全文获取类型
收费全文 | 110篇 |
免费 | 11篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 3篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有121条查询结果,搜索用时 671 毫秒
51.
Jackie Epila Hans Verbeeck Thomas Otim‐Epila Paul Okullo Elizabeth Kearsley Kathy Steppe 《African Journal of Ecology》2017,55(4):679-692
Maesopsis eminii is referred to as one of the most widely distributed African tree species. However, its occurrence in Africa has never been mapped and little is known as to how this species can sustain in different environments. To gain insight into Maesopsis’ ecology, we (i) made a synthesis of its functional trait data from the literature, (ii) investigated phenological patterns using data on four M. eminii trees from Yangambi, DR Congo, (iii) assessed an empirical provenance trial from Uganda on 600 Maesopsis trees and (iv) synthesized geo‐referenced point location maps of Maesopsis entailing WorldClim precipitation and temperature and FAO soils, rainfall and ecological zones for Africa. We found M. eminii to straddle the equator equidistantly in terms of latitude (10.97°N and 10.98°S) covering five forest types where twenty soil types and variable rainfall regimes support complex plant biodiversity. Maesopsis eminii was, however, largely concentrated in the tropical rainforest ecosystem which contains fertile Orthic Ferralsol soils. More than 97% of the point locations were found where annual precipitation was >1000 mm, and 82% occurred where average annual temperature was 22–28°C. Its functional traits, phenology and provenance trial findings explained its occurrence in Africa. 相似文献
52.
Terrestrial biosphere models need better representation of vegetation phenology: results from the North American Carbon Program Site Synthesis 总被引:2,自引:0,他引:2
Andrew D. Richardson Ryan S. Anderson M. Altaf Arain Alan G. Barr Gil Bohrer Guangsheng Chen Jing M. Chen Philippe Ciais Kenneth J. Davis Ankur R. Desai Michael C. Dietze Danilo Dragoni Steven R. Garrity Christopher M. Gough Robert Grant David Y. Hollinger Hank A. Margolis Harry McCaughey Mirco Migliavacca Russell K. Monson J. William Munger Benjamin Poulter Brett M. Raczka Daniel M. Ricciuto Alok K. Sahoo Kevin Schaefer Hanqin Tian Rodrigo Vargas Hans Verbeeck Jingfeng Xiao Yongkang Xue 《Global Change Biology》2012,18(2):566-584
Phenology, by controlling the seasonal activity of vegetation on the land surface, plays a fundamental role in regulating photosynthesis and other ecosystem processes, as well as competitive interactions and feedbacks to the climate system. We conducted an analysis to evaluate the representation of phenology, and the associated seasonality of ecosystem‐scale CO2 exchange, in 14 models participating in the North American Carbon Program Site Synthesis. Model predictions were evaluated using long‐term measurements (emphasizing the period 2000–2006) from 10 forested sites within the AmeriFlux and Fluxnet‐Canada networks. In deciduous forests, almost all models consistently predicted that the growing season started earlier, and ended later, than was actually observed; biases of 2 weeks or more were typical. For these sites, most models were also unable to explain more than a small fraction of the observed interannual variability in phenological transition dates. Finally, for deciduous forests, misrepresentation of the seasonal cycle resulted in over‐prediction of gross ecosystem photosynthesis by +160 ± 145 g C m?2 yr?1 during the spring transition period and +75 ± 130 g C m?2 yr?1 during the autumn transition period (13% and 8% annual productivity, respectively) compensating for the tendency of most models to under‐predict the magnitude of peak summertime photosynthetic rates. Models did a better job of predicting the seasonality of CO2 exchange for evergreen forests. These results highlight the need for improved understanding of the environmental controls on vegetation phenology and incorporation of this knowledge into better phenological models. Existing models are unlikely to predict future responses of phenology to climate change accurately and therefore will misrepresent the seasonality and interannual variability of key biosphere–atmosphere feedbacks and interactions in coupled global climate models. 相似文献
53.
Reduced natural selection associated with low recombination in Drosophila melanogaster 总被引:8,自引:1,他引:7
Synonymous codons are not used equally in many organisms, and the extent of
codon bias varies among loci. Earlier studies have suggested that more
highly expressed loci in Drosophila melanogaster are more biased,
consistent with findings from several prokaryotes and unicellular
eukaryotes that codon bias is partly due to natural selection for
translational efficiency. We link this model of varying selection intensity
to the population-genetics prediction that the effectiveness of natural
selection is decreased under reduced recombination. In analyses of 385 D.
melanogaster loci, we find that codon bias is reduced in regions of low
recombination (i.e., near centromeres and telomeres and on the fourth
chromosome). The effect does not appear to be a linear function of
recombination rate; rather, it seems limited to regions with the very
lowest levels of recombination. The large majority of the genome apparently
experiences recombination at a sufficiently high rate for effective natural
selection against suboptimal codons. These findings support models of the
Hill-Robertson effect and genetic hitchhiking and are largely consistent
with multiple reports of low levels of DNA sequence variation in regions of
low recombination.
相似文献
54.
