全文获取类型
收费全文 | 77514篇 |
免费 | 3627篇 |
国内免费 | 56篇 |
专业分类
林业 | 3288篇 |
农学 | 2138篇 |
基础科学 | 535篇 |
8460篇 | |
综合类 | 17022篇 |
农作物 | 3237篇 |
水产渔业 | 3208篇 |
畜牧兽医 | 38248篇 |
园艺 | 832篇 |
植物保护 | 4229篇 |
出版年
2018年 | 808篇 |
2017年 | 898篇 |
2016年 | 783篇 |
2014年 | 825篇 |
2013年 | 2470篇 |
2012年 | 1654篇 |
2011年 | 2002篇 |
2010年 | 1309篇 |
2009年 | 1266篇 |
2008年 | 1992篇 |
2007年 | 1888篇 |
2006年 | 1837篇 |
2005年 | 1783篇 |
2004年 | 1689篇 |
2003年 | 1788篇 |
2002年 | 1669篇 |
2001年 | 1924篇 |
2000年 | 1874篇 |
1999年 | 1534篇 |
1997年 | 719篇 |
1995年 | 772篇 |
1994年 | 709篇 |
1993年 | 704篇 |
1992年 | 1529篇 |
1991年 | 1664篇 |
1990年 | 1716篇 |
1989年 | 1775篇 |
1988年 | 1660篇 |
1987年 | 1570篇 |
1986年 | 1659篇 |
1985年 | 1584篇 |
1984年 | 1326篇 |
1983年 | 1188篇 |
1982年 | 841篇 |
1981年 | 812篇 |
1980年 | 762篇 |
1979年 | 1341篇 |
1978年 | 1056篇 |
1977年 | 945篇 |
1976年 | 883篇 |
1975年 | 1006篇 |
1974年 | 1325篇 |
1973年 | 1244篇 |
1972年 | 1331篇 |
1971年 | 1271篇 |
1970年 | 1185篇 |
1969年 | 1030篇 |
1968年 | 842篇 |
1967年 | 971篇 |
1966年 | 832篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
133.
Teague WR 《New Zealand veterinary journal》1986,34(7):104-105
Of 32 calves given an unknown amount of a pluronic bloat mixture with their milk, 28 died in convulsions over 24 hours. Supportive therapy was unsuccessful. Concentrations of pluronic present in abomasal and rumenal contents supported a diagnosis of pluronic poisoning. 相似文献
134.
135.
Culberson WL 《Science (New York, N.Y.)》1985,228(4703):1084
136.
Keyes RW 《Science (New York, N.Y.)》1985,230(4722):138-144
Numerous development projects aimed at replacing the silicon technology that dominates computer logic with a faster alternative have been conducted throughout the past 25 years. None has succeeded. The alternatives are usually based on a device that switches very rapidly, and they neglect many other requirements of computer logic. In this article the essential physical factors that account for the success of transistors in digital applications are identified, as are the factors that are absent in proposed alternative devices. 相似文献
137.
A large proportion of plant species has originated through allopolyploidy: interspecific hybridization followed by chromosome doubling. Heterozygosity remains fixed in allopolyploids because of nonsegregation of parental chromosomes. Two allotetraploid species of the fern genus Asplenium show allozyme polymorphisms at loci that are polymorphic in their diploid progenitors, indicating that each has originated more than once and implicating continued gene flow from diploids to tetraploids. 相似文献
138.
139.
Hannon WJ 《Science (New York, N.Y.)》1985,228(4701):794
140.
Wilson EO 《Science (New York, N.Y.)》1985,228(4707):1489-1495
Studies on the social insects (ants, bees, wasps, and termites) have focused increasingly on sociogenesis, the process by which colony members undergo changes in caste, behavior, and physical location incident to colonial development. Caste is determined in individuals largely by environmental cues that trigger a sequence of progressive physiological restrictions. Individual determination, which is socially mediated, yields an age-size frequency distribution of the worker population that enhances survival and reproduction of the colony as a whole, typically at the expense of individuals. This "adaptive demography" varies in a predictable manner according to the species and size of the colony. The demography is richly augmented by behavioral pacemaking on the part of certain castes and programmed changes in the physical position of colony members according to age and size. Much of what has been observed in these three colony-level traits (adaptive demography, pacemaking, and positional effects) can be interpreted as the product of ritualization of dominance and other forms of selfish behavior that is still found in the more primitive insect societies. Some of the processes can also be usefully compared with morphogenesis at the levels of cells and tissues. 相似文献