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排序方式: 共有174条查询结果,搜索用时 15 毫秒
101.
Dmitri V. Sevenard Ralf‐Matthias Schoth Olesya Kazakova Enno Lork Gerd‐Volker Rschenthaler 《Heteroatom Chemistry》2008,19(5):474-482
The reactivity of bis(trifluoroacetyl)‐phenols toward selected λ3P derivatives was examined. In the case of dialkyl(isocyanato)phosphites, only one of both present trifluoracetyl moieties of substrate was involved. After addition of the phenolic OH moiety across the intermediary formed PN bond, tri‐, tetra‐, and pentacyclic α‐(trifluoromethyl)phosphoranes were produced in a highly diastereoselective reaction. An unusual deoxygenation of the intermediary hydroxyphosphorane was observed reacting 4‐methyl‐2,6‐bis‐(trifluoroacetyl)phenol with diethyl(trimethylsilyl)‐phosphite, and the subsequent hydrolysis gave γ‐hydroxy‐α‐(trifluoromethyl)phoshonate. On the contrary, during the reaction of the O‐silylated phenol with tris(trimethylsilyl)phosphite, a bis‐phosphonate was obtained that underwent heterocyclization to phosphono phosphole system. The mechanistic aspects of the studied reactions, as well as structural features of the synthesized compounds are discussed, based on the multinuclear NMR spectroscopy and X‐ray single crystal investigation data. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:474–482, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20451 相似文献
102.
Merlic CA Aldrich CC Albaneze-Walker J Saghatelian A Mammen J 《The Journal of organic chemistry》2001,66(4):1297-1309
The total syntheses of the potent protein kinase C inhibitors calphostins A, B, C, and D as well as a variety of structural analogues are reported. An aminobenzannulation reaction of an enantiopure chromium Fischer carbene complex is utilized to prepare a pentasubstituted naphthylamine. After optimization of side-chain substituents, conversion of the naphthylamine to an o-naphthoquinone was followed by biomimetic oxidative dimerization using trifluoroacetic acid and air yielding a 1:2 P/M mixture of atropisomeric perylenequinones. Thermal equilibration to a 3:1 P:M atropisomeric ratio and separation of the perylenequinones followed by side chain desymmetrization and functionalization led to the total synthesis of enantio- and diastereomerically pure calphostin C in only twelve steps from commercially available starting materials. In addition, calphostins A, B, D, and several structural analogues were prepared to evaluate biological activities. 相似文献
103.
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105.
Dr. Oleg O. Shyshkov Dr. Alexander A. Kolomeitsev Prof. Dr. Berthold Hoge Dr. Enno Lork Dr. Axel Haupt Mira Keßler Prof. Dr. Gerd-Volker Röschenthaler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(14):e202104308
Phosphoranides are interesting hypervalent species which serve as model compounds for intermediates or transition states in nucleophilic substitution reactions at trivalent phosphorus substrates. Herein, the syntheses and properties of stable trifluoromethylphosphoranide salts are reported. [K(18-crown-6)][P(CF3)4], [K(18-crown-6)][P(CF3)3F], and [NMe4][P(CF3)2F2] were obtained by treatment of trivalent precursors with sources of CF3− or F− units. These [P(CF3)4-nFn]− (n=0–2) salts exhibit fluorinating (n=1–2) or trifluoromethylating (n=0) properties, which is disclosed by studying their reactivity towards selected electrophiles. The solid-state structures of [K(18-crown-6)][P(CF3)4] and [K(18-crown-6)][P(CF3)3F] are ascertained by single crystal X-ray crystallography. The dynamics of these compounds are investigated by variable temperature NMR spectroscopy. 相似文献
106.
Dr. Martin Hejda Daniel Duvinage Enno Lork Prof. Dr. Antonín Lyčka Prof. Dr. Zdeněk Černošek Dr. Jan Macháček Dr. Sergey Makarov Prof. Dr. Sergey Ketkov Dr. Stefan Mebs Prof. Dr. Libor Dostál Prof. Dr. Jens Beckmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14577-14581
The aryltellurenyl cation [2-(tBuNCH)C6H4Te]+, a Lewis super acid, and the weakly coordinating carborane anion [CB11H12]−, an extremely weak Brønsted acid (pKa=131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C6H4Te][CB11H12], in which the Brønsted acidity (pKa 7.4 in MeCN) of the formally hydridic B−H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B−H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12- and 7-[2-(tBuN{H}CH)C6H4Te(CB11H11)] in ratios ranging from 62 : 38 to 80 : 20. 相似文献
107.
Six adducts of B(C6F5)3 and archetypical alcoholates and carboxylates, were prepared and isolated as crystalline sodium crown ether salts, [Na(15‐crown‐5)][CH3O · B(C6F5)3] ( 1 ), [Na(15‐crown‐5)][CH3CH2O · B(C6F5)3] ( 2 ), [Na(15‐crown‐5)][HCO2 · B(C6F5)3] ( 3 ), [Na(15‐crown‐5)][(H3CCO2 · B(C6F5)3] ( 4 ), [Na(15‐crown‐5)][(F3CCO2 · B(C6F5)3] ( 5 ), and [Na2(15‐crown‐5)3][C2O4 · 2 B(C6F5)3] ( 6 ). All compounds were fully characterized by multinuclear NMR‐ and IR spectroscopy, ESI MS spectrometry, and X‐ray crystallography. 相似文献
108.
Sascha Hoffmann Eugen Justus Michal Ratajski Enno Lork Detlef Gabel 《Journal of organometallic chemistry》2005,690(11):2757-2760
The reaction of B12H11NH3(1−) with carbodiimides can form guanidinium salts containing the boron cluster. Depending on the side chains of the carbodiimide, these derivatives of the B12H12(2−) cluster can be uncharged or can carry an overall positive or negative charge. This reaction allows the preparation of derivatives with aliphatic side chains, in contrast to the acylation reaction of and the formation of Schiff bases, both of which are successful only with aromatic acid chlorides or aromatic, respectively, α,β-unsaturated aldehydes. The acylation of with benzoyl chloride gives an N-protonated form of an imidoacid, carrying a single overall charge. 相似文献
109.
We study the influence of coupling strength and network topology on synchronization behavior in pulse-coupled networks of bursting Hindmarsh-Rose neurons. Surprisingly, we find that the stability of the completely synchronous state in such networks only depends on the number of signals each neuron receives, independent of all other details of the network topology. This is in contrast with linearly coupled bursting neurons where complete synchrony strongly depends on the network structure and number of cells. Through analysis and numerics, we show that the onset of synchrony in a network with any coupling topology admitting complete synchronization is ensured by one single condition. 相似文献
110.