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1.
Susan P. Mains 《GeoJournal》2004,59(4):253-264
For some time the US-Mexico border has been a symbol – and site – of conflict, collaboration, and transnational mobility.
Related to the border, the topic of undocumented immigration, and Mexican migrants in particular, has received considerable
attention in US mainstream media. Cinema in particular, provides a context for producing and interrogating discourses of nationalism,
nativism, and fear. The cinematic examples I draw on illustrate an ongoing fear (and terror) about borders and border crossing of various forms. In this paper I explore how narratives of borders and
nationhood are mapped onto immigrant bodies and border spaces through specific filmic representations. In order to undertake
this study I focus on three cinematic examples exploring immigration at the US-Mexico border – Touch of Evil, The Border and Lone Star. I examine how concepts of borders, race, and gender, and tropes of ‘The South’ are reterritorialized around immigrant bodies
and specific locales. I argue that an inability to control and ‘fix’ boundaries around possible ‘threats’ to specific US spaces
and identities is counteracted by displacing this fear onto more easily marked targets that are viewed as posing challenges
to US national (and personal) security, i.e., undocumented immigrants. At the same time, cinematic images illustrate that
the threats and spaces for immigrants themselves become increasingly marginalized, blurred, and frequently erased.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Kinematics of shear bands 总被引：2，自引：2，他引：0
Dimitrios Kolymbas 《Acta Geotechnica》2009,4(4):315-318
Shear bands appear at limit states of soil bodies. They are analysed as thin zones of localised deformation that takes place
as simple (i.e. dilatant) shear. It can be observed, however, that shear bands are discontinuous and also may be “reflected”
at rigid boundaries. These phenomena appear as incompatible with the assumed shear deformation. The analysis in this paper
reveals the kinematics of such “incompatibilities” in terms of continuous deformation fields. 相似文献
3.
Joy K. Adams 《GeoJournal》2010,75(3):303-314
Sustained migration of Hispanics and Anglos into Texas’s historical “German belt” has contributed to a significant decline
in the proportion of Central Texans claiming German ancestry. Under these circumstances, ethnic festivals are playing an increasingly
important role in maintaining the German-American identity of many of the region’s people and places. Organizers and participants
frequently tout the events’ inclusiveness, claiming that anyone can temporarily cross ethnic boundaries to become “German
for a day” within the festival context. However, participant observation and surveys of festival participants in three historically
German-American communities (Brenham, Fredericksburg, and New Braunfels) suggest that ethnic-themed events mirror processes
of racialization that have persisted in the region for more than 150 years. In this paper, I argue that, in helping to construct
“German” identities for the region’s people and places, German-themed events in Central Texas are implicitly involved in the
construction of “non-German” and, by extension “non-white,” ethnic identities. Further, event participation patterns reflect
a long-standing black-white racial dichotomy in the region. Within this ethnoracial hierarchy, Hispanics have long occupied
a liminal status that is reflected by their involvement in the production and consumption of German-themed events. I contend
that Hispanics’ participation in German heritage festivals reflects not only a historical process of “whitening” their racial
status but their increasing presence and power within the region. 相似文献
4.
Today, various types of fair trade systems propose new forms of relationships between producers and consumers. If several
studies have provided accurate understandings of consumers’ motivations to buy fair trade products, the specific kinds of
consumer involvement that are emphasized in those systems remain partly unknown. In France, controversies about the regulation
and organization of fair trade with producers from Southern countries has led to broader debates about how consumers can best
express their solidarity with producers. In these debates local food networks are often portrayed as good examples of fair
trade and as having potential to redefine the role of the consumer in the marketplace (or in commercial relations). Based
on examination of the type of mechanisms used to enrol consumers in local and fair trade networks, we have distinguished two
main kinds of consumers’ involvement. The first one may be called “delegation” and is based on market mechanisms. The second
one is called “empowerment” and is based on contractual mechanisms between consumers and producers and on the construction
of collective choices. This latter kind of consumer involvement points out the capacity of alternative food networks to empower
consumers in a more broadly political sense.
相似文献
| Claire LamineEmail: |
5.
