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101.
Dr. Kazuhiko Amakawa Dr. Lili Sun Dr. Chunsheng Guo Dr. Michael Hävecker Pierre Kube Prof. Dr. Israel E. Wachs Soe Lwin Prof. Dr. Anatoly I. Frenkel Dr. Anitha Patlolla Prof. Dr. Klaus Hermann Prof. Dr. Robert Schlögl Dr. Annette Trunschke 《Angewandte Chemie (International ed. in English)》2013,52(51):13553-13557
Highly dispersed molybdenum oxide supported on mesoporous silica SBA‐15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2–2.5 Mo atoms nm?2). X‐ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature‐programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O‐K‐edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity. 相似文献
102.
The AIE luminogen tetrakis(2-naphthalenyl)ethene (2-NA 4 E) was synthesized by Barton’s double extrusion diazo-thione coupling method from 2,2′-dinaphthyl thioketone and 2,2′-(diazomethylene)bisnaphthylene in 77 % yield. The structure of 2-NA 4 E was confirmed by its 1H NMR and 13C NMR spectra with full assignments. 2-NA 4 E and its parent tetraphenylethene (Ph 4 E) have been subjected to a comprehensive computational DFT study, in search of their conformational spaces. Seven conformers and two transition states of 2-NA 4 E have been located. Four conformers and one transition state of Ph 4 E have been located. The conformers of 2-NA 4 E and Ph 4 E are not overcrowded, as indicated by the contact distances in the fjord and cove regions. The relative free energies (ΔG 298) of the six most stable conformers of 2-NA 4 E are in the narrow range of 2.3 kJ/mol; they make comparable contributions (12–29 %) to the equilibrium mixture. The energy barriers for the diastereomerization D 2-Z,Z,Z,Z $ \rightleftharpoons $ ? D 2-E,E,E,E via the transition state C 1-Z,E,E,Z and for the enantiomerization C 2-Z,Z,E,E $ \rightleftharpoons $ ? C 2-E,E,Z,Z via the transition state C i -Z,E,Z,E are only 29.8 and 29.0 kJ/mol, respectively, indicating very rapid rates of diastereomerization and enantiomerization at room temperature. The values of naphthalenyl torsion angles and ethenic twist angles in 2-NA 4 E are almost identical to those in the parent Ph 4 E. The previously proposed “bulkiness” of the naphthalenyl substituents and the validity of the restriction of naphthalenyl rotation are challenged. The analysis of the AIE effect in 2-NA 4 E should take into account the intermolecular homochiral and heterochiral interactions between the conformers. 相似文献
103.
Ranjan Patra Israel Goldberg 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(8):819-821
The synthesis is reported of the tricarboxylic acid 3‐(3,5‐dicarboxybenzyloxy)benzoic acid (H3L) and the product of its reaction under solvothermal conditions with ZnII cations, namely poly[[μ6‐3‐(3,5‐dicarboxylatobenzyloxy)benzoato](dimethylformamide)‐μ3‐hydroxido‐dizinc(II)], [Zn2(C16H9O7)(OH)(C3H7NO)]n, the formation of which is associated with complete deprotonation of H3L. Its crystal structure consists of a single‐framework coordination polymer of the organic L3− ligand with ZnII cations in a 1:2 ratio, with additional hydroxide and dimethylformamide (DMF) ligands coordinated to the ZnII centres. The ZnII cations are characterized by coordination numbers of 5 and 6, being bridged to each other by hydroxide ligands. In the polymeric framework, the carboxylate‐ and hydroxy‐bridged ZnII cations are arranged in coordination‐tessellated columns, which propagate along the a axis of the crystal structure, and each L3− ligand links to seven different ZnII centres via Zn—O bonds of two different columns. The coordination framework, composed of [Zn2(L)(OH)(DMF)]n units, forms an open architecture, the channel voids within it being filled by the zinc‐coordinating DMF ligands. This report provides the first structural evidence for the formation of coordination polymers with H3L via multiple metal–ligand bonds through its carboxylate groups.<!?tpb=21.5pt> 相似文献
104.
105.
Isomeric acetylpyridines undergo regiospecific alkylation with methyl iodide under solid/liquid phase transfer conditions (aromatic solvent/KOH/18-crown-6) to give the corresponding isopropyl and/or tert-butyl pyridyl ketones, depending on reaction conditions. 相似文献
106.
