在研究物体的运动时,下列物体可看作质点的是( ) A.研究在校运动会上跳高运动员

题型:选择题

问题:

在研究物体的运动时,下列物体可看作质点的是(  )

A.研究在校运动会上跳高运动员的过杆动作

B.研究火车通过长江大桥所需的时间

C.研究跳水运动员的入水动作.

D.研究”婵娥”二号卫星的运动轨迹

考点:质点
题型:选择题

选择性蛋白尿的特点()

A.24小时蛋白量超过3.5g

B.多为大分子蛋白尿

C.多为球蛋白

D.以白蛋白为主的蛋白尿

E.24小时尿蛋白量<150mg

题型:选择题

违约

题型:选择题

与模拟微波、电力线载波相比,数字微波通信具有()等特点,目前是电力系统主要通信方式之一。

A.频带宽

B.成本低

C.通信容量大

D.抗干扰能力强

题型:选择题

(46) For centuries the smoking of tobacco in cigarettes, cigars, and pipes has produced controversy over possible health hazards, but only since the 1950’s has sufficient scientific evidence accumulated to make possible a thorough evaluation of the health risk.

Scientific investigation of the relationship of smoking and health gained impetus after the beginning of the 20th century, then an increase in lung cancer was noted. As the use of tobacco increased, studies improved. (47) Although some gaps in knowledge still exist, the information now available is sufficient to permit making sound judgments, based on the converging lines of evidence.

(48) Investigators have directed their principal consideration to cigarette smoking because the health consequences attributed to it far exceed those due to smoking cigars and pipes. The widespread popularity of cigarettes is comparatively recent in man’s use of tobacco. The smoking pattern began to change at the beginning of the 20th century. Since then, cigarettes have steadily become more popular than cigars and pipes. (49) In the United States. per capita cigarette consumption — calculated for all persons 15 years of age and older, regardless of whether they smoked—rose from 49 per year in 1900 to 3,888 in 1960. Per capita consumption of cigars, pipe tobacco, and chewing tobacco declined sharply in the same period. Data presented in 1966 indicated a sharp reduction in cigarette smoking in the United States for men under the age of 55 with the trend continuing to 1970.

Further increase in cigarette consumption for women of all ages was reported in 1966 and no further increase was noted 1966 and 1970. However, in 1970 overall per capita cigarette consumption rose.

By 1962 the Royal College of Physicians of London reported:" Cigarette smoking is a cause of lung cancer and bronchitis, and various other less common diseases. It delays healing of gastric and duodenal ulcers." Some scientists, however, expressed dissenting opinions.

The most widely publicized report in the United States was issued in 1964 by the Surgeon General’s Advisory Committee on Smoking and Health. (50) The principal judgment in the committee’s 150,000-word report was: "Cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate remedial action." The smokers of pipes and cigars were found to incur less health risk. However, the incidence of cancer and heart disease among them was found to be greater than among nonsmokers.

(50) The principal judgment in the committee’s 150,000-word report was: "Cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate remedial action."

题型:选择题

大气采样点的采样高度,一般距地面()为宜。

A.3m

B.1.5m

C.3.5

D.2.5m

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