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排序方式: 共有142条查询结果,搜索用时 15 毫秒
81.
Dugin Kaown Dong-Chan Koh D. Kip Solomon Yoon-Yeol Yoon Jaeha Yang Kang-Kun Lee 《Hydrogeology Journal》2014,22(5):1041-1054
Stable isotopes of water and 3H–3He were used to delineate recharge patterns and contaminant transport for a granitic regolith aquifer in an industrial complex in Wonju, South Korea, that has historically been contaminated with chlorinated solvents including trichloroethene (TCE) and carbon tetrachloride (CT). Groundwater recharge mainly occurred in upgradient forested areas while little recharge occurred in the downgradient industrial areas covered with extensive sections of impermeable pavement and paddy fields. δ18O and δD data indicated that groundwater was mainly derived from summer precipitation. The apparent groundwater ages using 3H–3He ranged from 1 to 4 yrs in the upgradient area and from 9 to 10 yrs in the downgradient area. Comparison of groundwater flow velocities based on Darcy’s law and those calculated with simple mass balance models and groundwater age supported the presence of preferential pathways for TCE movement in the study area. Measureable TCE was observed in groundwater irrespective of groundwater age. Considering the 3-yr duration of the TCE spill, 14 yrs before sampling, this indicates that TCE plumes were continuously fed from sources in the unsaturated zone after the spill ended and moved downgradient without significant degradation in the aquifer. 相似文献
82.
Assessing sustainability of groundwater resources on Jeju Island,South Korea,under climate change,drought, and increased usage 总被引:2,自引:0,他引:2
Aly I. El-Kadi Suzanne Tillery Robert B. Whittier Benjamin Hagedorn Alan Mair Kyoochul Ha Gi-Won Koh 《Hydrogeology Journal》2014,22(3):625-642
Numerical groundwater models were used to assess groundwater sustainability on Jeju Island, South Korea, for various climate and groundwater withdrawal scenarios. Sustainability criteria included groundwater-level elevation, spring flows, and salinity. The latter was studied for the eastern sector of the island where saltwater intrusion is significant. Model results suggest that there is a need to revise the current estimate of sustainable yield of 1.77?×?106 m3/day. At the maximum extraction of 84 % of the sustainable yield, a 10-year drought scenario would decrease spring flows by 28 %, dry up 27 % of springs, and decrease hydraulic head by an island-wide average of 7 m. Head values are particularly sensitive to changes in recharge in the western parts of the island, due to the relatively low hydraulic conductivity of fractured volcanic aquifers and increased groundwater extraction for irrigation. Increases in salinity are highest under drought conditions around the current 2-m head contour line, with an estimated increase of up to 9 g/L under 100 % sustainable-yield use. The study lists recommendations towards improving the island’s management of potable groundwater resources. However, results should be treated with caution given the available data limitations and the simplifying assumptions of the numerical modeling approaches. 相似文献
83.
This study shows dependence of the surface diurnal tidal stress on the internal structure of Europa. Its purpose is to investigate possibility of cracking of the icy shell. The stress is evaluated under the plausible model of the internal structure constrained by the gravity field data. The possible effective stress at the sub-Jovian point decreases with thickening of the shell, while it does not depend on the core radius and the thickness of the H2O layer. The range of this value is from 0.095 to 0.161 MPa, which does not exceed the tensile strength of ice. The stress required for the surface cracking would be mainly due to longer period deformations, especially non-synchronous rotation. And/or the actual strength of the ice at the surface would be smaller because of the preexisting cracks than that at a laboratory of the same temperature. 相似文献
84.
