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1 天前 · Carbon (from Latin carbo 'coal') is a chemical element; it has symbol C and atomic number 6. It is nonmetallic and tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 electrons. It belongs to group 14 of the periodic table.[16] Carbon makes up about 0.025 percent of Earth's ...
1 天前 · Phosphorus is a chemical element; it has symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth. It has a concentration in the Earth's crust of about one gram per kilogram (compare copper at about ...
- white, red and violet are waxy, black is metallic-looking
- white, red, violet, black and others (see Allotropes of phosphorus)
- 5.2 (silicon = 100)
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2 天前 · A protein is a polyamide. Secondary structure: regularly repeating local structures stabilized by hydrogen bonds. The most common examples are the α-helix, β-sheet and turns. Because secondary structures are local, many regions of different secondary structure can be present in the same protein molecule.
19 小時前 · Richard Phillips Feynman (/ ˈ f aɪ n m ə n /; May 11, 1918 – February 15, 1988) was an American theoretical physicist, known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, as well as his work in particle physics for which he proposed the parton model.
1 天前 · Eugenics (/juːˈdʒɛnɪks/ yoo-JEN-iks; from Ancient Greek εύ̃ (eû) 'good, well', and -γενής (genḗs) 'come into being, growing')[1] is a set of beliefs and practices that aim to improve the genetic quality of a human population.[2][3][4] Historically, eugenicists have attempted to alter human gene pools by excluding people and ...
3 天前 · LGBT is an initialism that stands for "lesbian, gay, bisexual, and transgender". It may refer to anyone who is non-heterosexual, non-heteroromantic, or non-cisgender, instead of exclusively to people who are lesbian, gay, bisexual, or transgender. A variant, LGBTQ, adds the letter Q for those who identify as queer (which can be synonymous with LGBT) or are questioning their sexual or gender ...
2 天前 · Infobox references. Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling ), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water.
