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961.
我国经济林林地稳定性研究   总被引:3,自引:0,他引:3  
利用我国16个省市的最近两期森林资源连清固定样地数据,计算和比较经济林和非经济林的保存率,平均年龄,期望寿命等,对我国经济林的林地稳定性,通过定量研究,最后得出我国经济林林地稳定性明显不如非经济林林地稳定性的结论。  相似文献   
962.
在同德县北巴滩进行了不同浓度蝗虫微孢子虫(N.L)小区试验和大面积推广试验,并在1997和1999年对防治效果作了调查,结果表明N.L不仅当年虫口减退率和感病率可达60%和50%以上(30天),而且在1997年、1999年防区内平均感病率仍保持在30%和40%。说明N.L具有较强的水平扩散能力和垂直感染能力,可持续、有效地控制蝗灾的发生。  相似文献   
963.
Abstract – The relationships between size and age at smolting and juvenile growth rates were examined for 13 populations of white-spotted charr ( Salvelinus leucomaenis ). Mean smolt length (ranging 142–210 mm in fork length) and smolt age (2.4–3.7 years) varied significantly among populations and there was a significant negative relationship between smolt length and age. Mean smolt length was positively correlated with mean specific growth rate from age 0 to 1 year, whereas mean smolt age was negatively correlated with specific growth rate. The present study shows that the freshwater environment conditions operating on juvenile growth are important for moulding the phenotypic characteristics of size and age at smolting.  相似文献   
964.
将不同直径牛卵泡内卵母细胞体外成熟培养22h后,对其体外受精后的卵裂率,胚胎发育速度和胚胎染色体异常发生率进行了研究。结果表明,体外受精后48h,直径3-6mm卵泡内卵母细胞外受精后的卵裂率明显高于直径1-2mm和7-10mm卵泡内卵母细胞体外受精后的卵裂率(P<0.05)。体外受精后48h,直径3-6mm包泡内卵母细胞体外受精后的胚胎的发育速度明显快于直径1-2mm和7-10mm卵泡组胚胎(P<0.05)。通过对不同卵裂期胚胎的染色体标本分析表明,直径1-2mm卵泡内卵母细胞体外受精后的胚胎染色体异常发生率明显高于直径3-6mm卵泡组(P<0.05),但与直径7-10mm卵泡组之间无显著性差异。  相似文献   
965.
Objective To determine the electrocardiographic and cardiopulmonary effects of romifidine with and without prior or concurrent administration of glycopyrrolate. Study design Randomized crossover experimental study. Animals Six (three male, three female) cross‐bred dogs weighing 23 ± 2.4 kg. Methods Baseline cardiopulmonary measurements were obtained in conscious dogs and one of five treatments was administered. Glycopyrrolate (G) 0.01 mg kg?1, or saline (S) 0.5 mL, were administered IM as premedication (Gp or Sp), or G was administered concurrently (Gc) with romifidine (RO). Treatments were as follows T1, Sp + RO 40 µg kg?1; T2, Gp + RO (40 µg kg?1); T3, Sp + RO 120 µg kg?1; T4, Gp + RO (120 µg kg?1); T5, Sp + Gc + RO (120 µg kg?1). Romifidine or RO + Gc was administered subcutaneously 20 minutes after premedication (time 0), and further measurements were taken 10, 20, 30, 60 and 90 minutes after RO. The main treatment effect was evaluated using two‐way anova for repeated measures, followed by one‐way anova and a post‐hoc least squares difference test with a modified Bonferroni correction (p < 0.02). A Student's t‐test was used to compare the effect of romifidine at 20 and 60 minutes versus baseline values (p < 0.05). Results Both low‐ and high‐dose RO (T1, T3) significantly decreased heart rate (HR), respiratory rate (RR), cardiac index (CI) and stroke volume index, and increased arterial blood pressure (SAP), systemic vascular resistance (SVR), pulmonary arterial occlusion pressure (PAOP) and central venous pressure. High‐dose RO produced greater increases in SVR and SAP measurements. Neither dose of RO produced an alteration in blood gas values or the alveolar to arterial oxygen gradient. Glycopyrrolate significantly increased HR and CI from 10 to 90 minutes between T1/T2 and T3/T4. Increases in SAP were dose related with significant differences between T1/T3 and T2/T4 at 90 and 10 minutes, respectively, and were highest in animals receiving Gp or