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排序方式: 共有392条查询结果,搜索用时 15 毫秒
1.
Richard G. Condon 《Human ecology: an interdisciplinary journal》1991,19(3):287-321
Birth seasonally at high latitudes is a complex phenomenon which is undoubtedly affected by a subtle interaction between environmental rhythmicity (most notably in photoperiod and temperature) and cultural adaption. There is intriguing evidence that human gonadotrophic activity (and hence fertility) may be affected by seasonal fluctuations in light intensity and duration. Nevertheless, cultural factors are important insofar as they mediate between environmental rhythmicity and human fertility/birth patterns. This article examines the distribution of births over several decades in an Inuit community located 300 miles north of the Arctic Circle. Several shifts in birth seasonality are noted, the most significant of which is a dramatic shift from pronounced seasonality in the 1970s to non-seasonality in the 1980s. Longitudinal ethnographic fieldwork has allowed an examination of social and economic changes accounting for the rather sudden disappearance of birth seasonality. These include increasing reliance upon wage employment and social assistance, decreased dependence upon subsistence hunting and trapping, changing attitudes on the part of young people entering their prime reproductive years, and the introduction of television, radio, and southern-style recreational activities. 相似文献
2.
肺癌在中国恶性肿瘤的发病率位居第一,随着低剂量薄层CT在肺癌筛查中的广泛应用,临床发现更多表现为非完全实性结节的肺腺癌,目前众多研究使CT影像学特征和肺腺癌病理的关系得到更进一步的认知,虽然CT能对部分非完全实性结节做出定性和定位诊断,但仍有部分非完全实性结节诊断困难,PET-CT结合了病灶的代谢信息和精确的定位信息,从而提高对肺部结节诊断的敏感性、特异性、准确性,综合多个文献PET-CT在非完全实性结节中的诊断分期价值较CT无明显提升,却在评估预后和制定合适手术方案上可以起到一定的作用,本文就PET-CT在SSN中的应用价值进行阐述。 相似文献
3.
Support for a physiological role of endogenous catecholamines in the stimulation of bovine luteal progesterone production 总被引:2,自引:0,他引:2
To determine if catecholamines were present in bovine luteal tissue, corpora lutea (CL) were obtained during the mid-luteal phase (Days 10-12) and the concentration of dopamine (DA) and norepinephrine (NE) was determined by high-performance liquid chromatography. Both DA and NE were detected in luteal tissue at mean concentrations of 41.9 +/- 5.73 and 10.2 +/- 2.51 ng/g for DA and NE, respectively. These concentrations represented a luteal content of 306.6 +/- 66.88 ng/CL for DA and 70.5 +/- 16.88 ng/CL for NE. In vitro, DA at concentrations of 1.0 mM to 0.01 mM stimulated the production of progesterone (P4, p less than 0.05). The response to DA was inhibited by propranolol (a beta-adrenergic receptor antagonist, p less than 0.05) but not by phentolamine, phenoxybenzamine (alpha-adrenergic receptor antagonists), or haloperidol (a DA receptor antagonist, p greater than 0.05). Neither L-tyrosine nor L-dopa altered P4 production (p greater than 0.05). Inhibition of DA beta-hydroxylase, the enzyme that catalyzes the conversion of DA to NE by FLA-63 blocked the DA-induced increases in luteal P4 production (p less than 0.05). These results demonstrate the existence of DA and NE in bovine luteal tissue and indicate that exogenous DA can be converted to NE in luteal tissue. The results support a physiological role for catecholamines in the stimulation of bovine luteal function. 相似文献
4.
Fumarate reductase of Escherichia coli: an investigation of function and assembly using in vivo complementation 总被引:3,自引:0,他引:3
Recombinant plasmids which carried portions of the Escherichia coli frd operon were constructed and their expression examined by in vivo complementation of E. Coli MI 1443. This strain lacked a chromosomal frd operon and was unable to grow anaerobically on glycerol and fumarate. Introduction of all four fumarate reductase subunits into E. coli MI1443 was essential for the restoration of growth. The FRD A, FRD B dimer (but neither subunit alone) was active in the benzyl viologen oxidase assay. Both FRD C and FRD D were required for membrane association of fumarate reductase and for the oxidation of reduced quinone analogues. Introduction into E. coli MI1443 of the frdABC and frdD genes on two separate plasmid vectors failed to restore anaerobic growth on glycerol and fumarate. Thus separation of the DNA coding for the FRD C and FRD D proteins affected the ability of fumarate reductase to assemble into a functional complex. 相似文献
5.
