首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   334篇
  免费   14篇
  国内免费   12篇
测绘学   18篇
大气科学   12篇
地球物理   59篇
地质学   137篇
海洋学   46篇
天文学   57篇
综合类   2篇
自然地理   29篇
  2024年   1篇
  2023年   1篇
  2022年   3篇
  2021年   2篇
  2020年   4篇
  2019年   9篇
  2018年   8篇
  2017年   10篇
  2016年   12篇
  2015年   10篇
  2014年   27篇
  2013年   14篇
  2012年   8篇
  2011年   18篇
  2010年   11篇
  2009年   24篇
  2008年   25篇
  2007年   15篇
  2006年   17篇
  2005年   14篇
  2004年   9篇
  2003年   8篇
  2002年   21篇
  2001年   11篇
  2000年   8篇
  1999年   2篇
  1998年   5篇
  1997年   4篇
  1996年   5篇
  1995年   2篇
  1993年   4篇
  1992年   4篇
  1991年   1篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   5篇
  1981年   2篇
  1980年   1篇
  1979年   8篇
  1978年   4篇
  1977年   6篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
排序方式: 共有360条查询结果,搜索用时 31 毫秒
221.
222.
We present a study that reconstructs the ancient courses of the Euphrates in part of the Mesopotamian floodplain west and southwest of the ancient site of Babylon. The focus is on tracing paleochannel courses, determining when these paleochannels were active, and understanding the patterns of avulsion. The research was carried out using a combination of geological, geomorphological, remote sensing, historical, and archaeological approaches. Fieldwork included “ground truthing” of the remote sensing work, manually drilling boreholes (up to 7 m in depth), sedimentary and geomorphological documentation and sample collection for radiocarbon dating. As a result, five main courses of the Euphrates in five different periods have been mapped in this area, including four previously unidentified and/or unlocated migrations that linked the different periods. The main courses are the Purattum Course (before 3100–1000 BC), the Arahtum Course (1000–125 BC), the Sura Course (125 BC to AD 1258), the Hilla Course (13th to 19th century AD), and the Hindiya Course (19th to 20th century AD). There has been an overall migration of the main channel from east to west across the study area over time. The location of avulsion nodes changed along the length of the river, mainly downstream over time, but with a cluster of avulsion events near Babylon and a notable man‐made interference in the 20th century at the Hindiya Barrage.  相似文献   
223.
Monetary valuation of ecosystem services enables more accurate accounting of the environmental costs and benefits of policies, but this has rarely been applied in developing countries. In such contexts, there are particular methodological and epistemological challenges that require novel valuation methodologies. This paper introduces a new participatory, deliberative choice experiment approach conducted in the Solomon Islands. The research aimed to determine the value people placed on ecosystem services and whether participatory interventions to elicit deeper held values influenced the preferences expressed. Results found that the initial willingness to pay for a number of tropical forest ecosystem services amounted to 30% of household income. Following deliberative intervention exercises, key ecosystem services effectively became priceless as participants were unwilling to trade them off in the choice experiment scenarios, regardless of financial cost. The group based deliberative approach, combined with participatory interventions, also resulted in significant learning for participants. This included a more sophisticated view of ecological-cultural linkages, greater recognition of deeper held values, and greater awareness of the consequences of human actions for the environment. The use of a group-based participatory approach instead of a conventional individual survey helped to overcome many of the practical difficulties associated with valuation in developing countries. Given the impact of learning on valuation outcomes, participation and deliberation should be integrated into valuation of any complex good, both in developing and developed economies. However, such a methodology raises questions about how valuation can deal with unwillingness to trade-off key ecosystem services, which results in the breakdown of monetary valuation methods. Evaluation of the appropriateness of valuation processes and methodologies for assessing deeper held values and use of mixed-method approaches will be essential to ensure policies take into account the extent to which human life is dependent on ecosystem services.  相似文献   
224.
Injury from causes such as falls, traffic accidents, or violence is a major public health issue globally. Injury prevention research aims to identify vulnerable populations and places by analyzing the spatial patterns of demographic and socio‐economic risk factors associated with elevated injury rates. The stakeholders in injury prevention and control are often distributed across government and public health institutions, non‐profits, and even the private sector (e.g. insurance firms). While this situation calls for distributed, online research tools, their implementation may conflict with health data confidentiality and license limitations for socio‐economic data. In this article, we present the Online Injury Atlas for Ontario, which was designed with the explicit goal of making use of, and contributing to, the Canadian Geospatial Data Infrastructure. We propose a service‐based architecture that integrates publicly accessible map services with protected data layers. Thereby, we demonstrate the benefits of using spatial data infrastructures alongside private data at different levels of protection. In addition, we discuss the extensive data processing needs and specific cartographic design requirements of a Web atlas in the health and social sciences domain.  相似文献   
225.
