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41.
Syntheses and Ring-Enlargement Reactions of 2-(4-Hydroxyalkyl)-2-nitrocycloalkanones Syntheses of the title compounds were achieved by [Pd{P(C6H5)3}4]-catalyzed reaction of 2-nitrocycloalkanones 3 with vinyloxirane followed by catalytic hydrogenation. By another route, the known methyl 4-(1-nitro-2-oxocycloalkyl)butanoates 6 were reduced to the corresponding aldehydes 7 which by NaBH4 reduction or methylation with (CH3)2Ti(i-Pr)2 were transformed to the alcohols 5 and 8 , respectively (Saheme 1). Treatment of 5 and/or 8 with KH/THF under reflux gave, via a 7-membered intermediate, the nitrolactones 12 and oxolactones 13 (Scheme 3). Compared with similar reactions running via 5- or 6-membered intermediates (see 1 and 2 ), the yields are distinctly lower. The natural occurring 12-tridecanolid ( 14 ) was synthesized. 相似文献
42.
U. Lohse H. Stach H. Thamm W. Schirmer A. A. Isirikjan N. I. Regent M. M. Dubinin 《无机化学与普通化学杂志》1980,460(1):179-190
Dealuminated Molecular Sieves of Y Type. Evaluation of Micro and Secundary Pore Volumes by Adsorption Measurements Isotherms of n-pentane, n-hexane, benzene, and nitrogen are measured in zeolite NaY and its dealuminated form (US-Ex), a molecular sieve that contains 99% SiO2. From these results follows that US-Ex is bidispers. The dealumination forms a system of secundary pores with radii in the range of 1.5–1.9 nm. Evaluating the volumes of the micro- and secundary pores it was shown, that the micropore volume of US-Ex amounts to 75% compared with zeolite NaY. The mechanism of the dealumination reaction is discussed. 相似文献
43.
Zusammenfassung Eine polarographisch-katalytische Methode zur Bestimmung von Molybdän in Gegenwart von Perchlorat- und Nitrationen wurde beschrieben. Molybdän bildet Stromstufen aus, deren Höhe der Depolarisatorkonzentration in der Lösung proportional ist. Wir verwendeten diese katalytischen Stufen zur Bestimmung von Molybdän im Spurenbereich zwischen 4×10–8M und 10–5 M in technischen und biologischen Produkten. Diese hohe Empfindlichkeit kann durch optimale Reaktionsbedingungen erreicht werden.
A polarographic catalytic method for the determination of traces of molybdenum in presence of perchlorate or nitrate ions
Summary Molybdenum forms current waves whose height is proportional to the concentration of the depolarisator in the solution. In the trace region between 4×10–8 M and 10–5 M we used these catalytic waves to determine molybdenum in technological and biological materials. Such high sensitivities can be obtained by an optimum of the reaction conditions.相似文献
44.
Cancer chemoprevention is a new and important medical science and much interest has been focused on catechins, not only for their antioxidant activity, but also because of their known antimutagenic and antitumorigenic properties. Green tea and black tea, which are among the most popular beverages consumed worldwide, contain many different catechins. Due to the instability of catechins in solutions with neutral or basic pH values the concentrations of catechins in tea decrease in time. In this presentation we used micellar electrokinetic chromatography to determine the real concentration of catechins between 0 and 60 min after the tea was brewed. 相似文献
45.
Wen CY Tersoff J Hillerich K Reuter MC Park JH Kodambaka S Stach EA Ross FM 《Physical review letters》2011,107(2):025503
Nanowire growth in the standard <111> direction is assumed to occur at a planar catalyst-nanowire interface, but recent reports contradict this picture. Here we show that a nonplanar growth interface is, in fact, a general phenomenon. Both III-V and group IV nanowires show a distinct region at the trijunction with a different orientation whose size oscillates during growth, synchronized with step flow. We develop an explicit model for this structure that agrees well with experiment and shows that the oscillations provide a direct visualization of catalyst supersaturation. We discuss the implications for wire growth and structure. 相似文献
46.
Ştefan Ţălu Sebastian Stach Joana Zaharieva Miroslava Getsova Denitsa Elenkova Maria Milanova 《International Journal of Polymer Analysis and Characterization》2014,19(7):648-660
The aim of this study was to investigate by atomic force microscopy and multifractal analysis the three-dimensional (3-D) of surface micromorphology of the complex of Tb(III) with the biscoumarin derivative 3,3′-[(4-hydroxyphenyl)methyl)]bis-(4-hydroxy-2H-1-benzopyran-2-one), Tb(C25H15O7)3 · 5H2O immobilized in transparent SiO2-based films by a simple casting technique. The 3-D surfaces contain irregularities of various orders spread on the surface due to the intrinsic method of surface preparation. We found that the micromorphology of all analyzed samples has multifractal characteristics. The generalized dimension D q and the singularity spectrum f(α) provided quantitative values that describe the degree of heterogeneity in the 3-D surface geometry at nanometer scale. The results showed that the larger the spectrum width Δα (Δα = α max ? α min ) of the multifractal spectra f(α), the more nonuniform is the surface micromorphology. These results demonstrate that multifractal analysis is a more precise and reliable tool for quantitative characterization of 3-D surface micromorphology. 相似文献
47.
Angular distributions of cross section and vector analyzing power have been measured for the 14N(d, p)15N reaction at Ed = 10 MeV for transitions to levels up to 8.6 MeV excitation in 15N. Distorted wave Born approximation calculations and calibration curves were used to determine total and orbital angular momenta and spectroscopic factors of the transferred neutrons. The results were compared with different theoretical approaches. 相似文献
48.
The vanadium-catalyzed oxidation of o-dianisidine by t-butyl hydroperoxide is studied for the determination of trace vanadium in non-aqueous media. In acetonitrile, vanadium acts as a one-eletron mediator between the reductant and oxidant. Mechanistic studies, based on e.p.r. spectrometry and visible spectrophotometry, show that the hydroperoxide oxidizes vanadium(IV) via a radical mecahnism. The kinetics of V(IV) oxidation are investigated and a rate equation is proposed. Oxidation of o-dianisidine by the vanadium(V) formed in a one-electron step with formation of the o-dianisidine radical completes the catalytic cycle, as shown by spectroelectrochemical measurements. The radical reacts further with excess of t-butyl hydroperoxide to form the diimine, which may be used for sensitive spectrophotometric monitoring of the indicator reaction at 450 nm. 相似文献
49.
By an invariant set in a metric space we mean a non-empty compact set K such that K = ⋃
i=1
n
T
i
(K) for some contractions T
1, …, T
n
of the space. We prove that, under not too restrictive conditions, the union of finitely many invariant sets is an invariant
set. Hence we establish collage theorems for non-affine invariant sets in terms of Lipschitzian retracts. We show that any
rectifiable curve is an invariant set though there is a simple arc which is not an invariant set.
相似文献
50.
This paper systematically demonstrates that energy-filtered transmission electron microscope (EFTEM) images of a planar interface between two single crystals have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the electron beam is parallel to the interface, but not directly on a zone axis. This off-axis orientation reduces diffraction contrast in the unfiltered (and zero-loss) image, which in turn, reduces residual diffraction contrast in single energy-filtered TEM (EFTEM) images, thickness maps, jump-ratio images, and elemental maps. Most importantly, this procedure produces EFTEM images that are more directly interpretable and, in most cases, possess superior spatial resolution compared to EFTEM images acquired directly on a zone axis. 相似文献