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《农业科学与技术》2016,(3)
A total of 15 pools were selected from a greenhouse, and they were randomly and evenly divided into three groups. In each group, one stocking density of Eriocheir sinensis was arranged. The results showed that after 45-d culture, the crab number per kilogram reached about 300 with survival rate of about 20%; the initial stocking density had significantly effect on the body size of E. sinensis on sel , instead on the survival rate of E. sinensis larvae. Therefore, it is feasible to conduct the culture of E. sinensis larvae in a pool in greenhouse. 相似文献
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美洲黑杨基因资源收存及其遗传评价的研究 总被引:14,自引:0,他引:14
从17个国家引进331个黑杨派无性系(其中52个美洲黑杨无性系),在山东省长清县营建我国第一个黑杨派无性系基因库。连续10年对基因库内美洲黑杨无性系进行了多性状系统研究,结果表明各无性系间在物候期、生长、生根、抗寒和抗病虫等方面均存在着显著的差异,遗传变异丰富;系间的主要性状与无性系起源纬度及各性状间存在一定相关性。主要材料性状变异的研究结果表明,38个8年生美洲黑杨无性系在木材基本密度、纤维长度无性系间变异达到极显著水平;木材密度和纤维长度与树高和胸径呈一定相关性;木材密度和纤维长度这两个性状在遗传上相互独立,受不同遗传机制控制。利用分子遗传标记RAPD技术研究库内美洲黑杨无性系DNA多态性,结果表明本库美洲黑杨DNA多态率为86%,再次证明本库美洲黑杨遗传多样性高,可为我国杨树改良提供丰富的育种材料。 相似文献
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本试验于1982~1983年在长沙进行,采用剪除叶片和穗部一次枝梗以调节“库”“源”的方法,研究了杂交水稻威优6号等三个组合的空秕粒分布以及“库”“源”与结实性的关系,空秕粒在一穗中的分布以下部枝梗和二次枝梗较多,上部枝梗和一次枝梗较少;空秕粒中空粒约占3/4;剪除部分叶片空秕粒提高,剪除穗部一次枝梗则可使结实率提高。 相似文献
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Soils and vegetation were analyzed in 20 lodgepole pine (Pinus contorta) forest stands, varying in age from 50 to 350 years, that had initiated following stand-replacing fire. Our goal was to determine how nitrogen availability (NH4+-N) and microbial community composition varied with stand age-class and to determine whether differences could be explained by canopy, soil, or understory characteristics. Gross NH4+ mineralization was measured using laboratory isotopic pool dilution, and microbial community composition was evaluated using microbial membrane lipids. The microbial community composition of stands in the 300-350 age class was distinct from stands in younger age classes. Microbial community composition among sites varied with pH, % organic matter, and phosphorus. Gross NH4+ mineralization rates averaged 1.45±0.07 mg NH4+ kg soil−1 d−1 while consumption averaged 1.37±0.20 mg NH4+ kg soil−1 d−1, resulting in low net NH4+ mineralization rates (0.08±0.18 mg NH4+ kg soil−1 d−1), but rates were not significantly different with stand age-class at p<0.05. At p<0.10, net NH4+ mineralization was significantly higher in the 300-350 age class compared to the 125-175 age class. None of the measured variables significantly explained NH4+ consumption and net mineralization patterns. However, gross NH4+ mineralization rates were best explained by information on microbial community structure (i.e. lipids). Variation among stands within a given age-classes was high, indicating that patterns of N cycling across landscapes reflect substantial heterogeneity among mature stands. 相似文献
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从电气安全的角度详细地分析了大型喷水池中电气设备运行环境以及对控制系统的要求,结合有关设计规范和作者的工程实际经验,讨论了电气设备多点控制的必要性以及由此带来的电气安全问题,提出为保证操作和维修人员电气安全,在电气设备控制系统设计中应采取的有关安全措施,并给出了具体的控制电路实例;同时讨论了大型喷水池在设计、施工、运行、维护等过程需特别注意的电气设备漏气、电气火灾以及雷电等方面的电气安全问题,并提 相似文献
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在胚胎移植生产中,用从新西兰引进的肉用绵羊品种无角陶赛特羊作供体进行规模化胚胎移植生产.超排结果表明:两次超排分别回收平均卵数为5.62枚和9.08枚;从不同年龄的无角陶赛特羊上获得总卵数差异不显著;配种后第7天冲取胚胎,以桑椹胚为最多,占总回收胚胎数的75.78%,配种后第8天回收的胚胎,以扩展囊胚和孵出囊胚数所占比例为最多,分别占总数的25.89%和31.75%;从两侧卵巢所观察到的黄体数和所回收的胚胎数差异不显著;用人工授精法比试验中的其它方法能显著提高所获得的有效胚胎数;用促卵泡素恒量注射、孕马血清两次注射法进行超排效果好,所获得的平均胚胎数为8.53枚,有效胚占回收总胚的百分率则增加到82.11%. 相似文献
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The problem of optimal standby capacity and its valuation in Power Pool is very important and complicated. On the basis of researching literatures concerned, this paper constructs an optimal standby capacity model and researches the problem of pricing optimal standby capacity and determining power price on the user-side. The result shows that the optimal standby capacity at some period t is completely determined by the probability distribution density function of power load demand at this period and surplus power loss and insufficient power loss, and the price of optimal standby capacity is determined by real power price of entering power grid and the power price of forecasting load demand, and the expected power price on the user-side consists of the settlement price with grid loss on generation-side and reasonable gains and expected additional loss. 相似文献