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   660篇
  免费   39篇
  国内免费   33篇
林业   34篇
农学   20篇
基础科学   23篇
  48篇
综合类   216篇
农作物   11篇
水产渔业   41篇
畜牧兽医   319篇
园艺   3篇
植物保护   17篇
  2024年   8篇
  2023年   11篇
  2022年   22篇
  2021年   33篇
  2020年   27篇
  2019年   34篇
  2018年   14篇
  2017年   17篇
  2016年   16篇
  2015年   24篇
  2014年   37篇
  2013年   63篇
  2012年   54篇
  2011年   49篇
  2010年   32篇
  2009年   37篇
  2008年   25篇
  2007年   31篇
  2006年   21篇
  2005年   15篇
  2004年   12篇
  2003年   20篇
  2002年   12篇
  2001年   22篇
  2000年   20篇
  1999年   13篇
  1998年   7篇
  1997年   7篇
  1996年   3篇
  1995年   13篇
  1994年   6篇
  1993年   5篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   3篇
  1988年   2篇
  1986年   2篇
  1983年   1篇
  1982年   1篇
排序方式: 共有732条查询结果,搜索用时 0 毫秒
721.
In most countries, owner responsibility exists under Common Law to manage and maintain dams according to current standards. However, farm dam safety in Australia is being flouted and the sustainability of farming businesses compromised because of the potential and severe consequences of dam failure. This paper explores management and policy issues associated with safety of farm dam water storage through a comparison of developments in two Australian states against international benchmarks. Historical review and a longitudinal study over a 12-year period provides the basis for case analysis and demonstrates the application of the benchmarked model policy selection guidelines. Research results show South Australia is lagging international best practice in a number of ways whilst Tasmania provides leadership. The contribution of this paper is a regulatory mix analysis approach, incorporating a cost-effective spillway safety engineering/accounting tool, developed and demonstrated through Australian case studies, that can be applied by any jurisdiction wanting to check and/or improve its farm dam safety management and provide a clearer analysis of the social and environmental costs and threats associated with on-farm dam safety issues.  相似文献   
722.
试验研究了发酵葡萄渣颗粒饲料对育肥牛生产性能的影响。选择26头平均体重为304 kg左右的西门塔尔杂种牛,按体重和性别随机分成2个处理组,每组13头,对照组日粮组成为自配肉牛精料补充料+青贮饲料+干草,试验组日粮组成为发酵葡萄渣颗粒饲料+青贮饲料+干草,试验期为60 d。试验结果表明,与对照组相比,育肥牛饲喂发酵葡萄渣颗粒饲料,日增重提高了5.89%(P0.05),料重比降低了2.79%(P0.05),头均毛利润提高了58.24元,经济效益提高了4.17%。  相似文献   
723.
人工草地绵羊系统母羊繁殖性能和羔羊育肥试验   总被引:2,自引:3,他引:2  
王元素  王文  徐震 《草业科学》2003,20(4):20-22
分别以考尔木母羊和考尔木公羊杂交羔羊(R×C)、考尔木母羊和罗姆尼公羊杂交羔羊(C×C)为试验对象,在优质人工草地上划区轮牧,进行考尔木母羊繁殖性能和羔羊育肥定期监测试验。结果表明:二系统羔羊初生重和断奶重几乎一样;断奶后,R×C系统羔羊体重比C×C系统高,7月龄出栏体重和1岁龄体重分别为:R×C系统35 5、44 0kg,C×C系统30 7、39 9kg;3月龄(断奶重)羔羊日增重最高,R×C和C×C系统分别为203 3、180g/d。系统间母羊繁殖性能指标基本一样。牧草生长季羔羊育肥效益分别为:R×C系统1925元/hm2、C×C系统1781元/hm2,为原系统(860元/hm2)的2 24、2 0倍。  相似文献   
724.
