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   10161篇
  免费   1530篇
  国内免费   634篇
测绘学   4232篇
大气科学   627篇
地球物理   1191篇
地质学   2807篇
海洋学   791篇
天文学   10篇
综合类   920篇
自然地理   1747篇
  2025年   4篇
  2024年   106篇
  2023年   114篇
  2022年   178篇
  2021年   247篇
  2020年   295篇
  2019年   315篇
  2018年   243篇
  2017年   390篇
  2016年   406篇
  2015年   418篇
  2014年   557篇
  2013年   797篇
  2012年   643篇
  2011年   631篇
  2010年   521篇
  2009年   682篇
  2008年   830篇
  2007年   832篇
  2006年   701篇
  2005年   592篇
  2004年   527篇
  2003年   474篇
  2002年   423篇
  2001年   313篇
  2000年   275篇
  1999年   207篇
  1998年   137篇
  1997年   109篇
  1996年   101篇
  1995年   59篇
  1994年   50篇
  1993年   44篇
  1992年   34篇
  1991年   16篇
  1990年   17篇
  1989年   13篇
  1988年   10篇
  1987年   5篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1982年   1篇
  1977年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
基于GIS的水资源管理信息系统   总被引:22,自引:0,他引:22  
地理信息系统(GIS)因为其强大的空间数据处理能力,为水资源管理提供了一个新颖、高效的工具。本文深入GIS的功能和水资源管理的实际,通过山西汾阳县的应用实例,阐述了应用ArchInfo/ArcView构建水资源管理信息系统过程中的信息收集、储存、分析以及二次开发的方法和过程,分析了两者结合应用的可行性和优越性,并讨论了这种方法在水资源系统模拟、辅助决策支持等方面的广泛应用前景。  相似文献   
12.
The aim of this study was to apply and to verify the use of fuzzy logic to landslide susceptibility mapping in the Gangneung area, Korea, using a geographic information system (GIS). For this aim, in the study, a data-derived model (frequency ratio) and a knowledge-derived model (fuzzy operator) were combined. Landslide locations were identified by changing the detection technique of KOMPSAT-1 images and checked by field studies. For landslide susceptibility mapping, maps of the topography, lineaments, soil, forest, and land cover were extracted from the spatial data sets, and the eight factors influencing landslide occurrence were obtained from the database. Using the factors and the identified landslide, the fuzzy membership values were calculated. Then fuzzy algebraic operators were applied to the fuzzy membership values for landslide susceptibility mapping. Finally, the produced map was verified by comparing with existing landslide locations for calculating prediction accuracy. Among the fuzzy operators, in the case in which the gamma operator (λ = 0.975) showed the best accuracy (84.68%) while the case in which the fuzzy or operator was applied showed the worst accuracy (66.50%).  相似文献   
13.
14.
城市化进程的快速发展对城市规划管理观念、方法和手段提出了更高的要求,通过科学技术手段尤其是信息化手段改进城市规划管理,提高城市规划水平已成为必然。本文以GIS为核心技术,采用SOA面向服务的体系结构设计思想,介绍了昆明市规划管理信息系统的逻辑框架、技术路线、数据库的设计和各个功能模块的实现,最后重点阐述了系统的关键技术及应用后可能取得的社会、经济效益。  相似文献   
15.
Agricultural practices, hydrology, and water quality of the 267-km2 Big Spring groundwater drainage basin in Clayton County, Iowa, have been monitored since 1981. Land use is agricultural; nitrate-nitrogen (-N) and herbicides are the resulting contaminants in groundwater and surface water. Ordovician Galena Group carbonate rocks comprise the main aquifer in the basin. Recharge to this karstic aquifer is by infiltration, augmented by sinkhole-captured runoff. Groundwater is discharged at Big Spring, where quantity and quality of the discharge are monitored. Monitoring has shown a threefold increase in groundwater nitrate-N concentrations from the 1960s to the early 1980s. The nitrate-N discharged from the basin typically is equivalent to over one-third of the nitrogen fertilizer applied, with larger losses during wetter years. Atrazine is present in groundwater all year; however, contaminant concentrations in the groundwater respond directly to recharge events, and unique chemical signatures of infiltration versus runoff recharge are detectable in the discharge from Big Spring. Education and demonstration efforts have reduced nitrogen fertilizer application rates by one-third since 1981. Relating declines in nitrate and pesticide concentrations to inputs of nitrogen fertilizer and pesticides at Big Spring is problematic. Annual recharge has varied five-fold during monitoring, overshadowing any water-quality improvements resulting from incrementally decreased inputs. Electronic Publication  相似文献   
16.
