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   2051篇
  免费   413篇
  国内免费   13篇
林业   319篇
农学   64篇
基础科学   71篇
  604篇
综合类   974篇
农作物   24篇
水产渔业   104篇
畜牧兽医   143篇
园艺   108篇
植物保护   66篇
  2025年   44篇
  2024年   94篇
  2023年   118篇
  2022年   101篇
  2021年   69篇
  2020年   90篇
  2019年   85篇
  2018年   70篇
  2017年   79篇
  2016年   93篇
  2015年   69篇
  2014年   104篇
  2013年   153篇
  2012年   181篇
  2011年   198篇
  2010年   174篇
  2009年   173篇
  2008年   117篇
  2007年   125篇
  2006年   85篇
  2005年   65篇
  2004年   55篇
  2003年   37篇
  2002年   13篇
  2001年   13篇
  2000年   9篇
  1999年   15篇
  1998年   18篇
  1997年   6篇
  1996年   2篇
  1995年   5篇
  1994年   1篇
  1993年   5篇
  1992年   2篇
  1991年   4篇
  1990年   1篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
排序方式: 共有2477条查询结果,搜索用时 0 毫秒
1.
    
Urban green infrastructure provides city dwellers numerous benefits. Among them, cultural ecosystem services (CES) are distinguished by being easily perceived and essential for people and their well-being. However, not all CES are equally easy to perceive, resulting with some of the CES categories being weakly explored. Research on CES also rarely considers elements of urban green infrastructure other than parks and forests. Therefore, there is a lack of research on different components of urban green infrastructure, especially tree-based, perceived in relation to CES. This paper presents the results of focus group participatory mapping implemented with citizens in the city districts of Zagreb on the perception of five selected CES categories in various types of urban green infrastructure. Our results show that participants perceived 13 different types of tree-based urban green infrastructure as providers of CES. We also distinguish patterns in the perception of CES categories and their connection with types of tree-based urban green infrastructure. Tree lines are perceived as providers of aesthetical experiences. Furthermore, forests and park forests are perceived in relation to place attachment and recreational activities, while parks are versatile and provide all explored CES. Other types that emerged as important were greenways, greenery around residential buildings and educational institutions, which provokes rethinking of a careful planning of the entire repertoire of urban green infrastructure.  相似文献   
2.
3.
现代农业面临的重要问题是公共信息服务方式滞后,需要我们与时俱进以集成理念创新服务方式,通过信息服务体系集成、信息资源集成、信息技术集成等,创造高附加值的产品和服务,保证现代农业集成式信息服务功能的实现。  相似文献   
4.
    
Natural tropical forests are highly diverse and are known to contribute to forest-based services such as pollination of nearby crops. Landscape changes cause spatial and temporal bee community changes, but consequences how the community changes affect pollination is not well analyzed. This paper addresses the effects of rainforest distance and on site flower resources in agro-forests on spatial and temporal variation in pollinator communities and the consequences for coffee pollination.  相似文献   
5.
Past monoculture forestry in China has contributed to countrywide ecological disasters and economic difficulties in forestry regions. China‘s new forestry programs, Natural Forest Conservation Program and Returning Farmlands to Forests Program, provide opportunities for ecosystem management of mountain forests in China. A decision support system, FORE-STAR, has been developed for better managing and protecting natural forests in Changbai Mountain area. It uses GIS-based forest inventory data at a scale of forestry bureau. The first version contains two sub-modules: forest operation and forest res-toration. Under each sub-module, users can compare several decision options and make optimal choices. It can help field for-esters, forest managers, and policy makers make multi-objective and consistent decisions in planning forest management at hierarchical administrative scales.  相似文献   
6.
    
