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   4363篇
  免费   324篇
  国内免费   279篇
测绘学   729篇
大气科学   171篇
地球物理   485篇
地质学   588篇
海洋学   477篇
天文学   7篇
综合类   411篇
自然地理   2098篇
  2024年   11篇
  2023年   42篇
  2022年   123篇
  2021年   144篇
  2020年   165篇
  2019年   193篇
  2018年   152篇
  2017年   203篇
  2016年   192篇
  2015年   225篇
  2014年   244篇
  2013年   385篇
  2012年   260篇
  2011年   296篇
  2010年   227篇
  2009年   231篇
  2008年   255篇
  2007年   241篇
  2006年   219篇
  2005年   210篇
  2004年   173篇
  2003年   168篇
  2002年   139篇
  2001年   109篇
  2000年   93篇
  1999年   75篇
  1998年   38篇
  1997年   36篇
  1996年   19篇
  1995年   16篇
  1994年   18篇
  1993年   10篇
  1992年   6篇
  1991年   4篇
  1990年   11篇
  1989年   3篇
  1988年   3篇
  1987年   3篇
  1986年   6篇
  1985年   6篇
  1984年   6篇
  1983年   1篇
  1982年   5篇
排序方式: 共有4966条查询结果,搜索用时 250 毫秒
71.
72.
东莞城市化过程中若干问题研究   总被引:10,自引:3,他引:10  
改革开放以来,东莞市积极吸纳海外资本与技术,通过“三来一补”企业的快速发展,带动了非农产业和小城镇的迅速发展。然而,受我国分散的工业化和农村城市化政策体制的影响,在快速城市化过程中也暴露出很多值得关注的问题。该文基于实地考察与问卷访谈,重点分析了土地利用效率低、外来人口集中以及基础设施建设与城市经济发展不相协调等问题,并提出协调城市化发展的对策。  相似文献   
73.
基于农用地价格体系的征用地价应用研究   总被引:5,自引:0,他引:5  
农用地价格体系和估价成果应用是当前农用地定级估价工作的难点和争论焦点,该文提出了农用地价格体系应以资源基准地价为基础,通过一系列修正,得出分级分区的征用基准地价、不转变用途的农地流转价、转变用途的农地转用价;以佛山市南海区的农用地估价成果为例,就其与现行征地补偿标准进行了比较,并与南海城区、广州市区城镇建设用地基准地价的相互衔接性进行了验算,应用成本逆推法,从城镇基准地价导出建设用地生地地价,在内涵一致的条件下相互比较。结果表明,按此地价体系建立的农用地征用价能够与城镇地价相衔接,可为城乡地价一体化的建立提供实证。  相似文献   
74.
基于卫星遥感的鲁西北季节性风沙化土地研究   总被引:7,自引:0,他引:7  
文章对鲁西北地区季节性风沙化土地的分布、特征及近20年来的演变做了初步的分析,阐述了该地区风沙化土地的成因及其危害,在肯定已有治沙成绩的基础上,就如何合理利用和改造这些土地提出了合理布局农田林网、地一步完善农田水利设施等意见和建议。  相似文献   
75.
In this study the arable land changes in two counties (Zigui and Xingshan) in the Three Gorges Reservoir area in China are investigated. The statistical data from the officially published statistical books are used to study these changes in the two counties during the past 50 years since 1949. The changes of arable land, changes of arable land per capita, and changes of multiple crop index in Zigui and Xingshan counties are examined. Using an index method, we conclude that the two counties are critical in the sustainable utilization of arable land.  相似文献   
76.
With the objectives to acquire the fundamental data of the territorial resource, understand the impacts of human activities on the land use and cover patterns and evaluate the potential of the future exploitation, an intensive land cover classification with an accuracy of 93% has been completed for North Ningxia by remote sensing technique based on the adoption of a combination method composed of texture training, maximum likelihood classification and post-processing such as re-allocation and aggregation. This classification result was incorporated with the contemporaneous socio-economic and meteorological data for cross-sectional regression modelling to reveal the spatial determinants of the land cover patterns and understand the human-environmental relationships. A tentative evaluation on the potential of soil exploitation in the near future was carried out in combination with our land use and cover change detection results aiming at supplying some useful references for the central and local governments in their sustainable land use planning.  相似文献   
77.
The probability of crane living in reedy wetlands can reach 100%, at the same time, the area of reed, the water level and adjacent water area are main factors which control the crane's habitat selection. We all know that all these factors are spatially heterogeneous. For the Xianghai wetland safety and to protect the Xianghai wetland habitat of crane, this paper has mainly identified a solution to these problems. The wetland information is extracted from the TM images, which reflect the whole wetland landscape and are very important for both quantitative analysis of remote sensing observation of the earth system and positioning analysis in GIS database that is automatically extracted from DEM. The DEM for Xianghai characteristics of topography is created. On the basis of the GRID SUBMODULE, applying the GIS spatial overlay analysis, the relationship between the water level and the reed area below the water level and the rating distribution maps of reed area above water level is established. When the water level reaches the altitude of 165 m, the reed area, 981.2 ha is maximum, i.e., the water level of 165 m is the optimal.  相似文献   
78.
ABSTRACT. The Shimentai Nature Reserve in Yingde County, Guangdong Province, China, established recently in a subtropical upland forest area, has served for ages as an essential and customary source of livelihood for local people. Assessment of forest usage indicates heavy reliance by villagers on its diversified biotic resources. This forest dependence, associated with socioeconomic factors such as distance from village, ethnic origin, out‐migration of rural youngsters, and a local tradition of conservation, is unlikely to decline in the near future. The reserve management recognizes the need to address the livelihood issues of local people and to win local support. A pragmatic adherence to provincial and higher‐level policies that exclude forest‐tapping activities could lead to more people‐versus‐park conflicts, which would dilute fundamental conservation objectives. A more enlightened and localized approach that nurtures a synergy between limited forest use and conservation while helping to develop new income sources could furnish workable alternatives.  相似文献   
79.
Converting farming slope land into artificial forestland or grassland is a major measure of soil/water conservation. Five conversion practices, namely, 1) a control plot still tilled with a crop (maize), 2) a folder grass-growing plot seeded with Lolium perenne , 3) a young alder tree-growing plot, 4) a pear orchard plot and 5)a bamboo plot intercropped with folder grass, were monitored to compare the soil conservation efficiency of those changes in Ya'an, Sichuan for 3 years between September 1998 and August 2001. Results showed that the 5 designed converting models functioned differently in erosion control. The most effective model was bamboo groves intercropped with folder grass (Lolium perenne). The folder grass (Lolium perenne) growing model was more effective than the pure pear orchard model. The least effective model was the young alder tree-growing slope, which was even less effective than the control (a slope without converted cultivation). Meanwhile, changes in the soil's physical properties r  相似文献   
80.
邵泽宝  刘乃行  王松江 《地下水》2003,25(4):251-253
水资源匮乏已成为当今社会发展不可回避的主要问题,成为制约国民经济快速、稳定、健康发展的“瓶颈”,解决这一问题成为当务之急,本文就城市节水存在的问题,提出了加强节水管理的综合性措施。  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