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1.
ABSTRACT

The mating calls of the Iberian midwife toads, A.o. boscai and A. cisternasii show clear differences. The calls of A.o. boscai have a shorter duration (104.8ms) and a lower fundamental frequency (1.33 kHz) than those of A. cisternasii (172.0 ms and 1.45 kHz), between 12° and 16°C. In both species signal duration was found to be influenced by temperature.  相似文献   

2.
离体血流循环切应力水平控制方法的研究   总被引:5,自引:0,他引:5  
本文应用流体力学及血流动力学理论和分析方法,建立了离体心血管循环系统的切应力水平控制方法。并采用该方法研制可精确控制切应变水平的模拟在体血流动力学环境的层流流动装置,用于研究动力学因素对人工培养的内皮细胞生物学特性影响。  相似文献   

3.
高砷区植物的生态与化学特征   总被引:50,自引:1,他引:50       下载免费PDF全文
 土壤砷污染是一种十分严重的环境问题,但目前尚无经济有效的治理方法。利用各种重金属的耐性与富集植物修复重金属污染土壤是当前的研究热点。通过对两个中国典型的砷矿区(炼砷区)土壤与植物的系统调查与采样分析,发现若干种植物对砷具有极强的耐性和不同程度的富集能力。砷在不同植物中的含量分别为:蜈蚣草(Pteris vittata)羽片1 600 mg·kg-1 DW,剑叶凤尾蕨(Pteris ensiformis)地上部1 230 mg·kg-1 DW,酸模(Rumex acetosa)地上部 440 mg·kg-1  相似文献   

4.
SUMMARY

The soils of Midmar dam catchment and the sediments of the Lions river are shown to have high P-retention properties. Present conditions result in little leaching of PO4 ?4 from the soils and favour a net transport of P from overlying water to the sediments. P levels in the water are likely to remain low even if the loading rate of P were increased substantially. It is postulated however that other factors may induce a release of P from the sediments and adversely affect the load carried by the water.  相似文献   

5.
在室内研究了水稻品种和氮肥水平对黑肩绿盲蝽对褐飞虱卵嗜好性的影响 ,及其与水稻挥发物的关系。双向选择试验表明 ,黑肩绿盲蝽对不同水稻品种上的褐飞虱卵有着不同的嗜好性 ,但对不同氮肥水平稻株上褐飞虱卵的嗜好性无明显差异。嗅觉试验表明 ,黑肩绿盲蝽对水稻健康苗挥发物的趋性明显地强于空白对照 ,对褐飞虱若虫为害苗挥发物的趋性强于健康苗 ,对褐飞虱雌成虫为害苗的趋性又强于若虫为害苗。不同品种的水稻挥发物对黑肩绿盲蝽的引诱作用存在明显差异 ,但不同氮肥水平的水稻挥发物间差异不显著。上述结果表明 ,水稻挥发物在黑肩绿盲蝽的捕食行为中起着重要作用。文中就如何改进水稻特性和栽培措施以增强天敌作用进行了讨论。  相似文献   

6.
Abstract Experiments were conducted in laboratory to study the impacts of rice genotypes and nitrogen levels on the preference of the egg predator, Cyrtorhinus lividipennis , for eggs of brown planthopper(BPH), Nilaparvata lugens (Stal), and their relation to the rice volatiles. In two-choice tests, the female predators showed different preference for BPH eggs on different rice genotypes, but not for BPH eggs on rice plants treated with different levels of nitrogen. The olfactory response test revealed that more predator oriented to the odour from healthy rice plants compared with the plain air (control); the predator preferred BPH nymph-damaged plants to healthy plants, and BPH female adult-damaged plants to BPH nymph-damaged plants. The comparative studies between rice genotypes and nitrogen levels indicated that there were obvious differences in attractiveness to the predator between rice genotypes, while there was no significant difference between rice plants treated with different levels of nitrogen. The results showed that rice volatiles played an important role in mediating the foraging behaviour of C. lividipennis . Implications for augmenting the effectiveness of natural enemies by adjusting rice attributes and cultural practices are discussed.  相似文献   

