蛤蜊岗不同贝龄四角蛤蜊数量性状的通径分析

为研究蛤蜊岗不同贝龄四角蛤蜊(Mactra veneriformis)形态性状与质量性状之间的相关性,采用相关分析、通径分析和多元回归分析等方法,对1~3龄四角蛤蜊的壳长(SL)、壳宽(SW)、壳高(SH)、活体湿重(BW)和软组织湿重(RW)等参数进行分析,建立形态性状与质量性状之间的回归方程。结果显示,不同生长阶段四角蛤蜊形态性状对质量性状的贡献存在极显著差异(P<0.01)。与1~3龄四角蛤蜊活体湿重最相关的形态性状均为壳宽。对软组织湿重影响最大的形态性状,在1龄贝为壳宽,在2龄和3龄贝为壳长。壳高对2龄四角蛤蜊活体湿重和软组织湿重的直接通径系数均未达到显著水平(P>0.05)。以活体湿重为目标性状时,1~3龄贝均应以壳宽为主要选择性状,并以壳长作为辅助选择性状;以软组织湿重为目标性状时,1龄贝应以壳宽为主要选择性状,同时辅以壳长;2龄和3龄贝均应以壳长为主要选择性状,并分别以壳宽和壳高作为2龄贝和3龄贝的辅助选择性状。研究结果可为蛤蜊岗四角蛤蜊良种选育提供基础数据。     

西宁林业产业结构及发展

阐述了西宁林业产业结构现状,分析了当前林业产业结构发展中存在的问题,提出西宁林业产业结构优化调整和发展措施。     

内燃机燃烧模型的发展现状

利用CFD技术对内燃机燃烧过程进行数值模拟已成为内燃机研究的重要工具。选用恰当的燃烧模型对准确预测内燃机燃烧过程具有重要意义。内燃机CFD燃烧模型主要针对自燃、预混燃烧和非预混燃烧3种燃烧模式,其中有些模型可以同时模拟2种模式或3种模式。内燃机新的燃烧系统的不断出现促进了燃烧模型的发展。本文以STAR—CD和FIRE软件为出发点,介绍了内燃机燃烧模型的发展现状。     

陕西苹果产业SWOT分析及发展策略

在分析陕西苹果产业的优势、劣势、机会、挑战的基础上,提出扩张发展型、竞争型、防御型、保守型4种战略方案。     

宜宾竹业发展战略初探

竹业是宜宾地区经济发展的一个重要产业,起步早、发展较快,但机械化程度不高,产品技术含量低,加工力量分散,形不成规模生产。为振兴宜宾竹业,本文就加快竹浆造纸支柱产业发展、建立竹业开发集团、建立西南最大的竹种园方面进行了发展战略探讨。     

《农业与工业化》：农机化理论宝库——“发展经济学”创始人张培刚博士论文初识

发展经济学创始人张培刚1945年的博士论文《农业与工业化》,是近代农业机械化理论之集大成者。由于社会和历史的原因,这一农业机械化理论宝库一直未被认真开发、应用于我国农业机械化的实践,以致走了不少弯路。随着一代经济学大师的离世,如今,挖掘、开发这一理论宝库,用之培养新型农业机械化人才,指导我国农机化实践,必将结出丰硕之果。     

Interaction between the effects of evaporation rate and amount of simulated rainfall on development of the free-living stages of Haemonchus contortus

A factorial experiment (3 x 4 x 2 x 3) was conducted in programmable incubators to investigate interaction between the effects of rainfall amount, rainfall distribution and evaporation rate on development of Haemonchus contortus to L3. Sheep faeces containing H. contortus eggs were incubated on sterilised soil under variable temperatures typical of summer in the Northern Tablelands of NSW, Australia. Simulated rainfall was applied in 1 of 3 amounts (12, 24 or 32 mm) and 4 distributions (a single event on the day after deposition, or the same total amount split in 2, 3 or 4 equal events over 2, 3 or 4 days, respectively). Samples were incubated at either a Low or High rate of evaporation (Low: 2.1-3.4 mm/day and High: 3.8-6.1 mm/day), and faeces and soil were destructively sampled at 4, 7 and 14 days post-deposition. Recovery of L3 from the soil (extra-pellet L3) increased over time (up to 0.52% at day 14) and with each increment of rainfall (12 mm: <0.01%; 24 mm: 0.10%; 32 mm: 0.45%) but was reduced under the High evaporation rate (0.01%) compared with the Low evaporation rate (0.31%). All rainfall amounts yielded significantly different recoveries of L3 under Low evaporation rates but there was no difference between the 12 and 24 mm treatments under the High evaporation rate. The distribution of simulated rainfall did not significantly affect recovery of infective larvae. Faecal moisture content was positively associated with L3 recovery, as was the ratio of cumulative precipitation and cumulative evaporation (P/E), particularly when measured in the first 4 days post-deposition. The results show that evaporation rate plays a significant role in regulating the influence of rainfall amount on the success of L3 transmission.     

扬子鳄胚胎背部皮肤及鳞甲的发生

本文观察了１６例不同时间的扬子鳄（Ａｌｌｉｇａｔｏｒｓｉｎｅｎｓｉｓ）胚胎背部皮肤及鳞甲的形态及组织发生过程。孵化第２０天，来自胚胎中胚层生皮节的间充质细胞开始向原始表皮下迁移，表皮仅具周皮层与生发层两层细胞。第２８天背部鳞片开始明显，左右鳞片之间出现很浅的鳞间沟，前后鳞片交界处的原始表皮、真皮层开始向外突出形成鳞甲原基。第３４天鳞甲原基突出伸长，第４０天背鳞的纵崤明显。第３４～５０天中，鳞甲后缘基部的表皮层向鳞甲前缘基部的真皮层不断内陷，鳞甲显著伸长并向体后方水平伸出。背部表皮在孵化第３４天出现三层细胞，第４０天周皮细胞中开始出现色素沉集。第５０天表皮具四层细胞，周皮层细胞中出现大量色素沉集。第６０天表皮分层与成体时相似，周皮层已退化。孵化第３４天真皮层细胞形态出现多样化，第４０天真皮可分上、下两层。第５０天真皮上层中形成交织的胶原纤维网，下层中形成平行走向的胶原纤维。本文简要讨论了扬子鳄鳞甲的形态发生特点。