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421.
Recent sediment accumulation and origin of shelf mud deposits in the Yellow and East China Seas 总被引:3,自引:0,他引:3
Modern (last 100 yr) accumulation rates of shelf mud deposits in the Yellow and East China Seas were investigated using the distribution of excess 210Pb (210Pbex) in sediment core samples. Compilation and merger of new and previously published data helped clarify sediment accumulation in these seas. The estimated accumulation rates, together with data of suspended sediment concentrations, provided findings on the sediment budget, origin, and transport pathway of the mud deposits. The overall accumulation distribution in the Yellow and East China Sea shelf revealed a general, cross-shelf decreasing trend along the sediment dispersal system away from the rivers, except for the South Sea (SSM) and southeastern Yellow Sea (SEYSM) mud patches found along the Korean coast. Notably, 210Pbex activity profiles within the SSM and the SEYSM yielded a relatively high accumulation rate of 2-5 mm/yr, implying a sedimentation rate of 4-15 × 107 tons per year in this coastal zone. Such an annual accumulation rate is about one order of magnitude greater than the total sediment discharge (6-20 × 106 tons/yr) from Korean rivers, suggesting an additional offshore source. The distribution pattern of the well-defined suspended plume clearly showed the possible transport and exchange of fine-grained sediments between the ECS shelf and the coastal area of Korea, especially during winter. Such a high accumulation in Korean coastal areas is attributable to the sediments supplied from the mud deposit of the ECS (i.e., SWCIM), with origins in Chinese rivers. Therefore, the Korean coastal area may be an important sink for some of Chinese river sediments being transported from the south by the Yellow Sea Warm Current. 相似文献
422.
A coupled ice-ocean isopycnal numerical model of the Southern Ocean is established tostudy the circulation and its seasonal variability in the region around the Kerguelen Plateau. An analysis of the simulated results shows significant stripe-like structure and non-zonal feature of the Antarctic Cir-cumpolar Current (ACC) in this region. ACC begins to bifurcate and to turn its direction before meeting the plateau. The southernmost branch of ACC is near to the Antarctic coast and displays its strong interaction with the westward Antarctic Slope Current. The northern branch of ACC has a tendency of annual variations while the southern one varies in a semiannual cycle. The variation phases of both branches are coincident with that of the wind stress in this region. 相似文献
423.
Archived data, together with field observations collected between 1980 and 1982 off the west coast of Korea, suggest that the onset of winter monsoon winds in late fall initiates a residual southward flow that potentially carries large volumes of resuspended bottom sediments into the Korea Strait. During the calm conditions of summer, muds are replenished by high river discharges and reform the band of soft material, which characteristically occurs as a series of mudflats near the coast. Thus, these mudflats serve as a temporary storage facility during summer accumulation and as a source during winter erosion. 相似文献
424.
Jin-Hyeob Kwak Woo-Jung Choi Sang-Sun Lim Seung-Heon Lee Sang-Mo Lee Scott X. Chang Jae-Woon Jung Kwang-Sik Yoon Soo-Myung Choi 《Environmental Geology》2008,53(6):1331-1338
Electrical conductivity of saturated soil extracts (ECe) in three reclaimed tideland (RTL) soils on the west coast of Korea decreased with time since reclamation, indicating natural
desalinization through leaching of salts by precipitation water. Soil N concentration increased with decreasing ECe. With the increase in soil N concentration, the δ15N decreased, likely caused by the input of 15N-depleted N sources. As N2-fixing plant species were found in the oldest RTL, atmospheric N2 fixation likely contributed to the increase in soil N concentration in the oldest RTL. Negative δ15N (−7.1 to −2.0‰) of total inorganic N (NH4
++NO3
−) and published data on N deposition near the study area indicate that atmospheric N deposition might be another source of
N in the RTLs. Meanwhile, the consistently negative δ15N of soil NO3
− excluded N input from chemical fertilizer through groundwater flow as a potential N source, since NO3
− in groundwater generally have a positive δ15N. The patterns of δ15N of NH4
+ (+2.3 to +5.1‰) and NO3
− (−9.2 to −5.0‰) suggested that nitrification was an active process that caused 15N enrichment in NH4
+ but denitrification was probably minimal which would otherwise have caused 15N enrichment in NO3
−. A quantitative approach on N budget would provide a better understanding of soil N dynamics in the studied RTLs. 相似文献
425.
Byoung-Young Choi Hyeon-Jung Kim Kangjoo Kim Seok-Hwi Kim Hwa-Jin Jeong Eungyu Park Seong-Taek Yun 《Environmental Geology》2008,54(2):335-345
Vertical variations of redox chemistry and groundwater quality were investigated in an alluvial aquifer beneath an agricultural
area, in which deep groundwaters are free of NO3, Fe, and Mn problems that are frequently encountered during the development of alluvial groundwaters. This study was performed
to identify and evaluate vertical chemical processes attenuating these chemical species in the study area. For this study,
the processes affecting groundwater chemistry were identified by factor analysis (FA) and the groundwater samples collected
from six multilevel samplers were hierarchically classified into three different redox zones by cluster analysis (CA) based
on the similarity of geochemical features. FA results indicated three major factors affecting the overall water chemistry:
agricultural activities (factor 1), redox reactions (factor 2), and remnant seawater (factor 3). The groundwater quality in
the study area was revealed to be controlled by a series of different redox reactions, resulting in different redox zones
as a function of depth. It was also revealed that the low Fe and Mn levels in the groundwater of the deeper part are associated
with sulfate reduction, which led to precipitation of Fe as iron sulfide and adsorption of Mn on it. 相似文献
426.
427.
The problem of the survival of a low-mass secondary orbiting a primary that becomes a planetary nebula is studied. The values of the mass of the primary are 1.0, 1.5, and 2.0M
; the values of the mass of the secondary 0.001M
, 0.01M
and 0.1M
. The orbital decay and mass of the secondary due to accretion and gravitational drag in the common envelope are presented. The possible application of the results to V471 Tau, UU Sge, WZ Sge and the Sun-Jupiter system are discussed. 相似文献
428.
429.
430.