全文获取类型
收费全文 | 143篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 19篇 |
地球物理 | 44篇 |
地质学 | 24篇 |
海洋学 | 47篇 |
天文学 | 3篇 |
综合类 | 2篇 |
自然地理 | 6篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 13篇 |
2012年 | 4篇 |
2011年 | 14篇 |
2010年 | 15篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有153条查询结果,搜索用时 15 毫秒
31.
Elemental and mineralogical changes in soils due to bioturbation along an earthworm invasion chronosequence in Northern Minnesota 总被引:1,自引:0,他引:1
Kathryn Resner Kyungsoo Yoo Cindy Hale Anthony Aufdenkampe Alex Blum Stephen Sebestyen 《Applied Geochemistry》2011
Minnesota forested soils have evolved without the presence of earthworms since the last glacial retreat. When exotic earthworms arrive, enhanced soil bioturbation often results in dramatic morphological and chemical changes in soils with negative implications for the forests’ sustainability. However, the impacts of earthworm invasion on geochemical processes in soils are not well understood. This study attempts to quantify the role of earthworm invasion in mineral chemical weathering and nutrient dynamics along an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota. Depth and rates of soil mixing can be tracked with atmospherically derived short lived radioisotopes 210Pb and 137Cs. Their radioactivities increase in the lower A horizon at the expense of the peak activities near the soil surface, which indicate that soil mixing rate and its depth reach have been enhanced by earthworms. Enhanced soil mixing by earthworms is consistent with the ways that the vertical profiles of elemental and mineralogical compositions were affected by earthworm invasion. Biologically cycled Ca and P have peak concentrations near the soil surface prior to earthworm invasion. However, these peak abundances significantly declined in the earthworm invaded soils presumably due to enhanced soil mixing. It is clear that enhanced soil mixing due to earthworms also profoundly altered the vertical distribution of most mineral species within A horizons. Though the mechanisms are not clear yet, earthworm invasion appears to have contributed to net losses of clay mineral species and opal from the A horizons. As much as earthworms vertically relocated minerals and elements, they also intensify the contacts between organic matter and cations as shown in the increased amount of Ca and Fe in organically complexed and in exchangeable pools. With future studies on soil mixing rates and elemental leaching, this study will quantitatively and mechanically address the role of earthworms in geochemical evolution of soils and forests’ nutrient dynamics. 相似文献
32.
W. M. Sung Y. S. Lee K. H. Kim Y. H. Jang J. H. Lee I. H. Yoo 《Environmental Earth Sciences》2011,64(7):1815-1821
This study presents the Bottom-hole pressure (BHP) behavior with different wettabilities and the optimal design scheme to
effectively inject CO2 into the Gorae-V aquifer. As a result, the injection rate and injectivity were increased as the wettability condition became
more water-wet. However, the more wettability condition becomes water-wet, the more the ultimate CO2 injection volume decreases. When the injectivity was 346 ton/day/Mpa at the Gorae-V aquifer, the aquifer can sustain CO2 injection at a rate of 2,425 tons per day over this time period. A design for a complete CCS system was developed based on
the existing off-shore pipeline in combination with new on-shore CO2 transport infrastructure, and a pressure of 12.8 MPa is required at the CO2 source to maintain this injection rate. 相似文献
33.
Gil Young Kim Bo Yeon Yi Dong Geun Yoo Byong Jae Ryu Michael Riedel 《Marine and Petroleum Geology》2011,28(10):1979-1985
The Gas Hydrate Research and Development Organization (GHDO) of Korea successfully accomplished both coring (hydraulic piston and pressure coring) and logging (logging-while-drilling, LWD, and wireline logging) to investigate the presence of gas hydrate during the first deep drilling expedition in the Ulleung Basin, East Sea of Korea (referred to as UBGH1) in 2007. The LWD data from two sites (UBGH1-9, UBGH1-10) showed elevated electrical resistivity (>80 Ω-m) and P-wave velocity (>2000 m/s) values indicating the presence of gas hydrate. During the coring period, the richest gas hydrate accumulation was discovered at these intervals. Based on log data, the occurrence of gas hydrate is primarily controlled by the presence of fractures. The gas hydrate saturation calculated using Archie’s relation shows greater than 60% (as high as ∼90%) of the pore space, although Archie’s equation typically overestimates gas hydrate saturation in near-vertical fractures. The saturation of gas hydrate is also estimated using the modified Biot-Gassmann theory (BGTL) by Lee and Collett (2006). The saturation values estimated rom BGTL are much lower than those calculated from Archie’s equation. Based on log data, the hydrate-bearing sediment section is approximately 70 m (UBGH1-9) to 130 m (UBGH1-10) in thickness at these two sites. This was further directly confirmed by the recovery of gas hydrate samples and pore water freshening collected from deep drilling core during the expedition. LWD data also strongly support the interpretation of the seismic gas hydrate indicators (e.g., vent or chimney structures and bottom-simulating reflectors), which imply the probability of widespread gas hydrate presence in the Ulleung Basin. 相似文献
34.
