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   17836篇
  免费   1211篇
  国内免费   1121篇
测绘学   4443篇
大气科学   1220篇
地球物理   1390篇
地质学   2421篇
海洋学   889篇
天文学   812篇
综合类   1573篇
自然地理   7420篇
  2024年   62篇
  2023年   132篇
  2022年   737篇
  2021年   806篇
  2020年   797篇
  2019年   929篇
  2018年   657篇
  2017年   922篇
  2016年   863篇
  2015年   881篇
  2014年   887篇
  2013年   1427篇
  2012年   1070篇
  2011年   1080篇
  2010年   736篇
  2009年   872篇
  2008年   894篇
  2007年   1056篇
  2006年   956篇
  2005年   787篇
  2004年   743篇
  2003年   600篇
  2002年   503篇
  2001年   367篇
  2000年   313篇
  1999年   225篇
  1998年   202篇
  1997年   129篇
  1996年   93篇
  1995年   68篇
  1994年   72篇
  1993年   53篇
  1992年   53篇
  1991年   32篇
  1990年   27篇
  1989年   16篇
  1988年   22篇
  1987年   21篇
  1986年   15篇
  1985年   25篇
  1984年   15篇
  1983年   10篇
  1982年   5篇
  1981年   4篇
  1980年   3篇
  1971年   1篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
991.
This paper briefly presents the research progress of the State Major Basic Research Project 2001CB309400, “Theory and Application for Retrieval and Fusion of Spatial and Temporal Quantitative Information from Complex Natural Environment”. Based on the rapid advancement of synthetic aperture radar (SAR) imagery technology, information theory of fully polarimetric scattering and applications in polarimetric SAR remote sensing are developed. To promote the modeling of passive microwave remote sensing, the vector (polarized) radiative transfer theory (VRT) of complex natural media such as inhomogeneous, multi-layered and 3-dimensional VRT is developed. With these theoretical progresses, data validation and retrieval algorithms for some typical events and characteristic parameters of earth terrain surfaces, atmosphere, and oceans from operational and experimental remote sensing satellites are studied. Employing remote sensing, radiative transfer simulation, geographic information systems (GIS), land hydrological process, and data assimilation, the Chinese land data assimilation system (CLDAS) is established. Towards the future development of China’s microwave meteorological satellites, employing remote sensing data of currently available SSM/I (special sensor microwave/imager), AMSU (advanced microwave sounding unit), MTI (microwave temperature imager), etc., with ground-based measurements, several operational algorithms and databases for atmospheric precipitation, water vapor and liquid water in clouds, and other hydrological/hydrological applications are developed. To advance China’s SAR and InSAR (interferometric SAR) technologies, the image processing and analysis of ERS (European remote sensing), Radarsat SAR, and Chinese SAR, etc., the software platforms are accomplished. Based on the researches of multi-information fusion, some simulations, identification, and information extractions of the targets from complex background clutter scenes are studied. Some experiments of radio wave propagation in anomalous atmospheric status are also carried out. Translated from Advances in Earth Science, 2007, 22(2): 111–125 [译自: 地球科学进展]  相似文献   
992.
Fuzzy Modeling for Reserve Estimation Based on Spatial Variability   总被引:1,自引:0,他引:1  
This article addresses a new reserve estimation method which uses fuzzy modeling algorithms and estimates the reserve parameters based on spatial variability. The proposed fuzzy modeling approach has three stages: (1) Structure identification and preliminary clustering, (2) Variogram analysis, and (3) Clustering based rule system. A new clustering index approach and a new spatial measure function (point semimadogram) are proposed in the paper. The developed methodology uses spatial variability in each step and takes the fuzzy rules from input-output data. The model has been tested using both simulated and real data sets. The performance evaluation indicates that the new methodology can be applied in reserve estimation and similar modeling problems  相似文献   
993.
物流地理学研究评述   总被引:1,自引:0,他引:1  
基于前人的研究,试图从物流地理学的学科属性、研究对象、学科体系、具体研究内容以及研究手段等方面进行探讨。物流地理学是一门综合性的边缘学科,其研究对象为物流活动区位、空间组织及其与地理环境的关系;内部分支包括理论物流地理学、部门物流地理学、区域物流地理学、城市物流地理学及企业物流地理学;具体研究内容应宏观与微观相结合,主要包括物流地理学的理论与研究方法,物流活动的空间组织形式及区域差异,行业物流活动的发生、发展及分布规律,城市(乡村)物流系统规划,企业物流活动的组织与空间分布规律等。  相似文献   
994.
文章以大连市为例,研究人口变化与城市人工地貌间的动态关系.研究表明:在城市发展的不同阶段,由于市内外、市内各区间的人口变化影响,使得城市人工地貌体在水平与垂直空间上不断地增长和重组.具体表现在近10年来3个阶段上的过渡,即城市人工地貌的发育模式经历了从"以水平发展为主-水平和垂直复合式发展-以垂直发展为主"的转变过程.对市内4个区人口、建筑面积以及建筑高度变化的相关分析,进一步体现了人口对各类型人工地貌体分布的驱动过程.  相似文献   
995.
