排序方式: 共有15条查询结果,搜索用时 428 毫秒
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Pätzold M Andert TP Asmar SW Anderson JD Barriot JP Bird MK Häusler B Hahn M Tellmann S Sierks H Lamy P Weiss BP 《Science (New York, N.Y.)》2011,334(6055):491-492
Asteroid 21 Lutetia was approached by the Rosetta spacecraft on 10 July 2010. The additional Doppler shift of the spacecraft radio signals imposed by 21 Lutetia's gravitational perturbation on the flyby trajectory were used to determine the mass of the asteroid. Calibrating and correcting for all Doppler contributions not associated with Lutetia, a least-squares fit to the residual frequency observations from 4 hours before to 6 hours after closest approach yields a mass of (1.700 ± 0.017) × 10(18) kilograms. Using the volume model of Lutetia determined by the Rosetta Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) camera, the bulk density, an important parameter for clues to its composition and interior, is (3.4 ± 0.3) × 10(3) kilograms per cubic meter. 相似文献
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Gesunde Pflanzen - Der Anbau von Winterraps (Brassica napus L.) wird durch das Auftreten tierischer Schaderreger begleitet, wodurch ein intensiver Insektizid-Einsatz nötig ist.... 相似文献
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TL Morkved M Lu AM Urbas EE Ehrichs HM Jaeger P Mansky TP Russell 《Science (New York, N.Y.)》1996,273(5277):931-933
Local control of the domain orientation in diblock copolymer thin films can be obtained by the application of electric fields on micrometer-length scales. Thin films of an asymmetric polystyrene-polymethylmethacrylate diblock copolymer, with cylindrical polymethylmethacrylate microdomains, were spin-coated onto substrates previously patterned with planar electrodes. The substrates, 100-nanometer-thick silicon nitride membranes, allow direct observation of the electrodes and the copolymer domain structure by transmission electron microscopy. The cylinders aligned parallel to the electric field lines for fields exceeding 30 kilovolts per centimeter, after annealing at 250°C in an inert atmosphere for 24 hours. This technique could find application in nanostructure fabrication. 相似文献
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In Europe, farmers are encouraged to reduce pesticide use. Pesticide use intensity in arable farming depends on many factors. Numerous studies report a high variance in pesticide use between farms. The aim of the present study is to identify farm specific determinants for the intensity of pesticide use. We investigated which farm characteristics and pesticide management factors are related to lower or higher pesticide use intensity. Data on chemical plant protection measures of 30 farms in two districts of North East Germany were examined for five field crops from 2005 until 2014. In the present study we investigated the pesticide use intensities described as Standardized Treatment Index (STI) of ten representative farms. Yield data and information on the field-specific soil quality were available from these ten farms. We used multiple regressions to estimate the relationship between farm characteristics and pesticide use. 相似文献
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PO Wennberg TF Hanisco L Jaegle DJ Jacob EJ Hintsa EJ Lanzendorf JG Anderson R Gao ER Keim SG Donnelly LAD Negro DW Fahey SA McKeen RJ Salawitch CR Webster RD May RL Herman MH Proffitt JJ Margitan EL Atlas SM Schauffler F Flocke CT McElroy TP Bui 《Science (New York, N.Y.)》1998,279(5347):49-53
The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected. 相似文献
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为实现对农产品“从农田到餐桌”的全方位的监控,从如何确定农产品“身份”出发,结合全球统一性的EAN·UCC编码体系,制定了农产品编码标准,设计了农产品追溯条码方案,并基于.net平台实现了农产品追溯标签的自动生成与打印。 相似文献
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Sierks H Lamy P Barbieri C Koschny D Rickman H Rodrigo R A'Hearn MF Angrilli F Barucci MA Bertaux JL Bertini I Besse S Carry B Cremonese G Da Deppo V Davidsson B Debei S De Cecco M De Leon J Ferri F Fornasier S Fulle M Hviid SF Gaskell RW Groussin O Gutierrez P Ip W Jorda L Kaasalainen M Keller HU Knollenberg J Kramm R Kührt E Küppers M Lara L Lazzarin M Leyrat C Lopez Moreno JJ Magrin S Marchi S Marzari F Massironi M Michalik H Moissl R Naletto G Preusker F Sabau L Sabolo W Scholten F 《Science (New York, N.Y.)》2011,334(6055):487-490
Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles. 相似文献
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食品安全控制中条码质量追溯标签的设计与应用 总被引:8,自引:1,他引:7
sunch@nercita.org.cn或schheng@.com 《中国农学通报》2006,22(5):98-98
(1中国科学院生态环境研究中心,北京 100085;2国家农业信息化工程技术研究中心,北京 100089) 相似文献
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Janet Andert Ella Wessén Gunnar Börjesson Sara Hallin 《Journal of Soils and Sediments》2011,11(8):1399-1407