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991.
论述了黑龙江省开展计划烧除的重要性、风险性、必要性和可行性,提出了规范计划烧除技术实施和管理的具体措施和办法. 相似文献
992.
993.
One 50 m × 50 m standard plot was sampled in a natural forest of Populus euphratica in Awati County, situated at the edge of the Tarim Basin, Xinjiang Uygur Autonomous Region, China. The field investigation was conducted with a contiguous grid quadrate method. By means of a test of variance/mean value ratio, aggregation intensity index and theoretical distribution models, the spatial distribution pattern and the dynamics of primary populations in P. euphratica forest were studied. The results showed that the spatial distribution pattern of two dominant arbor populations conformed to clumped distribution. The aggregation intensity of the P. euphratica population was higher than that of P. pruinosa population. The spatial distribution pattern of two companion plant populations in the shrub layer also conformed to clump type, though the aggregation intensity of Tamarix chinensis was higher. In the herb layer, the distribution patterns of Glycyrrhiza uralensis and Asparagus persicus conformed respectively to a clumped pattern and a random pattern. The results of a Taylor power method test and Iwao’s regression model also verified that both P. euphratica and P. pruinosa populations belong to a clumped pattern. Although the distribution pattern of P. pruinosa population at different development stages all belonged to a clumped distribution pattern, the aggregation intensity dropped gradually along with age development. The distribution patterns of the P. euphratica population at different development stages changed from random type to clumped type, and further to random type. The differences in spatial distribution patterns of different populations at different development stages were related not only to ecological and biological characteristics of each species in the communities in the light of competitive exclusion principle among the populations, but were also closely related to the habitats in which the species lived in. __________ Translated from Journal of Southwest Forestry College, 2007, 27(2): 1–5 [译自: 西南林学院学报] 相似文献
994.
995.
【目的】检测致病性大肠埃希氏菌中超广谱β-内酰胺酶(Extendβ-lactamase,ESBLs)的基因型,指导兽医临床合理用药。【方法】对产生ESBL的5株致病性大肠埃希氏菌,设计并合成TEM-1和SHV-1两对引物,用PCR方法进行了ESBLs耐药质粒的DNA扩增、测序和基因型分析【结果】以产生ESBLs细菌的ESBLs耐药质粒为模板均扩增出了与预期片段大小相符的TEM型ESBL产物,但都没有扩出SHV型ESBL产物。【结论】结果提示国内畜禽产生ESBLs的致病性大肠埃希氏菌未通过质粒进行细菌间耐药基因的交换;ESBLs的产生与动物种属没有关系;为克服细菌的该类耐药性问题,应该进行头孢噻呋复方制剂的研究。 相似文献
996.
997.
大豆高蛋白育种的亲本选配和后代选择的研究——Ⅰ大豆杂交F_2、F_3、F_4代蛋白质含量的遗传变异特点 总被引:2,自引:1,他引:2
用蛋白质含量不同的九个亲本配成六个组合,对其F_2、F_3、F_4代蛋白质含量的遗传基因作用方式和遗传参数等进行了系统的研究。试验结果表明,除C_2外,其它五个组合的蛋白质含量遗传主要是基因的加性效应,可用中亲值预测杂交后代蛋白质含量的平均表现。组合C_2除基因的加性效应外,还存在显性效应。多数组合蛋白质含量的遗传力一般中等偏高且随着世代的升高而增加。不同组合F_2、F_3、F_4代蛋白质含量变异系数和遗传进度较大,以及高蛋白超亲个体的普遍存在,均表明了早期世代选择高蛋白个体的必要性和可能性。 相似文献
998.
999.
1000.
Bark beetle species in natural stands of spruce, Picea crassifolia (Kom.) were investigated in Maixiu Forest Park, Qinghai Province, northwest China, during 2005 and 2007. Two pioneer Ips species, Ips nitidus Eggers and Ips shangrila Cognato and Sun were found. I. nitidus occurs naturally in northwest China. I. shangrila is a new species in the world. In the past, it was confused with I. mannsfeldi Wachtl in China. The damage of these two Ips species has been very severe in Maixiu and the morphological and bio-logical characteristics were studied. I. nitidus starts to fly in early May and prefers the mid to lower part of the host tree to colonize as its habitat. I. shangrila always infests from the top of the trunk, especially in branches larger than 3 cm in diameter in the crowns and sometimes even colonizes entire young trees. The two Ips species are the most destructive secondary bark beetles on P. crassifolia and always cause mortality of trees by their cooperation. 相似文献