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   251篇
  免费   13篇
  国内免费   3篇
林业   20篇
农学   2篇
  70篇
综合类   49篇
农作物   12篇
水产渔业   22篇
畜牧兽医   31篇
园艺   1篇
植物保护   60篇
  2023年   2篇
  2022年   2篇
  2021年   2篇
  2020年   2篇
  2019年   5篇
  2018年   2篇
  2017年   2篇
  2016年   9篇
  2015年   3篇
  2014年   7篇
  2013年   11篇
  2012年   12篇
  2011年   23篇
  2010年   8篇
  2009年   6篇
  2008年   9篇
  2007年   9篇
  2006年   13篇
  2005年   13篇
  2003年   7篇
  2002年   3篇
  2001年   9篇
  2000年   6篇
  1999年   6篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1995年   1篇
  1994年   2篇
  1993年   8篇
  1992年   8篇
  1991年   8篇
  1990年   4篇
  1989年   9篇
  1988年   6篇
  1987年   5篇
  1986年   3篇
  1985年   4篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1979年   5篇
  1975年   1篇
  1974年   2篇
  1973年   4篇
  1970年   1篇
  1969年   1篇
  1964年   5篇
  1963年   2篇
排序方式: 共有267条查询结果,搜索用时 15 毫秒
71.
This study evaluated the effects of priming on emergence responses of purple coneflower (Echinacea purpurea L. Moench) seeds. The seeds that differ in seed size were either primed with moistened vermiculite (solid matrix priming) or primed in non-aerated −0.5 MPa polyethylene glycol 6000 solution at 25 °C for 6 days (osmopriming), followed by air-drying to their initial moisture level. The tetrazolium staining tests indicated that both large and small seeds were biochemically viable. No notable difference in germination percentage was found between large and small seeds. However, extensive cavity was visible in portions of small seeds in comparison with large seeds. Large seeds accumulated more antioxidants and had greater activities of anti-oxidative enzymes than small seeds. They also had greater isocitrate lyase and malate synthase activities than small seeds. As a result, large seeds had higher emergence percentage and faster emergence speed as compared to that of small seeds. Both solid matrix priming and osmopriming increased emergence percentage and shortened mean emergence time of purple coneflower seeds by increasing the activities of anti-oxidative enzymes and decreasing the levels of malondialdehyde and total peroxide accumulation. Moreover, priming also enhanced the anti-oxidative activities of treated seeds. The activities of isocitrate lyase and malate synthase were also increased in primed seeds. The enhanced anti-oxidation and lipid-carbohydrate conversion activities might explain in part why primed purple coneflower seeds emerged better than non-primed seeds.  相似文献   
72.
 从北京郊区患有类似花叶病害的菜豆株上分离到一种线条状病毒(长约700至750nm)并于1983至1986年间加以研究。在温室内接种可以侵染菜豆、蚕豆、豌豆、大豆、决明、苋色藜及昆诺藜而不能侵染被接种的任何茄科植物.同标准的菜豆普遍花叶病毒(BCMV)相比,它不侵染茄科植物例如黄花烟(Nicotiana rustica)和矮牵牛(Petunia hybrida)在菜豆叶上也不产生坏死枯斑.此外它能侵染蚕豆、大豆、豌豆及决明而BCMV则不能.BCMV能侵染豇豆而这一分离物则不能.此分离物的物理性状为:钝化温度=56-580℃(十分钟),硫释限点=10-3至10-4,180℃下存治期为3天,A260/280=1.12.菜豆受侵叶组织易用光学显微镜观察到内含体包括一种片层叠合体.在电镜下超薄切片中可以看到风轮状体.极易用汁液摩接及用桃蚜(Myzus persic(接种.此病毒的衣壳蛋白亚基的分子量经测定为32,000道尔顿.此病毒与下列病毒即菜豆普通花叶病毒,菜豆黄色花叶病毒,黑眼豇豆花叶病毒,豌豆种传花叶病毒,三叶草黄脉病毒,莴苣花叶病毒及甜菜花叶病毒的抗血清均无反应.由于它在菜豆的"一窝猴"品种的叶片上产生沿脉黄色小点,因此认为这是一种新的独立的病毒,称之为菜豆和性黄色花叶病毒.  相似文献   
73.
在田间的小麦丛矮病非典型病株申常常分离到北方禾谷花叶病毒(NCMV)及玉米粗缩病毒(MRDV)两种病原物。单独用前者接种,仅表现小麦丛矮症,单独用后者接种,仅表现小麦蓝矮症,即植株矮化、暗绿、分蘖减少,叶坚挺。两者混合侵染时,往往表现两者的混合症状,但以何种病毒占优势而倾向于优势病毒的症状。典型丛矮症植株中电镜检出弹状病毒粒体,40—70×270—400nm尺度与日本报导的稍异。典型丛矮病株中不存在玉米粗缩病毒的粒体。小麦丛矮病毒很可能是北方禾谷花叶病毒的一种地方性株系。  相似文献   
74.
