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61.
A generation procedure of Ritz vectors to control the inclusion of static effect and the number of vectors in mode superposition dynamic analysis is presented. The original algorithm of the Ritz vectors15 is modified to improve stability in the generation procedure and to include the use of static residual. To reject unimportant Ritz vectors, cut-off criteria, which are based on the participation of mass distribution and spatial load distribution, are proposed. Numerical examples are presented to illustrate the effectiveness of the derived Ritz vectors over the eigenvectors and the performance of the cutoff criteria in the mode superposition dynamic analysis. 相似文献
62.
Chemical and physical weathering in a hot‐arid,tectonically active alluvial system of Anza Borrego Desert,California 下载免费PDF全文
Investigation of chemical and physical weathering of bedrock and alluvial sediment in the Anza Borrego Desert, California, sheds light on weathering processes in hot‐arid systems and clarifies interpretations of climate from alluvial sediment. All of the alluvial sediment in the study area emanates from Cretaceous tonalite of the Peninsular Range, enabling exploration of the effects of external variables – climate, transport distance and tectonics – on the physical and chemical properties of the sediment. Chemical weathering in this area is dominated by plagioclase alteration observed in both bedrock outcrops and sediment, evinced most clearly by changes in the Eu anomaly. Biotite chemical weathering, manifested by interlayer K+ loss, is not evident in bedrock, but clearly observed in the sediment. Despite the weak intensity of chemical weathering (Chemical Index of Alteration = 56 to 62), fine‐grained (<63 μm) sediment displays a clear weathering trend in A–CN–K space and contains up to 25% clay minerals. Physical abrasion and grain‐size reduction in biotite during transport predominates in the sediment, whereas physical (insolation) weathering affecting bedrock is inferred from estimates of differential thermal expansion of mineral phases in response to extreme temperature changes in the study area. Chemical alteration and Brunauer–Emmett–Teller surface area both increase within the active Elsinore fault zone at the distal end of the depositional transect, reflecting tectonic‐induced fracturing and associated accelerated weathering. Extensive fracturing, together with a more humid Pleistocene climate, probably facilitated in situ bedrock weathering, preceding arid alluvial deposition in the Holocene. This study demonstrates that both climate and tectonic processes can affect chemical and physical weathering, resulting in alteration of plagioclase, leaching of K+ from biotite in the sediment and formation of clay minerals, even in hot, arid systems. 相似文献
63.
This study investigates a freshwater budget in the Yellow and East China Seas (YECS) using a global f general circulation
model with a regional focus on the YECS. A freshwater budget analysis finds that major freshwater contributors over the YECS
change seasonally. In summer, freshwater inflow from Changjiang and positive precipitation minus evaporation (P-E) dominates
freshwater outflow across the boundaries around the YECS, resulting in net freshwater gain in the YECS. In winter, evaporation,
intensified by strong winds, dominates freshwater inflow from Changjiang and precipitation, while net freshwater transport
across the boundaries around the YECS is negligible, causing freshwater loss in total over the YECS. Although P-E has often
been assumed to be negligible by supposing that the annual mean of precipitation is nearly equal to that of evaporation, this
study suggests that P-E needs to be included in the seasonal freshwater budget in the YECS. 相似文献
64.
Joo M Raymond MA McNeil VH Huggins R Turner RD Choy S 《Marine pollution bulletin》2012,65(4-9):150-166
The Great Barrier Reef (GBR) catchment area has been monitored simultaneously for sediment and nutrient exports from 10 priority catchments discharging into the GBR lagoon between 2006 and 2009. This allows GBR catchment-wide exports to be estimated and spatially compared within a discrete time-frame. Elevated levels of sediment and nutrient exports were recorded in all monitored catchments as compared to pre-European estimates, but vary around previous estimates of mean annual loads. During the period of monitoring, the Burdekin and Fitzroy catchments contributed the highest sediment and nutrient exports, however when loads were normalised for area, these catchments produced the lowest unit yields. In contrast, the highest yields were produced in the wetter and proportionately more intensively cultivated Johnstone, O'Connell, and Pioneer catchments particularly for dissolved nitrogens. This assessment offers the necessary scientific foundation for future monitoring, assessment, and management of sediment and nutrient loads entering the GBR. 相似文献
65.