Evelyn J. Peters 《GeoJournal》2006,65(4):315-327
Recent work in political geography has emphasised how scale plays a role in constituting relationships and identities. Historically,
the Canadian federal government has taken responsibilities for social services for First Nations people on reserves, leaving
this responsibility to provinces for First Nations people in cities. This constitutes First Nations women as individuals with
Aboriginal rights only on reserves, and as part of mainstream society in urban areas. First Nations women have challenged
the definitions of their identities embedded in these scales of service provision. In presenting alternative geographies for
organising the provision of services, they demonstrate the importance of paying attention to the diversity of women’s everyday
geographies in the city.
This is a phrase from Vicki English’s (1993) presentation to the Royal Commission on Aboriginal Peoples, where she argues that treaty rights to housing, education, medicare
and other services should not be confined to the boundaries of reserves.
I use the term “First Nations” to refer to people who identify themselves as such, including people who are and are not registered
pursuant to the Indian Act. By “Aboriginal peoples” I mean the descendants of the indigenous people in Canada, including First Nations people, Métis
and Inuit. The Census of Canada uses the term “North American Indian” to refer to First Nations people, and I employ this
terminology for clarity in some cases.
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6.
In this work some examples of “twisting” of the Earth in the geologic past are given: displacement of the northern parts of
the global submeridional structures to the west relative to their southern parts; the rotation of the “geodynamic pair” of
Siberia-Laurentia in the Proterozoic; sinistral displacement of the Northern Hemisphere relative to the Southern Hemisphere
after the collapse of the last Pangaea; the equatorial rotation of the continental plates; oblique orientation of the global
network of planetary fracturing; an inclination of the axis of submeridional compression; sinistral “beveling”; the dextral
“twisting” of Venus. All these examples confirm the idea of possible sinistral “twisting” of the Earth that has been proposed
by many authors. The cause of such “twisting” is unclear, although it is likely connected with the Earth’s rotation around
its axis. Some of these examples show that many paleomagnetic reconstructions can be usefully discussed in a tectonophysical
aspect. Moreover, in connection with this data, the development of a new scientific field, called “paleomagnetic tectonophysics”, is possible. 相似文献
7.
Yu. B. Gladenkov 《Stratigraphy and Geological Correlation》2010,18(6):660-673
The problems of zonal stratigraphy of the early 21st century are discussed. The great advances achieved in recent years in
using zones in geological practice are noted. At the same time, attention is drawn to the controversies existing in the interpretation
of the concepts “biostratigraphic zone” and “chronozone,” in the methods of drawing the boundaries of such zones, and in the
assessment of the spatial scale of zones and in the understanding of them as stratigraphic units. 相似文献
8.
Government policies intended to reduce flood losses can increase the potential for catastrophe by stimulating development
inside the floodplain, a phenomenon referred to as the “safe development paradox.” New Urbanist design has the potential to
both exacerbate and alleviate flood risks. Because they are built at relatively high densities, New Urbanist developments
can exacerbate risk by placing more people and property in harm’s way. Conversely, New Urbanist design features theoretically
better enable designers of New Urbanist developments to avoid floodplain portions of project sites than designers of conventional
subdivisions. Using a sample of New Urbanist developments in the US that contain floodplain portions within their boundaries,
this paper focuses on whether and why these developments locate built structures inside the floodplain. The authors find that
roughly 30% of the developments locate structures inside the floodplain, and that the odds of locating structures inside the
floodplain increase with the proportion of the project site located inside the floodplain and decrease with the presence of
government policies that prohibit residential development in the floodplain. The authors also identify confusion among government
planners regarding the distinction between pre and postconstruction floodplain boundaries. A subset of New Urbanist developments
is found to have built structures located outside the postconstruction floodplain boundary, but inside the preconstruction
floodplain boundary. This finding is cited as an example of the “safe development paradox” in action. The authors recommend
changes in New Urbanist design codes and local government floodplain management to increasingly direct new development away
from the floodplain. 相似文献
9.