Infectious bursal disease virus (IBDV) causes a contagious immunosuppressive disease in chickens. The aim of the present study is to develop an enzyme-linked immunosorbent assay (ELISA) using the expressed VP2 or VP3 protein of IBDV as the coating antigen for detecting antibodies to IBDV. Experimental results were compared with virus neutralization assay and a commercial-available ELISA. These assays were used to examine the sera from farm chickens and chickens vaccinated experimentally. The VP3-based ELISA had a higher correlation coefficient (R(2)) of 0.812 with a commercial ELISA kit at a serum dilution of 1:500 than that of VP2-based ELISA (R(2)) of 0.671. The relative sensitivity between virus neutralization and VP2-ELISA and VP3-ELISA was 96% (251/262) and 100% (262/262), respectively, and that between virus neutralization and a commercial ELISA was 99% (257/261). Additionally, compared with virus neutralization assay, the reference technique for diagnosing IBDV, VP3-based ELISA had an agreement value of 99%, superior to that of VP2-based ELISA (95%) or the commercial kit (89%). These results revealed that the capability of either VP2-ELISA or VP3-ELISA in detecting the field chicken sera was comparable to the commercial one, which is generally used to replace the virus neutralization assay. However, the preparation of VP3 is derived from an Escherichia coli expression system with a high yield and purification efficiency by Ni(2+)-NTA gels, which is more favorable to the insect cell-derived particles formed by VP2. Therefore, VP3-ELISA could be developed as an efficient and low cost diagnostic method for IBDV infection in field chickens.  相似文献   
75.
 用尤力克柠檬和葡萄柚作指示植物,鉴定广西、广东、湖南、江西、浙江、四川等6个省(区)的873株柑桔中有691株受苗黄型衰退病毒感染,说明这种病毒的分布相当普遍。  相似文献   
76.
棉苗黑斑病的致病菌在关中棉区初步认为是 Alternaria tenuis Nees 与棉成株期叶片上的致病菌不同。病菌孢子借气流传布。种子带菌率虽然很高,但诱发苗病率却很低,因此,种子消毒或采用轮栽来控制这个病害,是不能达到预期效果的。病害发生与棉苗受冻、强风对棉苗的伤害以及棉苗阶段发育有密切的关系。各年发病期有早有晚,但以真叶出现时为易感阶段。本文阐述了棉苗生育阶段、气候条件与发病的关系,为预测病害发生的物候与气象参考条件提供了资料。棉株伤害与发病有关系,建议在生产上适当降低播种量,提高播种质量,适期早疏苗、早间苗;以减轻由于伤损而导致病害侵染。品种与病害发生的关系不显著。试验证明,使用波尔多液加1059于降温前喷射效果较好。  相似文献   
77.
 窖藏白菜腐烂是由许多细菌造成的。最重要的是Erwinia aroideaeE.phytophthora以及被认为是腐生菌的三种芽孢杆菌Bacillus pumilus,B.poly-myxaB.subtilis。试验证明在一定条件下后者能引致明显的腐烂。  相似文献   
78.
Several of the endothelial cell polypeptide mitogens that have been described probably play a role in blood vessel homeostasis. Two overlapping complementary DNA clones encoding human endothelial cell growth factor (ECGF) were isolated from a human brain stem complementary DNA library. Southern blot analysis suggested that there is a single copy of the ECGF gene and that it maps to human chromosome 5 at bands 5q31.3 to 33.2 A 4.8-kilobase messenger RNA was present in human brain stem messenger RNA. The complete amino acid sequence of human ECGF was deduced from the nucleic acid sequence of these clones; it encompasses all the well-characterized acidic endothelial cell polypeptide mitogens described by several laboratories. The ECGF-encoding open reading frame is flanked by translation stop codons and provides no signal peptide or internal hydrophobic domain for the secretion of ECGF. This property is shared by human interleukin-1, which is approximately 30 percent homologous to ECGF.  相似文献   
79.
Human fertilization begins when spermatozoa bind to the extracellular matrix coating of the oocyte, known as the zona pellucida (ZP). One spermatozoan then penetrates this matrix and fuses with the egg cell, generating a zygote. Although carbohydrate sequences on the ZP have been implicated in sperm binding, the nature of the ligand was unknown. Here, ultrasensitive mass spectrometric analyses revealed that the sialyl-Lewis(x) sequence [NeuAcα2-3Galβ1-4(Fucα1-3)GlcNAc], a well-known selectin ligand, is the most abundant terminal sequence on the N- and O-glycans of human ZP. Sperm-ZP binding was largely inhibited by glycoconjugates terminated with sialyl-Lewis(x) sequences or by antibodies directed against this sequence. Thus, the sialyl-Lewis(x) sequence represents the major carbohydrate ligand for human sperm-egg binding.  相似文献   
80.
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