全文获取类型
收费全文 | 160009篇 |
免费 | 7500篇 |
国内免费 | 7963篇 |
专业分类
林业 | 15881篇 |
农学 | 15780篇 |
基础科学 | 7591篇 |
24636篇 | |
综合类 | 32613篇 |
农作物 | 8186篇 |
水产渔业 | 7889篇 |
畜牧兽医 | 47390篇 |
园艺 | 4128篇 |
植物保护 | 11378篇 |
出版年
2023年 | 755篇 |
2022年 | 1951篇 |
2021年 | 3042篇 |
2020年 | 2928篇 |
2019年 | 3015篇 |
2018年 | 5433篇 |
2017年 | 6217篇 |
2016年 | 4559篇 |
2015年 | 4123篇 |
2014年 | 4120篇 |
2013年 | 6369篇 |
2012年 | 7210篇 |
2011年 | 9576篇 |
2010年 | 8618篇 |
2009年 | 7714篇 |
2008年 | 8330篇 |
2007年 | 8578篇 |
2006年 | 6426篇 |
2005年 | 5851篇 |
2004年 | 4007篇 |
2003年 | 3848篇 |
2002年 | 3241篇 |
2001年 | 3666篇 |
2000年 | 3991篇 |
1999年 | 3800篇 |
1998年 | 2813篇 |
1997年 | 2410篇 |
1996年 | 2228篇 |
1995年 | 2236篇 |
1994年 | 2045篇 |
1993年 | 1928篇 |
1992年 | 2513篇 |
1991年 | 2342篇 |
1990年 | 2345篇 |
1989年 | 2108篇 |
1988年 | 1914篇 |
1987年 | 1608篇 |
1986年 | 1549篇 |
1985年 | 1416篇 |
1984年 | 1200篇 |
1983年 | 1090篇 |
1979年 | 1022篇 |
1978年 | 804篇 |
1977年 | 737篇 |
1974年 | 768篇 |
1973年 | 833篇 |
1972年 | 807篇 |
1971年 | 751篇 |
1970年 | 731篇 |
1969年 | 751篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
101.
This study was conducted to evaluate the effects of dietary vitamin K (menadione) on bone quality in cage-raised broilers. Three hundred and sixty male broilers were randomly allotted to one of six treatments, with six replicate pens per treatment and 10 chicks per pen. Broilers were fed one of six diets including a control diet or the control diet plus graded levels of vitamin K (0.5 mg/kg, 2 mg/kg, 8 mg/kg, 32 mg/kg and 128 mg/kg). Water and feed were provided ad libitum during the 7-week experimental period. Results indicated that vitamin K supplementation of broilers diets significantly effected bone quality and feed efficiency. The treatment containing vitamin K at 8 mg/kg improved growth performance (during weeks 6-7) and bone quality (during weeks 0-3). In our study, hydroxyapatite binding capacity of serum osteocalcin (during weeks 0-3), bone breaking strength, bone flexibility, bone ash weight increased linearly (P < 0.05) and bone mineral density, bone mineral content increased quadratically (P < 0.05) with increasing supplementation of vitamin K. In conclusion, to gain optimum bone quality and broiler performance, our studies suggest that the concentration of vitamin K in broilers diets should be 8 mg/kg, 2 mg/kg, and 2 mg/kg, for the starter, grower and finisher phases, respectively. Furthermore, it was shown that the starter period is an important phase for improving bone quality. In addition, this study validated the mechanism of vitamin K effects on bone quality. Vitamin K boosts the carboxylation of osteocalcin and decreases the concentration of serum under-carboxylated osteocalcin enhancing hydroxyapatite binding capacity of serum osteocalcin and improving bone quality. 相似文献
102.
103.
104.
105.
106.
C Richardson W P Taylor S Terlecki E P Gibbs 《American journal of veterinary research》1985,46(9):1912-1922
Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia. 相似文献
107.
108.
Periodontal disease. Etiology and pathogenesis 总被引:1,自引:0,他引:1
Periodontal disease is the number-one cause of the early loss of teeth in dogs and cats. Some of the factors in the adult animal that play a major role in the development of periodontal diseases are discussed in this article, including overcrowding, malocclusions, diet, developmental defects, and metabolic and systemic disease. 相似文献
109.
110.
优化了S1核酸酶突变检测体系,结果表明(1)扩增法比杂交法产生异源双链DNA更节省时间;(2)PCR产物可以直接作为突变检测的底物;(3)适当降低反应温度、适当增加反应缓冲液中的NaCl浓度、适当缩短反应时间可提高突变检测效果。 相似文献