This paper demonstrates techniques for pre-eruption prediction of lahar-inundation zones in areas where a volcano has not
erupted within living memory and/or where baseline geological information about past lahars could be scarce or investigations
to delimit past lahars might be incomplete. A lahar source (or proximal lahar-inundation) zone is predicted based on ratio
of vertical descent to horizontal run-out of eruptive deposits that spawn lahars. Immediate post-eruption distal lahar-inundation
zones are predicted based on “pre-eruption” distal lahar-inundation zones and on spatial factors derived from a digital elevation
model. Susceptibility to distal lahar-inundation is estimated by weights-of-evidence, by logistic regression and by evidential
belief functions. Predictive techniques are applied using a geographic information system and are tested in western part of
Pinatubo volcano (Philippines). Predictive maps are compared with a forecast volcanic-hazard map through validation against
a field-based volcanic-hazard map. The predictive model of proximal lahar-inundation zone has “true positive” prediction accuracy,
“true negative” prediction accuracy, “false positive” prediction error and “false negative” prediction error that are similar
to those of the forecast volcanic-hazard map. The predictive models of distal lahar inundation zones have higher “true positive”
prediction accuracy and lower “false negative” prediction error than the forecast volcanic-hazard map, although the latter
has higher “true negative” prediction accuracy and lower “false positive” prediction error than the former. The results illustrate
utility of proposed predictive techniques in providing geo-information could be used, howbeit with caution, for planning to
mitigate potential lahar hazards well ahead of an eruption that could generate substantial source materials for lahar formation. 相似文献
10.
Fezer Fritz Prof. Dr. Reichenbach Bernhard Witschel Christian MA Hell Günter Prof. Dr.-Ing. Duster Manfred Dipl.-Ing Heidrich Brigitte 《GeoJournal》1987,14(4):467-478
Airphotos have been used for topographic survey since the Twenties. The “European Space Agency” (ESA), the “Deutsche Forschungs-
und Versuchsanstalt für Luft- und Raumfahrt” (DFVLR) and “Carl Zeiss” have modified this successful technique for spacecraft
and recently have tested the system over four continents. Each of these satellite photos covers a region of 189×189 km to
the scale of 1∶800000 and may be enlarged to 1∶250000 or 1∶100000. Between the altitudes of 200 and 300 km, mapmaking or-revision
seems to be economic in zones or in countries, where existing maps are of minor quality or outdated. In this paper, examples
from deserts and semideserts in the Sudan are presented. 相似文献
11.
Jishu-bosai-soshiki, or Jishubo for short, with a literal meaning of “autonomous organization for disaster reduction”, is a neighborhood association for
disaster preparedness and rescue activity. In this paper, the role of Jishubo in the context of participatory disaster management in Japan is discussed. Although the formation of Jishubo is not legally mandated, local governments exercise a great deal of persuasion on the inhabitants of their community to organize
and participate in disaster management activities. Therefore, participants in Jishubo activities tend to be guided and mobilized with a soft touch by local governments rather than being truly self-motivated,
with the objective of reducing disaster risks in their residential areas. There have been several studies on community participatory
management conducted in a number of countries, including New Zealand, the USA and Europe, which will serve as a reference
in our study. However interesting, the cultural comparison of the “Western” and “Japanese” approaches to community disaster
management, is beyond the scope of this paper, the aim of which is to determine a case of community disaster management in
Japan. This paper addresses the background behind the development of Jishubo and discusses the uniqueness and limits of this softly mobilized participatory movement in Japan. Based on a case study in
Kishiwada City, Osaka, the motivations driving people to participate in disaster management activities organized for Jishubo members is examined. In conclusion, we derive some policy implications and suggest possible approaches for improving the
effectiveness of Jishubo and increasing the motivation of people to participate. We also propose that the roles of administrative bodies in Japan,
such as non-profit organizations, be better incorporated into community’s participatory disaster reduction activities. 相似文献
12.
