首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Effect of previous x-irradiation on the response of brain to injury   总被引:1,自引:0,他引:1  
J W Hopewell  E A Wright 《Nature》1967,215(5108):1405-1406
  相似文献   

2.
3.
J B Cavanagh 《Nature》1968,219(5154):626-627
  相似文献   

4.
对荒漠沙蜥成体代谢率和心率等生理指标的温度适应性进行了研究,旨在检测不同温度下成体荒漠沙蜥的静止代谢率、心率和呼吸频率的差异.结果显示:成体荒漠沙蜥的静止代谢率和心率随外界温度的升高而明显上升,但呼吸频率的上升并不显著.雌雄两性间,雄性蜥蜴呼吸频率对温度变化的依赖性比雌性的略强,且35?C下雄性的代谢率显著高于雌性的.这些生理特征与荒漠沙蜥的生境和活动特点直接相关.我们推测25~35?C荒漠沙蜥可能更多地依赖于提高心率和增加血流量来调整代谢率.  相似文献   

5.
环境控制对企业环境业绩的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
为明确环境控制对企业环境业绩的影响,寻求环境控制与企业环境业绩的平衡发展,满足企业可持续发展需要、十八大生态文明建设要求及环境污染改善需求,选择政府和企业这两个环境控制主体,研究它们对企业环境业绩的影响方向和影响程度。以10家企业10年的数据为基础,运用统计软件SPSS 17.0,采用回归分析进行实证研究,得出了这样的结论:各影响因素中对企业环境业绩影响程度最强的是政府环境控制中的政府环境经济政策,其次是企业环境控制中的企业环境认证,并且影响方向都是正向的。  相似文献   

6.
7.
8.
对常见蔬菜废物进行好氧降解研究,探讨温度对蔬菜废物好氧生物降解过程的影响,为控制堆肥化条件、改善蔬菜废物好氧生物降解效果提供一定依据.结果表明,中温和高温条件下蔬菜废物好氧生物降解过程区别较大,高温可显著提高粗淀粉的降解速率和最终降解率,而中温有利于粗蛋白质初期降解速率的提高;从微生物相的差异看出高温有利于细菌数量增长,中温有利于放线菌数量增长,其差异导致生物质的降解率的不同.  相似文献   

9.
Olszewski TD  Erwin DH 《Nature》2004,428(6984):738-741
The fossil record preserves numerous natural experiments that can shed light on the response of ecological communities to environmental change. However, directly observing the community dynamics of extinct organisms is not possible. As an alternative, neutral ecological models suggest that species abundance distributions reflect dynamical processes like migration, competition, recruitment, and extinction. Live-dead comparisons suggest that such distributions can be faithfully preserved in the rock record. Here we use a maximum-likelihood approach to show that brachiopod (lamp shell) abundance distributions from four temporally distinct ecological landscapes from the Glass Mountains, Texas (of the Permian period), exhibit significant differences. Further, all four are better fitted by zero-sum multinomial distributions, characteristic of Hubbell's neutral model, than by log-normal distributions, as predicted by the traditional ecological null hypothesis. Using the neutral model as a guide, we suggest that sea level fluctuations spanning about 10 Myr altered the degrees of isolation and exchange among local communities within these ecological landscapes. Neither these long-term environmental changes nor higher-frequency sea level fluctuations resulted in wholesale extinction or major innovation within evolutionary lineages.  相似文献   

10.
Seed germination in response to diurnal fluctuations of temperature   总被引:20,自引:0,他引:20  
Thompson K  Grime JP  Mason G 《Nature》1977,267(5607):147-149
Diurnal fluctuations in temperature may initiate or accelerate germination in certain flowering plants, and the effectiveness of the stimulus varies according to the amplitude of fluctuation and the presence or absence of light. Attempts to assess the adaptive significance of the phenomenon, however, have been limited by the scarcity of data for species of contrasted ecology. We report here an investigation of germination responses to fluctuating temperatures, conducted on seeds of herbaceous species collected from native populations near Sheffield. The results suggest that requirements for diurnal fluctuations in temperature are characteristic of the germination of species from particular types of habitat and provide mechanisms which cause seeds to germinate at times and in places favourable for seedling establishment.  相似文献   

