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71.
Gregory R. Lumpkin Miguel Pruneda Katherine L. Smith Karl R. Whittle Nestor J. Zaluzec 《Journal of solid state chemistry》2007,180(4):1512-1518
The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation-anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature. 相似文献
72.
Castro K Pérez-Alonso M Rodríguez-Laso MD Etxebarria N Madariaga JM 《Analytical and bioanalytical chemistry》2007,387(3):847-860
Non-destructive and non-invasive micro-Raman fibre optic and micro-XRF analyses were performed to study a wallpaper from the
beginning of the 19th century. The complementarity of these two non-destructive techniques is shown in this work. The analysed
artwork is considered one of the most beautiful wallpapers ever manufactured according to the catalogues and books; it is
known as Chasse de Compiègne, manufactured by Jacquemart, Paris, in 1812. During the analysis, an unexpected pigment was detected by both analytical techniques:
lead-tin yellow type II. This pigment was used until ca. 1750, when other yellow pigments replaced it, thus it is very difficult
to find it in paintings afterwards. Together with this pigment, red lead, Prussian blue, brochantite, yellow iron oxide, calcium
carbonate, vermilion, carbon black of animal origin (bone black), lead white, and raw and burnt sienna were also determined
by combining the analytical information provided by both techniques. A possible degradation of brochantite to antlerite is
also discussed. 相似文献
73.
Karl R. Whittle Gregory R. Lumpkin Frank J. Berry Katherine L. Smith Nestor J. Zaluzec 《Journal of solid state chemistry》2007,180(2):785-791
Garnets, A3B2C3O12, are an important group of minerals and have potential uses in the safe immobilisation of high-level nuclear waste. They have been found naturally to incorporate Zr, Ti and Fe, three elements of interest in the safe storage of nuclear waste. Kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, is a naturally occurring garnet that contains Zr in a high percentage∼30 wt%. For such a material to be of potential immobilisation for nuclear waste the structure needs to be completely understood. Electron channelling studies have shown that the Zr/Ti cations are located on the Y-site, with the Al/Fe cations located on the Z-site. This work has investigated synthetic analogues of kimzeyite, Ca3(Zr,Hf)2(Al,Fe,Si)3O12, by neutron powder diffraction, using the C2 spectrometer at the Chalk River nuclear facility, coupled with 57Fe Mössbauer spectroscopy. Such work has allowed the structure of the synthetic material to be determined along with the distribution of cations across the X (CN=8), Y (CN=6), and Z (CN=4) sites. Results have shown that it is possible to synthesise Ca3(Zr,Hf)2(Al,Fe,Si)3O12 with a range of Al/Fe ratios containing Zr and Hf. The Mössbauer data has indicated the Fe is located on the Z site. The structural analyses show that the unit cell changes linearly as a function of composition, and analysis of the disorder indicates that the Zr, Hf reside on the Y site and the Al, Fe, and Si reside on the Z site. 相似文献
74.
Esquena J Nestor J Vílchez A Aramaki K Solans C 《Langmuir : the ACS journal of surfaces and colloids》2012,28(33):12334-12340
A novel and simple single-step method for the preparation of meso/macroporous silica materials is described, which consists in templating in highly concentrated emulsions with a cubic liquid crystal in the continuous phase. Tetraethyl orthosilicate (TEOS) was solubilized in the aqueous continuous phase of highly concentrated emulsions stabilized by C(12)(EO)(8) and a PEO-PPO-PEO block copolymer nonionic surfactant, with a cubic liquid crystalline phase of the Fd3m type. The resulting silica materials were characterized by small-angle X-ray scattering, nitrogen sorption and transmission electron microscopy. The results showed that a dual pore size distribution was obtained, consisting of mesopores in the nanometer range and macropores between 1 and 5 μm. These dual meso/macroporous silicas with bimodal pore size distribution can possess specific surface areas higher than 400 m(2)/g. 相似文献
75.
