全文获取类型
收费全文 | 268篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
273篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 3篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 16篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 2篇 |
排序方式: 共有273条查询结果,搜索用时 0 毫秒
11.
12.
Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER
endoplasmic reticulum
- RER
rough endoplasmic reticulum 相似文献
13.
Using lettuce (Lactuca sativa L., cv. Grand Rapids) embryos in osmotica, we have demonstrated that when the growth rates of the embryonic axes of seeds treated with red (R) or far-red (FR) light are equalized, the axes of R-treated seeds develop a 3.4-bar decrease in water potential (paper No. III).As axial growth begins, reserve protein and phytin decrease rapidly, concomitant with increases in reducing sugars, -amino nitrogen, and inorganic and esterified soluble phosphates. However, no differences between the axes of R-and FR-treated seeds are found with respect to the changes in these compounds, indicating that these changes arise as a result of growth and are not under immediate phytochrome control. Little change in the total lipid content is found in either treatment. The axes of FR-treated seeds hydrolyze endogenous sucrose at a greater rate thant those of R-treated seeds. Axes of R-treated seeds accumulate K+ and Na+ to a greater extent than those of FR-treated seeds. When potassium salts are added to the incubation medium, R induces increased K+ uptake by the axis and greater medium acidification by the axis. Malate and other organic acids and acidic amino acids increase at equal rates in both treatments, indicating that inorganic anions may also be taken up to balance the ionic charges. The results are compatible with the assumption that changes in the osmotic and pressure potentials of the embryonic axes of R-treated seeds are the result of a phytochrome-stimulated proton pump which, in whole dormant seeds, would initiate water-potential changes allowing the embryos to overcome the mechanical restraint of the surrounding seed layers, resulting in germination.Abbreviations FR
far-red light
- PEG
polyethylene glyeol 4000
- Pfr
far-red-absorbing form of phytochrome
- R
red light
III=Carpita et al. 1979 相似文献
14.
种子休眠与萌发的分子生物学的研究进展 总被引:22,自引:0,他引:22
休眠与萌发是植物种子对环境变化的适应特征,受许多基因调控和环境因子的影响.利用数量遗传学方法(如QTL分析)和突变等手段已对休眠和萌发特性进行了深入的遗传学研究.近些年来,随着分子生物学的快速发展,种子休眠和萌发研究已经深入到分子水平.分子生物学技术的运用,特别是基因表达、基因组测序和以双向凝胶电泳及质谱分析为技术基础的蛋白质组学分析,已成为研究种子休眠和萌发的新工具和新方向.本文主要就利用分子生物学方法研究种子休眠与萌发的进展给予简要综述. 相似文献
15.
The aquatic duckweed Spirodela polyrhiza propagates itself vegetatively by forming turions – bud‐like perennation organs – in the autumn, which spend the winter on the bottom of ponds and then germinate in the following spring and proliferate on the water surface. Newly formed turions usually require a period of cold after‐ripening and light to germinate effectively, but an ample supply of exogenous sugar can lead to germination even in the dark and independent of after‐ripening. The results of the present study indicate that the availability of readily metabolised carbohydrates is a determining factor for turion germination. Freshly harvested turions do not contain soluble, low‐molecular weight carbohydrates at a level sufficient to allow germination to take place, but after‐ripened turions do. Augmentation of the soluble carbohydrate content during after‐ripening derives from gradual breakdown of reserve starch of the turions. The long time required for any germination to be observed in turions incubated in darkness and the limited frequency of germination in the dark (about 50% of turion population), even with an ample external sugar, supply emphasise that both after‐ripening and light are essential for ensuring rapid germination and subsequent frond proliferation at an ecologically appropriate time. The carbohydrate supply required for rapid proliferation of the fronds produced at germination is provided by the rapid light‐induced breakdown of turion reserve starch. 相似文献
16.
The control of field tuber dormancy in the yam (Dioscorea cayenensis–D. rotundata complex) is poorly understood. Although studies have examined single environmental factors and chemical treatments that might prolong tuber dormancy and storage, only a few were focused on further tuber sprouting. The present study concerns microtubers obtained by in vitro culture. When microtubers were harvested (after 9 months of culture) and directly transferred on a new medium without hormones, the tubers rapidly sprouted in in vitro conditions. No dormancy was observed in this case. Harvested microtubers were also stored dry in jars in sterile conditions during 2 to 18 weeks before in vitro sprouting. In this case, microtubers stored during 18 weeks sprouted more rapidly than those stored 8 weeks. A constant “dormancy-like period” (storage duration + sprouting delay) was observed, between 20 and 28 weeks respectively for the more rapid and the slower microtubers. The size of the tubers used for the storage had great influence on further sprouting. The larger they were, the better they sprouted. Light during storage had no effect on the sprouting delay while a temperature of 25 °C permit a quicker sprouting than 18 °C. The medium used to obtain microtubers could also have an effect on sprouting rate. 相似文献
17.
