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31.
Pinto FG Andrada D Magalhães CG Nunes BR de Amorim FR Franco MB Saint'pierre TD da Silva JB Curtius AJ 《Analytical and bioanalytical chemistry》2005,383(5):825-832
Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation
to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO3 and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the
permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same
occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity,
Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the
best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using
this last modifier, the following dilutions with the HNO3 and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined
peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic
mass of 26±0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching
calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95%
confidence level. Recovery tests were carried out and the recoveries were in the range 100–103%, with relative standard deviation
better than 9%. The limit of detection (LOD, 3 sd, n=10) was 3.0 μg L−1 in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration
of the analytical signal. 相似文献
32.
Alexandra Mara De Amorim Ana Cristina Franzoi Paula Nunes Oliveira Alfredo Tibúrcio Nunes Pires Almir Spinelli José Roberto Bertolino 《Journal of Polymer Science.Polymer Physics》2009,47(22):2206-2214
The influence of molecular weight and the amount of the poly(vinylpyrrolidone) (PVP) on the growth of poly(vinylpyrrolidone)–based films on copper surfaces was studied by electrochemical, infrared and electronic spectroscopy, and thermogravimetric methods. Complex polymer/metal ions were deposited onto a copper surface, as the result of the electrochemically generated reaction of copper cations with PVP and SCN?, in sulfuric acid media. Spontaneous film growth on copper surfaces was generated and characterized as a Cu(II)/PVP/SCN? complex. Infrared spectra and thermal gravimetric curves of the films generated at + 0.7 V were compared with the chemically synthesized complex, and show the same patterns. The oxidation process can be described as: Cu(0)→Cu(I) and Cu(I)→Cu(II), and the copper complex formed at more positive potentials was characterized as Cu(II)/PVP/SCN?, with copper bonded to the oxygen atom of PVP and thiocyanate ligand N‐linked. This study focuses on the complex formation on a copper surface in acid media and its characterization through electrochemical and spontaneously generated reactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2206–2214, 2009 相似文献
33.
With the motivation that critical dimensionsD≠4 might be suggesting that string theories have not been completely formulated, we study more general alternatives. We first consider a direct extension in the world-sheet formulation withN B bosons andN F fermions and analyze the conditions for canceling the anomaly in all possible combinations ofN B ,N F andD. Later on we incorporate degrees of freedom of antisymmetric tensors to the previous model. The only possibility to cancel the anomaly in this case is withN B =N F =1 and the our everyday spacetime dimensionD=4. 相似文献
34.
Angel Bustamante Enrico Mattievich Helio S. de Amorim Ivo Vencato Máximo M. Silveira 《Hyperfine Interactions》2005,166(1-4):599-603
The crystal structure of synthetic ferrous hureaulite, Fe5 2+ (H2O)4(PO4H)2(PO4)2, was refined from single-crystal X-ray data. It is monoclinic, space group C2/c, with a=17.487(4), b=9.017(2), c=9.338(2) Å, β=96.27(3)°, V=1463.6(6) Å3, Z=4 and D calc=3.327 g/cm3. This end member of the hureaulite series was crystallized under distinctly acidic conditions, by a method that gives perfect crystals, large enough for X-ray single crystal studies. The main feature of the hureaulite structure is that it has an equal number of normal (PO4)3+ and acid (PO4H)2+ tetradentate groups. These are centered on Fe2+ atoms and share corners with edge-linked octahedra, forming pentamer units. The five Fe2+ atoms are distributed on three distinct sites in these units. This can be directly observed in the Mössbauer spectrum at 295 K, which contains three doublets whose relative intensities correspond to the 1:2:2 distributions of crystallographic sites. 相似文献
35.
Sakari Leino Patrick JC May Paavo Alku Lassi A Liikkanen Hannu Tiitinen 《BMC neuroscience》2007,8(1):78
Background
In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment. 相似文献36.
37.
In this work we study the geodesic motion on a noncommutative space–time. As a result we find a non-commutative geodesic equation and then we derive corrections of the deviation angle per revolution in terms of the non-commutative parameter when we specify the problem of Mercury’s perihelion. In this way, we estimate the noncommutative parameter based in experimental data. 相似文献
38.
Ricardo Amorim 《Zeitschrift fur Physik C Particles and Fields》1995,67(4):695-700
We study the Hamiltonian path integral formulation for generic systems with first class and linear second class constraints.ift01001@ufrj 相似文献
39.
Eduardo Lutterbach Bandeira Marcelo Amorim Savi Paulo Cesar da Camara Monteiro Jr. Theodoro Antoun Netto 《Archive of Applied Mechanics (Ingenieur Archiv)》2006,76(3-4):133-144
This contribution deals with the nonlinear analysis of shape memory alloy (SMA) adaptive trusses employing the finite element method. Geometrical nonlinearities are incorporated into the formulation together with a constitutive model that describes different thermomechanical behaviors of SMA. It has four macroscopic phases (three variants of martensite and an austenitic phase), and considers different material properties for austenitic and martensitic phases together with thermal expansion. An iterative numerical procedure based on the operator split technique is proposed in order to deal with the nonlinearities in the constitutive formulation. This procedure is introduced into ABAQUS as a user material routine. Numerical simulations are carried out illustrating the ability of the developed model to capture the general behavior of shape memory bars. After that, it is analyzed the behavior of some adaptive trusses built with SMA actuators subjected to different thermomechanical loadings. 相似文献
40.
Madeira PJ Faddoul M Afonso MB Vaz PD Fernandez MT Leal JP 《Journal of mass spectrometry : JMS》2011,46(7):640-648
Some antioxidant mechanisms displayed by several phenolic compounds relate with OH bond dissociation energy. One way for its determination, in the gas-phase, relies on acidity measurements. Gas-phase acidities were determined experimentally, applying the kinetic method, for chromanol and four dimethoxyphenols, and theoretically through quantum chemical DFT calculations for chromanol, six dimethoxyphenols and 3,4,5-trimethoxyphenol. The experimental acidity order, 2,3-dimethoxyphenol > 3,5-dimethoxyphenol > 2,6-dimethoxyphenol > 3,4-dimethoxyphenol ≈ phenol > chromanol shows good agreement with the theoretical acidity order, 2,5-dimethoxyphenol > 2,3-dimethoxyphenol > 3,4,5-trimethoxyphenol > 3,5-dimethoxyphenol ≈ 2,4-dimethoxyphenol > 2,6-dimethoxyphenol > 3,4-dimethoxyphenol > phenol > chromanol. These acidity trends were rationalized in terms of the substituent effects on the thermodynamic stabilities both of the parent phenols and the corresponding phenoxide ions. DFT calculations also evidenced the occurrence of intramolecular C-H···O hydrogen bonds whenever there are vicinal substituents (either OH, O(-) or OCH(3)) which induce further stabilization of the geometries. 相似文献