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91.
The statistics of persistent events, recently introduced in the context of phase ordering dynamics, is investigated in the case of the one-dimensional lattice random walk in discrete time. We determine the survival probability of the random walker in the presence of an obstacle moving ballistically with velocity v, i.e., the probability that the random walker remains up to time n on the left of the obstacle. Three regimes are to be considered for the long-time behavior of this probability, according to the sign of the difference between v and the drift velocity V¯ of the random walker. In one of these regimes (v>V¯), the survival probability has a nontrivial limit at long times which is discontinuous at all rational values of v. An algebraic approach allows us to compute these discontinuities as well as several related quantities. The mathematical structure underlying the solvability of this model combines elementary number theory, algebraic functions, and algebraic curves defined over the rationals. 相似文献
92.
J.M. Luck T.M. Nieuwenhuizen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):483-500
No direct imaging is possible in turbid media, where light propagates diffusively over length scales larger than the mean
free path .The diffuse intensity is, however, sensitive to the presence of any kind of object embedded in the medium, e.g. obstacles or defects. The long-ranged effects of isolated objects in an otherwise homogeneous, non-absorbing medium can be
described by a stationary diffusion equation. In analogy with electrostatics, the influence of a single embedded object on
the intensity field is parametrized in terms of a multipole expansion. An absorbing object is chiefly characterized by a negative
charge, while the leading effect of a non-absorbing object is due to its dipole moment. The associated intrinsic characteristics
of the object are its capacitance Q or its effective radius ,and its polarizability P. These quantities can be evaluated within the diffusion approximation for large enough objects. The situation of mesoscopic
objects, with a size comparable to the mean free path, requires a more careful treatment, for which the appropriate framework
is provided by radiative transfer theory. This formalism is worked out in detail, in the case of spherical and cylindrical
objects of radius R, of the following kinds: (i) totally absorbing (black), (ii) transparent, (iii) totally reflecting. The capacitance, effective
radius, and polarizability of these objects differ from the predictions of the diffusion approximation by a size factor, which
only depends on the ratio .The analytic form of the size factors is derived for small and large objects, while accurate numerical results are obtained
for objects of intermediate size .For cases (i) and (ii) the size factor is smaller than one and monotonically increasing with ,while for case (iii) it is larger than one and decreasing with .
Received: 7 August 1998 / Accepted: 3 September 1998 相似文献
93.
The reaction of MoO2(acac)2 with 1,1??-[phosphinicobis(methylene)]-ferrocene in ethanol at 120?°C and in the presence of triethylamine results in the octametallic cluster Mo4(??3-O)4(??2-O2P(CH2)2Fc)4O4. If the reaction is carried out in the absence of triethylamine a mixture of products are obtained of which the identity of the compound produced was hypothesized but not definitively established. Mo4(??3-O)4(??2-O2P(CH2)2Fc)4O4 is characterized by IR and 31P-NMR spectroscopy along with the single crystal X-ray determination of its structure. The crystal structure of 1,1??-bis(chloromethyl)ferrocene is also detailed. 相似文献
94.
95.
John S. Maass Matthias Zeller Daniel Holmes Craig A. Bayse Rudy L. Luck 《Journal of Cluster Science》2011,22(2):193-210
The reaction of MoO2(acac)2 and dibenzylphosphinic acid in ethanol leads to a red distorted cubic tetrameric cluster, Mo4(??3-O)4(??2-O2P(CH2C6H5)2)4O4, and a pink open mixed-valent cluster, Mo4(??3-O)2(??2-O2P(CH2C6H5)2)6O6, when the reduction is carried out at 120 and 75 °C, respectively. 95Mo NMR spectroscopy revealed a singlet for Mo4(??3-O)4(??2-O2P(CH2C6H5)2)4O4 (1) at 584.9 ppm (????1/2 = 4500 Hz) and two resonances for Mo4(??3-O)2(??2-O2P(CH2C6H5)2)6O6 (2) at 238.8 ppm (????1/2 = 1250 Hz) and 6.4 ppm (????1/2 = 5999 Hz), which were assigned to the Mo(V) and Mo(VI) sites, respectively. DFT geometries and 95Mo DFT-GIAO chemical shifts for Mo4(??3-O)4(??2-O2P(CH3)2)4O4 (3) and Mo4(??3-O)2(??2-O2P(CH3)2)6O6 (4) are consistent with X-ray crystallography and 95Mo NMR of 1 and 2. The open complex, Mo4(??3-O)2(??2-O2P(CH2C6H5)2)6O6·2(CH2Cl2), exhibits a central Mo(V)?CMo(V) single bond at 2.6217(5) Å with each Mo(V) atom bonded to one oxo (trans-disposed) terminal ligand. 相似文献
96.
