全文获取类型
收费全文 | 310篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
343篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 7篇 |
2012年 | 13篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 11篇 |
2007年 | 20篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有343条查询结果,搜索用时 15 毫秒
61.
R. Iestyn Woolway Ian D. Jones Stephen C. Maberly Jon R. French David M. Livingstone Donald T. Monteith Gavin L. Simpson Stephen J. Thackeray Mikkel R. Andersen Richard W. Battarbee Curtis L. DeGasperi Christopher D. Evans Elvira de Eyto Heidrun Feuchtmayr David P. Hamilton Martin Kernan Jan Krokowski Alon Rimmer Kevin C. Rose James A. Rusak David B. Ryves Daniel R. Scott Ewan M. Shilland Robyn L. Smyth Peter A. Staehr Rhian Thomas Susan Waldron Gesa A. Weyhenmeyer 《PloS one》2016,11(3)
Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored. 相似文献
62.
Control of invertase synthesis in sugar cane. Loci of auxin and glucose effects 总被引:8,自引:5,他引:3 下载免费PDF全文
In tissue slices from rapidly expanding internodes of sugar cane the vacuolar invertase level is a function of the balance between synthesis and destruction. The enzyme is destroyed in the tissue at an approximately constant rate with a half time of 2 hours. Invertase synthesis is regulated by both auxin and glucose. From studies with inhibitors of protein and RNA synthesis we conclude that auxin alters the rate of synthesis and glucose increases the rate of destruction of messenger RNA required for the production of invertase. 相似文献
63.
The solubilization of a glucuronyltransferase involved in pea (Pisum sativum var. Alaska) glucuronoxylan synthesis. 下载免费PDF全文
A glucuronyltransferase involved in glucuronoxylan biosynthesis was obtained from the epicotyls of 1-week-old etiolated pea (Pisum sativum var. Alaska) seedlings and was solubilized in Triton X-100, a non-ionic detergent. The enzyme was inactivated by SDS and inhibited by Derriphat 160 and cholic acid. The enzyme was active in the presence of NN-dimethyldodecylanium-N-oxide, but was not solubilized by it. The stimulatory effect of UDP-D-xylose on the particulate and solubilized enzymes was the same, but the optimum Mn2+ concentration was lower for the solubilized enzyme, and the product formed by the solubilized enzyme has altered structure and solubility properties. Gel filtration of the solubilized enzyme on Sepharose CL-6B permitted partial separation of the stimulatory effect of UDP-D-xylose from the activity in the absence of UDP-D-xylose. The solubilized enzyme was more stable than the particulate enzyme and could be stored for 2 weeks at -20 degrees C without loss of activity. 相似文献
64.
65.
Background
Pathway-targeted or low-density arrays are used more and more frequently in biomedical research, particularly those arrays that are based on quantitative real-time PCR. Typical QPCR arrays contain 96-1024 primer pairs or probes, and they bring with it the promise of being able to reliably measure differences in target levels without the need to establish absolute standard curves for each and every target. To achieve reliable quantification all primer pairs or array probes must perform with the same efficiency. 相似文献66.
Louis Nadelson Rex Culp Suzan Bunn Ryan Burkhart Robert Shetlar Kellen Nixon James Waldron 《Evolution》2009,2(3):458-473
State and national standards call for teaching evolution concepts as early as kindergarten, which provides motivation to continue
developing science instruction and curriculum for young learners. The importance of addressing students’ folk theories regarding
science justifies teaching evolution early in K-12 education. In this project, we developed, implemented, and researched standards-based
lessons to teach elements of evolution (speciation and adaption) to kindergarteners and second graders. Our lessons attended
to the students’ prior knowledge, and utilized inquiry and modeling to teach and assess their ability to recognize patterns
of similarity and differences among organisms. Using their products and comments as evidence, it was apparent the students
were able to communicate recognition of patterns and effectively apply their knowledge in near transfer activities, indicating
they achieved our learning objectives. This provides support for teaching evolution concepts in the early grades and evidence
of the ability for young children to effectively engage in supported inquiry and modeling for learning science. 相似文献
67.
