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   421篇
  国内免费   6篇
  完全免费   102篇
  2019年   7篇
  2018年   15篇
  2017年   10篇
  2016年   15篇
  2015年   18篇
  2014年   27篇
  2013年   16篇
  2012年   34篇
  2011年   30篇
  2010年   16篇
  2009年   26篇
  2008年   21篇
  2007年   32篇
  2006年   34篇
  2005年   35篇
  2004年   22篇
  2003年   19篇
  2002年   22篇
  2001年   14篇
  2000年   8篇
  1999年   16篇
  1998年   6篇
  1997年   9篇
  1996年   7篇
  1995年   8篇
  1994年   8篇
  1993年   10篇
  1992年   9篇
  1991年   5篇
  1990年   6篇
  1989年   5篇
  1988年   3篇
  1987年   7篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1980年   2篇
  1979年   3篇
  1977年   1篇
排序方式: 共有529条查询结果,搜索用时 31 毫秒
1.
A new acid-tolerant nitrogen-fixing bacterium associated with sugarcane   总被引:27,自引:2,他引:25  
During surveys of bacteria possibly responsible for N2 fixation in sugarcane, root and stem samples were collected in four sugarcane-growing regions in Brazil. A new microaerobic N2-fixing bacterium was isolated from most samples of washed roots and stems from all regions. Isolation procedures were based on semisolid diluted sugarcane juice medium followed by replication to N-free 10% sugar medium acidified with acetic acid to pH 4.5. The new bacterium is an aerobic rod, motile by 1 to 3 lateral flagella, fixes N2 in semisolid media under air but not in liquid media except when a starter dose of N is added. It has no nitrate, reductase and N2 fixation proceeds in the presence of 10mM NO 3 . Best growth occurs with high sucrose concentrations (10%). Growth occurs up to 30% sucrose but not at 35%. Acid is formed reaching a final pH of below 3.0. Growth and N2 fixation proceed at this acidity. Ethanol is used for growth and is “overoxidised” (oxidized to CO2 and H2O). Acetic and lactic acids are also oxidized to CO2 and H2O. Acids produced from glucose are consumed with precipitation of CaCO3. Dark brown colonies are formed on potato agar with 10% sugar and dark orange colonies on N poor agar (20 mg yeast extract per 1) containing bromothymol blue. In view of the distinct characteristics which do not allow identification within either Frateuria, Gluconobacter, Acetobacter or any known N2-fixing bacterium a new genus and species are proposed and namedSaccharobacter nitrocaptans.  相似文献
2.
In Brazil the long-term continuous cultivation of sugarcane with low N fertiliser inputs, without apparent depletion of soil-N reserves, led to the suggestion that N2-fixing bacteria associated with the plants may be the source of agronomically significant N inputs to this crop. From the 1950s to 1970s, considerable numbers of N2-fixing bacteria were found to be associated with the crop, but it was not until the late 1980s that evidence from N balance and 15N dilution experiments showed that some Brazilian varieties of sugarcane were able to obtain significant contributions from this source. The results of these studies renewed the efforts to search for N2-fixing bacteria, but this time the emphasis was on those diazotrophs that infected the interior of the plants. Within a few years several species of such `endophytic diazotrophs' were discovered including Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, H. rubrisubalbicansand Burkholderia sp. Work has continued on these endophytes within sugarcane plants, but to date little success has been attained in elucidating which endophyte is responsible for the observed BNF and in what site, or sites, within the cane plants the N2 fixation mainly occurs. Until such important questions are answered further developments or extension of this novel N2-fixing system to other economically important non-legumes (e.g. cereals) will be seriously hindered. As far as application of present knowledge to maximise BNF with sugarcane is concerned, molybdenum is an essential micronutrient. An abundant water supply favours high BNF inputs, and the best medium term strategy to increase BNF would appear to be based on cultivar selection on irrigated N deficient soils fertilised with Mo.  相似文献
3.
High output genetic mapping of polyploids using PCR-generated markers   总被引:16,自引:0,他引:16  
Summary The polymerase chain reaction (PCR) with arbitrarily selected primers has been established as an efficient method to generate fingerprints that are useful in genetic mapping and genomic fingerprinting. To further increase the productivity of mapping and fingerprinting efforts, we have altered existing protocols to include the use of the Stoffel fragment, which is derived from genetically engineered Taq polymerase. We also optimized the thermal profile of the reaction to increase the number of useful primers. In mapping of the genome of Saccharum spontaneum SES 208, a polyploid wild relative of sugarcane, these modifications allowed for an increase of 30% in the number of loci screened per primer, and an 80% increase in the number of polymorphisms per primer. Furthermore, the enzyme cost per reaction was decreased approximately 1.6-fold. Finally, there was an increase from about 70% to about 97% in the number of primers that were useful (i.e., gave a reproducible fingerprint) using our protocol. We have placed some of these markers into linkage groups.  相似文献
4.
由高粱花叶病毒和甘蔗花叶病毒引发的浙江甘蔗花叶病害   总被引:15,自引:0,他引:15  
陈炯  陈剑平 《病毒学报》2002,18(4):362-366
从浙江省5个地区采集表现花叶症状的甘蔗病叶,用马铃薯Y病毒科简并引物做PCR扩增及测序鉴定。序列分析表明,5个甘蔗样品均含有高粱花叶病毒(SrMV),其中3个样品中还存在甘蔗花叶病毒(SCMV)的复合侵染,序列比较和系统进化树分析表明,浙江甘蔗样品中的SrMV序列彼此很相似,核苷酸同源性大于93%,与已报道的4个美国分离物在CP区域同源性很高,但是3′非编码区的同源性却仅为70%左右。SCMV欧洲和中国玉米分离及美国,南非和澳大利亚甘蔗分离物分别形成两个远缘群体,浙江甘蔗分离群体位位于两者之间;群体间CP氨基酸序同源性均大于80%,甘蔗和玉米上的SCMV差异明显,多为无义突变。  相似文献
5.