11.
为研究环境温度对活立木内电阻值的影响,采用树木电阻断层成像仪在不同温度下对落叶松和小叶杨两种活立木进行检测,获取截面二维电阻图像并分析其变化,量化横截面内各点电阻值及其与温度之间的关系。结果表明:①落叶松横截面心材电阻值较低,边材较高。随温度降低,边材红色区域(高电阻区)面积减少,心材蓝色区域(低电阻区)面积增大; 而小叶杨电阻图像呈现完全相反的规律。但随温度降低,两树种整体平均电阻值均增大。②样本立木电阻值与环境温度之间存在极显著的指数函数关系(P<0.01),模型相关系数R≥0.822,小叶杨甚至高于0.926,因此认为模型有很好的拟合优度。 ③在落叶松样本立木中,当温度大于0 ℃时,横截面内沿径向分布的各点电阻值之间变化不明显,最大差值为1 236 Ω(3.0 ℃时); 而温度小于0 ℃时波动很大,最大差值达到3 299 Ω(-5.0 ℃时),曲线存在较为明显的两个波谷和中间一个波峰。④在小叶杨样本立木中,随环境温度降低,横截面内沿径向分布的各点电阻值都呈增大趋势; 从边缘到髓心再到另一侧边缘,沿径向分布的电阻值呈由低向高逐渐增大、到最大值后再逐渐降低的趋势。  相似文献   

12.
Dehydrins, known as the D-11 subgroup of late embryogenesis abundant (LEA) protein, are an immunologically distinct family of proteins, which typically accumulate in desiccation-tolerant seed embryo or in vegetative tissues in response to various environmental stresses such as drought, salinity and freezing. The existence of conservative sequences designated as K, S, and Y segments is a structural feature of dehydrins, and the K segment found in all dehydrins represents a highly conserved 15 amino acid motif (EKKGIMDKIKEKLPG) and forms an amphiphilicα-helix. According to the arrangement of these domains and clustering analysis, dehydrins are subdivided into 5 subtypes: YnSK, Kn, KnS, SKn and YnK. Different types of dehydrins are induced by different environmental stress in plants. Study results showed that dehydrins might play important protective roles under abiotic stress via a number of different mechanisms, including improving or protecting enzyme activities by the cryoprotective activity in responding to freeze/thaw or dehydration; stabilizing vesicles or other endomembrane structures by function as the membrane stabilizer during freeze induced dehydration, and preventing the membrane system from the oxidative damage induced by reactive oxygen radicals as the radical scavenger. Here, the gene expression and molecular mechanisms of dehydrin in response to stress in plants are discussed.  相似文献   

13.
Dehydrins, known as the D-11 subgroup of late embryogenesis abundant (LEA) protein, are an immunologically distinct family of proteins, which typically accumulate in desiccation-tolerant seed embryo or in vegetative tissues in response to various environmental stresses such as drought, salinity and freezing. The existence of conservative sequences designated as K, S, and Y segments is a structural feature of dehydrins, and the K segment found in all dehydrins represents a highly conserved 15 amino acid motif (EKKGIMDKIKEKLPG) and forms an amphiphilic α-helix. According to the arrangement of these domains and clustering analysis, dehydrins are subdivided into 5 subtypes: YnSK, Kn, KnS, SKn and YnK. Different types of dehydrins are induced by different environmental stress in plants. Study results showed that dehydrins might play important protective roles under abiotic stress via a number of different mechanisms, including improving or protecting enzyme activities by the cryoprotective activity in responding to freeze/thaw or dehydration; stabilizing vesicles or other endomembrane structures by function as the membrane stabilizer during freeze induced dehydration, and preventing the membrane system from the oxidative damage induced by reactive oxygen radicals as the radical scavenger. Here, the gene expression and molecular mechanisms of dehydrin in response to stress in plants are discussed.  相似文献   

