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101.
本文提出了管理信息系统可行性研究的必要性,论述了管理信息系统可行性研究的对象,讨论了管理信息系统可行性研究的步骤和内容问题。 相似文献
102.
Heterochromatin protein 1 modifies mammalian PEV in a dose- and chromosomal-context-dependent manner 总被引:11,自引:0,他引:11
Festenstein R Sharghi-Namini S Fox M Roderick K Tolaini M Norton T Saveliev A Kioussis D Singh P 《Nature genetics》1999,23(4):457-461
Locus control regions (LCRs) are gene regulatory elements in mammals that can overcome the highly repressive effects normally associated with heterochromatic transgene locations (for example the centromere) in mice. Deletion of essential LCR sequences renders the cognate gene susceptible to this form of repression, so a proportion of the cells from transgenic mice that would normally express the transgene are silenced-a phenomenon known as position effect variegation (PEV). We show here that PEV can also occur when the transgene is non-centromeric and that the extent of variegation can be developmentally regulated. Furthermore, by overexpressing a mammalian homologue (M31) of Drosophila melanogaster heterochromatin protein 1 (HP1; refs 7,8) in transgenic mouse lines that exhibit PEV, it is possible to modify the proportion of cells that silence the transgene in a dose-dependent manner. Thus, we show M31 overexpression to have two contrasting effects which are dependent on chromosomal context: (i) it enhanced PEV in those lines with centromeric or pericentromeric transgene locations; and (ii) it suppressed PEV when the transgene was non-centromeric. Our results indicate that components or modifiers of heterochromatin may have a chromosomal-context-dependent role in gene silencing and activation decisions in mammals. 相似文献
103.
为提高软件项目案例相似度算法的精确度,在分析传统的基于匹配函数的相似度算法基础上,结合软件项目案例的特点,建立了基于神经网络的软件项目案例相似度算法模型,通过对已完成项目案例学习,模型自动计算案例各个特征之间的权重,解决了人为给定特征权值的主观性,使软件项目案例相似度的更加准确,为软件项目相似案例搜索提供依据. 相似文献
104.
Soderberg AM Berger E Page KL Schady P Parrent J Pooley D Wang XY Ofek EO Cucchiara A Rau A Waxman E Simon JD Bock DC Milne PA Page MJ Barentine JC Barthelmy SD Beardmore AP Bietenholz MF Brown P Burrows A Burrows DN Bryngelson G Byrngelson G Cenko SB Chandra P Cummings JR Fox DB Gal-Yam A Gehrels N Immler S Kasliwal M Kong AK Krimm HA Kulkarni SR Maccarone TJ Mészáros P Nakar E O'Brien PT Overzier RA de Pasquale M Racusin J Rea N York DG 《Nature》2008,453(7194):469-474
Massive stars end their short lives in spectacular explosions--supernovae--that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their 'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding. 相似文献
105.
B2C环境下网络服务质量对顾客忠诚的影响机理 总被引:7,自引:0,他引:7
从B2C环境下消费者与网络商店的整体交易过程出发,在界定网络服务质量的概念及其构成维度的基础上,构建了一个B2C环境下网络服务质量对顾客忠诚的影响机理模型.研究结果表明:网络服务质量可以划分为服务过程质量、服务结果质量和服务补救质量三个维度,这三个维度会通过网络顾客满意这个中间变量正向影响顾客忠诚,服务结果质量还直接通过顾客信任正向影响顾客忠诚.服务过程质量和服务补救质量对顾客信任的影响不显著. 相似文献
106.
Bis JC Kavousi M Franceschini N Isaacs A Abecasis GR Schminke U Post WS Smith AV Cupples LA Markus HS Schmidt R Huffman JE Lehtimäki T Baumert J Münzel T Heckbert SR Dehghan A North K Oostra B Bevan S Stoegerer EM Hayward C Raitakari O Meisinger C Schillert A Sanna S Völzke H Cheng YC Thorsson B Fox CS Rice K Rivadeneira F Nambi V Halperin E Petrovic KE Peltonen L Wichmann HE Schnabel RB Dörr M Parsa A Aspelund T Demissie S Kathiresan S Reilly MP Taylor K Uitterlinden A Couper DJ Sitzer M 《Nature genetics》2011,43(10):940-947
Carotid intima media thickness (cIMT) and plaque determined by ultrasonography are established measures of subclinical atherosclerosis that each predicts future cardiovascular disease events. We conducted a meta-analysis of genome-wide association data in 31,211 participants of European ancestry from nine large studies in the setting of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. We then sought additional evidence to support our findings among 11,273 individuals using data from seven additional studies. In the combined meta-analysis, we identified three genomic regions associated with common carotid intima media thickness and two different regions associated with the presence of carotid plaque (P < 5 × 10(-8)). The associated SNPs mapped in or near genes related to cellular signaling, lipid metabolism and blood pressure homeostasis, and two of the regions were associated with coronary artery disease (P < 0.006) in the Coronary Artery Disease Genome-Wide Replication and Meta-Analysis (CARDIoGRAM) consortium. Our findings may provide new insight into pathways leading to subclinical atherosclerosis and subsequent cardiovascular events. 相似文献
107.
Fox TE Finnegan CM Blumenthal R Kester M 《Cellular and molecular life sciences : CMLS》2006,63(9):1017-1023
The era of sphingolipid-based therapeutics is upon us. A large body of work has been accumulating that demonstrates the distinct biological roles of sphingolipids in maintaining a homeostatic environment and in responding to environmental stimuli to regulate cellular processes. It is thus necessary to further investigate alterations in sphingolipid-metabolism in pathological conditions and, in turn, try to exploit altered sphingolipid-metabolizing enzymes and their metabolites as therapeutic targets. This review will examine how advances in the fields of drug delivery, drug discovery, synthetic chemistry, enzyme replacement therapy, immunobiology, infectious disease and nanotechnology have delivered the potential and promise of utilizing and/or targeting sphingolipid metabolites as therapies for diverse diseases. 相似文献
108.
Deary IJ Yang J Davies G Harris SE Tenesa A Liewald D Luciano M Lopez LM Gow AJ Corley J Redmond P Fox HC Rowe SJ Haggarty P McNeill G Goddard ME Porteous DJ Whalley LJ Starr JM Visscher PM 《Nature》2012,482(7384):212-215
Understanding the determinants of healthy mental ageing is a priority for society today. So far, we know that intelligence differences show high stability from childhood to old age and there are estimates of the genetic contribution to intelligence at different ages. However, attempts to discover whether genetic causes contribute to differences in cognitive ageing have been relatively uninformative. Here we provide an estimate of the genetic and environmental contributions to stability and change in intelligence across most of the human lifetime. We used genome-wide single nucleotide polymorphism (SNP) data from 1,940 unrelated individuals whose intelligence was measured in childhood (age 11 years) and again in old age (age 65, 70 or 79 years). We use a statistical method that allows genetic (co)variance to be estimated from SNP data on unrelated individuals. We estimate that causal genetic variants in linkage disequilibrium with common SNPs account for 0.24 of the variation in cognitive ability change from childhood to old age. Using bivariate analysis, we estimate a genetic correlation between intelligence at age 11 years and in old age of 0.62. These estimates, derived from rarely available data on lifetime cognitive measures, warrant the search for genetic causes of cognitive stability and change. 相似文献
109.
110.
以一个基于面向对象的企业集成模型为研究背景,针对企业物料管理的实际,运用面向对象的系统设计方法和面向对象的程度设计语言C ̄(++)和ROCK,在计算机上实现了相应的物料采购系统。 相似文献