二三维一体化在Skyline与SuperMap6R中的实现对比   总被引:1,自引:1,他引:1  
GIS技术的不断进步促进了二三维一体化技术的发展,针对该技术对比了两类软件平台:Skyline和SuperMap6R,分析了两类平台各自的技术特点以及二三维一体化实现技术,实现了三维数据网络发布,并得出结论.  相似文献   
17.
高精度的数字地图是正确匹配车辆位置的基础。详细分析了地图数据的地理误差和拓扑误差的误差形式,路网数据模型的常见误差因素和改进策略,最后介绍了不同地图匹配算法对地图质量的敏感性和可行性。根据可能出现的误差对现有数字地图和匹配算法加以改进,弥补了原有数字地图带来的不精确缺陷。跑车实验证明,考虑了数字地图误差影响的匹配算法可以明显提高定位精度,减小车辆定位误差。  相似文献   
18.
东喜马拉雅南迦巴瓦峰地区地质构造十分复杂,对该区板块缝合带的空间位置问题,长期以来,一直认为沿雅鲁藏布江呈弧形展布。笔者以ETM+为主要信息源,以遥感与GIS为技术支撑,对南峰地区的断裂构造进行了详细的遥感解译分析,从构造统计分析的角度对断裂构造进行定量研究,从分维值及趋势值的空间分布及变化特征分析,认为缝合带的南东段、北段大致沿雅鲁藏布江展布,而北西段位于雅鲁藏布江的北西侧,沿东久-米林(断裂带)展布,这也与近几年来开展了1∶25万区域地质调查获得的新认识相一致。  相似文献   
19.
Water quality parameters associated with siltation (non‐volatile and volatile suspended solids), oxygen depletion (chemical and biochemical oxygen demand), nutrient enrichment (N, P), toxicity (Pb, Zn, Cu, Cr, Ni, Cd), and human pathogenic micro‐organisms (coliforms, faecal coliforms, faecal streptococci) were measured in baseflow and stormflow from a residential catchment in Hamilton, New Zealand, from November 1979 to December 1981. A macro‐invertebrate survey was conducted. All parameters, except nitrogen, were predominantly associated with particulate material, and closely followed suspended solids behaviour during storm runoff. The concentrations of these particulate parameters are linearly related to suspended solid concentrations, which implies a reasonable consistency in the particulate source material, probably attributable to the uniform stable land use. The runoff was enriched with nitrate (from septic tank seepage) and the particles by Zn, Pb, and Cu. There was little or no enrichment of the particulates with phosphorus, nitrogen, organic matter, Cr, or Ni relative to catchment soils. Ni, Cr, and Cd were generally below detection limits. Dissolved reactive phosphorus and NH4 +‐N levels were low and unimportant in total P or N leaving the catchment. Most organic matter was particulate and only slowly degraded, and consequently the biological oxygen demand was only a small fraction (c. 13%) of chemical oxygen demand. Interpretation of the water quality data allows some tentative predictions to be made of potential receiving water impacts. It is doubtful that urban runoff will cause significant oxygen depletion, although the high level of organic‐rich particulate material could lead to a deterioration of receiving water sediments and affect benthic invertebrates. Urban runoff may be an important source of nutrients, but (apart from nitrate) its importance depends on the amount of suspended material in the runoff rather than increased input of nutrients from urban‐related activities. Bacterial counts indicate a poor water quality. The impact of metals will depend largely on the bioavailability of the particulate‐bound fraction. The key to the understanding of transport, treatment, and impact of most potential pollutants in urban runoff is probably their association with particulate materials.  相似文献   
20.
Outlier trimming and homogeneity checking/correction were performed on the monthly precipitation time series of various lengths from 267 stations in Turkey. Outlier values are usually found during dry summer months, and are concentrated mostly over the southern parts of the country, where the dry period is most pronounced, implying natural extremes rather than wrong measurements. Homogeneity analysis was done using the Standard Normal Homogeneity Test, on an individual monthly basis, which led to many non‐testable series due to lack of reference stations, especially during summer months. Yet, remaining testable months were usually helpful for the assessment of homogenity, revealing a well distributed set of stations that proved to be homogeneous. There were still a number of stations which either could not be tested efficiently, or were classified as inhomogeneous. Lack of metadata is argued to be largely responsible for inefficient homogeneity testing. Copyright © 2008 John Wiley & Sons, Ltd.  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