A discontinuity in the late Pleistocene alluvial deposits,Hwacheon‐ri,Gyeongju, Korea: Occurrences and paleoenvironmental implication 下载免费PDF全文
Hoil Lee In Sung Paik Hyun Joo Kim Hee‐Cheol Kang Won Gyeong Seol Jin‐Young Lee 《Island Arc》2018,27(4)
A sedimentary discontinuity is present in the late Pleistocene alluvial deposits exposed along the cliff in stream side, Gyeongju, Korea. Sedimentological study, Optically Stimulated Luminescence (OSL) age dating, and X‐ray diffraction (XRD), and X‐ray fluorescence spectrometer (XRF) analyses were conducted in order to interpret the origin of the discontinuity surface. Based on the sedimentological study, these deposits can be divided into three distinct stages, in ascending order: (Stage 1) development of a braided stream flowing from south to north and deposition by debris flows from the mountain aside the stream during and/or after deposition of the braided stream; (Stage 2) deposition by intermittent events during a state of stagnation after the abandonment or migration of the previously existed braided stream; and (Stage 3) deposition of gravels from debris flows from the mountain aside the stream. Hornfelsic gravels are common in Stage 1, whereas andesitic gravels are predominant in Stage 3, suggesting the provenance change from Stage 1 to Stage 3. The discontinuity surface is laterally extensive and marked by a distinct carbonaceous dark grey horizon between Stage 2 and Stage 3. It is characteristic that rootlets mineralized by vivianite are present, and iron‐oxide crusts are cutting across irregularly below the discontinuity surface. It is thus interpreted that the shift of depositional environment from an alluvial plain (Stage 2) (125 ka) to an alluvial fan (Stage 3) (94–55 ka) was an alluvial response to sea level change from the interglacial to the glacial. The development of iron‐oxide crusts and diagenetic vivianite in the discontinuity surface suggests humid condition persisted during the paleoclimatic shift from the last interglacial to the last glacial stages. 相似文献
66.
67.
Bhavya P. S. Kim Bo Kyung Jo Naeun Kim Kwanwoo Kang Jae Joong Lee Jae Hyung Lee Dabin Lee Jang Han Joo HuiTae Ahn So Hyun Kim Yewon Min Jun-Oh Kang Min Gu Yun Mi Sun Kang Chang Keun Lee Sang Heon 《Ocean Science Journal》2019,54(1):1-14
Ocean Science Journal - Biochemical composition of phytoplankton is a key indicator of the physiological and nutritional status of phytoplankton. A balanced biochemical pattern represents a healthy... 相似文献
68.
Since the 1980s, the coastal wetlands in Korea have been rapidly degraded and destroyed mainly due to reclamation and landfills
for coastal development. In order to recover damaged coastal environments and to develop wetland restoration technologies,
a 4-year study on ecological the restoration of coastal vegetated ecosystems was started in 1998. As one of a series of studies,
a small-scale experiment on salt marsh restoration was carried out from April 2000 to August 2001. The experiment was designed
to find effective means of ecological restoration through a comparison of the changes in environmental components and species
structure between two different experimental plots created using sediment fences, one with and one without small canals. Temporal
variation in surface elevation, sedimentary facies, and benthic species were measured seasonally in each plot and in the adjacent
natural reference sites. Monthly exposure occurred from 330 cm to mean sea level, which represents the critical tidal level
(CTL) at which salt marsh plants colonize. Vegetation, especially Suaeda japonica, colonized the site the following spring and recovered to a similar extent in the natural marshes 16 months later. The sedimentary
results indicated that the sediment fences had effects on particle size and sediment accumulation, especially in the plot
with small canals. This experiment also showed that tidal height, especially that exceeding the CTL, is an important factor
in the recovery of the benthic fauna of salt marshes. From these results, we suggested that designs for the restoration of
salt marsh ecosystems must consider the inclusion of a tidal height exceeding CTL, as this may allow reconstruction of the
previous natural ecosystem without artificial transplanting. 相似文献
69.
