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31.
Silica gel surfaces modified with 2- or 4-aminopyridine groups were used to adsorb MCl2 (M = Co, Ni, Cu, Zn) from ethanol and acetone solutions at 298 K. The chemisorption isotherms fitted a modified Langmuir equation very well and are similar for all cations. The capacity of anchored 4-aminopyridine (SIL4) in adsorbing the metallic ion is larger than that of the immobilized 2-aminopyridine (SIL2). The maximum retention capacity has the sequence Cu> Co> Zn in acetone for both surfaces, and Zn> Co> Cu> Ni for SIL2, and Zn> Cu> Co> Ni for SIL4 in ethanol. For a given cation, the variation in enthalpy of solvent-solute exchange on the surface is always larger in ethanol. This process seems to be related to the enthalpy of solvation of the cation involved in the exchange. 相似文献
32.
Intramolecular C-H insertion using NHC-di-rhodium(II) complexes: the influence of axial coordination
In this work we show that the intramolecular C-H insertion of diazo-acetamides catalysed by di-rhodium(II) complexes can be highly influenced by the axial ligand on the di-rhodium(II) complex. Axially monocoordinated NHC-Rh2(OAc)4 complexes have a distinct reactivity from the parent Rh2(OAc)4 complex affording the cyclisation products in different rates and selectivities. Surprisingly, a new reaction mode emerged when using these complexes which led to a decarbonylation pathway. 相似文献
33.
An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations. 相似文献
34.
Elisana Afonso Moura Lidiane Pinto Correia Márcia Ferraz Pinto José Valdilânio Virgulino Procópio Fábio Santos de Souza Rui Oliveira Macedo 《Journal of Thermal Analysis and Calorimetry》2010,100(1):289-293
This article had studied the thermal characterization of the raw material and different fluconazole crystals, obtained through
recrystallization with different solvents using thermoanalytical techniques (TG, DTA, DSC-50, DSC Photovisual, DSC-60) and
Pyr-GC/MS. The results confirmed that the fluconazole volatilizes without decomposition until 250 °C. Pyr-GC/MS showed hexachlorobenzene
like impurities in fluconazole raw material. 相似文献
35.
G.?BaraldiEmail author A.?Perea C.?N.?Afonso 《Applied Physics A: Materials Science & Processing》2011,105(1):75-79
We study the dynamics of ions produced upon ablation of Al and ceramic Al2O3 targets using nanosecond laser pulses at 193 nm (6.4 eV) as a function of the laser fluence from threshold up to 12 J cm−2. An electrical (Langmuir) probe located at 40 mm from the target surface has been used for determining the ion yield and
calculating the kinetic energy distributions. The results for both targets show the existence of a significant amount of ions
having kinetic energies >200 eV (≈20% around threshold fluence), and kinetic energies are up to >1.5 keV. The results are
related with the existence of direct photonionization processes caused by the photon energy of the laser being higher than
the ionization potential of Al (5.98 eV). Comparison of the ion yield when ablating the two types of targets for fluences
above threshold to data reported in the literature suggests that the magnitude of the yield and its threshold are parameters
depending on the thermal properties of the target rather than on the laser wavelength. Around threshold, the different behavior
of ion yield when ablating Al and Al2O3 targets suggests that the threshold for neutral aluminium and ion species in the case of ablation of the Al2O3 target must be similar. 相似文献
36.
Alternate pulsed laser deposition from the host (Al2O3) and dopant (Er, Yb) targets has been used to prepare artificially nanostructured films in which the rare earth ion-ion separation is controlled in the nanometer scale in order to control energy transfer between ions. One series of films was prepared in the standard on-axis configuration, i.e. a static substrate being centred with respect to the plasma expansion axis. A second series of films was prepared by rotating the substrate with respect to a shifted axis parallel to the plasma expansion one (off-axis configuration). The latter configuration leads to films with enhanced thickness and Er related photoluminescence intensity uniformity. More interestingly, the Er related photoluminescence lifetime in as-grown films increases up to 2.5 ms, which is much higher than the maximum value of 1 ms obtained for the on-axis configuration films. This enhancement is discussed in terms of a decrease of defect density when using the off-axis configuration. 相似文献
37.
