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   7344篇
  免费   367篇
  国内免费   661篇
林业   740篇
农学   471篇
基础科学   1352篇
  1123篇
综合类   3476篇
农作物   161篇
水产渔业   277篇
畜牧兽医   491篇
园艺   70篇
植物保护   211篇
  2024年   63篇
  2023年   204篇
  2022年   285篇
  2021年   325篇
  2020年   269篇
  2019年   323篇
  2018年   147篇
  2017年   237篇
  2016年   265篇
  2015年   265篇
  2014年   414篇
  2013年   369篇
  2012年   579篇
  2011年   635篇
  2010年   529篇
  2009年   465篇
  2008年   409篇
  2007年   455篇
  2006年   393篇
  2005年   370篇
  2004年   325篇
  2003年   191篇
  2002年   156篇
  2001年   142篇
  2000年   92篇
  1999年   77篇
  1998年   70篇
  1997年   61篇
  1996年   44篇
  1995年   45篇
  1994年   29篇
  1993年   25篇
  1992年   23篇
  1991年   23篇
  1990年   18篇
  1989年   18篇
  1988年   16篇
  1987年   8篇
  1986年   2篇
  1984年   3篇
  1962年   1篇
  1956年   2篇
排序方式: 共有8372条查询结果,搜索用时 15 毫秒
51.
ObjectiveTo collect data about the current practice of recovering horses from general anesthesia and recovery personnel safety.Study designOnline survey.MethodsAn online questionnaire, including questions on general demographic data, recovery drugs, modality and characteristics of equine recovery and morbidity and mortality, was designed and distributed via e-mail to equine practitioners worldwide.ResultsPractitioners from 22 countries completed 373 questionnaires; 53% of the participants were board-certified equine surgeons, and the remainder were board-certified anesthesiologists (18%), large animal residents (8%), general practitioners (7%), large animal interns (6%), anesthesia residents (4.5%) and veterinary technicians (1.6%). Respondents were employed by academia (58%) or private practice (42%). Of the respondents employed at a university, 93% had a board-certified anesthesiologist on staff compared with 7% of respondents employed at a private practice. Most of the respondents assist horses during recovery, with 23% assisting every recovery and 44% assisting recovery in the majority of cases. Reasons for choosing to assist horses during recovery were: orthopedic procedures (57%), neurological deficits (49%), bad health (47%), history of poor recovery (44%), foals (42%), draft breeds (30%), magnetic resonance imaging (17%) and computed tomography (16%). Unacceptable recoveries were reported by 77% of participants. Commonly reported complications during recovery with any method were: orthopedic injury (66%), myopathy (54%), skin abrasion (53%) and airway obstruction (37%). The incidences of unacceptable quality of recovery (p = 0.09) or personnel injury (p = 0.56) were not different between assisted and nonassisted recoveries; however, more equine fatalities were reported for assisted recoveries (p < 0.006). Practitioners in academia reported more unacceptable recoveries (p < 0.0007) and personnel injuries (p < 0.002) compared with those in private practice.ConclusionsThe method of recovery differs among hospitals. Recovery personnel injuries associated with assisting horses during recovery are an important and previously unreported finding.  相似文献   
52.
为初步鉴定并挖掘出猪戊型肝炎病毒(Hepatitis E virus,HEV)ORF3蛋白影响HepG2细胞核黄素代谢信号通路的lncRNA-mRNA调控网络,本试验通过构建腺病毒过表达载体,制备高滴度过表达腺病毒,介导猪 HEV-ORF3在HepG2细胞中实现过表达。Western blotting检测ORF3蛋白过表达成功后,运用lncRNA高通量组学测序,筛选出差异表达的lncRNA并进行靶向差异基因预测,对lncRNA靶向差异基因进行GO功能和KEGG通路富集分析,初步鉴定出与核黄素代谢信号通路相关的lncRNA-mRNA调控网络。Western blotting结果显示,在约为12 ku处出现目的条带,说明成功实现腺病毒介导猪HEV-ORF3在HepG2细胞中过表达。lncRNA高通量组学测序结果显示,共发现102个显著差异表达lncRNAs表达量上调,80个显著差异表达lncRNAs表达量下调。GO功能和KEGG通路富集分析显示,初步挖掘出lncRNA(MSTRG.13995.2)和lncRNA(MSTRG.1960.1)可能是与核黄素代谢信号通路相关的显著差异表达lncRNA,分别通过顺式调控其靶向基因APC-5和FLAD1来影响核黄素代谢信号通路。本试验初步鉴定出lncRNA(MSTRG.13995.2)-APC5和lncRNA(MSTRG.1960.1)-FLAD1可能是影响HepG2细胞核黄素代谢信号通路的lncRNA-mRNA调控网络。  相似文献   
53.
