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101.
Eglinton G Douglas AG Maxwell JR Ramsay JN Ställberg-Stenhagen S 《Science (New York, N.Y.)》1966,153(3740):1133-1135
The most abundant free fatty acids present in a sample of shale from the Green River Formation (Eocene, about 60 x 10(6) years) from Sulfur Creek are the acylic C(19) and C(20) isoprenoid acids. The dominance of these acids parallels the abundance of the corresponding hydrocarbons pristane and phytane. 相似文献
102.
Two additional urinary metabolites of the chemical oncogen 3-hydroxyxanthine are now identified as 8-chloroxanthine and 8-methylmercaptoxanthine. Such products are thought to be derived from a reactive intermediate which can be tentatively considered to be a proximate oncogen. Since each of these 8-substituted xanthines has also been obtained in vitro by reactions of 3-acetoxyxanthine with chloride ion or methionine, their production in vivo can be explained as resulting through the metabolic formation of an activated ester with a reactivity similar to that of the chemical model. 相似文献
103.
Michel E Baglin A Auvergne M Catala C Samadi R Baudin F Appourchaux T Barban C Weiss WW Berthomieu G Boumier P Dupret MA Garcia RA Fridlund M Garrido R Goupil MJ Kjeldsen H Lebreton Y Mosser B Grotsch-Noels A Janot-Pacheco E Provost J Roxburgh IW Thoul A Toutain T Tiphène D Turck-Chieze S Vauclair SD Vauclair GP Aerts C Alecian G Ballot J Charpinet S Hubert AM Lignières F Mathias P Monteiro MJ Neiner C Poretti E de Medeiros JR Ribas I Rieutord ML Cortés TR Zwintz K 《Science (New York, N.Y.)》2008,322(5901):558-560
Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. 相似文献
104.
105.
Størmer L 《Science (New York, N.Y.)》1969,164(3885):1276-1277
New finds of nonscorpionid arachnids in the Lower Devonian Nellenk?pfchen Shale of Alken an der Mosel, Germany, give valuable iniformation on the first appearance of terrestrial arachnids. 相似文献
106.
Markó IE Stérin S Buisine O Mignani G Branlard P Tinant B Declercq JP 《Science (New York, N.Y.)》2002,298(5591):204-206
The hydrosilylation reaction enables the production of silicon polymers. Platinum-carbene complexes are reported that catalyze the hydrosilylation reaction of alkenes with remarkable efficiency and exquisite selectivity and avoid the formation of platinum colloids. By-products, typically encountered with previous catalytic systems, are suppressed with these platinum derivatives. 相似文献
107.
Hillenmeyer ME Fung E Wildenhain J Pierce SE Hoon S Lee W Proctor M St Onge RP Tyers M Koller D Altman RB Davis RW Nislow C Giaever G 《Science (New York, N.Y.)》2008,320(5874):362-365
Genetics aims to understand the relation between genotype and phenotype. However, because complete deletion of most yeast genes ( approximately 80%) has no obvious phenotypic consequence in rich medium, it is difficult to study their functions. To uncover phenotypes for this nonessential fraction of the genome, we performed 1144 chemical genomic assays on the yeast whole-genome heterozygous and homozygous deletion collections and quantified the growth fitness of each deletion strain in the presence of chemical or environmental stress conditions. We found that 97% of gene deletions exhibited a measurable growth phenotype, suggesting that nearly all genes are essential for optimal growth in at least one condition. 相似文献
108.
109.
We report on stimulated Raman scattering in an approximately 1-meter-long hollow-core photonic crystal fiber filled with hydrogen gas under pressure. Light was guided and confined in the 15-micrometer-diameter hollow core by a two-dimensional photonic bandgap. Using a pulsed laser source (pulse duration, 6 nanoseconds; wavelength, 532 nanometers), the threshold for Stokes (longer wavelength) generation was observed at pulse energies as low as 800 +/- 200 nanojoules, followed by a coherent anti-Stokes (shorter wavelength) generation threshold at 3.4 +/- 0.7 microjoules. The pump-to-Stokes conversion efficiency was 30 +/- 3% at a pulse energy of only 4.5 microjoules. These energies are almost two orders of magnitude lower than any other reported energy, moving gas-based nonlinear optics to previously inaccessible parameter regimes of high intensity and long interaction length. 相似文献
110.
We report the cancellation of the soliton self-frequency shift in a silica-core photonic crystal fiber with a negative dispersion slope. Numerical and experimental results show that stabilization of the soliton wavelength is accompanied by exponential amplification of the red-shifted Cherenkov radiation emitted by the soliton. The spectral recoil from the radiation acts on the soliton to compensate for the Raman frequency shift. This phenomenon may find applications in the development of a family of optical parametric amplifiers. 相似文献