Jong-Hwa Chun Byong-Jae Ryu Byeong-Kook Son Ji-Hoon Kim Joo Yong Lee Jang-Jun Bahk Hag-Ju Kim Kyung Sik Woo Odette Nehza 《Marine and Petroleum Geology》2011,28(10):1787-1800
A mound related to a cold vent in a columnar seismic blanking zone (CSBZ) was formed around site UBGH1-10 in the central Ulleung Basin (2077 m water depth), East Sea, Korea. The mound is 300–400 m wide and 2–3 m high according to multi-beam bathymetry, 2–7 kHz sub-bottom profiler data, and multi-channel reflection seismic data. Seafloor topography and characteristics were investigated using a remotely operated vehicle (ROV) around site UBGH1-10, which is located near the northern part of the mound. The origin of the mound was investigated through lithology, mineralogy, hydrate occurrence, and sedimentary features using dive cores, piston cores, and a deep-drilling core. The CSBZ extends to ∼265 ms two-way traveltime (TWT) below the seafloor within a mass-transport deposit (MTD) unit. Gas hydrate was entirely contained 6–141 m below the seafloor (mbsf) within hemipelagic deposits intercalated with a fine-grained turbidite (HTD) unit, characteristically associated with high resistivity values at site UBGH1-10. The hydrate is commonly characterized by veins, nodules, and massive types, and is found within muddy sediments as a fracture-filling type. Methane has been produced by microbial reduction of CO2, as indicated by C1/C2+, δ13CCH4, and δD4CH analyses. The bowl-shaped hydrate cap revealed at 20–45 ms TWT below the seafloor has very high resistivity and high salinity, suggesting rapid and recent gas hydrate formation. The origin of the sediment mound is interpreted as a topographic high formed by the expansion associated with the formation of the gas hydrate cap above the CSBZ. The lower sedimentation rate of the mound sediments may be due to local enhancement of bottom currents by topographic effects. In addition, no evidence of gas bubbles, chemosynthetic communities, or bacterial mats was observed in the mound, suggesting an inactive cold vent. 相似文献
70.
Jong-Kuk Choi Hyun-Joo Oh Bon Joo Koo Joo-Hyung Ryu Saro Lee 《Estuarine, Coastal and Shelf Science》2011
The purpose of this study was to apply probabilistic models to the mapping of the potential polychaeta habitat area in the Hwangdo tidal flat, Korea. Remote sensing techniques were used to construct spatial datasets of ecological environments and field observations were carried out to determine the distribution of macrobenthos. Habitat potential mapping was achieved for two polychaeta species, Prionospio japonica and Prionospio pulchra, and eight control factors relating to the tidal macrobenthos distribution were selected. These included the intertidal digital elevation model (DEM), slope, aspect, tidal exposure duration, distance from tidal channels, tidal channel density, spectral reflectance of the near infrared (NIR) bands and surface sedimentary facies from satellite imagery. The spatial relationships between the polychaeta species and each control factor were calculated using a frequency ratio and weights-of-evidence combined with geographic information system (GIS) data. The species were randomly divided into a training set (70%) to analyze habitat potential using frequency ratio and weights-of-evidence, and a test set (30%) to verify the predicted habitat potential map. The relationships were overlaid to produce a habitat potential map with a polychaeta habitat potential (PHP) index value. These maps were verified by comparing them to surveyed habitat locations such as the verification data set. For the verification results, the frequency ratio model showed prediction accuracies of 77.71% and 74.87% for P. japonica and P. pulchra, respectively, while those for the weights-of-evidence model were 64.05% and 62.95%. Thus, the frequency ratio model provided a more accurate prediction than the weights-of-evidence model. Our data demonstrate that the frequency ratio and weights-of-evidence models based upon GIS analysis are effective for generating habitat potential maps of polychaeta species in a tidal flat. The results of this study can be applied towards conservation and management initiatives for the macrofauna of tidal flats. 相似文献