全文获取类型
| 收费全文 | 231748篇 |
| 免费 | 12765篇 |
| 国内免费 | 169篇 |
专业分类
| 林业 | 9341篇 |
| 农学 | 7299篇 |
| 基础科学 | 1545篇 |
| 28718篇 | |
| 综合类 | 40750篇 |
| 农作物 | 8975篇 |
| 水产渔业 | 11610篇 |
| 畜牧兽医 | 117135篇 |
| 园艺 | 3091篇 |
| 植物保护 | 16218篇 |
出版年
| 2018年 | 3149篇 |
| 2017年 | 3562篇 |
| 2016年 | 3256篇 |
| 2015年 | 2759篇 |
| 2014年 | 3496篇 |
| 2013年 | 8930篇 |
| 2012年 | 6455篇 |
| 2011年 | 8019篇 |
| 2010年 | 5147篇 |
| 2009年 | 5262篇 |
| 2008年 | 7841篇 |
| 2007年 | 7474篇 |
| 2006年 | 7062篇 |
| 2005年 | 6550篇 |
| 2004年 | 6331篇 |
| 2003年 | 6445篇 |
| 2002年 | 6044篇 |
| 2001年 | 7119篇 |
| 2000年 | 6962篇 |
| 1999年 | 5598篇 |
| 1998年 | 2401篇 |
| 1997年 | 2376篇 |
| 1996年 | 2219篇 |
| 1995年 | 2704篇 |
| 1994年 | 2418篇 |
| 1993年 | 2306篇 |
| 1992年 | 4667篇 |
| 1991年 | 4885篇 |
| 1990年 | 4835篇 |
| 1989年 | 4837篇 |
| 1988年 | 4443篇 |
| 1987年 | 4527篇 |
| 1986年 | 4665篇 |
| 1985年 | 4510篇 |
| 1984年 | 3725篇 |
| 1983年 | 3364篇 |
| 1982年 | 2334篇 |
| 1981年 | 2154篇 |
| 1979年 | 3458篇 |
| 1978年 | 2876篇 |
| 1977年 | 2422篇 |
| 1976年 | 2327篇 |
| 1975年 | 2471篇 |
| 1974年 | 3057篇 |
| 1973年 | 3107篇 |
| 1972年 | 2975篇 |
| 1971年 | 2696篇 |
| 1970年 | 2546篇 |
| 1969年 | 2508篇 |
| 1967年 | 2160篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
991.
1. Muscle fibre composition, capillary-fibre ratio and mitochondrial density of the Iliotibialis lateralis muscle were monitored during growth from the age of 8 weeks to sexual maturity (24 weeks) in sedentary birds and in birds subjected to regular treadmill exercise. 2. The Iliotibialis lateralis muscle consists almost exclusively of type IIA and IIB fibres with a small percentage of "unclassified" fibres. Over the 16-week period of growth there was no change in fibre composition but a marked fibre hypertrophy linked with a fall in the capillary-fibre ratio. Mitochondrial volume density increased with age but this was not significant. 3. Exercise significantly increased the IIA:IIB fibres ratio from 0.77 to 1.1 but had no significant effect on any other measured characteristics. 4. It is concluded that exercise at the intensity and duration employed (10-15 min daily, ca. 70-80% maximum oxygen consumption) has little effect on the growth and development of avian skeletal muscle although there was evidence of an increased oxidative capacity of the muscle. 相似文献
992.
993.
994.
Efficacy of parenteral antibiotics for disease prophylaxis in feedlot calves 总被引：9，自引：9，他引：0 
下载免费PDF全文
下载免费PDF全文 Harland RJ Jim GK Guichon PT Townsend HG Janzen ED 《The Canadian veterinary journal. La revue veterinaire canadienne》1991,32(3):163-168
Trimethoprim-sulfadoxine (TMPSDX) and two formulations of oxytetracycline (OTC) were examined for their prophylactic efficacy in feedlot calves when given by intramuscular injection on arrival at a large commercial feedlot. The study included 2,112 high-risk feeder calves that developed disease early in the feeding period. Both formulations of OTC reduced bovine respiratory disease morbidity during the first two weeks on feed and for the entire feeding period by 15-19% (p<0.05), and they also reduced all fatal fibrinous pneumonia by 67% and 84% (p<0.05). All three drugs significantly reduced all fatal disease in animals first treated during the second week on feed, but not for the overall feeding period. Oxytetracycline with 2-pyrrolidone reduced the incidence of all fatal disease by 44% (p<0.05) during the entire feeding period. The case fatality risk for calves first treated during the second week on feed was lower (p<0.05) in the TMPSDX group and in the OTC with polyvinyl-pyrrolidone group. 相似文献
995.
996.
"Benchmark" - a large observational study of Ontario beef breeding herds: Study design and collection of data 下载免费PDF全文
下载免费PDF全文 McDermott JJ Alves DM Anderson NG Martin SW 《The Canadian veterinary journal. La revue veterinaire canadienne》1991,32(7):407-412
The methods used in a large field study which investigated the health and productivity of Ontario beef breeding herds are described. Beginning in the calving season of 1986, 180 breeding herds on 170 randomly sampled farms were followed for a two year period, using producer records and annual farm visits.
The response (cooperation) rate among the eligible producers initially contacted was 70%. Approximately two-thirds of producers maintained individual animal records, primarily calving season records. Approximately 40% recorded disease occurrences.
The advantages, disadvantages, and interpretation of “on-farm” observational studies are discussed.
相似文献997.
998.
999.
1000.