- 行业: Library & information science
- Number of terms: 152252
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The National Library of Medicine (NLM), on the campus of the National Institutes of Health in Bethesda, Maryland, is the world's largest medical library. The Library collects materials and provides information and research services in all areas of biomedicine and health care.
Analytic study of epidemiological study in which subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome. The main feature of the method is observation of a large population for a prolonged period (years), with comparison of incidence rates of the given disease in groups that differ in exposure levels.
Industry:Biology; Chemistry
Equation expressing the build up and decay in concentration of a substance (usually in plasma) based on first order uptake and elimination in a one compartment model, having the form
C = (ƒDκ<sub>a</sub>/V(κ<sub>a</sub> - κ<sub>e</sub>))(exp(-κ<sub>e</sub>t) - exp(-κ<sub>a</sub>t))
where C is the concentration and D the dose of the substance, ƒ the fraction absorbed, and V the volume of distribution. κ<sub>a</sub> and κ<sub>e</sub> are the first order rate constants of uptake and elimination, respectively, and t is time.
Industry:Biology; Chemistry
Potential for a substance to come in contact with a living organism and then interact with it. This may lead to absorption.
Note: A substance trapped inside an insoluble particle is not bio-accessible although substances on the surface of the same particle are accessible and may also be bio-available. Bio-accessibility, like bio-availability, is a function of both chemical speciation and biological properties. Even surface-bound substances may not be accessible to organisms which require the substances to be in solution.
Industry:Biology; Chemistry
Estimate of the proportion of a population which dies during a specified period. The numerator is the number of persons dying during the period; the denominator is the size of the population, usually estimated as the mid-year population. The death rate in a population is generally calculated by the formula:
10<sup>n</sup> (Number of deaths during a specified period) / (Number of persons at risk of dying during the period)
where n is usually either 3 or 5 giving rates per 1 000 or per 100 000 people in the population studied.
Industry:Biology; Chemistry
Known amount of a homogeneous material, assumed to be taken with negligible sampling error.
Note 1: The term is usually applied to fluids.
Note 2: The term “aliquot” is usually used when the fractional part is an exact divisor of the whole; the term “aliquant” has been used when the fractional part is not an exact divisor of the whole (e.g., a 15 mL portion is an aliquant of 100 mL).
Note 3: When an aliquot is taken of a laboratory sample or test sample or the sample is otherwise subdivided, the samples have been called split samples.
Industry:Biology; Chemistry
Member of a superfamily of heme-containing mono-oxygenases involved in xenobiotic metabolism, cholesterol biosynthesis, and steroidogenesis, in eukaryotic organisms found mainly in the endoplasmic reticulum and inner mitochondrial membrane of cells. ‘P-450’ refers to the observation that a solution of this enzyme exposed to carbon monoxide strongly absorbs light at a wavelength of 450nm compared with the unexposed solution, (a difference spectrum caused by a thiolate in the axial position of the heme opposite to the carbon monoxide ligand).
Industry:Biology; Chemistry
1. Substance in appreciable amount which, when associated with a trace of a specified substance, will carry the trace with it through a chemical or physical process.
2. Person who is heterozygous, that is carries only one allele, for a recessive genetic character leading to disease, and hence does not, under most circumstances, display the disease phenotype but can pass it on to the next generation.
3. Gas, liquid, or solid substance (often in particulate form) used to absorb, adsorb, dilute or suspend a substance to facilitate its transfer from one medium to another.
Industry:Biology; Chemistry
1. Volume of blood or plasma or mass of an organ effectively cleared of a substance by elimination (metabolism and excretion) divided by time of elimination.
2. (in pulmonary toxicology) Volume or mass of lung cleared divided by time of elimination; used qualitatively to describe removal of any inhaled substance which deposits on the lining surface of the lung.
3. (in renal toxicology) Quantification of the removal of a substance by the kidneys by the processes of filtration and secretion; clearance is calculated by relating the rate of renal excretion to the plasma concentration.
Industry:Biology; Chemistry
1. Process of one material (absorbate) being retained by another (absorbent). Note: The process may be the physical solution of a gas, liquid, or solid in a liquid, attachment of molecules of a gas, vapor, liquid, or dissolved substance to a solid surface by physical forces, etc.
2. Transfer of some or all of the energy of radiation to matter which it traverses. Note: Absorption of light at bands of characteristic wavelengths is used as an analytical method in spectrophotometry to identify the chemical nature of molecules, atoms or ions and to measure the concentrations of these species.
Industry:Biology; Chemistry
Amount concentration of oxygen taken up through the respiratory activity of micro-organisms growing on organic compounds present when incubated at a specified temperature (usually 20° C) for a fixed period (usually 5 days). It is regarded as a measure of that organic pollution of water which can be degraded biologically but includes the oxidation of inorganic material such as sulfide and iron(II). The empirical test used in the laboratory to determine BOD also measures the oxygen used to oxidize reduced forms of nitrogen unless their oxidation is prevented by an inhibitor such as allyl thiourea.
Industry:Biology; Chemistry
