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101.
We report on a recent calculation of the properties of the DNN system, a charmed meson with two nucleons. The system is analogous to the ${{\bar {K}}NN}$ system substituting a strange quark by a charm quark. Two different methods are used to evaluate the binding and width, the Fixed Center approximation to the Faddeev equations and a variational calculation. In both methods we find that the system is bound by about 200 MeV and the width is smaller than 40 MeV, a situation opposite to the one of the ${{\bar {K}}NN}$ system and which makes this state well suited for experimental observation. 相似文献
102.
In the prolonged absence of catastrophic disturbance, ecosystem retrogression occurs, and this involves increased nutrient limitation, and reduced aboveground and belowground ecosystem processes rates. Little is known about how the nitrogen and carbon stable isotope ratios (δ15N and δ13C) of plants, soils and consumer organisms respond to retrogression in boreal forests. We investigated a 5000 year chronosequence of forested islands in the boreal zone of northern Sweden, for which the time since lightning‐induced wildfire increases with decreasing island size, leading to ecosystem retrogression. For this system, tissue δ15N of three abundant plant species (Betula pubescens, Vaccinium myrtillus and Pleurozium schreberi) and humus all increased as retrogression proceeded. This is probably due to enhanced ecosystem inputs of N by biological fixation, and greater dependency of the plants on organic N during retrogression. The δ13C of B. pubescens and plant‐derived humus also increased during retrogression, probably through nutrient limitation increasing plant physiological stress. Unlike the plants, δ15N of invertebrates (lycosid spiders and ants) did not increase during retrogression, probably because of their partial dependence on aquatic‐derived prey that had a variable δ15N signature. The δ13C of the invertebrates increased as retrogression proceeded and converged towards that of an aquatic prey source (chironomid flies), suggesting increased dependence on aquatic‐derived prey during retrogression. These results show that measurement of δ15N and δ13C of plants, soils, and consumers across the same environmental gradient can provide insights into environmental factors that drive both the aboveground and belowground subsystems, as well as the linkages between them. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
103.
Kenji Iino Katsuhiko Maruo Hidenobu Arimoto Koji Hyodo Tetsu Nakatani Yukio Yamada 《Optical Review》2003,10(6):600-606
We have calculated the characteristics of reflected near infrared light, which is incident on the skin surface, scattered in the skin tissue and detected, in the wavelength range from 1000 nm to 1900 nm. We have used a Monte Carlo method to calculate the propagation path, the average photon visit depth, the average photon path length, etc. for the cases of short source-detector distances, to which the isotropic scattering approximation cannot be applied. An experiment to validate the simulation results was also conducted using a liquid phantom. 相似文献
104.
105.
J. H. Kim F. Saito Y. Nagashima T. Kurihara A. Goto Y. Itoh T. Hyodo 《Radiation Physics and Chemistry》2000,58(5-6):759-762
Spin-polarized low-energy positrons were considered as useful probes for studying electron spin states of both surface and bulk materials. Due to the spin-dependent interactions between electrons and positrons, the formation of positronium (Ps), an electron-positron bound system, can be distinguished from different electron spin states. Recently, a positron source of 18F has been developed for a spin polarized slow positron beam at the institute of physical and chemical research (RIKEN). The design of an electrostatic positron beam will be discussed in conjunction with a spin rotator. 相似文献
106.
Naoki Suzuki Akimitsu Takamori Junpei Baba Junichi Matsuda Toshio Hyodo Yasushi Okamoto Hiroshi Miyagi 《Radiation Physics and Chemistry》2000,58(5-6):593-596
Positron lifetime spectra for general purpose polystyrene (GPPS), polybutadiene rubber (PBR), and their copolymers, styrenebutadiene rubber (SBR) and high impact polystyrene (HIPS) have been measured. It has been found that the free volumes in the copolymers are smaller than the average over the individual polymers, due to the interfacial interaction between the styrene and rubber phases. A long-lived component with a mean lifetime of about 123 ns was observed in the spectrum for deformed HIPS, showing the existence of ortho-positronium (o-Ps) in the deformation induced crazes. 相似文献
107.
Positron lifetime spectra have been measured in two kinds of carbon nanotube powders as a function of temperature range between 32 and 296 K. It has been found that all spectra are essentially temperature-independent in the above temperature range. The results of analysis show that there are three components in the powders of carbon nanotube with an average diameter of 30 nm, and four components in the powders of carbon nanotube with typical diameters of around 15 nm. The average values of lifetime components obtained at various temperatures are about 220, 390 ps, and 2.0 ns for the former, and about 140, 300, 650 ps and 6.4 ns for the latter. 相似文献
108.
Tani Masahiko Gu Ping Hyodo Masaharu Sakai Kiyomi Hidaka Takehiko 《Optical and Quantum Electronics》2000,32(4-5):503-520
We have reviewed and discussed the generation of continuous-wave terahertz radiation by the photomixing of dual-mode lasers, which includes a multi-mode laser diode (LD), a dual-mode microchip laser, a monolithic dual-mode DBR LD, and a widely tunable dual-mode external cavity LD. It is demonstrated by several experiments that the beat frequency of a dual-mode laser is more stable than the original laser modes because of the common-mode rejection effect. We also suggest a novel scheme by which the optical beat is stabilized to less than 1 kHz and its frequency can be precisely determined as well. 相似文献
109.
110.
We demonstrate the generation of optical pulses at a repetition rate of 64 GHz directly from a frequency-modulated (FM) mode-locked fiber laser. This is achieved by phase modulation at 16 GHz and by initiating of higher-order FM mode locking by use of an intracavity Fabry-Perot filter with a free spectral range of 64 GHz. This process yielded transform-limited pulses with a width of 3.3 ps. We investigated the operating characteristics of the laser and compared them with the characteristics that were predicted theoretically. 相似文献