共查询到20条相似文献，搜索用时 656 毫秒
1.
An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6–17°C/km. The estimated heat flow values fall in the range of 28–53 mW/m2, with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14–42°C/km, with the corresponding heat flow values falling in the range of 36–89 mW/m2. Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. The thermal models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts. 相似文献
2.
《Journal of African Earth Sciences》1999,28(3):641-652
Data from sixteen deep walls drilled for oil exploration purposes in the Anambra Basin of southeastern Nigeria indicate large variations in temperature gradients and heat flow within the basin. Geothermal gradients vary between 25 and 49 ± 1°C km−1, while heat flow estimates are in the range 48 to 76 ± 3 mW m−2. The highest geothermal gradients and heat flow values were computed for the wells located in the southwestern part of the basin north of Onitsha and Asaba. This part of the basin coincides with zones of thick, low conductivity sediments, low ground surface elevation, and hydraulic discharge zones. The general direction of increase in geothermal gradient, originally projected as south to north by earlier workers dealing with the Niger Delta data and the very limited well data from the Anambra Basin, is inconsistent with the results of the present study.The distribution of subsurface temperatures, geothermal gradients and heat flow is found to be directly related to the basin hydrodynamics - higher geothermal gradients and heat flow in areas of low hydraulic head distribution. Hydrocarbon metamorphism and migration appear to have been greatly influenced by the movements of circulating meteoric waters. A higher level of organic maturity of sediments should be expected in the southwestern zone, where the thermal anomaly exists. However, owing to hydrodynamic activities, tertiary migration would have taken place leaving many traces of residual hydrocarbons. The several cases of fluorescence noticed in wells in the southwestern zone of the Anambra Basin are taken as evidence that this process may indeed have taken place in the geological past of the basin. 相似文献
3.
L.B. Reid G. Bloomfield L.P. Ricard C. Botman P. Wilkes 《Australian Journal of Earth Sciences》2013,60(7):1033-1048
Exploration of Perth's geothermal potential has been performed by the Western Australian Geothermal Centre of Excellence (WAGCoE). Detailed vertical temperature and gamma ray logging of 17 Western Australia Department of Water's (DoW) Artesian Monitoring (AM) wells was completed throughout the Perth Metropolitan Area (PMA). In addition, temperature logs from 53 DoW AM wells measured in the 1980s were digitised into LAS format. The logged data are available in the WAGCoE Data Catalogue. Analysis of the gamma ray logs yielded the first estimates of radiogenic heat production in Perth Basin formations. Values by formation ranged between 0.24 and 1.065 μW m?3. The temperature logs provide a picture of true formation temperatures within shallow sediments in the Perth Basin. A three-dimensional model of the temperature distribution was used to produce maps of temperature at depth and on the top of the Yarragadee aquifer. The temperature data were interpreted with a one-dimensional conductive heat model. Significant differences between the model and the observations was indicative of heat moving via non-conductive mechanisms, such as advection or convection. Evidence of non-conductive or advective heat flow is demonstrated in most formations in the region, with significant effects in the aquifers. Average conductive geothermal gradients range from 13°C km?1 to 39°C km?1, with sandstone formations exhibiting average gradients of approximately 25°C km?1, while insulating silt/shale formations show higher average gradients of over 30°C km?1. To produce preliminary heat flow estimates, temperature gradients were combined with thermal conductivities measured elsewhere. The geometric mean heat flow estimates range between 64 mW m?2 to 91 mW m?2, with the standard deviation of the arithmetic mean heat flow ranging between 15 and 23 mW m?2. The study characterises the shallow temperature regime in the Perth Metropolitan Area, which is of direct relevance towards developing commercial geothermal projects. 相似文献
4.
