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141.
Piperno S Cohen H Bendikov T Lahav M Lubomirsky I 《Physical chemistry chemical physics : PCCP》2012,14(16):5551-5557
It has recently been reported that Teflon and polyethylene (PE) if rubbed by polymethylmethacrylate (PMMA) or Nylon as well as non-rubbed PMMA and Nylon induce "redox" reactions, including those of the reduction of Pd(+2) and Cu(+2) ions. On this basis, it was deduced that these dielectric materials may hold ?10(13)-10(14) of "hidden" electrons cm(-2), a value at least three orders of magnitude higher than the charge that a dielectric surface can accumulate without being discharged in air. The "hidden" electrons were termed "cryptoelectrons". In variance to these reports, we offer here an alternative interpretation. Our model is supported by X-ray photoelectron spectroscopy, contact angle and vibrating electrode (modified Kelvin probe) measurements performed on representative examples. Rubbing of the polymers was found to transfer polymer fragments between the rubbed surfaces altering their physical properties. The transferred polymer fragments promote adsorption of Cu(2+) and Pd(2+) ions. It was found that Teflon and PE rubbed with PMMA and Nylon, and non-rubbed PMMA and non-rubbed Nylon do not induce "redox" reactions of Cu(2+) and Pd(2+) ions but adsorb these ions on their surfaces. Furthermore, the earlier reported reduction of Pd(2+) to Pd(0) by electrons, as detected by catalytic activity of Pd(0) in a Cu-plating bath, can be alternatively explained by reduction of adsorbed Pd(2+) by the reducing agents of the bath itself. Based on these findings, we support the hypothesis that charging of dielectric polymers is due to ions or free radicals rather than electrons and there is no evidence to invoke a hypothesis of "cryptoelectrons". 相似文献
142.
143.
Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts 下载免费PDF全文
Dr. Lisa J. Enman Dr. Michaela Burke Stevens Meir Haim Dahan Dr. Michael R. Nellist Prof. Maytal Caspary Toroker Prof. Shannon W. Boettcher 《Angewandte Chemie (International ed. in English)》2018,57(39):12840-12844
Iron cations are essential for the high activity of nickel and cobalt‐based (oxy)hydroxides for the oxygen evolution reaction, but the role of iron in the catalytic mechanism remains under active investigation. Operando X‐ray absorption spectroscopy and density functional theory calculations are used to demonstrate partial Fe oxidation and a shortening of the Fe?O bond length during oxygen evolution on Co(Fe)OxHy. Cobalt oxidation during oxygen evolution is only observed in the absence of iron. These results demonstrate a different mechanism for water oxidation in the presence and absence of iron and support the hypothesis that oxidized iron species are involved in water‐oxidation catalysis on Co(Fe)OxHy. 相似文献
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145.
Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine 下载免费PDF全文
Dr. Elena Meirzadeh Shiri Dishon Dr. Isabelle Weissbuch Dr. David Ehre Prof. Dr. Meir Lahav Prof. Dr. Igor Lubomirsky 《Angewandte Chemie (International ed. in English)》2018,57(18):4965-4969
Metastable polymorphs commonly emerge when the formation of the stable analogues is inhibited by using different solvents or auxiliaries. Herein, we report that when glycine is grown in aqueous solutions in the presence of low concentrations of different co‐solvents, only alcohols and acetone, unlike water and acetic acid, are selectively incorporated in minute amounts within the bulk of the α‐polymorph. These findings demonstrate that although water binds more strongly to the growing face of the crystal, alcohols and acetone are exclusively incorporated, and thus serve as efficient inhibitors of this polymorph, leading to the precipitation of the β‐form. These solvents then create polar domains detectable by pyroelectric measurements and impedance spectroscopy. These results suggest that in the control of crystal polymorphism with co‐solvents, one should consider also the different desolvation rates in addition to the energy of binding to the growing faces of the crystal. 相似文献
146.