旅游区位的理论已被广泛地运用到旅游空间的优化和布局中.就旅游区位的5个因子方面分析了日本客源市场的现状、发展前景;并根据对西安入境外国人进行的1008份市场调查问卷、通过数理方法分析比较取得的结果,探讨了以增长极、中心地、点-轴、带状、网状等多层次、多边的西安旅游市场开发的空间布局和旅游线路优化组合的模式.最后就开发西安的日本市场,提出了相应的对策和建议,对细分旅游市场和有针对性的市场促销有一定的参考价值.  相似文献   
996.
城市发展空间外拓对其边缘区乡村影响较大,旅游化是乡村发展过程中有别于工业化的一种形式.在对山东省日照市王家皂村农户问卷调研所得数据基础上对旅游化的效应进行评价,得出:旅游化使得村民旅游经济收入得以迅速增加;村民就业结构发生较大变化,农村劳动力向单部门经济转移;村民旅游参与意识增强,对旅游经济前景普遍看好;生活环境与质量发生改变,社区问题开始显现;正、负旅游示范效应影响并存,社区社会生态平衡面临挑战等结论,并对旅游化效应的社会意义进行了探讨.  相似文献   
997.
准格尔丘陵沟壑区五分地沟流域土地覆盖分析   总被引:1,自引:0,他引:1  
以准格尔丘陵沟壑区五分地沟流域为研究区,应用彩红外航片和IKONOS卫星影像,绘制了1987、2002年土地覆盖/植被类型图,并数字化基于地面土地利用调查绘制的1979年土地利用图.利用景观格局指数,评价了研究区土地覆盖/植被空间格局现状及土地覆盖类型动态变化;并以ETM 数据为信息源,绘制了2002年土地覆盖/植被类型图.研究表明:2002年研究区土地覆盖/植被呈现出一个耕地、草地、人工乔木林和人工灌木林以及种植稀疏灌木的草地高度镶嵌的景观格局特征;20年内土地覆盖类型发生了显著的变化,景观异质性增强.基于研究区景观的高度破碎化,绘制小流域精细尺度土地覆盖图,高空间分辨率遥感数据十分必要.  相似文献   
998.
Intra‐urban cooling rates were monitored for a year in the centre of Göteborg on the Swedish west coast. Five sites with different building geometry ‐ from dense canyon to open space ‐ within a radius of 300 m were analysed. Results showed two modes of cooling during the night. In the first mode, the cooling was site‐dependent ‐the open space cooled the most and the dense canyon the least. In the second mode, which began about 3–4 hours after sunset, all sites cooled at the same rate. Our hypothesis is that in the early part of the evening both radiative divergence and sensible heat dominate the cooling. However, as the evening progresses, a spatially homogeneous inversion is established which controls the radiative cooling, making the cooling independent of both surface geometry and surface type. From April to November the sites cooled rapidly around sunset and the cooling slowly decreased during the rest of the night. However, between December and March, the cooling was less intense, with an almost constant rate during the entire night. It has been suggested that this might be the result of the draining of stored solar heat during the summer and a continuous flux of anthropogenic heating during the winter.  相似文献   
999.
This paper provides a new discussion of how people learn through deliberative processes, drawing upon empirical analysis of a novel public engagement process for urban river restoration. Such critical evaluation is rare and yet will be crucial to both theoretical development and learning about engagement practice, not least in a policy area subject to strong regulatory drivers for public participation. The analysis supports two important learning mechanisms – the use of 'gatekeepers' of knowledge, interests and values, and the privileging of narrative. It provides new evidence of instrumental and communicative learning about shared priorities and criteria for effective river restoration that evolved through the deliberative process and directly informed the restoration scheme. It is important to question whether and how such site or context-specific learning might inform other restoration schemes. Finally, the paper questions the often ignored issue of expert learning, not least the issue of the link between individual and organizational learning.  相似文献   
1000.
以新疆艾比湖地区为研究区,通过对现有荒漠化监测指标体系的归纳分析,界定了复合荒漠化概念.利用遥感影像数据提取研究区各类荒漠化的现状与动态变化信息.研究结果表明:单一主导因子荒漠化类型面积占荒漠化土地总面积的82.29%,复合荒漠化面积占17.71%.2002~2005年,艾比湖湖面面积缩小了322.5073 km2,相应的总体土地荒漠化面积增加了7.18%,复合荒漠化面积增加了133%.土地荒漠化的过程同时也发生了变化,风蚀、复合荒漠化增加而土地盐渍化减少,荒漠化程度加重,复合荒漠化类型增加并向其他土地类型扩展.  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