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101.
研究了一类多时滞的离散捕食系统,运用差分方程的比较原理,得到了保证系统种群持续生存的充分条件,并对定理条件可实现性进行了实例数值验证. 相似文献
102.
Hede Gong Yiping Zhang Yuhong Liu Guoping Yang Zhiyun Lu 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(4):384-388
Abstract In this paper, the spatial-temporal dynamics of soil moisture content was investigated in an evergreen broad-leaved forest and a tea tree plantation in Ailao Mountains, which was dominated by Fagaceae (Castanopsis wattii and Lithocarpus xylocarpus). Soil moisture content was studied between January 2005 and December 2006 at different depths (from 0–150 cm) with a neutron probe. The results showed that mean soil moisture content in the evergreen broad-leaved forest was usually higher than in the tea tree plantation in the dry season, whereas it was lower than the tea tree plantation in the rainy season. In addition, mean soil moisture content was depth dependent, and in the 10–50 cm layer the spatial variability was due to the active root zone within this depth area in two types of land use. From 50–150 cm, the spatial variability was slightly increasing in the evergreen broad-leaved forest or relatively stable in the tea tree plantation. Our study also showed that soil moisture content was higher and more stable under the evergreen broad-leaved forest than the tea tree plantation, hence we stress that evergreen broad-leaved forest plays an important role in holding soil moisture. It is suggested that the protection of evergreen broad-leaved forest should be strengthened. 相似文献
103.
几种杀螨剂对3种叶螨的毒力比较 总被引:1,自引:0,他引:1
作者于 1 996年对二斑叶螨 (TetranychusurticaeKoch)、朱砂叶螨 [T .cinnabarinus(Boisdural) ]和山楂叶螨 (T .viennensisZacher)进行了三氯杀螨醇、甲氰菊酯、哒螨酮、霸螨灵等 4种杀螨剂的毒力测定 ,并对 3种叶螨在LC50 和LC95水平上 ,比较了相互之间的毒力差别。结果表明 ,二斑叶螨的毒力最高 ,朱砂叶螨次之 ,山楂叶螨毒力最低。 相似文献
104.
105.
Y-M. Chang D. Gianola B. Heringstad & G. Klemetsdal 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2006,123(5):290-300
Robust threshold models with multivariate Student's t or multivariate Slash link functions were employed to infer genetic parameters of clinical mastitis at different stages of lactation, with each cow defining a cluster of records. The robust fits were compared with that from a multivariate probit model via a pseudo‐Bayes factor and an analysis of residuals. Clinical mastitis records on 36 178 first‐lactation Norwegian Red cows from 5286 herds, daughters of 245 sires, were analysed. The opportunity for infection interval, going from 30 days pre‐calving to 300 days postpartum, was divided into four periods: (i) ?30 to 0 days pre‐calving; (ii) 1–30 days; (iii) 31–120 days; and (iv) 121–300 days of lactation. Within each period, absence or presence of clinical mastitis was scored as 0 or 1 respectively. Markov chain Monte Carlo methods were used to draw samples from posterior distributions of interest. Pseudo‐Bayes factors strongly favoured the multivariate Slash and Student's t models over the probit model. The posterior mean of the degrees of freedom parameter for the Slash model was 2.2, indicating heavy tails of the liability distribution. The posterior mean of the degrees of freedom for the Student's t model was 8.5, also pointing away from a normal liability for clinical mastitis. A residual was the observed phenotype (0 or 1) minus the posterior mean of the probability of mastitis. The Slash and Student's t models tended to have smaller residuals than the probit model in cows that contracted mastitis. Heritability of liability to clinical mastitis was 0.13–0.14 before calving, and ranged from 0.05 to 0.08 after calving in the robust models. Genetic correlations were between 0.50 and 0.73, suggesting that clinical mastitis resistance is not the same trait across periods, corroborating earlier findings with probit models. 相似文献
106.
107.
Comparison of the Sensitivity of Landscape-fire-succession Models to Variation in Terrain, Fuel Pattern, Climate and Weather 总被引:1,自引:0,他引:1
Geoffrey J. Cary Robert E. Keane Robert H. Gardner Sandra Lavorel Mike D. Flannigan Ian D. Davies Chao Li James M. Lenihan T. Scott Rupp Florent Mouillot 《Landscape Ecology》2006,21(1):121-137
The purpose of this study was to compare the sensitivity of modelled area burned to environmental factors across a range of
independently-developed landscape-fire-succession models. The sensitivity of area burned to variation in four factors, namely
terrain (flat, undulating and mountainous), fuel pattern (finely and coarsely clumped), climate (observed, warmer & wetter,
and warmer & drier) and weather (year-to-year variability) was determined for four existing landscape-fire-succession models
(EMBYR, FIRESCAPE, LANDSUM and SEM-LAND) and a new model implemented in the LAMOS modelling shell (LAMOS(DS)). Sensitivity
was measured as the variance in area burned explained by each of the four factors, and all of the interactions amongst them,
in a standard generalised linear modelling analysis. Modelled area burned was most sensitive to climate and variation in weather,
with four models sensitive to each of these factors and three models sensitive to their interaction. Models generally exhibited
a trend of increasing area burned from observed, through warmer and wetter, to warmer and drier climates with a 23-fold increase
in area burned, on average, from the observed to the warmer, drier climate. Area burned was sensitive to terrain for FIRESCAPE
and fuel pattern for EMBYR. These results demonstrate that the models are generally more sensitive to variation in climate
and weather as compared with terrain complexity and fuel pattern, although the sensitivity to these latter factors in a small
number of models demonstrates the importance of representing key processes. The models that represented fire ignition and
spread in a relatively complex fashion were more sensitive to changes in all four factors because they explicitly simulate
the processes that link these factors to area burned.
The US Government's and the Canadian Government's right to retain a non-exclusive, royalty-free license is acknowledged 相似文献
108.
重组质粒pP18PH3上含有SINPV的部分蛋白激酶基因。SINPV部分的蛋白激酶氨基酸序列与HaN-PV、HzNPV、SpliNPV、AfNPV、AcNPV、LdNPV蛋白激酶的氨基酸序列的同源性分别为45%、89%、37%、44%、38%和37%,其上含有蛋白激酶特征序列IVHANDVKLENVL。 相似文献
109.
尾叶桉、细叶桉、赤桉、粗皮桉、巨桉(简称桉树类,下同)和马占相思、粗果相思及薄果相思(简称相思类,下同)等8个树种,在水土严重流失的贫瘠丘陵地经7年的生长试验,结果表明:除巨桉和细叶桉在该立地生长较缓慢外,其余6个树种生长快,产量较高。尤其是尾叶桉和马占相思,7年生胸径年均生长量在1.0cm以上,单位面积生物量(地上部分鲜重,下同)为52.69t/hm2和43.67t/hm2。不同树种的生长比较:桉树类树种(除巨桉外)4年生以前胸径、树高和生物量生长均比相思类树种生长快,4年后相思类树种逐渐赶上或超过桉树类树种。性状生长高峰期分别为:胸径桉树类为2年生(细叶桉1年生)、相思类为3~4年生,树高桉树和相思类均为1年生,生物量桉树类为2~3年生、相思类为4~6年生。 相似文献
110.