收费全文 | 250787篇 |
免费 | 16385篇 |
国内免费 | 5271篇 |
林业 | 26157篇 |
农学 | 16170篇 |
基础科学 | 5068篇 |
44493篇 | |
综合类 | 32976篇 |
农作物 | 20497篇 |
水产渔业 | 17956篇 |
畜牧兽医 | 74766篇 |
园艺 | 9929篇 |
植物保护 | 24431篇 |
2023年 | 1876篇 |
2022年 | 3379篇 |
2021年 | 4561篇 |
2020年 | 4751篇 |
2019年 | 5554篇 |
2018年 | 5115篇 |
2017年 | 6419篇 |
2016年 | 6098篇 |
2015年 | 6472篇 |
2014年 | 7982篇 |
2013年 | 18790篇 |
2012年 | 8749篇 |
2011年 | 10481篇 |
2010年 | 10783篇 |
2009年 | 10859篇 |
2008年 | 9363篇 |
2007年 | 7978篇 |
2006年 | 8263篇 |
2005年 | 6884篇 |
2004年 | 6099篇 |
2003年 | 5386篇 |
2002年 | 4728篇 |
2001年 | 4845篇 |
2000年 | 4383篇 |
1999年 | 4136篇 |
1998年 | 3965篇 |
1997年 | 4019篇 |
1996年 | 3754篇 |
1995年 | 4282篇 |
1994年 | 3654篇 |
1993年 | 3358篇 |
1992年 | 3116篇 |
1991年 | 3241篇 |
1990年 | 2935篇 |
1989年 | 2902篇 |
1988年 | 2499篇 |
1987年 | 2567篇 |
1986年 | 2433篇 |
1985年 | 2835篇 |
1984年 | 2847篇 |
1983年 | 2779篇 |
1982年 | 2486篇 |
1981年 | 2464篇 |
1980年 | 2467篇 |
1979年 | 2396篇 |
1978年 | 2284篇 |
1977年 | 2202篇 |
1976年 | 2051篇 |
1975年 | 1795篇 |
1974年 | 1800篇 |
2. The cells from both sources were shown to have the characteristics of adipocyte precursor cells. On reaching confluence, lipoprotein lipase activity was induced and the cells from both strains accumulated large amounts of lipid in the presence of chicken serum.
3. Measurement of cell number over time in culture and calculation of cell doubling times showed that cells from broilers proliferated at a faster rate than those derived from layer‐strain chickens. This was the case whether primary or secondary cell cultures were used. Primary cultures of broiler cells had a doubling time of 22 h versus 39 h for layer cells.
4. The contribution of such a difference in proliferative rate to the differential rate of adipose tissue growth between broiler and layer strains observed in vivo is discussed. 相似文献
2. Chicks were given diets containing 200 g C 8/kg diet, 200 g C 10/kg diet or 200 g LCT/kg diet in experiment 1. As early as 30 min after feeding, cumulative food intake in both MCT‐supplemented diets decreased significantly compared with the diet containing LCT.
3. To determine if endogenous cholecystokinin (CCK) was responsible for the decrease in food intake caused by MCT, birds were injected with the CCK‐A receptor antagonist devazepide (DVZ, 1 mg/kg BW) before diet presentation. DVZ had no effect on food intake with either LCT‐ or MCT‐supplemented diets.
4. In experiment 3, chicks were given a choice between either diets containing LCT and C 8, LCT and C 10, or C 8 and C 10 to confirm whether or not the palatability of the diets was influenced by the dietary fat sources. There was no difference in food intake between C 8 and C 10‐supplemented diets. However, chicks preferred the LCT‐supplemented diet compared with either of the diets containing MCT. 相似文献
2. During the first 24 weeks of lay about 95% of eggs were laid in nest boxes in treatments N and DN. Slightly fewer were laid in boxes where doors were present. Over 90% were laid in dust baths in D cages without doors and 67% with doors, which birds learned to open. Prelaying behaviour was least disturbed in nest boxes, most disturbed on the floor and intermediate in dust baths.
3. Fully developed dust bathing occurred in D and DN as bouts lasting 5 to 10 minutes; its incidence, surprisingly, was greater when doors were present and greater still when nest boxes were present, even though it was not performed in them. It was also performed by some hens in nest boxes in N (without doors). In N with doors and in control cages, dust bathing occurred on the bare floor in truncated form, as serial bouts each lasting only about 10 s. This truncated dust bathing was also occasionally observed in D and DN.
4. Plumage, foot and claw damage were less in hens from modified cages than from controls. Egg production was very good in all treatments but more eggs from control cages were downgraded because they were dirty or cracked.
5. When a choice was available birds generally partitioned their behaviour appropriately between nest box and dust bath. In N and DN virtually all prelaying and nesting behaviour took place in the nest boxes. Matching between dust bathing and the environment was less close; the reasons for its relatively low incidence and occurrence in truncated form outside dust baths remain to be established. 相似文献
2. The response in shell thickness to ahemeral lighting was more rapid (2.2 d) than for egg weight (4.2 d).
3. Differences between genotypes were evident in both the speed and magnitude of response.
4. Overall, egg weight and shell thickness on the 28‐h cycle were 7% and 8% greater than on 24 h.
5. The allometric increase indicates that the increase in shell weight was on average 14% more than the increase in egg weight. 相似文献