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21.
Sekiya and Takeda [2003, Earth Planets Space 55, 263-269] showed that the hydrodynamic gas flow around a dust aggregate larger than the mean free path of gas molecules prevents the growth of the body. In contrast to Wurm et al. [2004, Astrophys. J. 606, 983-987], we argue that this conclusion is not altered even if we take account of the effect of the flow through a porous dust aggregate. 相似文献
22.
Local time variation of geomagnetic transfer functions 总被引:1,自引:0,他引:1
Masahiko Takeda 《Geophysical Journal International》1997,130(3):765-770
The local time (LT) variation of the geomagnetic transfer function at the 32-min period was examined for observatories distributed worldwide. Two distinct variation types (types 1 and 2) were found in the real part of A. Type 1 is conspicuous at lower latitudes and its seasonal variation is small, whereas type 2 is found at higher latitudes and has its maximum in summer. These two types of LT variation are seen globally and are conspicuous when solar activity is high. The amplitudes of both types of variation vary from 0.018 to 0.078, and are independent of the mean values at each observatory. These values are relatively small, but the amplitude of Chambon la Foret is larger than the mean value, which shows that Au changes its sign in local time. The amplitudes of type 1 and 2 variations decrease and increase with geomagnetic latitude, respectively. These features suggest that they are generated by some global external fields. The most probable cause is the Sq field, although the Dp field may contribute to type 1 variation. On the other hand, for the islands of the Pacific Ocean at low latitudes, such as Honolulu and Chichijima, the type 1 variation appears not in the real but in the imaginary part of A, which suggests that currents induced in the ocean also contribute to the local time variation. 相似文献
23.
Crystal-field theory was applied to Fe2+ ions in three types of silicates in an attempt to assign all the major absorption bands with only one parameter to adjust. Coulomb potential energy field were calculated by Fourier method based on all the actual atomic coordinates refined by X-ray diffraction studies. Perturbed d-electron splitting energies of the central Fe2+ ion were calculated by introducing Configuration Interaction (CI) method for the lowest energy spectral states. All the major absorption bands observed in powdered bronzite, augite, and olivine, were assigned to the transitions between those calculated energy levels by optimizing only one parameter that expresses expansion or contraction of d-electron cloud. The result of the calculations gives almost the same assignments as the other previous works for bronzites, different assignments for augites, and a possibility of the existence of the fourth band hidden in the composite 1-μm band of olivines. 相似文献
24.
Insaf S. Babiker Mohamed A. A. Mohamed Kaori Komaki Keiichi Ohta Kikuo Kato 《Journal of Oceanography》2004,60(3):553-562
Changes in patterns of undetectability and molar ratios of dissolved nutrients in the euphotic zone of the oligotrophic western
North Atlantic Ocean were investigated utilizing the Bermuda Atlantic Time-series Study (BATS) data set of the US Joint Global
Ocean Flux Study (JGOFS). Our aim was to examine the temporal dynamics of nutrient stocks over a decade (1989∼1998) and to
gain insight into the interactions between the different biotic and abiotic factors underlying BATS. Patterns of nutrient
undetectability clearly revealed the depleted nature of the nutrients in surface water at the BATS location, particularly
phosphorous. The N:P ratio was consistently far above the nominal Redfield ratio (mean, 38.5) but was significantly lower
during the 1993∼1994 period (22.1). Over the same period the proportion of samples depleted in N only increased while the
proportion of samples depleted in P only decreased. This indicates an overall reduction of N relative to P in the surface
water at BATS during the 1993∼1994 period, the reasons for this anomaly, though, are not clear. The correlation analysis between
the biotic and abiotic variables at BATS has indicated some interesting relationships that can help understand some of the
parameters affecting nutrient stocks in the euphotic zone and their consequent impacts on marine biota. Although nutrient
stocks in the oligotrophic environment are limited, they might be subject to interannual variation that may become anomalous
in some cases. These variations might underlay significant feedback mechanisms by affecting marine productivity, the prime
factor controlling the sequestration of atmospheric CO2 by the oceans.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
Nutrient-enrichment bottle experiments in the northwestern Indian Ocean surface waters were conducted to investigate phytoplankton growth following enrichments with either NH4+, NO3−, Fe or Fe + NO3−. Stimulation of phytoplankton growth could be achieved by the addition of either NH4+ or NO3− under the ambient Fe concentrations, but the most significant increases in Chl a, POC, and cell densities were observed in the Fe + NO3−-amended culture. Iron addition caused more rapid responses of phytoplankton growth in the Fe + NO3− treatment than those in the NO3− and NH4− treatment. However, the Fe-enrichment treatment revealed minimal growth of phytoplankton because of severe major nutrient deficiency and was similar to the control treatment. Increases in the cell density of diatoms and spherical phytoplankton cells (< 10 μm) were significant in the NH4+-enriched samples, whereas NO3− enrichment alone had little effect on the diatoms. Simultaneous addition of Fe and NO3− stimulated maximal growth of phytoplankton, in particular in diatoms, coccolithophorids and Phaeocystis type colonies. However, the dominance of coccolithophorids and Phaeocystis type colonies in the Fe + NO3− treatment may be interpreted as resulting from Si-limitation. The high N/P ratio for phytoplankton nutrient uptake in the N-amended culture indicates the possibility of some P-limited growth. From these results, we conclude that in the northwestern Indian Ocean, Fe and major nutrients are co-limiting phytoplankton production during the northeast monsoon. Iron appeared to affect the ability of phytoplankton to respond quickly to transient nutrient inputs. 相似文献
26.
