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   1963篇
  免费   352篇
  2024年   2篇
  2023年   22篇
  2022年   5篇
  2021年   22篇
  2020年   50篇
  2019年   129篇
  2018年   160篇
  2017年   153篇
  2016年   197篇
  2015年   124篇
  2014年   139篇
  2013年   406篇
  2012年   111篇
  2011年   118篇
  2010年   93篇
  2009年   58篇
  2008年   86篇
  2007年   75篇
  2006年   50篇
  2005年   23篇
  2004年   42篇
  2003年   30篇
  2002年   21篇
  2001年   27篇
  2000年   35篇
  1999年   6篇
  1998年   18篇
  1997年   18篇
  1996年   14篇
  1995年   15篇
  1994年   11篇
  1993年   3篇
  1992年   6篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1987年   4篇
  1986年   3篇
  1985年   4篇
  1982年   5篇
  1980年   3篇
  1979年   2篇
  1977年   6篇
  1976年   2篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
  1969年   1篇
  1968年   1篇
  1951年   1篇
排序方式: 共有2315条查询结果,搜索用时 15 毫秒
991.
The results of the first elemental and structural physicochemical analyses (SEM–EDX, TXRF, XRD, FTIR, GC and EDXRF) of Early Neolithic red pigment samples from the region of Valencia confirm one of the earliest uses of cinnabar (HgS) in Spain (5300 to 5000 cal bc ). They also inform on the storage of massive quantities of hematite and the development of specific technologies of hematite‐based paint production and use. The samples were recovered at the three most significant Early Neolithic sites of the Mediterranean coast of Spain: Cova de l'Or (Beniarrés, Alacant), Cova de la Sarsa (Bocairent, Valencia) and Cova Fosca (Vall d'Ebo, Valencia), which together have provided the most important European collection of Cardial ceramic ware (chronoculturally diagnostic of the Early Neolithic).  相似文献   
992.
The main objective of this study was to analyze spatially and temporally groundwater level changes using geographic information systems and spatial analysis with respect to urban development, groundwater withdrawal, and groundwater recharge potential. The study focused on Waukesha County in southeastern Wisconsin, where urban development has been accelerating while groundwater has been declining over the last several decades. We analyzed data about groundwater withdrawal, groundwater level, land use/land cover, and precipitation utilizing correlation analysis, geographically weighted regression, land use change analysis, and map overlay. Our findings include the following: the extent of urban areas expanded faster in regions with high recharge potential than in those with low or moderate recharge potential; the correlation of urban growth with groundwater level is highly variable over time and space; and changes in groundwater level are strongly related to the spatial distribution of groundwater withdrawal. The study pinpointed the need to consider the spatial unevenness of groundwater withdrawal in understanding the changes in groundwater level and groundwater recharge potential for better management of groundwater resources. Un análisis espacio‐temporal de los cambios de nivel de aguas subterráneas en relación con el crecimiento urbano y de las aguas subterráneas de recarga para el Condado de Waukesha, Wisconsin El objetivo principal de este estudio es analizar espacial y temporalmente los cambios del nivel de aguas subterráneas utilizando sistemas de información geográfica (SIG) y análisis espacial con respecto al desarrollo urbano, la extracción de agua subterránea, y el potencial de recarga. El área de estudio es el condado de Waukesha, en el sureste de Wisconsin, donde el desarrollo urbano se ha acelerado mientras que las aguas subterráneas han disminuido en las últimas décadas. Se analizaron los datos sobre la extracción y nivel de aguas subterráneas, la cobertura vegetal/uso del suelo, y la precipitación utilizando un análisis de correlación, una regresión ponderada geográficamente (geographically weigted regression ‐GWR), un análisis de cambio de uso del suelo, y la superposición de mapas (map overlay). Los resultados muestran que: (1) la extensión de las zonas urbanas se incrementó más rápidamente en regiones con alto potencial de recarga que en áreas con potencial de recarga de bajo o moderado; (2) la correlación entre el crecimiento urbano y el nivel de aguas subterráneas es muy variable tanto temporal como espacialmente; y, (3) los cambios en el nivel de aguas subterráneas están fuertemente relacionados con la distribución espacial de las actividades de extracción del recurso. El estudio identificó la necesidad de considerar la irregularidad del patrón espacial de la extracción de aguas subterráneas con el fin de mejorar la comprensión de los cambios en el nivel y el potencial de recarga y así promover una mejor gestión de los recursos hídricos subterráneos. 本研究主要目的在于通过地理信息系统(GISs)和空间分析的时空视角,对城市发展的地下水水位变化,地下水开采和地下水潜在补给进行分析。本文研究区为威斯康星州东南部的沃基肖县,该区在过去近几十年里城市快速增长而地下水急剧减少。通过地下水开采、地下水水位、LUCC(土地利用/土地覆盖LULC)和降水的数据分析,采用方法包括相关分析、地理加权回归模型(GWR)、土地利用变化分析和地图叠加分析。研究结果包括:(1)高地下水补给的城市地域范围的扩大幅度快于中等或低补给地区;(2)城市增长与地下水水位的相关性在时间和空间上是高度变化的;(3)地下水开采的空间分布与地下水位的变化呈强相关。研究精确地指出,为更好管理地下水资源,在理解地下水位变化和地下水潜在补给时需考虑地下水开采的空间不均匀。  相似文献   
993.