Macrofaunal burrows increase the surface area of the sediment-water interface, which has a great impact on the metabolism of aerobic microbes and the oscillation of reduced metabolites within the sediment. Given the importance of macrofauna in surficial sediments, the aim of this study is to examine the effects of burrow architectures on dissolved oxygen diffusion rates in comparison with unburrowed sediment, and thereby to evaluate the theoretical assumption used for modeling solute distribution in the burrow system using field samples. Employing microsensors, horizontal oxygen profiles were measured on a micrometer scale around burrows of seven invertebrates in tidal flats of the west coast of Korea. Oxygen diffusion distance through the burrow walls of seven invertebrates showed spatio-temporal variation with a range of 0.6 to 2.9 mm. Two groups of burrows were identified based on their oxygen diffusive properties relative to unburrowed sediments: 1) oxygen penetration similar to that of ambient sediments and 2) clearly enhanced oxygen penetration. Differences in the diffusive properties of the burrow wall were related to the burrow depth and diameter, existence of mucus lining on the wall, sediment grain size, and tidal phases. Also inhabitant activity was an important factor affecting oxygen penetration, which is discussed in the paper. These results further demonstrate that simplified assumptions (i.e. burrow structures are viewed as direct biogeochemical extensions of the sediment-water interface) may not be exact representation of the nature. 相似文献
85.
Tadahiko Tsuruta Hisaya Harada Toshiharu Misonou Toshiyuki Matsuoka Yasuyuki Hodotsuka 《Journal of Oceanography》2017,73(5):547-558
Investigations including a bathymetric survey, sonic prospecting, and vibrocoring were performed to understand the horizontal and vertical distribution of 137Cs in seabed sediments in shallow seas with depths less than 30 m near the Fukushima Daiichi Nuclear Power Plant. Especially, features of 137Cs distributions in deeper sections of the seabed sediments were studied to evaluate the vertical heterogeneity of 137Cs distribution in the seabed sediments in shallow seas. The distribution area of the seabed sediments was less than half of the investigation area, and the locations of the seabed sediments were divided into flat and terrace-like seafloors based on their topographical features. The thicknesses of the seabed sediment layers were mostly <2 m. The 137Cs inventories in the seabed sediments varied from 13 ± 1 to 3,510 ± 26 kBq m?2, and continuous distributions of 137Cs at depths greater than 81 cm were observed. The 137Cs distributions were not uniform; however, the 137Cs inventories tended to be larger near the base of the steeper ascending slopes than in the terrace-like seafloors themselves. Based on the relationship between the 137Cs inventories and mean shear stress, features of the seafloor topography were inferred to be significant control factors governing the horizontal and vertical distribution of 137Cs in the seabed sediments. Rapid changes and multiple peaks in the vertical profile of the 137Cs distributions suggest that they are related to pulse input caused by heavy-rain events. Change in the 137Cs inventories with depth in this study are larger than those reported in previous studies, indicating earlier results of 137Cs inventories per unit in seabed sediments in shallow seas, especially near the river mouth, which drains a radiologically highly-contaminated basin, were underestimated. 相似文献
86.
The α − β transition of quartz was successfully observed with using a single sample by means of the rectangular parallelepiped
resonance (RPR) method. An oriented rectangular parallelepiped of α-quartz single crystal was prepared and the resonant frequencies
of 30–11 vibrational modes were measured from room temperature to 700°C. The softening of quartz crystal was observed as the
significant reduction of resonant frequencies near the α–β transition. The present study is the first application of the RPR
method to the study of phase transition. The complete set of elastic constants of α- and β-quartz were determined as a function
of temperature by the least-squares inversion of the measured frequency data obtained by a single run. This is a merit yielded
by the RPR method. It is shown near the α − β transition in both α- and β-quartz that the elastic parameters decrease proportionally
to |T−T
0|−n
, where T is temperature and T
0 is the transition temperature, 573.0°C for α-quartz and 574.3°C for β-quartz. It was also seen that linear incompressibilities
K
1 = (C
11
+C
12
+C
13)/3 and K
3 = (C
33
+2C
13)/3 decrease rapidly toward the transition, whereas, shear moduli C
44, C
S1 = (C
11
+C
33
-2C
13)/4 and C
S3 = (C
11
-C
12)/2 = C
66 decrease only slightly. The shear modulus C
S3 = C
66 increased slightly in α-quartz. The elastic properties of isotropic aggregate of quartz were calculated, and it is shown
that the longitudinal wave velocity significantly decreases at the α − β transition, whereas, the shear wave velocity decreases
only slightly. 相似文献
87.
