全文获取类型
收费全文 | 71篇 |
免费 | 4篇 |
专业分类
化学 | 55篇 |
数学 | 1篇 |
物理学 | 19篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2013年 | 2篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 2篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1967年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有75条查询结果,搜索用时 625 毫秒
21.
Robert George Acres Sarah Louise Harmer David Allan Beattie 《Journal of synchrotron radiation》2010,17(5):606-615
Synchrotron‐based photoemission electron microscopy (PEEM; probing the surface region) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS; probing the uppermost surface layer) have been used to image naturally heterogeneous samples containing chalcopyrite (CuFeS2), pentlandite [(Ni,Fe)9S8] and monoclinic pyrrhotite (Fe7S8) both freshly polished and exposed to pH 9 KOH for 30 min. PEEM images constructed from the metal L3 absorption edges were acquired for the freshly prepared and solution‐exposed mineral samples. These images were also used to produce near‐edge X‐ray absorption fine‐structure spectra from regions of the images, allowing the chemistry of the surface of each mineral to be interrogated, and the effect of solution exposure on the mineral surface chemistry to be determined. The PEEM results indicate that the iron in the monoclinic pyrrhotite oxidized preferentially and extensively, while the iron in the chalcopyrite and pentlandite underwent only mild oxidation. The ToF‐SIMS data gave a clearer picture of the changes happening in the uppermost surface layer, with oxidation products being observed on all three minerals, and significant polysulfide formation and copper activation being detected for pyrrhotite. 相似文献
22.
Maire P Königsmann M Sreekanth A Harmer J Schweiger A Grützmacher H 《Journal of the American Chemical Society》2006,128(20):6578-6580
A [16 + 1] valence electron configured rhodium aminyl radical complex could be synthesized and characterized in detail by pulse EPR spectroscopy and DFT calculations. The unpaired electron is delocalized over the metal center and two adjacent nitrogens. H-abstraction reactions from thiols and triethylsilane show that the spin density is predominantly localized on both nitrogens. 相似文献
23.
24.
Macquarrie DJ Tavener SJ Harmer MA 《Chemical communications (Cambridge, England)》2005,(18):2363-2365
Perfluorinated sulfonic acids have been immobilised into mesoporous silica frameworks by a one-step process, representing the first example of the successful incorporation of charged silanes using this route, and have been shown to be excellent catalysts for Br?nsted acid catalysed transformations. 相似文献
25.
Based on Brownian ratchets, a counterintuitive phenomenon has recently emerged-namely, that two losing games can yield, when combined, a paradoxical tendency to win. A restriction of this phenomenon is that the rules depend on the current capital of the player. Here we present new games where all the rules depend only on the history of the game and not on the capital. This new history-dependent structure significantly increases the parameter space for which the effect operates. 相似文献
26.
Parrondo's games present an apparently paradoxical situation where individually losing games can be combined to win. In this article we analyze the case of two coin tossing games. Game B is played with two biased coins and has state-dependent rules based on the player's current capital. Game B can exhibit detailed balance or even negative drift (i.e., loss), depending on the chosen parameters. Game A is played with a single biased coin that produces a loss or negative drift in capital. However, a winning expectation is achieved by randomly mixing A and B. One possible interpretation pictures game A as a source of "noise" that is rectified by game B to produce overall positive drift-as in a Brownian ratchet. Game B has a state-dependent rule that favors a losing coin, but when this state dependence is broken up by the noise introduced by game A, a winning coin is favored. In this article we find the parameter space in which the paradoxical effect occurs and carry out a winning rate analysis. The significance of Parrondo's games is that they are physically motivated and were originally derived by considering a Brownian ratchet-the combination of the games can be therefore considered as a discrete-time Brownian ratchet. We postulate the use of games of this type as a toy model for a number of physical and biological processes and raise a number of open questions for future research. (c) 2001 American Institute of Physics. 相似文献
27.
