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   171篇
  免费   18篇
  国内免费   3篇
财政金融   2篇
工业经济   11篇
计划管理   25篇
经济学   12篇
综合类   8篇
贸易经济   26篇
农业经济   85篇
经济概况   23篇
  2024年   5篇
  2023年   12篇
  2022年   20篇
  2021年   14篇
  2020年   8篇
  2019年   4篇
  2018年   9篇
  2017年   7篇
  2016年   4篇
  2015年   4篇
  2014年   6篇
  2013年   8篇
  2012年   4篇
  2011年   12篇
  2010年   16篇
  2009年   7篇
  2008年   5篇
  2007年   2篇
  2006年   7篇
  2005年   5篇
  2004年   5篇
  2003年   7篇
  2002年   9篇
  2001年   6篇
  2000年   2篇
  1996年   2篇
  1995年   1篇
  1992年   1篇
排序方式: 共有192条查询结果,搜索用时 0 毫秒
21.
微生物强化采油技术研究现状及应用前景   总被引:1,自引:0,他引:1  
介绍了微生物强化采油技术的基本概念、机理和发展现状,讨论了该技术的研究方法、优点及应用条件,并展望了微生物强化采油技术的应用前景。  相似文献   
22.
将具有氧化性的有机废水池作为电池的阳极,具有还原性的重金属废水池作为电池的阴极,利用微生物燃料电池( MFC)同时处理有机废水和重金属废水.结果表明,利用铜离子溶液作阴极, MFC最大电压可达到0.277 V,最大功率密度为33.49 mW/m2,COD的去除率为31.6%,铜的去除率可达42%;利用银离子溶液作阴极,MFC最大电压可达到0.311 V,最大功率密度为42.21 mW/m2, COD的去除率为64.6%,银的去除率可达78%.即不管是从产电角度还是从废水处理角度考虑,都是以银离子废水作阴极优于铜离子.  相似文献   
23.
利用制药厂的废水生产农用测土配方肥,方法可行,生产操作简单,做到废物循环利用,实现了经济、社会和环境三效益的统一.  相似文献   
24.
简要介绍了国内外盆栽花卉培养介质,分为天然壤土堆肥和无壤土堆肥,其施肥方式也有区别;对盆栽花卉活力剂研究特点进行了综述,根据我国盆土实际情况,研制出了盆栽花卉活力剂。  相似文献   
25.
Evaluating the impact of rising fertilizer prices on crop yields   总被引:3,自引:0,他引:3       下载免费PDF全文
Because of tensions on fossil energy and phosphorus markets, the rise in fertilizer prices observed during the last decades may continue in the future, putting into question production pathways relying heavily on crop intensification. To evaluate how, in this context, economic choices may alter crop yields, we first construct different fertilizer price scenarios to 2050 based on an econometric relation with oil and gas prices. Other possible scenarios, such as the continuation of historical trends, are also considered. The resulting changes in fertilizer price range between +0.8% and +3.6% per year over the 2005–2050 period. These scenarios are tested in a global land‐use model incorporating an endogenous representation of the land–fertilizer substitution. We find that the supply‐side response to rising fertilizer prices could lower crop yields in 2050 from ?6% to ?13%, with a corresponding increase in global cropland area ranging between 100 and 240 Mha if the demand for food and nonfood products has to be met. The sensitivity of these results is tested with regard to assumptions on food consumption, change in potential yield and nutrient use efficiency.  相似文献   
26.
由磷肥企业副产氟硅酸制备氟化钠的研究   总被引:1,自引:0,他引:1  
重点介绍了以磷肥企业副产氟硅酸为原料制备氟化钠的新工艺。首先用氨水氨化脱硅得到氟化铵溶液,再向氟化铵溶液加氯化钠合成氟化钠。对影响反应的温度、时间、物料配比等因素进行了探讨,得出具体工艺为:(1)氨化反应:H2SiF6浓度在12%~14%之间,氨水过量25%,反应温度为60~70℃,反应时间120min。(2)氟化钠合成:氯化钠过量15%~20%,反应温度85~90℃。产物氟化钠纯度大于98%,收率大于80%。  相似文献   
27.
High fertilizer price volatility makes production planning and inventory management difficult, so accurate fertilizer price forecasts would be beneficial. This article evaluates commercial forecasts for urea and diammonium phosphate (DAP) prices based on forecast accuracy and optimal forecast properties. Most forecasts pass the tests, but forecasts for the US New Orleans urea and the US Gulf DAP markets, in particular, do not and thus show potential to be improved.  相似文献   
28.
为探究朝鲜族传统发酵泡菜中核心菌群,本文采用高通量宏基因测序技术对8种泡菜中的群落多样性和丰度进行分析.结果表明,8种泡菜具有高度的细菌多样性,且不同样品间存在一定的共性和差异.细菌水平上,优势菌门为蓝藻门(Cyanobacteria)和厚壁菌门(Firmicutes);优势菌属为链球菌属(Streptophyta)、...  相似文献   
29.
This paper provides a review and evaluation of different food‐risk prioritization and management frameworks that have been developed by governmental food‐safety authorities, regulatory agencies and non‐governmental institutions worldwide. It emphasizes the need for a new science‐ and risk‐based system approach to microbial risk prioritization. We find that most studies and projects argue for a systematic and multi‐disciplinary approach to risk prioritization but nevertheless lack it. Human and public health issues have constituted the core focus of food‐risk analysis in food‐borne risk prioritization studies, where the majority of studies use the concept of disease burden. Even though it is widely recognized that economic and market‐level impacts of microbial hazards and preventive interventions to reduce food‐borne risks are crucial to the performance of industries and markets, they are almost never accounted for in risk prioritization frameworks.  相似文献   
30.
Past studies of the use of soil fertility management strategies by farmers usually model input use decisions based on the neoclassical utility/profit maximization principle in which farmers use soil fertility management inputs primarily to increase revenues and profits. However, there is, to date, no study that explains exactly how this decision-making process occurs and the role which personal values play in driving the choice of soil fertility management inputs. This article systematically maps the relationship between choice of soil fertility management strategy (attributes), its outcomes (consequences) and the personal values that motivate the choice. It specifically uses the means-end chain approach to construct hierarchical value maps that relate the attributes to consequences, and ultimately to the personal values. The study finds that the use of soil fertility management strategies by peri-urban fresh vegetable growers is driven by five personal values, namely happiness, comfortable life, independence, good/healthy life and achievement of life goals. It also finds that while farmers seek to increase profit (hence incomes), profit maximization is not the end driver of the use of soil fertility management inputs. It concludes that a lot more goes into farmers’ decision-making process relating to the use of soil fertility management practices than can be explained by the neoclassical profit/utility maximization principle. The study discusses the policy implications of these findings.  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