7.
微囊藻毒素在滇池鱼体内的积累水平及分布特征   总被引:2,自引:0,他引:2  
为了解富营养化水体中鱼体内微囊藻毒素(MC)的积累水平及其分布特征,2003年4月和9月份两次在滇池试验区采集了鲢、鳙和草鱼等鱼种,用ELISA方法对鱼体中肝、肾、空肠、胆、肌肉等不同组织中MC的含量进行了检测。结果表明,MC在所有样品中均能检测到,且主要分布在鱼体的肝肾脏和消化道等器官,而肌肉和非消化道器官中毒素含量相对较低。不同鱼种不同组织对MC的富集程度也明显不同,鲢鳙中肝脏和肾脏这两个主要的靶器官对MC的蓄积能力就远高于草鱼。同时,不同季节MC在鱼体内的积累水平也明显不同,4月份鱼样中MC的含量普遍低于9月份鱼样中MC的含量。最后按照WHO生活饮用水安全标准的建议进行推算,所有鱼肉中的MC均没有超过其推荐的人体每日可允许摄入量(≤0.04μg/kg人体重),初步推断鱼肉中MC暂时还未危及到人体健康,但仍具有潜在的风险性。  相似文献   

8.
本文针对长白山区低肥力白浆土壤,在三因素五水平最优回归设计田间试验的基础上,应用多元统计分析的方法,建立了氮磷钾三种肥料对六龄参根产量影响的肥料效应数学模型。通过对此模型的数学分析,得知氮磷钾三种肥料对六龄参根的产量均有显著影响。其综合增产效应依次为NK>N>K>P,而三种肥料的线性增产效应依次为N>K>P。当三种肥料在一定条件下单独使用时,其增产效应依次为N>K>P。同时确定了最高产量施肥量和最大利润施肥量,由等产线确定了合理施肥区。  相似文献   

9.
Nasonia vitripennis is a parasitoid wasp that harbors several non-Mendelian sex-ratio distorters. These include MSR (Maternal Sex Ratio), a cytoplasmic element that causes nearly all-female families, and PSR (Paternal Sex Ratio), a supernumerary chromosome that causes all-male families. As in other hymenoptera, N. vitripennis has haplodiploid sex determination. Normally, unfertilized (haploid) eggs develop into males and fertilized (diploid) eggs develop into females. The PSR chromosome violates this normal pattern; it is inherited through sperm, but then causes destruction of the paternal chromosomes (except itself), thus converting diploid fertilized eggs (normally females) into haploid eggs that develop into PSR-bearing males. PSR is an extreme example of “parasitic” or “selfish” DNA. Because N. vitripennis has a highly subdivided population structure in nature, population-level selection may be important in determining the dynamics of PSR in natural populations. A theoretical analysis shows that subdivided population structure reduces PSR frequency, whereas high fertilization proportion (such as produced by the MSR element) increases PSR frequency. Population experiments using two deme sizes (3- and 12-foundress groups) and strains producing two fertilization proportions [wild-type (LabII)–57–67% female, and MSR (MI)–90–93% female] confirm these predictions. PSR achieved frequencies over 0.90 in 12–foundress group MSR populations in contrast to 0.20–0.40 in wild-type 12–foundress populations. PSR was selected against in wild-type populations composed of three-foundress groups. In MSR populations with three-foundress groups, presence of PSR selected against the MSR cytoplasmic element, eventually leading to low frequencies of both PSR and MSR. Complicated dynamics may occur when these two sex-ratio distorters are both present in highly subdivided populations. The existence of PSR in natural populations may depend on the presence of MSR. Results indicate that population subdivision could be important in determining the frequency of sex ratio distorters in N. vitripennis.  相似文献   

