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71.
Studies have been made of the effect of heating tungsten and iridium field-ion emitters in the presence of an applied electrostatic potential. Although the original intention was to induce plastic deformation as a result of field stresses, and hence to investigate surface slip step formation, it is clear from the image contrast observed that, rather than inducing slip, the procedure instead leads to the formation of fine-scale thermal facets. Earlier reported attempts to deliberately induce surface slip in this way must also be reinterpreted in terms of thermal facet formation. 相似文献
72.
73.
Summers JE Torres RR Shimizu Y 《The Journal of the Acoustical Society of America》2004,116(2):958-969
An improved statistical-acoustics model of high-frequency sound fields in coupled rooms is developed by incorporating into prior models geometrical-acoustics corrections for both energy decay within subrooms and energy transfer between subrooms. The conditions under which statistical-acoustics models of coupled rooms are valid approximations to geometrical acoustics are examined by comparison of computational geometrical-acoustics predictions of decay curves in two- and three-room systems with those of both improved and prior statistical-acoustics models. The accuracy of the decay model used within subrooms is found to have a primary influence on the accuracy of predictions in coupled systems. Likewise, nondiffuse transfer of energy is shown to significantly affect decay of energy in systems of coupled rooms. The decrease in energy density of the reverberant field with distance from the source, which is predicted by geometrical acoustics, is found to result in spatial dependence of decay-curve shape for certain coupling geometries. Geometrical effects are shown to contribute to the failure of statistical-acoustics models in the case of strong coupling between subrooms; thus, previously proposed statistical-acoustics criteria cannot predict the point at which the models break down with consistent accuracy. 相似文献
74.
Analytical modelling of end thermal coupling in a solid-state laser longitudinally bonded by a vertical-cavity top-emitting laser diode 下载免费PDF全文
The intrinsic features involving a circularly symmetric beam
profile with low divergence, planar geometry as well as the increasingly
enhanced power of vertical-cavity surface-emitting lasers (VCSELs)
have made the VCSEL a promising pump source in direct end bonding to
a solid-state laser medium to form the minimized, on-wafer
integrated laser system. This scheme will generate a surface contact
pump configuration and thus additional end thermal coupling to the
laser medium through the joint interface of both materials, apart from
pump beam heating. This paper analytically models temperature
distributions in both VCSEL and the laser medium from the end thermal
coupling regarding surface contact pump configuration using a
top-emitting VCSEL as the pump source for the first time. The
analytical solutions are derived by introducing relative temperature
and mean temperature expressions. The results show that the end
contact heating by the VCSEL could lead to considerable temperature
variations associated with thermal phase shift and thermal lensing
in the laser medium. However, if the central temperature of the
interface is increased by less than 20~K, the end contact heating
does not have a significant thermal influence on the laser medium. In
this case, the thermal effect should be dominated by pump beam
heating. This work provides useful analytical results for further
analysis of hybrid thermal effects on those lasers pumped by a direct
VCSEL bond. 相似文献
75.
In stochastic models of chemically reacting systems that contain bimolecular reactions, the dynamics of the moments of order up to n of the species populations do not form a closed system, in the sense that their time-derivatives depend on moments of order n + 1. To close the dynamics, the moments of order n + 1 are generally approximated by nonlinear functions of the lower order moments. If the molecule counts of some of the species have a high probability of becoming zero, such approximations may lead to imprecise results and stochastic simulation is the only viable alternative for system analysis. Stochastic simulation can produce exact realizations of chemically reacting systems, but tends to become computationally expensive, especially for stiff systems that involve reactions at different time scales. Further, in some systems, important stochastic events can be very rare and many simulations are necessary to obtain accurate estimates. The computational cost of stochastic simulation can then be prohibitively large. In this paper, we propose a novel method for estimating the moments of chemically reacting systems. The method is based on closing the moment dynamics by replacing the moments of order n + 1 by estimates calculated from a small number of stochastic simulation runs. The resulting stochastic system is then used in an extended Kalman filter, where estimates of the moments of order up to n, obtained from the same simulation, serve as outputs of the system. While the initial motivation for the method was improving over the performance of stochastic simulation and moment closure methods, we also demonstrate that it can be used in an experimental setting to estimate moments of species that cannot be measured directly from time course measurements of the moments of other species. 相似文献
76.
Ryan M. Summers Sridhar Gopishetty Sujit K. Mohanty Mani Subramanian 《Central European Journal of Chemistry》2014,12(12):1271-1279
Caffeine is a natural plant product found in many drinks, including coffee, tea, soft and energy drinks. Due to caffeine’s presence in the environment, microorganisms have evolved two different mechanisms to live on caffeine. The genetic maps of the caffeine N-demethylation pathway and C-8 oxidation pathway have been discovered in Pseudomonas putida CBB5 and Pseudomonas sp. CBB1, respectively. These genes are the only characterized bacterial caffeine-degrading genes, and may be of great value in producing fine chemicals, biofuels, and animal feed from coffee and tea waste. Here, we present preliminary results for production of theobromine and 7-methylxanthine from caffeine and theobromine, respectively, by two strains of metabolically engineered E. coli. We also demonstrate complete decaffeination of tea extract by an immobilized mixed culture of Klebsiella and Rhodococcus cells. These processes provide a first level demonstration of biotechnological utilization of coffee and tea waste. 相似文献
77.
78.
E. A. Goode W. H. Summers A. Schachkeldjan 《Analytical and bioanalytical chemistry》1934,98(3-4):137-137
79.
80.
Diquaternary salts of 2,4-di-(4-pyridyl)-1,3,5-triazines have been prepared. The salts can be regarded as reversible one electron transfer systems with redox potentials (E0) of about ?0·44 V in the pH range 7·0–8·5. 2,4-Bis-(4-methyl-4-pyridinio)-1,3,5-triazinediium dihalides are effective post-emergent herbicides at application rates of 4–6 kg/hectare. 相似文献