Despite their ecological, economic and social importance, grasslands in areas with Mediterranean climates continue to receive limited scientific, political and media attention. The main objectives of this review are to compare and contrast dryland grasslands in the ‘Old World’ regions of the Mediterranean basin (southern Europe, western Asia and North Africa) with those of ‘New World’ regions with Mediterranean climates (Australia and Chile) and to identify common research priorities. The common characteristics and differences in climate, soils, native vegetation, importance of the livestock sector and the socio‐economic background for the different Mediterranean environments are examined. Past trends and the current status of temporary and permanent Mediterranean grasslands are also described. Some common issues between these regions are as follows: (i) adaptation to climate change; (ii) increasing persistence and drought survival of both annual and perennial species; (iii) the important role of forage legumes; (iv) maintaining grassland plant diversity; and (v) improved ecosystem services, such as carbon sequestration, control of soil erosion and wildfires, and preservation of both wild and domestic biodiversity. The favourable climate in these regions, which allows year‐round grazing and the growth of legumes, should be exploited to improve the sustainability of grassland‐based, extensive farming systems and the quality of their animal products, while at the same time improving ecosystem services. The decreasing support for grassland research and development programmes requires increased international scientific and technical cooperation among the few institutions operating in the different Mediterranean‐climate areas of the World to provide innovative and sustainable solutions to farmers.  相似文献   
7.
    
Grain legumes play an important role in community livelihood and in the national economy in Kenya. Unfortunately, in many African countries, production doesn't satisfy the demand in grains due to various constrains. Understanding farmers practices and behavior in the management of grain legume pests is a crucial step in the development of sustainable management strategies. A total of 216 farmers were surveyed in eight districts of eastern Kenya to evaluate farmers' knowledge and perceptions of grain legume pests; to examine current pest management practices, and to identify other production constraints. Grain legumes are grown by a wide age-group of farmers, with both genders equally represented. Chemical control remains the main pest management strategy, and, to ensure pesticide effectiveness, farmers also use increased application rates, chemical alternation, frequent application and mixtures of chemicals. While farmers used other control measures, they showed only limited interest in biological control. The majority of the farmers had experience in grain legume farming and were able to identify the major pests, which were the legume flower thrips Megalurothrips sjostedti Trybom, the cowpea aphid Aphis craccivora Koch and the legume pod borer Maruca vitrata Fabricius. Our survey revealed that education and proximity to extension services contributed significantly to farmers' knowledge of grain legume pests, suggesting the need to provide continuous training and capacity building on integrated pest management in grain legume farming. The study also suggests integration of other pest management strategies such as the use of early maturing varieties, biopesticides and biofertilizer to reduce the use of chemical for sustainable pest management.  相似文献   
8.
用生态经济型植物控制豚草的"绿色污染"   总被引:5,自引:0,他引:5  
豚草是一种严重危害农业生产、人体健康和生物环境的恶性杂草,是一种典型的“绿色污染”。根据群落演替规律,采用具有生态和经济功能的树种创造不利豚草生长的环境,人为创建多物种和谐共存的植物群落,能降低豚草的种群优势,使单一种群优势转变为良性演替的生态系统。  相似文献   
9.
朱宏武  罗丹  贺炜  刘晓波 《安徽农业科学》2014,(34):12184-12186
根据省级气象业务和服务工作所需,省局搭建一套面向气象业务高效、稳定、省内多业务单位能共用的专业WEBGIS平台.在此针对平台多源异构数据的高效管理,多种类、多时次、多维度气象专题产品定制生成以及平台服务器集群的高可用性等关键技术做了相关研究,这些研究对于气象数据和产品的空间分析、可视化发布及跨行业实现信息共享具有非常积极的意义.  相似文献   
10.
通过分析高校图书馆社会化服务的可行性、优势及现状,认为地方高校图书馆开展社会化服务不仅必要,而且完全可行。根据我国高校图书馆社会化服务存在的法律政策缺失、思想认识误区、服务数量较少、服务方式被动、服务限制多、效果差等突出问题,并结合地方实际情况有针对性地提出地方高校图书馆开展社会化服务应坚持的策略和具体途径。  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