收费全文 | 118499篇 |
免费 | 6646篇 |
国内免费 | 70篇 |
林业 | 5773篇 |
农学 | 4245篇 |
基础科学 | 749篇 |
14794篇 | |
综合类 | 16900篇 |
农作物 | 4331篇 |
水产渔业 | 6227篇 |
畜牧兽医 | 63265篇 |
园艺 | 1526篇 |
植物保护 | 7405篇 |
2018年 | 1797篇 |
2017年 | 1916篇 |
2016年 | 1840篇 |
2015年 | 1598篇 |
2014年 | 1932篇 |
2013年 | 4538篇 |
2012年 | 3457篇 |
2011年 | 4173篇 |
2010年 | 2826篇 |
2009年 | 2799篇 |
2008年 | 4155篇 |
2007年 | 3980篇 |
2006年 | 3841篇 |
2005年 | 3548篇 |
2004年 | 3509篇 |
2003年 | 3483篇 |
2002年 | 3252篇 |
2001年 | 4228篇 |
2000年 | 4084篇 |
1999年 | 3314篇 |
1998年 | 1448篇 |
1997年 | 1323篇 |
1996年 | 1244篇 |
1995年 | 1368篇 |
1994年 | 1301篇 |
1993年 | 1216篇 |
1992年 | 2547篇 |
1991年 | 2690篇 |
1990年 | 2865篇 |
1989年 | 2619篇 |
1988年 | 2464篇 |
1987年 | 2372篇 |
1986年 | 2347篇 |
1985年 | 2238篇 |
1984年 | 1882篇 |
1983年 | 1644篇 |
1982年 | 1069篇 |
1979年 | 1671篇 |
1978年 | 1307篇 |
1977年 | 1122篇 |
1976年 | 1121篇 |
1975年 | 1146篇 |
1974年 | 1304篇 |
1973年 | 1346篇 |
1972年 | 1348篇 |
1971年 | 1266篇 |
1970年 | 1241篇 |
1969年 | 1198篇 |
1967年 | 1085篇 |
1966年 | 1033篇 |
2. The difference in growth‐promoting activity between streptomycin, which was active, and kanamycin which was not, was not related to their effects on the flora adhering to the wall of the crop, jejunum or ileum, to their relative toxicity to the chick nor to differences in their stability in the diet.
3. When low concentrations ofkanamycin or streptomycin were given, the antibiotic was concentrated in the caecal contents. In contrast, penicillin was undetectable in the caeca of birds given high concentrations of benzyl penicillin.
4. In chicks given benzyl penicillin, the numbers of Streptococcus faecium increased at the expense of Strep, faecalis. This probably resulted from changes in the crop flora.
5. Birds given high dietary concentrations of benzyl penicillin showed improved weight gains, in spite of increased numbers of Escherichia coli in the small intestine. 相似文献
2. Liver fat, carcass fat, liver weight and body weight increased markedly at the onset of sexual maturity.
3. Within the liver, the protein to DNA ratio did not alter significantly during development; glycogen was not consistently depleted by egg production.
4. Liver fat content was significantly correlated with carcass fat, liver weight and DNA concentration, and plasma total lipid and cholesterol, independent of stage of development; with body weight, liver protein, moisture, and protein to DNA ratio, excluding the period prior to commencement of sexual maturation; and with plasma phospholipid during lay.
5. Obesity was a feature of faster growing fowls which matured earlier, consumed more, utilised food less efficiently for egg production and produced fewer saleable eggs. 相似文献
2. In both experimental phases birds on treatment 3 produced significantly fewer eggs of smaller mean weight and shell weight. Plasma calcium, inorganic phosphorus concentrations and alkaline phosphatase activity were indicative of decreased calcium status. 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