全文获取类型
收费全文 | 155篇 |
免费 | 10篇 |
专业分类
165篇 |
出版年
2018年 | 1篇 |
2014年 | 1篇 |
2010年 | 3篇 |
2007年 | 3篇 |
2006年 | 9篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 4篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1959年 | 5篇 |
1958年 | 17篇 |
1957年 | 14篇 |
1956年 | 7篇 |
1955年 | 4篇 |
1954年 | 9篇 |
1953年 | 10篇 |
1952年 | 3篇 |
1951年 | 4篇 |
1950年 | 8篇 |
1949年 | 6篇 |
1948年 | 6篇 |
1947年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有165条查询结果,搜索用时 0 毫秒
81.
CAROLIN A. REBERNIG GERALD M. SCHNEEWEISS KATHARINA E. BARDY PETER SCHÖNSWETTER JOSE L. VILLASEÑOR RENATE OBERMAYER TOD F. STUESSY HANNA WEISS‐SCHNEEWEISS 《Molecular ecology》2010,19(16):3421-3443
Pleistocene climatic fluctuations had major impacts on desert biota in southwestern North America. During cooler and wetter periods, drought‐adapted species were isolated into refugia, in contrast to expansion of their ranges during the massive aridification in the Holocene. Here, we use Melampodium leucanthum (Asteraceae), a species of the North American desert and semi‐desert regions, to investigate the impact of major aridification in southwestern North America on phylogeography and evolution in a widespread and abundant drought‐adapted plant species. The evidence for three separate Pleistocene refugia at different time levels suggests that this species responded to the Quaternary climatic oscillations in a cyclic manner. In the Holocene, once differentiated lineages came into secondary contact and intermixed, but these range expansions did not follow the eastwardly progressing aridification, but instead occurred independently out of separate Pleistocene refugia. As found in other desert biota, the Continental Divide has acted as a major migration barrier for M. leucanthum since the Pleistocene. Despite being geographically restricted to the eastern part of the species’ distribution, autotetraploids in M. leucanthum originated multiple times and do not form a genetically cohesive group. 相似文献
82.
EMBRYONAL antigens found in malignant neoplasms but not in homologous normal adult tissues have been much studied. Recently, universal embryonal tissue components were detected in different types of carcinomas of mice1. Our work indicates that immunologically definable embryonic cell components are universally present in human carcinomas. 相似文献
83.
In plants held under long days in the vegetative stage, youngexpanding leaves of poinsettia (Euphorbia pulcherrima Willd.Brilliant Diamond) are the main source of axillarybud inhibition, while the apical bud, which includes the meristem,primordial leaves and small unfolded leaves, is a secondaryinhibition source. Removal of these expanding leaves resultedin rapid release and growth of axillary buds. Decapitation ofthe apical bud resulted in delayed axillary bud release. Inreproductive plants kept in short days, the pigmented bractsare the primary source of axillary bud inhibition and the cyathiaare the secondary source. Applications of NAA substitutedfor both young leaves and bract inhibition maintainedapical dominance. The concentration of endogenous auxin washighest in the apical bud. However, when calculated on wholeorgan basis the auxin level was greater in young developingvegetative leaves and in reproductive bracts than in the apicalbud. Euphorbia pulcherrima Willd, apical bud, apical dominance, auxin, correlative inhibition, cyathia, poinsettia, IAA, NAA 相似文献
84.
85.
86.
87.
TIM ARNOLD GUY J. D. KIRK MATTHIAS WISSUWA MICHAEL FREI FANG‐JIE ZHAO THOMAS F. D. MASON DOMINIK J. WEISS 《Plant, cell & environment》2010,33(3):370-381
In an earlier study, we found that rice (Oryza sativa) grown in nutrient solution well‐supplied with Zn preferentially took up light 64Zn over 66Zn, probably as a result of kinetic fractionation in membrane transport processes. Here, we measure isotope fractionation by rice in a submerged Zn‐deficient soil with and without Zn fertilizer. We grew the same genotype as in the nutrient solution study plus low‐Zn tolerant and intolerant lines from a recombinant inbred population. In contrast to the nutrient solution, in soil with Zn fertilizer we found little or heavy isotopic enrichment in the plants relative to plant‐available Zn in the soil, and in soil without Zn fertilizer we found consistently heavy enrichment, particularly in the low‐Zn tolerant line. These observations are only explicable by complexation of Zn by a complexing agent released from the roots and uptake of the complexed Zn by specific root transporters. We show with a mathematical model that, for realistic rates of secretion of the phytosiderophore deoxymugineic acid (DMA) by rice, and realistic parameters for the Zn‐solubilizing effect of DMA in soil, solubilization and uptake by this mechanism is necessary and sufficient to account for the measured Zn uptake and the differences between genotypes. 相似文献
88.
89.
90.