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排序方式: 共有1334条查询结果,搜索用时 15 毫秒
1.
报道了武汉市外来入侵植物新记录一种,为桔梗科Campanulaceae异檐花属Triodanis卵叶异檐花Triodanis perfoliata subsp.biflora(Ruiz et Pavon)Lammers。卵叶异檐花原产于美洲,在武汉地区是首次发现,凭证标本保存于长江文明馆(武汉自然博物馆)。 相似文献
2.
在对广东省主要珍贵树种上的线虫进行调查时从格木Erythrophleum fordii上分离到一种隐皮孢囊线虫,经形态特征观察和测量数据分析,将其鉴定为卡勒萨隐皮孢囊线虫Cryphodera kalesari。其诊断特征为:雌虫椭圆形至近球形,头部具有1个唇盘和2~3个唇环,口针长33.6~37.8μm,阴门唇突出,阴门与肛门之间区域凹陷,肛阴距为42~72μm;2龄幼虫头部具1个明显的唇盘和3个唇后环纹,口针长24.8~29.5μm,口针基部球前缘凹陷,侧区3条侧线,尾长圆锥形,长38~53.5μm,尾末端细圆,透明尾长17.1~25.1μm,侧尾腺孔位于肛门后2~5环;雄虫未发现。本研究首次获得了卡勒萨隐皮孢囊线虫的rDNA(LSU D2D3和ITS)序列,为此线虫的鉴定提供了可靠的分子数据。本研究还分析了卡勒萨隐皮孢囊线虫与本属其他种类的系统进化关系。卡勒萨隐皮孢囊线虫为中国的地理新记录种。格木为隐皮孢囊线虫的新寄主。 相似文献
3.
农机跨区作业紧急调配算法适宜性选择 总被引:7,自引:6,他引:1
目前农机跨区紧急作业中供需信息不对称,农机部门缺乏科学合理的紧急调配方案,无法在紧急状况下指导农机进行及时有效的调配。针对上述问题,该文研究了农机跨区作业紧急调配模型和算法。首先分析了多机多任务紧急调配过程,建立了以最小化调配成本和损失为目标的紧急调配模型,提出了基于距离最近优先的多机多任务紧急调配算法(shortest-distance first algorithm,SDFA)和基于贡献度最大优先的多机多任务紧急调配算法(max-ability first algorithm,MAFA),前者是搜索当前距离最近的农田和农机,进行优先分配,后者是搜索当前贡献度最大的农田和农机并进行优先分配。采用该文算法对河北省邯郸市2017年的真实数据以及随机生成的农田和农机实例库进行计算与分析可知,当农机数量充足时,算法MAFA的平均调配成本要比SDFA的平均调配成本降低4.34%。当农机不足时,SDFA的平均损失和平均调配成本要比MAFA的平均损失和平均调配成本分别下降了12.79%和4.11%。进一步验证可知,当农田数量为6时,上述2种算法比笔者之前提出的基于非合作博弈紧急调配算法(non-cooperative game algorithm,NCGA)的平均运算性能均提升25%以上,当农田数量为30时,性能均提升41%。该研究可为农机管理部门紧急调配与决策分析提供科学依据。 相似文献
4.
Effects of photoperiod,light intensity,turbidity and prey density on feed incidence and survival in first feeding yellow tang (Zebrasoma flavescens)(Bennett) 下载免费PDF全文
Zebrasoma flavescens (Bennett) aquaculture is limited by high mortality during first feeding. Photoperiod, light intensity, turbidity and prey density are culture parameters that have been shown to affect feed incidence and survival in some food fish species, offering a logical starting point to improve first feeding in Z. flavescens. This study aimed to determine the effect of photoperiod, light intensity, turbidity and prey density on feed incidence and survival in larval yellow tang age 3 DPH to 5 DPH (days post hatch). Larvae were reared in four photoperiods (24L:0D, 16L:8D, 12L:12D, 0L:24D), four light intensities (1,500, 3,000, 4,500 and 6,500 lx), three turbidity ranges (0 cells/ml, 100,000–200,000 cells/ml and 400,000–600,000 cells/ml) and four prey densities (1, 3, 6 and 9 per mL). Photoperiod at 16L:8D and 12L:12D significantly increased feed incidence; 16L:8D significantly increased survival. Light intensities at 3,000 and 4,500 lx significantly increased feed incidence. Larvae reared in 400,000–600,000 cells/ml fed and survived significantly better than those in clear water. Larvae in 1 per mL fed and survived significantly less than those fed at 6 per mL. 相似文献
5.