The GALO system is applied to the numerical reconstruction of burial and thermal histories of the West Bashkirian lithosphere from the Riphean to the present. An analysis of the variation in tectonic subsidence of the basin during its development is utilized to estimate approximately the mantle heat flow variations. Our variant of basin evolution suggests that after cooling in the Early Riphean, the rather weak thermal reactivations have not led to considerable heating of the lithosphere in the study region. Surface heat flow decreased from relatively high values in the Early Riphean (60–70 mW/m2 in the eastern area and 40–50 mW/m2 in the western part) to present-day values of 32–40 mW/m2. In spite of the relatively low temperature regime of the basin as a whole, a syn-rifting deposition of more than 10 km of limestone, shale and sandstone in the Riphean resulted in rather high temperatures (180–190 °C) at the base of present-day sedimentary blanket in the eastern area. In agreement with the observed data, computed present-day heat flow through the sediment surface increases slightly from 32 to 34 mW/m2 near the west boundary of the region to 42 mW/m2 near the boundary of the Ural Foldbelt, whereas the heat flow through the basement surface decreases slightly from 28–32 to 24–26 mW/m2 in the same direction. The mantle heat flow is only 11.3–12.7 mW/m2, which is considerable lower than mean heat flow of the Russian Platform (16–18 mW/m2) and comparable with the low heat flow of Precambrian shields. 相似文献
5.
Research on the characteristics and influencing factors of terrestrial heat flow in Guizhou Province 
下载免费PDF全文
下载免费PDF全文 Wei Shuai-chao Liu Feng Zhang Wei Wang Gui-ling Yuan Ruo-xi Liao Yu-zhong Yan Xiao-xue 《地下水科学与工程》2022,10(2):166-183
Terrestrial heat flow is an important physical parameter in the study of heat transfer and thermal structure of the earth and it has great significance in the genesis and development and utilization potential of regional geothermal resources. Although several breakthroughs in geothermal exploration have been made in Guizhou Province. The terrestrial heat flow in this area has not been properly measured, restricting the development of geothermal resources in the province. For this reason, the terrestrial heat flow in Guizhou was measured in this study, during which the characteristics of heat flow were determined using borehole thermometry, geothermal monitoring and thermal property testing. Moreover, the influencing factors of the terrestrial heat flow were analyzed. The results show that the thermal conductivity of rocks ranges from 2.0 W/(m·K) to 5.0 W/(m·K), with an average of 3.399 W/(m·K); the heat flow varies from 30.27 mW/m2 to 157.55 mW/m2, with an average of 65.26 ± 20.93 mW/m2, which is slightly higher than that of the average heat flow in entire land area in China. The heat flow in Guizhou generally follows a dumbbell-shaped distribution, with high values present in the east and west and low values occurring in the north and south. The terrestrial heat flow is related to the burial depths of the Moho and Curie surface. The basaltic eruptions in the Emeishan led to a thinner lithosphere, thicker crust and lateral emplacement, which dominated the basic pattern of heat flow distribution in Guizhou. In addition, the dichotomous structure of regional active faults and concealed deep faults jointly control the heat transfer channels and thus influence the terrestrial heat flow. 相似文献
6.
Geothermal gradients are estimated to vary from 31 to 43 °C/km in the Yinggehai Basin based on 99 temperature data sets compiled from oil well data. Thirty-seven thermal conductivity measurements on core samples were made and the effects of porosity and water saturation were corrected. Thermal conductivities of mudstone and sandstone range from 1.2 to 2.7 W/m K, with a mean of 2.0±0.5 W/m K after approximate correction. Heat flow at six sites in the Yinggehai Basin range from 69 to 86 mW/m2, with a mean value of 79±7 mW/m2. Thick sediments and high sedimentation rates resulted in a considerable radiogenic contribution, but also depressed the heat flow. Measurements indicate the radiogenic heat production in the sediment is 1.28 μW/m3, which contributes 20% to the surface heat flow. After subtracting radiogenic heat contribution of the sediment, and sedimentation correction, the average basal heat flow from basement is about 86 mW/m2.Three stages of extension are recognized in the subsidence history, and a kinematic model is used to study the thermal evolution of the basin since the Cenozoic era. Model results show that the peak value of basal heat flow was getting higher and higher through the Cenozoic. The maximum basal heat flow increased from 65 mW/m2 in the first stage to 75 mW/m2 in the second stage, and then 90 mW/m2 in the third stage. The present temperature field of the lithosphere of the Yinggehai Basin, which is still transient, is the result of the multistage extension, but was primarily associated with the Pliocene extension. 相似文献
7.
