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排序方式: 共有2475条查询结果,搜索用时 187 毫秒
31.
黄碧 《农业图书情报学刊》2010,22(10):199-201
早期阅读是培养和提高学前儿童语言、想象、思维、情感、审美等能力的重要途径。针对早期阅读存在的误区,从少儿图书馆的角度提出了转变传统观念、完善服务设施、提高图书馆员综合素质、保障经费来源等应对措施。 相似文献
32.
Abstract – The persistent effects of embryonic temperature stress and individual parentage on fry swimming performance were examined in a cross‐fertilisation experiment using sockeye salmon (Oncorhynchus nerka). A fixed‐velocity test of burst swimming was used to assess the endurance capacity and behavioural performance of individual fry from 10 offspring families incubated at 12, 14 or 16 °C to hatch and then reared through yolk absorption and exogenous feeding stages in a common posthatch environment (average 6.9 °C). Fry burst swim time (BST) was influenced by an interaction between incubation temperature and family identity. Average BST was longer for fry from the 12 °C prehatch treatment compared to 14 and 16 °C, although differences were largely attributable to temperature effects on average fry size. Behavioural observations revealed that fish incubated at 16 °C performed more poorly, having a larger proportion of individuals that required stimulation to swim, fatigued more frequently or were classified as ‘nonswimmers’. Within all three incubation temperature treatments, mean BST varied significantly among offspring families, independent of fry mass and length. An interesting relationship was observed within the 16 °C treatment, whereby families with higher survivorship were characterised with lower mean BSTs. Collectively, these findings demonstrate that exposure to high temperatures in early sockeye salmon development can result in persistent, parentally mediated effects on fry performance. As such, these results provide important insight into how elevated temperature events during egg incubation may affect early life history selection processes and survival in stages beyond when the stressor is experienced. 相似文献
33.
M. C. Rebolledo M. Dingkuhn P. Péré K. L. McNally D. Luquet 《Journal of Agronomy and Crop Science》2012,198(5):374-384
Achieving early vigour, that is, rapid dry matter accumulation, is a priority in rice crop improvement, but this trait is complex and not well understood genetically and physiologically. This study tested the hypothesis that the development rate (DR) contributes to early vigour. Two diversity panels were phenotyped during vegetative stage for traits constituting early vigour (shoot dry weight, SDW; relative growth rate, RGR) or contributing to early vigour (tillering, leaf size, DR). The first panel comprised 169 genotypes from all major genetic groups of Oryza sativa and was phenotyped under irrigated upland conditions in the field (Philippines, Exp1). The second panel with 190 genotypes representing the diversity of the tropical japonica group was phenotyped in pots in a greenhouse (Montpellier, France, Exp2). Results from field and pot experiment pointed out that DR, tillering and leaf size were positively correlated with RGR and SDW, although the contribution of leaf size was small. DR was positively correlated with tillering but both were negatively correlated with leaf size. DR vs. RGR correlation was conserved in subsets of genotypes with similar leaf size and tillering, suggesting an effect of DR on RGR independent of the other traits. DR is a promising, still underexploited trait contributing to rice early vigour, requiring further genetic and physiological characterization. 相似文献
34.
Coppo JA 《Veterinary research communications》2001,25(6):449-459
The purposes of the study were to obtain the confidence intervalsfor serum fructosamine concentrations in unweaned and early weaned calves, to verify the changes in this glycated protein during growth, when glucaemia declines, and to assess the changes in both parameters attributable to stress or alarm. Sixty out of 120 suckling half-bred zebu calves (60–75 days old) were weaned at day 0 and then received a commercial balanced diet, while the remainder continued to suck. Blood samples were taken at 0, 7, 14, 21, 28, 60, 90 and 120 days and the serum fructosamine and glucose concentrations were measured by conventional methods. Both biochemical parameters declined with time, but there were no statistical differences between the unweaned and weaned calves. The fall in fructosamine concentration correlated significantly with the decline in glucose concentrations in both groups. The confidence interval for fructosamine concentration decreased with age, from 294–303 mol/L at 2 months old to 215–232 mol/L at 6 months old. At the same time, glucaemia declined from 7.5–8.6 mmol/L to 4.8–5.3 mmol/L. Acute elevations in glucaemia, especially in the younger calves, were attributed to alarms, such as those caused by handling and blood extraction. The absence of resultant increases in fructosamine concentration discounts the existence of prolonged hyperglucaemias (stress) in early weaned calves. 相似文献
35.
分析了湖南早稻生产滑坡的原因,并从品种(组合)和栽培技术方面分析了湖南早稻的增产潜力及提出了今后发展的对策。 相似文献
36.
37.
Molina R Galina CS Maquivar M Estrada S Chávez A Díaz GS 《Veterinary research communications》2003,27(8):671-680
In order to evaluate the reproductive effect of a rotational breeding system, the pregnancy rate of 69 Zebu cows was assessed, 32 late postpartum (211±93 days postpartum, LP) and 37 early postpartum (averaging 63±8 days after calving, EP). In the LP group, 60% (19/32) were cycling before exposure to the bulls but only 38% (14/37) in the EP group. The two groups were dissimilar from the start (p<0.05). The cows were exposed in a rotational breeding system, with six Brahman bulls with previous sexual experience paired off in three groups (A–B, C–D and E–F). The cows were exposed to each pair of bulls for a period of 3 weeks, with one week in between each period, when the females were without the presence of a male. In the LP group, the pair of bulls A–B obtained a pregnancy rate of 72% (23/32), whereas for bulls C–D the pregnancy rate was 33% (3/9) and for bulls E–F the pregnancy rate was 67% (4/6). In contrast, for the EP cows, bulls A–B obtained a pregnancy rate of 32% (12/37), bulls C–D a pregnancy rate of 67% (12/18) and for bulls E–F a pregnancy rate of 55% (6/11). The percentage pregnancy obtained using the pair of bulls A–B differed (p<0.05) between LP and EP, whereas for bulls C–D and E–F it was similar. The pregnancy rate was different (p<0.05) in the first 3 weeks of mating for the LP group, the highest number of cows becoming pregnant during the first 3 weeks of the study. In contrast, the highest number of pregnancies in EP occurred evenly during the last 6 weeks. This study suggests that the reproductive performance of pairs of bulls in a 9-week rotational programme with the overall pregnancy rate is similar (94% in the LP and 81% in the EP). However, the time taken for the females to become pregnant, and hence the performance of the bulls, is related to the average number of days postpartum for the cows. 相似文献
38.
39.
沥青混合料的孔隙率是一个重要的设计参数,其对于沥青路面的强度和使用性能有着重要的影响。在施工时,由于施工条件和设备的影响,不可能达到设计的孔隙率,于是一般要求用压实度作为施工时的一个控制指标,将沥青路面施工后的孔隙率控制在一个可接受的范围。在路面使用的初期,必然会有一段时间处于未完全压实工作状态,这种工作状态下,沥青路面能够提供的是未完全稳定的早期强度。在设计时,需要对比多个级配的混合料,确定合理的早期强度。 相似文献
40.