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排序方式: 共有744条查询结果,搜索用时 31 毫秒
731.
732.
Bertram TH Perring AE Wooldridge PJ Crounse JD Kwan AJ Wennberg PO Scheuer E Dibb J Avery M Sachse G Vay SA Crawford JH McNaughton CS Clarke A Pickering KE Fuelberg H Huey G Blake DR Singh HB Hall SR Shetter RE Fried A Heikes BG Cohen RC 《Science (New York, N.Y.)》2007,315(5813):816-820
We present a statistical representation of the aggregate effects of deep convection on the chemistry and dynamics of the upper troposphere (UT) based on direct aircraft observations of the chemical composition of the UT over the eastern United States and Canada during summer. These measurements provide unique observational constraints on the chemistry occurring downwind of convection and the rate at which air in the UT is recycled. These results provide quantitative measures that can be used to evaluate global climate and chemistry models. 相似文献
733.
Four cesium beam clocks flown around the world on commercial jet flights during October 1971, once eastward and once westward, recorded directionally dependent time differences which are in good agreement with predictions of conventional relativity theory. Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59 +/- 10 nanoseconds during the eastward trip and gained 273 +/- 7 nanoseconds during the westward trip, where the errors are the corresponding standard deviations. These results provide an unambiguous empirical resolution of the famous clock "paradox" with macroscopic clocks. 相似文献
734.
Barnes JW Brown RH Turtle EP McEwen AS Lorenz RD Janssen M Schaller EL Brown ME Buratti BJ Sotin C Griffith C Clark R Perry J Fussner S Barbara J West R Elachi C Bouchez AH Roe HG Baines KH Bellucci G Bibring JP Capaccioni F Cerroni P Combes M Coradini A Cruikshank DP Drossart P Formisano V Jaumann R Langevin Y Matson DL McCord TB Nicholson PD Sicardy B 《Science (New York, N.Y.)》2005,310(5745):92-95
Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80 degrees W and 20 degrees S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot, reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena. 相似文献
735.
736.
Essman SC 《Clinical Techniques in Small Animal Practice》2005,20(1):46-51
Cystography is a radiographic study performed to aid in evaluation of the urinary bladder for extramural, mural, or intraluminal lesions. These lesions may primarily involve the urinary bladder or may be an extension of disease from adjacent organs. Cystography is easy to perform with relatively few complications. Different types of cystography (positive versus negative contrast) may be used depending on the type of information that the clinician hopes to obtain. Although a valuable technique, it is important to correlate the findings on cystography with other clinical information to arrive at the final diagnosis. 相似文献
737.
The recent development of equine genome maps by the equine genome community and the complete sequencing of the horse genome performed at the Broad Institute have accelerated the pace of genetic discovery. This review focuses on genetic diseases in the horse for which a mutation is currently known, including hyperkalemic periodic paralysis, severe combined immunodeficiency, overo lethal white syndrome, junctional epidermolysis bullosa, glycogen branching enzyme deficiency, malignant hyperthermia, hereditary equine regional dermal asthenia, and polysaccharide storage myopathy. Emphasis is placed on the prevalence, clinical signs, etiology, diagnosis, treatment and prognosis for each disease. 相似文献
738.
Galland S Mora N Abert-Vian M Rakotomanomana N Dangles O 《Journal of agricultural and food chemistry》2007,55(18):7573-7579
This work describes the chemical synthesis of O-aryl-beta-D-glucosides and 1-O-beta-D-glucosyl esters of hydroxycinnamic acids. In particular, O-aryl-beta-D-glucosides were efficiently prepared via a simple diastereoselective glycosylation procedure using phase transfer conditions. Despite the lability of its ester linkage, 1-O-beta-D-caffeoylglucose could also be obtained using a Lewis acid catalyzed glycosylation step and a set of protective groups that can be removed under neutral conditions. Hydroxycinnamic acid O-aryl-beta-D-glucosides were then quantitatively investigated for their affinity for the naturally occurring anthocyanin malvin (pigment). Formation of the pi-stacking molecular complexes (copigmentation) was characterized in terms of binding constants and enthalpy and entropy changes. The glucosyl moiety did not significantly alter these thermodynamic parameters, in line with a binding process solely involving the polyphenolic nuclei. 相似文献
739.
Jennifer R. McCall Kathryn T. Sausman Devon M. Keeler Ariel P. Brown Stephanie L. Turrise 《Marine drugs》2022,20(4)
Brevetoxins are a suite of marine neurotoxins that activate voltage-gated sodium channels (VGSCs) in cell membranes, with toxicity occurring from persistent activation of the channel at high doses. Lower doses, in contrast, have been shown to elicit neuroregeneration. Brevetoxins have thus been proposed as a novel treatment for patients after stroke, when neuron regrowth and repair is critical to recovery. However, findings from environmental exposures indicate that brevetoxins may cause inflammation, thus, there is concern for brevetoxins as a stroke therapy given the potential for neuroinflammation. In this study, we examined the inflammatory properties of several brevetoxin analogs, including those that do and do not bind strongly to VGSCs, as binding has classically indicated toxicity. We found that several analogs are toxic to monocytes, while others are not, and the degree of toxicity is not directly related to VGSC binding. Rather, results indicate that brevetoxins containing aldehyde groups were more likely to cause immunotoxicity, regardless of binding affinity to the VGSC. Our results demonstrate that different brevetoxin family members can elicit a spectrum of apoptosis and necrosis by multiple possible mechanisms of action in monocytes. As such, care should be taken in treating “brevetoxins” as a uniform group, particularly in stroke therapy research. 相似文献
740.
Stephanie Brodie Alistair J. Hobday James A. Smith Jason D. Everett Matt D. Taylor Charles A. Gray Iain M. Suthers 《Fisheries Oceanography》2015,24(5):463-477
Defining the oceanic habitats of migratory marine species is important for both single species and ecosystem‐based fisheries management, particularly when the distribution of these habitats vary temporally. This can be achieved using species distribution models that include physical environmental predictors. In the present study, species distribution models that describe the seasonal habitats of two pelagic fish (dolphinfish, Coryphaena hippurus and yellowtail kingfish, Seriola lalandi), are developed using 19 yr of presence‐only data from a recreational angler‐based catch‐and‐release fishing programme. A Poisson point process model within a generalized additive modelling framework was used to determine the species distributions off the east coast of Australia as a function of several oceanographic covariates. This modelling framework uses presence‐only data to determine the intensity of fish (fish km?2), rather than a probability of fish presence. Sea surface temperature (SST), sea level anomaly, SST frontal index and eddy kinetic energy were significant environmental predictors for both dolphinfish and kingfish distributions. Models for both species indicate a greater fish intensity off the east Australian coast during summer and autumn in response to the regional oceanography, namely shelf incursions by the East Australian Current. This study provides a framework for using presence‐only recreational fisheries data to create species distribution models that can contribute to the future dynamic spatial management of pelagic fisheries. 相似文献