14.
环境温度对道路微波除冰效率的影响   总被引:2,自引:0,他引:2  
为了实现冬季道路微波快速除冰,对微波除冰过程中的路面材料、环境温度、冰厚、冰层杂质含量(质量分数)、微波加热模式和波导口距路面高度等因素对微波除冰效率产生的影响进行了分析;并对关键影响因素之一的环境温度进行了仿真和试验研究。研究结果表明:相同情况下,环境温度越低,除冰效率就越低;微波加热停止最佳时刻应在路面与冰层结合处温度升至0℃后、结合处冰层开始融化前,具体时刻要靠实际路况确定。  相似文献   

15.
模拟膜下滴灌技术,进行了不同温度下的点源入渗实验,分析温度对土壤湿润体形状,水平湿润半径,垂直湿润深度以及湿润体含水量的影响,结果表明,湿润体近似为半椭球体,随着入渗时间的延长,湿润体不断增大;温度越高,湿润半径和深度越大,而土体平均含水量越小。  相似文献   

16.
随着西部经济快速发展,冻土区工程日趋活跃,冻土灾害问题愈显突出。为了减少灾害,提高工程耐久性,必须进行冻土区地基承载力的力学特性与温度变化的关系研究。采用青海省果洛州海拔4 200 m处冻土,在室内模拟不同环境负温与升温温差的冻土常规三轴压缩试验,得到冻土在不同环境负温、不同升温温差下的应力-应变曲线以及强度-温度关系曲线。试验结果表明,低温冻土到高温冻土的破坏特征是由脆性破坏过渡到塑性破坏,其应力应变关系由广义双曲线模型变为邓肯-张模型;环境负温与升温温差的不同,使得冻土强度折减不同;设计冻土区地基承载力时,需根据当地温度和升温温差等变化特点修正冻土区地基承载力特征值。  相似文献   

17.
综述了温度对生命体寿命的作用,包括温度参与调节特定基因表达和细胞信号传导通路,温度对能量代谢、氧化还原水平、免疫功能和热量限制的影响。介绍了一种将温度系数引入死亡率定律的假设,以此计算温度与寿命之间的关系,为探究温度对寿命的直接影响提供参考和依据。  相似文献   

18.
复合材料墙体室内温度响应的研究   总被引:1,自引:1,他引:0  
针对建筑物内人体的热舒适性与内墙壁面温度的相关性,建立了具有复合材料墙体的房间内温度响应的数学模型。结果显示,在相同的加热(制冷)条件下,由相同材质、相同尺寸组合构成的复合材料墙体,在不同的材料排列方式的情况下,室内的温度响应有很大的不同,这对间歇性供热房间内人体的热舒适性有较大的影响。  相似文献   

19.
【目的】研究克恩氏冬青叶片应答低温胁迫的蛋白表达情况,探讨克恩氏冬青耐寒的作用机理。【方法】以2年生幼苗为试材,对其进行-8 ℃和-16 ℃低温胁迫处理,运用双向电泳技术(2-DE)结合质谱技术(MALDI-TOF/TOF MS)检测并分析叶片差异表达蛋白,并对差异蛋白进行了生物信息学分析。【结果】在低温胁迫下,克恩氏冬青幼苗叶片中蛋白表达发生了明显变化,胁迫前后发现共有31个显著差异的蛋白质点,经质谱检测及数据库检索,成功鉴定了其中23个差异表达蛋白点。对其中的20个蛋白成功进行了功能分类,主要涉及蛋白质和氨基酸代谢、光合作用、氧化还原平衡、防御作用、碳水化合物代谢、脂类代谢、氮素代谢等生物学过程。【结论】克恩氏冬青应答低温胁迫是多种蛋白质共同作用的结果,主要通过调节多种代谢过程中的相关蛋白表达来发挥作用。  相似文献   

20.
对硅太阳能电池温度特性进行实验研究。在无光照条件下,太阳能电池可看做成一个PN结,正向电流在确定外加电压下是随着温度升高而增大的。用高压氙灯模拟太阳光,测得太阳能下电池不同温度的光照特性。温度升高使得太阳能电池短路电流Isc小幅升高,开路电压Voc降低明显,填充因子下降,光电转换效率明显下降。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号