Eko Siswanto Junwu Tang Hisashi Yamaguchi Yu-Hwan Ahn Joji Ishizaka Sinjae Yoo Sang-Woo Kim Yoko Kiyomoto Keiko Yamada Connie Chiang Hiroshi Kawamura 《Journal of Oceanography》2011,67(5):627-650
A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag440). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for TChl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (TChl2i in case-2 waters), TTSM (regionally tuned Tassan??s TSM algorithm), and Tag440 or Cag440 (regionally tuned Tassan??s or Carder??s ag440 algorithm) were able to retrieve Chl-a, TSM, and ag440 with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, TChl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. TChl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified TChl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw555) > 2 mW cm?2 ??m?1 sr?1 (TChl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from TChl2s (for case-2 waters) to MOCChl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag440 using SeaWiFS Rrs, we recommend empirical algorithms for TTSM (pre-SeaWiFS-modified form) and MTag440 or MCag440 (SeaWiFS Rrs-modified forms of Tag440 or Cag440). These could retrieve with uncertainties as high as 82 and 52%, respectively. 相似文献
35.
The sampling error formalism by North and Nakamoto (1989) has been widely referenced in research papers on sampling using
space-borne sensors or ground-borne sensors. However, their formalism is found to not only underestimate the sampling error,
especially for the raingauge network case, but also not be applicable for the cases of using a line of raingauges or microwave
attenuation measurements. In this paper, the sampling error formalism has been revised and applied to the same sampling design
and the same rainrate model as in North and Nakamoto (1989) for the comparison. The sampling error estimated using the revised
formula was found to be more than 50% higher than that by North and Nakamoto (1989). For the case of using a line of raingauges
we found that the sampling error converges to a certain value, not zero as in North and Nakamoto formalism, as the number
of gauges increases. The microwave attenuation measurements case, which is the same as the case of using a line of infinite
raingauges, also gives non-zero sampling errors. Finally, the combined sampling using both satellite and ground-borne sensors
(e.g., raingauge network, a line of raingauges, or microwave attenuation measurements) was reviewed to check their design
orthogonality and estimated the sampling errors for the combination of satellite and raingauge network case to see its behavior
depending on various settings of these two different measurements. 相似文献
36.
The Korea (Tsushima) Strait is an important seaway through which the warm Tsushima Current flows into the East Sea (Japan
Sea). A paleogeographic map constrained by a regional sea-level curve developed on the basis of a number of recent 14C radiocarbon dates suggests that the Korea Strait was not closed during the last glacial period. Rather, it was open as a
channel-like seaway linking the western North Pacific and the East Sea. Some fraction of the paleo-Tsushima Current inflow
presumably continued at that time through the Korea Strait. The activity of the paleo-Tsushima Current is evidenced by the
distribution pattern of river-derived lowstand deposits, consisting of a beach/shoreface complex and lowstand deltaic wedges.
Received: 16 April 1999 / Revision accepted: 25 February 2000 相似文献
37.
Temporal coherence is closely related to single path phase rate. The single path phase rates in a shallow water environment were obtained by applying two different multipath models [Dyson, Munk, and Zetler, J. Acoust. Soc. Am., vol. 59, pp. 1121-1133, 1976 and Mikhalevsky, J. Acoust. Soc. Am., vol. 66, pp. 751-762, 1979] on simulated data with internal waves. The estimated phase rates were consistent between the two models. In contrast, previous application of the same models on deep water data showed a factor of 8 difference in their phase rates. The phase rates derived from the models become independent of range after a uniform phase distribution is reached in the (-/spl pi/,/spl pi/) region. The shallow water coherence time varies considerably with depth at a given range. The depth dependence is explained with a correlation function constructed with mode depth functions. 相似文献
38.
