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71.
Ionic‐Radius‐Driven Selection of the Main‐Group‐Metal Cage for Intermetalloid Clusters [Ln@PbxBi14−x]q− and [Ln@PbyBi13−y]q− (x/q=7/4, 6/3; y/q=4/4, 3/3)
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Dr. Rodica Ababei Prof. Dr. Werner Massa Bastian Weinert Patrik Pollak Dr. Xiulan Xie Dr. Rodolphe Clérac Dr. Florian Weigend Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):386-394
Reactions of the binary, pseudo‐homoatomic Zintl anion (Pb2Bi2)2? with Ln(C5Me4H)3 (Ln=La, Ce, Nd, Gd, Sm, Tb) in the presence of [2.2.2]crypt in ethane‐1,2‐diamine/toluene yielded ten [K([2.2.2]crypt)]+ salts of lanthanide‐doped semimetal clusters with 13 or 14 surface atoms. Single‐crystal X‐ray diffraction and energy‐dispersive X‐ray spectroscopy indicated the presence of the anions [Ln@Pb6Bi8]3?, [Ln@Pb3Bi10]3?, [Ln@Pb7Bi7]4?, or [Ln@Pb4Bi9]4? in single or double salts; the latter showed various ratios of the components in the solid state. The anions are the first ternary intermetalloid clusters comprising only elements of the sixth period of the periodic table, namely, Pb, Bi and lanthanides. This study, which was complemented by ESI mass spectrometry and 139La NMR spectroscopy in solution, rationalizes a continuous development of the ratio of 13:14‐atom cages with the ionic radius of the embedded Ln3+ ion, which seems to select the most suitable cage type. Quantum chemical investigations helped to analyze this situation in more detail and to explain the observed subtle influence of the atomic radii. Magnetic measurements confirmed that the embedded Ln3+ ions keep their expected paramagnetic or diamagnetic nature. 相似文献
72.
Christian R. Samanamu Nicholas F. Materer Charles S. Weinert 《Journal of organometallic chemistry》2012
The germanium-based neo-pentane analogue (Me3Ge)4Ge has been characterized by UV/visible spectroscopy, cyclic voltammetry, and 73Ge NMR spectroscopy as well as by density functional theory (DFT) calculations. The absorption maximum for (Me3Ge)4Ge is blue-shifted relative to those for other related branched oligogermanes (Ph3Ge)3GeH and (Ph3Ge)3GePh, and this species is also the most difficult to oxidize among these three compounds. DFT calculations indicate the HOMO of (Me3Ge)4Ge is stabilized relative to those for both tetragermanes by ca. 0.5 eV and therefore the theoretical and experimental results are in agreement. The 73Ge NMR spectrum of (Me3Ge)4Ge exhibits two resonances and the feature corresponding to the central formally zero-valent germanium atom is shifted far upfield and was observed at δ ?339 ppm. 相似文献
73.
I. G. Hill C. M. Weinert L. Kreplak B. P. van Zyl 《Applied Physics A: Materials Science & Processing》2009,95(1):81-87
Self-assembled monolayers are widely used to modify the gate dielectric/semiconductor interface in organic thin-film transistors.
By modifying the interaction between the molecular semiconductor and the substrate, thin-film ordering and the electronic
properties of the semiconducting channel can be controlled. The modified semiconductor/dielectric properties result in macroscopically
observed changes in the charge-carrier mobilities, threshold voltages, subthreshold swing and transfer characteristic hysteresis.
The latter two are determined by the density of charge-trapping states at the interface. Here, we investigate the influence
of the thickness of the self-assembled monolayer, via the alkyl chain length in n-alkyl phosphonic acid-based monolayers on
SiO2, on the electronic properties of pentacene-based organic thin-film transistors. Rather than a monotonic increase or decrease
in performance with increasing chain length, we have found that the optimum performance occurs with chains of 8–10 carbon
atoms. Atomic force microscopy shows a correlation between pentacene crystalline grain size and transistor performance. 相似文献
74.
The thermal expansion of a fluid combined with a temperature-dependent viscosity introduces nonlinearities in the Navier-Stokes equations unrelated to the convective momentum current. The couplings generate the possibility for net fluid flow at the microscale controlled by external heating. This novel thermomechanical effect is investigated for a thin fluid chamber by a numerical solution of the Navier-Stokes equations and analytically by a perturbation expansion. A demonstration experiment confirms the basic mechanism and quantitatively validates our theoretical analysis. 相似文献
75.
R. Megha S. Kotresh CH. V. V. Ramana S. C. Vijaya Kumari S. Thomas 《Composite Interfaces》2017,24(1):55-68
In the present work, both polypyrrole (PPy) and optimized polypyrrole–magnesium ferrite (PPy-MgFe2O4) hybrid nanocomposite were synthesized separately by simple oxidative chemical polymerization method and then structurally characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The FTIR spectrum of the composite showed the presence of characteristic absorption bands of both PPy and MgFe2O4 in the composite confirming interfacial interaction of PPy with MgFe2O4. That this interaction is not affected by crystalline behaviour of predominant MgFe2O4 particles but that MgFe2O4 has embedded in PPy matrix was confirmed by XRD studies. Agglomerated granular spherical morphology of the composite was confirmed by SEM studies. Decrease in AC conductivity of the composite as compared to PPy due to the formation of interfacial heterojunction barrier between p-type PPy and n-type MgFe2O4 was confirmed experimentally and well supported theoretically by calculating binding energy, hopping distance and density of states at Fermi level of PPy and the composite as per CBH model. 相似文献
76.
77.
Quantitative in situ infrared spectroscopy in combination with kinetic analysis is utilized to derive mechanistic aspects for the reaction of methanol with ammonia on Brønsted acidic mordenite. Under non-reactive conditions, a coadsorption complex between methanol and ammonia is found, in which only ammonia is in direct interaction with the Brønsted acid sites of the zeolite. This complex is proposed to be the precursor for the formation of protonated methylamines in the zeolite pores which are formed in sequential order up to tetramethylammonium ions. These methylamines are unable to desorb under reaction conditions in the absence of ammonia. They leave the surface either by ammonia adsorption assisted desorption or by scavenging of methyl groups from protonated methylamines by ammonia. Both steps are concluded to be potentially rate determining. 相似文献
78.
79.
We investigate the stability properties of numerical methodsfor weakly singular Volterra integral equations of the secondkind. Our theory extends the stability theory of linear multistepmethods for ordinary differential equations. We introduce theconcepts of A-stability, A()-stability etc. for Abel-Volterraequations. The stability region is characterized in terms ofthe weights of the method. It is shown that the order of anA-stable convolution quadrature cannot exceed 2. Further westudy the stability properties of implicit Adam methods, withparticular emphasis on the question of A()-stability. 相似文献
80.