收费全文 | 131936篇 |
免费 | 7395篇 |
国内免费 | 88篇 |
林业 | 5376篇 |
农学 | 4269篇 |
基础科学 | 831篇 |
16998篇 | |
综合类 | 21322篇 |
农作物 | 5276篇 |
水产渔业 | 6684篇 |
畜牧兽医 | 67881篇 |
园艺 | 1800篇 |
植物保护 | 8982篇 |
2020年 | 1177篇 |
2019年 | 1374篇 |
2018年 | 2030篇 |
2017年 | 2330篇 |
2016年 | 2094篇 |
2015年 | 1742篇 |
2014年 | 2224篇 |
2013年 | 5290篇 |
2012年 | 4114篇 |
2011年 | 5093篇 |
2010年 | 3245篇 |
2009年 | 3389篇 |
2008年 | 4972篇 |
2007年 | 4666篇 |
2006年 | 4353篇 |
2005年 | 4088篇 |
2004年 | 3850篇 |
2003年 | 3973篇 |
2002年 | 3542篇 |
2001年 | 4150篇 |
2000年 | 4252篇 |
1999年 | 3372篇 |
1998年 | 1474篇 |
1997年 | 1387篇 |
1996年 | 1288篇 |
1995年 | 1529篇 |
1994年 | 1358篇 |
1993年 | 1222篇 |
1992年 | 2580篇 |
1991年 | 2700篇 |
1990年 | 2584篇 |
1989年 | 2602篇 |
1988年 | 2368篇 |
1987年 | 2348篇 |
1986年 | 2427篇 |
1985年 | 2340篇 |
1984年 | 1881篇 |
1983年 | 1677篇 |
1982年 | 1149篇 |
1979年 | 1748篇 |
1978年 | 1397篇 |
1977年 | 1151篇 |
1976年 | 1212篇 |
1975年 | 1292篇 |
1974年 | 1500篇 |
1973年 | 1514篇 |
1972年 | 1405篇 |
1971年 | 1304篇 |
1970年 | 1250篇 |
1969年 | 1283篇 |
2. The responses of birds pretreated as described above to a single injection of corticotrophin (30 IU/kg) were determined.
3. A similar degree of hyperglycaemia had developed in both groups after 2 h but thereafter the responses differed: the concentration of plasma glucose did not increase further in those pretreated with corticotrophin and had begun to decrease at 6 h, whereas that of the birds pretreated with saline increased progressively.
4. The concentrations of plasma corticosterone had increased similarly in the two groups to a peak at 2 h but there was a significantly more rapid decrease in the birds pretreated with corticotrophin.
5. Both groups showed a transient hypercholesteraemia but the increase was significant only in the group that had previously received saline.
6. There were decreases in the concentrations of adrenal cholesterol in both groups. The decrease, in absolute terms, was 2–4 times greater in the group receiving corticotrophin for the first time: percentage changes were similar, however. 相似文献
2. Realised heritability estimates calculated after five generations of selection were : 0–37 + 0.04 for weight gain (WG); 0.44 + 0.05 for food consumption (FC); 0.21 + 0.04 for food conversion ratio (FCR).
3. Realised genetic correlation estimates were: WG and FC, +0.71 ±006; WG and FCR, ‐0.40±0.09; FC and FCR, +0.27 + 0.09.
4. Zero‐generation heritability and genetic correlation estimates were greater than the realised estimates, and sex linkage appeared to be important in the expression of all three traits.
5. The genetic correlation between FC and FCR was asymmetrical with considerable positive response in FCR in line F (rg = +0.79) but negligible response in FC in line E (rg = —0.01).
6. There was an apparent plateau in response in FCR in line E from the third to the fifth selected generations. 相似文献