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   14734篇
  免费   760篇
  国内免费   1629篇
林业   1542篇
农学   1645篇
基础科学   1016篇
  2321篇
综合类   5297篇
农作物   1080篇
水产渔业   672篇
畜牧兽医   1919篇
园艺   768篇
植物保护   863篇
  2024年   119篇
  2023年   329篇
  2022年   695篇
  2021年   737篇
  2020年   740篇
  2019年   722篇
  2018年   493篇
  2017年   733篇
  2016年   603篇
  2015年   738篇
  2014年   748篇
  2013年   917篇
  2012年   1248篇
  2011年   1211篇
  2010年   1057篇
  2009年   956篇
  2008年   885篇
  2007年   756篇
  2006年   583篇
  2005年   489篇
  2004年   295篇
  2003年   236篇
  2002年   198篇
  2001年   191篇
  2000年   176篇
  1999年   201篇
  1998年   158篇
  1997年   119篇
  1996年   133篇
  1995年   128篇
  1994年   100篇
  1993年   85篇
  1992年   71篇
  1991年   57篇
  1990年   58篇
  1989年   50篇
  1988年   42篇
  1987年   16篇
  1986年   10篇
  1985年   9篇
  1984年   6篇
  1983年   4篇
  1982年   6篇
  1980年   3篇
  1979年   4篇
  1965年   1篇
  1964年   1篇
  1956年   1篇
  1955年   1篇
  1948年   1篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
31.
Adenosine diphosphate‐ribosylation factors (Arfs) are a family of guanosine triphosphate‐binding proteins involved in fundamental biological processes including secretion, endocytosis, phagocytosis, cytokinesis, cell adhesion and tumor cell invasion. We report here the molecular cloning, chromosome localization and expression analysis of porcine Arf1–6, of which Arf1–3 (Class I) have >93% similarity to each other and encode nearly similar proteins with 181 amino acids in length. Arf4 and Arf5 (Class II) are 78–81% homologous to Class I Arfs and both encode a protein of 180 amino acids, Arf6 (Class III) shows 64–68% homology to the other Arfs and encodes 175 amino acids. With radiation hybrid mapping, porcine Arf1–6 are assigned to chromosomes 14q21‐q22, 12p14, 5p12‐q11, 13q21.1, 18q24, 1q21‐q27, respectively. Moreover, real‐time quantitative RT‐PCR assays show that porcine Arf1‐6 are ubiquitous in all tissues examined, with the highest levels in the kidney and stomach and the lowest in muscle and the heart. This is the first report of molecular characterization of the Arf gene family in pigs.  相似文献   
32.
[目的]研究复合预混料对奶牛抗氧化作用的影响.[方法]把20头奶牛随机分成2组,分别为试验组和对照组,试验组奶牛精料补充料中添加2%预混料,180 d后测定试验组和对照组血清中T-SOD、GSH-Px活性和MDA含量.[结果]与对照组相比,试验组可以提高T-SOD和GSH-Px的活性,降低MDA含量.[结论]添加复合预混料可以提高奶牛的抗氧化能力.  相似文献   
33.
为了更好地预防仔猪黄痢,选取野生分离菌株HN2001(K88ab)、HN2002(K88ac)、HN2003(K88ad)、HN2004(K99)、HN2005(987p)和HN2006(F41)培养后用低温磁力搅拌法提取菌毛,制成5批多价菌毛混合油乳剂灭活苗。试验结果表明,5批多价灭活疫苗对小鼠的平均保护率达95.0%,为进一步进行本体动物试验提供了有价值的参考资料。  相似文献   
34.
To clone adiponectin (ADPN) gene from Shaziling porcine adipocyte and construct its eukaryotic expression vector, total RNA was extracted from subcutaneous fatty tissue. One pair of specific primers was designed by Primer 5.0 software according to the sequence of ADPN gene of porcine available in GenBank. The ADPN gene was amplified by PCR from cDNA and cloned into pMD18‐T vector to construct recombinant clonal vector pMD‐ADPN, sequenced and analysed. A recombinant expression plasmid pPICZaA‐ADPN was constructed by subcloning the cloned ADPN gene into the linearized pPICZaA vector. Then, the plasmid pPICZaA‐ADPN was expressed in Pichia pastoris (GS115) by electrotransformation. Western blot and Bradford analysis were used to determine the target protein induced by methanol. Results showed that the genome size of ADPN was 732 bp and encoded 244 amino acid, the nucleotide sequence of ADPN shared 100% identity with that of porcine available in GenBank. Western blot and Bradford analysis showed that the recombinant ADPN was expressed in GS115 correctly and has certain immune activity. The expression level of ADPN was 28.5 μg/ml. In conclusion, the recombinant ADPN could express in eukaryotic expression vector pPICZaA‐ADPN constructed in this study effectively.  相似文献   
35.
