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191.
海南岛万泉河口沉积环境演变 总被引:11,自引:0,他引:11
根据对柱样沉积物210Pb定年及有机碳、硫和有机碳同位素含量分析, 研究万泉河口沉积环境演变. 硫和δ13C均自19世纪初期开始持续减少, 硫从1.92%逐渐减少到0.36%, δ13C从8722;20.63‰减少到8722;23.64‰. C/S比在20世纪之前一直很稳定, 处于0.47~0.80之间, 有机碳与硫呈正相关; 在此之后, C/S比急剧增加, 至表层为3.94, 硫的含量与有机碳的增加没有相关关系. 结果表明在19世纪之前万泉河口尚为开阔的海湾, 处于正常海洋环境,未形成被沙坝围封的泻湖, 海水能够直接出入. 19世纪初期开始, 随着玉带滩沙坝向北发育, 河口逐渐被围拦成泻湖型, 进入的海水量逐渐减少; 在19与20世纪之交, 水体已开始明显淡化, 发展成为今天近乎淡水的泻湖. 相似文献
192.
In modernindustry thin film on the substratc has much important role to decide the properties ofproduct especially for electrical optical wear-resistant etc production. There aresome technical methods to prepare thin film including plasma spray physical vapordeposition 《广西师范大学学报(自然科学版)》2003,21(Z4):284-285
In modern industry,thin film on the substratc has much important role to decide the properties of product, especially for electrical, optical and wear-resistant etc, production. There are some technical methods to prepare thin film,including plasma spray,physical vapor deposition (PVD),chemical vapor deposition (CVD) and sol-gel,etc. Among of them,sol-gel method has been developed a popular tech nique for preparing thin films. 相似文献
193.
H. Yamagishi 《Cellular and molecular life sciences : CMLS》1996,52(6):583-586
The heart beat of early juveniles of the littoral isopodLigia exotica occurred at a frequency of 250 to 350/min, associated with rhythmic activity of the heart muscle. Each burst was composed of a slow depolarizing potential with superimposed spike potentials. The spike potential was eliminated by perfusion with TTX-containing or Na+-free saline. In TTX-saline, the slow potential was unchanged in frequency and amplitude. By current injection into the heart muscle, the rhythm of the slow potential was phase-shifted and its frequency was changed in a membrane potential-dependent manner. These results show that the heart ofLigia early juveniles acts as an endogenous muscle oscillator generating oscillatory slow potentials and Na+-dependent spikes. 相似文献
194.
Antioxidant survey to assess antagonism to redox stress using a prokaryotic and an eukaryotic system
H. Baker B. DeAngelis O. Frank M. Khalil S. H. Hutner E. R. Baker 《Cellular and molecular life sciences : CMLS》1996,52(6):597-599
Using a prokaryote (Escherichia coli) and a metazoa-resembling eukaryote (Ochromonas danica), we surveyed antioxidants which might overcome redox stress imposed by menadione sodium bisulphite (MD) and buthionine sulphoximine (BSO). BSO oxidant stress was evident only inO. danica; MD oxidant stress was evident in both organisms. Glutathione, its precursors, e.g. cysteine, homocysteine, and 2-oxo-4-thiazolidine carboxylic acid, and red blood cells, emerged as prime antioxidants for relieving BSO and MD oxidant stress. BSO and MD oxidant activity and antioxidant-annulling effect inO. danica were judged comparable to those found in animal cells whereas the resultsE. coli were not entirely equivalent. TheO. danica system emerged as a practical, rapid, and useful system for pinpointing oxidant stressors and antioxidants, and shows promise for studies with mammalian systems. 相似文献
195.
