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71.
Takahito Kataoka Tomoki Tozuka Swadhin Behera Toshio Yamagata 《Climate Dynamics》2014,43(5-6):1463-1482
Using both observational and reanalysis data, evolution processes of a regional climate phenomenon off Western Australia named recently “Ningaloo Niño (Niña)” are studied in detail. It is also shown that the Ningaloo Niño (Niña) has significant impacts on the precipitation over Australia. The Ningaloo Niño (Niña), which is associated with positive (negative) sea surface temperature (SST) anomalies and atmospheric anomalies off the western coast of Australia, peaks during austral summer and is classified into two types based on the difference in the evolution process. The first type called a locally amplified mode develops through an intrinsic unstable air–sea interaction off the western coast of Australia; an anomalous cyclone (anticyclone) generated by positive (negative) SST anomalies forces northerly (southerly) alongshore wind anomalies, which induce coastal downwelling (upwelling) anomalies, and enhance the positive (negative) SST anomalies further. The second type called a non-locally amplified mode is associated with coastally trapped waves originating in either the western tropical Pacific, mostly related to El Niño/Southern Oscillation, or the northern coast of Australia. Positive (negative) SST anomalies in both modes are associated with an anomalous low (high) off the western coast of Australia. The sea level pressure (SLP) anomalies in the locally amplified mode are regionally confined with a cell-like pattern and produce a sharp offshore pressure gradient along the western coast of Australia, whereas those in the non-locally amplified mode tend to show a zonally elongated pattern. The difference is found to be related to conditions of the continental SLP modulated by the Australian summer monsoon and/or the Southern Annular Mode. 相似文献
72.
73.
Temporal variations of the net Kuroshio transport and its relation to atmospheric variations 总被引:1,自引:0,他引:1
Shusaku Sugimoto Kimio Hanawa Kumiko Narikiyo Megumi Fujimori Toshio Suga 《Journal of Oceanography》2010,66(5):611-619
Temporal variations of the net Kuroshio transport are investigated using long-term hydrographic data from repeat section of
the 137°E meridian from the south of Japan (34°N) to New Guinea (1°S) conducted by the Japan Meteorological Agency. In this
study, boundaries of the Kuroshio and the Kuroshio Counter Current (KCC) are defined based on the sea surface dynamic height
distribution. Westward flows associated with the KCC and cold-core eddy north of the Kuroshio are removed from the eastward
flow associated with the Kuroshio in order to estimate the net Kuroshio transport strictly. The net Kuroshio transport reveals
low-frequency variations: significant signals on a decadal (about 10-year) timescale. The variations of net Kuroshio transport
are predominantly caused by changes in the magnitude of oceanic current speed fields associated with a vertical movement of
the main pycnocline depth around the southern boundary of the Kuroshio: deepening of the main pycnocline around the southern
boundary of the Kuroshio forms a sharp northern upward-tilting slope of the isopycnal surfaces at the Kuroshio region, and
eventually the net Kuroshio transport increases together with the Kuroshio eastward transport. By using a wind-driven hindcast
model, it is found that the main pycnocline depth variation results from the first-mode baroclinic Rossby waves attributable
to two types of Aleutian Low (AL) changes: a change in the magnitude of AL and meridional movement of AL. 相似文献
74.
Characteristics of coastal trapped waves along the southern and eastern coasts of Australia 总被引:1,自引:0,他引:1
The spatial structures and propagation characteristics of coastal trapped waves (CTWs) along the southern and eastern coasts
of Australia are investigated using observed daily mean sea level data and results from a high-resolution ocean general circulation
model (OGCM), and by conducting sensitivity studies with idealized numerical models. The results obtained from the sea level
observations show that shortterm variations, with a typical period of 1 to 2 weeks, dominate the sea level variability in
the southern half of Australia. The signal propagates anticlockwise around Australia with a propagation speed of 4.5 m/s or
faster in the western and southern coasts and 2.1 to 3.6 m/s in the eastern coast. Strong seasonality of the wave activity,
with large amplitude during austral winter, is also observed. It turns out that the waves are mainly generated by synoptic
weather disturbances in the southwestern and southeastern regions. The numerical experiment with idealized wind forcing and
realistic topography confirms that the propagating signals have characteristics of the CTW both in the southern and eastern
coasts. Sensitivity experiments demonstrate that the difference in the phase speed between the coasts and reduction of the
amplitude of the waves in the eastern coast are attributed to the different shape of the continental shelf in each region.
The structures and the propagation characteristics of the CTWs around Australia are well reproduced in OFES (OGCM for the
Earth Simulator) with dominant contribution from the first mode, although meso-scale eddies may modify the structure of the
CTWs in the eastern coast. It is also found that generation or reinforcement of the waves by the wind forcing in the southern
part of the eastern coast is necessary to obtain realistically large amplitude of the CTWs in the eastern coast. 相似文献
75.
Toshio Fukushima 《Celestial Mechanics and Dynamical Astronomy》1988,44(1-2):61-75
The Fermi coordinate system (or the non-rotating proper reference frame) is studied within the framework of the post-Newtonian approximation of general relativity. First its general functional form is found to consist of three parts; (1) the motion of the space origin of the Fermi coordinate system relative to the background one, (2) the Fermi-Walker tetrad transported along the world line of the space origin, and (3) the spacelike geodesic starting from the space origin. Next, the post-Newtonian expressions of the latter two are obtained under the condition that the first is given. Then the full coordinate transformation formula connecting the Fermi coordinate system to the background one is derived explicitly. The effectiveness of the Fermi coordinate system is discussed and the effective region is found to be a cylinder with the radius of about 0.5 kpc for the Fermi coordinate system comoving with the Earth. The mathematical way to derive the generalized Fermi coordinate system which Ashby and Bertotti defined is also shown. 相似文献
76.