We investigate conversion of a linearly-polarized Gaussian beam to a radially- or an azimuthally-polarized doughnut (0, 1)∗ Laguerre-Gaussian (LG) beams, performed with a spatially-variable retardation (SVR) plate. The SVR plate is composed of eight sectors of a λ/2 retardation plate, each one with different orientation of the to crystal’s slow axis. The analysis reveal that nearly-pure radially- or azimuthally-polarized LG(01)∗ beam with M2 = 2.2 can be obtained, while the transformation efficiency is 89.6%. In the experiments, performed with Nd:YAG laser, we transformed a Gaussian beam with M2 = 1.3 to a radially- and azimuthally-polarized (0, 1)∗ Laguerre-Gaussian beams with M2 = 2.5. We carefully characterized the polarization state of the obtained radially- and azimuthally-polarized beams, measuring Stokes parameters. The polarization purity of the obtained beams, calculated from the measured data, was as high as 96%. 相似文献
147.
We demonstrate experimentally the compression of femtosecond-scale pulses by two-photon gain in a compact electrically driven AlGaAs waveguide. Dynamic control of the pulse width from 240 to 140 fs is achieved by varying the current injection levels--in good agreement with the calculations. The pulse width is measured by a high-sensitivity intensity autocorrelator based on two-photon absorption in a GaAs photomultiplier tube. 相似文献
148.
Irina Rubinstein Grard Bolbach MarkusJ. Weygand Kristian Kjaer Isabelle Weissbuch Meir Lahav 《Helvetica chimica acta》2003,86(11):3851-3866
Racemic S‐ethyl thioesters of Nε‐stearoyllysine (= S‐ethyl (R,S)‐2‐amino‐6‐(stearoylamino)hexanethioate) and S‐ethyl thioesters of γ‐stearyl glutamic acid (=stearyl (R,S)‐4‐amino‐5‐(ethylsulfanyl)‐5‐oxopentanoate) self‐assemble as separated two‐dimensional crystalline monolayers within an achiral phospholipid environment of racemic 1,2‐dipalmitoylglycerol (DPG) and 1,2‐dipalmitoylglycero‐3‐phosphoethanolamine (DPPE), as demonstrated by grazing‐incidence X‐ray‐diffraction (GIXD) measurements performed on the surface of H2O. Lattice‐controlled polycondensation within these crystallites with deuterium‐enantiolabeled monomers was initiated by injecting aqueous solutions of Ag+ or I2/KI beneath the monolayers, which yielded mixtures of diastereoisomeric oligopeptides containing up to six to eight repeating units, as analyzed by MALDI‐TOF mass spectrometry. Analysis of the diastereoisomeric distribution showed an enhanced relative abundance of the oligopeptides with homochiral sequences containing three or more repeating units. Within the DPPE monolayers, the nucleophilic amino group of the phospholipid operates as an initiator of polymerization at the periphery of the monomer two‐dimensional crystallites. Enhanced relative abundance of enantiomerically enriched homochiral oligopeptides was obtained by the polycondensation of nonracemic monomers. This enhancement indicated a phase separation into racemic and enantiomorphous monomer crystallites within the phospholipid environment, although this separation could not be observed directly by GIXD. A possible role that might have been played by crystalline assemblies for the abiotic generation and amplification of oligopeptides with homochiral sequences is discussed. 相似文献
149.
Sofia Curland Christoph Allolio Leah Javitt Shiri Dishon Ben‐Ami Isabelle Weissbuch David Ehre Daniel Harries Meir Lahav Igor Lubomirsky 《Angewandte Chemie (International ed. in English)》2020,59(36):15575-15579
Electrofreezing experiments of super‐cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3?) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3O+) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO3? ions self‐assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice‐like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO3? and guanidinium (Gdm+), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl? and SO42? ions of different configurations reduce the icing temperature. 相似文献
150.