如图所示的平面直角坐标系中,虚线OM与x轴成45°角,在OM与x轴之间(包括x轴

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问题:

如图所示的平面直角坐标系中,虚线OM与x轴成45°角,在OM与x轴之间(包括x轴)存在垂直纸面向里、磁感应强度大小为B的匀强磁场,在y轴与OM之间存在竖直向下、电场强度大小为E的匀强电场,有一个质量为m,电荷量为q的带正电的粒子以某速度沿x轴正方向从O点射入磁场区域并发生偏转,不计带电粒子的重力和空气阻力,在带电粒子进入磁场到第二次离开电场的过程中,求

(1)若带电粒子从O点以速度V1进入磁场区域,求带电粒子第一次离开磁场的位置到O点的距离?

(2)若带电粒子第二次离开电场时恰好经过O点,求粒子最初进入磁场时速度V的大小?并讨论当V变化时,粒子第二次离开电场时速度大小与V大小的关系.

考点:向心力牛顿第二定律带电粒子在电场中运动的综合应用带电粒子在匀强磁场中的运动
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治疗虚劳肺气虚证,应首选的方剂是()。

A.清燥救肺汤

B.玉屏风散

C.百合固金汤

D.补肺汤

E.当归补血汤

题型:问答题

某校现有学生x人,比十年前增加了20%,则该校十年前的学生数是______.

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中新社2008年9月9日电  昨日沙尘暴突袭了敦煌、瓜州和玉门,风沙最大时局部地区能见度仅有400米,最小能见度仅有切米,这是玉门地区人秋第一场沙尘暴天气。结合我国沙尘天气分布图、沙尘暴路径示意图,回答问题。

图2一9

(l)人类不合理的生产活动是沙尘暴频发的重要原因。将下列备选答案的字母代号填人图2一10中的适当位置。

A.燃烧矿物燃料B.土质疏松C.风力加大D.二氧化碳增加E.过度放牧F.过度开垦G.气候变暖变干

图2一10

(2)从干湿状况看,沙尘暴发生的地区属于我国的____和____地区。

(3)近半个世纪以来,我国沙尘暴的发生呈现的趋势是________。

(4)试分析沙尘暴路径呈西北一东南走向的原因。

(5)近年来,我国北方地区沙尘暴现象日益加剧,分析主要原因有哪些?

(6)为了制止强沙尘暴次数增多和沙化速度加快的趋势,应采取的积极有效的措施是

A.开采地下水灌溉,变沙地为耕地和草地

B.在干旱地区减少耕地,扩大牧场,发展畜牧业

C.采取适当办法调整当地产业结构,以减轻对生态环境的压力

D.禁止干旱地区任何经济活动的开展,以保护当地脆弱的生态环境

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I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop"

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) She had only one small, flat bag with a few candies—fiftycent candies I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

8().

A.effort 

B.room 

C.time 

D.money

题型:问答题

典型的缺铁性贫血,红细胞呈现明显的()

A.大细胞低色素性

B.大细胞高色素性

C.小细胞低色素性

D.小细胞高色素性

E.正常细胞性

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