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61.
Triethylamine was very efficient in the dediazoniation of arenediazonium salt. The major product depended on the comparative molar ratio (r) of triethylamine to benzenediazonium salt. When r<0.5, anisole (ionic product) was a major, while benzene (radical product) was a major when r>1. 相似文献
62.
Chun‐Ho Wong Lai‐Sheung Choi Sui‐Lung Yim Dr. Kwun‐Ngai Lau Prof. Dr. Hak‐Fun Chow Sin‐Kam Hui Prof. Dr. Kong‐Hung Sze 《化学:亚洲杂志》2010,5(10):2249-2257
Two series of aliphatic hydrocarbon‐based G1–G3 dendritic 2‐ureido‐4‐pyrimidinones (UPy) ( S‐Gn )2 and ( L‐Gn )2, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p‐aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self‐assembling behavior and tautomeric preference of the dendritic UPy derviatives were examined by 1H NMR spectroscopy. The dimerization constants (Kdim*) of the DDAA tautomers were unchanged at 107 M ?1 in CDCl3 at both 25 and 50 °C, which were comparable to those of UPy compounds bearing other nonpolar substitutents. Furthermore, the lower limits on the K′dim* of the DADA tautomeric forms of the ( S‐Gn )2 and ( L‐Gn )2 series were determined to be 106 and 105 M ?1 in CDCl3, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the ( L‐Gn )2 dimers are more stable than those of ( S‐Gn )2 in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond‐mediated self‐assembling process. 相似文献
63.
The high-resolution (0.06 cm?1) FT-IR spectra of pyridine and pyridine-d5 at various path lengths (up to 10 m) have been obtained. These spectra reveal many new features that were not observed before. For example, the observation of many difference bands allows accurate determination of vibrational term values of some inactive and/or weak fundamental vibrations. The five CH stretching modes have been resolved for the first time. Frequency accuracy and internal consistency (since only high-resolution FT-IR data are used) are essential to the present analysis which provides accurate, isolated molecule term values for most of the fundamental vibrations of pyridine and pyridine-d5. These results will be useful for more accurate force field analyses and serve as a guide for future, higher-resolution rotational studies for which the perturbations can now be predicted with more certainty. 相似文献
64.
In this study, direct surface grafting of nanoporous alumina membranes and glass‐supported alumina films was carried out with three different fluorinated organic acids: trifluoroacetic acid, perfluoropentanoic acid and 2,3,4,5,6‐pentafluorobenzoic acid. Elemental surface composition and chemical environment of alumina were investigated using X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Alumina surfaces grafted with fluoro‐organic acids exhibited increased hydrophobic properties compared to ungrafted surfaces when measured using goniometry and atomic force microscopy (AFM). This work describes the evidence for surface chemical modification of alumina using direct reaction with organic acids. An AFM study of the adsorption of the immunoglobulin G (IgG) molecules on the fluoro‐organic‐acid‐grafted surfaces is reported. The results show that an ordered arrangement of immunoglobulin G structures with in‐filling of pores could be achieved only on the more hydrophobic fluoro‐organic‐acid‐grafted alumina membranes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
65.
Mandi J. Curtis Julia Beaumont Fadil Elamin Andrew S. Wilson Hannah E. C. Koon 《Rapid communications in mass spectrometry : RCM》2022,36(13):e9305
Rationale
Sampling of dentine for stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in the direction of tooth growth allows the study of temporal changes to the diet and physiological stress of an individual during tooth formation. Current methods of sampling permanent teeth using 1 mm increments provide temporal resolution of 6–9 months at best depending on the tooth chosen. Although this gives sufficient sample sizes for reliable analysis by mass spectrometry, sectioning the dentine across the incremental structures results in a rolling average of the isotope ratios. A novel method of incremental dentine collagen sampling has been developed to decrease the collagen increment size to 0.35 mm along the incremental structures, thus reducing averaging and improving the temporal resolution of short-term changes within the δ13C and δ15N values.Methods
This study presents data for a MicroMill-assisted sampling method that allows for sampling at 0.35 mm width × 1 mm depth increments following the incremental growth pattern of dentine. A NewWave MicroMill was used to sample the demineralised dentine section of modern donated human third molars from Sudan and compared to data from the same teeth using the 1 mm incremental sectioning method 2 established by Beaumont et al.Results
The δ13C and δ15N isotopic data showed an increased temporal resolution, with each increment providing data for 2–4 months of dentine formation.Conclusions
The data show the potential of this method for studying dietary reconstruction, nutritional stress, and physiological change with greater temporal resolution potentially to seasonal level and with less attenuation of the δ13C and δ15N values than was previously possible from human dentine.66.