An acute infectious diseases occurred in a koi farm in Fangshan district, Beijing, and it resulted in mortalities of more than 50%.The main symptoms of sick koi were gills necrosis, kidney erosion and edema,which were similar to the clinical signs of koi herpes virus disease (KHVD).But PCR tests showed negative results for KHV. For further diagnosis, bacterial cultures, transmission electron microscopy studies, virus isolation and PCR tests were used. Electron microscopic observation revealed pox virus particles having a size of about 200 nm×400 nm in the kidney. 548 and 180 bp fragments were amplified from organs of sick koi by PCR method using specific primers of carp edema virus (CEV). The fragments were sequenced and analysed. The results showed that they were shared 100% nucleotide identity with CEV-H504. All the results indicated that this disease was carp edema virus disease, caused by a kind of pox virus, CEV. This was the first report on the CEV of cultured koi in China.  相似文献   
36.
37.
Brucellosis, caused by a facultative intracellular pathogen Brucella, is one of the most prevalent zoonosis worldwide. Host infection relies on several uncanonical virulence factors. A recent research hotpot is the links between carbon metabolism and bacterial virulence. In this study, we found that a carbon metabolism-related pyruvate kinase (Pyk) encoded by pyk gene (locus tag BAB_RS24320) was associated with Brucella virulence. Determination of bacterial growth curves and resistance to environmental stress factors showed that Pyk plays an important role in B. abortus growth, especially under the conditions of nutrition deprivation, and resistance to oxidative stress. Additionally, cell infection assay showed that Pyk is necessary for B. abortus survival and evading fusion with lysosomes within RAW264.7 cells. Moreover, animal experiments exhibited that the Pyk deletion significantly reduced B. abortus virulence in a mouse infection model. Our results elucidated the role of the Pyk in B. abortus virulence and provided information for further investigation of Brucella virulence associated carbon metabolism.  相似文献   
38.
不同利用方式下伊犁绢蒿贮藏营养物质的比较   总被引:1,自引:0,他引:1  
2005~2006年采用实地调查与室内分析相结合的方式,对新疆昌吉市阿什里乡不同利用方式下的伊犁绢蒿根中可塑性贮藏营养物质变化进行了研究.结果表明:伊犁绢蒿的根中可溶性碳水化合物、蔗糖、淀粉、粗蛋白质含量在多年封育地、连续放牧地、禁牧一放牧地间差异极显著(P<0.01),且多年封育可促进可溶性碳水化合物、蔗糖、淀粉的积累,而连续放牧可以刺激粗蛋白质的增加;短期禁牧后再连续放牧,会引起贮藏营养物质的逐渐丧失,不利于草地恢复效果的保持.  相似文献   
39.
在青海省刚察县、兴海县河卡镇、称多县牧民定居点、玉树县结古镇等地用氢溴酸槟榔碱下泻法调查蔵犬119只,棘球绦虫感染8条,平均感染率为6.15%,感染强度1~327条。  相似文献   
40.
据世界动物卫生组织(OIE)和世界口蹄疫参考实验室(WRLFMD)样品检测报告,2018年全球共有50多个国家或地区报告发生口蹄疫疫情或检测到口蹄疫病毒。在亚洲、非洲,口蹄疫继续呈地方性或暴发流行,在欧洲(如俄罗斯和土耳其)及南美洲(哥伦比亚)的部分国家呈散发性流行。本文介绍了2018年全球口蹄疫发生情况,分析总结了全球口蹄疫流行特点,简述了全球防控进展,同时结合我国口蹄疫流行情况,对我国口蹄疫防控提出了相关建议。  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