全文获取类型
收费全文 | 193279篇 |
免费 | 10571篇 |
国内免费 | 114篇 |
专业分类
林业 | 7754篇 |
农学 | 5940篇 |
基础科学 | 1319篇 |
22822篇 | |
综合类 | 33952篇 |
农作物 | 7237篇 |
水产渔业 | 9493篇 |
畜牧兽医 | 99523篇 |
园艺 | 2383篇 |
植物保护 | 13541篇 |
出版年
2018年 | 2386篇 |
2017年 | 2656篇 |
2016年 | 2507篇 |
2015年 | 2184篇 |
2014年 | 2665篇 |
2013年 | 7219篇 |
2012年 | 4990篇 |
2011年 | 6169篇 |
2010年 | 3962篇 |
2009年 | 3997篇 |
2008年 | 6133篇 |
2007年 | 5821篇 |
2006年 | 5603篇 |
2005年 | 5282篇 |
2004年 | 5083篇 |
2003年 | 5168篇 |
2002年 | 4910篇 |
2001年 | 5938篇 |
2000年 | 5768篇 |
1999年 | 4672篇 |
1998年 | 1926篇 |
1997年 | 1969篇 |
1995年 | 2284篇 |
1994年 | 2031篇 |
1993年 | 1946篇 |
1992年 | 3982篇 |
1991年 | 4213篇 |
1990年 | 4308篇 |
1989年 | 4243篇 |
1988年 | 3952篇 |
1987年 | 4035篇 |
1986年 | 4106篇 |
1985年 | 3968篇 |
1984年 | 3419篇 |
1983年 | 3006篇 |
1982年 | 2077篇 |
1981年 | 1892篇 |
1980年 | 1844篇 |
1979年 | 3074篇 |
1978年 | 2498篇 |
1977年 | 2215篇 |
1976年 | 2017篇 |
1975年 | 2143篇 |
1974年 | 2789篇 |
1973年 | 2839篇 |
1972年 | 2726篇 |
1971年 | 2485篇 |
1970年 | 2346篇 |
1969年 | 2218篇 |
1967年 | 1981篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
202.
203.
204.
205.
206.
207.
J. L. HAMMERTON 《Weed Research》1967,7(4):331-348
Summary. Seeds of Polygonum persicaria from several sources, or from plants subjected to in lain treatments, were chilled for varying periods and incubated for a 3-week germination test period. Populations differed widely in seed weight and to some extent in the response to different periods of chilling. No relationship between this response and the climate of the locality of origin could be found. There was much variation in seed weight and germination behaviour between individual plants within populations. A total of four polymorphic seed categories were observed. The proportions of seeds in the two main categories varied widely between and within populations, and were affected by certain environmental factors. These factors also appeared to affect the degree of inter-plant variation in seed shape and germination behaviour.
Travaux sur les espàes indésirables du genre Polygonum L. V. Variations dans le poids des semences, leur comportement à la germination et leur polymorphisme chez P. persicaria L. 相似文献
Travaux sur les espàes indésirables du genre Polygonum L. V. Variations dans le poids des semences, leur comportement à la germination et leur polymorphisme chez P. persicaria L. 相似文献
208.
G. I. McINTYRK 《Weed Research》1962,2(3):165-176
Summary. Previous findings suggested that the translocation in Agropyron repens of 2,2-dichloropropionic acid (dalapon) may be considerably affected by the transpiration rate. This relationship has been studied further in the present investigation using 14 C-labelled material and autoradiography.
It was found that when dalapon was applied to the leaves and the treated plants were placed in darkness a reduction in the transpiration rate of ca. 90% was associated with a marked increase in the amount of dalapon translocation into the roots and tillers. The evidence provided by the autoradiographs was confirmed by a quantitative assay of the14 C present in the roots. It was also found, however, that translocation was not appreciably affected either by a 50% reduction in the light intensity or when the transpiration rate was reduced by placing the plaints under conditions of high humidity in the light or by the application of white petroleum jelly to the leaves. An alternative hypothesis, namely that the effect of darkness on the movement of the herbicide might be due to changes induced in the normal pattern of assimilate translocation was also investigated but was not supported by the results obtained. Further experimentss, in which various parts of the treated shoot were placed in the dark, suggested that the effect of darkness on the translocation of dalapon is exerted primarily on the treated leaf itself.
Etudes sur to migration dans Agropyron repens de l'acide 2,2-dichloropropionique marqué avec14 C 相似文献
It was found that when dalapon was applied to the leaves and the treated plants were placed in darkness a reduction in the transpiration rate of ca. 90% was associated with a marked increase in the amount of dalapon translocation into the roots and tillers. The evidence provided by the autoradiographs was confirmed by a quantitative assay of the
Etudes sur to migration dans Agropyron repens de l'acide 2,2-dichloropropionique marqué avec
209.
210.
J. L. HAMMERTON 《Weed Research》1965,5(1):13-26
Summary. Seeds of Polygonam persiaria were collected from seven localities during 1962. In 1963 plants of these seven populations were grown in the field and sampled at regular intervals over the period 21st June to 13th August. At all samplings there were differences between populations in total dry weight, in leaf area index and in total nitrogen content, and populations also differed in the date of flowering. The populations also differed significantly in relative growth rate, leaf area ratio, net assimilation rate and relative nitrogen absorption rate. The variations in net assimilation rate did not appear to be closely associated with variations in leaf area index. Certain growth attributes were correlated with the latitude of origin, and it is tentatively suggested that the populations may represent genetically distinct latitudinal ecotypes.
Études sur des espèces de mauvaises herbes du genre Polygonum L. 相似文献
Études sur des espèces de mauvaises herbes du genre Polygonum L. 相似文献