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61.
It has become a common practice to include diagnostics and archaeometric studies during a masterpiece restoration. The advantages and limits of this approach are now topic of discussion in the community of researchers that is growing up quickly. The bronze burial monument of Pope Sixtus IV (1471–84) by Antonio del Pollaiolo, now in the Treasure Museum in the Vatican was intended to be located at the center of a chapel, this explains its apparent asymmetry: lack of height and large base. The restoration of the burial monument started in May 2007, it was carried out by first fulfilling a series of non-invasive analyses using a transportable EDXRF to map the composition of the alloy and evaluate the diagnostic capabilities for deterioration processes of the bronze surface. As a consequence of the first non-invasive diagnostic campaign, a second campaign of micro invasive tests was planned and carried out. The samples were analysed with SEM-EDS and XRF techniques. In this article some of the results of the EDXRF tests will be shown together with the procedures set up to maximize the diagnostic information obtained and minimize the need of microsampling from the artefact. The results and the statistical analysis of data show that a straightforward planning of the measurements can give several, sometimes unexpected, results in the definition of the state of conservation of the monument and also from an archaeometric point of view. With a high amount of data, the use of statistical analysis is necessary, for example in our case, the analysis of the variance confirmed the hypothesis of the use of different alloys for the elements of the panels. 相似文献
62.
Mauro Cappelli Bernardino Castillo–Toledo Stefano Di Gennaro 《Journal of The Franklin Institute》2021,358(2):1308-1326
In this work, dynamic controllers are designed for reactor power, pressurizer water level, and pressure control in the primary circuit of a pressurized water reactor. These nonlinear controllers use super-twisting sliding-mode estimators to enhance their robustness versus parameter variations and external disturbances. Hence, the perturbative terms can be canceled by the control, thus improving the dynamic behavior of the controlled system. The designed controllers ensure good performances and better transient behavior, also in the presence of uncertainties and disturbances. A performance study of the proposed controllers is carried out in the presence also of unmodeled dynamics. 相似文献
63.
Ce Huang Awadhesh Narayan Enze Zhang Xiaoyi Xie Linfeng Ai Shanshan Liu Changjiang Yi Youguo Shi Stefano Sanvito Faxian Xiu 《国家科学评论(英文版)》2020,7(9):1468
WTe2, as a type-II Weyl semimetal, has 2D Fermi arcs on the (001) surface in the bulk and 1D helical edge states in its monolayer. These features have recently attracted wide attention in condensed matter physics. However, in the intermediate regime between the bulk and monolayer, the edge states have not been resolved owing to its closed band gap which makes the bulk states dominant. Here, we report the signatures of the edge superconductivity by superconducting quantum interference measurements in multilayer WTe2 Josephson junctions and we directly map the localized supercurrent. In thick WTe2 (, the supercurrent is uniformly distributed by bulk states with symmetric Josephson effect (). In thin WTe2 (10 nm), however, the supercurrent becomes confined to the edge and its width reaches up to and exhibits non-symmetric behavior . The ability to tune the edge domination by changing thickness and the edge superconductivity establishes WTe2 as a promising topological system with exotic quantum phases and a rich physics. 相似文献
64.
Drawing on a longitudinal case study of Alpha Chemicals, we use four complexity theory constructs – adaptive tension, enabling leadership, enhanced cooperation, and boundary spanning – to explain the continuous knowledge creation dynamics in Communities of practice (CoPs). Our findings show that the virtual cycle of knowledge creation results from CoPs oscillating between guided and self-directed modes. In a guided mode, adaptive tension and enabling leadership prevail, resulting in knowledge expansion. In a self-directed mode, enhancing cooperation and boundary spanning are the most significant, resulting in knowledge probing. This research uncovers the value of conceptualizing CoPs as complex adaptive systems with emergent and intentional processes coexisting to create a virtual knowledge creation cycle. Our findings complement the dominant theory on CoPs’ insights by moving beyond the control/autonomy debate and highlighting that knowledge creation dynamics results from a flexible combination and recombination of the different top-down and bottom-up forces. 相似文献
65.
Francesco Braghin Mauro Donzelli Stefano Melzi Edoardo Sabbioni 《Sports Engineering》2011,13(4):181-193
Up to now, the optimization of structural parameters affecting the performance of a bobsleigh has been carried out mainly
on the basis of athletes’ feedback, thus leading to a series of small modifications without univocal guidelines. Even though
on-track tests represent a basic step for the final tuning of the sled, experimentation does not seem to represent an appropriate
tool to objectively determine the influence of such structural parameters on the overall performance. In fact, their effect
can easily be masked by driving errors, changes in the ice surface conditions and temperature thus requiring repeated tests
for achieving statistical evidence. For this reason, numerical analysis, carried out with a 3D model of the bobsled, turns
out to be a privileged instrument to optimize bob design although limitations in the sled model (e.g. ice friction properties
that still have to be fully understood) may affect the obtained results. However, such tool is able to provide useful indications
only if a correct driver model is implemented. This work focuses on the development of a numerical model of a bobsleigh driver
that aims at reproducing the driving behaviour of real-world cup drivers and is basically made up of two steps: the identification
of the trajectory that allows minimizing run time and the determination of the driver’s inputs to exactly follow that trajectory.
For comparison purposes, the simulated driver’s inputs are compared with recorded ones on Cesana Pariol Olympic track. 相似文献
66.
This article explores teacher training by the alternation of classroom work and work analysis using an approach based on a social conception of meaning and action. The advantage of this approach is that it allows the development of professional activity in preservice teachers (PTs) to be assessed by tracking how the reflective tools acquired in training evolve in work and/or work analysis situations. The concepts of ‘meaning’ and ‘expectation’ are helpful in discussing the empirical data from a research program designed to evaluate the potential for PTs’ professional development offered by the alternating work/analysis programs of French University Institutes of Teacher Training. The main conclusions concern the need to organize PTs’ professional experiences within a training network so that PTs are not left on their own to face the diverse and complex situations of daily professional exercise. The effective procedures are those that allow PTs to construct concrete and circumstance‐based expectations that the professional rules they have learned are still operational. These expectations help PTs to efficiently calibrate and interpret the meaning of their work experience, while also allowing them to prepare to act differently. 相似文献
67.
Leonello Paoloni 《International Journal of Science Education》2013,35(4):365-377
Summaries English The didactic use of formulae in the teaching of chemistry as part of the individual culture should include the logics of their elaboration, and frame them into the basic postulates of the chemical doctrine. These postulates, in the form that was accepted since the last quarter of the 19th century, are discussed together with the assumptions embodied in the procedures for establishing the formulae as the source of the images of molecular structure. The limitations inherent in these procedures, and the influence they had upon the teaching of chemistry, are examined by analysing the exemplar cases of anthracene and of sydnones. Chemical formulae represent a practical code for the structure‐reactivity relationships, and therefore their current meaning in a quantum‐chemical interpretation is also discussed. It is suggested that the teaching of chemistry in the age range 13‐14 be based on the postulates and procedures of classical chemistry (1874‐1935), leaving the elementary introduction of quantum‐chemical concepts to the 15‐18 age range. 相似文献
68.
Leonello Paoloni 《International Journal of Science Education》2013,35(3):241-251
Summaries English The relationship between classical mechanics and quantum mechanics is illustrated by considering how we form the images of moving objects. Brownian motion is an helpful example because it can be analyzed in two related, but different frames which show how the images we construct depend on the conditions of our observation and on some intrinsic characters of the observed objects. 相似文献
69.
70.