Discrete multifractals 总被引：12，自引：0，他引：12
Qiuming Cheng 《Mathematical Geology》1997,29(2):245-266
The concept of multifractal modeling has been used intensively in various fields of science for characterizing measures with
self- similarity. It has been shown that multifractal modeling provides powerful tools for characterizing patterns in the
spatial distribution of geological quantities and objects. Existing multifractal models were proposed for the purpose of handling
spatially intertwined fractals with continuous fractal spectrum f(α) (or continuous codimension function C(γ)). In this paper, these conventional multifractals are termed “continuous multifractals” whereas multifractals with discrete
fractal dimensions are termed “discrete multifractals.” The properties of discrete multifractals are investigated. It is shown
by various artificial examples and a case study of stratigraphy of Ocean Drilling Program (ODP) site 645 that spatially intertwined
fractals/multifractals indeed can have discrete fractal dimensions. Histogram-and moment-based techniques are proposed for
discrete multifractal modeling and illustrated using the artificial examples. The new concept of discrete multifractals and
associated multifractal modeling yields not only techniques for characterizing multifractals with discrete fractal dimensions
but it also provides insight into the relationships between fractals, bifractals, and multifractals. 相似文献
13.
There is growing recognition among political ecologists of the need to examine shifting natural resource regimes and their
effects on livelihoods in “First World” places. This emerging literature has variously examined the “Third World within,”
the persistence of “subsistence activities” in the “First World,” and the “reterritorialization” of land tenure and access.
However, much of this work has tended to focus on traditional extractive industries in the American West, indigenous claims
to lands and resources in the U.S. and Canada, and non-timber resources on public lands. In contrast, we use a case study
of African-American sweetgrass basket-makers, associated with the Gullah culture, in South Carolina’s lowcountry to examine
the ways in which ongoing amenity-driven residential development is fundamentally reshaping resource access on private lands.
Historically, basket-makers harvested the materials (primarily sweetgrass or Mulenbergia filipes) needed for their culturally
important art form from accessible, rural, and privately held tracts of land in close proximity to their communities, but
development pressures and changes in resident interpretation of property rights has decreased access to basket-making resources.
The case is particularly illuminating, as it examines the emergence of ‘conservation subdivisions’ in the region and raises
important questions about what “rural uses” and users are being conserved through responses to exurban, suburban, and urban
development in formerly rural areas. 相似文献
14.
O. A. Bogatikov E. V. Sharkov A. V. Vesselovskii V. B. Mescheryakova 《Doklady Earth Sciences》2009,427(2):907-911
A geographic information system (GIS “Volcanic belts”) was used for analyzing the spatial and temporal relationship between
tectono-magmatic cycles in the Cenozoic that took place at the convergent plate boundaries, mostly in volcanic arc-back-arc
systems. The onset of back-arc basins and subaerial arc volcanism and their main evolutionary stages are shown to have occurred
about the same time. These processes are still ongoing, which is indicated by today’s active volcanoes, high heat flows, and
high deep-focus seismicity. The crust underlying both tectonic structures undergoes transformation, which results in a significant
thinning of the “granite” layer within the volcanic belts, whereas crust within the back-arc basins changes its properties
to the transitional (suboceanic) and oceanic type crusts. All processes that occur at the convergent plate boundaries can
be described within the arc-back-arc system, the principal dynamic components of which are the asthenospheric plume upwelling
above the continent edge and the oceanward-spreading plume head. This was accompanied by a gradual crustal thinning in the
back-arc region and the formation of areas with oceanic crust, as well as by involvement of crustal material, together with
rocks of the subducting slab, into subduction processes. As a result, the continental crust is removed from the tectonosphere
and stored in the “slab cemetery.” Only a minor portion of the crustal materials is returned to the surface as subduction-related
magmatism. 相似文献
15.
State-imposed borders inform socio-spatial identities, often encouraging divergent identities for those living of different sides of the border. However, these identities may be discursively appropriated by the groups affected by the borders, in order to manage their relations with the state. We describe how one group of aboriginal people in the Russian Far North forged a common identity based on evasion of state institutions in the 1930–1950s. This group, once articulated with state institutions and divided by the enforcement of a provincial/republican border, developed two socio-spatial identities––and employed these identities as counterhegemonic tactics to state pressures over their lifeways. As types of pressures change, the affordances that the borders provide also change, as evident in the shifting discourses of difference and similitude. 相似文献
16.
Surendra P. Verma 《Journal of Earth System Science》2000,109(1):79-88
This paper presents error propagation equations for modeling of radiogenic isotopes during mixing of two components or end-members.
