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901.
Jeong Ah Chang 《Journal of solid state chemistry》2009,182(4):749-756
Nanosized anatase and rutile TiO2 having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H2O2) in water/isopropanol media by a facile sol-gel process. The TiO2 nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO2 are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given. 相似文献
902.
Annarosa Mangone Lorena C. Giannossa Rocco Laviano Custode S. Fioriello Angela Traini 《Microchemical Journal》2009,91(2):214-221
Late Roman oil lamps from the archaeological site of Egnatia (Fasano, Brindisi, Italy) were characterized from physical–chemical, mineralogical and morphological points of view. Atomic Spectroscopy, Scanning Electron Microscopy and X-Ray Diffraction analyses were carried out on ceramic body and coatings with the aim of identifying the provenance of lamps, in order to arrive at a correct archaeological classification of finds and to outline their technological features.The analytical results show that the finds differ in raw materials and in production technology. The statistical multivariate treatment of compositional data of ceramic bodies groups the objects into two macro clusters and, according to a study of their different petrographic features and by a comparison with coeval pottery whose provenance is already known, suggests one group to have been imported from North Africa and the other to have been locally produced. Moreover, chemical results and in-depth archaeological analyses allow us to split the imported lamps into two subgroups, hypothesizing the first group to originate from central Tunisia and the second from the north of the same country.The analytical characterisation of finds, by different complementary techniques, has allowed us to identify the raw materials and the technological solutions used by the ancient potters from Egnatia to produce lamps. The potters made lamps which had an external appearance very similar to that of African prototypes, but which were nevertheless different as they employed the locally available materials. 相似文献
903.
A novel micellar selectivity triangle (MST) is developed and used to characterize and classify the chemical selectivities of pseudo-phases in electrokinetic chromatography (EKC). The MST scheme is, in concept, similar to the widely known solvent selectivity triangle (SST) originally developed by Snyder. However, the MST is based on linear solvation energy relationships. Thus it incorporates the solvation characteristics of both the pseudo-phase and the bulk solvent; while the SST is basically for classification of pure solvents. The similarities and differences of these pseudo-phases are determined by the relative scales of hydrogen bond donating ability (Xb), hydrogen bond accepting ability (Xa) and dipolarity (Xs). The MST scheme is used for characterization and classification of a wide range of pseudo-phases such as micelles, polymers, vesicles, liposomes, as well as mixed systems such as mixed micelles, mixed polymer–surfactants, organically modified pseudo-phases, etc. Over seventy pseudo-phases were examined and four clusters of pseudo-phases with different selectivity patterns are recognized that include pseudo-phases with strong hydrogen bond acidities (e.g. fluorinated micelles or micelles modified with fluorinated alcohols), strong hydrogen bond acceptor pseudo-phases (such as bile salts, liposomes, microemulsions, as well as biphasic octanol–water system), strong dipolar phase of a class of polymeric pseudo-phase, and pseudo-phases with intermediate hydrogen bonding and dipolarity [like sodium dodecyl sulfate (SDS) and its analogs as well as organically modified SDS]. The MST scheme is also useful in identifying pseudo-phases that closely resemble the selectivities of octanol–water for determination of octanol–water partition coefficients by EKC. 相似文献
904.
Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 μg L−1), the limit of detection (3σ), and the characteristic mass of beryllium were 2.50%, 0.009 μg L−1 and 0.42 pg, respectively. 相似文献
905.
On the structure and cure acceleration of phenol-urea-formaldehyde resins with different catalysts 总被引:2,自引:0,他引:2
Phenol-urea-formaldehyde (PUF) resins with different catalysts [calcium oxide (CaO), sodium carbonate (Na2CO3), zinc oxide (ZnO), and magnesium oxide (MgO)] were prepared to accelerate the cure of the resin at low temperature. The cure-acceleration effects of catalysts on chemical structure and cure characteristics of PUF resins were investigated by using both liquid 13C nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The liquid 13C NMR analysis indicated that the catalyst such as CaO seemed to present a retarded effect on the polycondensation reaction of phenolic components with urea units, while the Na2CO3 appeared to promote the self-condensation reaction of phenolic methylol groups at para position toward the formation of para-para methylene linkage. Both ZnO and MgO in PUF resins promoted self-condensation reaction of para methylol groups and condensation reaction of ortho methylol groups with para methylol groups. The catalysts such as Na2CO3, ZnO, and MgO can make PUF resins cure at a low temperature. Among these catalysts, the MgO had the most significant accelerating effect on polycondensation and cure reaction of PUF resin. 相似文献
906.
Smart templates for peak pattern matching with comprehensive two-dimensional liquid chromatography 总被引:1,自引:0,他引:1
Comprehensive two-dimensional liquid chromatography (LCxLC) generates information-rich but complex peak patterns that require automated processing for rapid chemical identification and classification. This paper describes a powerful approach and specific methods for peak pattern matching to identify and classify constituent peaks in data from LCxLC and other multidimensional chemical separations. The approach records a prototypical pattern of peaks with retention times and associated metadata, such as chemical identities and classes, in a template. Then, the template pattern is matched to the detected peaks in subsequent data and the metadata are copied from the template to identify and classify the matched peaks. Smart Templates employ rule-based constraints (e.g., multispectral matching) to increase matching accuracy. Experimental results demonstrate Smart Templates, with the combination of retention-time pattern matching and multispectral constraints, are accurate and robust with respect to changes in peak patterns associated with variable chromatographic conditions. 相似文献
907.
