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411.
Cu‐Based Catalyst Resulting from a Cu,Zn,Al Hydrotalcite‐Like Compound: A Microstructural,Thermoanalytical, and In Situ XAS Study 下载免费PDF全文
Dr. Stefanie Kühl Dr. Andrey Tarasov Dr. Stefan Zander Dr. Igor Kasatkin Dr. Malte Behrens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3782-3792
A Cu‐based methanol synthesis catalyst was obtained from a phase pure Cu,Zn,Al hydrotalcite‐like precursor, which was prepared by co‐precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al2O3 catalyst. Upon thermal decomposition in air, the [(Cu0.5Zn0.17Al0.33)(OH)2(CO3)0.17] ? mH2O precursor is transferred into a carbonate‐modified, amorphous mixed oxide. The calcined catalyst can be described as well‐dispersed “CuO” within ZnAl2O4 still containing stabilizing carbonate with a strong interaction of Cu2+ ions with the Zn–Al matrix. The reduction of this material was carefully analyzed by complementary temperature‐programmed reduction (TPR) and near‐edge X‐ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized CuI intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl2O4 spinel‐like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less‐embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings. 相似文献
412.
Regioselective Hydroarylation Reactions of C3 Electrophilic N‐Acetylindoles Activated by FeCl3: An Entry to 3‐(Hetero)arylindolines 下载免费PDF全文
Rodolphe Beaud Dr. Régis Guillot Prof. Cyrille Kouklovsky Dr. Guillaume Vincent 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7492-7500
A method for the direct and rare umpolung of the 3 position of indoles is reported. The activation of N‐acetylindole with iron(III) chloride allows the C?H addition of aromatic and heteroaromatic substrates to the C2?C3 double bond of the indole nucleus to generate a quaternary center at C3 and leads regioselectively to 3‐arylindolines. Optimization, scope (50 examples), practicability (gram scale, air atmosphere, room temperature), and mechanistic insights of this process are presented. Synthetic transformations of the indoline products into drug‐like compounds are also described. 相似文献
413.
David Ropartz Jérôme Lemoine Alexandre Giuliani Yann Bittebière Quentin Enjalbert Rodolphe Antoine Philippe Dugourd Marie-Christine Ralet Hélène Rogniaux 《Analytica chimica acta》2014
Carbohydrates have a wide variety of structures whose complexity and heterogeneity challenge the field of analytical chemistry. Tandem mass spectrometry, with its remarkable sensitivity and high information content, provides key advantages to addressing the structural elucidation of polysaccharides. Yet, classical fragmentation by collision-activated dissociation (CAD) in many cases fails to reach a comprehensive structural determination, especially when isomers have to be differentiated. In this work, for the first time, vacuum ultra-violet (VUV) synchrotron radiation is used as the activation process in tandem mass spectrometry of large oligosaccharides. Compared to low energy CAD (LE-CAD), photon activated dissociation brought more straightforward and valuable structural information. The outstanding feature was that complete series of informative ions were produced, with only minor neutral losses. Moreover, systematic fragmentation rules could be drawn thus facilitating the definitive assignments of fragment identities. As a result, most of the structures present in a complex mixture of oligogalacturonans could be comprehensively resolved, including many isomers differing in the position of methyl groups along the galacturonic acid backbone. 相似文献
414.
Dr. Marcello Gennari Deborah Brazzolotto Shengying Yu Dr. Jacques Pécaut Dr. Christian Philouze Mathieu Rouzières Dr. Rodolphe Clérac Dr. Maylis Orio Dr. Carole Duboc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18770-18778
It has recently been proposed that disulfide/thiolate interconversion supported by transition‐metal ions is involved in several relevant biological processes. In this context, the present contribution represents a unique investigation of the effect of the coordinated metal (M) on the Mn+?disulfide/M(n+1)+?thiolate switch properties. Like its isostructural CoII‐based parent compound, CoII 2 SS (Angew. Chem. Int. Ed. 2014 , 53, 5318), the new dinuclear disulfide‐bridged MnII complex MnII 2 SS can undergo an MII?disulfide/MIII?thiolate interconversion, which leads to the first disulfide/thiolate switch based on Mn. The coordination of iodide to the metal ion stabilizes the oxidized form, as the disulfide is reduced to the thiolate. The reverse process, which involves the reduction of MIII to MII with the concomitant oxidation of the thiolates, requires the release of iodide. The MnII 2 SS complex slowly reacts with Bu4NI in CH2Cl2 to afford the mononuclear MnIII?thiolate complex MnIIII . The process is much slower (ca. 16 h) and much less efficient (ca. 30 % yield) with respect to the instantaneous and quantitative conversion of CoII 2 SS into CoIIII under similar conditions. This distinctive behavior can be rationalized by considering the different electrochemical properties of the involved Co and Mn complexes and the DFT‐calculated driving force of the disulfide/thiolate conversion. For both Mn and Co systems, MII?disulfide/MIII?thiolate interconversion is reversible. However, when the iodide is removed with Ag+, the MII 2 SS complexes are regenerated, albeit much slower for Mn than for Co systems. 相似文献
415.
