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31.
T. Takakura 《Solar physics》1990,127(1):95-107
The Fokker-Planck equation is numerically solved to study the electron velocity distribution under steady heat conduction with an applied axial electric current in a model coronal loop.If the loop temperature is so high that the electron mean-free path is longer than the local temperature scale height along the loop, a velocity hump appears at about the local thermal electron velocity. The hump is attributed to cooler electrons moving up the temperature gradient to compensate for the runaway electrons moving down the gradient. If the ratio between the mean free path and temperature scale height is greater than about 2, negative absorption for the plasma waves can appear (waves grow). This effect is enhanced by the presence of axial electric current in the half of the coronal loop in which the electrons carrying the current are drifting up the temperature gradient. Thus, the plasma instability may occur in the coronal elementary magnetic flux tubes. Although the present paper is limited to show the critical condition and linear growth rate of the instability, the following scenarios may be inferred.If the flux tubes change from marginally stable to unstable against the plasma instability, due to an increase in the loop temperature, anomalous resistivity may suddenly appear because of the growth of plasma waves. Then a high axial electric field is induced that may accelerate particles. This could be the onset of impulsive loop flares.For a low electric current, if the loop temperature is sufficiently high to give the negative absorption for the plasma waves in a large part of the coronal loop, steady plasma turbulence may originate. This could be a source for the type I radio noise storm. 相似文献
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33.
S. S. Degaonkar T. Takakura P. Kaufmann J. E. R. Costa K. Ohki N. Nitta 《Solar physics》1983,86(1-2):237-238
From simultaneous high-time-resolution observations of solar X-rays from Hinotori and the millimeter waves at Itapetinga Radio Observatory in Brazil during a solar flare on November 4, 1981 at 1827 UT, short period ( 300 ms) pulsations have been detected in five time intervals of 2 s each. Both a cross-correlation analysis between X-rays and microwaves and a Fourier analysis were made to verify the significance of the quasi-periodic pulsations. The cross-correlation is significant but the pulsations could not be periodic oscillation.on leave of absence from Physical Res. Lab., Ahmedabad, India 相似文献
34.
T. Takakura 《Solar physics》1977,52(2):429-461
Numerical analysis of quasi-linear relaxation has been made for four models of electron beam with a finite length travelling through the plasma. In Model 4, a model atmosphere of the corona is adopted and also an increase in the cross-section of the electron beam is taken into account. The electron velocity distribution generally becomes a quasi-plateau form in limited velocity and time ranges. If, however, collisional decay of the fast electrons is too strong and the initial beam density is not high enough, the plateau does not appear. Collisional damping of plasma waves cannot be neglected, since the growth rate of the waves is strongly suppressed by the appearance of the quasi-plateau.An approximate formula for the velocity distribution of the solar electrons passing through the corona has been derived analytically taking into account not only the interaction with plasma waves, but also the collisional damping of the plasma waves and collisions with thermal particles. By the use of this formula, we can easily compute the time profile of the plasma waves caused by these solar electrons at any given place in the interplanetary space. The validity of this semi-analytical approach is checked by the numerical analysis of Model 4, showing a satisfactory fit between the numerical and semi-analytical results.The direct application of this method to the problems of type III radio bursts is left to a later paper. 相似文献
35.
36.
The ability of biodegradation for crude oil was examined for ten strains of marine bacteria. With regard to their degradation ability forn-alkanes the microorganisms tested could be divided into four groups, although the same result was not observed for microbial degradation of aromatic hydrocarbons obtained by the UV measurements. 相似文献
37.
Minoru Wada Yukiko Takano Saki Nagae Yuka Ohtake Yu Umezawa Shinichi Nakamura Makoto Yoshida Yukihiko Matsuyama Mitsunori Iwataki Satoshi Takeshita Tatsuya Oda 《Journal of Oceanography》2018,74(6):587-593
Acute and severe hypoxia associated with harmful algal bloom has become one of the major causes for the environmental deterioration of coastal areas. Although it is generally thought that a large part of the dissolved oxygen consumption at a bloom site is initiated by heterotrophic bacteria that attack organic matter derived from dead or dying algal cells, precise microbial processes leading to the hypoxia are yet to be examined. Here we show temporal dynamics of extracellular dissolved organic carbon (DOC) of the red tide forming raphidophyte Chattonella marina and bacterial populations associating with the algae under laboratory conditions. During the growth of non-axenic strains of C. marina, we monitored abundance of algae, associated bacteria, and DOC in the culture media. Bacterial cell abundance increased in response to the increase in DOC both at the beginning and the late log phase of the algal growth. Flow cytometric analysis revealed that transient increase in the percentage of respiratory-active bacterial cells also coincided with the timing of the increase in bacterial abundance and DOC. These results strongly suggest that DOC released from growing C. marina fuels respiration and growth of planktonic bacteria surrounding the algae. This has implications for the role of DOC released from C. marina bloom before the collapse in mediating interactions between neighboring algae and bacterial assemblage which may eventually lead to algal bloom-associated hypoxia. 相似文献
38.
T. Takakura K. Ohki N. Shibuya M. Fujii M. Matsuoka S. Miyamoto J. Nishimura M. Oda Y. Ogawara S. Ota 《Solar physics》1971,16(2):454-464
The location and size of a solar impulsive hard X-ray burst have been determined in one dimension to a considerable precision with a balloon-borne X-ray modulation collimator. The center of the X-ray source is on the line passing through the center of a big H flare region of 3 arc min. The size of the X-ray source is remarkably smaller and may be one arc min or less. 相似文献
39.
A large arcade associated with a long-duration soft X-ray emission was observed on May 19, 1992 by the Yohkoh soft X-ray telescope. This large arcade was formed along the inversion line and a filament eruption was observed as part of this event. Also associated with this event were solar energetic particles and an interplanetary shock observed near Earth. This event supports the idea that coronal mass ejections are large-scale eruptions along an inversion line, or a heliospheric current sheet. However, this event implies that present models on eruptions are not sufficient. 相似文献
40.
Simultaneous X-ray images in hard (20–40 keV) and softer (6.5–15 keV) energy ranges were obtained with the hard X-ray telescope aboard the Hinotori spacecraft of an impulsive solar X-ray burst associated with a flare near the solar west limb.The burst was composed of an impulsive component with a hard spectrum and a thermal component with a peak temperature of 2.8 × 107 K. For about one minute, the impulsive component was predominant even in the softer energy range.The hard X-ray image for the impulsive component is an extended single source elongated along the solar limb, rather steady and extends from the two-ribbon H flare up to 104 km above the limb. The centroid of this source image is located about 10 (7 × 103 km) ± 5 above the neutral line. The corresponding image observed at the softer X-rays is compact and located near the centroid of the hard X-ray image.The source for the thermal component observed in the later phase at the softer X-rays is a compact single source, and it shows a gradual rising motion towards the later phase. 相似文献