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排序方式: 共有393条查询结果,搜索用时 484 毫秒
91.
Structural Chemistry - The newly measured ionization potential of atomic astatine is discussed and compared with that of the recently determined value for polonium and for the other atomic... 相似文献
92.
JPC – Journal of Planar Chromatography – Modern TLC - Experiments and calculations show the importance of analytical management to reliable analytical results. A method with a... 相似文献
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In this article, I discuss Hawthorne’s contextualist solution to Benacerraf’s dilemma. He wants to find a satisfactory epistemology
to go with realist ontology, namely with causally inaccessible mathematical and modal entities. I claim that he is unsuccessful.
The contextualist theories of knowledge attributions were primarily developed as a response to the skeptical argument based
on the deductive closure principle. Hawthorne uses the same strategy in his attempt to solve the epistemologist puzzle facing
the proponents of mathematical and modal realism, but this problem is of a different nature than the skeptical one. The contextualist
theory of knowledge attributions cannot help us with the question about the nature of mathematical and modal reality and how
they can be known. I further argue that Hawthorne’s account does not say anything about a priori status of mathematical and modal knowledge. Later, Hawthorne adds to his account an implausible claim that in some contexts
a gettierized belief counts as knowledge. 相似文献
95.
(E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl diphosphate ( 1 ) is a key intermediate of the deoxyxylulose phosphate pathway of isoprenoid biosynthesis and a precursor of the plant hormone zeatin. The availability of this intermediate with various labeling patterns is pivotal for its use in biosynthetic studies. The number of positions, however, that can be easily labeled by chemical synthesis is limited, and the synthesis by means of recombinant enzymes is laborious and time consuming. We demonstrated that chromoplasts from Capsicum annuum, whose enzyme activity was impaired by freeze‐thawing, accumulate 1 . This observation built the basis for the development of a cell‐free system allowing the synthesis of this intermediate with labels in various positions. With 2C‐methyl‐D ‐erythritol 2,4‐cyclodiphosphate ( 5 ) as substrate, yields were in the range of 50%. 相似文献
96.
Grubišic Sonja Gruden-Pavlović Maja Niketić Svetozar R. Sakagami-Yoshida Narumi Kaizaki Sumio 《Transition Metal Chemistry》2003,28(1):37-42
The structure of trans-equatorial [Cr(edtrp)(H2O)] · 3H2O (edtrp3– is the anion of ethylenediamine-N,N,N-tripropionic acid) was determined by single crystal X-ray diffraction. The chromium(III) ion is surrounded octahedrally by the two nitrogen and three oxygen atoms of the quinquedentate edtrp3–, forming a five-membered diamine ring and the three six-membered -propionato chelate rings. The remaining coordination position is occupied by the H2O ligand. The crystal structure conformation is compared to the result of recent molecular mechanics analysis. The ring strain of R and G chelate rings was found to be in agreement with the previously proposed mechanisms for the C—N bond cleavage and recombination. 相似文献
97.
Interpretation of the results of determinations of free fluoride (Ff−) and total fluoride (Ft−) obtained with fluoride ISE while conducting elemental chemical analysis of bulk material of newly synthesized inorganic fluoride compounds is of crucial importance for the purpose of determination of purity and stoichiometry of these compounds. Knowledge of the properties and behavior of these compounds in aqueous media is therefore essential. Observations are presented on the determinations of the amounts of Ft− and Ff− in fluorinated compounds, in the particular hexafluoropnictate salts (PnF6−, Pn = P, As, Sb, Bi) as found in aqueous media and in some compounds with XeF2, AsF3 ligands. A critical look at the determined amounts of Ff−, Ft−and calculated amounts of bound fluoride (Fb−) is provided. 相似文献
98.
Tatiana V. Shubina Maja Remkar Valery Yu. Davydov Kirill G. Belyaev Alexey A. Toropov Bernard Gil 《Annalen der Physik》2019,531(6)
Nanotubes (NTs) of transition metal dichalcogenides (TMDs), were first synthesized more than a quarter of a century ago; nevertheless, many of their optical properties have so far remained basically unknown. Herein, the state of the art in the knowledge of the optical properties of TMD NTs is presented. First, general properties of multilayered crystals are evaluated, and available data on related NTs are analyzed. Then, the technology for the formation and the structural characteristics of NTs are represented, focusing on the structures synthesized by chemical transport reaction. The core of this work is the presentation of the ability of synthesized TMD NTs to emit bright photoluminescence (PL), which has been discovered recently. By means of micro‐PL spectroscopy of individual tubes, we show that excitonic transitions relevant to both direct and indirect band gaps contribute to the emission spectra of the NTs despite having the dozens of monolayers in their walls. The performance of the tubes as efficient optical resonators is highlighted, where confined optical modes strongly affect the emission. Finally, a brief conclusion is presented, along with an outlook of the future studies of this novel radiative member of the NTs family, which have unique potential for different nanophotonics applications. 相似文献
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