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   410篇
  免费   20篇
  国内免费   2篇
林业   22篇
农学   48篇
基础科学   6篇
  117篇
综合类   32篇
农作物   33篇
水产渔业   24篇
畜牧兽医   95篇
园艺   11篇
植物保护   44篇
  2023年   4篇
  2022年   16篇
  2021年   10篇
  2020年   16篇
  2019年   23篇
  2018年   36篇
  2017年   22篇
  2016年   23篇
  2015年   12篇
  2014年   16篇
  2013年   52篇
  2012年   22篇
  2011年   21篇
  2010年   9篇
  2009年   10篇
  2008年   15篇
  2007年   4篇
  2006年   5篇
  2005年   10篇
  2004年   6篇
  2003年   5篇
  2002年   2篇
  2001年   4篇
  2000年   1篇
  1999年   1篇
  1998年   3篇
  1997年   5篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   6篇
  1990年   4篇
  1989年   8篇
  1988年   6篇
  1987年   5篇
  1986年   5篇
  1985年   3篇
  1984年   4篇
  1983年   1篇
  1982年   2篇
  1980年   4篇
  1978年   1篇
  1975年   2篇
  1974年   2篇
  1971年   1篇
  1970年   1篇
  1967年   2篇
排序方式: 共有432条查询结果,搜索用时 0 毫秒
431.
Peste des petits ruminants (PPR) is an economically important disease that affect sheep and goat industry in Asia and Africa. In this study, we investigated the seroprevalence, and risk factors, of PPR in sheep and goat flocks from five different governorates (Irbid, Jarash, Ajloun, Mafraq and Zarka) located in Northern Jordan. Serum samples from 929 and 400 sheep and goats, respectively, corresponding to 122 sheep flock and 60 goats flock were collected. Seroprevalence was determined using PPR competitive ELISA. Health status and management information were collected using a semi-structured pre-tested questionnaire. The individual true prevalence of PPR in sheep and goats was 29 and 49%, respectively. The flock level true prevalence of PPR was 60 and 74% in sheep and goats, respectively. In both sheep and goat flocks, large flock size, visiting live animals market and inadequate veterinary services were identified as risk factors for PPR seropositivity. Mixed (sheep and goats) raising was identified as a risk factor for PPR seropositivity in sheep flocks only.  相似文献   
432.
This paper provides an overview of the issues in and approaches to measuring and enhancing the value of agricultural water in large irrigated river basins. It develops a framework and a set of indicators for valuing agricultural water by looking into various dimensions and underlying key factors that influence the value of water at micro, meso and macro levels. The indicators are applied to recent, primary- and secondary-level empirical data from the Indus basin Irrigation system of Pakistan. In addition, the paper compiles recent estimates of the value of agricultural water from 40 settings in 23 countries. Finally, the paper outlines measures for enhancing the value of agricultural water. The paper makes four main points: (1) The popular productivity indicators based on crop output do not capture the full range of benefits and costs associated with agricultural water use. (2) The value of agricultural water may not be as low as it is generally perceived or estimated when all major uses and direct and indirect benefits of water at various levels are properly accounted for. (3) The value of water varies across time and space, and the value to stakeholders at various scales (farmer, system manager, basin planner and national policy maker) could be quite different. For example, the estimate of agricultural water value in the upper Indus basin in Pakistan varies from US$0.04/m3 at the farm scale to US$0.22/m3 at the national scale. The farm-scale value is more relevant, e.g., for agricultural water charging policies, but for water-sector investments and allocation decisions, the national-scale value is important. The decision-making processes related to water sector investments, allocations, management, and charging/cost recovery schemes could be potentially misguided if key dimensions of water value that are related to water availability and use, benefits/costs, and temporal and spatial aspects are not properly accounted for in valuation. (4) Efforts should be directed not only at increasing the productivity of water in terms of mass of output per unit of water, but also the overall benefits or value of water at various levels for larger growth and poverty alleviation impacts, considering the sustainability of the systems.
Intizar HussainEmail:
  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