To determine associations between carpal and fetlock conformation and later performance, 292 two-year-old (2YO) Thoroughbred horses were examined at a public auction. Two observers graded carpal and fetlock conformation in the frontal view, and subject weights were estimated (weight tape), and height was measured. Subject age, gender, and workout distance and time were retrieved from sales data. Lifetime racing data was retrieved from the Jockey Club database. Mild to moderate deviations from straight forelimb conformation at the carpus or fetlock occurred in 85% of 2YO Thoroughbreds and had no substantive effect on lifetime racing performance. Carpal and fetlock conformation are associated. Greater age, female gender and faster workout were associated with better short and long-term racing outcomes. The ability to start a race at 2YO was associated with improvements in several measures of racing success. The lack of an association of forelimb conformation with most measures of racing performance will assist producers and consumers of young racing stock in the determination of the need for corrective procedures in young horses and the importance of deviations at purchase. Speed of workout and the ability to start at 2YO were associated with each other and with an improvement in several racing outcomes. 相似文献
6.
G. Øie T. Galloway M. Sørøy M. Holmvaag Hansen I.A. Norheim C.K. Halseth M. Almli M. Berg M.R. Gagnat P.‐A. Wold K. Attramadal A. Hagemann J.O. Evjemo E. Kjørsvik 《Aquaculture Nutrition》2017,23(1):3-17
The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first‐feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start‐feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long‐term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition. 相似文献
7.
2008年4月初在广东省饶平县对2006年5月人工孵化和培育的2龄条石鲷( Oplegnathus fasciatus)成熟亲鱼进行激素诱导,研究和观察条石鲷亲鱼初次性成熟的繁殖生物学。结果显示,在南海区全人工养殖的条石鲷亲鱼初次性成熟年龄为2龄,成熟亲鱼的最小型为全长245 mm、体质量610 g,最大个体为全长300 mm、体质量1450 g;产卵季节为4月10日~7月15日,产卵盛期为4月中旬至6月下旬;为升温产卵型鱼类,产卵温度为20.0~28.8℃,适宜的产卵温度为20.7~27.6℃;雌、雄亲鱼发育同步,个体大小和成熟年龄差别不大;雌鱼属于一年一次分批产卵类型,产卵期超过3个月;24尾初次性成熟雌性亲鱼的总产卵量为3180.0×104粒,日最高产卵量为341.5×104粒;其产卵量和受精卵质量与水温的变化关系密切,受精卵的浮卵率随温度的变化而变化,在水温相对衡定时,浮卵率相对稳定并维持在80%~95%的较高水平;受精卵平均卵径为(0.860±0.023)mm,油球径为(0.191±0.009)mm。 相似文献
8.
报道了海南岛被子植物5个新记录种。新记录种分别为三室黄麻(Corchorus trilocularis L.)、钻叶紫菀(Symphyotrichum subulatum(Michx.)G.L.Nesom)、光果姜(Zingiber nudicarpum D.Fang)、线纹香茶菜(Isodon lophanthoides(Buch.-Ham.ex D.Don)H.Hara)、狭序泡花树(Meliosma paupera Hand.-Mazz.)。凭证标本保存于中国热带农业科学院植物标本室(ATCH)。 相似文献
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