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   23546篇
  免费   1471篇
  国内免费   2560篇
林业   2554篇
农学   3273篇
基础科学   1991篇
  3995篇
综合类   7717篇
农作物   1371篇
水产渔业   969篇
畜牧兽医   3421篇
园艺   947篇
植物保护   1339篇
  2024年   56篇
  2023年   353篇
  2022年   871篇
  2021年   1148篇
  2020年   1049篇
  2019年   904篇
  2018年   706篇
  2017年   1046篇
  2016年   839篇
  2015年   1097篇
  2014年   1156篇
  2013年   1391篇
  2012年   1803篇
  2011年   1645篇
  2010年   1648篇
  2009年   1330篇
  2008年   1337篇
  2007年   1331篇
  2006年   1195篇
  2005年   998篇
  2004年   522篇
  2003年   431篇
  2002年   404篇
  2001年   404篇
  2000年   452篇
  1999年   482篇
  1998年   454篇
  1997年   324篇
  1996年   313篇
  1995年   299篇
  1994年   220篇
  1993年   216篇
  1992年   197篇
  1991年   139篇
  1990年   132篇
  1989年   141篇
  1988年   113篇
  1987年   66篇
  1986年   72篇
  1985年   74篇
  1984年   51篇
  1983年   52篇
  1982年   43篇
  1981年   33篇
  1980年   22篇
  1979年   2篇
  1965年   2篇
  1964年   2篇
  1963年   2篇
  1956年   7篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
71.
为了解甘肃省武威市骆驼蜱以及梨形虫病病原种类和分布情况,保护和开发骆驼产业,通过分子生物学检测手段,对采集的骆驼蜱虫与骆驼抗凝血样进行流行病学调查和分子生物学鉴定。采集的蜱虫经鉴定为亚洲璃眼蜱,说明亚洲璃眼蜱是该地的优势种;在蜱样品中检测到双芽巴贝斯虫阳性样品1份,说明当地存在通过蜱传播梨形虫病的风险。本研究对于提高该地区骆驼养殖业对蜱与梨形虫病危害和防控的认识具有积极意义,也为当地蜱以及梨形虫病防治提供了依据。  相似文献   
72.
为了掌握基层动物疫病预防控制机构发展现状,通过调研了解,黑龙江省84个市县级动物疫病预防控制机构的基础设施建设、仪器设备配置、人员队伍结构等情况有较大提升,但仍存在业务用房面积不达标,设备陈旧老化,物资储备欠缺,人员老龄化,工作经费不足和信息化管理薄弱等问题,难以适应当前动物疫病防控总体需要。这提示应进一步强化基础设施建设,更新仪器设备,加强防疫物资储备,健全冷链管理体系,充实专业队伍,建立经费保障机制和推动信息化平台建设,以期进一步推进基层动物疫控机构发展。  相似文献   
73.
Yang  Liuqing  Liu  Rui  Ju  Xiaotang 《Journal of Soils and Sediments》2020,20(3):1253-1263
Journal of Soils and Sediments - The work aimed to (1) better understand how C rate and type affecting N2O emissions when combined application with different N forms in a strong ammonia oxidation...  相似文献   
74.
旨在探讨添加混合微生物菌剂的发酵全混合日粮(Fermented total mixed ration,FTMR)对肉羊营养物质消化吸收功能和生长性能的影响。通过发酵和肉羊饲喂试验,测定了FTMR的品质变化、营养物质表观消化率、肉羊瘤胃发酵情况及日增重。结果表明:1)全混合日粮发酵后pH和中性洗涤纤维含量显著降低,乳酸和乙酸含量显著增加(P<0.05);2)试验组肉羊瘤胃液pH显著降低,氨态氮含量降低50%以上(P<0.05);粗蛋白质、粗脂肪、中性洗涤纤维、酸性洗涤纤维和酸性洗涤木质素(ADL)的利用率均显著高于对照组(P<0.05),尤其是ADL利用率提高了29.92%(P<0.05)。3)试验组平均日增重较对照组提高50%。综上,混合微生物菌剂加入全混合日粮发酵后,适口性增强,可改善肉羊瘤胃液环境,提高肉羊的消化吸收功能和生长性能,有利于提高秸秆饲料化利用效率。  相似文献   
75.
利用文献计量学方法,研究1989—2018年来土壤食物网研究领域的热点内容,概括土壤食物网的研究脉络及国际土壤食物网未来的研究方向。结果显示:土壤生物多样性、食物网的碳氮循环功能及管理方式对土壤食物网结构的干扰是现在研究热点,而土壤食物网功能多样性、系统稳定性、及土壤食物网对全球变化的响应则是新兴的研究方向。  相似文献   
76.
【目的】研究临床分离的大肠杆菌多重耐药株(R)与大肠杆菌标准株ATCC 25922(S)蛋白质差异表达情况,为进一步研究大肠杆菌耐药机理奠定基础。【方法】采用串联质谱标签(tandem mass tag,TMT)法结合平行反应监测(parallel reaction monitoring,PRM)技术,对大肠杆菌R和S株的全菌体蛋白进行定量蛋白质组学研究,筛选大肠杆菌多重耐药株(S)与敏感株(R)之间的差异表达蛋白,并对其生物信息学进行分析。【结果】共筛选出300个差异表达蛋白(Fold change≥1.3,P0.05),其中上调167个,下调133个,涉及的耐药相关通路主要包括细菌趋药性、ABC转运蛋白、β-内酰胺抗性等;PRM成功定量到13个差异蛋白,且PRM验证结果与TMT定量结果一致。【结论】筛选出多个与大肠杆菌耐药性相关的差异表达蛋白和通路。  相似文献   
77.
