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   113090篇
  免费   6360篇
  国内免费   64篇
林业   4617篇
农学   3777篇
基础科学   669篇
  13556篇
综合类   18787篇
农作物   4023篇
水产渔业   5775篇
畜牧兽医   59624篇
园艺   1344篇
植物保护   7342篇
  2018年   1565篇
  2017年   1729篇
  2016年   1596篇
  2015年   1333篇
  2014年   1637篇
  2013年   4182篇
  2012年   3010篇
  2011年   3615篇
  2010年   2490篇
  2009年   2470篇
  2008年   3646篇
  2007年   3478篇
  2006年   3237篇
  2005年   3056篇
  2004年   2977篇
  2003年   3098篇
  2002年   2768篇
  2001年   3786篇
  2000年   3831篇
  1999年   2964篇
  1998年   1177篇
  1997年   1174篇
  1996年   1063篇
  1995年   1350篇
  1994年   1154篇
  1993年   1110篇
  1992年   2404篇
  1991年   2594篇
  1990年   2574篇
  1989年   2493篇
  1988年   2312篇
  1987年   2351篇
  1986年   2346篇
  1985年   2203篇
  1984年   1907篇
  1983年   1628篇
  1982年   1089篇
  1979年   1694篇
  1978年   1307篇
  1977年   1204篇
  1976年   1123篇
  1975年   1218篇
  1974年   1462篇
  1973年   1486篇
  1972年   1454篇
  1971年   1326篇
  1970年   1281篇
  1969年   1282篇
  1968年   1043篇
  1967年   1153篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
992.
1. The effect of reducing food intake to 75% of the ad libitum intake was determined from hatching to 8 weeks in young Light Sussex chickens.

2. Restricted birds were lighter throughout the experiment.

3. Relative adrenal weight tended to be greater in restricted birds but the difference decreased with time.

4. There was no depletion of adrenal cholesterol: from week 5 there was a significantly greater amount in the adrenals of restricted birds.

5. After 1 week of restriction plasma corticosterone concentration was 73% greater than in controls. It decreased progressively, falling within the normal range at 5 weeks.

6. Restricted birds were hypoglycaemic from weeks 2 to 7 and hyper‐lipacidaemic throughout. A negative correlation between plasma glucose and free fatty acids was found.  相似文献   

993.
1. Starter diets containing either maize or salseed meal to replace the maize were fed to chicks over a period of 2 weeks.

2. Growth rate, food intake, food utilisation and proportion of dietary nitrogen retained were much poorer in chicks receiving salseed meal.

3. The chicks receiving salseed meal developed pathological lesions in liver and kidney.

4. The red blood cell count, white blood cell count, haemoglobin concentration and packed cell volume of the chicks receiving salseed meal were lower than those of chicks receiving maize.

5. The apparent metabolisable energy value of salseed meal was determined as 6.83 MJ/kg.  相似文献   

994.
Tobin TR 《Science (New York, N.Y.)》1981,214(4525):1147-1149
Male American cockroaches walk a zigzag path upwind toward a source of female sex pheromone. Although the maximum width of the pathway is regulated by the width of an odor plume, many turns are made before the edge of a wide plume is encountered. In addition to the pheromone regulation of the insect's orientation movements, an internal mechanism appears to influence the zigzag turning pattern.  相似文献   
995.
Following the discovery of the 11-year solar cycle signal in earth rotation, linear techniques were employed to investigate the amplitude and phase of the difference between ephemeris time and universal time (DeltaT) as a function of time. The amplitude is nonstationary. This difference was related to Delta(LOD), the difference between the length of day and its nominal value. The 11-year term in Delta(LOD) was 0.8 millisecond at the close of the 18th century and decreased below noise level from 1840 to 1860. From 1875 to 1925, Delta(LOD) was about 0.16 millisecond, and it decreased to about 0.08 millisecond by the 1950's. Except for anomalous behavior from 1797 to 1838, DeltaT lags sunspot numbers by 3.0 +/- 0.4 years. Since DeltaT lags Delta(LOD) by 2.7 years, the result is that Delta(LOD) is approximately in phase with sunspot numbers.  相似文献   
996.
997.
998.
999.
1000.
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