收费全文 | 215079篇 |
免费 | 13737篇 |
国内免费 | 643篇 |
林业 | 22844篇 |
农学 | 13822篇 |
基础科学 | 2929篇 |
40598篇 | |
综合类 | 12691篇 |
农作物 | 16986篇 |
水产渔业 | 15825篇 |
畜牧兽医 | 75112篇 |
园艺 | 6157篇 |
植物保护 | 22495篇 |
2021年 | 2397篇 |
2020年 | 2786篇 |
2019年 | 3589篇 |
2018年 | 3749篇 |
2017年 | 4139篇 |
2016年 | 4600篇 |
2015年 | 4173篇 |
2014年 | 5524篇 |
2013年 | 16071篇 |
2012年 | 5113篇 |
2011年 | 6764篇 |
2010年 | 6926篇 |
2009年 | 7605篇 |
2008年 | 6249篇 |
2007年 | 5244篇 |
2006年 | 5994篇 |
2005年 | 5203篇 |
2004年 | 5056篇 |
2003年 | 4877篇 |
2002年 | 4211篇 |
2001年 | 4477篇 |
2000年 | 4134篇 |
1999年 | 4196篇 |
1998年 | 3967篇 |
1997年 | 4029篇 |
1996年 | 3784篇 |
1995年 | 4290篇 |
1994年 | 3688篇 |
1993年 | 3404篇 |
1992年 | 3337篇 |
1991年 | 3535篇 |
1990年 | 3163篇 |
1989年 | 3125篇 |
1988年 | 2744篇 |
1987年 | 2785篇 |
1986年 | 2652篇 |
1985年 | 3064篇 |
1984年 | 3018篇 |
1983年 | 2901篇 |
1982年 | 2574篇 |
1981年 | 2508篇 |
1980年 | 2514篇 |
1979年 | 2630篇 |
1978年 | 2459篇 |
1977年 | 2359篇 |
1976年 | 2213篇 |
1975年 | 1995篇 |
1974年 | 2000篇 |
1973年 | 1928篇 |
1972年 | 1649篇 |
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. The relative weight of the duodenum and jejunum was higher in the light breed than in the heavy one, the reverse relationship was found for the ileum and caecum.
3. The relative growth of the pancreas, heart, cerebrum and cerebellum was greater in the light breed. 相似文献
2. Agonistic interactions were both more numerous and more severe (fights and peck avoidances) in groups of the local breed than in those of Rhode Island Reds.
3. The outcome of severe interactions favoured local males and Rhode Island females in the first experiment and Rhode Island males in the second.
4. Small body and comb size might account for the relatively high number of agonistic interactions and the submissiveness of local females and young males while physical strength or some other breed characteristic might account for the high number of agonistic interactions of local males as well as their dominance in breed encounters. 相似文献
2. In the first experiment, removal of food for 8 h/d from 42 to 56 d of age significantly improved food conversion efficiency of broilers on deep litter. Removal of food for 16 h/d or on alternate days tended to cause slower growth and also improved conversion efficiency.
3. In the second experiment, denial of food for 8 h/d did not significantly affect either growth rate or conversion efficiency of caged broilers. Denial of food on alternate days, from 28 d of age, depressed food intake and growth rate. Food restriction decreased dressing percentage regardless of the age of introduction. With 32, 40 or 48 h food denial each 72 h there was a large depression in growth rate and dressing percentage. Carcass dry matter was also less, indicating less carcass fat, when food was denied for 48 h each 72 h.
4. In the third experiment, growth rate of broilers on deep litter was significantly improved by denying food for 8 h/d from 28 d of age, and was significantly depressed by food denial on alternate days. This depression was significantly more severe if restriction started at 28 d rather than at 42 d of age. Conversion efficiency was not significantly improved by denial for 8 h/d.
5. In the last two experiments conversion efficiency was much worse in severe restriction. 相似文献
2. When this treated meal was fed to susceptible ("tainting") hens the concentration of trimethylamine in the eggs was decreased to much less than that required to cause taint. 相似文献
2. The dietary treatments had no significant effect upon food intake, egg output, shell thickness, shell deformation or specific gravity of the eggs.
3. The 28‐h cycle reduced mean rate of lay by 4.5%, increased egg weight by 5.8% and increased shell thickness by 9.4%. The proportion of eggs with shell faults revealed on candling was reduced from 4.1 % to 2.8%.
4. It is concluded from this and other sources that decreasing dietary phosphorus or modifying vitamin D supplements may sometimes lead to increases in shell thickness of the order of 1 to 2%, but that these changes are unlikely to result in a measurable reduction in the proportion of cracked eggs late in the laying year.
5. A 28‐h light‐dark cycle results in a longer and more uniform interval between consecutive ovipositions and thus gives reliable increases in shell thickness which are large enough to reduce the proportion of cracked eggs in many practical situations. Whether it is profitable to use an ahemeral cycle will depend upon the relative prices paid for eggs of different sizes. 相似文献
2. Triticale 72‐S appeared to be superior to triticale 131 as a direct replacement for maize, but both grains were inferior to maize as energy sources. 相似文献
2. The experimental diet was calculated to be low in energy and methionine and high in fibre by conventional standards. Birds ate up to 12% more of this diet, but the calculated intakes of energy and methionine were less than those of the corresponding controls.
3. White stocks fed on the experimental diet produced seven eggs less per bird than controls while the production of brown stocks was essentially unaffected.
4. The gross efficiency of energy utilisation for egg production was better with the experimental diet. 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. At spoilage the main organisms at 2 and — 1 °C on the carcasses wrapped in the oxygen‐permeable film were pseudomonads, producing unacceptable “off odours” when their numbers were >108/cm2. This occurred in about 10 d at 2 °C but in about 19 d at ‐ 1° C.
3. The effect of wrapping in the heat‐shrunk oxygen‐impermeable film was to delay or inhibit the growth of pseudomonads and thus extend the shelf‐life by more than 50% at either temperature. The predominant organisms isolated from the spoiling carcasses were atypical lactobacilli and enterobacteria.
4. Sensory assessment of the carcasses stored at — 1 °C by a trained panel indicated that, although less obvious “ off odours “ were produced by the micro‐organisms growing on the carcasses wrapped in the impermeable film, differences were detected at 33 d when the numbers of bacteria reached about 107/cm2 whilst at 41 d the meat was described as rancid. 相似文献