Gc. High‐dose RO groups (T3, T4) had higher values for SVR than low‐dose RO groups (T1, T2), unrelated to G administration. There was an increase in PAOP in all treatments. The oxygen extraction ratio was increased with all treatments: larger increases were observed in T1, T3 and T4 compared with only minimal changes in T2. Concurrent G administration was associated with an increased frequency of high‐grade second‐degree atrioventricular heart block with variable conduction at 10 and 20 minutes. Conclusions Romifidine produced effects consistent with other selective α2‐adrenoreceptor agonists. Glycopyrrolate offset the decrease in HR and partially offset the decrease in CI associated with RO administration. Glycopyrrolate premedication produced an initial tachycardia and added to the increase in SAP associated with RO. Concurrent G administration was associated with a higher frequency of dysrhythmias and is not recommended. Despite the decrease in RR, RO sedation did not alter blood gas values. Clinical relevance It appears likely that G administration prior to or concurrent with RO produces an increase in myocardial workload and oxygen demand suggesting that this combination should not be used in dogs with cardiomyopathy or heart failure. The improvement in oxygen extraction ratio with T2 suggests that G may be beneficial with lower doses of RO, nevertheless, the use of G and RO in cardiovascularly compromised patients is not advised.  相似文献   
966.
随着中国正式加入世贸组织,利率市场化改革已势在必行。之前,央行已制定出了利率市场化的大体框架并分步实施。当前流行于各类刊物的一些观点对利率市场化含义的理解尚不够准确。流行观点依据新老自由主义理论,强调市场“均衡利率”水平的重要性,忽略了利率结构问题。所谓的“均衡利率”实际上是不存在的,利率市场化改革的真实含义应当是:由中央银行决定基准利率水平,由市场决定利率结构。在银行业引入竞争机制是必要的前提。参9  相似文献   
967.
中草药对王鸽繁殖性能的影响   总被引:4,自引:1,他引:3  
利用催情中草药提高王鸽繁殖性能,将60对种鸽分成对照和试验组,进行了5个产蛋周期的试验。与对照组相比,试验组的产蛋周期缩短了4 ̄5d,孵化率、仔鸽成活率均提高了3%左右,28日龄时平均体重增加30g左右,30对种鸽年获利多1000余元。  相似文献   
968.
研究了在极化曲线测定的基础上,采用最优化方法测定腐蚀参数的方法,选用了3种非线性拟合的方法(高斯牛顿法、麦夸特法及离散型拉氏变换法),用能产生指定标准偏差的极化曲线模拟数值实验,对3种方法的实用性,从标准偏差、测量点的位置和数目、体系转移系数值等对方法的收敛性和计算结果的影响进行了考察.  相似文献   
969.
杂交水稻制种建立母本最佳穗层结构的探讨   总被引:3,自引:1,他引:2  
将制种田中喷施“九二0”后的母本穗层划分为高层穗、表层穗、平颈穗、包颈穗4个层次。对各种类型穗层的受粉原理、自然受粉状态,与结实率的关系进行了研究分析,提出了母本最佳穗层结构模式,以及在实践中可以采取稀播壮秧、密植等6项农艺措施和配套措施,来建立起母本最佳穗层结构  相似文献   
970.
The effect of plant water stress on net photosynthesis, leaf growth, yield and yield-related components were investigated in a single experiment in order to determine in which way water deficits affect sunflower yields.
Sunflower plants, grown under controlled temperature regimes, were stressed during budding, anthesis and seed filling by withholding water until the leaf water potential reached -1600 and -2000 kPa. Leaf area of unstressed plants significantly exceeded that of plants under severe stress during all growth stages investigated. The CO2 uptake rate per unit leaf area as well as the total uptake rate per plant, significantly diminished with stress, while this effect drastically increased during the reproductive phase of the plant. Although this resulted in significantly smaller heads and kernels, it did not affect the number of seeds borne in the inflorescence. Severe stress during anthesis and seed filling resulted in more empty kernels. Moderate and severe stress during budding significantly lowered both grain and oil yields while plants that experienced moderate stress during anthesis and seed filling significantly outyielded those under severe stress.  相似文献   
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