首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   40561篇
  免费   2417篇
  国内免费   286篇
林业   1917篇
农学   1538篇
基础科学   338篇
  5984篇
综合类   5787篇
农作物   1599篇
水产渔业   2047篇
畜牧兽医   20575篇
园艺   538篇
植物保护   2941篇
  2021年   435篇
  2020年   489篇
  2019年   515篇
  2018年   933篇
  2017年   970篇
  2016年   877篇
  2015年   710篇
  2014年   879篇
  2013年   1995篇
  2012年   1501篇
  2011年   1702篇
  2010年   1151篇
  2009年   1195篇
  2008年   1601篇
  2007年   1454篇
  2006年   1363篇
  2005年   1184篇
  2004年   1111篇
  2003年   1122篇
  2002年   977篇
  2001年   1287篇
  2000年   1257篇
  1999年   944篇
  1998年   399篇
  1997年   426篇
  1996年   352篇
  1995年   405篇
  1994年   349篇
  1992年   661篇
  1991年   783篇
  1990年   689篇
  1989年   726篇
  1988年   664篇
  1987年   627篇
  1986年   670篇
  1985年   593篇
  1984年   470篇
  1983年   416篇
  1979年   557篇
  1978年   433篇
  1977年   361篇
  1976年   371篇
  1975年   403篇
  1974年   460篇
  1973年   475篇
  1972年   453篇
  1970年   368篇
  1969年   403篇
  1968年   361篇
  1967年   359篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
Lead poisoning in Canada geese in Delaware   总被引:1,自引:0,他引:1  
  相似文献   
73.
74.
Sodium selenite was mixed in a commercial pig food so as to increase the original selenium content (0.126 ppm) by 1.2 ppm. The supplemented food was given to 7 pigs during 78 days. A control group of as many pigs was given the non-supplemented commercial food. The pigs were killed, starting 4 hours after the last selenium-supplemented food had been given and then with intervals during the next 14 days. Small but significant increases of tissue selenium were noticed in liver and striated muscle as compared with the control animals. The kidneys showed no increase.  相似文献   
75.
76.
77.
78.
1. An experiment was conducted to determine the effect of different dietary protein contents on the performance of naked neck (Na/na) and normally feathered (na/na) broilers.

2. Chicks from the two genotypes were reared in wire‐floored cages and divided at random into 3 groups. Birds were fed on high protein (HP, 12.99 MJ ME, 238 g crude protein/kg and 12.94 MJ ME, 216 g crude protein/kg from 0 to 3 and 3 to 7 weeks, respectively), medium protein (MP, 12.99 MJ ME, 219 g crude protein/kg and 12.87 MJ ME, 201 g crude protein/kg from 0 to 3 and 3 to 7 weeks), and low protein (LP, 12.94 MJ ME, 205 g crude protein/kg and 12.75 MJ ME, 184 g protein/kg from 0 to 3 and 3 to 7 weeks) diets.

3. The LP diets resulted in a significantly lower daily body weight gain of males from 0 to 3 weeks. Dietary protein content had no effect on body weight gain from 3 to 7 weeks, body weight at 7 weeks, and the food intake of birds. Carcase composition of birds from both genotypes was unaffected by dietary protein.

4. Naked neck birds had significandy higher body weights at 7 weeks. Yields of carcase and breast of Na/na males were significantly higher than those of na/na males. There were no significant differences between females from the two genotypes as regards carcase yield.

5. It was concluded that the dietary protein requirements of naked neck birds were similar to those for normally feathered birds.  相似文献   

79.
Four groups of five Romney lambs were treated by plunge dipping with one of four registered organophosphorus flystrike preventatives. Untreated lambs acted as controls. The sheep were challenged at weekly intervals with larval implants of organophosphate-susceptible and -resistant strains of Lucilia cuprina. All four treatments provided 19-21 weeks protection against susceptible larvae but chlorfenvinphos provided the longest protection (16-17 weeks), followed by propetamphos (15-16 weeks), dichlofenthion (10-13 weeks) and diazinon (9-13 weeks), against the resistant strain.  相似文献   
80.
The objective of this study was to determine if serum glutathione peroxidase activity reflects short-term changes in the selenium status of goats. Angora goat kids (n=14) were fed pelleted luceme containing 20 microg/kg of selenium, and treated orally with either selenium (0.1 mg/kg of liveweight weekly, as sodium selenate) or de-ionised water. Serum activity of glutathione peroxidase was increased in response to supplementation and differed from that of controls within 24 hours of supplementation. The change in serum glutathione peroxidase activity during the 21 days after the start of weekly supplementation closely followed changes in serum selenium concentration. The results of this study suggest that serum glutathione peroxidase activity reflects the short-term improvement in the selenium status of Angora goat kids following oral supplementation with sodium selenate.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号