994.
995.
ABSTRACT This paper examines the relationship between the level of public infrastructure and the level of productivity using panel data for the Spanish provinces over the period 1985–2004, a period that is particularly relevant due to the substantial changes occurring in the Spanish economy at that time. The underlying model used for the data analysis is based on the wage equation, which is one of a handful of simultaneous equations which when satisfied correspond to the short‐run equilibrium of New Economic Geography (NEG) theory. This is estimated using various spatial panel models with either fixed or random effects to allow for individual heterogeneity. Using these models, we find consistent evidence that productivity depends directly on the public capital stock endowment of each province, but also there is evidence of negative spillover effects from changes in capital stock in neighboring provinces.  相似文献   
996.
In 2008, the Ecuadorian Constituent Assembly became the first juridical body in the world to legalize what Michel Serres might have called a ‘natural contract.’ With the assistance of the U.S.‐based Community Environmental Legal Defense Fund, representatives at the Assembly in July of 2008 re‐wrote their 1998 constitution to include a landmark series of articles delineating the rights of nature — a notion long familiar to Indigenous communities in the Andean region, actively propagated by anthropologists like Claude Lévi‐Strauss at the French National Assembly as early as the 1970s, and often mocked by mainstream Western jurists for its conceptual confusion about the sorts of entities that can properly be said to have rights. Drawing on the experiences of activists currently engaged in the first national‐level lawsuit to make use of these rights as well as a range of both activists and non‐activists involved in alternative implementations of them, the article explores the possibilities, limitations, and paradoxes of this extension of rights‐based discourse. At a time when the natural world is increasingly being talked about at the United Nations and elsewhere not as a ‘rights‐holder,’ but as an ‘ecosystem services provider,’ I suggest that while the discourse of ‘rights' signals promising shifts in how Andean governments are conceptualizing agency and responsibility in ways that productively break with the trend toward marketization, it also runs the risk of providing the administration with symbolic cover for its intensifying commitment to what Eduardo Gudynas has called, a ‘new extractivism.'  相似文献   
997.
This paper discusses the rock art site of Almulihiah in north Saudi Arabia. The site consists of many carved rock panels of human and animal figures. The drawings depict camels (22%), ibex (10%) and ostrich (8%), although other animals such as goats, lizards and oryx are also present. An attempt is made to date the site by comparing it with other petroglyph sites in the country. The paper concludes with a discussion of the drawing styles present.  相似文献   
998.
999.
The aim of this work is to help gain a better understanding of the research conducted on territorial agglomerations of firms at a multidisciplinary level. To this end, an analysis was performed of the contents of the most significant scientific literature on economics, management, planning and development, urban studies and geography published over the period 1997–2006. From the results, a database of 142 papers from 43 journals was then elaborated. An analysis of these works reveals the level of development of the main lines of research in this field and, consequently, makes it possible to detect the topics that require greater attention and that can be the object of future research for researchers and academics. The main conclusions include the growing number of studies conducted on the subject in recent years, as well as a greater predominance of empirical research over conceptual work, and the existence of a significant change in the topics or lines of research throughout the period under study.  相似文献   
1000.
Regional policies seek to enable regions to increase their competitiveness and development, and as such one priority Objective of activities financed by Structural Funds is higher employment, higher productivity and economic activity. How efficiently the regions apply the funds is a fundamental issue for the development and continuity of regional policies. We therefore consider that determining the efficiency of European regional policies is an issue of high importance, and this is the main aim of this study. We have considered it appropriate to use the available information to apply a mathematical technique known as Data Envelopment Analysis (DEA), which allows us to calculate the technical efficiency and inefficiency of the Structural Funds applied in the Objective 1 regions for the period 2000–2006. Furthermore, we wish to determine if the regions have been more efficient in creasing their levels of employment or in increasing productivity. Our study applies this methodology along with other methods like regression analysis, profit analysis and factorial analysis to determine the variation in the rate of unemployment and productivity in these European Regions. The study reveals that only eight regions are efficient, although none of them is run in all the models.  相似文献   
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