。在[1]中,各变换阵在D(m)作用下,是通过另一种算子即所谓扩展(expansion)箅子表示它们的递归关系,本文则直接从D(m)给出三种变换的递归关系,这在计算上更为方便一些。  相似文献   
106.
刘倩倩  党云晓  张文忠  魏璐瑶 《地理科学》2021,41(12):2096-2106
利用2015年中国40个城市大规模问卷调查数据,采用贝叶斯多层级有序分类响应模型探讨了PM2.5污染对居民主观幸福感的影响,进而核算居民为减轻PM2.5污染的支付意愿。研究发现:PM2.5污染对主观幸福感具有显著的负向影响,PM2.5污染每增加1个单位,主观幸福感将下降0.040个百分点;家庭月收入对主观幸福感具有显著的正向影响,家庭月收入每增加1个单位,主观幸福感将提升0.026个百分点。支付意愿不仅受到家庭收入水平的影响,还受到居民所处城市空气质量的影响;在承受PM2.5污染的最初阶段,居民为改善空气质量的支付意愿最高。居民为改善空气质量愿意支付的金额平均为226元,占家庭月总收入的2.274%。  相似文献   
107.
Chen  Fahu  Wu  Shaohong  Cui  Peng  Cai  Yunlong  Zhang  Yili  Yin  Yunhe  Liu  Guobin  Ouyang  Zhu  Ma  Wei  Yang  Linsheng  Wu  Duo  Lei  Jiaqiang  Zhang  Guoyou  Zou  Xueyong  Chen  Xiaoqing  Tan  Minghong  Wang  Xunming  Bao  Anming  Cheng  Weixin  Dang  Xiaohu  Wei  Binggan  Wang  Guoliang  Wang  Wuyi  Zhang  Xingquan  Liu  Xiaochen  Li  Shengyu 《地理学报(英文版)》2021,31(1):3-45
Physical geography is a basic research subject of natural sciences.Its research object is the natural environment which is closely related to human living and development,and China's natural environment is complex and diverse.According to national needs and regional development,physical geographers have achieved remarkable achievements in applied basis and applied research,which also has substantially contributed to the planning of national economic growth and social development,the protection of macro ecosystems and resources,and sustainable regional development.This study summarized the practice and application of physical geography in China over the past 70 years in the following fields:regional differences in natural environments and physical regionalization;land use and land cover changes;natural hazards and risk reduction;process and prevention of desertification;upgrading of medium-and low-yield fields in the Huang-Huai-Hai region;engineering construction in permafrost areas; geochemical element anomalies and the prevention and control of endemic diseases;positioning and observation of hysical geographical elements;and identification of geospatial differentiation and geographical detectors. Furthermore, we have proposed the future direction of applied research in the field of physical geography.  相似文献   
108.
The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on the Red River flood plain near Hanoi, Vietnam. The groundwater chemistry was investigated in a transect of 100 piezometers. Results show an anoxic aquifer featuring organic carbon decomposition with redox zonation dominated by the reduction of Fe-oxides and methanogenesis. Enhanced PCO2 pressure causes carbonate dissolution to take place but mainly in the soil and unsaturated zone. The concentration of As increases over depth to a concentration of up to 550 μg/L. Most As is present as As(III) but some As(V) is always found. Arsenic correlates well with NH4, relating its release to organic matter decomposition and the source of As appears to be the Fe-oxides being reduced. Part of the produced Fe(II) is apparently reprecipitated as siderite containing less As. Results from sediment extraction indicate most As to be related to the Fe-oxide fractions. The measured amount of sorbed As is low. In agreement, speciation calculations for a Fe-oxide surface suggest As(III) to constitute only 3% of the surface sites while the remainder is occupied by carbonate and silica species. The evolution in water chemistry over depth is homogeneous and a reactive transport model was constructed to quantify the geochemical processes along the vertical groundwater flow component. A redox zonation model was constructed using the partial equilibrium approach with organic carbon degradation in the sediment as the only rate controlling parameter. Apart from the upper meter a constant degradation rate of 0.15 C mmol/L/yr could explain the redox zonation throughout the aquifer. Modeling also indicates that the Fe-oxide being reduced is of a stable type like goethite or hematite. Arsenic is contained in the Fe-oxides and is first released during their dissolution. Our model further suggests that part of the released As is adsorbed on the surface of the remaining Fe-oxides and in this way may be retarded.  相似文献   
109.
一次飑线过程的雷达回波分析与数值模拟   总被引:12,自引:2,他引:12       下载免费PDF全文
2003年4月12日, 一条飑线袭击了江西、福建、浙江三省, 所到之处出现冰雹、大风等强烈天气, 这次过程强度强, 影响范围大, 三省交界及附近区域有二十多个测站出现冰雹、大风, 冰雹直径有的达3 cm以上, 最大风速达32 m/s。该文利用建阳新一代天气雷达探测到的回波以及中尺度非静力数值模式 (MM5) 对这次过程进行数值模拟, 分析此次强对流过程。结果表明:雷达回波显示出飑线的带状强回波, 线状回波上呈现波型特征; 在数值模拟结果中看到在系统发生的带状区域内有多个中尺度涡旋存在, 在飑线内有中尺度涡旋簇和弓形回波。  相似文献   
110.
During the Meiyu period in June and July of 1998, intensified field observations have been carried out for the project “Huaihe River Basin Energy and Water Cycle Experiment (HUBEX)”. For studying Meiyu front and its precipitation in Huaihe River basin, the present paper has performed analysis on the middle and lower level wind fields in the troposphere by using the radar data obtained from the two Doppler radars located at Fengtai district and Shouxian County. From June 29 to July 3 in 1998, the continuous heavy precipitation occurred in Huaihe River basin around Meiyu front. The precipitation process on July 2 occurred within the observation range of the two Doppler radar in Fengtai district and Shouxian County. The maximum rainfall of the Meiyu front was over 100 mm in 24 h, so it can be regarded as a typical mesoscale heavy precipitation process related to Meiyu front. Based on the wind field retrieved from the dual Doppler radar, we find that there are meso-γ scale vertical circulations in the vertical cross-section perpendicular to Meiyu front, the strong upward motion of which corresponds to the position of the heavy rainfall area. Furthermore, other results obtained by this study are identical with the results by analyzing the conventional synoptic data years ago. For example: in the vicinity of 3 km level height ahead of Meiyu front there exists a southwest low-level jet; the rainstorm caused by Meiyu front mainly occurs at the left side of the southwest low-level jet; and the Meiyu front causes the intensification of the low-level convergence in front of it.  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