北京鹫峰公园主要人工林群落多样性研究

在野外调查基础上,对鹫峰公园侧柏林、油松林、栓皮栎林、栓皮栎与槲栎混交林及刺槐林5个植物群落进行了物种多样性的分析.结果表明：在5个人工林群落中,乔木、灌木、草本的层次分明,乔木层的多样性与灌木、草本层有一定的相关性;不同群落间各层次比较,栓皮栎与槲栎混交林具有较高的物种丰富度、多样性以及较高的优势度;在灌木层中,油松林具有较高的物种多样性和丰富度;在草本层中,刺槐林和栓皮栎林有较高的物种多样性和丰富度.     

有关拖网属具泥幕作用的效果

<正> 网板和网具在沿着海底运动时会造成强大的紊流混合回流,它所卷起的海底泥砂形成了泥幕。1979年我所渔捞室在海南岛陵水湾附近作实物网具潜水观察时很清楚地看到了这一情况。这种泥幕对鱼类会起到威吓作     

苏联渔船发展现状

苏联是世界上渔业最发达的国家之一，水产品产量居世界第二位．五、六十年代苏联水产品产量平均每年约递增14％，超过同期世界平均增长速度6．6％的一倍以上。1974年产量达最高峰10，132，210吨，1976年以后产量略有下降，但下降幅度不大(1979年9，113，399吨)，基本上是稳定的。苏联水产品产量的迅速增长，     

鱼虾颗粒饲料添加粘合剂的作用

近年来,我国海淡水养殖业发展很快,全国有海水养殖面积250多万亩,淡水养殖面积400多万亩,约占世界水产养殖产量的40%。水产养殖业的发展,带动了人工配合饲料加工业及其科学研究事业,同时也提出了一系列急需研究解决的重要课题,研制生产保形效果好、无毒、无害,作用方便、价格合理的水产饲料粘合剂,已成为目前鱼虾配合饲料生产技术中急待解决的技术难题之一。     

1996年度主题索引

使用说明1.本索引按主题法编制。2.检索款目由“款目词+说明词+顺序号”组成。款目词与说明词之间按“错行缩格”方式编排。每条款目通过概念的逻辑组配,表达了文献的中心内容。例 ATP精子,鲤,游动性,关系 961669用自然语言表达为:鲤鱼精子游动性与 ATP 的关系。     

国外渔船上网鼓轮的应用

本文阐述了国外网鼓轮在拖网、围网、刺网和停泊旋曳渔船上的应用情况，一些主要渔业国家生产的主要网鼓轮系列的特点和技术特性。     

森林采伐对迹地径流流量的影响

本文利用实验方法,对针阔混交林地实施不同方式森林采伐作业后,迹地和径流量发生的变化进行了样地实验研究。结果表明,皆伐对迹地径流量变化影响程度最大。     

Harmful and economic thresholds for rodent pests in the Alxa desert area under different grassland utilization patterns北大核心CSCD

The rodent damage threshold and the rodent economic threshold are indicators that must be clearly defined in the practice of grassland rodent prevention and control. Different grassland types or different utilization methods of the same grassland type have completely different values for these two indicators. The damage threshold is the population density of pests at which the grassland is obviously compromised, and the economic threshold is the population density at which further pest population increases will cause economic losses. The Alxa desert region is ecologically fragile, and rodents are endemic. This study selected continuous grazing areas and prohibited grazing areas in the desert area of Alxa Left Banner and from 2015 to 2019 to investigated the species and density of pests using the ‘mark and recapture’ method, together with sampling to investigate the aboveground plant biomass in the sample area in August. The measured rodent unit densities and their daily food intakes were used to estimate the amount of forage loss, and a regression equation was used to obtain a fitted relationship between the rodent density and the ratio of forage loss. It was found that: 1) The fitted curves for the ratio of pest density and forage loss in the continuous and prohibited grazing areas took the form of logistic three-parameter, S-shaped curves. 2) According to the regression equation, the damage threshold in continuous grazing areas was 26 standard rodent units·ha-1 and the economic threshold was 39.3 standard rodent units·ha-1. In prohibited grazing areas, the damage threshold was 33.2 standard rodent units·ha-1 and the economic threshold was 30.2 standard rodent units·ha-1. Thus, the economic threshold pest density of continuous grazing areas was slightly higher than that of prohibiting grazing areas. © 2022 Editorial Office of Acta Prataculturae Sinica. All rights reserved.     

茄子种高压电场分选的粒重分布试验与分析

茄子种落入高压静电场中，受到场强作用，将沿电场方向产生位移，不同场强作用，茄子种分离区会不同，不同分离区，种子的粒重也不相同，分布也不相同，它们之间存在着紧密相关作用，本文定量揭示了这种关系。     

森林采伐方式对伐后迹地光照条件及更新质量的影响

本文应用野外观测方法,对森林采伐方式（皆伐、择伐、带状皆伐）对迹地光照条件和作业后天然更新质量进行了局部性研究。结果表明,更新树种不仅与种源有关,而且还与光照条件显著相关,即与森林采伐方式有关。