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   2634篇
  免费   313篇
  国内免费   339篇
测绘学   646篇
大气科学   474篇
地球物理   771篇
地质学   562篇
海洋学   251篇
天文学   35篇
综合类   210篇
自然地理   337篇
  2024年   12篇
  2023年   10篇
  2022年   35篇
  2021年   51篇
  2020年   79篇
  2019年   94篇
  2018年   59篇
  2017年   102篇
  2016年   85篇
  2015年   97篇
  2014年   126篇
  2013年   234篇
  2012年   142篇
  2011年   151篇
  2010年   107篇
  2009年   175篇
  2008年   165篇
  2007年   155篇
  2006年   146篇
  2005年   134篇
  2004年   120篇
  2003年   138篇
  2002年   129篇
  2001年   132篇
  2000年   90篇
  1999年   94篇
  1998年   68篇
  1997年   53篇
  1996年   58篇
  1995年   48篇
  1994年   29篇
  1993年   37篇
  1992年   35篇
  1991年   20篇
  1990年   19篇
  1989年   20篇
  1988年   17篇
  1987年   11篇
  1985年   3篇
  1984年   1篇
  1979年   1篇
  1954年   4篇
排序方式: 共有3286条查询结果,搜索用时 31 毫秒
991.
遥感影像三维可视化在新疆西昆仑区域地质调查中的应用   总被引:2,自引:0,他引:2  
李胤  朱建南  崔艳梅 《江苏地质》2015,39(3):451-455
综合应用“3S”技术、遥感数字影像处理技术、虚拟现实等,通过遥感影像的几何校正、影像数据融合、高精度DEM生成和影像复合等技术,实现了新疆西昆仑地区遥感影像三维可视化。将遥感影像三维可视化及其影像动态分析运用于新疆西昆仑区域地质调查(1∶5万)工作,可提高地质填图效率、丰富地质填图成果  相似文献   
992.
孙文伟 《地下水》2015,(1):118-120
丘陵地区植被较差,堆积物比较松散,遇有异常暴雨过程,容易形成山洪泥石流,产生自然灾害,造成人员财产损失。分析国内外有关建设最新成果,对丘陵地区开展山洪泥石流预警系统建设工作进行研究,利用现有科学技术,规划设计分析预警工作的方法、步骤、流程、结果,为丘陵地区防洪体系建设提供科学合理的建设模型。  相似文献   
993.
Global solar radiation(GSR) is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation model(DEM) data as a representation of the complex terrain and multiplicity condition produces a series of topographic factors(e.g. slope, aspect, etc.). Based on 1 km resolution DEM data, meteorological observations and NOAA-AVHRR remote sensing data, a distributed model for the calculation of GSR over rugged terrain within the Yangtze River Basin has been developed. The overarching model permits calculation of astronomical solar radiation for rugged topography and comprises a distributed direct solar radiation model, a distributed diffuse radiation model and a distributed terrain reflectance radiation model. Using the developed model, a quantitative simulation of the GSR space distribution and visualization has been undertaken, with results subsequently analyzed with respect to locality and terrain. Analyses suggest that GSR magnitude is seasonally affected, while the degree of influence was found to increase in concurrence with increasing altitude. Moreover, GSR magnitude exhibited clear spatial variation with respect to the dominant local aspect; GSR values associated with the sunny southern slopes were significantly greater than those associated with shaded slopes. Error analysis indicates a mean absolute error of 12.983 MJm-2 and a mean relative error of 3.608%, while the results based on a site authentication procedure display an absolute error of 22.621 MJm-2 and a relative error of 4.626%.  相似文献   
994.
The Brazilian coast is characterized by dif- ferent tidal regimes and distinct meteorological influ- ences. The northern part has larger tidal amplitudes and is permanently affected by trade winds and tropical distur- bances; the southern portion has smaller tidal amplitudes and is frequently influenced by extratropical cyclone ac- tivity. Besides these aspects, many features regarding current structure and behavior are also present, such as the equatorial system of currents, the subtropical gyre and the corresponding western boundary currents, and the Bra- zil-Malvinas confluence region. Within this context, ef- forts were made to develop the BRAZCOAST system, capable of describing the processes that determine the oceanic circulation from large to coastal scales. A cus- tomized version of the Princeton Ocean Model (POM) was implemented in a basin-scale domain covering the whole of the tropical and southern Atlantic Ocean, with 0.5° spatial resolution, as well as three nested grids with (1/12)° resolution covering the different parts of the Bra- zilian shelf, in a one-way procedure. POM was modified to include tidal potential generator terms and a par- tially-clamped boundary condition for tidal elevations. The coarse grid captured large-scale features, while the nested grids detailed local circulations affected by bathymetry and coastal restrictions. An interesting aspect at the coarse grid level was the relevance of the Weddell Sea to the location of the tidal amphidromic systems.  相似文献   
995.
