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排序方式: 共有1618条查询结果,搜索用时 187 毫秒
141.
Neumann P Mizuochi N Rempp F Hemmer P Watanabe H Yamasaki S Jacques V Gaebel T Jelezko F Wrachtrup J 《Science (New York, N.Y.)》2008,320(5881):1326-1329
Robust entanglement at room temperature is a necessary requirement for practical applications in quantum technology. We demonstrate the creation of bipartite- and tripartite-entangled quantum states in a small quantum register consisting of individual 13C nuclei in a diamond lattice. Individual nuclear spins are controlled via their hyperfine coupling to a single electron at a nitrogen-vacancy defect center. Quantum correlations are of high quality and persist on a millisecond time scale even at room temperature, which is adequate for sophisticated quantum operations. 相似文献
142.
Acton L Bruner M Lemen J Tsuneta S Ogawara Y Nishimura J Bentley R Culhane L Canfield R Hudson H Doschek G Hiei E Hirayama T Kosugi T Watanabe T Lang J Makishima K Uchida Y 《Science (New York, N.Y.)》1992,258(5082):618-625
The Japanese Yohkoh satellite is now in orbit observing the sun with a set of x-ray imagers and x-ray and gamma-ray spectrometers. The data from this successful mission provide new information on solar flares and the sun's corona. This paper discusses the Yohkoh observations and presents a sample of the first scientific results from the mission. 相似文献
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Sugita S Ootsubo T Kadono T Honda M Sako S Miyata T Sakon I Yamashita T Kawakita H Fujiwara H Fujiyoshi T Takato N Fuse T Watanabe J Furusho R Hasegawa S Kasuga T Sekiguchi T Kinoshita D Meech KJ Wooden DH Ip WH A'Hearn MF 《Science (New York, N.Y.)》2005,310(5746):274-278
The impact cratering process on a comet is controversial but holds the key for interpreting observations of the Deep Impact collision with comet 9P/Tempel 1. Mid-infrared data from the Cooled Mid-Infrared Camera and Spectrometer (COMICS) of the Subaru Telescope indicate that the large-scale dust plume ejected by the impact contained a large mass (approximately 10(6) kilograms) of dust and formed two wings approximately +/-45 degrees from the symmetric center, both consistent with gravity as the primary control on the impact and its immediate aftermath. The dust distribution in the inner part of the plume, however, is inconsistent with a pure gravity control and implies that evaporation and expansion of volatiles accelerated dust. 相似文献
145.
Watanabe T Tomizawa S Mitsuya K Totoki Y Yamamoto Y Kuramochi-Miyagawa S Iida N Hoki Y Murphy PJ Toyoda A Gotoh K Hiura H Arima T Fujiyama A Sado T Shibata T Nakano T Lin H Ichiyanagi K Soloway PD Sasaki H 《Science (New York, N.Y.)》2011,332(6031):848-852
Genomic imprinting causes parental origin-specific monoallelic gene expression through differential DNA methylation established in the parental germ line. However, the mechanisms underlying how specific sequences are selectively methylated are not fully understood. We have found that the components of the PIWI-interacting RNA (piRNA) pathway are required for de novo methylation of the differentially methylated region (DMR) of the imprinted mouse Rasgrf1 locus, but not other paternally imprinted loci. A retrotransposon sequence within a noncoding RNA spanning the DMR was targeted by piRNAs generated from a different locus. A direct repeat in the DMR, which is required for the methylation and imprinting of Rasgrf1, served as a promoter for this RNA. We propose a model in which piRNAs and a target RNA direct the sequence-specific methylation of Rasgrf1. 相似文献
146.
脱落酸(Abscisic acid, ABA)对映异构体的生物活性比较 总被引:2,自引:0,他引:2
采用新方法精制脱落酸(ABA)异构体试样,改变以往靠光学离析法分离racemic型(SR)-(±)-ABA,提高了(S)-(+)-ABA与(R)-(-)-ABA两镜像体纯度。抑制生长试验和残留量分析结果表明:天然型(S)-(+)-ABA活性,显着高于非天然型(R)-(-)-ABA或(SR)-(±)-ABA活性。抑制莴苣种子发芽50%的活性强度(S)-(+)-ABA约是(R)-(-)-ABA的5倍,(SR)-(±)-ABA介于二者之间。抑制萝卜下胚轴生长试验,最显着有效期2~6天,(6天后差异渐小,8日甚微),生理作用期约为一周,(S)-(+)-ABA活性是(R)-(-)-ABA的3.6倍。差异原因可能是两异构体分子立体结构不同所致。 相似文献
147.
Matsuishi S Toda Y Miyakawa M Hayashi K Kamiya T Hirano M Tanaka I Hosono H 《Science (New York, N.Y.)》2003,301(5633):626-629
We removed approximately 100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO.7Al2O3, leading to the formation of high-density (approximately 2 x 10(21) cm-3) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F+ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity approximately 100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca24Al28O64]4+(4e-) may be regarded as a thermally and chemically stable single crystalline "electride." 相似文献
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149.
Cytokinin oxidase regulates rice grain production 总被引:25,自引:0,他引:25
Ashikari M Sakakibara H Lin S Yamamoto T Takashi T Nishimura A Angeles ER Qian Q Kitano H Matsuoka M 《Science (New York, N.Y.)》2005,309(5735):741-745
Most agriculturally important traits are regulated by genes known as quantitative trait loci (QTLs) derived from natural allelic variations. We here show that a QTL that increases grain productivity in rice, Gn1a, is a gene for cytokinin oxidase/dehydrogenase (OsCKX2), an enzyme that degrades the phytohormone cytokinin. Reduced expression of OsCKX2 causes cytokinin accumulation in inflorescence meristems and increases the number of reproductive organs, resulting in enhanced grain yield. QTL pyramiding to combine loci for grain number and plant height in the same genetic background generated lines exhibiting both beneficial traits. These results provide a strategy for tailormade crop improvement. 相似文献
150.