When tin is to be determined in such a complex matrix like aqua regia extracts of environmental samples by electrothermal atomic absorption spectrometry (ETAAS), spectral interferences occur when deuterium-lamp (D2) background correction is used, even using high pyrolysis temperature of 1400 °C achieved with palladium with citric acid chemical modifier. We have found that the further addition of NH4F to palladium with citric acid chemical modifier is essential for overcoming the above-mentioned problems for which aluminium oxide is most probably responsible. It is supposed, that NH4F enables volatilization of the alumina matrix formed by hydrolysis from the chloride salt and interfering in a gas phase via the formation of AlF3 which could be, in contrast to aluminium oxide, removed from the graphite furnace during the pyrolysis stage. Using the proposed chemical modifier, the direct and accurate determination of Sn in aqua regia extracts from rocks, soils and sediments is possible even when using matrix free standard solutions. This presumption was confirmed by the analysis of certified reference samples and by the comparison with inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) method. Characteristic mass and LOD value for the original sample (10-μL aliquots of sample) was 17 pg and 0.055 μg g−1, respectively. 相似文献
908.
F. Raposo M.A. de la Rubia M. Alaiz C. Cavinato G. Demirer B. Helmreich N. Martí J. Noguerol S. Picard 《Talanta》2009,80(1):329-337
In 2008, the first Proficiency Testing Scheme of Chemical Oxygen Demand (1stCOD-PTADG) was conducted to assess the results obtained for different research groups whose field work is mainly anaerobic digestion. This study was performed using four samples, two solid samples as raw materials and two solid samples to prepare high concentration suspended solid solutions. Invitations were sent to a large number of laboratories, mainly to anaerobic digestion research groups. Finally, thirty labs from sixteen countries agreed to participate, but for different reasons four participants could not send any data. In total, twenty-six results were reported to the COD-PT coordinator.This study showed the importance of continuous participation in proficiency testing (PT) schemes in order to compare the results obtained. Taking into account the lack of a general standard method and high quality certified reference materials (CRMs), the traceability of COD determination is not currently easy to check. In addition, the spread of participants’ results obtained was high and pointed to the advisability of using consensus values due to their unreliability. Therefore, the theoretical oxygen demand (ThOD) values were considered as assigned values for all the samples analysed. On the other hand, in this PT the established standard deviation (ESD) has been determined by the Horwitz modified function.Participants of this 1stCOD-PTADG were asked to give a short report on the analytical method used. Although all the participants used potassium dichromate as their oxidant reagent, their experimental procedures were very different. With the purpose of comparing the results obtained, the different experimental conditions used were classified into five methods, corresponding to two main categories, open and closed reflux. The performance of laboratories was expressed by the z-score, whose value is considered satisfactory when z-score ≤±2. The overall analytical data evaluation showed that 64% of z-scores obtained were outside the accepted limits. 相似文献
909.
A simple method for fabrication of sole composition nickel hexacyanoferrate modified electrode and its application 总被引:1,自引:0,他引:1
Nickel hexacyanoferrate film modified gold electrode was prepared by a simple chemical deposition procedure from a fresh prepared solution containing ferricyanide, Ni2+, and sodium nitrate. The resultant films have solo composition and are significantly stable as compared to the electrochemically deposited NiHCF films. For different concentrations of Na+ in the solution, the formal potential values of NiHCF shift according to the Nernstian behavior with a slope of 48 mV in the range of 10−4 to 1.0 M. The NiHCF film was also used for the electrocatalytic oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry increased with the ascorbic acid concentration. At a fixed potential under hydrodynamic conditions, the calibration plot was linear over the ascorbic acid concentration range 0.1-12 mM. 相似文献
910.
Structures, binding energies, harmonic frequencies, dipole moments, HOMO–LUMO energy gaps and particularly atoms in molecules
(AIM) analyses of some nanoannular carbon clusters (C4–C20) are investigated at B3LYP/6-31+G(d) level of theory. No correlation is found by plotting the calculated binding energies
as a functional number of carbon atoms of carbon clusters. The calculated binding energies sharply increase from C4 to C10 while slowly from C10 to C20. The binding energies of C4n+2 clusters including C6, C10, C14, and C18 have a clear increase when compared with others indicating their aromatic characters which is confirmed by results of HOMO–LUMO
energy gaps and geometrical parameters. AIM analyses show that most of our carbon clusters are topologically normal (non-conflict)
with stable structures. Nevertheless, the topological networks of small antiaromatic rings, C4 and C8, at their equilibrium geometries may change via molecular vibrations. The existence of straight bond paths in 3D molecular
graphs of carbon clusters with n > 10 implies that ring strains are decreased as the ring sizes grow. Except for C4 and C8, the ellipticity values for the remaining carbon clusters are small indicating that the C–C bond is conserved in these clusters.
Dipole moments of even-numbered structures are negligible, whereas odd-numbered ones have μ values of 0.09−0.73 D. 相似文献