排序方式: 共有19条查询结果,搜索用时 296 毫秒
1.
鱼类的顶流游泳行为是过鱼设施水力学设计的关键问题之一,获取鱼类在顶流游泳过程中的运动学参数将有助于研究目标鱼类的生理特性、游泳能力及其与水力环境因子的响应关系。本研究以鲢为对象,通过行为学分析软件对鲢在顶流游泳状态下顶流静止和顶流前进的行为中,水流速度U、摆尾频率f、相对摆尾振幅A、绝对游泳速度V和游泳加速度a之间进行了相关性分析。结果显示,鲢在顶流静止状态下,摆尾频率f与水流速度U呈现正相关性;相对摆尾振幅A为(0.0876±0.0098)BL,但与摆尾频率f之间没有明显的相关性;鲢在顶流前进状态下,不同水流速度U中摆尾频率f都要大于顶流静止状态下的摆尾频率,相对摆尾振幅A反而相差不大;摆尾频率f与绝对游泳速度V之间有显著的正相关性,但摆尾频率f与相对摆尾振幅A之间却没有明显的相关性;鲢在顶流前进的过程中,游泳加速度a会随着时间的变化而变化,大多数的游泳加速度为0.02 ga≤0.06 g(55.84%)。本研究主要在水槽中进行,流场环境比较单一,自然的流场环境相对复杂,复杂流场条件下鱼类行为与流场中水力因子之间的关系还需进一步研究。 相似文献
2.
微米木纤维模压制品握钉结合部载荷分布系数的确定方法 总被引:1,自引:1,他引:0
微米木纤维模压制品是通过细胞纵向劈裂而成的微米木纤维模压成型的新型高强度人造木基材料制品.以人造木基材料为主要材料的各种握钉力的计算均以栽荷沿轴向分布的积分方程为基础,而有关其栽荷分布系数的精确计算尤为重要.为此本文首先建立了握钉结合部裁荷分布的力学模型,然后给出了螺纹牙受力变形协调条件,推导出了轴向载荷分布强度与螺纹牙侧面上比压的关系式,分析了微米木纤维铺装纹理方向对其模压制品弹性模量的影响,从而详细地推导出了微米木纤维模压制品握钉结合部载荷分布系数的计算公式. 相似文献
3.
4.
Methods for holding of oocytes and embryos during shipment as well as for their cryopreservation can greatly aid equine reproductive management. Oocytes can be held at room temperature overnight or at cooler temperatures for two nights without affecting maturation or embryo development after intracytoplasmic sperm injection. In contrast, methods for cryopreservation of equine oocytes that support high rates of embryo development have not yet been established. Equine embryos may be held overnight at temperatures from 5°C to 19°C without reduction in viability, but longer holding periods, or higher holding temperatures, may be detrimental. Small equine embryos (<300 μm), either in vivo derived or in vitro produced, can be slow frozen or vitrified successfully. In the last decade, methods have been developed to allow in vivo–derived expanded blastocysts, up to Day 8, to be vitrified successfully after blastocoele collapse. These methods of shipment and preservation allow mare owners in remote locations to have access to sophisticated assisted reproductive technologies. 相似文献
5.
Soil properties varied in water retention; due to soil texture and organic matter content. Variations of texture in many soils are effected mostly to soil forming factors of parent materials of the soil, biological activities, climactic variation, and duration of soil reaction. While the organic matter contents are affected totally by the environmental conditions of the soils. Water holding capacity of different soils influences plants growth and development in diverse soil characteristics of the world and determines soil productivity. Water resources for agricultural activities are limited, particularly in arid environment and soil water holding capacity of arid soil is very low. Kuwait can be good example of arid environment with limited water resources for agriculture activities and possess soil of coarse texture with very low organic matter content (Anonymous, 1997). Agricultural development in Kuwait meets many problems for crop production and urban landscaping. Water resources are limited and the quality is deteriorating at the same time soil water holding capacity is very low. Enormous amount of water, particularly desalinated expensive water is wasted for agricultural activities. This paper will study various parts of Kuwaiti soils water holding capacity and develop water retention data for efficient water irrigation and improvement of plant growth. 相似文献
6.
于国丽 《山东省农业管理干部学院学报》2003,19(2):38-39
江泽民同志关于发展是党执政兴国的第一要务的重要论述,深刻揭示了发展与执政兴国的辩证关系,对于全面建设小康社会,加快推进社会主义现代化具有重大意义,我们要紧紧把执政兴国作为党的第一要务,正确处理好各方面的关系,促进经济社会协调发展。 相似文献
7.
木岩黄芪水分关系的研究 总被引:2,自引:0,他引:2
刘志民 《干旱区资源与环境》1991,(3)
本文选用水势、持水力、蒸腾强度等指标,分析了木岩黄芪的水分关系。在研究生境旱化的基础上,探讨了木岩黄芪的生长和繁殖与干旱的关系。 相似文献
8.
9.
研究玉米自交系繁殖过程中保种圃建立的理论和株系性状的选择依据对自交系性状的保持、保纯以及杂交种特性保持具有重要意义。利用3个不同纯度水平玉米自交系连续自交3代,在SSR水平上和SNP水平上检测玉米纯合度,并在S2和S3调查田间性状。利用不同初始纯合度的自交系建立保种圃应自交的代数。不同株系在SSR分子检测具有一致性的前提下,在SNP水平上仍然存在较高的杂合度,随初始纯合度升高自交纯合的效率减低,选择初始纯度高的材料有利于后代遗传位点的快速纯合。在田间选择自交系时,根据性状稳定性并结合自交代数依次进行。首先依据较易稳定纯合的群体目测性状;其次,数量性状中,果穗长、果穗直径、雄穗一级侧枝数、穗行数等可作为第二类依据的性状;最后,在自交高代选择穗位高/株高、行粒数、叶长、叶宽等较难稳定的性状。 相似文献
10.
小型背负式花生联合收获机的设计研究 总被引:4,自引:0,他引:4
介绍了国内外花生联合收获机的研制现状,阐述了小型背负式花生联合收获机的特点、结构设计、参数确定、试验情况以及应用前景。 相似文献