- 行业: Printing & publishing
- Number of terms: 178089
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- Company Profile:
McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A chemical element, Y, atomic number 39, and atomic weight 88.905. Yttrium resembles the rare-earth elements closely. The stable isotope <sup>89</sup>Y constitutes 100% of the natural element, which is always found associated with the rare earths and is frequently classified as one.
Industry:Science
A chemical element, Yb, atomic number 70, and atomic weight 173.04. Ytterbium is a metal element of the rare-earth group. There are 7 naturally occurring stable isotopes.
Industry:Science
A chemical element, Zn, atomic number 30, and atomic weight 65.38. Zinc is a malleable, ductile, gray metal. Because of chemical similarities among zinc, cadmium, and mercury, these three metals are classed together in a transition-elements subgroup of the periodic table.
Industry:Science
A chemical element, Zr, atomic number 40, atomic weight 91.22. Its naturally occurring isotopes are 90, 91, 92, 94, and 96. Zirconium is one of the more abundant elements, and is widely distributed in the Earth's crust. Being very reactive chemically, it is found only in the combined state. Under most conditions, it bonds with oxygen in preference to any other element, and it occurs in the Earth's crust only as the oxide, ZrO<sub>2</sub>, baddeleyite, or as part of a complex of oxides as in zircon, elpidite, and eudialyte. Zircon is commercially the most important ore. Zirconium and hafnium are practically indistinguishable in chemical properties, and occur only together.
Industry:Science
A chemical group in which oxygen and hydrogen are bonded and act as a single entity. In inorganic chemistry the hydroxyl group is known as the hydroxide ion (OH<sup>−</sup>), and it is frequently bonded to metal cations, for example, sodium hydroxide (NaOH). In organic chemistry it frequently acts as a functional group, for example, in an alcohol (ROH, where R represents an alkyl group).
Industry:Science
A chemical manufacturing process in which chemical transformation takes place, that is, the product differs chemically from the starting materials. Most chemical manufacturing processes consist of a sequence of steps, each of which involves making some sort of change in either chemical makeup, concentration, phase state, energy level, or a combination of these, in the materials passing through the particular step. If the changes are of a strictly physical nature (for example, mixing, distillation, drying, filtration, adsorption, condensation), the step is referred to as a unit operation. If the changes are of a chemical nature, where conversion from one chemical species to another takes place (for example, combustion, polymerization, chlorination, fermentation, reduction, hydrolysis), the step is called a unit process. Some steps involve both, for example, gas absorption with an accompanying chemical reaction in the liquid phase. The term chemical conversion is used not only in describing overall processes involving chemical transformation, but in certain contexts as a synonym for the term unit process. The chemical process industry as a whole has tended to favor the former usage, while the petroleum industry has favored the latter.
Industry:Science
A chemical of biological origin, other than an enzyme, that plays an important causal role in a plant disease. Most pathotoxins are produced by plant pathogenic fungi or bacteria, but some are produced by higher plants, and one has been reported to be the product of an interaction between a plant and a bacterial pathogen. Some pathogen-produced pathotoxins are highly selective in that they cause severe damage and typical disease symptoms only on plants susceptible to the pathogens that produce them. Others are nonselective and are equally toxic to plants susceptible or resistant to the pathogen involved. A few pathotoxins are species-selective, and are damaging to many but not all plant species. In these instances, some plants resistant to the pathogen are sensitive to its toxic product.
Industry:Science
A chemical or physical process that results in the death of soil organisms. This control method affects many organisms, even though the elimination of only specific weeds, fungi, bacteria, viruses, nematodes, or pests is desirable. Even if complete sterilization is achieved, it is short lived since organisms will recolonize this biological vacuum quite rapidly. Soil sterilization can be achieved through both physical and chemical means. Physical control measures include steam and solar energy. Chemical control methods include herbicides and fumigants. Dielectric heating and gamma irradiation are used less frequently as soil sterilization methods. Composting can be used to sterilize organic materials mixed with soil, but it is not used for the sterilization of soil alone. Soil sterilization is used in greenhouse operations, the production of high-value or specialty crops, and the control of weeds.
Industry:Science
A chemical process in which a compound is converted to one or more products by heat. By this definition, reactions that occur by heating in the presence of a catalyst, or in the presence of air when oxidation is usually a simultaneous reaction, are excluded. The terms thermolysis or thermal reaction have been used in essentially the same sense as pyrolysis.
Industry:Science
A chemical process in which the catalyst is present in a separate phase. In the usual case, the catalyst is a solid, and the reactants and product are in gaseous or liquid phases.
Industry:Science
