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51.
McGrath AJ Garrett GE Valgimigli L Pratt DA 《Journal of the American Chemical Society》2010,132(47):16759-16761
A persistent triptycenyl sulfenic acid is used as a model for cysteine-derived and other biologically relevant sulfenic acids in experiments which define their redox chemistry. EPR spectroscopy reveals that sulfinyl radicals are persistent and unreactive toward O(2), allowing the O-H bonding dissociation enthalpy (BDE) of the sulfenic acid to be readily determined by equilibration with TEMPO as 71.9 kcal/mol. The E° (RSO?/RSO(-)) and pK(a) of this sulfenic acid are also reported. 相似文献
52.
Frank J. Dinan Willis T. Schwartz Roger A. Wolfe Daniel S. Hojnicki Terry St. Clair J. Richard Pratt 《Journal of polymer science. Part A, Polymer chemistry》1992,30(1):111-118
Solution and solid-state proton decoupled 13C-NMR spectra were determined on two diimides derived from 4, 4′-oxydiphthalic anhydride. Comparison of the individual diimide spectra to that of a mixture of the two diimides indicates that ordering of these materials occurs in the solid state via charge transfer complex formation. A similar study was conducted using two isomeric dianhydrides, 4, 4′-isophthaloyldiphthalic anhydride (IDPA) and 4, 4′-terephthaloyldiphthalic anhydride (TDPA). The solution spectra of these compounds are similar and are those which would be expected for these compounds. However, their solid state spectra differ from each other. The solid-state spectrum of TDPA resembles its solution spectrum, whereas, that of IDPA differs greatly from its solution spectrum and indicates charge transfer complex formation occurs with this molecule. This difference is explained in terms of the stereochemistry of the two isomeric dianhydrides. 相似文献
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54.
F.L. Pratt S.J. Blundell P.A. Pattenden W. Hayes K.H. Chow A.P. Monkman T. Ishiguro K. Ishida K. Nagamine 《Hyperfine Interactions》1997,106(1-4):33-38
We report studies of spin dynamics in the conducting polymers polyaniline and polypyrrole using both μ+SR and μ-SR techniques. These measurements reveal characteristic field dependences and cutoff frequencies for the muon spin relaxation
which can be related to the spin diffusion process. Clear evidence is seen for increased spin localisation at low temperatures
where a crossover occurs from two or three dimensional spin diffusion to a one dimensional diffusion regime.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
55.
Ian Pratt‐Hartmann 《Mathematical Logic Quarterly》2015,61(6):474-515
We consider the two‐variable fragment of first‐order logic with counting, subject to the stipulation that a single distinguished binary predicate be interpreted as an equivalence. We show that the satisfiability and finite satisfiability problems for this logic are both NExpTime ‐complete. We further show that the corresponding problems for two‐variable first‐order logic with counting and two equivalences are both undecidable. 相似文献
56.
Priya MH Pratt LR Paulaitis ME 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13713-13718
We compare protein-protein and protein-polymer osmotic virial coefficients measured by static light scattering for aqueous solutions of lysozyme with low-molecular-weight, hydroxy-terminated (hPEG) and methyl-terminated (mPEG) poly(ethylene glycol) at two solution conditions: pH 7.0 and 0.01 M ionic strength, and pH 6.2 and 0.8 M ionic strength. We find that adding PEG to aqueous lysozyme solutions makes a net repulsive contribution to lysozyme-lysozyme interactions, independent of ionic strength and PEG end-group hydrophobicity. PEG end-group hydrophobicity has a profound effect on the magnitude of this contribution, however, at low ionic strength where mPEG-lysozyme attractive interactions become significant. The enhanced attractions promote mPEG-lysozyme preferential interactions at the expense of lysozyme self-interactions, which leads to lysozyme-lysozyme interactions that are more repulsive in the presence of mPEG. These preferential interactions also lead to the preferential exclusion of diffusable ions locally around the protein, which results in a pronounced ionic strength dependence of mPEG-mediated lysozyme-lysozyme interactions. 相似文献
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Rotationally resolved electronic spectra of several low frequency vibrational bands that appear in the S(1) ← S(0) transition of 4-fluorobenzyl alcohol (4FBA) in the collision-free environment of a molecular beam have been observed and assigned. Each transition is split into two or more components by the tunneling motion of the attached -CH(2)OH group. A similar splitting is observed in the microwave spectrum of 4FBA. Analyses of these data show that 4FBA has a gauche structure in both electronic states, but that the ground state C(1)C(2)-C(7)O dihedral angle of ~60° changes by ~30° when the photon is absorbed. The barriers to the torsional motion of the attached -CH(2)OH group are also quite different in the two electronic states; V(2) ~ 300 cm(-1) high and ~60° wide in the S(0) state, and V(2) ~ 300 cm(-1) high and ~120° wide (or V(2) ~ 1200 cm(-1) high and ~60° wide) in the S(1) state. Possible reasons for these behaviors are discussed. 相似文献
60.
Thiré N Cireasa R Staedter D Blanchet V Pratt ST 《Physical chemistry chemical physics : PCCP》2011,13(41):18485-18496
The predissociation dynamics of the vibrationless level of the first Rydberg 6s (B (1)E) state of CH(3)I has been studied by femtosecond-resolved velocity map imaging of both the CH(3) and I photofragments. The kinetic energy distributions of the two fragments have been recorded as a function of the pump-probe delay, and as a function of excitation within the umbrella and stretching vibrational modes of the CH(3) fragment. These observations are made by using (2 + 1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the state of CH(3) to detect specific vibrational levels of CH(3). The vibrational branching fractions of the CH(3) are recovered by using the individual vibrationally state-selected CH(3) distributions to fit the kinetic energy distribution obtained by using nonresonant multiphoton ionization of either the I or the CH(3) fragment. The angular distributions and rise times of the two fragments differ significantly. These observations can be rationalized through a consideration of the alignment of the CH(3) fragment and the effect of this alignment on its detection efficiency. Two additional dissociation channels are detected: one associated with Rydberg states near 9.2 eV that were observed previously in photoelectron studies, and one associated with photodissociation of the parent cation around 15 eV. 相似文献