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   3438篇
  免费   313篇
  国内免费   175篇
林业   366篇
农学   212篇
基础科学   99篇
  464篇
综合类   1200篇
农作物   93篇
水产渔业   433篇
畜牧兽医   779篇
园艺   93篇
植物保护   187篇
  2024年   36篇
  2023年   92篇
  2022年   177篇
  2021年   237篇
  2020年   189篇
  2019年   203篇
  2018年   124篇
  2017年   169篇
  2016年   153篇
  2015年   148篇
  2014年   185篇
  2013年   229篇
  2012年   243篇
  2011年   286篇
  2010年   202篇
  2009年   222篇
  2008年   171篇
  2007年   194篇
  2006年   127篇
  2005年   99篇
  2004年   79篇
  2003年   68篇
  2002年   47篇
  2001年   42篇
  2000年   31篇
  1999年   17篇
  1998年   29篇
  1997年   17篇
  1996年   21篇
  1995年   25篇
  1994年   16篇
  1993年   10篇
  1992年   7篇
  1991年   9篇
  1990年   7篇
  1989年   3篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1975年   1篇
排序方式: 共有3926条查询结果,搜索用时 93 毫秒
1.
Fish were fed a single‐strain yeast fraction (SsYF; 2 g/kg) or a multistrain yeast fraction (MsYF; 0.8 g/kg) for 10 weeks. The results demonstrated significant (p ≤ 0.03) elevations in weight gain, specific growth rate, protein efficiency ratio, and feed conversion ratio in fish fed the yeast fraction‐supplemented diets. In the distal intestine, a significant elevation in microvilli density was observed after 5 and 10 weeks of dietary supplementation with MsYF and SsYF, respectively, compared to control fed fish (p < 0.001). A significant elevation (p = 0.02) in the perimeter ratio was observed in fish fed diets supplemented with the yeast fractions. After 10 weeks of feeding on the experimental diets, Rt‐qPCR demonstrated a significant downregulation (p < 0.05) in the stress response genes, heat‐shock protein 70 (hsp70) and proliferating cell nuclear antigen (pcna), in fish fed diets supplemented with the yeast fractions. Significant (p < 0.05) elevations in interleukin 1‐beta (il1β) and interleukin‐10 (il10) gene expression were observed in fish fed diets supplemented with the MsYF compared to the other dietary groups. These findings suggest that feeding an MsYF specifically at a lower incorporation rate < 1 g/kg, compared to a commercial SsYF at 2 g/kg, is effective in improving the intestinal health status and growth performance of European seabass.  相似文献   
2.
阐述了森林健康理念和森林康养的基本概念,介绍了森林健康理念和森林康养的发展现状,分析了森林健康与森林康养产业之间的关系。结果表明:森林康养产业的理论基础就是基于森林健康理念继承发展来的,必然会促进森林健康产业的发展。运用森林健康理念指导森林康养产业发展是森林康养产业可持续发展的有效途径,森林健康理念在中国会不断完善和发展,也更有利于中国森林康养产业的发展。展望康养产业,会形成一种新的经济形态,成为国民福祉。  相似文献   
3.
Integrated crop–livestock–forest is a promising strategy to improve soil quality. It comprises four different integrated farming systems: crop–livestock, crop–forest, forest–livestock and crop–livestock–forest. This work systematically reviewed studies about integrated crop–livestock–forest systems and soil quality. A total of 92 papers were retrieved from the Web of Science—Clarivate Analytics platform, and the following information was analysed: publication year, institution, region of the studied site, type of integrated system, soil type, tillage system, maximum soil depth and the soil quality indicators assessed. Most studies were published in the second half of the 2010s. Brazil is a prominent focus of research about soil quality and integrated crop–livestock–forest systems, with significant contribution from its central and southern regions. The Embrapa was the main publishing institution, present in over one‐third of the studies. Crop–livestock was the most common integrated system, Ferralsols was the most common soil group, and most of the studied soils were clayey. No tillage was the main tillage system. Most studies focused on the topsoil, assessing physical and/or chemical soil quality indicators. More emphasis on biological indicators of soil quality is required, as well as assessments integrating biological, physical and chemical indicators of soil quality. Future works should compare different integrated systems, including assessments deeper in the soil profile, especially in systems with the forest component, and also in sandy and silty soils. Soil quality indicators that have been rarely used should be further tested. Novel indicators should be added to better understand the promotion of soil quality by integrated crop–livestock–forest systems.  相似文献   
4.
