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501.
The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining (13)C NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter
in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The molecular biaxiality order parameter
502.
Electron magnetic resonance (EMR) spectra of gadolinium-doped calcium fluoride have been studied at room temperature for Gd concentrations between 0.01 and 2.00 mol%. Gd3+ ions in sites with two different symmetries were observed. One of the sites, with cubic symmetry, is unstable at room temperature and decays with a time constant of 2.2 day−1. The other site, with tetragonal symmetry, is stable and is attributed to Gd3+ ions in substitutional sites next to a charge-compensating F− interstitial ion. The linewidth and intensity of the EMR spectrum with tetragonal symmetry increase with increasing Gd concentration. A theoretical calculation based on the concentration dependence of the EMR linewidth yields an effective range of the exchange interaction between Gd3+ ions in CaF2 of 0.774 nm, of the same order as that of Gd3+ ions in other cubic ionic compounds. 相似文献
503.
Caterina Trotta Dr. Gabriel Menendez Rodriguez Dr. Leonardo Tensi Dr. Alexander V. Yakimov Dr. Luca Rocchigiani Prof. Anna Donnadio Prof. Cristiano Zuccaccia Prof. Christophe Copéret Prof. Alceo Macchioni 《欧洲无机化学杂志》2023,26(26):e202300211
A stringent comparison between two pairs of molecular/immobilized water oxidation catalysts ([Cp*Ir(Me-pica)Cl], 1 , versus 1_SiO2 , Me-pica=κ2-N-methyl-picolinamide; [Cp*Ir(pysa)NO3], 2 , versus 2_SiO2 , pysa=κ2-pyridine-2-sulfonamide]) reveals distinctive catalytic trends. While the molecular compound 1 exhibits a substantial higher activity than the analogous immobilized system 1_SiO2 , under all the experimental conditions explored, the contrary is found with 2 that is far less active than its immobilized counterpart 2_SiO2 . This is explained by the unique tendency of 2 to form dimeric complexes [Cp*Ir-(κ2-μ2-Hpysa)(κ2-μ2-pysa)IrCp*], 2 a , in phosphate buffered solution at pH 7, and [Cp*Ir-(κ2-μ2-Hpysa)2IrCp*], 2 b , in water. 2 a and 2 b have been completely characterized in solution by multinuclear and multidimensional NMR spectroscopy. They have been also isolated as single crystals and their structure in solid state determined by X-Ray diffractometry. 2 a and 2 b appear to be off-cycle species, whose formation is detrimental for water oxidation activity, as indicated by the observation of a long induction period when 2 a is used as catalytic precursor. In addition, TOF versus ΔE (E−E0=−RT/nF ln([IO4−]/[IO3−]) trends for the first two runs do not overlap for catalyst 2 and TOFmax is remarkably higher in the second run upon the addition of fresh NaIO4. In the immobilized system 2_SiO2 the detrimental associative processes are likely inhibited leading to an activity higher than that of 2 . 相似文献
504.
Academic research and the financial industry have recently shown great interest in Machine Learning algorithms capable of solving complex learning tasks, although in the field of firms' default prediction the lack of interpretability has prevented an extensive adoption of the black-box type of models. In order to overcome this drawback and maintain the high performances of black-boxes, this paper has chosen a model-agnostic approach. Accumulated Local Effects and Shapley values are used to shape the predictors' impact on the likelihood of default and rank them according to their contribution to the model outcome. Prediction is achieved by two Machine Learning algorithms (eXtreme Gradient Boosting and FeedForward Neural Networks) compared with three standard discriminant models. Results show that our analysis of the Italian Small and Medium Enterprises manufacturing industry benefits from the overall highest classification power by the eXtreme Gradient Boosting algorithm still maintaining a rich interpretation framework to support decisions. 相似文献
505.
Protonated Porphyrins: Bifunctional Catalysts for the Metal-Free Synthesis of N-Alkyl-Oxazolidinones
Matteo Cavalleri Dr. Caterina Damiano Dr. Dr. Gabriele Manca Prof. Emma Gallo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202202729
The protonation of commercially available porphyrin ligands yields a class of bifunctional catalysts able to promote the synthesis of N-alkyl oxazolidinones by CO2 cycloaddition to corresponding aziridines. The catalytic system does not require the presence of any Lewis base or additive, and shows interesting features both in terms of cost effectiveness and eco-compatibility. The metal-free methodology is active even with a low catalytic loading of 1 % mol, and the chemical stability of the protonated porphyrin allowed it to be recycled three times without any decrease in performance. In addition, a DFT study was performed in order to suggest how a simple protonated porphyrin can mediate CO2 cycloaddition to aziridines to yield oxazolidinones. 相似文献
506.
Ranieri Bizzarri Vittorio Pellegrini Caterina Arcangeli Aldo Ferrari Riccardo Nifosì Pasqualantonio Pingue Valentina Tozzini Mauro Giacca Fabio Beltram 《Macromolecular Symposia》2004,218(1):283-292
The discovery of the photochromic characteristics of engineered green fluorescent proteins (GFPs) allows new proteomics and biomolecular electronic applications. In particular, photoreversibility among two distinct optical states can lead to the realization of a bio-optical high density storage memory. Here we review our recent work on an optically bistable GFP and we report the recent developments of self-assembly methods for spatial immobilization of proteins into well-definite 2D patterns. 相似文献