10.
基于2004—2015年三峡库区支流春季水华的监测数据,开展了三峡库区不同蓄水位下春季水华特征及趋势分析。结果表明:总共有26条支流发生春季水华,香溪河为水华发生概率最高的支流。水华藻类优势种主要是硅藻和甲藻,甲藻水华出现的概率随着蓄水位的增加而增加,但是在持续几年175 m蓄水之后,甲藻水华出现的频率下降,硅藻水华出现的频率增加。在175 m蓄水之前,水华发生期藻类密度、叶绿素a含量及水体营养盐水平相对较低,此后都有了较高的提升,但是在持续几年175 m蓄水之后,藻类密度、叶绿素a浓度以及营养盐浓度都有下降趋势。对藻密度及叶绿素a含量与主要环境因子进行主成分分析(Principal components analysis)发现,藻密度和叶绿素a与总磷、总氮、高锰酸盐指数聚类一簇,藻密度、叶绿素a浓度与总磷、溶解氧、高锰酸盐指数显著正相关。在蓄水之后,三峡库区支流营养水平有所增加,随着蓄水位的增加,三峡库区支流断面的平均流速降低,在合适的温度下,三峡库区支流水华易发生。  相似文献   

11.
髋骨性别分级判别分析法   总被引:2,自引:0,他引:2  
现有骨骼性别判别分析方法无疑是判别率最好的方法之一 ,但是否能在原基础上再提高一步 ?为此 ,本文选取 1 6项髋骨指标 ,制作“分级判别分析表”对 82副髋骨 (男42副 ,女40副 )进行分级性别判别分析 ,并与传统单因素及多因素判别分析法进行比较 ,3种方法最高正确判别率分别为 97.0 %、85 .4 %和 92 .1 % ,结果显示 :分级判别分析法可提高正确判别分析率 ,为考古学和法医学工作者提供了一种骨骼性别判别分析的新方法。  相似文献   

12.
Abstract: This is the first report of recordings of sounds from the pygmy right whale, Caperea marginata . The recordings were obtained in the presence of a juvenile in the harbor at Portland, on the southeastern corner of the Australian continent. Only one type of sound was heard-a short thump-like pulse or tone burst with a downsweep in frequency and decaying amplitude, with most energy between 60 and 120 Hz. The pulses occurred predominantly in pairs and once in a trio. The sounds are simpler than those of most baleen whales, but they show some similarity in characteristics. Source levels are in the lower end of the range determined for other species. There was no evidence to indicate the purpose of these sounds.  相似文献   

13.
Knowledge of tolerance to cryoprotectants is important in determining viability after biological freezing of algae. Six taxonomically diverse marine microalgae were evaluated for their tolerance to the widely used cryoprotectants dimethyl sulfoxide (DMSO) and methanol. Tetraselmis chuii Butcher survived exposure to 30% (v/v) DMSO and 25% methanol for periods of up to 4 h. All other species were more sensitive to high concentrations of these cryoprotectants. DMSO was lethal at 25% after a 15-min exposure of Rhodomonas baltica Karsten, Isochrysis off. galbana (strain T-ISO) Parke, and Nannochloropsis gaditana Lubian. Nannochloris atomus Butcher could tolerate only a 1-min exposure at this concentration; Chaetoceros gracilis Schutt completely lost viability when exposed to 20% for 60 min. Safe concentrations for DMSO incubations were similar (about 5% lower) to lethal thresholds. Methanol incubations did not significantly decrease cell viability at concentrations of 5% (1 min) for R. baltica, 25% (up to 60 min) for T. chuii, 15% (up to 120 min) for I. galbana, 5% (up to 60 min) for N. gaditana, 15% (up to 240 min) for Ch. gracilis, and 15% (up to 120 min) for N. atomus. Nannochloris atomus has the potential to be cryopreserved without the need for any cryoprotectant. The other five species were clearly dependent on a 15% DMSO preincubation to achieve a growth response after thawing from ?196° C. Only N. atomus and N. gaditana could be grown after being cryopreserved in the presence of 5% methanol.  相似文献   

14.
医学实验中常见设计类型的辨析及统计方法的合理选用   总被引:10,自引:0,他引:10  
目的帮助医学研究工作者提高对常见统计应用识别能力,提高对统计学的正确利用率。方法:明确阐述秒种常见医学实验设计类型的异同点和应用场合,揭示常见统计应用错误的实质和危害性。结果:给出不适合用t检验取代方差分析的充足理由和正确运用统计学的基本要领。结论:要提高实际工作者的统计学应用水平。需要经常对其进行统计培养,积极引导与统计学工作者开展科研协作。  相似文献   