Jinfeng, previously known as Lannigou, is the largest Carlin-type gold deposit in the Yunnan–Guizhou–Guangxi region in southwestern China. Gold mineralization in the Jinfeng deposit is almost entirely fault-hosted and structurally controlled, with very little disseminated ore occurring in the adjacent host rocks. The structural elements in the Jinfeng deposit can be subdivided into 3 groups comprising NS-, NW-, and NE-striking faults and folds, with NW-striking structures controlling the overall framework of the deposit. Four tectonic stages have been recorded in the Jinfeng area, i.e., rifting, orogenic compression, lateral transpression, and lithospheric extension. A series of contemporaneous normal faults, such as the N-striking and east-dipping F1 and F7 faults developed along the edges of a carbonate platform during basin rifting (D2–T2). These structures provided an initial framework for subsequent basin evolution, and also represent the principal hydrothermal conduits. A gradual change of the compression direction during the orogenic stage (T3) from E→W to NE→SW, gave rise to the NW-striking structures, including large, tight to overturned folds such as the Huangchanggou synclinorium and associated thrusts such as the F3 fault. The development of these orogenic, predominantly NE-dipping structures, as well as accompanying NE-striking dextral shear and transform faults (such as the F2 fault) along the margin of the Laizishan Dome established the structural pattern of the deposit area. The NW-striking folds were refolded by NE-striking superimposed folds during post-collisional lateral transpression (J1) and NW–SE directed compression. Oblique stress distribution gave rise to NS-trending compression and EW-trending extension, with dilational zones developing at the intersection of the F2 and the F3 faults east of the Laizishan dome. It is these dextral- and sinistral-normal dilational zones in which gold was precipitated during the main ore-forming event at Jinfeng. Following the main ore stage lithospheric extension occurred during the Yanshan stage (J2–K) resulting in minor reverse faults that in places cut pre-existing structures. The above four main structural deformation stages mirror the evolution of the Youjiang Basin from inception to basin inversion and post-orogenic collapse and renewed extension. Significant gold metallogenesis at Jinfeng occurred during the transition from collisional compression to extensional tectonics in the early Jurassic, and is focussed into intersections of F2 and F3 and fault splays adjacent to F3. This structurally controlled gold metallogenic model is likely to be applicable to analogous settings elsewhere in the Yunnan–Guizhou–Guangxi triangle area, and has implications for the targeting of Carlin-type gold mineralization in this region.  相似文献   
226.
This overview features the chemical background on condensation phenomena of the aluminum cation in aqueous solution. The formation of polycationic molecular clusters and nanosized solid phases of aluminum oxy(hydroxi)des is interpreted with illustrative mechanisms, building a bridge between solution chemistry and solid-state chemistry. The formation of the main structural types of aluminosilicates (zeolites, clays, imogolite) is also illustrated through the aqueous chemistry of aluminum and silicates.  相似文献   
227.
This paper discusses a secondary school education initiative focussing on environment and sustainability centred on a small urban stream. This initiative has passed through an engagement stage, involving the community and other schools, and is now being embedded in curriculum learning. A cross‐curricular learning programme has been trialled and points the way toward new types of educational models within secondary schools in accord with opportunities offered by the new school curriculum. Moreover, these opportunities have wider benefits across the primary, secondary and tertiary sectors as well as within the community. These benefits include vertically structured place‐based education, win‐win partnerships, rationalising of local resources and leadership and networking. Further developments within the context of integrated catchment management are ongoing.  相似文献   
228.
Groundwater, under sustainable management policies, can be an invaluable source of water to municipal, agricultural, and industrial sectors. Management, however, can be challenging given that historically, these resources have been privately owned and minimally regulated. This research details the development of a decision support system (DSS) which couples a GIS-based multi-criteria decision-making (MCDM) scheme with simulation-optimization routines to identify suitable regions for groundwater development and optimal preferences for apportioning those supplies to areas of demand in South Texas. The developed DSS consisted of three modules: (1) a GIS-based MCDM for identifying suitable locations for groundwater production; (2) a simulation-optimization model for estimating available groundwater; and (3) a transportation optimization model for redistributing the groundwater. Applying a comprehensive suite of nine exclusionary criteria in GIS resulted in only 15,304 km2 (5,909 mi2) suitable for groundwater production out of the original ~50,500 km2 (19,500 mi2). Two ideal sites were selected in the suitable region based on proposed major water supply projects in the study area. The projected groundwater extraction rates per month varied considerably over a year emphasizing a need for storage technologies. Furthermore, a transportation optimization model, which considered cost of storage and movement, was developed and applied to obtain the most optimal scheme to transport groundwater from potential supply centers located in Bee and Kennedy counties to projected water deficit areas of San Antonio, Laredo, and McAllen, TX, USA. Lastly, a full-factorial sensitivity analysis was carried out to check the impacts of the supply and demand factors on groundwater production and transport. Policies at the supply centers had a larger impact on the total availability of water, and policies at the demand centers had a larger impact on the total cost of the management scheme. Furthermore, an analysis of total volume stored in a storage and recovery system exhibited an inverse relationship with the groundwater development (supply side) policies and a direct relationship with the demand requirements. The developed DSS proved useful for determining the most optimal siting and distribution network for groundwater sources in South Texas.  相似文献   
229.
An erosion hazard map was elaborated using geomorphologic and lithological information; this was the base to characterize the erodibility of the territory. The aim of the proposed methodology is to define the areas where more detailed studies are necessary (e.g., to estimate rates of soil erosion, mitigation measurements, land use) to prevent future problems. Field work and remote sensing data (study of historical aerial photographs and satellite images) were used to understand the geomorphologic evolution and the current processes taking place in an area; this information was used to group the units according to its lithology, dynamic and slope inclination. The map was processed using the geographical information system and categorized in zones of very high, high, moderate, low and null fluvial erosion hazards. The map covers the Metropolitan Area of San Salvador, which is experiencing serious problems of mass wasting processes, collapse and settlements of foundations. Most affected areas belong to the Tierra Blanca Joven tephras which are unsaturated and cover most of the surface; nowadays, the urban projects and infrastructure resting in this material are suffering from extensive damage. The geotechnical information on the tephras shows a decrease in strength and collapsible behavior when saturated. Due to this, the use of Quickdraw tensiometers (suction) and TMS3 (soil moisture content) is proposed for monitoring. The methodology of erosion hazard mapping correlates well with mass wasting reported in the studied area, and for this reason, it could be a good way to protect the natural resources and improve the land use.  相似文献   
230.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号