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1.
The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed. 相似文献
2.
Charles Dane Napoli Karen S. Helfer Richard E. A. van Emmerik 《Entropy (Basel, Switzerland)》2022,24(6)
Postural behavior has traditionally been studied using linear assessments of stability (e.g., center of pressure ellipse area). While these assessments may provide valuable information, they neglect the nonlinear nature of the postural system and often lead to the conflation of variability with pathology. Moreover, assessing postural behavior in isolation or under otherwise unrealistic conditions may obscure the natural dynamics of the postural system. Alternatively, assessing postural complexity during ecologically valid tasks (e.g., conversing with others) may provide unique insight into the natural dynamics of the postural system across a wide array of temporal scales. Here, we assess postural complexity using Multiscale Sample Entropy in young and middle-aged adults during a listening task of varying degrees of difficulty. It was found that middle-aged adults exhibited greater postural complexity than did young adults, and that this age-related difference in postural complexity increased as a function of task difficulty. These results are inconsistent with the notion that aging is universally associated with a loss of complexity, and instead support the notion that age-related differences in complexity are task dependent. 相似文献
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6.
Juan Tapia-P Yipeng Cao Prof. Jaime Gallego Prof. Jorge M. Osorio-Guillén Prof. Dane Morgan Prof. Juan F. Espinal 《Chemphyschem》2022,23(11):e202200152
There is an ongoing effort to replace rare and expensive noble-element catalysts with more abundant and less expensive transition metal oxides. With this goal in mind, the intrinsic defects of a rhombohedral perovskite-like structure of LaMnO3 and their implications on CO catalytic properties were studied. Surface thermodynamic stability as a function of pressure (P) and temperature (T) were calculated to find the most stable surface under reaction conditions (P=0.2 atm, T=323 K to 673 K). Crystallographic planes (100), (111), (110), and (211) were evaluated and it was found that (110) with MnO2 termination was the most stable under reaction conditions. Adsorption energies of O2 and CO on (110) as well as the effect of intrinsic defects such as Mn and O vacancies were also calculated. It was found that O vacancies favor the interaction of CO on the surface, whereas Mn vacancies can favor the formation of carbonate species. 相似文献
7.
Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. It is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this Letter, we transfer the concept of heuristic rule extraction to a large library of ab initio calculated information, and we demonstrate that this can be developed into a tool for crystal structure prediction. 相似文献
8.
Jonas Enebro Dane Momcilovic Matti Siika-aho Sigbritt Karlsson 《Cellulose (London, England)》2009,16(2):271-280
The benefits of applying cellulose selective enzymes as analytical tools for chemical structure characterization of cellulose
derivatives have been frequently addressed over the years. In a recent study the high selectivity of cellulase Cel45A from
Trichoderma reesei (Tr Cel45A) was utilized for relating the chemical structure to the flow properties of carboxymethyl cellulose (CMC). However,
in order to take full advantage of the enzymatic hydrolysis the enzyme selectivity on the cellulose substrate must be further
investigated. Therefore, the selectivity of Tr Cel45A on CMC was studied by chemical sample preparation of the enzyme products
followed by mass spectrometric chemical structure characterization. The results strongly suggest that, in accordance with
recent studies, also this highly selective endoglucanase is able to catalyze hydrolysis of glucosidic bonds adjacent to mono-substituted
anhydroglucose units (AGUs). Furthermore, the results also indicate that substituents on the nearby AGUs will affect the hydrolysis. 相似文献
9.
D. Dane Quinn 《Nonlinear dynamics》2009,57(4):623-633
The response of a nonlinear, damped Jeffcott rotor with anisotropic stiffness is considered in the presence of an imbalance.
For sufficiently small external torque or large imbalance, resonance capture or rotordynamic stall can occur, whereby the
rotational velocity of the shaft is unable to increase beyond the fundamental resonance between the rotational and translational
motion. This phenomena provides a mechanism for energy transfer from the rotational to the translational mode. Using the method
of averaging a reduced-order model is developed, valid near the resonance, that describes this resonant behavior. The equilibrium
points of these averaged equations, which correspond to stationary solutions of the original equations and rotordynamic stall,
are described as the applied torque, damping, and anisotropy vary. As the anisotropy increases, assumed to arise from increasing
shaft cracks, the torque required to eliminate the possibility of stall increases. However, when the system is started with
zero initial conditions, the minimum torque required to pass through the resonance is approximately constant as the anisotropy
increases. The predictions from the reduced-order model are verified against numerical simulations of the original equations
of motion. 相似文献
10.
XIAOPeng GUOXin-xin CUIYing-xin RobertE.Imhof DaneBicanic 《高等学校化学研究》2004,20(4):417-420
Opto-thermal transient emission radiometry(OTTER) is a infrared remote sensing technique, which has been successfully used in in vivo skin moisture content and skin moisture depth profiling measurements. In present paper, we extend this moisture content measurement capability to analyze the moisture content of fruit (tomato. grape, etc. ) skins, and to study the relationship between fruits ripening process and their sur-face moisture and moisture depth profiles. 相似文献