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排序方式: 共有311条查询结果,搜索用时 16 毫秒
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Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby 总被引:1,自引:0,他引:1
DK Yeomans J Barriot DW Dunham RW Farquhar JD Giorgini CE Helfrich AS Konopliv JV McAdams JK Miller WM Owen DJ Scheeres SP Synnott BG Williams 《Science (New York, N.Y.)》1997,278(5346):2106-2109
The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter. 相似文献
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Surface Deformation and Lower Crustal Flow in Eastern Tibet 总被引:99,自引:0,他引:99
LH Royden BC Burchfiel RW King E Wang Z Chen F Shen Y Liu 《Science (New York, N.Y.)》1997,276(5313):788-790
Field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern Tibetan plateau since about 4 million years ago. Instead, central eastern Tibet has been nearly stationary relative to southeastern China, southeastern Tibet has rotated clockwise without major crustal shortening, and the crust along portions of the eastern plateau margin has been extended. Modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle. This model also predicts east-west extension on the high plateau without convective removal of Tibetan lithosphere and without eastward movement of the crust east of the plateau. 相似文献
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马丽艳木·阿木东 谢仁娜依·甫拉提 卡依尔·玉素甫 艾尼江·尔斯曼 玛丽帕·吐达洪 程刚 祖母拉提·阿布都热依木 艾尔肯·热合曼 木合塔·阿不都克里木 《新疆农业科学》2011,48(5):832-840
[目的]了解新疆沙雅县胡杨林土壤可培养细菌的多样性.[方法]沙雅县胡杨林采集土壤样品,采用两种不同的培养基(LB,TSA)分离纯化细菌,并对它们进行16S rDNA测定和系统进化分析.[结果]分离纯化不同表型的57株细菌.对它们16S rDNA序列分析表明,57株菌分别属于3个大类群厚壁菌门(Firmicutes),放线菌门(Actinobacteria),γ-变形菌纲(γ-Proteobacteria),13个属,33个种;芽孢杆菌属是优势细菌种群,它占已测种群的67.2;.其中6株菌M28,M13,CT3,YS30-1,CM5,CL19初步被认为是潜在的新种(16S rDNA相似率为96.780;~97.961;).[结论]沙雅县胡杨林可培养细菌不仅具有比较高的多样性,并存在一些潜在的新的细菌菌种资源,极具进一步发掘的潜力. 相似文献
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[目的]了解新疆库米什一处金矿土壤可培养细菌的多样性及建立菌种资源库.[方法]采集库米什金矿土壤样品,采用两种不同培养基(LB,TSB)分离纯化细菌,对其进行形态观察(菌落及细胞)、生理测定、16SrDNA测序和系统进化分析.[结果]从两种培养基上总共得到50株细菌,根据基于16S rDNA的系统进化分析表明,50株菌分别属于3个大类群:厚壁菌门(Firmicutes ),放线菌门(Actinobacteria),γ-变形菌纲(γ-Proteobaeteria),12个属,30个分类单元.其中芽抱杆菌属(Bacillus)为优势细菌种群,占已测种群的63.3;.菌株L10-5与Bacillus foraminis (AJ717382)有96.463;的相似率,可能为潜在新种.[结论]库米什金矿土壤可培养细菌具有较高的多样性,存在潜在新菌种资源,值得进一步研究. 相似文献
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The effectiveness of intercropping tagetes with tomato in comparison with the natural root exudates of tagetes onMeloidogyne javanica nematode population and galls on tomato cultivated in sandy soil was studied. Both tagetes roots extracts and intercropping tagetes with tomato significantly reducedM. javanica nematode population, egg masses and galls on tomato. Intercropping tagetes with tomato was more effective in reducing root-knot nematode population and galls than treating tomato with natural root extracts of tagetes.Therefore, intercropping resistant plant with susceptible host to nematode is a new and good approach to nematode control.
With one table 相似文献
Zusammenfassung Es wurde die Wirkung des Pflanzens vonTagetes zwischen Tomaten im Vergleich zur Beigabe von Wurzel-Exudaten vonTagetes zu den Tomaten auf den NematodenMeloidogyne javanica in Sandboden untersucht. Beide Verfahren reduzierten signifikant die Zahl der Nematoden, die Eigelege und Gallenbildungen an den Tomaten. Jedoch wirkte die Zwischenpflanzung vonTagetes besser als die Hinzufügung vonTagetes-Wurzelexudaten.Auf Grund der Ergebnisse bietet das Zwischenpflanzen einer resistenten Pflanzenart zu einer nematoden-empfindlichen Pflanzenart einen neuen Weg der Nematodenbekämpfung.
With one table 相似文献
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The aim of this study is to reveal the energy balance of walnut in Central Anatolian Region in Turkey. This study has been conducted at the walnut cultivating facilities during the 2014–2015 production season in K?r?ehir, Konya, Nev?ehir and Ni?de provinces of Central Anatolian Region in Turkey, where walnut cultivation is intense. In the study, a total of 28 walnut cultivation facilities, yielding walnut, have been selected through Neyman method and surveys and observations have been performed in these facilities. The agricultural input energies and output energies used in walnut cultivation have been calculated to define the energy use efficiency. According to the study findings, the energy inputs in walnut cultivation are calculated respectively 17,851.33?MJ ha?1 (74.40%) chemical fertilizer energy, 2229.87?MJ ha?1 (9.29%) fuel energy, 1640.64?MJ ha?1 (6.83%) irrigation water energy, 1539?MJ ha?1 (6.41%) machine energy, 508.02?MJ ha?1 (%2.11) chemical energy, 180.35?MJ ha?1 (0.75%) human labour energy and 43.33?MJ ha?1 (0.18%) farm manure energy. Production outputs have been calculated as 14,679.52?MJ ha?1. Following the energy calculations, the output/input ratio, specific energy, energy efficiency and net energy calculations have been calculated respectively as 0.61, 30.20?MJ kg?1, 0.03?kg MJ?1 and ?9313.02?MJ ha?1. Benefit-cost ratio was calculated as 1.88, by dividing the gross value of production by the total cost of production per hectare in walnut production. 相似文献