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排序方式: 共有228条查询结果,搜索用时 281 毫秒
1.
C Gessert J Blossom P Sommers M D Canfield C Jones 《The Western journal of medicine》1989,150(2):226-230
Graduates of four rural and four urban family practice programs were interviewed to determine the nature of their practices and the factors that had influenced their practice location decisions. All programs gave residents substantial experience providing continuity of care for underserved populations. Of the 158 physicians surveyed, 58 (46%) were working in areas designated as underserved. The percentage of physicians in underserved areas was higher than that reported in other studies and was much higher than would be expected if practice sites were selected on the basis of population distribution alone. Notable differences in personal and practice characteristics were found between the physicians who chose to work in underserved areas and those who did not and between those who established practices in rural and in urban underserved areas. 相似文献
2.
Summary Cadmium and zinc uptake parameters were determined for intact corn (Zea mays L.) seedlings grown for 15 and 22 in nutrient solutions containing levels of Cd and Zn that were similar to those found in
soil solutions. Uptake of both elements was assumed to follow Michaelis-Menten kinetics. Calculations were based on the concentrations
of free ionic Cd (Cd2+) and Zn (Zn2+) rather than the total solution concentration. Rates of Zn uptake were measured by determining depletion of Zn for periods
of up to 30 h from solutions containing initial concentrations of 1.5 and 10μmol Zn 1−1. Depletion curves suggested that Zn uptake characteristics were similar at both levels of Zn in solution. The Imax for Zn
uptake decreased from 550 to 400 pmol m−2 root surface s−1 between 16 and 22 d of growth while Km decreased from 2.2 to 1.5 μmol Zn2+ 1−1. Cadmium uptake parameters were measured by controlling Cd2+ activities in nutrient solution betwen 6.3 to 164 nmol l−1 by continuous circulation of nutrient solution through a mixed-resin system. Imax for Cd uptake was 400 pmol m−2 root surface s−1 at 15 and 22 d of growth. The magnitude of Km increased from 30 to 100 nmol Cd2+ 1−1 during this time period. The Km value suggests that corn is efficient for Cd uptake. The results of these uptake studies
are consistent with the observed uptake of Zn and Cd by corn seedlings in soils. 相似文献
3.
P B Sommers M J Kronman K Brew 《Biochemical and biophysical research communications》1973,52(1):98-105
The quantum yield of tryptophan fluorescence of guinea-pig α lactalbumin is more than twice as large as found for the bovine, goat, or human proteins. This difference is due to the absence of Trp 60 from the guinea-pig amino acid sequence. It is proposed that the presence of this residue results in marked quenching of a second tryptophan residue for the other three proteins. Reference to the “lysozyme analogy model” suggests that the quenched residue is most likely Trp 104, which lies within 7Å of Trp 60, the latter lying within 6Å of two disulfide bridges. It is suggested that transfer of the excited state energy takes place from Trp 104 to 60 with subsequent quenching by the two vicinal disulfide bridges. These observations provide support for the validity of the “lysozyme analogy model”. 相似文献
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An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole. 相似文献
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Association of increased basement membrane invasiveness with absence of estrogen receptor and expression of vimentin in human breast cancer cell lines. 总被引:31,自引:0,他引:31
E W Thompson S Paik N Brünner C L Sommers G Zugmaier R Clarke T B Shima J Torri S Donahue M E Lippman 《Journal of cellular physiology》1992,150(3):534-544
Lack of estrogen receptor (ER) and presence of vimentin (VIM) associate with poor prognosis in human breast cancer. We have explored the relationships between ER, VIM, and invasiveness in human breast cancer cell lines. In the matrigel outgrowth assay, ER+/VIM- (MCF-7, T47D, ZR-75-1), and ER-/VIM- (MDA-MB-468, SK-Br-3) cell lines were uninvasive, while ER-/VIM+ (BT549, MDA-MB-231, MDA-MB-435, MDA-MB-436, Hs578T) lines formed invasive, penetrating colonies. Similarly, ER-/VIM+ cell lines were significantly more invasive than either the ER+/VIM- or ER-/VIM- cell lines in the Boyden chamber chemoinvasion assay. Invasive activity in nude mice was only seen with ER-/VIM+ cell lines MDA-MB-231, MDA-MB-435 and MDA-MB-436. Hs578T cells (ER-/VIM+) showed hematogenous dissemination to the lungs in one of five mice, but lacked local invasion. The ER-/VIM+ MCF-7ADR subline was significantly more active than the MCF-7 cells in vitro, but resembled the wild-type MCF-7 parent in in vivo activity. Data from these cell lines suggest that human breast cancer progression results first in the loss of ER, and subsequently in VIM acquisition, the latter being associated with increased metastatic potential through enhanced invasiveness. The MCF-7ADR data provide evidence that this transition can occur in human breast cancer cells. Vimentin expression may provide useful insights into mechanisms of invasion and/or breast cancer cell progression. 相似文献
8.
JA Kiernan 《Biotechnic & histochemistry》2013,88(5-6):203-210
Hexazonium pararosaniline is a valuable reagent that has been used in enzyme activity histochemistry for 50 years. It is an aqueous solution containing the tris-diazonium ion derived from pararosaniline, an aminotriarylmethane dye, and it contains an excess of nitrous acid that was not consumed in the diazotization reaction. Other investigators have found that immersion for 2 min in an acidic (pH 3.5) 0.0015 M hexazonium pararosaniline solution can protect cryostat sections of unfixed animal tissues from the deleterious effects of aqueous reagents such as buffered solutions used in immunohistochemistry, while preserving specific affinities for antibodies. In the present investigation hexazonium pararosaniline protected lymphoid tissue and striated muscle against the damaging effects of water or saline. The same protection was conferred on unfixed sections treated with dilute nitrous or hydrochloric acid in concentrations similar to those in hexazonium pararosaniline solutions. Model tissues (solutions, gels or films containing gelatin and/or bovine albumin) responded predictably to well known cross-linking (formaldehyde) or coagulant (mercuric chloride) fixatives. Hexazonium pararosaniline solutions prevented the dissolution of protein gels in water only after 9 or more days of contact, during which time considerable swelling occurred. It is concluded that there is no evidence for a “fixative” action of hexazonium pararosaniline. The protective effect on frozen sections of unfixed tissue is attributable probably to the low pH of the solution. 相似文献
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