问题 单项选择题

下列关于浸提方法应用的叙述,不正确的是()

A.渗漉法适用于有效成分含量较低的药材浸出

B.煎煮法广泛用于各类药材的浸提

C.浸渍法适用于黏性药材的浸提

D.水蒸气蒸馏法常用于含挥发性成分药材的提取

E.渗漉法不宜用于无组织结构药材的浸出

答案

参考答案:B

解析:渗漉法适用于贵重药材、毒性药材及高浓度制剂;也可用于有效成分含量较低药材的提取。但对新鲜药材、易膨胀的药材、无组织结构的药材不适用。因此选项A和E都是正确的。浸渍法适用于黏性药材、无组织结构的药材、新鲜及易于膨胀的药材、价格低廉的芳香性药材的浸提;水蒸气蒸馏法适用于含有挥发性成分的药材,因此选项C和D也是正确的。煎煮法适用于能溶于水,且对湿、热较稳定的有效成分的浸提,并非广泛用于各类药材,因此选项B是错误的。故选B

填空题
单项选择题

Immigrants are consumers as well as producers, so they create jobs as well as taking them. And the work they do need not be at the expense of native workers. Immigrants often hold jobs that natives are unwilling to accept at any feasible wage.

Also, immigrants sometimes help to keep industries viable (能存活的) that would otherwise disappear altogether, causing employment to fall. This was the conclusion of a study of the Los Angeles garment industry in the 1970s and 1980s. And when immigrants working for low wages do put downward pressure on natives’ wages, they may raise the (real) wages of natives in general by keeping prices lower than they otherwise would be.

In theory, then, the net effect of immigration on native wages is uncertain. Unfortunately, most of the empirical (经验主义的) research on whether immigrants make natives worse off in practice is also inconclusive except the effect, one way or the other, seems small. Most of this research has been done in America: if there were any marked influence on wages, that is where you would expect to find it, given the scale of immigration and the tendency of the newcomers to concentrate in certain areas. But most studies have compared wages and employment in areas with many immigrants to wages and employment in areas with few. For instance, one examined the impact of sudden and notorious inflow of refugees to Miami from the Cuban port of Mariel in 1980. Within the space of a few months, 125000 people had arrived, increasing Miami’s labor force by 7%. Yet the study concluded that wages and employment among the city’s natives, including the unskilled, were virtually unaffected. Another study examined the effect of immigration on wages and employment of those at the bottom of the jobs ladder-unskilled blacks and Hispanics. It found that a doubling of the rate of immigration had no detectable effect on natives.

The most recent work, admittedly, has tended to question these findings. Using more detailed statistics and more sophisticated methods than the earlier studies, this work has tended to find that immigrants’ wages take longer to rise to the level of the natives’ wages than has been supposed. This implies a more persistent downward pressure on the host economy’s labor market.

Typically these studies find that immigration does depress unskilled natives’ wages to a small extent. But nearly all economists would agree that the effects of immigration are insignificant in relation to other influences.

It is certain, according to empirical research, that ().

A. immigration has a positive effect on native wages

B. immigration makes unskilled blacks and Hispanics worse off

C. immigration has only a small effect on native wages

D. immigration has a marked influence on natives in areas with dense immigrant population