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81.
Campos-Fernández CS Schottel BL Chifotides HT Bera JK Bacsa J Koomen JM Russell DH Dunbar KR 《Journal of the American Chemical Society》2005,127(37):12909-12923
Reactions of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) with solvated first-row transition metals M(II) (M(II) = Ni, Zn, Mn, Fe, Cu) have been explored with emphasis on the factors that influence the identity of the resulting cyclic products for Ni(II) and Zn(II). The relatively small anions, namely [ClO4]- and [BF4]-, lead to the formation of molecular squares [{M4(bptz)4(CH3CN)8} subsetX][X]7, (M = Zn(II), Ni(II); X = [BF4]-, [ClO4]-), whereas the larger anion [SbF6]- favors the molecular pentagon [{Ni5(bptz)5-(CH3CN)10} subsetSbF6][SbF6]9. The molecular pentagon easily converts to the square in the presence of excess [BF4]-, [ClO4]-, and [I]- anions, whereas the Ni(II) square can be partially converted to the less stable pentagon under more forcing conditions in the presence of excess [SbF6]- ions. No evidence for the molecular square being in equilibrium with the pentagon was observed in the ESI-MS spectra of the individual square and pentagon samples. Anion-exchange reactions of the encapsulated ion in [{Ni4(bptz)4(CH3CN)8} subsetClO4][ClO4]7 reveal that a larger anion such as [IO4]- cannot replace [ClO4]- inside the cavity, but that the linear [Br3]- anion is capable of doing so. ESI-MS studies of the reaction between [Ni(CH3CN)6][NO3]2 and bptz indicate that the product is trinuclear. Mass spectral studies of the bptz reactions with Mn(II), Fe(II), and Cu(II), in the presence of [ClO4]- anions, support the presence of molecular squares. The formation of the various metallacyclophanes is discussed in light of the factors that influence these self-assembly reactions, such as choice of metal ion, anion, and solvent. 相似文献
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85.
PEG-400 as an efficient reaction medium for the synthesis of 2,4,5-triaryl-1H-imidazoles and 1,2,4,5-tetraaryl-1H-imidazoles 总被引:1,自引:0,他引:1
An efficient protocol for the one-pot multicomponent synthesis of various 2,4,5-triaryl- IH-imidazoles and 1,2,4,5-tetraaryl-1H-imidazoles using PEG-400 as reaction medium is described. This method has the advantages of good yields, less pollution and simple reaction conditions. 相似文献
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88.
Wolfgang Scherer Andrew C. Dunbar Jos E. Barquera‐Lozada Dominik Schmitz Georg Eickerling Daniel Kratzert Dietmar Stalke Arianna Lanza Piero Macchi Nicola P. M. Casati Jihaan Ebad‐Allah Christine Kuntscher 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(8):2535-2539
Square‐planar d8‐ML4 complexes might display subtle but noticeable local Lewis acidic sites in axial direction in the valence shell of the metal atom. These sites of local charge depletion provide the electronic prerequisites to establish weakly attractive 3c–2e M⋅⋅⋅H C agostic interactions, in contrast to earlier assumptions. Furthermore, we show that the use of the sign of the 1H NMR shifts as major criterion to classify M⋅⋅⋅H C interactions as attractive (agostic) or repulsive (anagostic) can be dubious. We therefore suggest a new characterization method to probe the response of these M⋅⋅⋅H C interactions under pressure by combined high pressure IR and diffraction studies. 相似文献
89.
Tetranuclear, Oxygen Centered Copper(II) Clusters Linked Together with Guanidine-Guanidinate Ligands
Gina M. Chiarella Doris Y. Melgarejo Andrey V. Prosvirin Kim R. Dunbar John P. Fackler 《Journal of Cluster Science》2010,21(3):551-565
The reaction of copper(I) chloride with Htbo (1,4,6-triazabicyclo[3.3.0]oct-4-ene) under reflux in THF with oxidation by oxygen,
produces a neutral cluster comprising two oxo-tetra-copper(II) units connected by six tbo− bridges three of them bind two and the other three bind four metals; each unit also contains three chlorine bridges and a
Htbo terminal ligand. Two different X-ray crystal structures (1a, 1b) have been determined and the magnetic behavior has been studied. The molar magnetic susceptibility measurements indicate
strong exchange interactions within an oxo cluster with coupling constants of J
1 = −163 cm−1 and J
2 = −1.1 cm−1, and a weak interaction across the guanidinate bridges of J
3 = −5.2 cm−1 of the octa-CuII cluster. 相似文献
90.
Brukman MJ Oncins Marco G Dunbar TD Boardman LD Carpick RW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(9):3988-3998
Two phosphonic acid (PA) self-assembled monolayers (SAMs) are studied on three aluminum oxide surfaces: the C and R crystallographic planes of single crystal alpha-alumina (sapphire) and an amorphous vapor-deposited alumina thin film. SAMs are either fully hydrogenated CH3(CH2)17PO3H2 or semifluorinated CF3(CF2)7(CH2)11PO3H2. Atomic force microscope (AFM) topographic imaging reveals that the deposited films are homogeneous, atomically smooth, and stable for months in the laboratory environment. Static and advancing contact angle measurements agree with previous work on identical or similar films, but receding measurements suggest reduced coverage here. To enable reproducible nanotribology measurements with the AFM, a scanning protocol is developed that leads to a stable configuration of the silicon tip. Adhesion for the semifluorinated films is either comparable to or lower than that for the hydrogenated films, with a dependence on contact history observed. Friction between each film and the tips depends strongly upon the type of molecule, with the fluorinated species exhibiting substantially higher friction. Subtle but reproducible differences in friction are observed for a given SAM depending on the substrate, revealing differences in packing density for the SAMs on the different substrates. Friction is seen to increase linearly with load, a consequence of the tip's penetration into the monolayer. 相似文献