Jeju Island is a volcanic island composed predominantly of permeable basalts. The island is poor in surface water but abundant in groundwater. No actual perennial streams exist and the water resources on the island are dependent almost entirely on groundwater. The groundwater bodies on the island are classified into three general categories: high level, basal and parabasal groundwaters. The parabasal groundwater is further subdivided into lower and upper parabasal groundwaters due to the position of the Seogwipo Formation, which is made up of sedimentary rocks with a low permeability. The distribution of each groundwater type was evaluated through analyses of the spatial distribution of the Seogwipo Formation and the hydraulic gradient of the groundwater. Basal groundwater emerges extensively along the coast of the eastern sector, less commonly along the coast of the western sector. Parabasal groundwater occurs extensively over most of the island except for the southern sector, where it occurs only locally in the coastal area. This paper presents a summary of several studies on the occurrence and features of groundwater resources on Jeju Island, the largest island in Korea. 相似文献
88.
M. Nakagawa M. Santosh S. Yoshikura M. Miura T. Fukuda A. Harada 《Gondwana Research》2006,9(4):530-538
The kaolin deposits at Melthonnakkal and Pallipuram mines form part of the Warkalli Formation belonging to the Tertiary sequence in southern Kerala and occur at the boundary between the Tertiary sequence and Precambrian granulite facies metapelites (khondalites). The sedimentary clays are composed mainly of kaolinite, quartz and gibbsite. XRD and SEM studies have revealed that kaolinite is well-crystallized variety and the platy crystals are scarcely broken in the sedimentary clays. These sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites, and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock. Besides, the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by Quaternary tropical weathering processes. 相似文献
89.
Norimasa Nishiyama Takehiko Yagi Shigeaki Ono Hirotada Gotou Tatsuhiko Harada Takumi Kikegawa 《Physics and Chemistry of Minerals》2007,34(3):131-143
In situ X-ray diffraction measurements of Fe- and Al-bearing MgSiO3-rich perovskite (FeAl-Pv), which was synthesized from a natural orthopyroxene, were performed at pressures of 19–32 GPa and
temperatures of 300–1,500 K using a combination of a Kawai-type apparatus with eight sintered-diamond anvils and synchrotron
radiation. Two runs were performed using a high-pressure cell with two sample chambers, and both MgSiO3 perovskite (Mg-Pv) and FeAl-Pv were synthesized simultaneously in the same cell. Thus we were able to measure specific volumes
(V/V
0) of Mg-Pv and FeAl-Pv at the same P−T conditions. At all the measurement conditions, values of the specific volume of FeAl-Pv are consistent with those of Mg-Pv
within 2 Standard Deviation, strongly suggesting that effect of incorporation of iron and aluminum on the thermoelastic properties
of magnesium silicate perovskite is undetectable in this composition, pressure, and temperature range. Two additional runs
were performed using a high-pressure cell that has one sample chamber and unit-cell volumes of FeAl-Pv were measured at pressures
and temperatures up to 32 GPa and 1,500 K, respectively. All the unit-cell volume data of FeAl-Pv perovskite were fitted to
the high temperature Birch–Murnaghan equation of state and a complete set of thermoelastic parameters of this perovskite was
determined with an assumption of K′
300,0 = 4. The determined parameters are K
300,0 = 243(3) GPa, (∂K
T,0/∂T)
P
= −0.030(8) GPa/K, a
0 = 2.78(18) × 10−5 K−1, and b
0 = 0.88(28) × 10−8 K−2, where a
0 and b
0 are the coefficients of the following expression describing the zero-pressure thermal expansion: α
T,0 = a
0 + b
0
T. The equation-of-state parameters of FeAl-Pv are in good agreement with those of MgSiO3 perovskite at the conditions corresponding to the uppermost part of the lower mantle. 相似文献
90.