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31.
已知许多植物抗病基因的蛋白质产物具有保守的结构域,如NBS、ILRR、TM等。根据烟草的N基因、亚麻的L6基因和拟南芥的RPS2基因的保守序列设计了1对简并引物,以应县小黑豆基因组DNA为模板,通过PCR扩增获得16个不同的RGA片段,大小为470~545bp,且不同程度地含有抗病基因的保守序列,如GGVGKTT、GSRII、GIPL等。与已知大豆、棉花RGA进行比较,发现获得的大豆。RGA和用相同引物扩增获得的棉花RGA核酸序列以及相应的氨基酸序列之间同源性较低,与已经克隆的大豆RGA及其氨基酸序列之间有较高的相似性。 相似文献
32.
研究了权重为区间数且对方案有模糊互补偏好关系的模糊多属性决策问题.首先,基于模糊互补判断矩阵的主观偏好信息,利用转换函数将决策信息一致化,并建立了目标规划模型.通过求解该模型得到属性的权重,运用加性加权法获得各方案的模糊综合属性值.其次,提出了基于方案的模糊正理想解与其模糊综合属性值相似度的方案排序法.该方法既能充分利用已有的客观信息,又能最大限度地体现决策者的主观意愿,且具有操作简便、易于上机实现的特点.该方法已应用于解决风险投资领域中项目评估问题. 相似文献
33.
一种改进的Item-based协同过滤推荐算法 总被引:2,自引:0,他引:2
分析了协同过滤推荐系统中存在的用户多兴趣和项目多内容问题,提出了一种基于项的协同过滤改进算法,算法综合考虑了项目自身属性和用户评价的影响。试验表明该算法有效的解决了用户的多兴趣和项目的多内容问题,并且在用户评分数据比较稀疏的情况下也能有较好的推荐精度。 相似文献
34.
11个灵芝菌株的栽培性状和酯酶同工酶研究 总被引:7,自引:0,他引:7
利用短段木熟料栽培法对11个灵芝菌株进行栽培,结果表明:不同灵芝的栽培性状互有差异。其中8、新6、6、12、13具较好的栽培性状(产量高、子实体形状好、产孢量大)。此外,通过PAGE分析,并分别测定相关的酶谱相似度(T)和联合系数(S),结果发现:S1与其余各菌株间的差异最为明显。与其它菌株的亲缘关系最远;亲缘关系最近的是6新6、新6C1、13C3(T,S值最大,T=1,S=1,6、新6、C1三菌株酶带数量和位置一样,但酶活性存在区别);另外具有较好栽培性状的菌株(8、新6、6、12、13)其酶活性都较强,表现为酶带宽且色深。 相似文献
35.
36.
The ecological processes responsible for the spatial assemblages of breeding bird communities in urban landscapes are more and more investigated. Indeed, understanding these processes is imperative to plan relevant management policies. We investigated breeding bird communities on 67 patches in the suburbs of Paris, France. We examined the role of patch characteristics and geographic distance between patches in determining similarity between bird assemblages. To do this, we proposed a new SØrensen similarity index based on estimators of change in community composition taking into account the detection probability of species. The patch occupancy by sedentary and migratory species was also estimated to compare their sensitivity to urbanization. Patches close to each other supported more similar bird assemblages, suggesting an effect of the spatial distribution of patches on bird dispersal and a posteriori on local community composition. Accounting for spatial location of patches, bird assemblage similarity was related to the similarity of the surrounding level of urbanization but not to the similarity of patch size or to the similarity of patch vegetation. The mean estimated occupancy rate of sedentary species was higher than that of migratory species in the whole study area. While sedentary species occupied patches surrounded by both moderate and high levels of urbanization, migratory ones primarily occupied patches surrounded by moderate levels of urbanization. Human choices in degrees, styles, and extent of urbanization, including designation and design of patches within an urban matrix, affect the composition of local bird communities. 相似文献
37.
38.
Ashraf?M.?El-Assar Robert?R.?Krueger Pachanoor?S.?Devanand Chih-Cheng?T.?ChaoEmail author 《Genetic Resources and Crop Evolution》2005,52(5):601-607
Forty-seven samples of date palm (Phoenix dactylifera L.) collected from eight locations in Egypt were studied using four sets of amplified fragment length polymorphism (AFLP)
markers with near infrared fluorescence labeled primers. These samples belonged to 21 named accessions and 9 of unknown pedigrees.
A total of 350 bands were scored and 233 (66.6%) were polymorphic. Twenty-seven Egyptian accessions and ‘Medjool’and ‘Deglet
Noor’accessions from California could beclassified into the major cluster. This major cluster may represent a major group
of date palm germplasm in North Africa. There were four other clusters, each containing one or two accessions. The variety
‘Halawy’and one accession of unknown provenance were most likely from hybridization between two clusters. Six groups of accessions
of which had the same names, revealed similar but not identical AFLP profiles suggesting these accessions might derive from
seedlings rather thanthrough clonal offshoot propagation. 相似文献
39.
Robert McDonald Meghan McKnight Elizabeth Selig Christy Violin 《Biological conservation》2005,126(1):24-40
The concept of an ecoregion, a discrete spatial area where species composition is presumed to be relatively homogeneous compared to that between areas, has become an increasingly common conservation tool. We test the effectiveness of one ecoregion delineation (World Wildlife Fund) in capturing patterns of change in species composition of birds, mammals, and trees across the United States (excluding Hawaii) and Canada, and describe the extent to which each ecoregion boundary is concurrent with relatively large changes in species composition. Digitized range maps were used to record presence/absence in 50 × 50 km equal-area grid cells covering the study area. Jaccard’s index of similarity was calculated for all pairs of cells in the same or adjacent ecoregions. The average rate at which similarity declined with geographic distance was calculated using pairs of cells within the same ecoregion (intra-ecoregion turnover) or using pairs of cells in adjacent ecoregions (inter-ecoregion turnover). The intra-ecoregion rate varies widely among ecoregions and between taxa, with trees having a faster rate of similarity decline than mammals or birds. For all three species groups, most ecoregion boundaries have similar rates across them (inter-ecoregion) than that within each adjacent ecoregion (intra-ecoregion), with the exception of zones of transition between biomes and major geographical features. Although the ecoregion concept is useful for many other conservation applications, the lack of systematic, high turnover rates along ecoregion boundaries suggests that ecoregions should not be used as a quantitative basis for delineating geographic areas of a particular taxonomic group. 相似文献
40.
Abha Jain A. K. Roy P. Kaushal D. R. Malaviya S. N. Zadoo 《Genetic Resources and Crop Evolution》2006,53(2):339-347
Isozyme banding pattern was studied in Guinea grass (Panicum maximum Jacq.), a widely cultivated grass having good fodder value. Similarity among 63 accessions collected from diverse sources
was worked out using five enzyme systems (SOD, GOT, ACP, Esterase and Peroxidase) following horizontal starch gel electrophoresis.
Biochemical markers such as isozymes are useful supplements in identifying the genetic variation present in any crop. A total
of 35 clear and unambiguous bands were used for analysis of which 8 bands were monomorphic. Polymorphism exhibited by 27 bands
from all five enzyme systems indicate presence of considerable diversity in this species. The dendrogram generated after UPGMA
and SAHN cluster analysis using Jaccard genetic distance showed that 63 accessions from diverse geographical locations could
be grouped in three main clusters, of which two could further be divided into sub-clusters. Although the clusters comprised
members from different locations, most of the accessions from similar geographical locations tended to cluster in same group. 相似文献