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排序方式: 共有218条查询结果,搜索用时 125 毫秒
41.
Carina R. Martins Lucas C. Ducati Cludio F. Tormena Roberto Rittner 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(5):1089-1096
The conformational isomerism of 2-chlorocyclopentanone and 2-bromocyclopentanone has been determined through the solvent dependence of the 1H NMR 3JHH coupling constants, theoretical calculations and infrared data, using the solvation theory for the treatment of NMR data. In 2-chlorocyclopentanone, the energy difference (EΨ-e − EΨ-a), in the isolated molecule at B3LYP level of theory, between the pseudo-equatorial (Ψ-e) and pseudo-axial (Ψ-a) conformers is 0.42 kcal mol−1, which decreases in CCl4 and in acetonitrile solutions, in good agreement with infrared data (νCO), despite the uncertainties of the latter method. The conformational equilibrium for 2-bromocyclopentanone is also between the Ψ-e and Ψ-a conformations, with an energy difference (EΨ-e − EΨ-a), in the isolated molecule at B3LYP level of theory, is 0.85 kcal mol−1 which decreases in CCl4 and in acetonitrile solutions, also in good agreement with infrared data. 相似文献
42.
Maribel Arroyo Sylvain Bernès Norma Calixto Carina Gómez 《Journal of fluorine chemistry》2006,127(1):22-28
A series of three new trithioether compounds containing fluorinated phenyl moieties, 1,3,5-(CH2SRf)3-2,4,6-(CH3)3C6, Rf = C6F5 (1), 4-HC6F4 (2), or 2-FC6H4 (3), were prepared by treatment of 1,3,5-(CH2Br)3-2,4,6-(CH3)3C6 with the corresponding Pb(SC6F5)2 or NaSRf. The new structures were verified by elemental analyses, IR, 1H NMR, 19F NMR spectroscopies, and mass spectra. The single crystal X-ray diffraction studies of 1-3 show a similar cis,trans,trans-conformation for the three fluorophenylthiomethyl groups attached to the central benzene ring with all dihedral angles between planes of central ring and external rings close to 0°, giving flat molecules. Comparing, 1-3 with closely related tripodal molecules built-up on 2,4,6-trimethylbenzene, arrangement of one SR group respect to others seems to be defined by the nature of the R substituent. Then in the case of 1-3, a parallel arrangement of rings is favored over an orthogonal one, which would bring the ortho-F atoms close to H atoms of the methylene groups. 相似文献
43.
Dr. Christian Pett Dr. Waqas Nasir Dr. Carina Sihlbom M. Sc. Britt‐Marie Olsson M. Sc. Vanessa Caixeta Dr. Manuel Schorlemer Dr. René P. Zahedi Prof. Göran Larson Dr. Jonas Nilsson Prof. Ulrika Westerlind 《Angewandte Chemie (International ed. in English)》2018,57(30):9320-9324
Distinct structural changes of the α2,3/α2,6‐sialic acid glycosidic linkages on glycoproteins are of importance in cancer biology, inflammatory diseases, and virus tropism. Current glycoproteomic methodologies are, however, not amenable toward high‐throughput characterization of sialic acid isomers. To enable such assignments, a mass spectrometry method utilizing synthetic model glycopeptides for the analysis of oxonium ion intensity ratios was developed. This method was successfully applied in large‐scale glycoproteomics, thus allowing the site‐specific structural characterization of sialic acid isomers. 相似文献
44.
Methyl 5-deoxy-5-iodo-pentofuranosides are reductively ring-opened and propargylated in a tandem fashion in the presence of zinc. The 1,7-enynes thus obtained are subjected to ring-closing enyne metathesis with catalyst B to produce functionalized 1-vinyl cyclohexenes. By adding BnNH(2) to the tandem reaction, an amino group can be introduced in the 1,7-enyne products. Addition of 2-TMS-ethynylcerium(III) chloride after the reductive ring-opening produces the corresponding 1,6-enynes. Further annulation of the product 1,3-dienes can be achieved through a Diels-Alder reaction with good control of stereochemistry. These procedures constitute efficient methods for rapid carbocyclization and annulation of carbohydrates to produce a variety of functionalized five- and six-membered ring systems. 相似文献
45.
The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0 ± 0.1 °C and ionic strength 0.1 M KNO3.Due to the basic pKa of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants.The proposed final model is: PbL, PbL2, PbL2(OH) and PbL2(OH)2 with overall stability constants values, as log β, 3.27 ± 0.06, 6.5 ± 0.1, 12.7 ± 0.1 and 17.27 ± 0.06, respectively.A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed. 相似文献
46.
Cyclization of N-3 substituted 3-thioureidopropanoic acids in isobutyric anhydride at high temperature resulted in the unexpected formation of N-3,N-1-substituted dihydrouracils, as confirmed by thorough spectroscopic characterization. A mechanism based on the identification of intermediates observed at lower reaction temperatures is proposed. 相似文献
47.
48.
Carina Vidovič Dr. Lydia M. Peschel Michael Buchsteiner Prof. Dr. Ferdinand Belaj Prof. Dr. Nadia C. Mösch-Zanetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14267-14272
Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C2H2)(CHCH-SPy)(SPy)] ( 4 ) and [W(CO)(C2H2)(CHCH-SPn)(SPn)] ( 5 ) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C2H2 molecule. Labelling experiments using C2D2 with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C2H2)(SPy)2] ( 6 ) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C2H2)n(MeCN)3−nBr2] (n=1 and 2; 7 ). All complexes represent rare examples in the field of W−C2H2 chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center. 相似文献
49.
50.
Carina Brunecker Dr. Jonas H. Müssig Dr. Merle Arrowsmith Dr. Felipe Fantuzzi Andreas Stoy Dr. Julian Böhnke Dr. Alexander Hofmann Dr. Rüdiger Bertermann Prof. Dr. Bernd Engels Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(39):8518-8523
Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt02 complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt−B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt−B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit. 相似文献