什么是弓箭
一种兵器,弓是一根用木头或其他有弹性的材料制成的狭板,把它弯起来并用弦绷紧;箭是一根尾部带羽毛的长木杆。把箭尾槽搭在弦上,然後向後拉箭,使弓产生足够的张力,松开後,箭即被推出。弓的材料从木头、骨头、金属到塑胶、纤维玻璃都有。箭头是用石头、骨头和金属制成。弓箭起源於史前时期。从古埃及时代到欧洲中世纪,在地中海一带和欧洲,弓是首要的兵器,在中国和日本使用的时间则更长些。匈奴、突厥、蒙古人,以及欧亚草原其他民族在打仗时精於骑射,骑马弓箭手是火药未发明前战争中最为致命的武器。弩,一种复合型的弓,和英格兰长弓使箭成为战场上令人生畏的飞行兵器。土耳其弓的威力对中世纪後期的战争也有巨大影响。在许多民族的文明史上,弓在军事上的重要性仅次於它作为狩猎器的价值。弓箭现在有时仍用在娱乐狩猎方面。亦请参阅archery。
bow and arrow
Weapon consisting of a strip of wood or other flexible material, bent and held in tension by a string. The arrow, a long wooden shaft with a pointed tip, is stabilized in flight by a feathered tail. The arrow is fitted to the string by a notch in the end of the shaft and is drawn back to produce tension in the bow, which propels the arrow when the string is released. Bow construction ranges from wood, bone, and metal to plastic and fiberglass; arrowheads have been made from stone, bone, and metal. The origins of the bow and arrow are prehistoric. The bow was a primary military weapon from Egyptian times through the Middle Ages in the Mediterranean world and Europe and even longer in China and Japan. The Huns, Turks, Mongols, and other peoples of the Eurasian steppes excelled in warfare as mounted archers; horse archers were the most deadly weapon system of pre-gunpowder warfare. The crossbow, the compound bow, and the English longbow made the arrow a formidable battlefield missile. The powerful Turkish bow had a great impact on warfare in the late Middle Ages. In many cultures, the bow's importance in warfare has been secondary to its value as a hunting weapon. It is still sometimes used for recreational hunting. See also archery.
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什么是农业中毒
农业、林业、牧业、渔业与养殖业生产过程中,接触有毒化学物质引起的中毒。农业从业人员接触各种有毒化学物质的机会较多,因此容易中毒。中毒有急、慢性,严重的中毒可导致死亡。有些毒物还可以引起肿瘤或子代畸形。在生产过程中,加强安全防护措施,能够有效地防止农业...
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什么是浸润
组织内侵入了异常的细胞或出现了正常情况下不应出现的机体细胞,以及某些病变组织向周围扩展的现象。在细胞内或间质中出现异常的物质、或原有的某些物质的堆积过多也称为浸润。有的变性或沉积也称为浸润。浸润大多为病理性的,但有时是为了治疗目的而人为的。它们...
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什么是羊水
充满羊膜腔位于胎体周围的液体。随着妊娠时期的不同,其来源、容量与组成亦有变化。妊娠早期羊水主要是由母体血浆通过胎膜进入羊膜腔的漏出液,澄清透明。妊娠中期起,胎儿尿液可能成为羊水的重要来源,此时羊水略混浊,并有白色小片状物质(脱落的毳毛、皮肤细胞、胎脂)悬...
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什么是六淫
自然界风、寒、暑、湿、燥、火六种致病因素的合称。“淫”有太过之意。风、寒、暑、湿、燥、火本指自然界六种不同的气候或环境状态,合称六气。若六气太过、不及或与季节时间不符,超过人体所能适应的限度,则成为致病因素,这种情况下的六气即成为六淫,或称六邪。六淫...