This study was designed to examine the effects of glycinin on growth, digestive ability, immune responses, antioxidant capacity and gene expression levels of golden crucian carp. Golden crucian carp were fed diets containing glycinin at 0, 30, 60, 90 and 120 g/kg, respectively, for 8 weeks. Body weight, weight gain percentage, specific growth rate and feed efficiency ratio were negatively related to the content of glycinin in diet. Activities of protease, acid phosphatase, alkaline phosphatase, lysozyme in hepatopancreas, and activities of catalase, glutathione peroxidase, superoxide dismutase, and total antioxidant capacity in the proximal intestine, mid intestine, distal intestine and hepatopancreas were negatively related to the content of glycinin in diet, whereas malondialdehyde in proximal intestine, mid intestine, distal intestine and hepatopancreas increased directly with the content of glycinin in diet. Furthermore, the relative expressions of TNF‐α and IL‐1β in proximal intestine, mid intestine and distal intestine increased directly with the content of glycinin in diet, whereas the relative expressions of TNF‐α and IL‐1β in hepatopancreas were negatively related to the content of glycinin in diets. The relative expressions of IL‐10 in proximal intestine, mid intestine, distal intestine and hepatopancreas all were negatively related to the content of glycinin in diets. In conclusion, reductions in growth, immunity and antioxidant capacity, intestine inflammation with dysfunction of digestive system occurred in golden crucian carp that fed a diet containing glycinin at 30 g/kg or higher after 8 weeks.  相似文献   
78.
Polyculture with Chinese shrimp Penaeus chinensis, jellyfish Rhopilema esculenta and razor clam Sinonovacula constricta (S.J.R) is a common aquaculture system in Dandong, China. Investigation on the composition and function of microbial communities and their relationship with environmental factors in aquaculture systems have crucial implications. Therefore, the sequencing of 16S rRNA gene was applied to profile the bacterial community composition of water and sediment in S.J.R polyculture system in the present study. Proteobacteria was the dominant phylum in S.J.R polyculture ponds following with Actinobacteria and Bacteroidetes in water; in contrast, more diverse phyla were detected in sediments. Water temperature, pH and dissolved oxygen were determined the bacterial community composition in the S.J.R polyculture systems. Specially, Planktomarina, PS1 clade, Candidatus Aquiluna and Fibrobacteres, which can resist the phytoplankton blooms or degrade the cellulose, were more abundant in water at the early stage of cultivation in the S.J.R polyculture system. Moreover, the functions of bacterial communities in water were mainly associated with cell communication mediated, while the functions related to basal metabolism were enriched in sediments. The findings of this study allowed us to better understand the bacterial community in the S.J.R polyculture system and accumulated data for the improvement of cultural management.  相似文献   
79.
Melatonin (MT) influences lipid metabolism in animals; however, the mechanistic effect of melatonin on liver fat and abdominal adipose deposition requires further clarity. In order to study the effects of melatonin on lipid metabolism, and hepatic fat and abdominal adipose deposition in animals, twenty Sprague–Dawley (SD) rats of 6 weeks of age with similar bodyweight were randomly divided into two groups: control (CTL) and MT-treated (10 mg/kg/day). During a 60-day experiment, food intake and bodyweight were measured daily and weekly respectively. At the end of treatment, blood samples were collected to collect plasma to quantify hormones and metabolic indicators of lipid metabolism. In addition, organ and abdominal adipose depots including liver, and omental, perirenal, and epididymal fat were weighed. Liver tissue was sampled for sectioning, long-chain fatty acid (LCFA) quantification, and gene chip and Real-time quantitative PCR (qPCR) analyses. The results showed that liver weight and index (ratio of liver weight to body weight) in MT group reduced by 20.69% and 9.63% respectively; omentum weight and index reduced by 59.88% and 54.93% respectively, and epididymal fat weight reduced by 45.34% (p = 0.049), relative to CTL. Plasma lipid indices, triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and total cholesterol (TC) with MT treatment decreased significantly compared with the control. Fat and 8 LCFA content in liver in MT group also decreased. Gene chip and qPCR demonstrated that there were 289 genes up-regulated and 293 genes down-regulated by MT. Further analysis found that the mRNA expression of lipolysis-related genes increased, while the mRNA expression of lipogenesis-related enzymes decreased (p < 0.05) with MT. This study concluded that melatonin greatly affected fat deposition, and hepatic LCFA supply and the expression of genes associated with lipogenesis and lipolysis.  相似文献   
80.
河南省2010-2018年果树发展趋势数据表明河南省果园种植面积缩减,园林水果产量稳步增长.苹果、桃、梨和葡萄是河南省四大主栽果树,其中苹果面积和产量远超其它树种.2018年河南省各省辖市果园面积和园林水果产量分析表明,南阳市果园面积居河南省第一,果树种类丰富;三门峡市园林水果产量河南省内第一.苹果优势产区集中在三门峡市、商丘市和洛阳市等,桃优势产区集中在南阳市、商丘市和周口市等,梨优势产区集中在商丘市和周口市等.河南省葡萄尚未形成产业优势集中区,区域分布极不平衡.  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