警惕外来危险害虫褐纹甘蔗象入侵   总被引:15,自引:0,他引:15  
张润志  任立  曾玲 《昆虫知识》2002,39(6):471-472
褐纹甘蔗象Rhabdoscelus lineaticollis(Heller)在菲律宾,日本和台湾,严重危害椰子等棕榈科植物和甘蔗。本文对褐纹甘蔗象的分类地位,形态特征,分布,寄主,扩散与危害,生物学特性等进行简要介绍。  相似文献
6.
Sugarcane mosaic virus (SCMV) is one of the most important virus diseases of maize in Europe. Genetic analysis on backcross five (BC5) progeny derived from the cross FAP1360A (resistant) × F7 (susceptible) confirmed that at least two dominant genes, Scm1 and Scm2, are required for resistance to SCMV in the progeny of this cross. With the aid of RFLP and SSR marker analyses, Scm1 was mapped in the region of 8.7 cM – between the nucleolus organizer region (nor) and RFLP marker bnl6.29 on the short arm of chromosome 6, while Scm2 was mapped to an interval of 26.8 cM flanked by the RFLP markers umc92 and umc102 near the centromere region of chromosome 3. Both chromosome regions were further enriched for AFLP markers by successful application of a bulked segregant analysis to this oligogenic trait. A total of 23 linked AFLP markers were identified, clustered in chromosome regions adjacent to either Scm1 or Scm2. Seven AFLP markers linked to Scm1 resided within the nor-bnl6.29 interval, and one of them, E3M8-1, showed no recombination with Scm1. Three AFLP markers linked to Scm2 are located between umc92 and umc102. Received: 13 October 1998 / Accepted: 18 January 1999  相似文献
7.
蔗渣水解液发酵乙醇的研究   总被引:14,自引:0,他引:14       下载免费PDF全文
研究了酵母(Pichiastipitis)Y7124在限制供氧条件下尽管反应初期葡萄糖消耗速率大于木糖,但在一定时间后,葡萄糖的消耗速率变慢,而木糖消耗速率变快直至耗尽的现象。建立了气升柱以P.Stipitis转化木糖为目的和以溢流柱Sacharomycescerivisiae转化残留葡萄糖为目的的串联发酵乙醇工艺,即流加5倍浓缩的蔗渣水解液,D=0.1h-1,还原糖总利用率为97.2%,酒精浓度为46.5g/L,生产率为4.1g/L·h。  相似文献
8.
甘蔗愈伤组织超低温保存中一些因素的研究   总被引:13,自引:0,他引:13  
对甘蔗愈伤组织超低温保存中几个主要因素进行了多方面的对比试验,为甘蔗愈伤组织的超低温保存提供了一套较佳的技术。实验结果表明:愈伤组织的适宜培养时间是10—15天。较好的冰冻保护剂是10%二甲亚砜(DMSO)+0.5mol/l 山梨糖醇,在0℃预处理30—45分钟。较佳的冰冻程序是以1℃/分的降温速度从0℃降到-40℃,停留1—3小时,然后浸入液氮中贮存。用自来水冲洗化冻同40℃水浴中化冻的效果一样良好。化冻后的愈伤组织在黑暗培养中生长好,存活率高。经过半年超低温保存后的愈伤组织在再培养中生长良好,并产生大量的新植株。此项结果为甘蔗种质的长期保存提供了可能性。  相似文献
9.
甘蔗ACC氧化酶基因片段的克隆与序列分析   总被引:11,自引:1,他引:10  
1- 氨基环丙烷-1-羧酸(ACC)氧化酶是植物乙烯合成的一个关键酶,乙烯作为一种内源激素,对植物生长、老熟过程有多方面的调节作用。根据报道的各种植物ACC氧化酶氨基酸序列上前后两个保守区设计两个简并引物,以甘蔗总DNA为模板,通过PCR扩增到一个940bp的基因片段。将片段序列在MCBI的BLAST软件上进行同源性搜寻,显示的63个序列全部是ACC氧化酶基因,因而认为克隆到的片段就是甘蔗ACC氧化酶基因的一个成员。经对不同植物来源的ACC氧化酶基因家族进行比较分析,去除一个103bp的“内含子“后,推导的氨基酸序列为279个残基,占推测全长氨基酸残基总数的86%左右。经同源性分析,序列与毛竹和水稻ACC氧化酶的同源率达到86%。系统进化分析表明,该序列最先与水稻、其次和香蕉的ACC氧化酶聚类,然后再与双子叶植物的ACC氧化酶聚类,符合按形态特征分类的血缘关系。基因的获得对下一步了解乙烯的合成表达与甘蔗生长、成熟过程之间的关系奠定了基础。  相似文献
10.
甘蔗种质间亲缘关系及特异标记的RAPD分析   总被引:11,自引:2,他引:9  
采用RAPD技术分析甘蔗种质问的亲缘关系及特异标记。筛选出25个扩增多态性较强的随机引物,构建了41份甘蔗种质的RAPD指纹图谱,并对RAPD数据进行UPGMA聚类分析。甘蔗栽培品种之间、栽培品种与近缘种之间以及近缘种相互间的遗传相似系数变异范围为0.56~0.92,表明所研究的甘蔗种质之间的亲缘关系较近。此外,发现某些甘蔗亲本种质具有特异RAPD标记带。  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