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   4225篇
  免费   207篇
  国内免费   284篇
林业   592篇
农学   232篇
基础科学   204篇
  1296篇
综合类   1808篇
农作物   48篇
水产渔业   117篇
畜牧兽医   95篇
园艺   108篇
植物保护   216篇
  2024年   7篇
  2023年   23篇
  2022年   55篇
  2021年   46篇
  2020年   52篇
  2019年   82篇
  2018年   52篇
  2017年   100篇
  2016年   129篇
  2015年   135篇
  2014年   201篇
  2013年   204篇
  2012年   326篇
  2011年   367篇
  2010年   310篇
  2009年   357篇
  2008年   353篇
  2007年   423篇
  2006年   363篇
  2005年   310篇
  2004年   221篇
  2003年   192篇
  2002年   120篇
  2001年   91篇
  2000年   50篇
  1999年   48篇
  1998年   26篇
  1997年   17篇
  1996年   9篇
  1995年   15篇
  1994年   12篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1989年   4篇
  1987年   1篇
  1977年   1篇
排序方式: 共有4716条查询结果,搜索用时 16 毫秒
1.
陈冬梅  刘璨 《森林工程》2004,20(3):53-55
在提出长株潭道路交通总体规划设想的前提下,分析长沙市路网,提出道路交通发展目标.  相似文献   
2.
城市空间形态定量化研究进展   总被引:2,自引:0,他引:2  
对国内外学者有关城市空间形态定量化的研究方法作了回顾与总结,主要介绍了基于GIS的定量分析法和分形维数法,并简要地对各种方法作了评论,使读者对目前在这一方面的研究情况有所了解,以便明确进一步深入研究的方向.  相似文献   
3.
图书馆学情报学核心期刊网络引文著者的计量分析   总被引:1,自引:1,他引:0  
以10种图书馆情报学核心期刊2002~2004年的载文情况为样本.对这3年来的网络引文的著者情况进行了调研、分析。包括著作所属单位、分布地区、以覆职祢、学历、年龄等,旨在更准确地研究图书情报界对网络学术信息的利用情况。  相似文献   
4.
This paper depicted the physiographic landscape features and natural vegetation situation of study area (the eastern Jilin Province), and expatiates the definition, basic characters and its development of Ecological Land Classification (ELC). Based on the combination of relief map, satellite photography for study area and vegetation inventory data of 480 sample sites, a 5-class and a 15-class ecological land type map was concluded according to 4 important factors including slope, aspect, vegetation and elevation. Ecological Classification System (ECS) is a method to identify, characterize, and map ecosystems. The Ecological Land Type (ELT) was examined and applied initially in eastern Jilin Province. Foundation item: This paper was supported by Chinese Academy of Sciences “100 people” project and the Open Research Station of Changbai Mountain Forest Ecosystem. Biography: XIAO Bao-ying (1974-), female, postgraduate in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China Responsible editor: Zhu Hong  相似文献   
5.
The study on the characteristics of spatial variability of soil nutrients and fertilizer recommendations in cotton field under certain conditions of agricultural management was conducted with GIS and systematic approach for soil nutrient constrains. The results showed that of the spatial variability of soil nutrient was greatly related to the management condition of previous crops. Grid sampling and variable rate application technology (VRAT) were the tools that would hopefully increase fertilizer efficiency. The fertilizers were applied where they were needed and at proper rate. Balance fertilization demonstration showed that fertilizer recommendations according to the available nutrient level in soil could decrease fertilizer cost with 657.4 yuan / ha and increase seed cotton yield by 19.8%. A net profit of the balanced fertilization was 5314.9 yuan / ha higher than that of local fertilization practice.  相似文献   
6.
TheApplicationofGIsinSmallWatershedClassificationinLoessPlateauZhuJinzhao,WuBin,BiHuaxing,ZhouChangqingCollegeofSoilandWaterC...  相似文献   
7.
使用GIS区划了白河林业局森林经营类型,并和原有的森林经营类型进行了比较。在数字化区划的森林经营类型中,二级系统被采纳。首先,白河林业局被区划为林地和非林地,其中,总面积的96%为林地,然后,林地区划为重点公益林,一般公益林和商品林。在重新区划的森林经营类型中,商品林达到总面积的45.0%,是最主要的森林经营类型:重点公益林和一般公益林分别为总面积的21.2%和29.9%。两个区划结果有很大的不同,在数字化区划的森林经营类型中,各类型斑块数量较多,面积较小,这些不同主要由使用数据,区划单位和区划方法的不同引起的。研究表明,GIS在区划森林经营类型时是一种有效的方法,二类数据和其它类型数据的结合是必要的。图2表4参22。  相似文献   
8.
森林资源GIS数据采集过程中质量控制方法的探讨   总被引:7,自引:0,他引:7  
结合湖南省森林资源管理系统GIS数据采集的实践,探讨了森林资源GIS数据采集过程中影响数据质量的主要因素,以及数据质量的检验、评价方法和工艺流程等,并给出了影响森林资源GIS数据采集质量的主要因素及其权重.  相似文献   
9.
Landscape-ecological mapping of the Netherlands   总被引:1,自引:0,他引:1  
The Landscape-ecological Mapping of the Netherlands project (LMN project) started in 1983 with the aim of establishing a landscape-ecological database for use in developing and evaluating national land-use plans. The project, working with grid cells of 1 km2, has four working objectives: a) development of mapping potential for basic landscape-ecological data, b) assessment of susceptibility to interventions, c) evaluation of significance for nature conservation and d) production of vulnerability maps, as a combination of susceptibility and significance. In addition to information on soil, groundwater, ecotopes, flora and fauna, the database also incorporates information on physiographical features and entire landscapes. The resulting database is a geographic information system (GIS). This article describes the second phase of the project (1985–1989), covering the Randstad area, and focusses on the methods and the applications potential of the database.  相似文献   
10.
Latvian legislation demands that forest protection belts are established around all cities and towns. The main goal of a protection belt is to provide suitable opportunities for recreation to urban dwellers and to minimise any negative impacts caused by urban areas on the surrounding environment. Legislation states the main principles to be adopted, which include the maximum area of protection belts, their integration in territorial development plans and restrictions placed on forest management activities. The largest part of the forest area around Riga is owned by the municipality of Riga, which, as a result, has two competing interests: to satisfy the recreational needs of the inhabitants of Riga, and to maximise the income from its property. In order to compile sufficient background information to solve this problem, the Board of Forests of Riga Municipality initiated the preparation of a proposal for the designation of a new protection belt.The proposal was based on the development and application of a theoretical framework developed during the 1980s. The analysis of the recreational value of the forest (5 classes of attractiveness) was carried out based on categories of forest type, dominant tree species, dominant age, stand density, distance from urban areas and the presence of attractive objects. Information was derived from forest inventory databases, digital forest maps and topographic maps. Additional information was digitised and processed using ArcView GIS 3.2. Local foresters were asked about the recreation factors unique to different locations, such as the number of visitors and the main recreation activities. From a recreational point of view and taking into account legal restrictions and development plans for the Riga region, it was proposed to create three types of zones in the forest: a protection belt, visually sensitive areas and non-restricted areas.  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