M. Jiménez de Castro R. SernaM.G. Marzoa A. CasteloC.N. Afonso E. Haro-Poniatowski 《Applied Surface Science》2011,257(12):5172-5174
This work reports optical transmission changes in layered Bi nanostructures (NSs) upon heating-cooling cycles up to temperatures above the melting temperature. The nanostructured films prepared by pulsed laser deposition consist of Bi NSs with different characteristic sizes that are organised in layers and embedded in an amorphous Al2O3 host. The spectral dependence of the optical transmission as well as its changes upon heating are reported. The combination of Bi NSs layers with more than one characteristic size allows controlling the width of the melting-solidification transition. Eventually, it is shown how a multiple temperature thermo-optical film can be designed and prepared. 相似文献
38.
M. Manso S. Pessanha F. Figueira S. Valadas A. Guilherme M. Afonso A. C. Rocha M. J. Oliveira I. Ribeiro M. L. Carvalho 《Analytical and bioanalytical chemistry》2009,395(7):2029-2036
The reddish-brown, brown or yellowish stains of circular or irregular shape known as foxing spots have been fully described
in conservation literature but still, this phenomenon does not find any scientific agreement since many hypotheses have been
raised concerning their origin. In this work a contribution to foxing definition not only focussed on its appearance but also
reported on its chemical information. For this purpose foxing stains present in drawings from two Portuguese artists dated
from the eighteenth to nineteenth centuries were observed under ultra-violet light and optical microscope and analysed by
three non-invasive spectroscopy techniques. The observations carried out on the stains provided information on their surface
morphology. The use of energy-dispersive X-ray fluorescence revealed a variation on the elemental content between foxing and
paper region. Although the results from X-ray diffraction analysis showed no signs of cellulose degradation in foxing stains,
Fourier-transformed infrared analysis revealed the presence of oxide groups. Both the information on the chemical nature and
surface morphology of the stains achieved in this study will contribute to increase foxing formation information and develop
future protocols for conservation purposes. 相似文献
39.
R. Serna C. N. Afonso F. Catalina N. Teixeira M. F. da Silva J. C. Soares 《Applied Physics A: Materials Science & Processing》1992,54(6):538-542
Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12 ns, 193 nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concentration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multilayer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers. 相似文献
40.
Identification and separation of saxitoxins using hydrophilic interaction liquid chromatography coupled to traveling wave ion mobility‐mass spectrometry
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Salomé Poyer Corinne Loutelier‐Bourhis Gaël Coadou Florence Mondeguer Julien Enche Anne Bossée Philipp Hess Carlos Afonso 《Journal of mass spectrometry : JMS》2015,50(1):175-181
The aim of this work was to develop a reliable and efficient analytical method to characterise and differentiate saxitoxin analogues (STX), including sulphated (gonyautoxins, GTX) and non‐sulphated analogues. For this purpose, hydrophilic interaction liquid chromatography (HILIC) was used to separate sulphated analogues. We also resorted to ion mobility spectrometry to differentiate the STX analogues because this technique adds a new dimension of separation based on ion gas phase conformation. Positive and negative ionisation modes were used for gonyautoxins while positive ionisation mode was used for non‐sulphated analogues. Subsequently, the coupling of these three complementary techniques, HILIC‐IM‐MS, permitted the separation and identification of STX analogues; isomer differentiation was achieved in HILIC dimension while non‐sulphated analogues were separated in the IM‐MS dimension. Additional structural characteristics concerning the conformation of STXs could be obtained using IM‐MS measurements. Thus, the collision cross sections (CCS) of STXs are reported for the first time in the positive ionisation mode. These experimental CCSs correlated well with the calculated CCS values using the trajectory method. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献