收费全文 | 304228篇 |
免费 | 16584篇 |
国内免费 | 1404篇 |
林业 | 24583篇 |
农学 | 14496篇 |
基础科学 | 3239篇 |
46306篇 | |
综合类 | 41217篇 |
农作物 | 17663篇 |
水产渔业 | 17658篇 |
畜牧兽医 | 125217篇 |
园艺 | 6697篇 |
植物保护 | 25140篇 |
2020年 | 3077篇 |
2019年 | 3876篇 |
2018年 | 4314篇 |
2017年 | 4831篇 |
2016年 | 5049篇 |
2015年 | 4660篇 |
2014年 | 5940篇 |
2013年 | 16654篇 |
2012年 | 7800篇 |
2011年 | 10121篇 |
2010年 | 8210篇 |
2009年 | 8528篇 |
2008年 | 9236篇 |
2007年 | 8299篇 |
2006年 | 8687篇 |
2005年 | 8008篇 |
2004年 | 7714篇 |
2003年 | 7449篇 |
2002年 | 6809篇 |
2001年 | 7659篇 |
2000年 | 7447篇 |
1999年 | 6442篇 |
1998年 | 4309篇 |
1997年 | 4340篇 |
1996年 | 4105篇 |
1995年 | 4734篇 |
1994年 | 4201篇 |
1993年 | 3888篇 |
1992年 | 5431篇 |
1991年 | 5805篇 |
1990年 | 5483篇 |
1989年 | 5429篇 |
1988年 | 4919篇 |
1987年 | 5027篇 |
1986年 | 5112篇 |
1985年 | 5185篇 |
1984年 | 4659篇 |
1983年 | 4322篇 |
1982年 | 3346篇 |
1981年 | 3193篇 |
1980年 | 3138篇 |
1979年 | 4123篇 |
1978年 | 3596篇 |
1977年 | 3144篇 |
1976年 | 3093篇 |
1974年 | 3458篇 |
1973年 | 3471篇 |
1972年 | 3196篇 |
1971年 | 3131篇 |
1970年 | 3021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. 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
2. In diets of 160 g protein/kg without added lysine, high‐protein wheats caused lower rates of production and egg size than conventional wheats in White Leghorns. Lysine supplementation of the former diets eliminated these differences.
3. The improvements in egg production and egg weight were significant with 1 g additional lysine/kg and egg production tended to improve further with 2 g additional lysine/kg, as did egg weight with all subsequent additions, but not significantly so.
4. With diets containing high‐protein wheats supplemented with lysine, high egg production and egg weight could be obtained without a protein supplement (e.g. soyabean meal).
5. In broiler‐breeders egg production was lower and food conversion poorer with high‐protein wheat despite added lysine. 相似文献
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. At lower speeds down to 2 μm/s Ef is constant.
3. Ef is reduced if the flat plate is replaced by a sphere or cylinder; the greater its curvature, the smaller Ef.
4. Ef for the narrow pole is greater and for the broad pole smaller than that for the equator but these differences may be due in part to . systematic differences in shell thickness as well as curvature. 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