Prof. Dr. Sjoerd Harder Dominik Naglav Dr. Christian Ruspic Prof. Dr. Claudia Wickleder Dr. Matthias Adlung Dr. Wilfried Hermes Dr. Matthias Eul Prof. Dr. Rainer Pöttgen Dr. Daniel B. Rego Prof. Dr. Frederic Poineau Prof. Dr. Kenneth R. Czerwinski Prof. Dr. Rolfe H. Herber Prof. Dr. Israel Nowik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12173-12173
107.
Marko Stojkovic Israel Joel Koenka Wolfgang Thormann Peter C. Hauser 《Electrophoresis》2014,35(4):482-486
A CE system featuring an array of 16 contactless conductivity detectors was constructed. The detectors were arranged along 70 cm length of a capillary with 100 cm total length and allow the monitoring of separation processes. As the detectors cannot be accommodated on a conventional commercial instrument, a purpose built set‐up employing a sequential injection manifold had to be employed for automation of the fluid handling. Conductivity measurements can be considered universal for electrophoresis and thus any changes in ionic composition can be monitored. The progress of the separation of Na+ and K+ is demonstrated. The potential of the system to the study of processes in CZE is shown in two examples. The first demonstrates the differences in the developments of peaks originating from a sample plug with a purely aqueous background to that of a plug containing the analyte ions in the buffer. The second example visualizes the opposite migration of cations and anions from a sample plug that had been placed in the middle of the capillary. 相似文献
108.
Chiguils-Prez Yureli Rodrguez-Hurtado Alejandro Israel Prez-Picaso Lemuel Ramrez-Marroqun Oscar Abelardo Martnez-Pascual Roxana Hernndez-Nez Emanuel Vias-Bravo Omar Lpez-Torres Adolfo 《Russian Journal of General Chemistry》2022,91(1):S123-S130
Russian Journal of General Chemistry - Herein, the synthesis of six new derivatives via molecular hybridization of imidazole or triazole and valine methyl ester as a rational design for accessing... 相似文献
109.
Joseph Israel Gurti Prof. Xun-Lei Ding Ya-Ya Wang Yan Chen Dr. Wei Li Dr. Xin Wang 《Chemphyschem》2022,23(14):e202200124
The reaction of N2 with trinuclear niobium and tungsten sulfide clusters Nb3Sn and W3Sn (n=0–3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N−N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb3Sn is generally higher than that of W3Sn. In the favorite reaction pathways, the adsorbed N2 changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N−N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb3Sn decreases because of the hindering effect of S atoms, while W3S and W3S2 have the highest reactivity among four W3Sn clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N2 are analyzed along the reaction pathways to show the activation process of the N−N bond in reactions. The charge transfer from the clusters to the N2 antibonding orbitals plays an essential role in N−N bond activation, which is more significant in Nb3Sn than in W3Sn, leading to the higher reactivity of Nb3Sn. The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR). 相似文献
110.
Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex
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Heather M. Neu Dr. Matthew G. Quesne Tzuhsiung Yang Dr. Katharine A. Prokop‐Prigge Prof. Kyle M. Lancaster James Donohoe Prof. Serena DeBeer Dr. Sam P. de Visser Prof. David P. Goldberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14584-14588
Addition of an anionic donor to an MnV(O) porphyrinoid complex causes a dramatic increase in 2‐electron oxygen‐atom‐transfer (OAT) chemistry. The 6‐coordinate [MnV(O)(TBP8Cz)(CN)]? was generated from addition of Bu4N+CN? to the 5‐coordinate MnV(O) precursor. The cyanide‐ligated complex was characterized for the first time by Mn K‐edge X‐ray absorption spectroscopy (XAS) and gives Mn?O=1.53 Å, Mn?CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN? complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e?‐reduced MnIII(CN)? complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000‐fold versus the same reaction for the parent 5‐coordinate complex. An Eyring analysis gives ΔH≠=14 kcal mol?1, ΔS≠=?10 cal mol?1 K?1. Computational studies fully support the structures, spin states, and relative reactivity of the 5‐ and 6‐coordinate MnV(O) complexes. 相似文献