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排序方式: 共有451条查询结果,搜索用时 937 毫秒
41.
Antonio J. Gómez-Núñez Benjamín Vargas-Quesada Félix de Moya-Anegón Wolfgang Glänzel 《Scientometrics》2011,89(3):741-758
In order to re-categorize the SCImago Journal & Country Rank (SJR) journals based on Scopus, as well as improve the SJR subject
classification scheme, an iterative process built upon reference analysis of citing journals was designed. The first step
entailed construction of a matrix containing citing journals and cited categories obtained through the aggregation of cited
journals. Assuming that the most representative categories in each journal would be represented by the highest citation values
regarding categories, the matrix vectors were reduced using a threshold to discern and discard the weakest relations. The
process was refined on the basis of different parameters of a heuristic nature, including (1) the development of several tests applying different thresholds, (2) the designation of a cutoff, (3) the number of iterations to execute, and (4) a manual review operation of a certain amount of multi-categorized journals. Despite certain shortcomings related with journal classification,
the method showed a solid performance in grouping journals at a level higher than categories—that is, aggregating journals
into subject areas. It also enabled us to redesign the SJR classification scheme, providing for a more cohesive one that covers
a good proportion of re-categorized journals. 相似文献
42.
Two paradigmatic approaches to the normalisation of citation-impact measures are discussed. The results of the mathematical
manipulation of standard indicators such as citation means, notably journal Impact Factors, (called a posteriori normalisation)
are compared with citation measures obtained from fractional citation counting (called a priori normalisation). The distributions
of two subfields of the life sciences and mathematics are chosen for the analysis. It is shown that both methods provide indicators
that are useful tools for the comparative assessment of journal citation impact. 相似文献
43.
Mono- and polyclonal antibodies have been used to study the localization and distribution of cytochrome P450 1A1 (CYP1A1) in cultured precision-cut liver slices with various immunohistochemical methods. Neither in non-incubated slices nor in slices incubated in the absence of beta-naphthoflavone (BNF) for 24 hrs was CYP1A1 immunohistochemically detectable. After incubation in the presence of BNF (25 microM), however, CYP1A1 was well visible in parenchymal and biliary epithelial cells. CYP1A1 was not evenly distributed, but was localized predominantly in hepatocyte layers near the surfaces of the slices. This distribution could be due to the preferential uptake of BNF by outer cell layers or due to functional changes of inner cells. Together with results obtained with other methods (e.g. RT-PCR) this investigation also demonstrates that precision-cut liver slices are a useful tool for the detection of in vitro induction of CYP1A1. 相似文献
44.
45.
H Schwarzenberg S Müller-Hülsbeck CC Glüer F Wesner M Heller 《Canadian Metallurgical Quarterly》1998,170(5):1181-1185
OBJECTIVE: Our objective was to compare intravascular sonography with digital subtraction angiography (DSA) in the assessment of luminal dimension and morphologic features of endovascular stents and stent grafts. MATERIALS AND METHODS: Thirty-seven pelvic and 24 femoral stents (12 Wall-stents; 27 covered and 22 uncovered nitinol stents) in 50 patients were evaluated 15 +/- 10 months after implantation by DSA and intravascular sonography. The degree of maximum instent restenosis as revealed by DSA and intravascular sonography was compared for each location. Morphologic features of the stents and stenoses were also assessed. RESULTS: Intravascular sonography and DSA correlated well (R2 = .96) in determining in-stent restenosis. In-stent restenosis was underestimated by 13% +/- 6% by DSA compared with intravascular sonography. Differences in determining in-stent restenosis with intravascular sonography and DSA were not associated with severity of stenosis or type of stent. Intravascular sonography revealed incomplete expansion of stents in 21 cases, whereas DSA revealed incomplete expansion of stents in seven cases. The intra- and interobserver variabilities in our study were 4% and 5%, respectively. CONCLUSION: In-stent restenoses are underestimated with DSA. Intravascular sonography is superior to DSA for detection of incomplete stent expansion. 相似文献
46.
47.
We present rules for the unsupervised learning of coincidence between excitatory postsynaptic potentials (EPSPs) by the adjustment of postsynaptic delays between the transmitter binding and the opening of ion channels. Starting from a gradient descent scheme, we develop a robust and more biological threshold rule by which EPSPs from different synapses can be gradually pulled into coincidence. The synaptic delay changes are determined from the summed potential--at the site where the coincidence is to be established--and from postulated synaptic learning functions that accompany the individual EPSPs. According to our scheme, templates for the detection of spatiotemporal patterns of synaptic activation can be learned, which is demonstrated by computer simulation. Finally, we discuss possible relations to biological mechanisms. 相似文献
48.
Ekkard Brinksmeier Ralf Gläbe Oltmann Riemer Sven Twardy 《Microsystem Technologies》2008,14(12):1983-1987
Molds for micro forming processes require specific functional surfaces to provide optimized tribological condition for forming
processes. Such topographies with microscopic dimensions can for instance be generated by lithographical methods. However,
a main disadvantage of these processes is their low flexibility, e.g. changing the structures to be generated causes extensive
adaptations in the manufacturing process. Therefore, mechanical precision machining processes like micro milling, micro grinding
and micro polishing are appropriate processes for the manufacture of micro molds of manifold shapes and with well suited micro
topographies. 相似文献
49.
Supercritical fluids and ionic liquids offer attractive opportunities for modifying and applying zeolites as adsorbents and catalysts. After a brief introduction to the most important properties of these solvents, examples of zeolite applications in supercritical fluids and ionic liquids from the recent literature are discussed. Particular emphasis is put on the influence of reaction media on the processes occurring in the zeolitic pore systems, e.g., during shape‐selective conversions in zeolite catalysts. The present potential and future challenges for the application of zeolites in supercritical fluids and ionic liquids are identified. Most attractive process options arise from a combined use of both ionic liquids and supercritical fluids in integrated reaction schemes. 相似文献
50.