E. S. Fiala R. S. Sodum M. Bhattacharya H. Li 《Cellular and molecular life sciences : CMLS》1996,52(9):922-926
Reaction with peroxynitrite at pH 7.4 and 37°C was found to increase the 8-oxodeoxyguanosine levels in calf thymus DNA 35-38-fold. This oxidation of deoxyguanosine, as well as the peroxynitrite-mediated nitration of tyrosine to 3-nitrotyrosine, was significantly inhibited by ascorbic acid, glutathione and (–)-epigallocatechin gallate, a polyphenolic antioxidant present in tea. For 50% inhibition of the oxidation of deoxyguanosine to 8-oxodeoxyguanosine, 1.1, 7.6 of 0.25 mM ascorbate, glutathione or (–)-epigallocatechin gallate, respectively, was required. For 50% inhibition of tyrosine nitration, the respective concentrations were 1.4, 4.6 or 0.11 mM. Thus, (–)-epigallocatechin gallate is a significantly better inhibitor of both reactions than either ascorbate or glutathione. Reaction of (–)-epigallocatechin gallate with peroxynitrite alone resulted in the formation of a number of products. Ultraviolet spectra of two of these suggest that the tea polyphenol and/or its oxidation products are nitrated by peroxynitrite. 相似文献
196.
Associations with ants, termed myrmecophily, are widespread in the butterfly family Lycaenidae and range from mere co-existence to more or less specific mutualistic or even parasitic interactions. Secretions of specialized epidermal glands are crucial for mediating the interactions. Transfer of nutrients (carbohydrates, amino acids) from butterfly larvae to ants plays a major role, but manipulative communication with the help of odour signals is also involved. By means of myrmecophily, lycaenid butterflies largely escape ant predation, and certain species gain protection through attendant ants or achieve developmental benefits from ant-attendance. Benefits to the ants range from minimal to substantial food rewards. While most lycaenid species maintain facultative relationships with a variety of ant genera, highly specific and obligatory associations have convergently evolved in a number of butterfly lineages. As a corollary, communication systems are largely unspecific in the former, but may be highly specialized in the latter. The sophisticated communication between obligate myrmecophiles and their host ants is tightly connected with the evolutionary rise of specialized life-cycles and thus is a source of augmenting diversity within the butterflies. 相似文献
197.
Concept of an extracellular regulation of muscular metabolic rate during heavy exercise in humans by psychophysiological feedback 总被引:12,自引:0,他引:12
H. -V. Ulmer 《Cellular and molecular life sciences : CMLS》1996,52(5):416-420
Efferent motor signals to skeletal muscles concern not only the space/time pattern of motion, but also the setting of muscular performance and through this the control of the current metabolic rate. For an optimal adjustment of metabolic rate during heavy exercise — e.g. in athletic competitions — a feedback control system must exist, including a programmer that takes into consideration a finishing point (teleoanticipation). The presented experiments, using Borg's scale, indicate the existence and functioning of a system for optimal adjustment of performance during heavy exercise and the relevance of teleoanticipatory effects. Thus motor learning includes not only somatosensory control, but also metabolic control. With regard to migratory birds, such metabolic control would have to operate in the individual as well as in the migrating flock as a whole. 相似文献
198.
用子波变换分析方法实时监测视觉诱发电位的潜伏期 总被引:1,自引:0,他引:1
诱发电位的实时监测在临床中有重要意义。本文提出利用多分辨率子波分析技术来实时监测视觉诱发电位的潜伏期。为克服随机噪声的影响,我们引入相邻响应的相关系数来修正所检测得的潜伏期的偏移,并应用前一次响应的波峰位置来决定当前的搜寻范围。实验表明,本方法能实时监测视觉诱发电位的潜伏期。 相似文献
199.
针对二进制第Ⅱ类混合自动请求重传差错控制系统流量偏低的问题,提出了基于Reed-Solomon(RS)码的多进制混合自动请求重传方案.该方案将信息经RS码编码后,采用多进制调制,信息部分与校验部分分开传输,码的可逆性使得仅由无误的校验部分便可恢复出信息,利于提高流量.数值结果表明,该方案在Rician衰落信道下的流量比传统的二进制方案有了明显提高,同时可靠性依然保持与二进制方案相同的水平. 相似文献
200.
网络时代,电子信息资源已成为人们进行科学研究、商业活动和共享信息的重要手段,与此同时,网上侵权行为也时有发生。指出了电子信息资源的侵权形式,探讨了在版权法允许的范围内合法利用电子信息资源的有关问题。 相似文献