The genes coding for human pro alpha 1(IV) collagen and pro alpha 2(IV) collagen are both located at the end of the long arm of chromosome 13. 总被引:5,自引:4,他引:1 下载免费PDF全文
C D Boyd S E Toth-Fejel I K Gadi M Litt M R Condon M Kolbe I K Hagen M Kurkinen J W Mackenzie E Magenis 《American journal of human genetics》1988,42(2):309-314
We have isolated and characterized a cDNA clone containing DNA sequences coding for the noncollagenous carboxy-terminal domain of human pro alpha 2(IV) collagen. Using this cDNA clone in both Southern blot analysis of DNA isolated from human-mouse somatic-cell hybrids and in situ hybridization of normal human metaphase chromosomes, we have demonstrated that the gene coding for human pro alpha 2(IV) collagen is located at 13q33----34, in the same position on chromosome 13 as the pro alpha 1(IV) collagen gene. 相似文献
6.
Keith Condon Douglas K. Charles James M. Cheverud Jane E. Buikstra 《American journal of physical anthropology》1986,71(3):321-330
The cementum annulation aging technique was evaluated in a sample of 80 clinically extracted premolars (age range 11–70 years). Demineralized thin sections (7μm) stained with hematoxylin were used. The correlation (r) between age and adjusted count (number of annulations added to age of tooth eruption) was 0.78 for the entire sample (N = 73) and 0.86 for a subsample in which teeth with periodontal disease were excluded (N = 55). Standard error of the estimates ranged from 4.7 to 9.7 years depending on sex and health status of the tooth. The technique provided significantly better estimates for females than for males. The overall inaccuracy (mean absolute error) of the technique was 6.0 years, with a bias (mean error) of 0.26 years. Reduced major axis regression of adjusted count on age produced a slope of 0.797 for the entire sample and 0.889 for the nonperiodontal disease subsample. These slopes are consistent with a hypothesis of annual deposition of cementum rings given a decrease in cementogenesis with increasing age. 相似文献
7.
8.
The influence of different sporulation temperatures (30, 37, 44 and 52°C) upon heat resistance of Bacillus subtilis was investigated.
Heat resistance was greater after higher sporulation temperatures. Relation of heat resistance and temperature of sporulation was not linear over all the range of temperatures tested. Heat resistance increased about tenfold in the range of 30–44°C. Sporulation at 52°C did not show any further increase in heat resistance.
This effect was constant over all the range of heating temperatures tested (100–120°C). z value remained constant ( z = 9°C).
Greater heat resistances at higher temperatures of sporulation were not due to selection of more heat resistant cells by a higher sporulation temperature. Spores obtained from cells incubated at 32 or 52°C always possessed heat resistances that corresponded to the sporulation temperature regardless of the incubation temperature of their vegetative cells. 相似文献
Heat resistance was greater after higher sporulation temperatures. Relation of heat resistance and temperature of sporulation was not linear over all the range of temperatures tested. Heat resistance increased about tenfold in the range of 30–44°C. Sporulation at 52°C did not show any further increase in heat resistance.
This effect was constant over all the range of heating temperatures tested (100–120°C). z value remained constant ( z = 9°C).
Greater heat resistances at higher temperatures of sporulation were not due to selection of more heat resistant cells by a higher sporulation temperature. Spores obtained from cells incubated at 32 or 52°C always possessed heat resistances that corresponded to the sporulation temperature regardless of the incubation temperature of their vegetative cells. 相似文献
9.
10.
Repression of biosynthetic enzyme synthesis in Pseudomonas putida is incomplete even when the bacteria are growing in a nutritionally complex environment. The synthesis of four of the enzymes of the arginine biosynthetic pathway (N-acetyl-alpha-glutamokinase/N-acetylglutamate-gamma-semialdehyde dehydrogenase, ornithine carbamoyltransferase and acetylornithine-delta-transaminase) could be repressed and derepressed, but the maximum difference observed between repressed and derepressed levels for any enzyme of the pathway was only 5-fold (for ornithine carbamoyltransferase). No repression of five enzymes of the pyrimidine biosynthetic pathway (aspartate carbamoyltransferase, dihydro-orotase, dihydro-orotate dehydrogenase, orotidine-5'-phosphate pyrophosphorylase and orotidine-5'-phosphate decarboxylase) could be detected on addition of pyrimidines to minimal asparagine cultures of P. putida A90, but a 1-5- to 2-fold degree of derepression was found following pyrimidine starvation of pyrimidine auxotrophic mutants of P. putida A90. Aspartate carbamoyltransferase in crude extracts of P. putida A90 was inhibited in vitro by (in order of efficiency) pyrophosphate, CTP, UTP and ATP, at limiting but not at saturating concentrations of carbamoyl phosphate. 相似文献