Eun Jin Yoo 《地理信息系统科学与遥感》2016,53(2):227-246
Demand for orthoimages is increasing as a crucial component of geographic information systems (GISs). Orthoimages are geometrically equivalent to planimetric maps, which show true geographic locations of terrain features. To produce orthoimages, geometric distortions from camera tilt and relief displacement from perspective images must be corrected. Traditionally, removing such distortions has been accomplished by differential rectification in a pixel-by-pixel fashion. However, this method cannot produce true orthoimages because of the double-mapping problem. We propose a method of generating patch-based true orthoimages for surface patches in buildings. The proposed method utilizes three-dimensional (3D) building model data. Patches from the data were projected onto aerial images to extract image patches and analysis of the superstructures was performed. Because orthoimages are generated for each building, the orthoimage quality is enhanced when using building data with a high level of detail. Instead of performing the complex visibility analysis of existing approaches, this article identifies occlusion areas based on unit surfaces of buildings and presents mutual recovery of occlusions using multiple images. To evaluate the feasibility of the method, experiments were performed with real datasets: (1) a building with a dome superstructure, (2) high-rise buildings close to each other, and (3) buildings with various shapes. 相似文献
39.
Late Quaternary sediments on the outer shelf of the Korea Strait and their paleoceanographic implications 总被引:1,自引:0,他引:1
D. I. Lim S. Kang H. S. Yoo H. S. Jung J. Y. Choi H. N. Kim I. H. Shin 《Geo-Marine Letters》2006,26(5):287-296
Sedimentological and micropaleontological characteristics of core sediments from the outer shelf of the Korea Strait, which connects the northern East China Sea and the East Sea (Sea of Japan), were investigated to elucidate the paleoceanographic environment, especially the timing of the Kuroshio inflow, since the last glacial maximum. The core sediments, containing continuous records of the last 15,000 years, are characterized by a relatively high mud content (more than 50%, on average) and well-developed tide-influenced sedimentary structures. Their mineralogy suggests that the material originated from the paleo-Nakdong River system, which extended across the shelf of the Korea Strait during low sea-level periods. Planktonic foraminifers reveal a series of well-defined changes in paleoceanographic conditions during the late Pleistocene–Holocene. Down-core variations in the abundance of four foraminiferal assemblages, i.e., cold, coastal, tropical–subtropical, and Kuroshio water groups comprising characteristic planktonic species, suggest the occurrence of a distinct paleoenvironmental change in the surface water at 7,000 years b.p., i.e., from 15,000 to 7,000 years b.p., the area was influenced by coastal waters whereas since ca. 7,000 years b.p., it has been under the influence of open-sea water related to the Kuroshio Current flow, associated with both higher temperature and higher salinity. In particular, Pulleniatina obliquiloculata increased markedly in abundance at this time, documenting the inflow of the Kuroshio into the study area. These data indicate that the coastal water stage terminated at ca. 7,000 years b.p. when the warm Kuroshio and its major branch, the Tsushima Current, began to flow into the East Sea, as is the case today. The intrusion of the Tsushima Current through the Korea Strait after ca. 7,000 years b.p. resulted in abrupt changes in sedimentation rates and a dramatic increase in abundance of the Kuroshio indicator species, P. obliquiloculata. 相似文献
40.
Even though rain rate is notorious for its spatial and temporal intermittency, its effect on the second‐order statistics of rain rate, especially the inter‐station correlation coefficients, has not been intensively evaluated before. This study has derived and compared the inter‐station correlation coefficient of rain rate for three cases of data: (1) only the positive measurements at both locations; (2) the positive measurements at either one or both locations; (3) all the measurements including zero measurement at both locations. For these three cases, the inter‐station correlation coefficients are analytically derived by applying the mixed bivariate log‐normal distribution. As an application example, the model parameters are estimated using the rain rate data collected at the Geum River basin, Korea, and the resulting inter‐station correlation coefficients are evaluated and compared with those estimated by applying the Gaussian distribution. We could find that highly biased inter‐station correlation coefficients are unavoidable when simply estimating them under the assumption of Gaussian distribution, or even when using the log‐transformed rain rate data. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献