Hiroshi Takeda 《Journal of Oceanography》1984,40(6):410-415
Waves which propagate along a vertical wall lying in an arbitrary direction on aβ-plane are derived as a generalization of Haurwitz waves (Haurwitz, 1940) whose direction of propagation is restricted to
the east-west direction. The waves are classified into two types. One consists of neutral waves, which correspond to a generalization
of Haurwitz waves. The other consists of waves with complex wavenumber and without energy flux. The phase of the waves also
propagates in the direction normal to the coast in an envelope except for the case in which the coast lies in the east-west
direction. 相似文献
27.
Hiroshi Takeda 《Journal of Oceanography》1984,40(6):432-436
Topographically trapped (subinertia) waves that propagate along a coast lying in an arbitrary direction on aβ-plane are studied. It is found that the waves also propagate in the direction normal to the coast within an envelope due
to theβ-effect. The dispersion relation is hardly affected by theβ-effect except in a long wavelength or long period range in which generalized Haurwitz waves (Takeda, 1984b) exist. In the
long wavelength or long period range, two types of waves exist: topographically trapped type waves and generalized Haurwitz
type waves. 相似文献
28.
Aoshio-hypoxic water which can be distinguished from surrounding coastal water by its milky blue-green color-is often observed at
the head of Tokyo Bay when coastal upwelling of sulfidic bottom water occurs during summer and early autumn. Optical properties
and the biological-chemical composition of suspended matter in theaoshio water were investigated using nearby “normal” coastal water as a reference.
Suspended matter in theaoshio water contributed to the large beam-attenuation coefficient and also to the strong upward radiance with maximal intensity
around 550 nm as a result of the scattering process. No significant difference in bacterial density was observed between samples
ofaoshio water and reference coastal water. The low chlorophylls concentration inaoshio water samples indicates that biological pigments may not play a dominant role in the color of theaoshio events.
The suspended particles inaoshio water samples had much higher contents of sulfur and manganese and a lower silicon content than those in reference coastal
water samples. The colloidal elemental sulfur and manganese-rich particles identified in theaoshio water appear to be oxidation products of dissolved sulfide and manganese (II) in the anoxic water.
On the basis of these findings, it may be concluded that there is a high probability that elemental sulfur and manganese-rich
particles are responsible for the color and turbidity inaoshio. 相似文献
29.
Daisuke Tsumune Jun Nishioka Akifumi Shimamoto Shigenobu Takeda Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):111
The first iron (Fe) – fertilization experiment in the western North Pacific was carried out using SF6 to trace the Fe-fertilized water mass. A solution in 10,800 liters of seawater of 350 kg of Fe and 0.48 M of SF6 tracer was released into the mixed layer over a 8 × 10 km area. On the first underway transects through the patch after the Fe release, we observed a significant increase of dissolved Fe (ave. 2.89 nM). The fertilized patch was traced for 14 days by on-board SF6 analysis. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch. The patch moved westward at a rate of 6.8 km d−1. Mixed layer depth increased from 8.5 to 15 m during the experiment. Horizontal diffusivity was determined by the change of SF6 concentration in the patch. The horizontal diffusivity increased during the experiment. We evaluate here the fate of Fe in a Fe-fertilized patch using the dilution rate determined from sulphur hexafluoride (SF6) concentration. Dissolved Fe concentrations subsequently decreased rapidly to 0.15 nM on Day 13. However, the dissolved Fe half-life of 43 h was relatively longer than in previous Fe-enrichment studies, and we observed a larger increase of the centric diatom standing stock and corresponding drawdown of macro-nutrients and carbon dioxide than in the previous studies. The most important reason for the larger response was the phytoplankton species in the western North Pacific. In addition, the smaller diffusivity and shallower mixed layer were effective to sustain the higher dissolved Fe concentration compared to previous experiments. This might be one reason for the larger response of diatoms in SEEDS. 相似文献
30.
The effects of long-term preservation on flow cytometric parameters of natural oceanic populations of pico-and nanophytoplankton
have been examined. Populations collected at oligotrophic subtropical and subarctic locations in the North Pacific were fixed
with glutaraldehyde and frozen in liquid nitrogen, according to Vaulot et al. (1989). During six months’ storage, chlorophyll red fluorescence declined in all the groups examined, while forward light
scatter was enhanced in Synechococcus and Prochlorococcus, and weakened in nanoeucaryotes. Cell loss was not significant except for Synechococcus. Caution is required when analyzing flow cytometric data of samples stored for more than a month. 相似文献