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2 天前 · Grandparents' Day. Mother's Day is a celebration honoring the mother of the family or individual, as well as motherhood, maternal bonds, and the influence of mothers in society. It is celebrated on different days in many parts of the world, most commonly in March or May. It complements similar celebrations honoring family members, such as ...
23 小時前 · Photosynthesis ( / ˌfoʊtəˈsɪnθəsɪs / FOH-tə-SINTH-ə-sis) [1] is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their activities.
23 小時前 · Venus is the second planet from the Sun. It is a terrestrial planet and is the closest in mass and size to its orbital neighbour Earth. Venus is notable for having the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover. At the surface it has a mean temperature of 737 ...
1 天前 · The apostrophe (' or ’) is a punctuation mark, and sometimes a diacritical mark, in languages that use the Latin alphabet and some other alphabets. In English, the apostrophe is used for three basic purposes: The marking of the omission of one or more letters, e.g. the contraction of "do not" to "don't" The marking of possessive case of ...
23 小時前 · 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 ...
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 ...
1 天前 · Stephen William Hawking, CH, CBE, FRS, FRSA (8 January 1942 – 14 March 2018) was an English theoretical physicist, cosmologist, and author who was director of research at the Centre for Theoretical Cosmology at the University of Cambridge.[6][17][18] Between 1979 and 2009, he was the Lucasian Professor of Mathematics at Cambridge, widely ...