Xianzhong Yan Xiangming Kong Youlin Xia Kong Hung Sze Guang Zhu 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,147(2):357
Recent developments in the direct observation of J couplings across hydrogen bonds in proteins and nucleic acids provide additional information for structure and function studies of these molecules by NMR spectroscopy. A JNN-correlated [15N, 1H] TROSY experiment proposed by Pervushin et al. (Proc. Natl. Acad. Sci. USA 95, 14147–14151, 1998) can be applied to measure hJHN in smaller nucleic acids in an E.COSY manner. However, it cannot be effectively applied to large nucleic acids, such as tRNATrp, since one of the peaks corresponding to a fast relaxing component will be too weak to be observed in the spectra of large molecules. In this Communication, we proposed a modified JNN-correlated [15N, 1H] TROSY experiment which enables direct measurement of hJHN in large nucleic acids. 相似文献
67.
68.
Two MCM-41 derived adsorbents have been tailor-made for the separation of silver and copper ions using the hard-soft, acid-base (HSAB) principle as the design guideline. NH2-MCM-41 containing "hard" Lewis base adsorption sites (i.e., RNH2) was prepared for the adsorption of the "hard" Lewis acid, Cu2+, and SH-MCM-41 with a grafted "soft" thiolpropyl base was prepared for the selective removal of Ag+, a "soft" Lewis acid. Single- and binary-component adsorption studies were conducted at different metal concentrations, solution compositions, and pH values. The experimental results showed that SH-MCM-41 has excellent affinity and capacity for silver adsorption and adsorbed only the silver ions with copper remaining in the solution. The selectivity was not affected by the metal concentration and composition, anion, and pH. Under similar experimental conditions, NH2-MCM-41 selectively adsorbed copper from the binary solution. The selectivity of NH2-MCM-41 remained for the copper at different pH values, although the adsorption capacity diminished at lower pH values. The type of anions used affected copper adsorption on NH2-MCM-41 with an increased copper uptake in the presence of the sulfate ions. A simple Freundlich adsorption model was sufficient to describe metal adsorption on SH-MCM-41 and NH2-MCM-41, and the LeVan and Vermeulen model was successfully used to predict the adsorption capacity and selectivity for binary-component adsorptions. 相似文献
69.
A general covariant conservation law of energy-momentum in complex general relativity is obtained by way of general displacement transformation in terms of Ashtekar's new variables. The energy is exactly the adm Hamiltonian on the constraint surface on condition that an appropriate time function is chosen. The energy-momentum is gauge covariant and commutes with all the constraints whence they are physical observables. Furthermore, the Poisson brackets of the momentum and the internalSU(2) charges form a 3-Poincaré algebra. 相似文献
70.
Hsiao-Hua K. Burke Nien Dak Sze 《Journal of Quantitative Spectroscopy & Radiative Transfer》1977,17(6):783-793
In this paper, we compare the variational and discrete ordinate methods applied to their simplest representative cases: the 2-step function variational method and the 2-stream approach. It is shown that both methods require minimal computational time. Numerical results of the source functions, intensities and fluxes for the problem of diffuse reflection by different plane-parallel isotropic atmospheres are compared between the two methods. Limitations of both approaches for different single scattering albedos and optical depths are discussed. It is also shown that the variational technique is a more efficient algorithm in handling multi-layer cloud conditions for radiative transfer problems. 相似文献