15.
Objective: The association of childhood overweight with cardiovascular risk factors seems to change by sex and age, which may indicate that hormonal status could be the cause of this different association. In this study, we analyzed the relationship of dehydroepiandrosterone sulfate (DHEA‐S) with the alterations associated with overweight by analyzing the influence of this hormone in the differences found in biochemical variables between normal‐weight and overweight prepubertal children. Research Methods and Design: The study included 684 6‐ to 8‐year‐old children (350 boys and 334 girls) categorized by the presence or absence of overweight, according to the age‐ and sex‐specific cut‐off points proposed for children. Lipid levels were determined by standard methods. DHEA‐S and insulin levels were measured by radioimmunoassay. Biochemical variables were compared between normal‐weight and overweight children by tertiles of DHEA‐S. Results: We observed that plasma high‐density lipoprotein‐cholesterol (HDL‐C) and apolipoprotein (apo)‐AI levels were significantly lower in overweight than in normal‐weight boys only in the highest tertile of DHEA‐S. No significant differences in plasma glucose levels, total cholesterol, low‐density lipoprotein‐cholesterol, or apo B were found between overweight and normal‐weight children in any DHEA‐S tertile. In a Spearman correlation analysis, we observed a significant and negative correlation for weight and BMI with HDL‐C and for weight and apo‐AI levels only in the highest tertile of DHEA‐S. Discussion: Our study showed that, in our prepubertal population, the association of overweight with decreased HDL‐C and apo‐AI levels was present only in boys within the highest levels of DHEA‐S, supporting the importance of hormonal influences on the association of metabolic alterations with overweight.  相似文献   

16.
The concentrations of zinc and copper in gastric juice of humans who had widely varying dietary zinc intake were evaluated. In order to compare this with zinc and copper levels of normal dietary individuals, we also determined the zinc and copper levels in healthy individuals' plasma and in cancer patient's natural tissue, all of whom had normal diets. The correlation coefficients between zinc and copper were 0.71, 0.45, and 0.55, respectively, in gastric juice, plasma, and tissue of normal dietary subjects. Such correlation changed and was destroyed when there was a high zinc level in gastric juice. When gastric juice zinc level changed from mean value 16.8 μmol/L to 262.5 μmol/L, the correlation coefficient varied from 0.71 to −0.04, and the copper level also varied from mean value 8.96 μmol/L to 4.89 μmol/L. These findings probably give the evidence to suggest that a high zinc level will restrain the copper level and break the balance of the human body's zinc and copper metabolism.  相似文献   

17.
18.
Paleoanthropology plays a significant role in the study of man and the research of his past. As we all know, the anthropologists in the last century followed the alternative trends of multiplying and reducing the number of taxonomic names. The present paper presents three different levels of taxonomic discussion concerning fossil hominids. These levels belong to different orders: empirical, theoretical and psychological, and they do not exist in isolation from each other. On the contrary, they are connected and interdependent. It shall also be argued that taxonomic controversies described below arise from both objective and subjective factors.  相似文献   

19.
应用间接免疫荧光法(IFA)检测166例不同产地(国产、进口)人用狂犬病疫苗免后血清抗体水平,结果:国产苗抗体阳转率为95.42%,GMT为9.48,进口苗抗体阳转率为62.85%,GMT为4.35。经统计学处理,二者差异有非常显著性意义(X2=28.61P<0.005),初步提示了国产的(浓缩)原代地鼠肾组织培养狂犬病疫苗比某进口VERO细胞狂犬病疫苗免疫效果要好,是一种高效、安全、价格便宜的预防狂犬病免疫制品  相似文献   

20.
The effects of three recently synthesized zinc-saccharide complexes (zinc-fructose, zinc-galactose and zinc-glucose) on blood -aminolevulinic acid dehydratase (ALAD) activity, glutathione (GSH), zinc-protoporphyrin (ZPP) and urinary -aminolevulinic acid (ALA) levels have been investigated to ascertain the utility of these complexes as zinc supplements and as preventive agents against lead intoxication in rats.  相似文献   

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