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81.
Polynuclear Cobalt Complexes. III. On meso-[(en)2Co(OH)2Co(en)2] (NO3)4 The structure of the title compound has been determined by X-ray analysis and refined to R = 0,060. The crystals are monoclinic, space group very probably C2/m, with cell dimensions a = 16,113(3), b = 10,946(2), c = 7,193(2) Å, β = 113,22(2)° and Z = 2. The configuration of the cation is ΔΛ IR. and UV./VIS. spectroscopic data are given. 相似文献
82.
An index theory for flows is presented which extends the classical Morse theory for gradient flows on compact manifolds. The theory is used to prove a Morse-type existence statement for periodic solutions of a time-dependent (periodic in time) and asymptotically linear Hamiltonian equation. 相似文献
83.
Synthesis and Biological Evaluation of the Antimicrobial Natural Product Lipoxazolidinone A
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Jonathan J. Mills Kaylib R. Robinson Troy E. Zehnder Prof. Joshua G. Pierce 《Angewandte Chemie (International ed. in English)》2018,57(28):8682-8686
Natural products have historically been a major source of antibiotics and therefore novel scaffolds are constantly of interest. The lipoxazolidinone family of marine natural products, with an unusual 4‐oxazolidinone heterocycle at their core, represents a new scaffold for antimicrobial discovery; however, questions regarding their mechanism of action and high lipophilicity have likely slowed follow‐up studies. Herein, we report the first synthesis of lipoxazolidinone A, 15 structural analogues to explore its active pharmacophore, and initial resistance and mechanism of action studies. These results suggest that 4‐oxazolidinones are valuable scaffolds for antimicrobial development and reveal simplified lead compounds for further optimization. 相似文献
84.
J. Baur U. Strauss G. Bruederl D. Eisert R. Oberschmid B. Hahn H. -J. Lugauer S. Bader U. Zehnder M. Fehrer V. H rle 《Journal of Crystal Growth》2001,230(3-4):507-511
We present a detailed study, on the influence of buffer strain on the MOVPE crystal growth mode in the QW active layer of high-brightness InGaN LEDs on SiC substrate. While highly strained buffers are related to InGaN QWs with homogeneous In-distribution, low In-concentration and reduced quantum efficiency, buffers with reduced strain are shown to induce InGaN-QW growth with a dot-like In-distribution, locally high In-concentration and good quantum efficiency. Using an optimised buffer technology, we developed extremely bright InGaN QW-LEDs with a brightness of more than 7 mW (at 460 nm and 20 mA) in a 5 mm radial lamp, good wavelength stability, low forward voltage, high ESD-stability and low ageing. 相似文献
85.
The small size and low damping of MEMS oscillators give rise to phenomena that are not observed routinely at the macroscopic scale. In this work we document and explain an experimentally observed transition in the response of a doubly clamped micromechanical oscillator with pretension. The transition from softening to hardening is repeatedly observed upon increasing the power of an incident sensing laser beam, a procedure routinely used to improve signal strength during optical detection of resonant motion of microstructures. At intermediate laser power, a novel resonant response that displays characteristics of both softening and hardening in the same sweep, is observed experimentally. Increased laser heating of a structure in tension may be expected to increase softening behavior. Using tools from non-linear dynamics and continuum mechanics, we show that the observed counter-intuitive behavior can be explained by a competition between the opposing responses of linear and non-linear stiffnesses to a change in temperature. 相似文献
86.
The synthesis and X-ray analysis of a racemic dilithiated S-ethyl-N-methyl-S-phenylsulfoximine cluster 2 with N,N,N′,N′-tetramethylethane-1,2-diamine (TMEDA) as coordinating solvent is presented. The lithium complex 2 consists of a mixed tetrameric mono- and dilithio salt. Unexpectedly, a separation of the enantiomers in mono-and dilithiated antipodes with respect to the chirality center on the S-atom is observed. Dilithiation of S-ethyl-N-methyl-S-phenylsulfoximine ( 1 ) affords a chiral dinucleophile which undergoes highly regie- and stereoselective alkylation reactions with bis-electrophiles. 相似文献
87.
88.
Abstract 13CO3 ?- substituted compounds with the aragonite structure show a fine structure of the out-of-plane vibration in the infrared spectra. A simple quantum mechanical model of coupled oscillators is developed to describe quantitatively the observed spectra. The spectra can be interpreted in terms of isolated 12CO 3 ?- and 13CO3 ?- clusters, whose eigenfunctions interact. The heavy ions have localized vibrations, whereas clusters of the light ion with more than one ion show only localized vibrations at small coupling; stronger coupling results in resonant modes. Intensitytransfer from light to heavy ion bands is explained and the consequences of interaction between different clusters are discussed. 相似文献
89.
Ralph A. Zehnder Shane M. Peper Brian L. Scott Wolfgang H. Runde 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(1):i3-i5
The title compound was obtained by reacting UO2 powder in 2 M K2CO3 with hydrogen peroxide. The compound contains individual [U(CO3)2O2(O2)]4− ions, which are linked via an extended network of K atoms and hydrogen bonding. The U atom is coordinated to two trans‐axial O atoms and six O atoms in the equatorial plane, forming distorted hexagonal bipyramids. The carbonate ligands are bound to the U center in a bidentate manner, with U—O bond distances ranging from 2.438 (5) to 2.488 (5) Å. The peroxo group forms a three‐membered ring with the U atom, with U—O bond distances of 2.256 (6) and 2.240 (6) Å. The U=O bond distances of 1.806 (5) and 1.817 (5) Å, and an O—U—O angle of 175.3 (3)° are characteristic of the linear uranyl(VI) unit. 相似文献
90.
Ralph A. Zehnder Robert A. Renn Frank R. Fronczek 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(10):m307-m310
The title compound, [Yb(C2H3O2)(OH)2]·0.5H2O, was obtained via hydrothermal reaction of Yb(CH3COO)3·H2O with NaOH at 443 K. The compound forms two‐dimensional layers with six crystallographically independent YbIII atoms. Four of these form YbO8 coordination polyhedra, while the coordination number of the remaining two YbIII atoms is 7. Five of these coordination polyhedra are interconnected mainly via hydroxide groups, as they build a narrow inner layer that extends infinitely within the ab plane. The sixth YbIII atom resides outside this inner layer and builds a terminal YbO8 coordination polyhedron on the layer surface. Its coordination environment comprises four carboxylate O atoms belonging to three different acetate entities, three hydroxide groups and one water molecule. Adjacent layers experience weak interactions via hydrogen bonds. The Yb—O distances lie in the range 2.232 (4)–2.613 (5) Å. 相似文献