全文获取类型
收费全文 | 266342篇 |
免费 | 15551篇 |
国内免费 | 1246篇 |
专业分类
林业 | 23929篇 |
农学 | 14377篇 |
基础科学 | 3209篇 |
44877篇 | |
综合类 | 28174篇 |
农作物 | 17377篇 |
水产渔业 | 16889篇 |
畜牧兽医 | 103312篇 |
园艺 | 6599篇 |
植物保护 | 24396篇 |
出版年
2021年 | 2694篇 |
2020年 | 3053篇 |
2019年 | 3838篇 |
2018年 | 4274篇 |
2017年 | 4772篇 |
2016年 | 4985篇 |
2015年 | 4543篇 |
2014年 | 5844篇 |
2013年 | 16489篇 |
2012年 | 7006篇 |
2011年 | 9189篇 |
2010年 | 7966篇 |
2009年 | 8407篇 |
2008年 | 8283篇 |
2007年 | 7446篇 |
2006年 | 7743篇 |
2005年 | 7007篇 |
2004年 | 6673篇 |
2003年 | 6501篇 |
2002年 | 5787篇 |
2001年 | 6209篇 |
2000年 | 5986篇 |
1999年 | 5460篇 |
1998年 | 4167篇 |
1997年 | 4187篇 |
1996年 | 3928篇 |
1995年 | 4444篇 |
1994年 | 3889篇 |
1993年 | 3597篇 |
1992年 | 4401篇 |
1991年 | 4680篇 |
1990年 | 4390篇 |
1989年 | 4294篇 |
1988年 | 3800篇 |
1987年 | 3904篇 |
1986年 | 3825篇 |
1985年 | 4004篇 |
1984年 | 3808篇 |
1983年 | 3566篇 |
1982年 | 2924篇 |
1981年 | 2813篇 |
1980年 | 2818篇 |
1979年 | 3455篇 |
1978年 | 3044篇 |
1977年 | 2788篇 |
1976年 | 2742篇 |
1975年 | 2583篇 |
1974年 | 2830篇 |
1973年 | 2720篇 |
1972年 | 2401篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
992.
In a seminal article in 1946, S. S. Stevens noted that the numerical measures then in common use exhibited three admissible groups of transformations: similarity, affine, and monotonic. Until recently, it was unclear what other scale types are possible. For situations on the continuum that are homogeneous (that is, objects are not distinguishable by their properties), the possibilities are essentially these three plus another type lying between the first two. These types lead to clearly described classes of structures that can, in principle, be incorporated into the classical structure of physical units. Such results, along with characterizations of important special cases, are potentially useful in the behavioral and social sciences. 相似文献
993.
994.
995.
996.
L K 《Science (New York, N.Y.)》1987,237(4819):1237-1238
997.
998.
1. Brown egg layers were fed diets differing in oil content, oil source and linoleic acid concentration and the effect on performance from 22 to 69 weeks of age was studied.
2. The birds responded with an increasing mean egg weight up to a linoleic acid intake of 2.75 g/bird d.
3. Increasing the intake of readily absorbable oil without increasing linoleic acid concentration did not increase mean egg weight. 相似文献
999.
1000.
To assess respiratory function in dogs with tick paralysis, respiratory measurements were recorded on 14 dogs experimentally infested with Ixodes holocyclus. There was a progressive fall in respiratory rate with no change in tidal volume, which resulted in a significant fall in minute respiratory volume in the latter stages of the disease. The fall in respiratory rate was possibly central in origin and was accompanied by an increased alveolar-arterial oxygen tension difference, probably caused by pulmonary congestion and oedema. The "grunting" respiration seen in tick paralysis was due to closure of the vocal cords during expiration and could represent an attempt to re-expand collapsed parts of the lung. 相似文献