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pregnancy
(Encyclopedia)pregnancy, period of time between fertilization of the ovum (conception) and birth, during which mammals carry their developing young in the uterus (see embryo). The average duration of pregnancy in h...solid waste
(Encyclopedia)solid waste, discarded materials other than fluids. In the United States in 1996, nearly 210 million tons—about 4.3 lb. (2 kg) per person daily (up from 2.7 lb./1.2 kg in 1960)—were collected and ...refraction
(Encyclopedia)refraction, in physics, deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass. O...AIDS, in medicine
(Encyclopedia)AIDS or acquired immunodeficiency syndrome, fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neuro...hockey, ice
(Encyclopedia)hockey, ice, team sport in which players use sticks to propel a hard, round disk into a net-backed goal. The NHL long regarded itself as the world's elite, but the overwhelming superiority of the ...tariff
(Encyclopedia)tariff, tax on imported and, more rarely, exported goods. It is also called a customs duty. Tariffs may be distinguished from other taxes in that their predominant purpose is not financial but economi...type
(Encyclopedia)type, for printing, was invented in China (c.1040), using woodblocks. Related devices, such as seals and stamps for making impressions in clay, had been used in ancient times in Babylon and elsewhere....phosphorus
(Encyclopedia)phosphorus fŏsˈfərəs [key] [Gr.,=light-bearing], nonmetallic chemical element; symbol P; at. no. 15; at. wt. 30.97376; m.p. 44.1℃; b.p. about 280℃; sp. gr. 1.82 at 20℃; valence −3, +3, or ...oxygen
(Encyclopedia)oxygen, gaseous chemical element; symbol O; at. no. 8; interval in which at. wt. ranges 15.99903–15.99977; m.p. −218.4℃; b.p. −182.962℃; density 1.429 grams per liter at STP; valence −2. T...ammonia
(Encyclopedia)ammonia, chemical compound, NH3, colorless gas that is about one half as dense as air at ordinary temperatures and pressures. It has a characteristic pungent, penetrating odor. Ammonia forms a minute ...Browse by Subject
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