介绍了LM-BP神经网络模型的原理及算法和模型的优点。针对实际水质评价问题,利用随机内插方法在地表水环境质量分级标准阈值间生成训练样本和检验样本,建立了新乡市卫河地面水环境质量综合评价的LM-BP神经网络模型,将模型应用于卫河2011年3月份、9月份的水质评价,并与单因子评价法、模糊综合评价法进行了比较分析。实验结果表明该模型设计合理,泛化能力强,收敛速度快,算法稳定,推导严谨,有较充分的理论依据,应用于水质评价具有其合理性、实用性和有效性,适用于作深入的水环境质量分析。  相似文献   
54.
针对国内外水质环境研究中水质样品异地监测分析存在的巨大缺陷,研究了水质自动监测系统。文章介绍了基于无线通讯传感器网络的简易水质自动监测系统,实现水质数据自动采集和实时上传,可以实现对钱塘江源头水质(衢州水质)进行更好的监测及保护。  相似文献   
55.
56.
Surveys were conducted in the five southern rice-producing states of Arkansas, Louisiana, Mississippi, Missouri and Texas in the United States during the 2018 and 2019 cropping seasons to determine the distribution and pathogenicity of fungal pathogens associated with seedling blight in rice. A total of 349 pathogenic fungal isolates were collected and identified as belonging to four genera: Rhizoctonia solani, Fusarium spp., Sclerotium rolfsii and Marasmius graminum based on morphological characteristics, molecular analysis and Koch's postulates. R. solani (252 out of 349 pathogenic isolates) was the most prevalent fungus isolated from diseased samples. Of the 252 pathogenic R. solani isolates, 245 were further classified as anastomosis group 11 (AG-11) and 7 as AG-4. Isolates of R. solani AG-4 and M. graminum were the most aggressive, with the highest stand loss (63% to 100%) and median disease rating (DR; 5.0), followed by isolates of R. solani AG-11 (stand loss = 4% to 100% and DR = 0.6 to 5.0), Fusarium spp. (stand loss = 26% to 48% and DR = 2.0 to 5.0) and S. rolfsii (stand loss = 33% to 48% and DR = 2.0 to 3.0) in causing seedling blight in rice. R. solani (62% to 83% of total pathogenic isolates) and Fusarium spp. (10% to 24% of total pathogenic isolates) were predominant in all the five states surveyed. S. rolfsii and M. graminum were present only in Louisiana and Texas. The results of this first systematic survey of rice seedling diseases in the southern United States will help develop effective fungicide seed treatment strategies for control of stand loss caused by seedling blight, one of the major factors limiting rice production.  相似文献   
57.
58.
为了解采后果品电特性变化机理,并探索基于电特性识别果品品质的方法,研究了桃采后电特性和生理特性的变化。结果表明,随着桃新鲜度下降,相对介电常数呈余弦规律变化,损耗角正切逐渐减小,呼吸高峰时相对介电常数最大。分析了电特性变化的原因,进而建立了采后桃电特性与生理特性之间的关系模型。以相对介电常数和损耗角正切为输入特征参数,应用BP神经网络技术识别桃的新鲜度等级,平均识别率为82%。  相似文献   
59.
提出了稀燃汽油机空燃比滑模-神经网络控制方案,采用滑模变结构控制对稀燃工况的空燃比进行反馈控制,采用神经网络实现对进气量的精确预测和油膜动态特性的前馈补偿,进而实现对稀燃发动机瞬态空燃比的精确控制。采用自行开发的电控系统,在一台稀燃发动机上进行了瞬态空燃比实验。实验结果表明:节气门急速变化时空燃比超调可以控制在1个空燃比单位以内,调整时间不超过3s;转速越低,节气门变化越剧烈;空燃比超调越大,调整时间越长。  相似文献   
60.
An algorithm of fault section diagnosis based on topology identification for distribution networks is presented. By decomposing the topologic matrix which describing the distribution network into two parts,one part only contain the complex coupling factor ,and the other ignore the complex coupling factor. Using this method, the fault zones in distribution network can be identified and isolated efficiently, and the vertexes of the zones can also be identified automatically. This approach adapts to the changefully network structures.  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