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71.
A method for producing a self-generated magnetic focussing structure for a beam of laser-generated relativistic electrons using a complex array of resistivity gradients is proposed and demonstrated using numerical simulations. The array of resistivity gradients is created by using a target consisting of alternating layers of different Z material. This new scheme is capable of effectively focussing the fast electrons even when the source is highly divergent. The application of this technique to cone-guided fast ignition inertial confinement fusion is considered, and it is shown that it may be possible to deposit over 25% of the fast electron energy into a hot spot even when the fast electron divergence angle is very large (e.g., 70° half-angle). 相似文献
72.
Bachega JF Bleicher L Horjales ER Santiago PS Garratt RC Tabak M 《Journal of synchrotron radiation》2011,18(1):24-28
Glossoscolex paulistus is a free-living earthworm encountered in south-east Brazil. Its oxygen transport requirements are undertaken by a giant extracellular haemoglobin, or erythrocruorin (HbGp), which has an approximate molecular mass of 3.6 MDa and, by analogy with its homologue from Lumbricus terrestris (HbLt), is believed to be composed of a total of 180 polypeptide chains. In the present work the full 3.6 MDa particle in its cyanomet state was purified and crystallized using sodium citrate or PEG8000 as precipitant. The crystals contain one-quarter of the full particle in the asymmetric unit of the I222 cell and have parameters of a = 270.8 ?, b = 320.3 ? and c = 332.4 ?. Diffraction data were collected to 3.15 ? using synchrotron radiation on beamline X29A at the Brookhaven National Laboratory and represent the highest resolution data described to date for similar erythrocruorins. The structure was solved by molecular replacement using a search model corresponding to one-twelfth of its homologue from HbLt. This revealed that HbGp belongs to the type I class of erythrocruorins and provided an interpretable initial electron density map in which many features including the haem groups and disulfide bonds could be identified. 相似文献
73.
74.
Summary A family of one-dimensional nonlinear dispersive wave equations is introduced as a model for assessing the validity of weak
turbulence theory for random waves in an unambiguous and transparent fashion. These models have an explicitly solvable weak
turbulence theory which is developed here, with Kolmogorov-type wave number spectra exhibiting interesting dependence on parameters
in the equations. These predictions of weak turbulence theory are compared with numerical solutions with damping and driving
that exhibit a statistical inertial scaling range over as much as two decades in wave number.
It is established that the quasi-Gaussian random phase hypothesis of weak turbulence theory is an excellent approximation
in the numerical statistical steady state. Nevertheless, the predictions of weak turbulence theory fail and yield a much flatter
(|k|−1/3) spectrum compared with the steeper (|k|−3/4) spectrum observed in the numerical statistical steady state. The reasons for the failure of weak turbulence theory in this
context are elucidated here. Finally, an inertial range closure and scaling theory is developed which successfully predicts
the inertial range exponents observed in the numerical statistical steady states. 相似文献
75.
I. I. Grandberg S. V. Tabak N. I. Bobrova A. N. Kost L. G. Vasina 《Chemistry of Heterocyclic Compounds》1966,1(3):271-274
Alkyl and aryl pyrazoles are acylated at position 4 by the chloroanhydrides and anhydrides of the lowest fatty and aromatic acids in the presence of catalytic amounts of sulfuric acid. Reaction is readily effected because it is the neutral pyrazole molecule which is being acylated. In individual cases 1, 3, 5-trimethylpyrazole can be alkylated at position 4 by the Friedel-Crafts reaction.For Part IL see [6]. 相似文献
76.
The dissociation constants (pK
a
) of isomeric hydroxy, amino, and carboxy substituted 1-phenylpyrazoles are determined. From the results certain conclusions are drawn regarding the distribution of electron density in the 1-phenylpyrazole ring, and regarding the effect (ortho effect) of substituents at position 5 on the basicities and acidities of these compounds.For Part LIV see [19]. 相似文献
77.
