收费全文 | 182058篇 |
免费 | 10029篇 |
国内免费 | 94篇 |
林业 | 7904篇 |
农学 | 6242篇 |
基础科学 | 1197篇 |
23284篇 | |
综合类 | 27282篇 |
农作物 | 6862篇 |
水产渔业 | 9399篇 |
畜牧兽医 | 95429篇 |
园艺 | 2442篇 |
植物保护 | 12140篇 |
2019年 | 1743篇 |
2018年 | 2771篇 |
2017年 | 3077篇 |
2016年 | 2857篇 |
2015年 | 2457篇 |
2014年 | 3080篇 |
2013年 | 7437篇 |
2012年 | 5482篇 |
2011年 | 6584篇 |
2010年 | 4519篇 |
2009年 | 4593篇 |
2008年 | 6661篇 |
2007年 | 6314篇 |
2006年 | 6001篇 |
2005年 | 5478篇 |
2004年 | 5469篇 |
2003年 | 5479篇 |
2002年 | 5090篇 |
2001年 | 6105篇 |
2000年 | 6013篇 |
1999年 | 4927篇 |
1998年 | 2061篇 |
1997年 | 2020篇 |
1996年 | 1835篇 |
1995年 | 2177篇 |
1994年 | 1891篇 |
1993年 | 1863篇 |
1992年 | 3786篇 |
1991年 | 3950篇 |
1990年 | 3980篇 |
1989年 | 3893篇 |
1988年 | 3575篇 |
1987年 | 3529篇 |
1986年 | 3472篇 |
1985年 | 3326篇 |
1984年 | 2738篇 |
1983年 | 2465篇 |
1982年 | 1619篇 |
1979年 | 2391篇 |
1978年 | 1897篇 |
1977年 | 1671篇 |
1976年 | 1577篇 |
1975年 | 1722篇 |
1974年 | 1955篇 |
1973年 | 2064篇 |
1972年 | 1980篇 |
1971年 | 1777篇 |
1970年 | 1777篇 |
1969年 | 1737篇 |
1967年 | 1502篇 |
2. Differences in weight gain between birds in cooled and uncooled houses ranged from 101.5 g at eight birds/m2 to 385 g at 16 birds/m2. Food consumption increased gradually with increasing bird density. Food conversion efficiency, meat yield and carcass conformation were much better in the cooled house than under conventional conditions.
3. The financial return/m2 ranged from 2.30 to 4.51 ID1 in the cooled house, compared with 2.01 to 2.77 ID in the uncooled house at different floor densities. 相似文献
2. Treatment with acetazolamide decreased the rate of shell formation by 44%; reduced the concentrations of water and Na+ in the albumen at the beginning of the plumping stage but increased the accumulation of water during plumping; increased the concentration of Cl‐ in the albumen after the 6‐h stage without any appreciable change in K+ and Ca2+ concentrations.
3. The computed relationships between the concentrations of different ions also showed that the transfer of water and Na+ were linked during egg formation, that a water‐independent, acetazolamide‐sensitive reabsorption of Na+ occurred after the 10‐h stage and that Na+ and Cl‐moved simultaneously up to 14 h but with the ratio of Cl‐ to Na+ three times higher in the treated group.
4. It is concluded that acetazolamide impairs the transfer of Na+ and Cl‐ between the albumen and the extracellular fluid and that secretion of Ca2+ into the uterine lumen seems to depend on Na+ and Cl‐ reabsorption. 相似文献
2. The following variance components were obtained: σ2(pen) = 255 g2, σ2(sire) = 1 260 g2, σ2(sire × hatch) = 1 997 g2,σ2(residual) = 19 708 g2.
3. It is concluded that the effectiveness of progeny testing for growth rate in broilers is severely restricted by sire x hatch interaction effects. 相似文献
2. The shells of such eggs were thinner than those of intact eggs in seven of the populations.
3. The number of defective eggs, the specific gravity of the eggs, and the percentage hen‐day egg production of normal eggs were significantly correlated within populations with the incidence of broken eggs.
4. No significant correlations were found within populations between the incidence of egg breakage and either egg weight, body weight, or shank length. 相似文献