Toshio Uchida 《Monthly notices of the Royal Astronomical Society》1998,297(1):315-322
The force-free magnetosphere around an obliquely rotating pulsar is studied. The basic equations reduce to two equations for two Euler potentials. One of the Euler potentials is regarded as a generalization of the stream function of the poloidal magnetic field lines in an axisymmetric rotator. Two divergence-free vectors become tangential to the surface on which this Euler potential is constant. 相似文献
77.
Toshio Fukushima Masa-Katsu Fujimoto Hiroshi Kinoshita Shinko Aoki 《Celestial Mechanics and Dynamical Astronomy》1986,38(3):215-230
The relation between the units and readings of time and space coordinates of terrestrial and barycentric reference frames is discussed from the viewpoint of general relativity. Attention is paid to the unit of space coordinates since the International Astronomical Union (IAU) regulates only the unit of time in the above two frames. Two definitions of unit of length are examined and their effects on the numerical expression of coordinate transformation, equations of planetary motions, and those for light propagation time are discussed. A clear conflict is found between the IAU (1976) recommendation on the definition of the time-scales in different frames of reference and the statement that all constants in the IAU (1976) new system of astronomical constants are defined in terms of the Internationsl System of units (SI units). One of the above two definitions is proposed to resolve this conflict by the least alteration to current procedures for analysing the recent astrometric observations such as the radar/laser rangings, the range and range-rate, and the very long baseline interferometric observations. Also, an interpretation of numerical values in the IAU (1976) new system of astronomical constants is presented. It is stressed that the definition proposed in this paper requires that a formula slightly different from that in current use be employed in the numerical transformation of readings of coordinates between the terrestrial and barycentric reference frames. 相似文献
78.
A one-dimensional numerical model with a level-2.5 turbulent closure scheme to provide vertical mixing coefficients has been
used to investigate the process by which the dichothermal water is formed in the Bering Sea, the density of which is about
26.6 sigma-theta. The water column to be simulated is assumed to move along a predetermined path. That is, the present model
is of the Lagrangian-type. Surface boundary conditions are given using the climatologies of heat, freshwater and momentum
fluxes. In order to obtain a plausible moving speed of the water column along the path, pre-liminary experiments were done
using the surface fluxes in the central part of the Bering Sea for the initial temperature and salinity profiles at the entrance
of the Sea. As a result, it was found that the temperature minimum layer, i.e., the dichothermal water with temperature similar
to the climatology at the exit of the Bering Sea, was formed after about two years of integration. Based on the result, the
movement speed of the water column along the path was set as 4.5 cm/s in the standard run. It was found that this model could
plausibly reproduce the subsurface temperature minimum layer. That is, the dichothermal water was formed in the winter mixed
layer process in the Bering Sea. The existence of the subsurface halocline (pycnocline) prohibited the deeper penetration
of the winter mixed layer, and therefore water with a temperature colder than that under the mixed layer was formed in the
mixed layer due to wintertime surface cooling. In the warming season this water remains as the subsurface temperature minimum
layer between the upper seasonal thermocline and the lower halocline.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
79.
The clay minerals in the 18 core samples collected from the northern, equatorial and southeastern Indian Ocean are illite, chlorite, montmorillonite and kaolinite. In the fraction finer than 2 in the surface layer (top to 5 cm deep) of each core, the relative abundance of clay minerals varies widely from area to area. Kaolinite possesses the maximum proportion of the clay mineral composition and chlorite has the minimum proportion.Kaolinite is particularly dominant in sediments near off the northwestern coast of Australia. In the factions finer and coarser than 2 of the surface layer, montmorillonite and kaolinite tend to be abundant in the fraction finer than 2, and chlorite and illite tend to be abundant in the fraction coarser than 2. In some cores, kaolinite-rich layers in sediments which are considered to have been transported by turbidity currents from the Bay of Bengal are found. Turbidity currents appear partly a role in transport of sediments to the equatorial Indian Ocean.As to the relation between the vertical change of clay mineral composition and geochronological data, montmorillonite and kaolinite tend to be more abundant in interglacial ages than in glacial ages, while illite and chlorite tend to exhibit opposite trend.Muscovite and biotite highly concentrated in the cores Ka-9 and Ka-15 collected from the equatorial Indian Ocean seem to originate from granite or gneiss of Ceylon and/or India. 相似文献
80.
Toshio Yamagata 《Journal of Oceanography》1981,37(4):219-225
This article reviews the author's study on waves in planetary fluids for which the Okada Prize of the Oceanographical Society
of Japan was awarded in 1981. The contents of the review are i) some connections of planetary waves with the large-scale ocean
circulation, ii) stability of planetary waves, iii) the relationship between mean currents and planetary waves, iv) the influence
of topography on the mean current, v) a simple relationship between wave dissipation and viscous boundary layers and vi) some
ageostrophic effects on large-scale phenomena. Studies now in progress and related suggestions are also described and discussed
in the article 相似文献