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171.
172.
Pászti Z Hakkel O Keszthelyi T Berkó A Balázs N Bakó I Guczi L 《Langmuir : the ACS journal of surfaces and colloids》2010,26(21):16312-16324
Gold based model systems exhibiting the structural versatility of nanoparticle ensembles and being accessible for surface spectroscopic investigations are expected to provide new information about the adsorption of carbon monoxide, a key process influencing the CO oxidation activity of this noble metal in nanoparticulate form. Accordingly, in the present work the interaction of CO is studied with an ion bombardment modified Au(111) surface by means of a combination of photoelectron spectroscopy (XPS and UPS), sum frequency generation vibrational spectroscopy (SFG), and scanning tunneling microscopy (STM). While no adsorption was found on intact Au(111), data collected on the ion bombarded surface at cryogenic temperatures indicated the presence of stable CO adsorbates below 190 K. A quantitative evaluation of the C 1s XPS spectra and the surface morphology explored by STM revealed that the step edge sites created by ion bombardment are responsible for CO adsorption. The identification of the CO binding sites was confirmed by density functional theory (DFT) calculations. Annealing experiments up to room temperature showed that at temperatures above 190 K unstable adsorbates are formed on the surface under dynamic exposure conditions that disappeared immediately when gaseous CO was removed from the system. Spectroscopic data as well as STM records revealed that prolonged CO exposure at higher pressures of up to 1 mbar around room temperature facilitates massive atomic movements on the roughened surface, leading to its strong reordering toward the structure of the intact Au(111) surface, accompanied by the loss of the CO binding capacity. 相似文献
173.
Peter Baláž Parviz Pourghahramani Erika Dutková Martin Fabián Jaroslav Kováč Alexander Šatka 《Central European Journal of Chemistry》2009,7(2):215-221
PbS nanocrystals using surfactant assisted mechanochemical route has been successfully prepared. The methods of XRD, SEM,
surface area and particle size measurements were used for nanocrystals characterization. The XRD patterns confirmed the presence
of galena PbS (JCPDS 5–592) whatever treatment conditions were applied. The strong observable peaks indicate the highly crystalline
nature in formation of PbS nanostructures where preferential crystal growth in the (200) direction after chelating agent (EDTANa2•2H2O) addition has been observed. The mean volume weighted crystallite size 4.9 nm and 35 nm has been calculated from XRD data
using Williamson-Hall method for PbS synthesized without and/or with chelating agent, respectively corresponding with surface
weighted crystallites sizes of 2.9 and 18.8 nm. The sample prepared without surfactant yields the smaller crystallites and
the higher microstrain compared with surfactant assisted synthesis. The obtained results illustrate a possibility to manipulate
crystal morphology by combining effect of milling and surfactant application.
相似文献
174.
An equitable coloring of a graph is a proper vertex coloring such that the sizes of any two color classes differ by at most one. The least positive integer k for which there exists an equitable coloring of a graph G with k colors is said to be the equitable chromatic number of G and is denoted by χ=(G). The least positive integer k such that for any k′ ≥ k there exists an equitable coloring of a graph G with k′ colors is said to be the equitable chromatic threshold of G and is denoted by χ=*(G). In this paper, we investigate the asymptotic behavior of these coloring parameters in the probability space G(n,p) of random graphs. We prove that if n?1/5+? < p < 0.99 for some 0 < ?, then almost surely χ(G(n,p)) ≤ χ=(G(n,p)) = (1 + o(1))χ(G(n,p)) holds (where χ(G(n,p)) is the ordinary chromatic number of G(n,p)). We also show that there exists a constant C such that if C/n < p < 0.99, then almost surely χ(G(n,p)) ≤ χ=(G(n,p)) ≤ (2 + o(1))χ(G(n,p)). Concerning the equitable chromatic threshold, we prove that if n?(1??) < p < 0.99 for some 0 < ?, then almost surely χ(G(n,p)) ≤ χ=* (G(n,p)) ≤ (2 + o(1))χ(G(n,p)) holds, and if < p < 0.99 for some 0 < ?, then almost surely we have χ(G(n,p)) ≤ χ=*(G(n,p)) = O?(χ(G(n,p))). © 2009 Wiley Periodicals, Inc. Random Struct. Alg., 2009 相似文献
175.
The terminal AsS and PS complexes [(N(3)N)W(ES)] (N(3)N=N(CH(2)CH(2)NSiMe(3))(3); E=P (3), As (4)) were synthesised by reaction of [(N(3)N)W[triple chemical bond]As] and [(N(3)N)W[triple chemical bond]P], respectively, with cyclohexene sulfide. Both complexes present very short W--E and E--S bond lengths. The bonding was investigated by density functional theory (DFT) calculations using the fragment calculation method and natural bond orbital (NBO) analysis. According to the fragment analysis, in which the complexes were separated in an ES and a (N(3)N)W fragment, the bonding in complexes 3, 4 and [(N(3)N)W(SbS)] (5) is realised over a set of two sigma (1 sigma and 2 sigma) and two degenerate pi molecular orbitals (MOs) (1 pi and 2 pi). The 1 sigma MO is a bonding MO extended over the N(ax)-W-E-S core, whereas the 2 sigma MO is localised mainly on the E-S fragment. The 1 pi set is a E-S localised bonding molecular orbital, whereas the 2 pi set is in phase with respect to W-E but in antiphase with respect to E-S. Both methods indicate bond orders around two for both the E--S and the W--E bonds. The polarity of the complexes was examined by Hirshfeld charge analysis. This shows that complexes 3 and 4 are only slightly polarised, whereas 5 is moderately polarised toward the sulphur. As suggested by the computational results, the pi system in complexes 3-5 is best described by two three-centre four-electron bonds. 相似文献
176.
