收费全文 | 7604篇 |
免费 | 495篇 |
国内免费 | 5篇 |
林业 | 420篇 |
农学 | 327篇 |
基础科学 | 16篇 |
1428篇 | |
综合类 | 839篇 |
农作物 | 684篇 |
水产渔业 | 606篇 |
畜牧兽医 | 3168篇 |
园艺 | 119篇 |
植物保护 | 497篇 |
2023年 | 42篇 |
2022年 | 108篇 |
2021年 | 162篇 |
2020年 | 180篇 |
2019年 | 223篇 |
2018年 | 208篇 |
2017年 | 215篇 |
2016年 | 269篇 |
2015年 | 242篇 |
2014年 | 280篇 |
2013年 | 406篇 |
2012年 | 504篇 |
2011年 | 613篇 |
2010年 | 323篇 |
2009年 | 287篇 |
2008年 | 446篇 |
2007年 | 453篇 |
2006年 | 403篇 |
2005年 | 380篇 |
2004年 | 353篇 |
2003年 | 306篇 |
2002年 | 299篇 |
2001年 | 167篇 |
2000年 | 139篇 |
1999年 | 97篇 |
1998年 | 45篇 |
1997年 | 32篇 |
1996年 | 36篇 |
1995年 | 32篇 |
1994年 | 25篇 |
1993年 | 32篇 |
1992年 | 37篇 |
1991年 | 37篇 |
1990年 | 35篇 |
1989年 | 45篇 |
1988年 | 39篇 |
1987年 | 50篇 |
1986年 | 21篇 |
1985年 | 39篇 |
1984年 | 29篇 |
1983年 | 37篇 |
1982年 | 20篇 |
1981年 | 27篇 |
1978年 | 28篇 |
1977年 | 24篇 |
1976年 | 29篇 |
1974年 | 26篇 |
1973年 | 28篇 |
1972年 | 30篇 |
1971年 | 18篇 |
2. Age at first egg, body‐weight gain and egg production were affected by energy allowance. Birds on the lower energy allowances came into lay later than birds on the higher energy allowances and at a lower body weight.
3. Body‐weight gain decreased with decreasing energy allowance. The decrease in egg output in response to decreasing energy allowance resulted from more birds ceasing to lay and fewer birds laying on more than 3 d per week. Similar changes in the distribution of rates of lay were observed on each treatment as the flock aged.
4. The relationship between body‐weight gain and egg number on each treatment was negative from 21 to 36 weeks, but became less consistent with age.
5. Protein intake had little effect on body weight. At the lowest energy allowance, egg number and egg weight decreased with increasing protein allowance. This effect was not observed on the higher energy allowances. 相似文献
2. Body‐weight gain and carcass fat and water content increased and fertility decreased with increasing energy allowance. Maximum egg production occurred at an energy intake of 1.73 MJ AME/bird d.
3. Differences in egg weight and hatchability were related to differences in both energy and protein intake. The highest egg weight occurred at the highest allowance of energy and protein. Hatchability was depressed where the daily allowances of protein and energy were in a ratio of more than 15 g protein: 1 MJ AME.
4. Apart from egg size no significant effects on reproductive performance were observed when dietary protein intake was varied from 27 to 19.5 g/bird d.
5. Requirements of broiler breeder hens for protein during lay may be lower than previously thought. For the strain used a protein intake of 19.5 g/bird d appeared adequate provided essential amino acid concentrations were maintained.
6. The close relationships between body weight and energy allowance and the latter and egg production make body‐weight gain a useful guide to management. A body‐weight gain of about 1.1 kg from 21 to 36 weeks of age was associated with optimum performance in this study. 相似文献