a.

• n.
  • a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation

    同义词： angstrom angstrom unit A

  • any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes

    同义词： vitamin A antiophthalmic factor axerophthol A

  • one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)

    同义词： deoxyadenosine monophosphate A

  • (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA

    同义词： adenine A

  • the basic unit of electric current adopted under the Systeme International d'Unites

    同义词： ampere amp A

  • the 1st letter of the Roman alphabet

    同义词： A letter a

  • the blood group whose red cells carry the A antigen

    同义词： A type A group A

以上来源于: WordNet