The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on the autoxidation process of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) is addressed in the present work. The complex oligomeric assembly of hemoglobin subunits may influence the autoxidation rate and the exponential decay behavior. Kinetic studies were developed using UV-vis measurements at 415 nm. These spectroscopic measurements are analyzed at two pH values, 7.0 and 9.0, where the hemoglobin presents different oligomeric assembly. At pH 7.0 a high stability of the native form of the oxy-hemoglobin is observed, while at pH 9.0 an intense dissociation of the oligomer is promoted by alkalization. This difference is evident by comparison of the rate constants in the absence of surfactant: at pH 7.0 the kinetics presents a mono-exponential behavior with a rate constant of 0.27 x 10(-4)s(-1) while at pH 9.0 a bi-exponential behavior was observed with rate constant increase to 7 x 10(-4)s(-1) (fast process) and 1 x 10(-4)s(-1) (slow process). In the autoxidation induced by SDS two factors affect significantly the process rate, namely, the oligomeric arrangement of the hemoglobin and the strength of the interaction between SDS and HbGp. At pH 7.0, for SDS concentrations up to 0.3mM, a mono-exponential behavior was observed, showing rate constants around 0.4 x 10(-4)s(-1), which suggest that the hemoglobin still maintains the more compact structure observed at this pH for the native protein. In the SDS concentration range 0.75-1.0mM, the mono-exponential process changes into a bi-exponential behavior with rate constants varying from 48 x 10(-4) up to 99 x 10(-4)s(-1) for the fast process and from 1.7 x 10(-4) up to 3.7 x 10(-4)s(-1) for the slow process, suggesting hemoglobin dissociation. At pH 9.0, a bi-exponential decay is observed for all studied SDS concentration range, presenting rate constants from 11.0 x 10(-4) up to 179 x 10(-4)s(-1) for the fast process and from 1.0 x 10(-4) up to 8 x 10(4)s(-1) for the slow process probably due to hemoglobin dissociation, which is already present in the absence of surfactant. At pH 7.0, the highly packed native protein structure should inhibit the autoxidation process, but the SDS/HbGp interaction is more intense as compared to pH 9.0, due to the acid pI value, promoting oligomeric dissociation. So, the autoxidation process is regulated at pH 7.0 by the interaction with SDS, which triggers oligomeric dissociation and increase of autoxidation rate. At pH 9.0, the autoxidation process should be very fast, probably due to the oligomeric dissociation, which is already present in the absence of surfactant. At alkaline pH, the interaction with SDS seems be weaker than at pH 7.0. This behavior at pH 7.0 can be observed through the higher autoxidation rate for the faster chains and it is associated to the acid pI of the giant extracellular hemoglobins. 相似文献
78.
A. Tabak 《Journal of Thermal Analysis and Calorimetry》2009,95(1):31-36
The alumina-dye composites were prepared by treating the basic alumina with the water solutions of Reactive Red 120 (RR 120)
and Reactive Blue 15 (RB 15) dyes. The bands of low intensities in the 1400–1600 cm−1 region and at 783 cm−1 in the IR spectra of these composites point out that the dye species is bound weakly to the surface. In the case of mechanochemical
adsorption of dye molecules, the asymmetric and symmetric S(=O)2 and the S-O-C stretching bands together with the vibrations of aromatic ring revealed that dye types under dry conditions
interacted effectively with alumina surface. After the heating of the alumina dye complexes in the temperature range 150–350°C,
the intensities of the IR and XRD peaks for adsorbed types decreased. The endothermic peaks over 200°C and the bigger total
mass losses for the alumina-dye composites can be ascribed to the decomposition of dye species retained by the alumina surface.
The mass losses on TG curves of the alumina-dye complexes up to ∼800°C exhibit the removal of black residues occurred by decomposition
of first adsorbed products. The thermal analysis data also point out that the water molecules bonded strongly to the alumina
surface and dye types compete to accommodate at the surface active sites. 相似文献
79.
Hang HC Yu C Ten Hagen KG Tian E Winans KA Tabak LA Bertozzi CR 《Chemistry & biology》2004,11(3):337-345
The polypeptide N-acetyl-alpha-galactosaminyltransferases (ppGalNAcTs, also abbreviated ppGaNTases) initiate mucin-type O-linked glycosylation and therefore play pivotal roles in cell-cell communication and protection of tissues. In order to develop new tools for studying mucin-type O-linked glycosylation, we screened a 1338 member uridine-based library to identify small molecule inhibitors of ppGalNAcTs. Using a high-throughput enzyme-linked lectin assay (ELLA), two inhibitors of murine ppGalNAcT-1 (K(I) approximately 8 microM) were identified that also inhibit several other members of the family. The compounds did not inhibit other mammalian glycosyltransferases or nucleotide sugar utilizing enzymes, suggesting selectivity for the ppGalNAcTs. Treatment of cells with the compounds abrogated mucin-type O-linked glycosylation but not N-linked glycosylation and also induced apoptosis. These uridine analogs represent the first generation of chemical tools to study the functions of mucin-type O-linked glycosylation. 相似文献
80.
M. Tabak 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):265-272
There is a need to develop alternate energy sources in the coming century because fossil fuels will become depleted and their
use may lead to global climate change. Inertial fusion can become such an energy source, but significant progress must be
made before its promise is realized. The high-density approach to inertial fusion suggested by Nuckolls et al. leads reaction
chambers compatible with civilian power production. Methods to achieve the good control of hydrodynamic stability and implosion
symmetry required to achieve these high fuel densities will be discussed. Fast Ignition, a technique that achieves fusion
ignition by igniting fusion fuel after it is assembled, will be described along with its gain curves. Fusion costs of energy
for conventional hotspot ignition will be compared with those of Fast Ignition and their capital costs compared with advanced
fission plants. Finally, techniques that may improve possible Fast Ignition gains by an order of magnitude and reduce driver
scales by an order of magnitude below conventional ignition requirements are described. 相似文献