8.
Heat flow in active tectonic zones as the Baikal rift is a crucial parameter for evaluating deep anomalous structures and lithosphere evolution. Based on the interpretation of the existing datasets, the Baikal rift has been characterized in the past by either high heat flow, or moderately elevated heat flow, or even lacking a surface heat flow anomaly. We made an attempt to better constrain the geothermal picture by a detailed offshore contouring survey of known anomalies, and to estimate the importance of observed heat flow anomalies within the regional surface heat output. A total of about 200 new and close-spaced heat flow measurements were obtained in several selected study areas in the North Baikal Basin. With an outrigged and a violin-bow designed thermoprobe of 2–3-m length, both the sediment temperature and thermal conductivity were measured. The new data show at all investigated sites that the large heat flow highs are limited to local heat flow anomalies. The maximum measured heat flow reaches values of 300–35000 mW/m2, but the extent of the anomalies is not larger than 2 to 4 km in diameter. Aside of these local anomalies, heat flow variations are restricted to near background values of 50–70 mW/m2, except in the uplifted Academician zone. The extent of the local anomalies excludes a conductive source, and therefore heat transport by fluids must be considered. In a conceptual model where all bottom floor heat flow anomalies are the result of upflowing fluids along a conduit, an extra heat output of 20 MW (including advection) is estimated for all known anomalies in the North Baikal Basin. Relative to a basal heat flow of 55–65 mW/m2, these estimations suggest an extra heat output in the northern Lake Baikal of only 5%, corresponding to a regional heat flow increase of 3 mW/m2. The source of this heat can be fully attributed to a regional heat redistribution by topographically driven ground water flow. Thus, the surface heat flow is not expected to bear a signal of deeper lithospheric thermal anomalies that can be separated from heat flow typical for orogenically altered crust (40–70 mW/m2). The new insights on the geothermal signature in the Baikal rift once more show that continental rifting is not by default characterized by high heat flow. 相似文献
9.
牛驼镇凸起是冀中拗陷中一个显著的次级正向构造,其地理位置见图1。1973—1978年进行石油普查和勘探时,在该区相继发现了地下热水,引起了人们的注意,先后对热水的分布有过报道和论述[1,2]。鉴于牛驼镇凸起(包括容城凸起)地热异常在华北平原具有代表性,我们在石油部门的协助下,在本区较系统地开展了地温测量并收集有关资料进行研究。本文试图剖析这个典型地区地温场的特点,作为圈定和预测华北平原地热异常区以及分析地下热水分布规律的基础。 相似文献
10.
Heat flow increases northward along Intermontane Belt in the western Canadian Cordillera, as shown by geothermal differences
between Bowser and Nechako sedimentary basins, where geothermal gradients and heat flows are ∼30 mK/m and ∼90 mW/m2 compared to ∼32 mK/m and 70 –80 mW/m2, respectively. Sparse temperature profile data from these two sedimenatary basins are consistent with an isostatic model
of elevation and crustal parameters, which indicate that Bowser basin heat flow should be ∼20 mW/m2 greater than Nechako basin heat flow. Paleothermometric indicators record a significant northward increasing Eocene or older
erosional denudation, up to ∼7 km. None of the heat generation, tectonic reorganization at the plate margin, or erosional
denudation produce thermal effects of the type or magnitude that explain the north–south heat flow differences between Nechako
and Bowser basins. The more southerly Nechako basin, where heat flow is lower, has lower mean elevation, is less deeply eroded,
and lies opposite the active plate margin. In contrast, Bowser basin, where heat flow is higher, has higher mean elevation,
is more deeply eroded, and sits opposite a transform margin that succeeded the active margin ∼40 Ma. Differences between Bowser
and Nechako basins contrast with the tectonic history and erosion impacts on thermal state. Tectonic history and eroded sedimentary
thickness suggest that Bowser basin lithosphere is cooling and contracting relative to Nechako basin lithosphere. This effect
has reduced Bowser basin heat flow by ∼10–20 mW/m2 since ∼40 Ma. Neither can heat generation differences explain the northerly increasing Intermontane Belt heat flow. A lack
of extensional structures in the Bowser basin precludes basin and range-like extension. Therefore, another, yet an unspecified
mechanism perhaps associated with the Northern Cordilleran Volcanic Province, contributes additional heat. Bowser basin’s
paleogeothermal gradients were higher, ∼36 mK/m, before the Eocene and this might affect petroleum and metallogenic systems. 相似文献
11.
