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71.
Atsushi Tsuda Hiroshi Kiyosawa Akira Kuwata Mamiko Mochizuki Naonobu Shiga Hiroaki Saito Sanae Chiba Keiri Imai Jun Nishioka Tsuneo Ono 《Progress in Oceanography》2005,64(2-4):189
Phytoplankton species composition was analyzed inside and outside of the iron-enriched patch during the SEEDS experiment. Before the iron-enrichment, the phytoplankton community consisted of similar proportions of pico-, nano- and micro-sized phytoplankton, and the micro-phytoplankton was dominated by the pennate diatom Pseudo-nitzschia turgidula. Although all the diatoms, except the nano-sized Fragilariopsis sp., increased during the two weeks of the observation period, the flora in the patch dramatically changed with the increase of phytoplankton biomass to a centric diatom-dominated community. Neritic diatoms, especially Chaetoceros debilis, showed higher growth rates than other diatoms, without any delay in the initiation of growth after the enrichment, and accounted for 90% of the micro-phytoplankton after day 9. In contrast, the oceanic diatoms showed distinct delays in the initiation of growth. We conclude that the responses of the diatoms to the manipulation of iron concentration were different by species, and the fast and intensive response of the phytoplankton to iron-enrichment resulted from the presence of a small amount of neritic diatoms at the study site. The important factors that determine the dominant species in the bloom are the potential growth rates under an iron-replete condition and the growth lag. Abundant species in the patch are widely distributed in the North Pacific and their relative contributions in the Oyashio area and at Stn KNOT are high from spring to summer. However, a characteristic difference of species composition between the SEEDS bloom and natural blooms was the lack of Thalassiosira and Coscinodiscus species in the patch, which usually account for a major part of the phytoplankton community under blooming conditions in the western North Pacific. 相似文献
72.
Masakichi Nishimura Shigeki Konishi Katsuhiko Matsunaga Kohtaro Hata Tsuneo Kosuga 《Journal of Oceanography》1983,39(6):295-300
Seventy percent of 342 seawater samples collected in the Bering Sea, North and South Pacific, Japan Sea, East and South China Seas, and Indian Ocean had concentrations of “total” mercury ranging from 3 to 6 ng Hg l?1 with an arithmetic mean of 5.3 ng l?1 and a geometric mean of 5.0 ng l?1. In some cases, a higher concentration was observed at the surface, at the halocline or thermocline, or in the bottom water. But in general, there was no consistent correlation between mercury concentration and depth, except for a statistical tendency for mercury concentration to be slightly higher in the surface water. This tendency suggests that mercury in the ocean is supplied from the atmosphere by rain washout. The latitudinal variation of surface mercury concentrations showed that the maximum concentration at each latitude decreased from 40°N to 30°S. This variation provides evidence that atmospheric mercury is emitted mainly from continental areas naturally or anthropogenically. 相似文献
73.
Akihiro Shiomoto Katsuyuki Sasaki Toru Shimoda Satsuki Matsumura 《Journal of Oceanography》1994,50(2):209-222
Primary productivity was measured byin situ method using13C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1–1 h–1 although a very large value, 7.96 gC l–1 h–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m–2 d–1 although a very large value, 2,109 mgC m–2 d–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l–1 in many cases, and the maximum was 4.61 g l–1 in spring and 7.53 g l–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a
–1 h–1 although higher values, 3–6 gC gChl.a
–1 h–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region. 相似文献
74.
Seasonal fluctuations of cell density of cyanobacteria and other picophytoplankton in Iwanai Bay,Hokkaido, Japan 总被引:1,自引:0,他引:1
In Iwanai Bay, which is located on the Japan Sea coast in Hokkaido, seasonal fluctuations in cell densities of phycoerythrin-dominant cyanobacteria and chlorophyll-dominant, other picophytoplankton were examined. Cell densities of cyanobacteria and other picophytoplankton ranged from 1.4×105 to 1.9×108 and from 4.0×104 to 4.3×106 cells 1–1, respectively. The cell densities of both groups tended to increase after spring diatom bloom with remarkable fluctuations from June to August. This tendency was caused by the vertical distributions of both groups. The maximum density layer shifted from 0–20 m depth in April–June to 20–50 m depth in August–October. Cyanobacteria were dominant in picophytoplankton community which accounted for 73–99% of the total cell density during the whole year. Present results show that the picophytoplankton community in Iwanai Bay was influenced by a single water mass system (Tsushima Warm Current) during the whole year.This is contribution No. 254 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University. 相似文献
75.
Hiroshi Murakami Kosei Sasaoka Kohtaro Hosoda Hajime Fukushima Mitsuhiro Toratani Robert Frouin B. Greg Mitchell Mati Kahru Pierre-Yves Deschamps Dennis Clark Stephanie Flora Motoaki Kishino Sei-Ichi Saitoh Ichio Asanuma Akihiko Tanaka Hiroaki Sasaki Katsumi Yokouchi Yoko Kiyomoto Hiroaki Saito Cécile Dupouy Absornsuda Siripong Satsuki Matsumura Joji Ishizaka 《Journal of Oceanography》2006,62(3):373-393
The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April
2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between
GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for
aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI
ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences
(MedPD) between GLI and in-situ data were 14.1–35.7% for nLws at 380–565 nm, 52.5–74.8% nLws at 625–680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6%
for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products
are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated
in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that
we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection
for further applications, including coastal monitoring and the combined use of products from multiple sensors. 相似文献
76.
