全文获取类型
收费全文 | 295篇 |
免费 | 3篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 8篇 |
地球物理 | 64篇 |
地质学 | 67篇 |
海洋学 | 91篇 |
天文学 | 39篇 |
综合类 | 2篇 |
自然地理 | 31篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2014年 | 5篇 |
2013年 | 20篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 9篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 218 毫秒
61.
Adjustments to satellite constrained navigation are required to match SeaBeam bathymetric data at track crossings due to errors in dead reckoning and inaccuracies in satellite fixes. By shifting one of the SeaBeam swaths involved in a track crossing relative to the other and calculating the sum of the squares of the differences in bathymetry within the area of overlapping coverage, we map a two-dimensional error surface whose minimum corresponds to the best estimate of the correction to navigation required at the crossing point. Estimates of the covariance of this correction are derived from the error surface. We employ the curve fitting technique of Tarantola and Valette (1982) to invert for a smooth correction function to a starting model of the position of the ship as a function of time. This technique incorporates formal errors assigned to dead reckoning, satellite fixes, and the shifts required to match bathymetric swaths at crossing points in a simultaneous inversion for the correction function for all tracks within the study area.In a test of the method in a study area on the southern Mid-Atlantic Ridge, a data set involving two cruises, 30 days of SeaBeam data, and 753 track crossings, we found that crossing SeaBeam swaths can potentially resolve the relative position of the ship on the two tracks to within 30 to 70 m. The inversion procedure yielded a much better constrained navigation function and much improved match of bathymetry. The final model of the navigation fit crossing shifts about as well as satellite data (with respect to their assigned data errors) with the RMS value of the crossing shifts decreasing from 1200 m in the original satellite-constrained navigation to 200 m in the final solution. However, the potential resolution of position using SeaBeam swaths was not fully achieved in the solution because there are systematic bathymetric artifacts in SeaBeam data, multiple local minima in the error surfaces in highly lineated topography, inadequate dead reckoning data, occasional bad satellite fixes, and limitations on the short period corrections allowed in the model. 相似文献
62.
Baroclinic eddies south of Cheju Island in the East China Sea 总被引:3,自引:0,他引:3
The detailed structures of baroclinic eddies, that is, an anticlockwise circulation in the upper layer and a clockwise one in the lower layer south of Cheju Island in the East China Sea have been revealed by intensive field observation. Such baroclinic eddies are accompanied by the southward spreading of the Yellow Sea Bottom Cold Water. 相似文献
63.
Osamu Shida Tomonori Hamatsu Akira Nishimura Akifumi Suzaki Jun Yamamoto Kazushi Miyashita Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822
The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes. 相似文献
64.
A numerical experiment on the sedimentation processes in the Yellow Sea and the East China Sea 总被引:6,自引:0,他引:6
Sedimentation processes of suspended matter supplied from the Huanghe (Yellow River) and the Changjiang are investigated with the use of a three-dimensional numerical model of the Yellow Sea and the East China Sea which includes the tidal current, residual flow and wind waves. Suspended matter supplied from the Huanghe mainly deposits in the Bohai Sea and that from the old river mouth of the Huanghe and from the Changjiang in the central part of the Yellow Sea or south of Cheju Island. The calculated results well reproduce the observed sedimentation pattern qualitatively except for the offshore area of the southeastern coast of China. 相似文献
65.
Temporal variations in sediment carbon content were tracked by sampling every 2 weeks for 6 to 33 months at 6 tidal flat stations with different carbon content levels (0.05–1.64%) in a single estuary. Three temporal series of current velocity at 5 cm above the sediment were also obtained. Non-cohesive and cohesive sediment stations differed in patterns of temporal variation in sediment carbon content, suggesting the difference in processes controlling sediment carbon content. In the stations of non-cohesive sandy sediment with relatively low carbon content (0.05–0.15%), sediment carbon content fluctuated within ranges specific to each station. In these stations, current velocity data suggested that frequency of sand resuspension washing out sediment carbon controls sediment carbon content level. In the stations of cohesive sediment with relatively high carbon content (0.77–1.64%), sediment carbon contents showed some unusual upward and downward peaks, recovered to usual levels specific to the stations, and was always kept higher than that in the non-cohesive sediment stations. We speculate that in the cohesive sediment stations, sand inputs may significantly control processes establishing the consolidated sediments with various carbon content levels. Spatial transitions from non-cohesive to cohesive sediments and from low to high sediment carbon contents likely occur as sand resuspension at spring tides become more irregular and less frequent. Based on these results, conceptual models describing physical processes controlling sediment carbon content at the studied stations were proposed. 相似文献
66.
The generation, variation, and disappearance of the thermohaline front at the mouth of Tokyo Bay were investigated using water
temperature data obtained by a commercial ferry boat in 1987. The thermohaline front was generated south of Kan-non-zaki in
mid November 1987 after the beginning of sea-surface cooling. It moved northward to Kan-non-zaki until the end of the year.
The thermohaline front was most intense in February and March and disappeared in late March 1987 when sea-surface warming
began. 相似文献
67.
Takashi Sakamaki Osamu Nishimura Ruichi Sudo 《Estuarine, Coastal and Shelf Science》2006,67(4):653-663
We determined the range of the tidal variations in nutrient flux across the sediment–water interface and elucidated mechanisms of the flux variation in two estuarine intertidal flats (one sand, one mud) in northeastern Japan. Nutrient flux was measured using in situ light and dark chambers, which were incubated for 2 h, 2–6 times per day. Results showed that nutrient concentration in overlying water varied by tide and was also affected by sewage-treated water inflow. The nutrient fluxes responded quickly to the tidal variation in overlying water chemistry and the range of the variation in flux was as large as the seasonal-scale variation reported in previous studies. In the sand flat, salinity increase likely enhanced benthos respiration and led to increases in both O2 consumption and PO43− regeneration under low illumination, while benthic microalgae were likely to actively generate O2, uptake PO43− and suppress PO43− release under high illumination (>900 μmol photons m−2 s−1). Also in the mud flat, PO43− flux was related with O2 flux, although the range of temporal variation in PO43− flux was small. In both the flats, NH4+ flux was always governed by NH4+ concentration in the overlying water; either an increase in NH4+ uptake or a decrease in NH4+ release was observed as the NH4+ concentration rose due to inflow of river water or input of sewage-treated water. Although NO3− tended to be released in both tidal flats when low NO3− concentration seawater dominated, their relationship was likely to be weakened under conditions of low oxygen consumption and suppressed denitrification. It is likely that tidal variation in nutrient flux is governed more by the nutrient concentration than other factors, such as benthic biological processes, particularly in the case where nutrient concentration in the overlying water is relatively high and with wide amplitude. 相似文献
68.
Eriko Kamiya Shinji Izumiyama Masahiko Nishimura James G. Mitchell Kazuhiro Kogure 《Journal of Oceanography》2007,63(1):101-112
Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine
environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria.
Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances
of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation
of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation
did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower
decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution
is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility
that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered. 相似文献
69.
70.
A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system. 相似文献