In porous sediments of the Ishikari Lowland, there is a gradual increase in the background geothermal gradient from the Ishikari
River (3–4 °C 100 m–1) to the southwest highland area (10 °C 100 m–1). However, the geothermal gradient at shallow depths differs in detail from the background distribution. In spite of convective
heat-flow loss generally associated with groundwater flow, heat flow remains high (100 mW m–2) in the recharge area in the southwestern part of the Ishikari basin, which is part of an active geothermal field. In the
northeastern part of the lowland, heat flow locally reaches 140 mW m–2, probably due to upward water flow from the deep geothermal field. Between the two areas the heat flow is much lower. To
examine the role of hydraulic flow in the distortion of the isotherms in this area, thermal gradient vs. temperature analyses
were made, and they helped to define the major components of the groundwater-flow system of the region. Two-dimensional simulation
modeling aided in understanding not only the cause of horizontal heat-flow variations in this field but also the contrast
between thermal properties of shallow and deep groundwater reservoirs.
Electronic Publication 相似文献
12.
Temperature measurements carried out on 9 hydrocarbon exploration boreholes together with Bottom Simulating Reflectors (BSRs) from reflection seismic images are used in this study to derive geothermal gradients and heat flows in the northern margin of the South China Sea near Taiwan. The method of Horner plot is applied to obtain true formation temperatures from measured borehole temperatures, which are disturbed by drilling processes. Sub-seafloor depths of BSRs are used to calculate sub-bottom temperatures using theoretical pressure/temperature phase boundary that marks the base of gas hydrate stability zone. Our results show that the geothermal gradients and heat flows in the study area range from 28 to 128 °C/km and 40 to 159 mW/m2, respectively. There is a marked difference in geothermal gradients and heat flow beneath the shelf and slope regions. It is cooler beneath the shelf with an average geothermal gradient of 34.5 °C/km, and 62.7 mW/m2 heat flow. The continental slope shows a higher average geothermal gradient of 56.4 °C/km, and 70.9 mW/m2 heat flow. Lower heat flow on the shelf is most likely caused by thicker sediments that have accumulated there compared to the sediment thickness beneath the slope. In addition, the continental crust is highly extended beneath the continental slope, yielding higher heat flow in this region. A half graben exists beneath the continental slope with a north-dipping graben-bounding fault. A high heat-flow anomaly coincides at the location of this graben-bounding fault at the Jiulong Ridge, indicating vigorous vertical fluid convection which may take place along this fault. 相似文献
13.
Bottom-hole temperature values from approximately 36,000 wells in Alberta. Saskatchewan and Manitoba, Canada, have been used to study thermal gradients and heat flow density there. It is found that variations of heat flow density with depth occur throughout the Prairies basin. Differences in heat flow density exist between the Mesozoic + Cenozoic and Paleozoic sediments and are related to the hydrodynamics which is controlled by the topography. The heat flow density through the Mesozoic + Cenozoic of the upper part of the section is less than that in the Paleozoic formations of the lower part of the section in recharge areas, but greater in discharge areas. A zone in which heat flow is approximately constant with depth extends down the central part of the basin between the recharge and discharge areas. Heat flowdensity in this zone lies between 60 mW m?2 and 80 mW m?2 and is thought to be representative of the deep crustal heat flow density. It is suggested that temperature variations on the Precambrian basement that are not depth related may be associated with anomalous heat flow regimes in the lower crust. 相似文献
14.