Summary The discrete isoperimetric problem is to determine the maximal area
polygon with at most <InlineEquation ID=IE"1"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"2"><EquationSource
Format="TEX"><![CDATA[$]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>k$ vertices and of a given
perimeter. It is a classical
fact that the unique optimal polygon on the Euclidean plane is the regular one.
The same statement for the hyperbolic plane was proved by K\'aroly Bezdek [1]
and on the sphere by L\'aszl\'o Fejes T\'oth [3]. In the present paper we
extend the discrete isoperimetric inequality for ``polygons' on the three
planes of constant curvature bounded by arcs of a given constant geodesic
curvature. 相似文献
177.
Andrea Schindler Gábor Balázs Manfred Zabel Christian Gröger Robert Kalbitzer Manfred Scheer 《Comptes Rendus Chimie》2010,13(8-9):1241-1248
The reaction of the 1,2,4-triphosphaferrocene [Cp*Fe(η5-P3C2tBu2)] (1) with CuX (X = Cl, Br, I) in a 1:1 stoichiometric ratio leads to the formation of the oligomeric compounds [{Cu(μ-X)}6(μ6-X)Cu(MeCN)3{μ,η2-(Cp*Fe(η5-P3C2tBu2))}2{μ3,η3-(Cp*Fe(η5-P3C2tBu2))}] (X = Cl (2), Br (3)) and [{Cu(μ-I)}3{Cu(μ3-I)}3Cu(μ6-I){μ,η2-(Cp*Fe(η5-P3C2tBu2))}3{η1-(Cp*Fe(η5-P3C2tBu2))}] (4) revealing Cu(I) halide cages surrounded by 1,2,4-triphosphaferrocene moieties. The reaction of [Cp*Fe(η5-P3C2tBu2)] with CuI in a 1:4 stoichiometry leads to the formation of the two-dimensional polymer [{Cu(μ-I)}4{Cu(μ3-I)(MeCN)}2{μ3,η3-(Cp*Fe(P3C2tBu2))}]n (5). The oligomeric compounds show dynamic behavior in solution monitored by 31P NMR spectroscopy. All compounds are additionally characterized by single crystal X-ray diffraction. 相似文献
178.
Gréta Gergely Ferenc Wéber István Lukács Levente Illés Attila L. Tóth Zsolt E. Horváth Judit Mihály Csaba Balázsi 《Central European Journal of Chemistry》2010,8(2):375-381
Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid. The phases obtained depended
on the ratio of calcined eggshell/ seashell to phosphoric acid, the calcination temperature and the mechanochemical activation
method (ball milling or attrition milling). The HAp structures were characterized by X-ray diffraction, scanning electron
microsopy and infrared spectroscopy. Attrition milling was more effective than ball milling, yielding nanosize, homogenous
and pure Hap.
相似文献
179.
Epibatidine (EPB) (1), an alkaloid isolated from the skin of the Ecuadorian poison frog, Epipedobates tricolor has attracted attention because of its exceptionally powerful analgesic properties: several hundred times greater than those of morphine, and the fact that it acts at nicotine rather than opiate receptors. Although the substance is toxic, it does serve as a lead compound in the development of drugs for pain relief as well as treatment of disorders whose pathogenesis involves nicotinic receptors. In this article, isolation, synthetic methods, effect on neuronal and neuromuscular nicotinic receptors, therapeutic potential, toxicity, nicotinic pharmacophore structural modifications related issues of 1 are discussed. 相似文献
180.
Acid-base properties and metal-binding abilities of tris(2-carboxyethyl)phosphine (TCEP), a newly introduced thiol group protectant, were studied in solution, using potentiometry, (1)H and (31)P NMR, and UV-vis spectroscopy, and also in the solid state by X-ray diffraction. Stability constants of complexes of the P-oxide of TCEP (TCEPO) were established by potentiometry. The list of metal ions studied included Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II). Cu(II) catalyzed oxidation of TCEP to TCEPO. For all other systems ML complexes were found as major species at neutral pH with TCEP and TCEPO. Monoprotonated MHL species were also detected in weakly acidic conditions for all TCEP complexes and for the Pb(II) complex of TCEPO, while hydrolytic MH(-1)L complexes were found for TCEP at the weakly alkaline pH range. The NiL(4) complex was found to form at excess of TCEP. Overall, the complexes were found to be rather weak, with log beta(ML) values around 3-5 for TCEP and 1.5-2.5 for TCEPO. The phosphorus pK(a) value for TCEP, 7.68, suggests that it can be a good buffer for studies at physiological pH. 相似文献