18.
The seeds of Paris polyphylla var. yunnanensis are deeply dormant, and they remain dormant for 18 months or longer in their natural environment. Periodic exposure of the seeds to a low-temperature of 4 °C broke the dormancy in about 16 weeks (112 days). The most effective temperature stratification scheme was an interval of 14 days at 4 °C and 14 days at 22 °C. Both GA3 and ethephon significantly enhanced the germination rate during the stratification treatment. The seed coat, particularly the mesophyll outer layer of the seed coat, strongly inhibited the germination. With removal of the seed coat and exposure of the uncoated seeds to 600 mg/l GA3 for 48 h before the temperature stratification of 14 days at 4 °C and 14 days at 22 °C for 112 days, a germination percentage as high as 95.3% of the seeds was attained in about 160 days. 相似文献
19.
Vorwerk S Biernacki S Hillebrand H Janzik I Müller A Weiler EW Piotrowski M 《Planta》2001,212(4):508-516
Three of the nitrilase isoenzymes of Arabidopsis thaliana (L.) Heynh. are located on chromosome III in tandem and these genes (NIT2/NIT1/NIT3 in the 5′→3′ direction) encode highly similar polypeptides. Copy DNAs encompassing the entire coding sequences for all three
nitrilases were expressed in Escherichia coli as fusion proteins containing a C-terminal hexahistidine extension. All three nitrilases were obtained as enzymatically active
proteins, and their characteristics were determined, including a detailed comparative analysis of their substrate preferences.
All three nitrilases converted indole-3-acetonitrile (IAN) to indole-3-acetic acid (IAA), albeit, compared to the most effective
substrates found, phenylpropionitrile (PPN), allylcyanide, (phenylthio)acetonitrile and (methylthio)acetonitrile, with low
affinity and velocity. The preferred substrates are either naturally occurring substrates, which may originate from glucosinolate
breakdown, or they are close relatives of these. Thus, a major function of NIT1, NIT2 and NIT3 is assigned to be the conversion
to carboxylic acids of nitriles from glucosinolate turnover or degradation. While all nitrilases exhibit a similar pH optimum
around neutral, and NIT1 and NIT3 exhibit a similar temperature optimum around 30 °C independent of the substrate analyzed
(IAN, PPN), NIT2 showed a remarkably different temperature optimum for IAN (15 °C) and PPN (35–40 °C). A potential role for
NIT2 in breaking seed dormancy in A. thaliana by low temperatures (stratification), however, was ruled out, although NIT2 was the predominantly expressed nitrilase isoform
in developing embryos and in germinating seeds, as judged from an analysis of β-glucuronidase reporter gene expression under
the control of the promoters of the four isogenes. It is possible that NIT2 is involved in supplying IAA during seed development
rather than during stratification.
Received: 13 May 2000 / Accepted: 14 August 2000 相似文献
20.
Genes associated with the end of dormancy in grapes 总被引:11,自引:0,他引:11
Pacey-Miller T Scott K Ablett E Tingey S Ching A Henry R 《Functional & integrative genomics》2003,3(4):144-152
A grape bud EST library was constructed and 4,270 ESTs sequenced. The library clones were arrayed for the purpose of investigating the level of gene expression over time, particularly leading up to the buds release from dormancy. The arrays were hybridized with P33-labeled probes produced from samples of buds collected at weekly intervals. These probes covered the time from 9 weeks prior to bud burst until just after the emergence of the shoots. Expression patterns from these genes have been examined. It was found that 74% of the genes in the data set were homologous to known proteins. Genes were then assigned to functional categories according to their primary BLAST match. Of these 13% were involved with photosynthesis, 13% with disease resistance and defense, 5% energy, 12% metabolism, 20% protein production and processing, 25% cell structure and plant growth and the remaining 12% were unclassified The expression pattern of a selection of candidate genes retrieved from literature previously reporting an association with dormancy changes was assessed. On closer examination most of these genes relate to the oxidative processes and stress responses within the cell. The results of this study show that even in the dormant state, gene expression in the buds is high. 相似文献