共查询到20条相似文献，搜索用时 93 毫秒
1.
甜菜杂种优势研究进展 总被引：1，自引：1，他引：0
杂种优势利用是提高作物产量及品质的有效途径。20世纪初,主要用显性和超显性两种假说解释杂种优势。随着现代生物学的发展,对杂种优势现象的研究更加深入。笔者从活性基因效应与杂种优势、遗传距离与杂种优势、遗传连锁图谱构建与杂种优势及数量性状基因位点（QTL）与杂种优势四个方面概括了国内外甜菜杂种优势遗传基础的新见解。从甜菜杂种优势育种理论、雄性不育系（MS系)、自交系的选育及甜菜雄性不育品种的选育等方面综述了目前甜菜杂种优势利用的研究进展,并对未来甜菜杂种优势育种的研究方向进行了展望。 相似文献
2.
作物杂种优势遗传基础研究进展 总被引：13，自引：1，他引：12
杂种优势是生物界的一种普遍现象,可以大幅度提高作物产量和改良作物品质,具有巨大的商用价值。杂种优势遗传基础的研究一直是近百年来遗传和育种学家研究的热点和难点问题。笔者综述了杂种优势遗传基础的两个经典假说－显性假说和超显性假说的基本观点、不足之处。同时概括了利用分子生物学手段解释杂种优势遗传基础的一些新的学术见解,如：上位性效应与杂种优势、基因网络系统与杂种优势、遗传平衡与杂种优势、活性基因效应与杂种优势、遗传差异与杂种优势、QTL效应与杂种优势、基因表达调控与杂种优势,并列举了部分学说的分子证据。以期使人们能够了解杂种优势遗传基础的发展历程和最新研究动态。 相似文献
3.
4.
5.
6.
棉花杂种优势表达机理研究进展 总被引：14，自引：4，他引：14
从棉花杂种优势性状表现、配合力分析、生理生化研究、遗传距离与杂种优势关系等方面分析了棉花杂种优势机理研究进展,并提出了从基因水平研究棉花杂种优势,更能确切地反映杂种优势表达机理。 相似文献
7.
8.
9.
10.
11.
Abstract: This paper shows that an important requirement of the MIRAB model, economic success in the host country, is a characteristic of Pacific Islander migrants to the USA and their offspring. Pacific Islanders improved their economic lot in the 1980s and again in the 1990s. Part of this improvement was due to increases in their human capital: Pacific Islanders acquired more education, work experience and better English language skills. This upgrading allowed more workers to acquire white‐collar jobs and to increase their earnings. 相似文献
12.
13.
Recent studies have found evidence of a local employment multiplier’s effect. For the most part, these studies provide an average estimate for all labor markets. In this paper, we examine how the average local employment multiplier, the effect of an exogenous increase in employment in the tradable sector on total employment, depends on the characteristics of the local labor market. Specifically, we estimate the average multipliers for coastal, noncoastal, large, and small metropolitan statistical areas (MSAs) across different time periods using the data of 333 US MSAs. Overall, we find a reduced form of local employment multiplier ranging from 1.38 to 2.24, which is within the range of typically estimated local employment multipliers. In addition, the characteristics of the local labor market matter. The local multipliers appear larger in noncoastal and large MSAs. For small and coastal metros, the multiplier is closer to 1.5 than to 2.0 while in the case of large and noncoastal metros, it is closer to 2.0 than to 1.5. The local multipliers are also sensitive to the time period considered. 相似文献
14.
大棚栽培多数是长年连作,密闭条件好,土壤中农药的残留问题就更加明显。实验证明藻类植物地木耳可在大棚中生存。通过在大棚种植的蔬菜旁种植地木耳,可使大棚土壤和蔬菜中农药含量降低,降低幅度约为59%。 相似文献
15.
大棚栽培多数是长年连作,密闭条件好,土壤中农药的残留问题就更加明显。实验证明藻类植物地木耳可在大棚中生存。通过在大棚种植的蔬菜旁种植地木耳,可使大棚土壤和蔬菜中农药含量降低．降低幅度约为59％。 相似文献
16.
A collection of 51 accessions of Phaseolus vulgaris L. from N.W. of the Iberian Peninsula was evaluated for phenological, morphological, and agronomic characters for two years to study patterns of variation. Data were subjected to cluster analysis by variables choice, and six groups could be identified. These in turn corresponded to each previously described races ‘Nueva Granada’ and ‘Chile’ of South American origin, and races ‘Durango’ and ‘Mesoamerica’ of Middle American domestication center. Accessions falling in race ‘Nueva Granada’ had two distinct gene pools. 相似文献
17.
18.
近20年我国棉花生产主栽品种概况及其评价 总被引：6，自引：4，他引：6
本文以大量的数据 ,对近 2 0年来我国棉花品种的数量及其推广面积进行了综合评述 ,从中总结出各产棉省棉花生产发展历程及趋势。 1 999年始 ,棉花放开经营 ,2 0 0 1年始 ,棉花生产及其后续产品完全进入市场 ,棉花作为我国“战略物资”的时代已一去无返。面对即将进入 WTO及其后的挑战与机遇 ,棉花生产及育种重点必将以市场的需求为调整目标 ,文中谨以此为依据宏观提出今后的发展建议 ,以飨读者 相似文献
19.
20.
LI Ting-ting 《保鲜与加工》2007,(3):22-26
Disaster prevention is the main reason of building origin and its direct developing motivation.The hakka's ancestor migrated from the Yellow River drainage basin for escaping the wars and built the dwellings with the style of homeland building,which comes to the first formation of the traditional architecture.Through the understanding the nature disasters and the results of disaster prevention,the hakka changed the plan and body of the building.The traditional dwellings in their matured stage improve their life-span by application of the disasters prevention measures. 相似文献