全文获取类型
收费全文 | 25578篇 |
免费 | 3768篇 |
国内免费 | 1394篇 |
专业分类
林业 | 1197篇 |
农学 | 2107篇 |
基础科学 | 304篇 |
3644篇 | |
综合类 | 7568篇 |
农作物 | 1703篇 |
水产渔业 | 3810篇 |
畜牧兽医 | 6832篇 |
园艺 | 1031篇 |
植物保护 | 2544篇 |
出版年
2024年 | 139篇 |
2023年 | 286篇 |
2022年 | 610篇 |
2021年 | 849篇 |
2020年 | 1204篇 |
2019年 | 1741篇 |
2018年 | 1372篇 |
2017年 | 1713篇 |
2016年 | 1629篇 |
2015年 | 1394篇 |
2014年 | 1493篇 |
2013年 | 2043篇 |
2012年 | 2358篇 |
2011年 | 2051篇 |
2010年 | 1584篇 |
2009年 | 1347篇 |
2008年 | 1201篇 |
2007年 | 1265篇 |
2006年 | 997篇 |
2005年 | 737篇 |
2004年 | 658篇 |
2003年 | 542篇 |
2002年 | 445篇 |
2001年 | 438篇 |
2000年 | 414篇 |
1999年 | 308篇 |
1998年 | 248篇 |
1997年 | 200篇 |
1996年 | 243篇 |
1995年 | 204篇 |
1994年 | 162篇 |
1993年 | 137篇 |
1992年 | 119篇 |
1991年 | 132篇 |
1990年 | 112篇 |
1989年 | 109篇 |
1988年 | 72篇 |
1987年 | 54篇 |
1986年 | 28篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1962年 | 3篇 |
1956年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
MARCY J. SOUZA JONATHAN S. WALL ALAN STUCKEY GREGORY B. DANIEL 《Veterinary radiology & ultrasound》2011,52(3):340-344
Positron emission tomography (PET) is often used to stage and monitor human cancer and has recently been used in a similar fashion in veterinary medicine. The most commonly used radiopharmaceutical is 2‐Deoxy‐2‐[18F]‐Fluoro‐d ‐glucose (18F‐FDG), which is concentrated and trapped within cells that use glucose as their energy substrate. We characterized the normal distribution of 18F‐FDG in 10 healthy Hispaniolan Amazon parrots (Amazona ventralis) by performing whole body PET scans at steady state, 60 min after injection. Significant variability was found in the intestinal activity. Avian species are known to reflux fluid and electrolytes from their cloaca into their colon. To evaluate reflux as the cause of variability in intestinal distribution of 18F‐FDG, dynamic PET scans were performed on the coelomic cavity of six Hispaniolan Amazon parrots from time 0 to 60 min postinjection of radiotracer. Reflux of radioactive material from the cloaca into the colon occurred in all birds to varying degrees and occurred before 60 min. To evaluate the intestinal tract of clinical avian patients, dynamic scans must be performed starting immediately after injection so that increased radioactivity due to metabolism or hypermetabolic lesions such as cancer can be differentiated from increased radioactivity due to reflux of fluid from the cloaca. 相似文献
33.
The consumption of poultry meats exceeds 50% of total meat consumption. With the outbreak of bovine spongiform encephalopathy and foot and mouth disease, the consumption of poultry meat is set to increase. The use of meat bone meal derived from cattle and pigs is prohibited. Therefore, plant protein has to be used more frequently and the importance of the study of amino acid nutrition is increasing. In order to improve dietary efficiency, it is necessary to elucidate the exact amino acid requirements of poultry. The amino acid requirements are not constant and are affected by various factors. By using the plasma amino acid concentration as a parameter, it is possible to predict the amino acid requirements within a short period using a small number of animals repeatedly. By satisfying the amino acid requirements through supplementing crystalline amino acids, it is possible to reduce dietary protein and excretory nitrogen simultaneously. However, when the dietary protein is reduced, the abdominal fat tends to increase. This is solved by deciding the optimum dietary protein level, but it is difficult to control the taste of poultry meat by dietary amino acids. 相似文献
34.
35.
36.
Hamid Reza Taheri Hadi Nasiri Rasoul Ahmadkhani 《Journal of animal physiology and animal nutrition》2019,103(4):1090-1098
This study investigated effect of increasing level of dietary sodium using sodium bicarbonate or sodium chloride on growth performance, mortality, characteristics of carcass, organs and tibia, calcium and phosphorus of serum in broilers reared in a high‐altitude area (1,700 m above sea level). A total of 588 Ross 308 male broiler chicks were used in seven treatments, six replicates per treatment of 14 birds per each from 1 to 38 d of age. Seven dietary treatments consisted of a basal diet (with 0.16% sodium and 0.23% chloride), top‐dressed for six diets to give three supplementary levels of sodium (0.07%, 0.14% and 0.21%) from sodium bicarbonate (respectively by 0.26%, 0.52% and 0.78%) or sodium chloride (respectively by 0.18%, 0.36% and 0.54%), resulting in seven diets with total sodium and chloride levels of 0.16% and 0.23%, 0.23% and 0.23%, 0.30% and 0.23%, 0.37% and 0.23%, 0.23% and 0.33%, 0.30% and 0.44%, 0.37% and 0.55% respectively. Increasing sodium level improved feed conversion ratio (FCR) linearly and quadratically. However, when FCR was calculated without adjusting for feed intake of mortalities, the enhanced sodium level did not improve this parameter. Increasing sodium level via sodium chloride enhanced ascites mortality, total mortality, relative weight of heart and right ventricle linearly. Increasing sodium level reduced serum calcium and enhanced serum phosphorus linearly; however, there was a linear tendency to increase tibia ash when sodium level was enhanced by sodium bicarbonate (p = 0.08) or sodium chloride (p = 0.07). Increasing sodium level via sodium bicarbonate tended (p = 0.08) to reduce tibia strength linearly. In conclusion, a diet with 0.16% sodium and 0.23% chloride is enough for broiler chicken reared in a high‐altitude area, and increasing dietary sodium level via sodium chloride has detrimental effect on survivability of broiler in such condition. 相似文献
37.
38.
39.
营养学中氨基酸平衡的度量 总被引:8,自引:0,他引:8
本文基于聚类分析理论,提出了失衡度(IBD)这一新的化学指数,借以定量地研究蛋白质营养中的氨基酸平衡问题。当样品中氨基酸完全平衡时,IBD取值为零;而当其氨基酸平衡最差时。IBD取值为1。IBD的氨基酸增量模型为非对称最大值式;且IBD与变异系数(CV)之间有着密切的关系。通过IBD这一指数,可以对各种单一饲料的蛋白质营养价值加以分类列等;通过计算两种以上饲料蛋白质混合物的IBD,可以从理论上预测它们之间是否互补,以及何时发生最佳互补关系。若引申IBD的概念框架,还可以用来研究其它养分之间的平衡关系,并有助于实现计算机配方过程的自动鉴别和筛选。 相似文献
40.