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81.
Nicholas P. McKay David L. Dettman Robert T. Downs Jonathan T. Overpeck 《Journal of Raman spectroscopy : JRS》2013,44(3):469-474
The potential for using Raman spectroscopy to measure stable oxygen isotope ratios (18O/16O) in carbonates is evaluated by measuring the Raman spectra and isotope ratios of a suite of 60 synthesized, 18O‐enriched calcite crystals ranging in composition from natural abundance (0.2 mole‐% 18O) to 1.2 mole‐% 18O. We determined the Raman‐inferred isotopic ratios (RRaman) by fitting curves to the ν1 symmetric stretching peak at 1086 cm−1 and the smaller satellite peak, associated with the ν1 stretching mode of singly substituted carbonate groups (C16O218O) at 1065 cm−1. The ratio of the two peak areas shows a 1:1 correspondence with the 18O/16O ratios derived from standard mass spectrometry methods, confirming that the relative intensities of the ν1 symmetric stretching peaks is a direct measure of the isotopic ratio in the carbonates. The 1‐sigma uncertainties of the RRaman values of the individual crystals were 0.00079 (384‰ PDB) and 0.00043 (210‰ PDB) for the four‐crystal sample means. This level of uncertainty is much too high to provide significant estimates of natural variability; however, there are multiple prospects for improving the accuracy and precision of the technique. Carbon isotope ratios in carbonates cannot be measured by our approach, but our results highlight the potential of Raman‐based isotope ratio measurement for C and other elements in minerals and organic compounds. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
82.
Hans-Dieter Scharf 《Angewandte Chemie (International ed. in English)》1974,13(8):520-533
Monohalo- and dihalovinylene carbonates constitute a new class of cyclophiles which permit simultaneous introduction of masked α-hydroxyketo and α-diketo functions, respectively, into the cycloadducts. Demasking can be performed by simple hydrolysis. Solvolytic opening of the carbonate ring leads to glycolic acid derivatives in the case of the monohalo compounds and to glyoxylic acid derivatives with the dihalo compounds. Preparation of the title compounds, their potential as synthetic reagents, and the chemistry of their simple reaction products are surveyed from a preparative viewpoint. 相似文献
83.
A catalytic system of triethanolamine/potassium iodide (KI) was proved to be efficient for the chemical fixation of CO2 with epoxide. It was found that triethanolamine with dual function could activate both CO2 and epoxides. Effects of parameters such as catalyst molar ratio and amount, reaction time, pressure, and temperature were studied systematically. As a result, 99% propylene oxide conversion as well as 99% propylene carbonate selectivity could be obtained under the optimal reaction condition. Furthermore, the catalyst was found to be applicable to a variety of terminal epoxides, providing the corresponding cyclic carbonates in good yields and selectivity. Moreover, the catalyst could be reused five times without loss of activity. This work presents an example of a cheap and efficient catalyst for the chemical fixation of CO2 to high-value chemicals, which could help to improve the catalytic efficiency and decrease cost of products for larger applications. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.] 相似文献
84.
The first Lewis base-catalysed allylic sulfuration of Morita–Baylis–Hillman (MBH) adducts derived from ketones (isatins) has been developed, which affords C3-quaternary oxindole derivatives bearing thio-group at 3-position in good to excellent yield (up to 98% yield) under mild reaction conditions. Significantly, the potential utility of the protocol also has been demonstrated by gram-scale synthesis of 3-alkylthio-2-oxindole (3ae), a low catalyst loading (0.3 mol %) and facile conversion of resulting product (3ad) into functionalized pyrrolidinone (5ad). 相似文献
85.
Diego Garay-Ruiz Prof. Dr. Carles Bo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11618-11626
The heterolytic decomposition of tert-butyl peroxyformate to tert-butanol and carbon dioxide, catalyzed by pyridine, is a long-known example of a reaction whose kinetics are strongly affected by solvent polarity. From DFT and ab initio methods together with the SMD implicit solvation model, an extension on the formerly accepted mechanism is proposed. This novel proposal involves the formation of a carbonic acid ester intermediate and its further decomposition, through an unreported pyridine-mediated stepwise route. Computed barriers for this mechanism at DLPNO/CCSD(T)-def2-TZVP are in excellent agreement with experimental kinetic data across different solvents. Furthermore, the strong relationships between activation energies, geometric parameters in the transition state and the characteristics of the different solvents are also analyzed in depth. 相似文献
86.
87.
Ben. J. Tickner Dr. Wissam Iali Dr. Soumya S. Roy Dr. Adrian C. Whitwood Prof. Simon B. Duckett 《Chemphyschem》2019,20(2):241-245
The formation and hyperpolarization of an [Ir(H)2(amine)(IMes)(η2-imine)]Cl complex that can be created in a hyperpolarized nuclear singlet state is reported. These complexes are formed when an equilibrium mixture of pyruvate, amine (benzylamine or phenylethylamine), and the corresponding imine condensation product, react with preformed [Ir(H)2(amine)3(IMes)]Cl. These iridium α-carboxyimine complexes exist as two regioisomers differentiated by the position of amine. When examined with para-hydrogen the hydride resonances of the isomer with amine trans to hydride become strongly hyperpolarized. The initial hydride singlet states readily transfer to the corresponding 13C2 state in the labelled imine and exhibit magnetic state lifetimes of up to 11 seconds. Their 13C signals have been detected with up to 420 fold signal gains at 9.4 T. On a longer timescale, and in the absence of H2, further reaction leads to the formation of neutral carbonate containing [Ir(amine)(η2-CO3)(IMes)(η2-imine)]. Complexes are characterized by, IR, MS, NMR and X-ray diffraction. 相似文献
88.
Beom Kyu Min Gieun Kim Hwa Jung Roh Da Young Seo Jae Nyoung Kim 《Tetrahedron letters》2018,59(17):1674-1678
Various spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety have been synthesized via [3+2] annulation reaction of carbon disulfide and the nitrogen ylides derived from Morita-Baylis-Hillman carbonates of isatins. 2,3-Dihydro- and 2,5-dihydrothiophene-2-thione moieties were formed selectively depending on steric hindrance around the nitrogen ylides. 相似文献
89.
Frost RL Dickfos MJ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(1):143-146
The Raman spectra of shortite and barytocalcite complimented with infrared spectra have been used to characterise the structure of these carbonate minerals. The Raman spectrum of barytocalcite shows a single band at 1086cm(-1) attributed to the (CO(3))(2-) symmetric stretching mode, in contrast to shortite where two bands are observed. The observation of two bands for shortite confirms the concept of more than one crystallographically distinct carbonate unit in the unit cell. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of both shortite and barytocalcite. 相似文献
90.
Copolymerization of racemic propylene oxide with carbon dioxide is investigated in the presence of economically inexpensive and effective achiral salophenCo(III)X [salophen = N,N'-bis(3,5-di-tert-butylsalicylidene)-phenylenediimine, X = pentaflorobenzoate] catalyst and tetrabutyl ammonium bromide as co-catalyst. Effects of different variables like monomer to catalyst ratio, catalyst/co-catalyst ratio, temperature, pressure of CO2 on molecular weight, yield and selectivity of poly(propylene carbonate) [PPC] have been investigated. The maximum Mw of 25.8 g/mol has been obtained at 15 bar and 50°C. All the samples were found to have excellent polydispersity near to 1. 相似文献