全文获取类型
收费全文 | 150794篇 |
免费 | 7497篇 |
国内免费 | 91篇 |
专业分类
林业 | 6397篇 |
农学 | 4327篇 |
基础科学 | 1027篇 |
16228篇 | |
综合类 | 31983篇 |
农作物 | 6036篇 |
水产渔业 | 6402篇 |
畜牧兽医 | 75578篇 |
园艺 | 1711篇 |
植物保护 | 8693篇 |
出版年
2018年 | 1605篇 |
2017年 | 1737篇 |
2016年 | 1687篇 |
2014年 | 1660篇 |
2013年 | 5265篇 |
2012年 | 3422篇 |
2011年 | 4198篇 |
2010年 | 2771篇 |
2009年 | 2707篇 |
2008年 | 4210篇 |
2007年 | 3908篇 |
2006年 | 3819篇 |
2005年 | 3624篇 |
2004年 | 3678篇 |
2003年 | 3694篇 |
2002年 | 3568篇 |
2001年 | 4265篇 |
2000年 | 4228篇 |
1999年 | 3267篇 |
1997年 | 1456篇 |
1995年 | 1662篇 |
1994年 | 1563篇 |
1993年 | 1502篇 |
1992年 | 3175篇 |
1991年 | 3439篇 |
1990年 | 3425篇 |
1989年 | 3483篇 |
1988年 | 3210篇 |
1987年 | 3287篇 |
1986年 | 3406篇 |
1985年 | 3314篇 |
1984年 | 2688篇 |
1983年 | 2467篇 |
1982年 | 1681篇 |
1981年 | 1602篇 |
1980年 | 1491篇 |
1979年 | 2536篇 |
1978年 | 2064篇 |
1977年 | 1756篇 |
1976年 | 1674篇 |
1975年 | 1824篇 |
1974年 | 2326篇 |
1973年 | 2353篇 |
1972年 | 2385篇 |
1971年 | 2295篇 |
1970年 | 2148篇 |
1969年 | 1904篇 |
1968年 | 1531篇 |
1967年 | 1710篇 |
1966年 | 1498篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
The relative persistence of 2,4-D, MCPA and 2,4,5-T in some Saskatchewan soils was assessed under laboratory conditions. Under moist conditions, 2,4-D and MCPA showed half-life times of between 14 and 41 days but the MCPA half-life was usually 1 or 2 days longer. 2,4,5-T exhibited a half-life period over twice the length of the other chemicals. The half-life times were directly correlated to microbial plate counts, the larger numbers of soil microorganisms being associated with shorter residence times. Half-lives depended on soil moisture content and the best moisture levels for chemical loss appeared to be just less than field capacity. The use of 14C in 2,4-D incubation studies showed that the initial cleavage of the 2,4-D molecule was associated with the ether linkage and was not a decarboxylation. 相似文献
932.
933.
Propagules of Trichoderma generally formed less than 3 per cent of the total fungal propagules in a variety of forest soils in the southeastern U.S. and Washington State. The largest populations were found in the F and H organic horizons of the forest floor or under conditions of excessive moisture. T. viride Pers. ex S.F. Gray and T. polysporum (Link ex Pers.) Rifai were largely restricted to cool temperate regions; whereas, T. harzianum Rifai was characteristic of warm climates. T. koningii Oud. and T. hamatum (Bon.) Bain, were the most widely distributed species aggregates and were found in all the climatic regions investigated. Under conditions of excessive moisture, strains of T. hamatum and T. pseudokoningii Rifai were the dominant forms. 相似文献
934.
Standard boring attachments which can be fitted to chain-sawswere used to power increment borers. They were successfullyused to detect decay in trees, stumps, and logs, in a programmeof research in Fomes annosus. 相似文献
935.
936.
937.
938.
939.
940.
Inoculations by Peridermium pini (Pers) Lev. aeciospores ofscalpel wounds 2 mm deep on current year's Pinus sylvestrisL. shoots gave more numerous infections than shallower wounds.Some lesions resulting from these infections developed pycnidialdroplets and a few also produced aecial blisters within thefirst year after infection. Infection of P. sylvestris by P.pini can take place by direct stomatal penetration. This wasobserved only inside the needle sheaths of trees with previousnatural infections and was not observed on healthy trees. Thehyphae that developed from these penetrations passed intercellularlythrough the mesophyll to the vascular tissue where they proliferated. 相似文献