These equations can be used to estimate errors on an isotopic ratio in the mixture of two components, as a function of the
analytical errors or the total errors of geological field sampling and analytical errors. Two typical cases (“Small errors”
and “Large errors”) are illustrated for mixing of Sr isotopes. Similar examples can be formulated for the other radiogenic
isotopic ratios. Actual isotopic data for sediment and basalt samples from the Cocos plate are also included to further illustrate
the use of these equations. The isotopic compositions of the predicted mixtures can be used to constrain the origin of magmas
in the central part of the Mexican Volcanic Belt. These examples show the need of high quality experimental data for them
to be useful in geochemical modeling of magmatic processes. 相似文献
17.
The sediment-hosted disseminated gold deposits in the Oinling region are of sedimentation-slight-metamorphic origin superimposed by hydrothermal reworking at moderate-low temperatures and are well comparable with the typical Carlin gold deposits in the United States.In view of the confusing concept concerning the “sediment-hosted”and “Carlin-type” gold deposits,the authors propose that the term“sediment-hosted gold deposit”should be used in a broad sense which encompasses at least the four subtypes,i.e.,the Carlin type,the metamorphic fine clastic type,the hydrothermal sedimentary type and the vein type.In oter words,the “Carlin-type”should not be used as a synonym for “sediment-hosted”but is recommended as a subtype under the general category of “sediment-hosted gold deposits” 相似文献
18.
Martin R. Lee Kim A. Waldron I. Parsons William L. Brown 《Contributions to Mineralogy and Petrology》1997,127(3):291-304
Braid microperthitic alkali feldspars in the Klokken, South Greenland and Coldwell, Ontario syenite intrusions have bulk-compositional
variations along grain boundaries called pleated rims. These, together with vein microperthites in aplites which cross-cut the syenites, have been investigated by SEM and TEM.
We distinguish two main types of pleated rims, “arched ” and “parallel-sided ”, consisting of alternating Ab- and Or-rich areas on (001), which are 0.5–300 μm in length normal to (010) and 0.2–20 μm
in width along (010). The smallest pleats, which occur on intracrystalline boundaries in Klokken feldspars, are fully coherent
and composed of low albite and low microcline. Above the heads of some of the coarser pleats, braid microperthite grades into
a film crypto- and micro-perthite and antiperthite microtexture called a “transitional zone” containing roughly planar lamellae of low albite and tweed orthoclase. During pleat development, local alternating volumes
form in which the proportions of the phases differ ( phase separation) and the morphology of the intergrowths changes from braided to straight in response to this change in local bulk composition.
Straightening is also accompanied by transformation of low microcline to tweed orthoclase. The coarsest pleats, which occur
along grain boundaries in feldspars from the Coldwell syenite, are semi- or in-coherent and have a thick coherent and semicoherent
transitional zone. Coarsening of pleats and development of the transitional zone has been facilitated by diffusion of “water”
into grain interiors. In many cases, pleated rims have suffered deuteric alteration, by dissolution–reprecipitation processes,
through the action of a water-rich fluid from the grain boundary, in which tweed orthoclase was transformed into irregular
microcline and micropores developed. Vein microperthites in aplites from Klokken, and by extension the vein microperthites
almost universal in most alkali granites, are interpreted to have formed by propagation of pleat heads across entire crystals
during pervasive interaction with water.
Received: 10 June 1996 / Accepted: 12 December 1996 相似文献
19.
Becoming “Hispanic” in the “New South”: Central American immigrants’ racialization experiences in Atlanta,GA, USA 总被引：1，自引：0，他引：1
Robert A. Yarbrough 《GeoJournal》2010,75(3):249-260
For many migrants from Latin America, “Hispanic/Latino(a)” is an identity that they encounter in the United States with which
they were unfamiliar in their home countries and must negotiate in their everyday lives in a new context. Specifically, immigrants
from Central America are unlikely to see themselves as “Hispanic” or “Latino(a)” prior to living in the United States, more
often identifying with their home country, city, town, village, or neighborhood. This paper draws on racialization theory
and twenty-seven in-depth interviews with Central American immigrants in Atlanta, GA to examine this process of identity negotiation
across the traditionally black/white racialized landscapes of a “New South” city. Interview participants adopt a racialized
Hispanic identity through a complex process involving the interplay between how they think of themselves and their perceptions
of how native-born Atlantans view them. The interview analysis presented herein demonstrates that although Central American
immigrants actively negotiate a Hispanic racialized moniker, they do so within an urban context dominated by native-born residents
whose racialized assumptions lump Spanish-speaking, brown skinned individuals into a monolithic “Mexican” category. Thus the
ways in which racialized difference is constructed in contemporary Atlanta for recent Central American immigrants is very
much bound up in such false presumptions of national identity and cultural group belonging. 相似文献
20.
