收费全文 | 273991篇 |
免费 | 16157篇 |
国内免费 | 666篇 |
林业 | 24100篇 |
农学 | 14083篇 |
基础科学 | 2964篇 |
44124篇 | |
综合类 | 29267篇 |
农作物 | 17359篇 |
水产渔业 | 17295篇 |
畜牧兽医 | 110712篇 |
园艺 | 6388篇 |
植物保护 | 24522篇 |
2020年 | 2899篇 |
2019年 | 3689篇 |
2018年 | 4176篇 |
2017年 | 4534篇 |
2016年 | 4931篇 |
2015年 | 4386篇 |
2014年 | 5748篇 |
2013年 | 16418篇 |
2012年 | 6731篇 |
2011年 | 8760篇 |
2010年 | 7571篇 |
2009年 | 8116篇 |
2008年 | 8128篇 |
2007年 | 7197篇 |
2006年 | 7692篇 |
2005年 | 6962篇 |
2004年 | 6780篇 |
2003年 | 6691篇 |
2002年 | 5961篇 |
2001年 | 6653篇 |
2000年 | 6252篇 |
1999年 | 5811篇 |
1998年 | 4227篇 |
1997年 | 4293篇 |
1996年 | 3998篇 |
1995年 | 4617篇 |
1994年 | 4008篇 |
1993年 | 3712篇 |
1992年 | 4769篇 |
1991年 | 5058篇 |
1990年 | 4721篇 |
1989年 | 4770篇 |
1988年 | 4242篇 |
1987年 | 4231篇 |
1986年 | 4295篇 |
1985年 | 4517篇 |
1984年 | 4113篇 |
1983年 | 3810篇 |
1982年 | 3076篇 |
1981年 | 2894篇 |
1980年 | 2891篇 |
1979年 | 3675篇 |
1978年 | 3184篇 |
1977年 | 2988篇 |
1976年 | 2811篇 |
1975年 | 2698篇 |
1974年 | 2984篇 |
1973年 | 2984篇 |
1972年 | 2702篇 |
1971年 | 2606篇 |
2. With the pheasant as sire, fertility was 7.lb6%, but with the fowl it was 19.lb5%; hatchability of fertile eggs, however, was similar, 42% and 41% respectively.
3. Only one exencephalic hybrid was obtained when the sire was the pheasant but 70 were noted when the fowl was sire. The incidence of this malformation in hatched chicks was 12 times more in crosses with the fowl as sire than in the reverse cross.
4. The frequency of exencephaly was greater with Rhode Island Red, Barred Leghorn or White Leghorn roosters than with Columbian Rock roosters. 相似文献
2. In a period of sexual quiescence on short photoperiods (6L : 18D) LH concentrations were higher during the hours of darkness in both sexes.
3. Transfer to long photoperiods (16L : 8D) stimulated a rapid increase in LH and FSH concentrations. This was maintained for between 2 to 3 months when the concentrations of both gonadotrophins decreased as the birds became photorefractory.
4. Return to short photoperiods had no immediate effect on the concentrations of LH and FSH in females. The concentration of LH was increased during the 3rd week of short photoperiods when the hens were moulting.
5. LH concentrations fluctuated during the ovulatory cycle and were highest about 6 h before ovulation. 相似文献
2. Chemical tests indicated 72.5% of the total lysine in HFM was available.
3. Total lysine concentration of 11.3 g/kg diet maximised performance during the period 0 to 34 d.
4. Reduction in dietary methionine content during the period 0 to 34 d from 4.2 g/kg to 3.2 g/kg did not depress performance on diets containing 60 g HFM/kg.
5. The results indicate that at least 57% by weight of the total sulphur amino acid requirement of broilers can be provided by cystine. 相似文献