Detailed studies of terrestrial heat flow in southern and central Alberta estimated on the basis of an order of magnitude larger data base than ever used before (33653 bottom-hole temperature data from 18711 wells) and thermal conductivity values based on detailed rock studies and measured rock conductivities show significant regional and local variations and variations with depth. Heat flow values were estimated for each 3 × 3 township/range area (28.8 × 28.8 km). A difference in heat flow exists between Paleozoic and Mesozoic strata. Generally lower heat flow values are observed in the strata above the Paleozoic erosional surface (20–75 mW m−2). Much higher values are estimated for the Younger Paleozoic formations, with large local and regional variations between 40 and 100 mW m−2.Average heat flow values based on heat flow determinations below and above the Paleozoic surface that agree within 20% show an increase from values less than 40 mW m−2 in southern and southwestern Alberta to values as high as 70 mW m−2 in central Alberta. The predominance of regional downward groundwater flows in Mesozoic strata seem to be responsible for the generally observed heat flow increase with depth.The results show that the basin heat flow pattern is influenced by water movement and even careful detailed heat flow measurements will not give correct values of background steady-state heat flow within the sedimentary strata. 相似文献
15.
Jacek?Majorowicz Jan??afanda Torun- Working Group 《International Journal of Earth Sciences》2008,97(2):307-315
High-precision temperature measurements were carried out up to a depth of 2,930 m in the 5.5-km-deep well Torun-1, 26 years
after completion of drilling. The temperature log provides equilibrium thermal state information for the Polish Lowland at
the western margin of the Precambrian craton. Geothermal gradient calculated from the equilibrium temperature log, together
with estimates of thermal conductivity from ‘net rock’ geophysical well logging analysis and available core measurements,
yields heat flow in the range 50–60 mW/m2 below 2-km depth. Heat flow of 50 mW/m2 plus ∼10 mW/m2 generated within thick sediments and highly metamorphosed sedimentary wedge is typical for the western margin of the Precambrian
East European craton. Heat-flow variations with depth can be explained by a model of surface-temperature changes >10°C (glaciation
to Holocene).
Torun-1 Working Group: Marta Wróblewska, Jacek Majorowicz, Jan Szewczyk, Jan Šafanda, Vladimír Cermák 相似文献
16.
Analysis of factors affecting heat flow density determination in the Liaohe Basin,North China 总被引：1，自引：0，他引：1
Structural relief of the pre-Cenozoic basement and groundwater flow have been found to be the two most important factors affecting the heat flow density determinations in the Liaohe Basin. The reason for the significant effect of basement relief upon subsurface temperature and heat flow density patterns is the strong contrast of thermal conductivity between basement rock and the sedimentary cover. Simplified model computations indicate that the heat flow density in the region of basement uplift is 1.35 times greater than that in the region of depressions. Field observations indicate that the temperatures at shallow depths (less than 1200 m) are strongly perturbed by groundwater flow leading to reduced temperatures and geothermal gradients in the Neogene formation. Comparison of observed and calculated gradients reveals that reduced gradients and heat flow density occur in the groundwater recharge area whereas these parameters are enhanced in the discharge area. After taking the perturbing factors into account, a regional heat flow value of 65 ± 9 mW/m2 is obtained. 相似文献
17.
Heat flow variations with depth in Europe can be explained by a model of surface temperature changes >10°C. New heat flow
map of Europe is based on updated database of uncorrected heat flow values to which paleoclimatic correction is applied across
the continent. Correction is depth dependent due to a diffusive thermal transfer of the surface temperature forcing of which
glacial–interglacial history has the largest impact. It is obvious that large part of the uncorrected heat flow values in
the existing heat flow databases from wells as shallow as few hundreds of meters is underestimated. This explains some very
low uncorrected heat flow values 20–30 mW/m2 in the shields and shallow basin areas of the craton. Also, heat flow values in other areas including orogenic belts are
likely underestimated. Based on the uncorrected and corrected heat flow maps using 5 km × 5 km grid, we have calculated average
heat flow values (uncorrected heat flow: 56.0 mW/m2; SD 20.3 mW/m2 vs. corrected heat flow: 63.2 mW/m2; SD 19.6 m/Wm2) and heat loss for the continental part. Total heat loss is 928 E09 W for the uncorrected values versus corrected 1050 E09 W. 相似文献
18.