Ole Mallow Monther A. Khanfar Moritz Malischewski Pamela Finke Malte Hesse Enno Lork Timo Augenstein Frank Breher Jeffrey R. Harmer Nadezhda V. Vasilieva Andrey Zibarev Artem S. Bogomyakov Konrad Seppelt Jens Beckmann 《Chemical science》2015,6(1):497-504
One-electron oxidation of two series of diaryldichalcogenides (C6F5E)2 (13a–c) and (2,6-Mes2C6H3E)2 (16a–c) was studied (E = S, Se, Te). The reaction of 13a and 13b with AsF5 and SbF5 gave rise to the formation of thermally unstable radical cations [(C6F5S)2]˙+ (14a) and [(C6F5Se)2]˙+ (14b) that were isolated as [Sb2F11]– and [As2F11]– salts, respectively. The reaction of 13c with AsF5 afforded only the product of a Te–C bond cleavage, namely the previously known dication [Te4]2+ that was isolated as [AsF6]– salt. The reaction of (2,6-Mes2C6H3E)2 (16a–c) with [NO][SbF6] provided the corresponding radical cations [(2,6-Mes2C6H3E)2]˙+ (17a–c; E = S, Se, Te) in the form of thermally stable [SbF6]– salts in nearly quantitative yields. The electronic and structural properties of these radical cations were probed by X-ray diffraction analysis, EPR spectroscopy, and density functional theory calculations and other methods. 相似文献
28.
Xiuxiu Yang Dr. Thomas L. Gianetti Joshua Harbort Dr. Michael D. Wörle Dr. Lilin Tan Prof. Dr. Cheng‐Yong Su Pascal Jurt Assoc. Prof. Jeffrey R. Harmer Prof. Dr. Hansjörg Grützmacher 《Angewandte Chemie (International ed. in English)》2016,55(39):11999-12002
We report the synthesis of a series of ruthenium complexes supported by the phosphine olefin ligand tropPPh2 (trop=5‐H‐dibenzo‐[a,d]cyclohepten‐5‐yl) in the oxidation states 0, +I, and +II, formed via successive one‐electron oxidization steps from Ru0(tropPPh2)2. The bidentate character of the tropPPh2 ligand and its steric hindrance force the complexes to adopt uncommon geometries, which were investigated by X‐ray diffraction analysis. EPR data of the mononuclear RuI complex reveal couplings of the unpaired spin with the ruthenium and two phosphorus nuclei, as well as the olefinic protons which show that the spin is mainly localized on the RuI center. 相似文献
29.
Harmer J Finazzo C Piskorski R Ebner S Duin EC Goenrich M Thauer RK Reiher M Schweiger A Hinderberger D Jaun B 《Journal of the American Chemical Society》2008,130(33):10907-10920
Methanogenic archaea utilize a specific pathway in their metabolism, converting C1 substrates (i.e., CO2) or acetate to methane and thereby providing energy for the cell. Methyl-coenzyme M reductase (MCR) catalyzes the key step in the process, namely methyl-coenzyme M (CH3-S-CoM) plus coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. The active site of MCR contains the nickel porphinoid F430. We report here on the coordinated ligands of the two paramagnetic MCR red2 states, induced when HS-CoM (a reversible competitive inhibitor) and the second substrate HS-CoB or its analogue CH3-S-CoB are added to the enzyme in the active MCR red1 state (Ni(I)F430). Continuous wave and pulse EPR spectroscopy are used to show that the MCR red2a state exhibits a very large proton hyperfine interaction with principal values A((1)H) = [-43,-42,-5] MHz and thus represents formally a Ni(III)F430 hydride complex formed by oxidative addition to Ni(I). In view of the known ability of nickel hydrides to activate methane, and the growing body of evidence for the involvement of MCR in "reverse" methanogenesis (anaerobic oxidation of methane), we believe that the nickel hydride complex reported here could play a key role in helping to understand both the mechanism of "reverse" and "forward" methanogenesis. 相似文献
30.