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61.
Fred Ames Shelton 《The Journal of the Operational Research Society》1987,38(3):269-275
Acceptance of the adaptive-filtering parameter-estimation process has been mixed. Much of the variability between studies may result from the particular learning factor selected and may be further affected by the type of standardization used. The author presents a modification of the Makridakis and Wheelwright adaptive-filtering algorithm. This modified algorithm provides superior performance and simplifies the selection of the learning factor when used with simple autoregressive processes. 相似文献
62.
Sazanovich IV Alamiry MA Best J Bennett RD Bouganov OV Davies ES Grivin VP Meijer AJ Plyusnin VF Ronayne KL Shelton AH Tikhomirov SA Towrie M Weinstein JA 《Inorganic chemistry》2008,47(22):10432-10445
A combination of picosecond time-resolved infrared spectroscopy, picosecond transient absorption spectroscopy, and nanosecond flash photolysis was used to elucidate the nature and dynamics of a manifold of the lowest excited states in Pt(phen-NDI)Cl 2 ( 1), where NDI = strongly electron accepting 1,4,5,8-naphthalene-diimide group. 1 is the first example of a Pt (II)-diimine-diimide dyad. UV/vis/IR spectroelectrochemistry and EPR studies of electrochemically generated anions confirmed that the lowest unoccupied molecular orbital (LUMO) in this system is localized on the NDI acceptor group. The lowest allowed electronic transition in Pt(phen-NDI)Cl 2 is charge-transfer-to-diimine of a largely Pt-->phen metal-to-ligand charge-transfer (MLCT) character. Excitation of 1 in the 355-395 nm range initiates a series of processes which involve excited states with the lifetimes of 0.9 ps ( (1)NDI*), 3 ps ( (3)MLCT), 19 ps (vibrational cooling of "hot" (3)NDI and of "hot" NDI ground state), and 520 mus ( (3)NDI). Excitation of 1 with 395 nm femtosecond laser pulses populates independently the (1)MLCT and the (1)NDI* excited states. A thermodynamically possible decay of the initially populated (1)MLCT to the charge-transfer-to-NDI excited state, [Pt (III)(phen-NDI (-*))Cl 2], is not observed. This finding could be explained by an ultrafast ISC of the (1)MLCT to the (3)MLCT state which lies about 0.4 eV lower in energy than [Pt (III)(phen-NDI (-*))Cl 2]. The predominant decay pathway of the (3)MLCT is a back electron transfer process with approximately 3 ps lifetime, which also causes partial population of the vibrationally hot ground state of the NDI fragment. The decay of the (1)NDI* state in 1 populates vibrationally hot ground state of the NDI, as well as vibrationally hot (3)NDI. The latter relaxes to form (3)NDI state, that is, [Pt(phen- (3)NDI)Cl 2]*, which possesses a remarkably long lifetime for a Pt (II) complex in fluid solution of 520 mus. The IR signature of this excited state includes the nu(CO) bands at 1607 and 1647 cm (-1), which are shifted considerably to lower energies if compared to their ground-state counterparts. The assignment of the vibrational bands is supported by the density-functional theory calculations in CH 2Cl 2. Pt(phen-NDI)Cl 2 acts as a modest photosensitizer of singlet oxygen. 相似文献
63.
64.
H.C. Hamaker S.D. Bader G. Zajac R.N. Shelton A.J. Bevolo H.E. Horng 《Solid State Communications》1983,48(7):589-591
Auger and photoemission studies for Y(Rh1?xRux)4B4 superconductors elucidate the mechanism for the abrupt drop in Tc near x=0.5. The B -states admix more strongly with Ru than Rh -states, thereby yielding low-Tc values for Ru-rich compounds due to broadening of the -band feutures. These effects underlie a previous suggestion that the preservation of Rh4 tetrahedral units is essential for high-Tc values in ternary boride compounds. 相似文献
65.
R.J. Stierman K.A. Gschneidner T.-W.E. Tsang F.A. Schmidt P. Klavins R.N. Shelton J. Queen S. Legvold 《Journal of magnetism and magnetic materials》1983,36(3):249-254
The magnetic susceptibility of electrotransport purified Sc single crystals was measured from 0.7 to 295 K. Both the easy (χa) and hard (χc) directions were measured using a microcomputer controlled Faraday apparatus. Above 50 K the present results agree with earlier work on a less pure sample, but below 50 K the present results are lower by as much as 4%. In addition the maximum at ≈ 30 K and the minimum at ≈ 6 K are much more pronounced in the purer material, and the susceptibility increases rapidly as the temperature approaches 0 K. Electrical resistivity measurements were made on the same single crystals from 1.6 to 300 K. The resistance ratios were 365 for the a-axis crystal and 274 for the c-axis crystal. At 300 K, ρa ≈ 2.5 ρc. 相似文献
66.
