- 行业: Printing & publishing
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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 circular extrachromosomal genetic element that is ubiquitous in prokaryotes and has also been identified in a number of eukaryotes. In general, bacterial plasmids can be classified into two groups on the basis of the number of genes and functions they carry. The larger plasmids are deoxyribonucleic acid (DNA) molecules of around 100 kilobase (kb) pairs, which is sufficient to code for approximately 100 genes. There is usually a small number of copies of these plasmids per host chromosome, so that their replication must be precisely coordinated with the cell division cycle. Their replication genes are clustered within a small segment of the genome. Larger plasmids usually can mediate their own transfer from cell to cell by bacterial conjugation. The genes mediating transmissibility are clustered in a segment of approximately 25 kb. The other regions (around 70 kb) of these larger plasmids can accommodate as many as 70 additional genes which determine a variety of properties (see <b>table</b>). The plasmids in the second group are smaller in size, about 6–10 kb. These plasmids may harbor 6–10 genes and are usually present in multiple copies (10–20 per chromosome). Although the smaller plasmids do not carry transfer genes, many of them can be mobilized to recipient cells if a larger transmissible plasmid is present in the same host cell.
Industry:Science
A citrus fruit, <i>Citrus paradisi</i>. It apparently arose as a hybrid of shaddock or pummelo and sweet orange in the West Indies. Its first recorded mention was in Barbados in 1750, and the first use of the term grapefruit occurred in Jamaica in 1814. It was thought to have been introduced into Florida by Count Odelle Phillipe near Safety Harbor on Tampa Bay around 1823. The term grapefruit was derived from the tree's tendency to produce large clusters of fruit, as grape vines do.
Industry:Science
A class (also known as Filicineae) of the plant division Polypodiophyta containing a large group of plants commonly called ferns. They are widely distributed throughout the world with their greatest development in the moist tropics.
Industry:Science
A class (formerly Lycopodiopsida) of the division Lycophyta. It probably evolved in the Early Devonian from a zosterophyllopsid ancester; all six constituent taxonomic orders had probably evolved by the end of the Devonian.
Industry:Science
A class coextensive with the division Euglenophycota, comprising unicellular colorless or photosynthetic flagellates with very distinctive cytological characters. In protozoological classification, these organisms constitute an order, Euglenida, of the class Phytomastigophora. Although photosynthetic euglenoids are like Chlorophycota in containing chlorophyll <i>a</i> and <i>b</i>, in most other respects they are so different from those algae as to suggest an independent phylogenetic origin of their pigments. About 1000 species have been described and classified into about 40 genera and 6 orders.
Industry:Science
A class in the phylum Mollusca that is exclusively marine and contains the extant members—squids, cuttlefishes, octopuses, and the chambered nautiluses—and the fossil taxa—ammonoids, nautiloids, and belemnoids. The earliest known cephalopod fossils date to roughly 500 million years ago from the Upper Cambrian of northeast China. Fossilized external shells of the extinct subclass Ammonoidea and the nearly extinct subclass Nautiloidea are interpreted as indicating that these animals were shallow-living and slow-moving. Despite the thousands of species of such shelled cephalopods that have been recognized, all are extinct except for six species in two surviving genera, <i>Nautilus</i> and <i>Allonautilus</i>. Other living cephalopods, all predators in the subclass Coleoidea with internal shells, number over 725 species, with many more likely to be recognized.
Industry:Science
A class in the phylum Mollusca, comprising two orders, Gadilida and Dentaliida. The class is wholly marine; it is common and probably most diverse in the deep sea, and poorly represented in brackish, littoral, or estuarine habitats. Scaphopods are characterized by a tapering tubular shell with two apertures: the large ventral aperture that the foot extends out of and a small dorsal aperture. The tapering shells found in the Dentaliida give the class its common names tusk or tooth shells. Adult scaphopods range in length from about 3 to 150 mm. The shell consists of aragonite arranged in three or four layers.
Industry:Science
A class of algae (also known as Haptophyceae) in the chlorophyll <i>a-c</i> phyletic line (Chromophycota). In protozoological classification these organisms constitute an order, Prymnesiida or Haptomonadida, in the class Phytamastigophora. Most of the approximately 300 species of prymnesiophytes are biflagellate monads.
Industry:Science
A class of Bryozoa confined to fully marine water. The Stenolaemata include several thousand species distributed among four orders: Cystoporata, Trepostomata, Cryptostomata, and Cyclostomata (=Tubuliporata). The commonly recognized order Fenestrata likely is part of the Cryptostomata. First appearing late in the Early Ordovician, stenolaemates expanded quickly to dominate bryozoan assemblages through the Early Cretaceous. By mid-Cretaceous, the calcified gymnolaemate order Cheilostomata, which originated in the Late Jurassic, had increased in diversity and abundance to equal that of stenolaemates, eventually surpassing the stenolaemates, which are now a minor part of the bryozoan fauna in most marine environments.
Industry:Science
A class of bryozoans. Predominantly marine, gymnolaemates possess lophophores which are circular in basal outline and zooecia which are short, wide, vaselike or boxlike.
Industry:Science
