氮素有效性比率 nitrogen availability ratio
氮素有效性比率 nitrogen availability ratio
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Text 3Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a dive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper.The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth in seawater, so that at 30 meters in seawater a diver is exposed to a pressure of about 4 atmospheres. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meters are present at five times their usual pressure. Nitrogen, which composes 80 per cent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmospheres, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen cause under these pressurized helium does not exert a similar narcotic effect.As a scuba diver descends, the pressure of nitrogen in the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. The reverse occurs when the diver surfaces; the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints.Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend and even rupture. This condition is called air embolism. To avoid this event, a diver must ascend slowly, never at a rate exceeding the rise of the exhaled air bubbles, and must exhale during as- cent.31. What does the passage mainly discuss?A) The equipment divers use.B) The effects of pressure on gases in the human body.C) How to prepare for a deep dive.D) The symptoms of nitrogen bubbles in the bloodstream.
It can be inferred from the passage that which of the following presents the greatest danger to diver?A) Pressurized helium.B) Nitrogen diffusion.C) Nitrogen bubbles.D) An air embolism.
流动性比率是现金规划中的重要指标，下列关于流动性比率的说法正确的是（）。A、流动性比率=流动性资产／每月支出B、流动性比率=净资产／总资产C、流动性比率=结余／税后收入D、流动性比率=投资资产／净资产
单选题流动性比率是现金规划中的重要指标，下列关于流动性比率的说法正确的是（）。A流动性比率=流动性资产／每月支出B流动性比率=净资产／总资产C流动性比率=结余／税后收入D流动性比率=投资资产／净资产
单选题The three basic elements necessary for any fire are （）.Aheat, gas, and flamesBfuel, heat, and oxygenCheat, nitrogen, and fuelDfuel oil, nitrogen, and oxygen
填空题土壤氮素的有效化过程包括（）、（）、（）三种。