M. D. Lan S. J. Peng J. Z. Liu R. N. Shelton 《Applied Physics A: Materials Science & Processing》1994,59(2):169-172
We have studied the zero-field-cooled magnetic relaxation in the melt-textured ErBa2Cu3O7– ceramic material. The magnetic relaxation rate dM/d (ln t) exhibits strong temperature and field dependence in the temperature range up to 80 K and the field range up to 5.5 T. The magnetic relaxation behavior observed in the melt-textured ErBa2Cu3O7– ceramic sample is similar to that in single crystals. The magnetization to noise ratio is much improved, in particular, for temperatures approaching the superconducting transition temperature and for low magnetic fields. Several theoretical models were explored to fit the experimental data. 相似文献
67.
Sumpter BG Kumar P Mehta A Barnes MD Shelton WA Harrison RJ 《The journal of physical chemistry. B》2005,109(16):7671-7685
Computational simulations were used to investigate the dynamics and resulting structures of several para-phenylenevinylene (PPV) based polymers and oligomers (PPV, 2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene --> MEH-PPV and 2,5,2',5'-tetrahexyloxy-7,8'-dicyano-p-phenylenevinylene --> CN-PPV). The results show how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution-phase preparation. Secondary structural organization is induced by using the solution-phase structures to generate solvent-free single molecule nanoparticles. Isolation of these single molecule nanostructures from microdroplets of dilute solution results in the formation of electrostatically oriented nanostructures at a glass surface. Our structural modeling suggests that these oriented nanostructures consist of folded PPV conjugated segments with folds occurring at tetrahedral defects (sp3 C-C bonds) within the polymer chain. This picture is supported by detailed experimental fluorescence and scanning probe microscopy studies. We also present results from a fully quantum theoretical treatment of these systems which support the general conclusion of structure-mediated photophysical properties. 相似文献
68.
This paper adapts Bayesian Markov chain Monte Carlo methods for application to some auto-regressive conditional duration models. Subsequently, the properties of these estimators are examined and assessed across a range of possible conditional error distributions and dynamic specifications, including under error mis-specification. A novel model error distribution, employing a truncated skewed Student-t distribution is proposed and the Bayesian estimator assessed for it. The results of an extensive simulation study reveal that favourable estimation properties are achieved under a range of possible error distributions, but that the generalised gamma distribution assumption is most robust and best preserves these properties, including when it is incorrectly specified. The results indicate that the powerful numerical methods underlying the Bayesian estimator allow more efficiency than the (quasi-) maximum likelihood estimator for the cases considered. 相似文献
69.
Xu Y Getman RB Shelton WA Schneider WF 《Physical chemistry chemical physics : PCCP》2008,10(39):6009-6018
As catalysis research strives toward designing structurally and functionally well-defined catalytic centers containing as few active metal atoms as possible, the importance of understanding the reactivity of small metal clusters, and in particular of systematic comparisons of reaction types and cluster sizes, has grown concomitantly. Here we report density functional theory calculations (GGA-PW91) that probe the relationship between particle size, intermediate structures, and energetics of CO and NO oxidation by molecular and atomic oxygen on Pt(x) clusters (x = 1-5 and 10). The preferred structures, charge distributions, vibrational spectra, and energetics are systematically examined for oxygen (O(2), 2O, and O), CO, CO(2), NO, and NO(2), for CO/NO co-adsorbed with O(2), 2O, and O, and for CO(2)/NO(2) co-adsorbed with O. The binding energies of oxygen, CO, NO, and of the oxidation products CO(2) and NO(2) are all markedly enhanced on Pt(x) compared to Pt(111), and they trend toward the Pt(111) levels as cluster size increases. Because of the strong interaction of both the reactants and products with the Pt(x) clusters, deep energy sinks develop on the potential energy surfaces of the respective oxidation processes, indicating worse reaction energetics than on Pt(111). Thus the smallest Pt clusters are less effective for catalyzing CO and NO oxidation in their original state than bulk Pt. Our results further suggests that oxidation by molecular O(2) is thermodynamically more favourable than by atomic O on Pt(x). Conditions and applications in which the Pt(x) clusters may be effective catalysts are discussed. 相似文献
70.
Conjugated polydiacetylene (PDA) possessing stimuli-responsive properties has been intensively investigated for developing efficient sensors. We report here fluorescence resonance energy transfer (FRET) in liposomes synthesized using different molar ratios of dansyl-tagged diacetylene and diacetylene-carboxylic acid monomers. Photopolymerization of diacetylene resulted in cross-linked PDA liposomes. We used steady-state electronic absorption, emission, and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). We found that the monomer ratio of acceptor to donor ( R ad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. For R ad = 10 000, the acceptor emission intensity was amplified by more than 18 times when the liposome solution was heated from 298 to 338 K. A decrease in R ad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to insertion of dansyl in the bilayer of the liposomes, which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. Furthermore, receptor tagged onto PDA liposomes can interact with ligands present on proteins, enzymes, and cells, which will produce emission sensing signal. Therefore, using the present approach, there exist opportunities for designing FRET-based highly sensitive and selective chemical and biochemical sensors. 相似文献