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1.
有时我们会被问及这样的问题:你最喜欢一年中的哪段时光?对我来说,春天最令人愉快,大自然从冷漠的冬天中苏醒,生命的力量又开始涌动,树叶生长,蓓蕾绽放,眼前的一切生机盎然,令人赏心悦目。在这大自然生命复苏的时刻,我们的心也为之狂喜,但是美景不会永恒,叶子会到达它生命的极限,花蕾盛开后就会走向枯萎。  相似文献   
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Tylobolus utahensis Chamberlin, the only representative of the genus occurring in the southwestern deserts, ranges from central Inyo County, California, to the western periphery of Kane County, Utah. This distribution roughly corresponds to the northern limit of the Mojave Desert ecosystem and is also shown by the millipede Piedolus utus Chamberlin. (Spirobolida: Atopetholidae) and the centipede Theatops posticus (Say) (Scolopendromorpha: Cryptopidae). Tylobolus fredericksoni Causey, ostensibly from Douglas County, Kansas, is designated "" nomen dubium "" and disregarded pending collection of fresh material; Narceus gordanus (Chamberlin) is deleted from South Carolina and Tennessee. Tyobolus uncigerus (Wood) occurs north of the Columbia River in Klickitat County, Washington, and Hiltonius thebanus Chamberlin is referable to Onychelus Cook in the family Atopetholidae.  相似文献   
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Mapping of mutation causing Friedreich's ataxia to human chromosome 9   总被引:29,自引:0,他引:29  
Friedreich's ataxia is an autosomal recessive disease with progressive degeneration of the central and peripheral nervous system. The biochemical abnormality underlying the disorder has not been identified. Prompted by the success in localizing the mutations causing Duchenne muscular dystrophy, Huntington's disease and cystic fibrosis, we have undertaken molecular genetic linkage studies to determine the chromosomal site of the Friedreich's ataxia mutation as an initial step towards the isolation and characterization of the defective gene. We report the assignment of the gene mutation for this disorder to chromosome 9p22-CEN by genetic linkage to an anonymous DNA marker MCT112 and the interferon-beta gene probe. In contrast to the clinical variation seen for the disorder, no evidence of genetic heterogeneity is observed.  相似文献   
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Summary Aqueous humor taurine concentrations were found to be significantly higher (p<0.01) than that of the plasma in anesthetized rabbits. Topical application of 2 mg terbutaline lowered intraocular pressure (p<0.001), but did not alter aqueous taurine content.Supported by National Eye Institute grants Nos EY05430 (JMR) and EY02156 (DEP).Acknowledgments. We thank Dr J. Gintautas, this institution, for translating reference 18 and Dr S. Y. Schmidt, Massachusetts Eye and Ear Infirmary, for valuable advice.  相似文献   
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After methane, ethane is the most abundant hydrocarbon in the remote atmosphere. It is a precursor to tropospheric ozone and it influences the atmosphere's oxidative capacity through its reaction with the hydroxyl radical, ethane's primary atmospheric sink. Here we present the longest continuous record of global atmospheric ethane levels. We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010. We attribute this to decreasing fugitive emissions from ethane's fossil fuel source--most probably decreased venting and flaring of natural gas in oil fields--rather than a decline in its other major sources, biofuel use and biomass burning. Ethane's major emission sources are shared with methane, and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane's atmospheric growth rate to slow. Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10-21 teragrams per year (30-70 per cent) of the decrease in methane's global emissions, significantly contributing to methane's slowing atmospheric growth rate since the mid-1980s.  相似文献   
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Summary Autoradiographs ofVicia faba lateral root-tip meristems were prepared following a 30 min pulse with3H-thymidine. 1/3 of all interphase nuclei in the meristem are labeled, most with a uniform distribution of silver grains. 2–5% of labeled nuclei show specific nucleolus DNA labeling.  相似文献   
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The milliped genus Narceus Rafinesque, 1820 (Spirobolida: Spirobolidae) occupies parts or all of 2 Canadian provinces, Québec and Ontario; every U.S. state east of the Mississippi River; and 9 states to the west including Minnesota, Iowa, Missouri, Arkansas, Louisiana, Nebraska, Kansas, Oklahoma, and Texas. Records are detailed for the "western" states and New England and include the first from Minnesota, Connecticut, Delaware, and Maine; occurrence is projected for southeastern Minnesota and the Delmarva Peninsula. The genus presently comprises 2 valid species that are endemic to Florida— N. gordanus (Chamberlin, 1943) and N. woodruffi Causey, 1959—and 2 of uncertain status that occur throughout the generic range and are referenced as the " N. americanus/annularis complex"; geographic evidence suggests greater diversity, particularly in the south, and a 2nd generic revision is in order to update the existing one by Keeton (1960). Records cluster within a large, semicontinuous area whose northern, southern, and western range extremes, respectively, are Saint-Nicolas, Lévis Census Division, Québec; Key West, Monroe County, Florida, and northeastern Duval County and Rockport, Aransas County, Texas; and Garner State Park, Uvalde County, Texas. The eastern limit is the Atlantic Ocean, and records are available from Cape Cod and Tuckernuck Island, Massachusetts; Long Island, New York; Cape Hatteras, North Carolina; and James Island, South Carolina. The projected western boundary, based on peripheral localities, angles southwestward from Omaha, Nebraska, to Uvalde County; and the northern boundary passes through central Iowa and Wisconsin (encompassing the Door Peninsula) and the southern periphery of the Upper Peninsula of Michigan. The lone Minnesota locality, from Lyon County in the southwest, lies substantially north of the projected border in Iowa and well west of the expected area of occurrence in southeastern Minnesota. The northernmost record west of the Mississippi River, it may represent an allopatric population that extends westward into eastern South Dakota.  相似文献   
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