Stphane L. Eeckhoudt Jean-Pierre Desager Yves Horsmans Ann J. De Winne Roger K. Verbeeck 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,710(1-2):165-171
A sensitive high-performance liquid chromatographic method is described for the quantification of midazolam and 1′-hydroxymidazolam in human plasma. Sample (1 ml plasma) preparation involved a simple solvent extraction step with a recovery of approximately 90% for both compounds. An aliquot of the dissolved residue was injected onto a 3 μm capillary C18 column (150 mm×0.8 mm I.D.). A gradient elution was used. The initial mobile phase composition (phosphate buffer–acetonitrile, 65:35) was maintained during 16 min and was then changed linearly during a 1-min period to phosphate buffer–acetonitrile, 40:60. The flow-rate of the mobile phase was 16 μl/min and the eluate was monitored by UV detection. The limits of quantification for midazolam and 1′-hydroxymidazolam were 1 ng/ml and 0.5 ng/ml, respectively. The applicability of the method was demonstrated by studying the pharmacokinetics of midazolam, and its major metabolite 1′-hydroxymidazolam, in human volunteers following i.v. bolus administration of a subtherapeutic midazolam dose (40 μg/kg). 相似文献
55.
Kappa-chain constant-region gene sequences in genus Rattus: coding regions are diverging more rapidly than noncoding regions 总被引:2,自引:0,他引:2
We have determined the nucleotide sequence of a 1,200-base pair (bp)
genomic fragment that includes the kappa-chain constant-region gene (C
kappa) from two species of native Australian rodents, Rattus leucopus
cooktownensis and Rattus colletti. Comparison of these sequences with each
other and with other rodent C kappa genes shows three surprising features.
First, the coding regions are diverging at a rate severalfold higher than
that of the nearby noncoding regions. Second, replacement changes within
the coding region are accumulating at a rate at least as great as that of
silent changes. Third, most of the amino acid replacements are localized in
one region of the C kappa domain--namely, the carboxy-terminal "bends" in
the alpha-carbon backbone. These three features have previously been
described from comparisons of the two allelic forms of C kappa genes in R.
norvegicus. These data imply the existence of considerable evolutionary
constraints on the noncoding regions (based on as yet undetermined
functions) or powerful positive selection to diversify a portion of the
constant-region domain (whose physiological significance is not known).
These surprising features of C kappa evolution appear to be characteristic
only of closely related C kappa genes, since comparison of rodent with
human sequences shows the expected greater conservation of coding regions,
as well as a predominance of silent nucleotide substitutions within the
coding regions.
相似文献
56.
Becca Asquith Angelina J Mosley Adrian Heaps Yuetsu Tanaka Graham P Taylor Angela R McLean Charles RM Bangham 《Retrovirology》2005,2(1):1-9
Background
Cellular infection with human immunodeficiency virus (HIV) both in vitro and in vivo requires a member of the chemokine receptor family to act as a co-receptor for viral entry. However, it is presently unclear to what extent the interaction of HIV proteins with chemokine receptors generates intracellular signals that are important for productive infection.Results
In this study we have used a recently described family of chemokine inhibitors, termed BSCIs, which specifically block chemokine-induced chemotaxis without affecting chemokine ligands binding to their receptors. The BSCI termed Peptide 3 strongly inhibited CCR5 mediated HIV infection of THP-1 cells (83 ± 7% inhibition assayed by immunofluoresence staining), but had no effect on gp120 binding to CCR5. Peptide 3 did not affect CXCR4-dependent infection of Jurkat T cells.Conclusion
These observations suggest that, in some cases, intracellular signals generated by the chemokine coreceptor may be required for a productive HIV infection. 相似文献57.
Nathalie Fieremans Marijke Bauters Stefanie Belet Jelle Verbeeck Anna C. Jansen Sara Seneca Filip Roelens Elfride De Baere Peter Marynen Guy Froyen 《Human genetics》2014,133(11):1359-1367
Xq28 microduplications of MECP2 are a prominent cause of a severe syndromic form of intellectual disability (ID) in males. Females are usually unaffected through near to complete X-inactivation of the aberrant X chromosome (skewing). In rare cases, affected females have been described due to random X-inactivation. Here, we report on two female patients carrying de novo MECP2 microduplications on their fully active X chromosomes. Both patients present with ID and additional clinical features. Mono-allelic expression confirmed complete skewing of X-inactivation. Consequently, significantly enhanced MECP2 mRNA levels were observed. We hypothesize that the cause for the complete skewing is due to a more harmful mutation on the other X chromosome, thereby forcing the MECP2 duplication to become active. However, we could not unequivocally identify such a second mutation by array-CGH or exome sequencing. Our data underline that, like in males, increased MECP2 dosage in females can contribute to ID too, which should be taken into account in diagnostics. 相似文献
58.
R Quintero‐Torres HA Castillo‐Matadamas Jeff F Young RM Bermúdez Cruz 《Luminescence》2014,29(5):440-444
Relaxation dynamics is universal in science and engineering; its study serves to parameterize a system's response and to help identify a microscopic model of the processes involved. When measured data for a phenomenon cannot be fitted using one exponential, the choice of an alternative function to describe the decay becomes nontrivial. Here, we contrast two different, but fundamentally related approaches to fitting nontrivial decay curves; exponential decomposition and the gamma probability density function. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
59.
60.
Narayan P Subramaniyam Outi RM Väisänen Katrina E Wendel Jaakko AV Malmivuo 《Nonlinear biomedical physics》2010,4(Z1):S4