Asier Vallejo Aresatz Usobiaga Irantzu Martinez‐Arkarazo Ailette Prieto Nestor Etxebarria Olatz Zuloaga Luis A. Fernández 《Journal of separation science》2010,33(1):104-111
Cup horn boosters are miniaturized ultrasound baths that maximize efficiency and precision. The optimization of an ultrasonic‐assisted derivatization step by means of a cup horn booster and the determination of estrone, 17β‐estradiol, estriol, 17α‐ethynyl estradiol and mestranol was developed by GC‐MS. Different derivatization reagents and solvents were studied for maximizing the di‐derivatization of 17α‐ethynyl estradiol under ultrasound energy. Only N,O‐bis(trimethylsilyl)trifluoroacetamide with 1% of trimethylchlorosilane in pyridine gave satisfactory results and this mixture was further used in the optimization of the ultrasound assisted derivatization. The experiment designs included sonication time (1–10 min), sonication power (20–80%), sonication cycles (1–9), derivatization reagent volume (25–125 μL) and solvent volume (25–125 μL). Once the optimum conditions were fixed, the effect of organic matter and the frequency of the water bath change were studied. Finally, the validation of the analytical method was carried out using spiked natural and synthetic waters. Recoveries (natural (138–70%) and synthetic (112–89%)), the LODs (0.35–1.66 ng/L), and LOQs (1.16–5.52 ng/L) and the precision (0.2–5.3%) of the method were studied. This is the first work in the literature where a cup horn booster is used with the aim of minimizing derivatization time during the determination of estrogenic compounds. 相似文献
76.
77.
On Priestley Spaces of Lattice-Ordered Algebraic Structures 总被引:1,自引:0,他引:1
The laws defining many important varieties of lattice-ordered algebras, such as linear Heyting algebras, MV-algebras and l-groups, can be cast in a form which allows dual representations to be derived in a very direct, and semi-automatic, way. This is achieved by developing a new duality theory for implicative lattices, which encompass all the varieries above. The approach focuses on distinguished subsets of the prime lattice filters of an implicative lattice, ordered as usual by inclusion. A decomposition theorem is proved, and the extent to which the order on the prime lattice filters determines the implicative structure is thereby revealed. 相似文献
78.
79.
Castro K Sarmiento A Maguregui M Martínez-Arkarazo I Etxebarria N Angulo M Barrutia MU González-Cembellín JM Madariaga JM 《Analytical and bioanalytical chemistry》2008,392(4):755-763
A complete study of several English polychromed alabaster sculptures is presented. The support, pigment, and binders were
characterised by combining μEDXRF, μRaman, and FTIR spectroscopies. Among the pigments, minium, vermilion, lead white, carbon
black, red iron oxide, and a degraded green copper pigment were determined, together with gold leaf. The presence of the rare
mineral moolooite (copper oxalate) was also found as a degradation product in the green areas, where weddellite (calcium oxalate
dihydrate) was also determined. These facts, together with degradation of the green copper pigment, suggest microbiological
degradation of the original materials. Remains of glue and a varnish were also determined by FTIR spectroscopy and principal-components
analysis (PCA) of the spectra. Finally, PCA analysis was carried out to confirm whether the pieces came from the same quarry. 相似文献
80.
John K. Gallos Pygmalion S. Lianis Nestor A. Rodios 《Journal of heterocyclic chemistry》1994,31(2):481-487
A series of substituted furazano[3,4-b]quinoxaline 1-oxides have been prepared by oxidation of the respective 2,3-bis(hydroxyimino)-1,2,3,4-tetrahydroquinoxalines with nitric acid and their structure was confirmed by means of their nmr spectra. A very rapid equilibrium occurs between their two isomeric N-oxide forms via the dinitroso equivalent, and the influence of the 6(7)-substituents on the equilibrium is discussed. These compounds were easily deoxygenated by triphenylphosphine in quantitative yields to the corresponding furazans. The electron impact mass spectra of both of the above series of compounds have also been recorded and their fragmentation pattern is discussed. 相似文献