68.
69.
Waldron RT Rey O Zhukova E Rozengurt E 《The Journal of biological chemistry》2004,279(26):27482-27493
Oxidative stress induced by cell treatments with H(2)O(2) activates protein kinase D (PKD) via a protein kinase C (PKC)-dependent signal transduction pathway (Waldron, R. T., and Rozengurt, E. (2000) J. Biol. Chem. 275, 17114-17121). Here we show that oxidative stress induces PKC-dependent activation loop Ser(744) and Ser(748) phosphorylation to mediate dose- and time-dependent activation of PKD, both endogenously expressed in Swiss 3T3 cells and stably overexpressed in Swiss 3T3-GFP.PKD cells. Although oxidative stress induced PKD activation loop phosphorylation and activation with identical kinetics, both were dose-dependently blocked by preincubation of cells with selective inhibitors of PKC (GF109203X and G?6983) or c-Src (PP2). Inhibition of Src tyrosine kinase activity eliminated oxidative stress-induced direct PKD tyrosine phosphorylation, but only partially attenuated activation loop phosphorylation and activation. Mutation of a putative tyrosine phosphorylation site on PKD, Tyr(469) to phenylalanine, had no effect on its activation by oxidative stress in transfected COS-7 cells. Similarly, a mutant with Tyr(469) replaced by aspartic acid had increased basal activity but was also further activated by oxidative stress. Thus, PKD tyrosine phosphorylation at this site neither produced full activation by itself nor was required for oxidative stress-induced activation mediated by activation loop phosphorylation. In addition to PKD activation, activation loop phosphorylation in response to oxidative stress also redistributed activated PKD to cell nuclei, as revealed by PKD indirect immunofluorescence, imaging of a PKD-green fluorescent protein fusion construct (GFP-PKD), and analysis of nuclear pellets. Cell preincubation with G?6983 strongly diminished H(2)O(2)-induced nuclear relocalization of GFP-PKD. Taken together, these results indicate that PKC-mediated PKD Ser(744) and Ser(748) phosphorylation induced by oxidative stress integrates PKD activation with redistribution to the nucleus. 相似文献
70.
Studies involving transgenic plants with modifications in the lignin pathway reported to date, have received a relatively
preliminary characterisation in relation to the impact on vascular integrity, biomechanical properties of tissues and carbon
allocation to phenolic pools. Therefore, in this study transgenic tobacco plants (Nicotiana tabacum cv XHFD 8) expressing various levels of a bacterial 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) gene have been characterised
for cell wall and related morphological changes. The HCHL enzyme converts p-coumaroyl-CoA to 4-hydroxybenzaldehyde thereby rerouting the phenylpropanoid pathway. Plants expressing high levels of HCHL
activity exhibited reduced lignin deposition, impaired monolignol biosynthesis and vascular integrity. The plants also exhibited
reduction in stem toughness concomitant with a massive reduction in both the cell wall esterified and soluble phenolics. A
notable result of redirecting the carbon flux was the wall-bound accretion of vanillin and vanillic acid, probably due to
the shunt pathway. Intracellular accumulation of novel metabolites such as hydroxybenzoic and vanillic acid derivatives also
occurred in the transgenic plants. A line with intermediate levels of HCHL expression conferred correspondingly reduced lignin
deposition, toughness and phenolics. This line displayed a normal morphology but distorted vasculature. Coloration of the
xylem has been previously attributed to incorporation of alternative phenolics, whereas results from this study indicate that
the coloration is likely to be due to the association of low molecular weight phenolics. There was no evidence of increased
growth or enhanced cellulose biosynthesis as a result of HCHL expression. Hence, rerouting the phenylpropanoid biosynthetic
pathway quantitatively and qualitatively modifies cell wall-bound phenolics and vascular structure. 相似文献