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   17901篇
  免费   81篇
  国内免费   2篇
林业   3712篇
农学   1319篇
基础科学   140篇
  2966篇
综合类   880篇
农作物   2165篇
水产渔业   1860篇
畜牧兽医   1839篇
园艺   1139篇
植物保护   1964篇
  2023年   17篇
  2022年   9篇
  2021年   26篇
  2020年   39篇
  2019年   46篇
  2018年   2773篇
  2017年   2727篇
  2016年   1217篇
  2015年   103篇
  2014年   55篇
  2013年   86篇
  2012年   885篇
  2011年   2249篇
  2010年   2135篇
  2009年   1309篇
  2008年   1410篇
  2007年   1680篇
  2006年   116篇
  2005年   191篇
  2004年   182篇
  2003年   235篇
  2002年   120篇
  2001年   20篇
  2000年   60篇
  1999年   20篇
  1998年   15篇
  1997年   17篇
  1996年   13篇
  1995年   8篇
  1994年   9篇
  1993年   20篇
  1992年   19篇
  1991年   8篇
  1990年   10篇
  1989年   12篇
  1988年   15篇
  1987年   6篇
  1985年   6篇
  1984年   7篇
  1983年   10篇
  1982年   6篇
  1980年   4篇
  1979年   9篇
  1978年   5篇
  1977年   9篇
  1976年   7篇
  1975年   18篇
  1974年   4篇
  1970年   4篇
  1968年   6篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
This study reports on action research efforts that were aimed at developing institutional arrangements beneficial for soil fertility improvement. Three stages of action research are described and analyzed. We initially began by bringing stakeholders together in a platform to engage in a collaborative design of new arrangements. However, this effort was stymied mainly because conditions conducive for learning and negotiation were lacking. We then proceeded to support experimentation with alternative arrangements initiated by individual landowners and migrant farmers. The implementation of these arrangements too ran into difficulties due to intra-family dynamics and ambiguities regarding land tenure. Further investigations to find out how ambiguities could be tackled revealed that the local actors themselves had taken initiatives towards developing institutional innovations to reduce ambiguities. However, there is still considerable scope for further development of these self-organized innovations. The article ends with a reflection on inter-disciplinary action research, where it is argued that making “mistakes” is an inherent and necessary characteristic in action research that aims to address complex social issues.
Samuel Adjei-NsiahEmail:
  相似文献   
993.
The reaction to conventional agriculture and food systems has generated a host of alternative social movements in the past several decades. Many progressive agrifood researchers have researched these movements, exploring their strengths, weaknesses, and failures. Most such research is abstracted from the movements themselves. This paper proposes a new way of self-organization that, while fulfilling traditional university demands on researchers, will provide research support for progressive agrifood movements by transcending the boundaries of disciplines and individual universities.
William H. FriedlandEmail:

William H. Friedland   is Professor Emeritus at the University of California, Santa Cruz where his research continues on commodity systems, wine and grapes, the globalization of agriculture and food, and exploring ways to strengthen alternative social movements to subvert the dominant paradigm.  相似文献   
994.
Within-field variations in potential grain yield may be due to variations in plant available soil water. Different water holding capacities affect yield differently in different years depending on weather. By estimating plant-water availability in different weathers, scenarios could be created of how yield potential and thereby fertilizer demand may vary within fields. To test this, measured cereal grain yields from a dry, a wet and an intermediate year were compared with different soil moisture related variables in a Swedish arable field consisting of clayey and sandy areas. Soil water budget calculations based on weather data and maximum plant available water (PAW), estimated from soil type and rooting data, were used to assess drought. A reasonable correlation between estimated and measured soil moisture was achieved. In the dry year, drought days explained differences in yield between the clayey and the sandy soil, but yield was better explained directly by maximum PAW, elevation, clay content and soil electrical conductivity (SEC). Yield correlated significantly with SEC and elevation within the sandy soil in the dry year and within the clayey soil in the wet year, probably due to water and nitrogen limitation respectively. Dense SEC, elevation and yield data were therefore used to divide the field into management zones representing different risk levels for drought and waterlogging. These could be used as a decision support tool for site-specific N fertilization, since both drought and waterlogging affect N fertilization demand.  相似文献   
995.
Analysis of the long-term Global Aerosol Climatology Project data set reveals a likely decrease of the global optical thickness of tropospheric aerosols by as much as 0.03 during the period from 1991 to 2005. This recent trend mirrors the concurrent global increase in solar radiation fluxes at Earth's surface and may have contributed to recent changes in surface climate.  相似文献   
996.
Through a discursive and organizational analysis we seek to understand the Biosafety Protocol and the place of socioeconomic regulation of agricultural biotechnology in it. The literature on the Protocol has been fairly extensive, but little of it has explored debates over socioeconomic regulation during the negotiation process or the regulatory requirements specified in the final document. This case is especially important at a time when the spread of neoliberalism is increasingly associated with deregulation, because it sheds light on the conditions under which circumvention of the market is deemed legitimate and socio-economic regulation of agricultural technology is possible. Daniel Lee Kleinman is a professor in the Department of Rural Sociology at the University of Wisconsin, Madison, where he is also affiliated with the Holtz Center for Science and Technology Studies and the Integrated Liberal Studies Program. He is the author and editor of a number of books, including Impure Cultures: University Biology and the World of Commerce (2003). Abby J. Kinchy is a PhD candidate in the Departments of Sociology and Rural Sociology at the University of Wisconsin, Madison. Her current research examines the controversies surrounding the genetic “contamination” of Mexican maize and Canadian canola.  相似文献   
997.
998.
999.
1000.
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