Sanae Chiba Tsuneo Ono Kazuaki Tadokoro Takashi Midorikawa Toshiro Saino 《Journal of Oceanography》2004,60(1):149-162
An analysis of the time series data sets collected from the 1960s to 1990s in the Oyashio Water revealed signs of alteration
in the physical, chemical and biological properties of the water column in the western subarctic North Pacific. Wintertime
salinity, phosphate concentration and apparent oxygen utilization (AOU) in the subsurface increased linearly over the 30 years.
At the same time, salinity and phosphate in the surface mixed layer decreased. An increase in the density gradient in the
surface and subsurface suggested that the water column stratification intensified, reducing the vertical exchange of water
properties during the period. The Net Community Production (NCP), estimated from the phosphate consumption from February through
August, also declined. Water column Chl a was approximately halved and diatoms decreased by one order of magnitude in spring, consistent with the multi-decadal decreasing
trend of NCP. Zooplankton biomass was also nearly halved during the same period. In contrast, wintertime Chl a increased by 63% and diatom abundance doubled. Developmental timing became earlier in Neocalanus flemingeri, and spring occurrence of N. plumchrus increased after the 1980s. Reduced vertical water exchange might have limited nutrient supply to the level, decreasing winter-summer
NCP for these three decades. It is speculated that, in the meantime, the earlier stabilization of the surface layer might
have enhanced wintertime diatom production in the Oyashio's light-limited environment. This condition could allow zooplankton
to effectively utilize diatoms from earlier timing, resulting in the apparent early developmental timing and abundance increase.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
To examine whether the regime shift in 1998 that has been variously reported to have occurred in the oceanographic conditions
of the central and eastern North Pacific also occurred in the Oyashio region, western North Pacific, we compared data over
the period 1990–2003. Oceanographic conditions were compared before 1997 with those after 1998, using the A-line dataset (1990–2003) obtained by the oceanographic surveys of the Hokkaido National Fisheries Research Institute, Fisheries
Research Agency (HNFRI/FRA). Seasonal changes of the monthly-mean SST (as temperature in the surface layer) show a significant
increase in spring after 1998. After 1998, the mean concentration of chlorophyll a at the surface was higher in spring than that before 1997. This was more remarkable in the main current of the Oyashio. These
changes suggest that the spring phytoplankton bloom in the Oyashio region after 1998 was larger in magnitude and initiated
earlier. Consumption of nutrients during the spring bloom and standing stock of netplankton also shows a distinct difference
between the time period before 1997 and after 1998. These results support the occurrence of the regime shift around 1998 in
the Oyashio region. The changes of hydrographical conditions accompanying with the 1998 regime shift are discussed. The hydrographic
mechanism of enhancement of primary productivity during the spring phytoplankton bloom was not fully clarified, though. Results
in this study may support the usefulness of the A-line dataset for analysis of long-term variability in the western subarctic Pacific. 相似文献
78.
Evaluation of various satellite sensors for waterline extraction in a coral reef environment: Majuro Atoll, Marshall Islands 总被引:4,自引:0,他引:4
Hiroya Yamano Hiroto Shimazaki Tsuneo Matsunaga Albon Ishoda Caleb McClennen Hiromune Yokoki Kazuhiko Fujita Yoko Osawa Hajime Kayanne 《Geomorphology》2006,82(3-4):398-411
The ability of five satellite sensor bands (IKONOS band 4, Terra ASTER bands 3 and 4, and Landsat ETM+ bands 4 and 5) was examined to extract the waterline at coral reef coasts (Majuro Atoll, Marshall Islands) using different wavelength regions (near infrared [NIR] and shortwave infrared [SWIR]) and different spatial resolutions (4, 15, and 30 m). After performing georeferencing and normalization of the images, density slicing was used to extract the waterline. Comparisons of extracted waterline positions with ground-level data for eight transects and global positioning system (GPS) tracks of the island shorelines showed that NIR bands were superior to SWIR bands because of the characteristics of the coral reef coasts, including a lack of foam and suspended sediments (which can affect the NIR wavelength region, if present) and the presence of remnant water on reef flats during low tide (which can affect the SWIR wavelength region). A linear relationship was found between the estimation errors of waterline positions and the spatial resolutions of the NIR sensors. Analysis on estimation errors and image costs showed that Terra ASTER band 3 was the most cost-effective sensor for extracting waterlines with reasonable accuracy. The results serve as general guidelines for using satellite-derived data to estimate intertidal topography and detect and monitor shorelines in coral reef environments. 相似文献
79.
Abstract The central part of Abukuma metamorphic belt consists of two geologic units, the Gosaisho Group and the Takanuki Group. Although the deformation styles differ between the Gosaisho and the Takanuki Groups, their rock facies show a gradual transition. In both Groups early regional low-pressure (over 3 kb) metamorphism has been overprinted by contact metamorphism. Evidence for the P/T condition of the regional metamorphism is recorded in cores of armored minerals. Metamorphic zones have been defined on mineral rim assemblages of meta-mafite, meta-pelite and meta-calc-siliceous schist and on the degree of graphitization of meta-pelite. The mineral-core chemistry of plagioclase, Ca-amphibole and garnet changes with increasing metamorphic grade, and indicates that the regional metamorphism of the Gosaisho Group took place in a high pressure region of the andalusite stability field. The Takanuki metamorphic rocks are structurally overlain by the Gosaisho Group and have undergone regional metamorphism whose conditions have passed near the triple point of Al-silicates and kyanite has crystallized. The contact aureoles in both groups are developed around middle Cretaceous granitic intrusions. Rims of plagioclase, Ca-amphibole and garnet overgrew on the mineral-cores during the contact metamorphism. The regional metamorphism began after the sedimentation of Jurassic chert and was succeeded by the contact metamorphism in the middle Cretaceous. 相似文献
80.