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2 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 ...
2 天前 · 1. /. 3. A quark ( / kwɔːrk, kwɑːrk /) is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. [1] All commonly observable matter is composed of up quarks, down quarks and electrons.
- 1st, 2nd, 3rd
- fermionic
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5 天前 · Structure of a typical L-alpha-amino acid in the "neutral" form Amino acids are organic compounds that contain both amino and carboxylic acid functional groups.[1] Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins.[2] Only these 22 appear in the genetic code of life.[3 ...
1 天前 · The number π (/ p aɪ /; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159.The number π appears in many formulae across mathematics and physics.It is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although fractions such as are commonly used to ...
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 ...
2 天前 · Four UN members (Cuba, Liechtenstein, Monaco and North Korea) do not belong to the IMF hence their economies are not ranked below. Kosovo, despite not being a member of the United Nations, is a member of IMF. Taiwan is not a IMF member but it is still listed in the official IMF indices. Several leading GDP-per-capita (nominal) jurisdictions may ...
2 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 ...