为掌握典型药物在农作物中的污染特征及健康风险,保障农产品质量安全,利用超声萃取-固相萃取-高效液相色谱/串联质谱(LC-MS/MS)技术,对围场县全县马铃薯中5大类(磺胺类、四环素类、氟喹诺酮类、大环内酯类及其他类)25种药物污染水平及富集效果进行了调查,并对健康风险进行了评价。结果表明,有20种目标物被检出,不同目标物检出率差异显著,检出含量范围为0.13~3.67μg·kg-1,单种污染物最高检出含量为17.0μg·kg-1。马铃薯对目标污染物的富集系数范围在0.01~39.6之间,最大富集系数为61.8。畜禽粪便是马铃薯中药物残留的主要来源,尽管整体检出水平和健康风险相对较低,但长期摄入与协同作用引发的潜在健康风险不容忽视。因此,仍需严控污染源头,推进畜禽粪便安全资源化利用,确保农田环境质量及农产品安全品质。  相似文献   
5.
A method developed to evaluate the cumulative effect of wetland mosaics on water quality was applied to 33 lake watersheds in the seven-county region surrounding Minneapolis-St. Paul, Minnesota. A geographic information system (GIS) was used to record and measure landscape variables derived from aerial photos. Twenty-seven watershed land-use and land-cover variables were reduced to eight principal components which described 85% of the variance among watersheds. Relationships between lake water quality variables and the first six principal components plus an index of lake mixis were analyzed through stepwise multiple regression analysis. A combination of three landscape components (wetland/watershed area, agriculture/wetlands, and forest/soils components) explained 49% of the variance in a trophic state index, even though most of the lakes examined were already highly eutrophic, and thus were influenced by internal loading. The regression equations explained a range of 14 to 76% of the variation in individual water quality variables. Forested land-use was associated with lower lake trophic state, chloride, and lead. High lake trophic state was associated with agricultural land-use and with wetland distance from the lake of interest. The extent of wetlands was associated with low total lead and high color in lakes downstream. Wet meadows or herbaceous, seasonally-flooded wetlands contributed more to lake water color than did cattail marshes.  相似文献   
6.
采用生态系统健康的理论和评价方法分析评价农田生态环境问题具有重要的理论和现实意义,应用生态健康指数定量评价农田健康水平是生态系统管理的重要内容。以武川县农田为研究对象,选择水分、生物量、幅宽等代表性指标,分析了不同作物覆盖下农田生态健康指数。结果表明:不同种植模式间农田健康指数差别明显。播种期较早的小麦田最为健康,没有采用地膜覆盖的马铃薯田健康指数最低,而采用地膜覆盖的马铃薯田健康指数比较高。推广小麦栽培和覆膜栽培是北方农牧交错带农田很好的经营管理模式,具有推广价值,是缓解该地区环境的有效手段之一。  相似文献   
7.
乌梁素海湿地环境与资源地理信息系统的研究   总被引:6,自引:0,他引:6  
本系统建立乌梁素海湿地基础地形库、生态库、资源库、工程档案库、遥感影像库等基础数据库及信息发布系统 ,使 GPS、GIS、RS紧密结合 ,同时实现了专家决策支持系统与地理信息系统之间的一体化集成。本系统可以为乌梁素海湿地生态治理与资源开发提供全方位的数据信息及其管理 ,对生态工程规划与实施方案进行优化设计 ,并提供实时监控服务。  相似文献   
8.
乌梁素海生态恢复机理与工程技术的研究   总被引:2,自引:1,他引:2  
在我国干旱区典型草型湖泊—乌梁素海设立试验基地 ,进行生态恢复工程试验研究。研究表明 :乌梁素海受富营养化影响 ,正在向芦苇沼泽—碱蓬盐化草甸—白刺荒漠方向演化。生态恢复机理是 :( 1 )减少大型水生植物有机氮、磷向底质的沉降 ,削弱内源性营养物负荷的积累与储备 ;( 2 )减少大型水生植物死亡后矿化成氨态氮 ;( 3)控制底质中有机氮向水体释放生成氨态氮。采用机械化方式收割大型水生植物转移营养盐 ,抑制生物促淤效应以及对芦苇区进行园田化生态管理是乌梁素海生态恢复的关键技术 ,也是乌梁素海环境与资源持续发展的核心问题  相似文献   
9.
植物生长物质的使用与绿色果品生产   总被引:3,自引:1,他引:3  
 针对人们对植物生长物质的种种偏见,阐述了植物激素与动物激素以及植物生长调节剂的重要区别,提出了植物激素对人体无毒性,植物生长调节剂可以运用于大多数绿色果品生产的建议。  相似文献   
10.
The ostrich is an important animal in many livestock industries. A significant threat to this industry is losses from diseases. Newcastle disease is a notifiable, highly contagious viral infection of ostriches. Avian influenza may be transmitted from waterfowl, shorebirds and gulls to ostriches. Borna disease virus is a viral neurotropic infection spread mainly by rodents and felines. Crimean‐Congo hemorrhagic fever is a viral disease transmitted by Hyalomma ticks to humans. Avipoxvirus afflicts ostrich chicks and is transmitted by mosquitoes or by direct contact with a pox lesion. Maintenance of a healthy and profitable enterprise requires the implementation, with assistance from the local veterinary authority, of comprehensive, practical and effective methods of health management and preventative medicine.  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