全文获取类型
收费全文 | 17993篇 |
免费 | 1560篇 |
国内免费 | 9篇 |
专业分类
19562篇 |
出版年
2023年 | 90篇 |
2022年 | 189篇 |
2021年 | 397篇 |
2020年 | 225篇 |
2019年 | 278篇 |
2018年 | 359篇 |
2017年 | 311篇 |
2016年 | 489篇 |
2015年 | 828篇 |
2014年 | 917篇 |
2013年 | 1081篇 |
2012年 | 1452篇 |
2011年 | 1319篇 |
2010年 | 889篇 |
2009年 | 842篇 |
2008年 | 1103篇 |
2007年 | 1116篇 |
2006年 | 991篇 |
2005年 | 1029篇 |
2004年 | 942篇 |
2003年 | 866篇 |
2002年 | 835篇 |
2001年 | 162篇 |
2000年 | 137篇 |
1999年 | 194篇 |
1998年 | 244篇 |
1997年 | 167篇 |
1996年 | 150篇 |
1995年 | 113篇 |
1994年 | 125篇 |
1993年 | 123篇 |
1992年 | 111篇 |
1991年 | 88篇 |
1990年 | 123篇 |
1989年 | 102篇 |
1988年 | 89篇 |
1987年 | 92篇 |
1986年 | 59篇 |
1985年 | 90篇 |
1984年 | 103篇 |
1983年 | 63篇 |
1982年 | 88篇 |
1981年 | 71篇 |
1980年 | 51篇 |
1979年 | 50篇 |
1978年 | 43篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1975年 | 20篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The cellular pathway of sugar uptake in developing cotyledons of Vicia faba L. and Phaseolus vulgaris L. seed was evaluated using a physiological approach. The cotyledon interface with the seed coat is characterised by a specialised dermal cell complex. In the case of Vicia faba cotyledons, the epidermal component of the dermal cell complex is composed of transfer cells. Sucrose is the major sugar presented to the outer surface of both cotyledons and it is taken up from the apoplasm unaltered. Estimated sucrose concentrations within the apparent free space of Vicia and Phaseolus cotyledons were 105 and 113 mM respectively. Rates of in-vitro uptake of [14C]sucrose by cotyledon segments or by whole cotyledons following physical removal or porter inactivation of the outer cells demonstrated that, for both Vicia and Phaseolus cotyledons, the dermal cell complexes are the most intense sites of sucrose uptake. Accumulation of [14C]sucrose in the storage parenchyma of whole cotyledons was directly affected by experimental manipulation of uptake by the outer cell layers and plasmolytic disruption of the interconnecting plasmodesmata. These findings indicated that sucrose accumulated by the dermal cell complexes is transported symplasmically to the storage parenchyma. Overall, it is concluded that the dermal cell complexes of the developing legume embryo, irrespective of the presence or absence of wall ingrowths, are the major sites for the uptake of sucrose released from the maternal tissues to the seed apoplasm. Thereafter, the accumulated sucrose is transported radially inward through the symplast to the storage parenchyma.Abbreviations AFS
apparent free space
- CF
5-(6)-carboxyfluorescein
- CFDA
5-(6)-carboxyfluorescein diacetate
- Mes
2-(N-morpholino)ethanesulfonic acid
- PCMBS
p-chloromercuribenzenesulfonic acid
- SRG
sulphorhodamine G
The investigation was supported by funds from the Research Management Committee, The University of Newcastle and the Australian Research Council. One of us, R. McDonald, gratefully acknowledges the support of an Australian Postgraduate Research Award. We are grateful to Stella Savoury for preparing the photomicrographs. 相似文献
32.
33.
34.
George V. Triantaphyllidis Godelieve R. J. Criel Theodore J. Abatzopoulos Patrick Sorgeloos 《Hydrobiologia》1997,357(1-3):155-163
Eleven morphometric and one meristic character in 15 parthenogeneticArtemia populations have been studied by using discriminant andcluster analysis as well as scanning electron microscopy.Discriminant analysis revealed five main groups of morphologicalpatterns: (i) the coastal Chinese populations together with apopulation from Kazakhstan, (ii) the inland Chinese salt lakepopulations, (iii) the Greek populations, (iv) one African populationfrom Namibia and (v) a Chinese population from Xuyu (Jiangsuprovince). Cluster analysis was not always in agreement withdiscriminant analysis and these results are discussed. 相似文献
35.
36.
37.
Patrick von Aderkas 《Economic botany》1984,38(1):14-23
Although the ostrich fern, Matteuccia struthiopteris,is distributed throughout much of the Northern Hemisphere, its consumption as a spring vegetable has been largely restricted to the tables of the Maritime Provinces in Canada and neighboring Maine in the United States. However, in little more than a decade the demand has expanded beyond these traditional boundaries, due to the present availability of the frozen product. The heart of the industry is undoubtedly New Brunswick. The harvest of 200 t/yr is approximately 4 times that of Maine, and from an historical vantage the traditional use as a spring vegetable is with the New Brunswickers as well. In light of the present high demand for the product and the reports of localized overpicking, a review of the economic history, resource management and attempts at cultivation is presented. 相似文献
38.
Application of the Indirect Immunoperoxidase Stain Technique to the Flagella of Azospirillum brasilense 总被引:1,自引:0,他引:1 下载免费PDF全文
An indirect immunoperoxidase stain was used to demonstrate by electron microscopy that an antigenic difference exists between the polar flagellum and the lateral flagella of Azospirillum brasilense ATCC 29145. 相似文献
39.
40.