收费全文 | 315022篇 |
免费 | 17026篇 |
国内免费 | 1436篇 |
林业 | 24903篇 |
农学 | 14575篇 |
基础科学 | 3255篇 |
47948篇 | |
综合类 | 41890篇 |
农作物 | 17879篇 |
水产渔业 | 18292篇 |
畜牧兽医 | 132060篇 |
园艺 | 6776篇 |
植物保护 | 25906篇 |
2020年 | 3147篇 |
2019年 | 3950篇 |
2018年 | 4642篇 |
2017年 | 5172篇 |
2016年 | 5231篇 |
2015年 | 4714篇 |
2014年 | 6040篇 |
2013年 | 16699篇 |
2012年 | 8567篇 |
2011年 | 11149篇 |
2010年 | 8633篇 |
2009年 | 8957篇 |
2008年 | 10248篇 |
2007年 | 9424篇 |
2006年 | 9519篇 |
2005年 | 8827篇 |
2004年 | 8455篇 |
2003年 | 8256篇 |
2002年 | 7466篇 |
2001年 | 8178篇 |
2000年 | 8006篇 |
1999年 | 6911篇 |
1998年 | 4370篇 |
1997年 | 4390篇 |
1996年 | 4116篇 |
1995年 | 4754篇 |
1994年 | 4156篇 |
1993年 | 3867篇 |
1992年 | 5525篇 |
1991年 | 5837篇 |
1990年 | 5572篇 |
1989年 | 5492篇 |
1988年 | 4915篇 |
1987年 | 4974篇 |
1986年 | 5010篇 |
1985年 | 5091篇 |
1984年 | 4584篇 |
1983年 | 4154篇 |
1982年 | 3280篇 |
1981年 | 3086篇 |
1980年 | 3079篇 |
1979年 | 4094篇 |
1978年 | 3540篇 |
1977年 | 3166篇 |
1976年 | 3097篇 |
1975年 | 3044篇 |
1974年 | 3420篇 |
1973年 | 3366篇 |
1972年 | 3037篇 |
1971年 | 2963篇 |
2. Challenge with T‐strain IBV decreased body weight and induced kidney hypertrophy and kidney asymmetry.
3. Haematocrit was reduced in birds challenged with the Australian T‐strain IBV and plasma uric acid was elevated in unvaccinated birds exposed to the IBV challenge.
4. Challenge with T‐strain IBV caused significant increases in urinary water losses, accompanied by decreased urine osmolality and increased fractional excretion of sodium, calcium and potassium.
5. Vaccination at 1‐d‐old with Vic S‐strain IBV provided a limited degree of protection against an heterologous challenge with T‐strain IBV at 15 d of age. 相似文献
2. Xylanase supplementation improved food conversion ratios by 2·2–2·9% and body weight gain by 0·2–2·5%. This was independent of wheat characteristics but slightly dependent on the wheat content of the diet. These effects were related to a lowering of digesta viscosity.
3. Differences in extract viscosity of wheat were not reflected in broiler digesta viscosity.
4. Reduction of digesta viscosity resulted in only a slight improvement of litter score. Reduced intestinal viscosity decreased relative pancreas weight and to a lesser extent relative small intestinal weight.
5. Baking quality wheat Baldus gave better performance than the feed quality wheats Apollo and Slejpner.
6. It was concluded that xylanase supplementation of wheat‐based diets invariably had a positive effect on broiler performance. 相似文献
2. There are small changes in concentration between weeks for individual birds, but no changes between consecutive days within weeks or times within days.
3. It is recommended that future attempts to assess the relationship between variation in blood and yolk cholesterol concentrations estimate blood cholesterol concentration from two samples taken a week apart. 相似文献
2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake.
3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens.
4. Similar growth rates, although slightly lower in FL, were obtained with low‐ and high‐protein diets. However, NEAA supplementation of the low‐protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines. 相似文献
2. Chicks fed on the tannin‐containing diets exhibited a high mortality and significant decreases in body‐weight as well as lower food intakes and higher food intake:weight gain ratios (P<0.01). In rats there was no mortality but the growth and food intake were adversely affected (P< 0.05).
3. Histological changes occurred in the ileal mucosa of chicks. Atrophy and shortening of villi with distortion of their architecture were observed. Similar histological disorders but less pronounced were also found in rats.
4. Histopathology of the liver of both chicks and rats showed an hydropic degeneration of hepatocytes, clearly more severe in the former than in the latter. 相似文献