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排序方式: 共有3142条查询结果,搜索用时 15 毫秒
991.
992.
Askebjer P Barwick SW Bergström L Bouchta A Carius S Coulthard A Engel K Erlandsson B Goobar A Gray L Hallgren A Halzen F Hulth PO Jacobsen J Johansson S Kandhadai V Liubarsky I Lowder D Miller T Mock PC Morse R Porrata R Price PB Richards A Rubinstein H Schneider E Sun Q Tilav S Walck C Yodh G 《Science (New York, N.Y.)》1995,267(5201):1147-1150
The optical properties of the ice at the geographical South Pole have been investigated at depths between 0.8 and 1 kilometer. The absorption and scattering lengths of visible light ( approximately 515 nanometers) have been measured in situ with the use of the laser calibration setup of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino detector. The ice is intrinsically extremely transparent. The measured absorption length is 59 +/- 3 meters, comparable with the quality of the ultrapure water used in the Irvine-Michigan-Brookhaven and Kamiokande proton-decay and neutrino experiments and more than twice as long as the best value reported for laboratory ice. Because of a residual density of air bubbles at these depths, the trajectories of photons in the medium are randomized. If the bubbles are assumed to be smooth and spherical, the average distance between collisions at a depth of 1 kilometer is about 25 centimeters. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated. 相似文献
993.
Saleska SR Miller SD Matross DM Goulden ML Wofsy SC da Rocha HR de Camargo PB Crill P Daube BC de Freitas HC Hutyra L Keller M Kirchhoff V Menton M Munger JW Pyle EH Rice AH Silva H 《Science (New York, N.Y.)》2003,302(5650):1554-1557
The net ecosystem exchange of carbon dioxide was measured by eddy covariance methods for 3 years in two old-growth forest sites near Santarém, Brazil. Carbon was lost in the wet season and gained in the dry season, which was opposite to the seasonal cycles of both tree growth and model predictions. The 3-year average carbon loss was 1.3 (confidence interval: 0.0 to 2.0) megagrams of carbon per hectare per year. Biometric observations confirmed the net loss but imply that it is a transient effect of recent disturbance superimposed on long-term balance. Given that episodic disturbances are characteristic of old-growth forests, it is likely that carbon sequestration is lower than has been inferred from recent eddy covariance studies at undisturbed sites. 相似文献
994.
Miller G 《Science (New York, N.Y.)》2011,332(6029):530-532
995.
Hazuda DJ Young SD Guare JP Anthony NJ Gomez RP Wai JS Vacca JP Handt L Motzel SL Klein HJ Dornadula G Danovich RM Witmer MV Wilson KA Tussey L Schleif WA Gabryelski LS Jin L Miller MD Casimiro DR Emini EA Shiver JW 《Science (New York, N.Y.)》2004,305(5683):528-532
We describe the efficacy of L-870812, an inhibitor of HIV-1 and SIV integrase, in rhesus macaques infected with the simian-human immunodeficiency virus (SHIV) 89.6P. When initiated before CD4 cell depletion, L-870812 therapy mediated a sustained suppression of viremia, preserving CD4 levels and permitting the induction of virus-specific cellular immunity. L-870812 was also active in chronic infection; however, the magnitude and durability of the effect varied in conjunction with the pretreatment immune response and viral load. These studies demonstrate integrase inhibitor activity in vivo and suggest that cellular immunity facilitates chemotherapeutic efficacy in retroviral infections. 相似文献
996.
Counselman CC Gourevitch SA King RW Pettengill GH Prinn RG Shapiro II Miller RB Smith JR Ramos R Liebrecht P 《Science (New York, N.Y.)》1979,203(4382):805-806
To determine the wind directions and speeds on Venus, as each Pioneer probe fell to the surface we tracked its motion in three dimensions using a combination of Doppler and long-baseline radio interferometric methods. Preliminary results from this tracking, coupled with results from test observations of other spacecraft, enable us to estimate the uncertainties of our eventual determinations of the velocity vectors of the probes with respect to Venus. For altitudes below about 65 kilometers and with time-averaging over 100-second intervals, all three components of the velocity should have errors of the order of 0.3 meter per second or less. 相似文献
997.
Hazuda DJ Felock P Witmer M Wolfe A Stillmock K Grobler JA Espeseth A Gabryelski L Schleif W Blau C Miller MD 《Science (New York, N.Y.)》2000,287(5453):646-650
Integrase is essential for human immunodeficiency virus-type 1 (HIV-1) replication; however, potent inhibition of the isolated enzyme in biochemical assays has not readily translated into antiviral activity in a manner consistent with inhibition of integration. In this report, we describe diketo acid inhibitors of HIV-1 integrase that manifest antiviral activity as a consequence of their effect on integration. The antiviral activity of these compounds is due exclusively to inhibition of one of the two catalytic functions of integrase, strand transfer. 相似文献
998.
Electron microscopic autoradiography indicates that only a fraction of ribosome-containing reticulocytes (from phenylhydrazine-treated rabbits) is capable of active protein synthesis in vitro. Ribosomes, and, indeed, polyribosomes, do not appear to limit the rate of protein synthesis. 相似文献
999.
1000.
Rhesus Macaque Genome Sequencing Analysis Consortium Gibbs RA Rogers J Katze MG Bumgarner R Weinstock GM Mardis ER Remington KA Strausberg RL Venter JC Wilson RK Batzer MA Bustamante CD Eichler EE Hahn MW Hardison RC Makova KD Miller W Milosavljevic A Palermo RE Siepel A Sikela JM Attaway T Bell S Bernard KE Buhay CJ Chandrabose MN Dao M Davis C Delehaunty KD Ding Y Dinh HH Dugan-Rocha S Fulton LA Gabisi RA Garner TT Godfrey J Hawes AC Hernandez J Hines S Holder M Hume J Jhangiani SN 《Science (New York, N.Y.)》2007,316(5822):222-234