Characteristics and Formation Mechanism of the Geothermal Field in the North China Downfaulted Basin
Chen Moxiang Wang Jiyang Wang Ji' an Deng Xiao Yang Shuzhen Xiong Liangping Zhang Juming 《《地质学报》英文版》1990,64(3):329-343
The geothermal field is mainly controlled by the regional tectonic framework characterized by alternationsof uplifted and depressed basement. and exhibits a similar zoned distribution of temperatures. In the upliftedarea the geothermal gradient (G) and terrestrial heat flow value(q) of the Cenozoic sedimentary cover are rela-tively high, with G=3.5-5.0℃/100m and q=63-84mW/m~2; whereas in the depressions they are rela-tively low, with G=2.7-3.5℃/100m and q=46-59mW/m~2. In the whole region, G=3.58℃/100m and q=61.5±13.4nW/m~2, indicating a comparatively high geothermal background and the presence of localgeothermal anomalies. A comparison of the results of mathematical simulation of the geothermal field with themeasured values shows a good agrecment between them. The geothermal difference between various tectonicunits is caused chiefly by the lateral and vertical variation of thermal properties of shallow crustal rocks. Thisphenomenon can be regarded as the result of redistribution of relatively uniform heat flows from the deep crustin the surficial part of the crust in the process of their upward conduction. 相似文献
19.
FENG Renpeng ZUO Yinhui YANG Meihu ZHANG Jiong LIU Zhi ZHOU Yongshui HAO Qingqing 《《地质学报》英文版》2019,93(2):283-296
Owing to the lack o f terrestrial heat flow data, studying lithospheric thermal structure and geodynamics of the Yingen-Ejinaqi Basin in Inner Mongolia is limited. In this paper, the terrestrial heat flow o f the Chagan sag in the YingenEjinaqi Basin were calculated by 193 system steady-state temperature measurements of 4 wells, and newly measuring 62 rock thermal conductivity and 20 heat production rate data on basis o f the original 107 rock thermal conductivity and 70 heat production data. The results show that the average thermal conductivity and heat production rate are 2.11 ±0.28 W/(m.K) and2.42±0.25 nW/m~3 in the Lower Cretaceous o f the Chagan sag. The average geothermal gradient from the Lower Suhongtu 2 Formation to the Suhongtu 1 Fonnation is 37.6 °C/km, and that o f the Bayingebi 2 Formation is 27.4 °C/km. Meanwhile, the average terrestrial heat flow in the Chagan sag is 70.6 mW/m~2. On the above results, it is clear that there is an obvious negative correlation between the thermal conductivity o f the stratum and its geothermal gradient. Moreover, it reveals that there is a geothermal state between tectonically stable and active areas. This work may provide geothermal parameters for further research o f lithospheric thermal structure and geodynamics in the Chagan sag. 相似文献
20.
The Dniepr–Donets Basin (DDB) is a Late Devonian rift structure located within the East-European Craton. Numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin.The numerical models suggest that heat flow was relatively high during Late Carboniferous and/or Permian times. The relatively high heat flow is probably related to an Early Permian re-activation of tectonic activity. Reconstructed Early Permian heat flow values along the axial zone of the rift are about 60 mW/m2 and increase to 90 mW/m2 along the northern basin margin. These values are higher than those expected from tectonic models considering a single Late Devonian rifting phase. The calibration data are not sensitive to variations in the Devonian/Carboniferous heat flow. Therefore, the models do not allow deciding whether heat flows remained high after the Devonian rifting, or whether the reconstructed Permian heat flows represent a separate heating event.Analysis of the vitrinite reflectance data suggest that the northeastern Dniepr–Donets Basin is characterised by a low Mesozoic heat flow (30–35 mW/m2), whereas the present-day heat flow is about 45 mW/m2. 相似文献