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排序方式: 共有1017条查询结果,搜索用时 15 毫秒
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When a short, intense flash of light is absorbed by the outer segments of squid photoreceptors fixed in glutaraldehyde, a voltage appears briefly across the retina. The waveform depends on the relative amounts of rhodopsin and its various stable photoproducts present at the beginning of the flash. Each light-absorbing species present contributes a characteristic voltage component which is summed in the gross waveform. The heating effect of the absorbed light produces a small, long-lasting thermoelectric voltage as well. When this thermal effect is corrected for, interconversion of equal numbers of rhodopsin and acid metarhodopsin molecules by a flash results in a fast voltage waveform whose time integral is zero. Thus the charge flowing in one direction in the retina when rhodopsin is converted to acid metarhodopsin by one photon is apparently exactly reversed when acid metarhodopsin is reconverted to rhodopsin by another. 相似文献
955.
Catterall WA 《Science (New York, N.Y.)》2001,294(5550):2306-2308
956.
Oliveira AA Mota RA Pereira GC Langoni H Souza MI Navegantes WA Sá ME 《The Onderstepoort journal of veterinary research》2001,68(4):275-279
The prevalence of Leptospira interrogans serovars in dairy cattle was determined by analyzing 464 serum samples from cows on 15 properties in Garanhuns municipal district, Pernambuco State, Brazil. A microscopic seroagglutination test including 12 serovars of Leptospira interrogans as antigens was used. Samples with titres 100 were considered positive. Two hundred and twenty-one (47.63%) of the samples were positive to one or more serovars. The prevalence of the serovars was hardjo (21.98%), bratislava (15.73%), castellonis (11.64%), tarassovi (10.56%), pyrogenes (1.72%), icterohaemorrhagiae (1.08%), pomona (0.86%), wolffi (0.86%), grippotyphosa (0.86%), djasiman (0.43%), canicola (0.21 %), and copenhageni (0.21%). 相似文献
957.
De Ceulaer KM Van Ginneken CJ Philips WA Weyns A 《Anatomia, histologia, embryologia》2007,36(4):300-310
This study highlights the importance of interstitial cells of Cajal (ICs) in gastrointestinal disease. Human research is already considering IC pathologies but in veterinary research IC pathologies are rarely studied. Nevertheless, recent studies of ICs show a growing interest in the pathophysiology of gastrointestinal diseases and emphasize the consideration of this cell type in the pathophysiology of veterinary gastrointestinal malfunctions. 相似文献
958.
White WH Gutierrez JA Naylor SA Cook CA Gonzalez IC Wisehart MA Smith CK Thompson WA 《Veterinary parasitology》2007,146(1-2):58-65
The neurotransmitter serotonin (5-hydroxy tryptamine or 5HT) regulates key physiological processes in nematodes such as locomotion and feeding. PAPP (p-amino-phenethyl-m-trifluoromethylphenyl piperazine) is a known agonist of the 5-HT(1Hc) receptor of the barber pole worm, Haemonchus contortus. In this study, PAPP was highly active against L3-stage larvae of H. contortus and Trichostrongylus colubriformis in an in vitro larval migration assay, with EC50 values of 9.36 and 11.8 microM, respectively, that were comparable to levamisole (10.2 microM) and superior to pyrantel (55.39 microM). When administered orally or subcutaneously to nematode infected gerbils, PAPP provided >99% efficacy against H. contortus and >98% efficacy against Teladorsagia circumcincta at 100 mg/kg, comparable to levamisole at 10 mg/kg. Drug titration revealed significant activity down to 50 mg/kg against these two species. Spectrum was limited, however, with somewhat lower efficacy (83%) in T. colubriformis infected gerbils at 100 mg/kg. Oral delivery of hydrochloride, acetate and phosphate salts of PAPP to nematode infected gerbils did not result in an increase in either potency or spectrum. The finding that PAPP exhibits significant anthelmintic activity suggests that the nematode-specific serotonergic system is a viable target for future anthelmintic discovery. 相似文献
959.
This cross-sectional study was conducted to determine the prevalence and antimicrobial resistance of Salmonella species in swine reared in the intensive (indoor) and extensive (outdoor) ABF production systems at farm and slaughter in North Carolina, U.S.A. We sampled a total of 279 pigs at farm (extensive 107; intensive 172) and collected 274 carcass swabs (extensive 124; intensive 150) at slaughter. Salmonella species were tested for their susceptibility against 12 antimicrobial agents using the Kirby-Bauer disk diffusion method. Serogrouping was done using polyvalent and group specific antisera. A total of 400 salmonellae were isolated in this study with a significantly higher Salmonella prevalence from the intensive (30%) than the extensive farms (0.9%) (P<0.001). At slaughter, significantly higher Salmonella was isolated at the pre- and post-evisceration stages from extensively (29% pre-evisceration and 33.3% post-evisceration) than the intensively (2% pre-evisceration and 6% post-evisceration) reared swine (P<0.001). The isolates were clustered in six serogroups including B, C, E1, E4, G and R. Highest frequency of antimicrobial resistance was observed against tetracycline (78.5%) and streptomycin (31.5%). A total of 13 antimicrobial resistance patterns were observed including the pentaresistant strains with ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline resistance pattern observed only among isolates from the intensive farms (n=28) and all were serotype Salmonella typhimurium var. Copenhagen. In conclusion, this study shows that multidrug resistant Salmonella are prevalent in ABF production systems despite the absence of antimicrobial selection pressure. In addition, it also highlights the possible role played by slaughterhouse and other environmental factors in the contamination and dissemination of antimicrobial resistant Salmonella in ABF production systems. 相似文献
960.
Beiersdorfer P Boyce KR Brown GV Chen H Kahn SM Kelley RL May M Olson RE Porter FS Stahle CK Tillotson WA 《Science (New York, N.Y.)》2003,300(5625):1558-1559
In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory. 相似文献