Alfons Penzkofer Meike Luck Tilo Mathes Peter Hegemann 《Photochemistry and photobiology》2014,90(4):773-785
The photodynamics of the recombinant rhodopsin fragment of the histidine kinase rhodopsin HKR1 from Chlamydomonas reinhardtii was studied by absorption and fluorescence spectroscopy. The retinal cofactor of HKR1 exists in two Schiff base forms RetA and RetB. RetA is the deprotonated 13‐cis‐retinal Schiff base (RSB) absorbing in the UVA spectral region. RetB is the protonated all‐trans RSB absorbing in the blue spectral region. Blue light exposure converts RetB fully to RetA. UVA light exposure converts RetA to RetB and RetB to RetA giving a mixture determined by their absorption cross sections and their conversion efficiencies. The quantum efficiencies of conversion of RetA to RetB and RetB to RetA were determined to be 0.096 ± 0.005 and 0.405 ± 0.01 respectively. In the dark thermal equilibration between RetA and RetB with dominant RetA content occurred with a time constant of about 3 days at room temperature. The fluorescence emission behavior of RetA and RetB was studied, and fluorescence quantum yields of ?F(RetA) = 0.00117 and ?F(RetB) = 9.4 × 10?5 were determined. Reaction coordinate schemes of the photodynamics are developed. 相似文献
97.
Two molybdenum (VI) hydrogen-bonded network polymers [MoO2F4]·(4,4′-H2bpd)(H2O)2 (1) and [MoO2Cl3(H2O)]·(4,4′-H2bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo
compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental
analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the
complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a cross-linked
hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO3 as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO4
− by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity
and a very high selectivity for the formation of cyclooctene oxide.
An erratum to this article can be found at 相似文献
98.
Scott A. Gabel Linda A. Luck Lawrence G. Werbelow Robert E. London 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,128(2)
The13C multiplet structure of
-[1-13C,1-2H]glucose complexed to theEscherichia coliperiplasmic glucose/galactose receptor has been studied as a function of temperature. Asymmetric multiplet patterns observed are shown to arise from dynamic frequency shifts. Multiplet asymmetry contributions resulting from shift anisotropy–dipolar cross correlations were found to be small, with optimal fits of the data corresponding to small, negative values of the correlation factor, χCD-CSA. Additional broadening at higher temperatures most probably results from ligand exchange between free and complexed states. Effects of internal motion are also considered theoretically, and indicate that the order parameter for the bound glucose is ≥0.9. 相似文献
99.
This paper presents a measurement method to determine the velocity flow field and the temperature in a cross-section of an
aerosol chamber by means of the ultrasonic computer tomography. The required high measurement resolution of the propagation
time of the ultrasonic impulse through the medium is obtained by a special signal processing technique. Since the propagation
direction of a sonic wave in a non-stationary medium is not straight-lined, a ray linking procedure was developed that traces
the rays. The combination of the precise propagation time measurement, the ray linking method and a vector algebraic reconstruction
technique leads to a␣computer tomographic measurement system for the determination of the temperature distribution and the
velocity flow field in a cross-section.
Received on 9 June 1997 相似文献
100.
E. Luck 《Fresenius' Journal of Analytical Chemistry》1871,10(1):310-322
Ohne Zusammenfassung 相似文献