Farzin Ghanadi Maziar Arjomandi Benjamin S. Cazzolato Anthony C. Zander 《Journal of Turbulence》2013,14(8):705-728
This study investigates the changes in the structure of a turbulent boundary layer downstream of a flow-excited Helmholtz resonator. To this end, a fully developed turbulent boundary layer over a resonator mounted flush with a flat plate was simulated by implementing a large eddy simulation (LES). To assist in understanding the effect of the resonator on the flow structure, a sensitivity study was undertaken by changing the main geometrical parameters of the resonator. The results demonstrated that when the boundary layer thickness equals the orifice length, the cross-stream component of velocity fluctuations penetrates the boundary layer, resulting in a reduction of the turbulence intensity by up to 12%. Therefore, it is concluded that a Helmholtz resonator has the potential to reduce the instabilities within the boundary layer. These investigations also assist in identifying the optimal parameters to delay turbulence events within the grazing flow using Helmholtz resonators. 相似文献
416.
Alfred Basiner Carlotto von Rentelen Brant und Arthur Zander 《Fresenius' Journal of Analytical Chemistry》1882,21(1):617-621
Ohne Zusammenfassung 相似文献
417.
M. Abad J. P. Díaz Varela B. F. López Martinolich M. del C. Vannicola M. Zander 《Central European Journal of Mathematics》2006,4(4):547-561
In this paper we give a term equivalence between the simple k-cyclic Post algebra of order p, L
p,k, and the finite field F(p
k) with constants F(p). By using Lagrange polynomials, we give an explicit procedure to obtain an interpretation Φ1 of the variety V(L
p,k) generated by L
p,k into the variety V(F(p
k)) generated by F(p
k) and an interpretation Φ2 of V(F(p
k)) into V(L
p,k) such that Φ2Φ1(B) = B for every B ε V(L
p,k) and Φ1Φ2(R) = R for every R ε V(F(p
k)). 相似文献
418.
Dr. Tristan Doussineau Dr. Carole Mathevon Dr. Lucie Altamura Dr. Charlotte Vendrely Dr. Philippe Dugourd Dr. Vincent Forge Dr. Rodolphe Antoine 《Angewandte Chemie (International ed. in English)》2016,55(7):2340-2344
Amyloid fibrils are self‐assembled protein structures with important roles in biology (either pathogenic or physiological), and are attracting increasing interest in nanotechnology. However, because of their high aspect ratio and the presence of some polymorphism, that is, the possibility to adopt various structures, their characterization is challenging and basic information such as their mass is unknown. Here we show that charge‐detection mass spectrometry, recently developed for large self‐assembled systems such as viruses, provides such information in a straightforward manner. 相似文献
419.
Cover Picture: Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time‐Dependent Density Functional Theory (ChemPhysChem 19/2016) 下载免费PDF全文
420.
Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time‐Dependent Density Functional Theory 下载免费PDF全文
Dr. Alexander Jan Kulesza Evgenii Titov Dr. Steven Daly Dr. Radosław Włodarczyk Dr. Jörg Megow Prof. Dr. Peter Saalfrank Dr. Chang Min Choi Dr. Luke MacAleese Dr. Rodolphe Antoine Dr. Philippe Dugourd 《Chemphyschem》2016,17(19):3129-3138
Action spectroscopy has emerged as an analytical tool to probe excited states in the gas phase. Although comparison of gas‐phase absorption properties with quantum‐chemical calculations is, in principle, straightforward, popular methods often fail to describe many molecules of interest—such as xanthene analogues. We, therefore, face their nano‐ and picosecond laser‐induced photofragmentation with excited‐state computations by using the CC2 method and time‐dependent density functional theory (TDDFT). Whereas the extracted absorption maxima agree with CC2 predictions, the TDDFT excitation energies are blueshifted. Lowering the amount of Hartree–Fock exchange in the DFT functional can reduce this shift but at the cost of changing the nature of the excited state. Additional bandwidth observed in the photofragmentation spectra is rationalized in terms of multiphoton processes. Observed fragmentation from higher‐lying excited states conforms to intense excited‐to‐excited state transitions calculated with CC2. The CC2 method is thus suitable for the comparison with photofragmentation in xanthene analogues. 相似文献