Summary ?Results of experimental investigations in the dry system PtS-PdS-NiS at 1100°C, 1000°C, and 900°C are presented. The phases
observed at 1100°C are “cooperite” and a melt, at 1000°C “cooperite”, “braggite”, and a melt and at 900°C “cooperite”, “braggite”,
“vysotskite”, Ni1−xS, and a melt. At 1100°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 2.7 atomic per cent and the Pd-content
limit in Ni-free “cooperite” is 12.8 atomic per cent. At 1000°C the maximum solubility of Ni in ideal, Pd-free “cooperite”
is 3.3 atomic per cent and the Pd-content in Ni-free “cooperite” is 13.7 atomic per cent. The “braggite” composition ranges
from Pt0.56Pd0.38Ni0.06S and Pt0.59Pd0.41S in a Ni-saturated and Ni-free environment respectively to Pt0.18Pd0.80Ni0.02S and Pt0.14Pd0.86S respectively. At 900°C the maximum Ni-content in ideal Pd-free “cooperite” is 3.1 atomic per cent and the Pd-limit in Ni-free
“cooperite” is 12.5 atomic per cent. The “braggite” composition ranges from Pt0.59Pd0.29Ni0.12S and Pt0.60Pd0.40S for a Ni-saturated and Ni-free environment respectively, to Pd0.91Ni0.09S and PdS respectively. The Ni-content in “braggite” and “vysotskite” increases slightly with increasing Pt/Pd ratios and
is higher at 900°C than at 1000°C. Comparison of experimental trends with cooperite, braggite, and vysotskite analyses from
the literature implies high temperatures of formation for Pt-Pd-Ni sulphides in placers if Ni-saturation is assumed.
Received October 1, 1998;/revised version accepted September 7, 1999 相似文献
Zusammenfassung ?Synthetischer ,,Cooperit”, ,,Braggit” und “Vysotskit” im System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C Ergebnisse experimenteller Untersuchungen im trockenen System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C werden dargestellt. Bei 1100°C sind die Phasen “Cooperit” und Schmelze, bei 1000°C “Cooperit”, “Braggit” und Schmelze und bei 900°C “Cooperit”, “Braggit”, “Vysotskit”, Ni1−xS und Schmelze stabil. Bei 1100°C ist die maximale L?slichkeit von Ni in idealem, Pd-freiem “Cooperit” 2.7 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.8 Atomprozent. Bei 1000°C ist die maximale L?slichkeit von Ni in idealem, Pd-freien “Cooperit” 3.3 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 13.7 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.56Pd0.38Ni0.06S und Pt0.18Pd0.80Ni0.02S in einem Ni-ges?ttigtem und zwischen Pt0.59Pd0.41S und Pt0.14Pd0.86S in einem Ni-freien Umfeld. Bei 900°C liegt die maximale L?slichkeit von Ni in idealem Pd-freien “Cooperit” bei 3.1 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.5 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.59Pd0.29Ni0.12S und Pd0.89Ni0.08S in einem Ni-ges?ttigten und zwischen Pt0.59Pd0.40S und PdS in einem Ni-freien Umfeld. Der Nickelgehalt in “Braggit” und “Vysotskit” nimmt mit zunehmendem Pt/Pd Verh?ltnis zu und ist bei 900°C h?her als bei 1000°C. Ein Vergleich der experimentellen Trends mit Cooperit, Braggit und Vysotskit Analysen aus der Literatur weist auf eine Hochtemperaturbildung der Pt-Pd-Ni Sulfide in Seifenlagerst?tten hin, wenn man von Nickels?ttigung ausgeht.
Received October 1, 1998;/revised version accepted September 7, 1999 相似文献