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91.
This article introduces a new semi‐implicit, staggered finite volume scheme on unstructured meshes for the modelling of rapidly varied shallow water flows. Rapidly varied flows occur in the inundation of dry land during flooding situations. They typically involve bores and hydraulic jumps after obstacles such as road banks. Near such sudden flow transitions, the grid resolution is often low compared with the gradients of the bathymetry. Locally the hydrostatic pressure assumption may become invalid. In these situations, it is crucial to apply the correct conservation properties to obtain accurate results. An important feature of this scheme is therefore its ability to conserve momentum locally or, by choice, preserve constant energy head along a streamline. This is achieved using a special interpolation method and control volumes for momentum. The efficiency of inundation calculations with locally very high velocities, and in the case of unstructured meshes locally very small grid distances, is severely hampered by the Courant condition. This article provides a solution in the form of a locally implicit time integration for the advective terms that allows for an explicit calculation in most of the domain, while maintaining unconditional stability by implicit calculations only where necessary. The complex geometry of flooded urban areas asks for the flexibility of unstructured meshes. The efficient calculation of the pressure gradient in this, and other semi‐implicit staggered schemes, requires, however, an orthogonality condition to be put on the grid. In this article a simple method is introduced to generate unstructured hybrid meshes that fulfil this requirement. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
92.
S. Landsberger A. Simsons J. R. Kramer J. J. Drake S. Vermette B. Shuter P. Ihssen 《Journal of Radioanalytical and Nuclear Chemistry》1987,110(2):333-343
Instrumental neutron activation analysis has been successfully employed in three distrinct acid precipitation studies. These include the determination of ten (Al, Br, Ca, Cl, Cu, I, Mg, Mn, Na and V) elements in urban rainfall, elevated aluminum concentrations in acidified lakes and major ions (Ca, Cl, K, Mg and Na) in small-mouth bass kept in controlled pH environments. Quality control was assured by analyzing two certified standard reference materials prepared by the National Bureau of Standards (NBS 1643a) and National Research Council of Canada (hepatopancreas TORT-1 marine biological tissue). 相似文献
93.
The localization length of one-dimensional disordered systems with statistically correlated random potentials is studied both numerically and analytically. The results indicate that the localization length generally increases when the correlation function is positive. In the presence of anticorrelation effects the localization length may be shorter than in the uncorrelated case. 相似文献
94.
The density of states, and the phase diagram of localization in a three-dimensional disordered tight binding model with box, Gaussian, and Lorentzian distribution of the site energies is numerically determined. The influence of the behaviour of the spectral density on the position of the mobility edge is discussed. Extended states are found outside the unperturbed band for the box and the Gaussian distribution. This implies the existence of two metal-insulator transitions at certain energies which may be attributed to the breakdown of potential localization, and the breakdown of quantum interference localization, respectively. The general validity of the scaling hypothesis in the localization theory is discussed in view of these results. 相似文献
95.
C.-X. Ji M. L. Huang M. J. Kramer C. Zhang K. S. Wu Y. Yang Y. A. Chang 《Applied Physics A: Materials Science & Processing》2010,99(2):471-475
Pt0.5−x
Mn0.5+x
films were prepared by sputtering deposition of Pt foil and Mn target to study the order-disorder transition from a thermodynamic
metastable fcc (A1) phase to L10 phase. Both Differential Scanning Calorimetry and High Temperature X-Ray Diffraction studies showed the phase transformation
from fcc to the L10 structure for the Pt0.50Mn0.50 and Pt0.40Mn0.60 samples but along completely different kinetic paths. A composition dependent phase transformation was observed by comprehensive
Differential Scanning Calorimetry studies on a series of Pt0.5−x
Mn0.5+x
samples. The changes of the lattice parameter and the cell volume of L10 Pt0.5−x
Mn0.5+x
as a function of composition suggest that the anti-site is not the dominant point defect for L10 Pt0.5−x
Mn0.5+x
. 相似文献
96.
Elmar Cohors-Fresenborg Silke Kramer Frank Pundsack Johann Sjuts Norbert Sommer 《ZDM》2010,42(2):231-244
The relationship between practised monitoring activities and performance, especially in mathematics was examined within three nested studies. The first study deals with problems of faulty term rewritings submitted to three groups of subjects—10th to 13th graders, differing in their mathematical performance—whose task was to find the mistakes. Moreover, a questionnaire on the practice and appreciation of monitoring activities was developed. The third study, first, repeats the first study with a similar population and secondly adds interviews with some of the subjects while solving additional items concerning faulty term rewritings. Studies 1 and 3 show similar success in finding mistakes and in the replies to the questionnaire within the various groups. Furthermore, the third study points up that the subject’s answers do neither predict the practised monitoring nor the success in the test. However, the success correlates significantly with the practised monitoring. For a deeper understanding concerning the role of metacognition in explaining performance, the second study examined two of the groups who had already been involved in the first study. These were assigned some problems of a matrices test as used in cognitive psychology. While trying to solve the problem, their eye movements were recorded by means of an eye-tracker. Afterwards they had to justify their solutions in an interview. The eye movements were analysed, the verbal comments classified. Again, the groups differ in their problem solving success, dependant on the quality of the monitoring practised. Altogether, the results of the three studies elucidate the importance of practised metacognitive monitoring activities not only for success in school algebra, but furthermore the ability and the willingness to do it is deeper anchored in a person than just a trained behaviour for school algebra. 相似文献
97.
98.
99.
Gerhard Kramer 《Fresenius' Journal of Analytical Chemistry》1937,109(1-2):16-25
Ohne Zusammenfassung 相似文献
100.