在甘肃临夏农牧交错区开展了牦牛、犏牛舍饲育肥试验,研究不同精粗比(0∶10、2∶8、3∶7、4∶6)的日粮(Ⅰ组和Ⅱ组日粮)饲喂家畜的效果。结果表明,在临夏地区2011年10月底至次年3月进行牦牛、犏牛易地育肥,家畜适应性强,育肥效果明显。饲喂Ⅰ组日粮的牦牛日增重比对照(传统精料配制方式饲喂)提高了32.43%,增重率提高了5.04%,增重效果显著(P0.05);饲喂Ⅱ组日粮的牦牛日增重比对照提高了26.98%,增重率提高了3.81%,增重效果显著(P0.05);饲喂Ⅰ组日粮的犏牛日增重比对照提高了29.26%,增重率提高了6.94%,增重效果显著(P0.05);饲喂Ⅱ组日粮的犏牛日增重比对照提高了28.82%,增重率提高了6.21%,增重效果显著(P0.05)。因此,在临夏地区推行农牧系统耦合、易地育肥牦牛和犏牛的产业发展模式,不仅可以增加农耕区居民的经济收入,而且可以减轻草原牧区的载畜压力,实现生态和经济的良性耦合。  相似文献   
725.
The decision to release a new transgenic crop variety for planting in the European Union (EU) is a decision under irreversibility and uncertainty. We use a real option model to assess the ex-ante incremental benefits and costs of the decision to release Bt maize and HT maize in the EU-15 member states. The analysis uses Eurostat data for modelling the benefits and costs of non-transgenic maize using partial equilibrium models. The farm-level benefits and costs of Bt maize and HT maize are derived from field trials conducted within the EU-funded ECOGEN project in combination with secondary data sources. Adoption curves, hurdle rates and Maximum Incremental Social Tolerable Irreversible Costs (MISTICs) are calculated at country level for selected EU-15 member states. In general, the results show that the MISTICs on a per capita level are very small confirming previous results calculated in values for the year 1995. The MISTICs per farm are much larger. This indicates a problem for decision makers.  相似文献   
726.
The economic effects of the implementation of regulations on aquaculture farms in the United States, while of concern, are not well understood. A national survey was conducted of salmonid (trout and salmon) farms in 17 states of the United States to measure on‐farm regulatory costs and to identify which regulations were the most costly to this industry segment. The response rate was 63%, with a coverage rate of 94.5% of the U.S. production of salmonids. The regulatory system resulted in increased national on‐farm costs of $16.1 million/year, lost markets with a sales value of $7.1 million/year, lost production of $5.3 million/year, and thwarted expansion attempts estimated at $40.1 million/year. Mean farm regulatory costs were $150,506/farm annually, or $2.71/kg; lost markets with annual sales values of $66,274/farm; annual lost production of $49,064/farm; and an annual value of thwarted expansion attempts estimated at $375,459/farm. Smaller‐scale farms were affected to a disproportionately greater negative extent than larger‐scale farms. Per‐farm regulatory costs were, on average, greater for foodfish producers than for producers selling to recreational markets, but per‐kg regulatory costs were greater for those selling to recreational compared to foodfish markets. Regulatory costs constituted 12% of total production and marketing costs on U.S. salmonid farms. The greatest regulatory costs were found to be effluent discharge regulations. The majority of regulatory costs were fixed costs, but regulatory barriers to expansion precluded compensatory adjustments to the business in spite of growing demand for salmonid products. Results of this study show that the on‐farm regulatory cost burden is substantial and has negatively affected the U.S. salmonid industry's ability to respond to strong demand for U.S. farm‐raised salmonid products. Results also suggest that the regulatory system has contributed to the decline in the number of U.S. salmonid farms. While regulations will necessarily have some degree of cost to farms, the magnitude of the on‐farm regulatory cost burden on U.S. salmonid farms calls for concerted efforts to identify and implement innovative regulatory monitoring and compliance frameworks that reduce the on‐farm regulatory cost burden.  相似文献   
727.