This article examines the spatial characteristics of public service supply and the factors influencing such supply in cities of Sichuan Province, China using spatial-autocorrelation and spatial econometric models with statistical data in 2012. The results demonstrate that expenditures on different types of public services present different spatial autocorrelation patterns. Although the spatial differences in basic public service expenditures are relatively small, a clear fan-shaped spillover to the east can be seen in Chengdu City. Chengdu also shows high clustering of advanced public service expenditures, being a typical core-periphery pattern. Post-earthquake reconstruction expenditures are clustered in the "5.12 Wenchuan earthquake" region and spill over toward cities to the east. The efficiency of public services in the mountainous areas in western Sichuan is low and exhibits a pattern of low-low spatial autocorrelation. The efficiency of public service supply is affected by economic, social, political and geographical factors. Based on the results of this analysis, we recommend a supply strategy that incorporates different types of public services and a specialized public service supply strategy for mountainous areas. Overall public service efficiency should be enhanced by focusing on narrowing the gap in farmers' income among regions and accelerating urbanization. Decision-makers should consider moresupportive policies with regard to providing basic public services in mountainous areas to ensure an equalized supply of basic public services. To enhance the efficiency of advanced public service supply, additional growth pole should be encouraged and incentivized; however, investments are required to drive the development of the peripheral regions through regional economic integration. Both software and hardware types of infrastructure are required to supply services efficiently during post-disaster reconstruction.  相似文献   
996.
新疆土地利用空间结构和布局分析   总被引:1,自引:0,他引:1       下载免费PDF全文
基于2008年新疆土地利用数据,采用计量地理学模型,并借助SPSS软件和ArcGIS软件,对新疆各地州(市)的土地利用数量结构和空间格局现状进行了定量分析,并与全国土地利用结构对比。结果表明:新疆现状土地资源具有明显的地域差异,北疆地区土地利用程度明显优于南疆,这种差异与所处的地理位置、地形地貌密切相关;土地利用结构的多样性和集中度由北向南递减;新疆的土地利用结构单一,各地区的土地利用类型组合系数普遍不高,反映出新疆土地利用的整体功能还有很大的提升空间。  相似文献   
997.
Crop monitoring during the growing season is important for regional management decisions and biomass prediction. The objectives of this study were to develop, improve and validate a scale independent biomass model. Field studies were conducted in Huimin County, Shandong Province of China, during the 2006–2007 growing season of winter wheat (Triticum aestivum L.). The field design had a multiscale set-up with four levels which differed in their management, such as nitrogen fertilizer inputs and cultivars, to create different biomass conditions: small experimental fields (L1), large experimental fields (L2), small farm fields (L3), and large farm fields (L4). L4, planted with different winter wheat varieties, was managed according to farmers’ practice while L1 through L3 represented controlled field experiments. Multitemporal spectral measurements were taken in the fields, and biomass was sampled for each spectral campaign. In addition, multitemporal Hyperion data were obtained in 2006 and 2007. L1 field data were used to develop biomass models based on the relation between the winter wheat spectra and biomass: several published vegetation indices, including NRI, REP, OSAVI, TCI, and NDVI, were investigated. A new hyperspectral vegetation index, which uses a four-band combination in the NIR and SWIR domains, named GnyLi, was developed. Following the multiscale concept, the data of higher levels (L2 through L4) were used stepwise to validate and improve the models of the lower levels, and to transfer the improved models to the next level. Lastly, the models were transferred and validated at the regional scale using Hyperion images of 2006 and 2007. The results showed that the GnyLi and NRI models, which were based on the NIR and SWIR domains, performed best with R2 > 0.74. All the other indices explained less than 60% model variability. Using the Hyperion data for regionalization, GnyLi and NRI explained 81–89% of the biomass variability. These results highlighted that GnyLi and NRI can be used together with hyperspectral images for both plot and regional level biomass estimation. Nevertheless, additional studies and analyses are needed to test its replicability in other environmental conditions.  相似文献   
998.
标准灰色模型GM(1,1)以序列第一个分量作为初始条件进行灰色微分建模,未能充分利用序列中的新信息;其背景值的构造本质上采用了数值积分中的梯形法,精度不高。针对上述缺点,提出一种基于粒子群算法的灰色预测模型,即PSOGM(1,1)模型,对初始值和背景值参数进行优化,并将模型应用于岩体变形分析中。计算结果表明,PSOGM(1,1)模型具有较高的预测精度,可作为变形分析的一种新方法。  相似文献   
999.
目前国内市场上的电子商务平台多以商品交易为主,信息表达过于平面化、信息访问缺乏立体式的可延伸性。改变传统的电子商务管理与发展模式,深入利用GIS、虚拟仿真、数据仓库、数据挖掘等技术及时全面采集各种商务信息,建立基于二三维GIS的电子商务基础平台,发展智能商务的应用,形成城市"数字商务"地理信息平台是符合当前城市发展的趋势。本文以广州市数字商务地理信息公共平台建设为例,详细介绍了基于GIS的城市数字商务平台建设内容与实现的关键技术,包括二三维地图平台建设技术,突破技术难题的二三维地图的联动切换显示技术,商务专题数据库和POI数据库建立以及虚拟广告功能实现技术等,为城市数字商务地理信息平台建设提供有价值的参考。  相似文献   
1000.
本文研究在数字城市地理空间框架相关成果的基础上,通过共享地理信息公共平台基础地理数据,提出城乡规划一张图数据库组织结构及建设标准,在共享联合的基础上实现规划项目管理信息化、规划业务审批电子化、规划决策管理一体化的建设思路与方法,并以数字黄冈地理空间框架城乡规划管理信息系统建设为示范进行系统实践应用,替代有纯文本的办公环境,以一体化的数据管理方式为规划审批与决策提供信息化手段与支持。  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