[目的]比较不同饲喂方法对肉牛育肥的影响,为肉牛育肥方法的选取提供参考依据。[方法]选用40头体重相近的育肥公牛,随机分成试验组和对照组,在试验组使用TMR饲喂方式,对照组使用先粗料后精料的饲喂方法,进行两种饲喂方法对育肥牛产肉性能、饲料报酬和经济效益的分析比较。[结果]对照组试验全期增重和日增重极显著高于试验组(P<0.01),试验组每增重1 kg消耗干物质10.76 kg,对照组仅为8.35 kg,对照组头均多收益为383.24元。[结论〗采用先粗料后精料的饲喂方式对肉牛育肥更合适。  相似文献   
728.
The primary factors which are likely to mould future non-urban land use patterns in Australia are identified. Over the past three decades the rate of increase in land productivity in Australia has been higher than for any other OECD country. Land degradation does not appear to have seriously threatened agricultural output over the last 45 years. However, there is cause for concern that land degradation, attributable to past activities, may only now be exerting a significant impact on productivity in some regions. Many of the services provided by natural resources have been underpriced; consequently, there has been a bias in agricultural research towards technologies that enhance on-site productivity, but which impose excessive external social costs. Underpricing of native trees from state-owned and managed forests appears to have caused excessive exploitation of these forests and lowered the establishment of softwood and hardwood plantations. Many important land use and land cover issues remain unresolved in Australia's rangelands, including questions relating to the optimum grazing pressures, the role of fires in the suppression of unpalatable shrubs and appropriate management strategies for controlling numbers of large kangaroos and rabbits and protecting the natural habitat of threatened species of native animals. The riparian zone, which acts as a crucial buffer between rivers and their catchments, has been one of the most neglected environments in Australia, possibly because river banks, floodplains and wetlands do not fit neatly into the category of land or water. It is widely accepted that the aboriginal peoples must be involved in seeking to achieve the sustainable use of our natural resources. How to achieve the appropriate participation and involvement of aboriginal peoples is a problem that is yet to be fully resolved. In many respects, renewable natural resource systems in Australia are unique. Knowledge creation and application will be a most important resource for the future management of our agricultural forestry and natural resource systems. The solutions to many of the major renewable resource problems do not depend on technology alone. Institutional changes and incentive structures are required that recognize and take account of the pervasive and complex interrelationships between human reactions and responses in their production and consumption activities and the environment.  相似文献   
729.
探索如何高效率地解决集体建设用地流转租赁制中可能存在的"敲竹杠"问题,有助于优化我国集体建设用地租赁流转方式。企业生产设备的资产专用性高,产生的可占用准租金高,使企业面临被村集体"敲竹杠"的风险。江苏宜兴市通过流转双方互惠协议和声誉机制等自动实施契约联结,且租赁交易受到第三方干预机制——市政府文件中明确履约保证的约束,共同避免了村集体的"敲竹杠"行为。为促进集体建设用地租赁制健康发展,应借鉴宜兴"长租短约制",延长租赁期限,稳定租赁关系,避免土地所有者通过抽回土地的威胁来"敲竹杠"。同时,政府应发挥市场规范者的角色,建立清晰的违约责任惩处机制。  相似文献   
730.
肉牛强度育肥高新技术应用效果   总被引:6,自引:0,他引:6  
经调查,山西省某国营煤矿肉牛育肥场,聘请高级科技人员,采用最新的科研成果--E-N和XDCP蛋白新体系,配套应用添加剂和饲管新技术,使强度育肥生产技术经济指标达到罗高水平。88头育肥牛平均饲养142d,日增重1.32kg,料重比2.44。其中始300kg以上的21头,强度育肥98d,日增重2.29kg,料重比1.89。按市价计算,每增重1kg毛刺3.87元,头均1128.62元,取得了育肥期短,增  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