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   594篇
  免费   5篇
  599篇
  2023年   7篇
  2021年   1篇
  2020年   14篇
  2019年   17篇
  2018年   28篇
  2017年   26篇
  2016年   24篇
  2015年   13篇
  2014年   21篇
  2013年   120篇
  2012年   15篇
  2011年   20篇
  2010年   22篇
  2009年   17篇
  2008年   11篇
  2007年   15篇
  2006年   10篇
  2005年   6篇
  2004年   3篇
  2003年   11篇
  2002年   13篇
  2001年   11篇
  2000年   12篇
  1999年   42篇
  1998年   30篇
  1997年   10篇
  1996年   4篇
  1995年   7篇
  1994年   5篇
  1993年   2篇
  1992年   3篇
  1991年   3篇
  1990年   3篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   4篇
  1982年   4篇
  1981年   4篇
  1980年   6篇
  1979年   2篇
  1978年   4篇
  1977年   6篇
  1976年   1篇
  1975年   3篇
  1967年   1篇
  1966年   1篇
排序方式: 共有599条查询结果,搜索用时 15 毫秒
21.
22.
    
Tie-rods are essential structural elements, which have been employed for centuries in masonry historical buildings, either during the construction or in successive strengthening interventions, with the aim of containing dangerous horizontal actions. The actual work conditions of these tie-rods, which are strongly influenced by their load history, are difficult to be quantified theoretically, and an effective method for their measure is of great importance in order to ensure the efficiency of these elements during the time and the stability of the entire building. Common measurements are often carried out adopting models based upon significant simplifications, like, for example, hinges at the extremities. These assumptions, rarely represent the real work conditions for anchorages. In this work, a non-destructive testing method is presented, based upon sophisticated dynamical models that can take into consideration many of the circumstances neglected by the simplified models. Four case studies are extensively described, trying to embrace the most common situations in term of peculiar features of the building, structural configuration, and load history. The discussion of the results yields the safety margin of the rod with respect to the material failure and provides important indications about the overall stability of the whole building.  相似文献   
23.
24.
    
This paper addresses the interaction between information technology (IT) and agglomeration. The literature distinguishes two types of interactions, namely a substitution effect and a complementarity effect. We conceptualise a third effect, namely a ‘spillover’ mechanism, by which IT allows places in close proximity of large cities to ‘borrow size’ and sustain greater product variety. We test these mechanisms using detailed data on restaurant cuisine variety in the Netherlands, and the IT dimension is measured through the use and penetration of online restaurant reviews. We find that IT complements cuisine variety in cities, and induces spillovers to smaller places near larger ones, allowing smaller places to sustain ‘rare’ cuisines that were traditionally only present in larger cities. As such, IT leads to the spread of agglomeration benefits such as local product variety over larger territories.  相似文献   
25.
Grasslands pose a particular problem for archaeological survey involving artifact assessment, as no material is plowed up to the surface. Although finds in molehills are often the only source of information available on sites with such low visibility, an archaeology of molehills has thus far been largely disregarded. Yet, by applying a low-cost and time-efficient methodology, both the potential and the pitfalls of molehill archaeology come to the forefront. At the medieval harbor site of Monnikerede, it was possible to assess material culture and to locate certain structural elements. However, when artifact densities were compared with the underlying geophysical anomalies, a more complex relationship appeared at the level of individual features.  相似文献   
26.
    
Roman plasters sampled from different houses at the archaeological site of Herculaneum, Italy, (2010–12) were studied by means of petrography, thermal analysis and X‐ray fluorescence. Herculaneum plasters are composed by preparatory layers (arriccio) with a thickness of several centimetres and are based on a calcitic binder and volcanic scoriae as aggregates, covered by a thin final layer characterized by a low granulometry. Most of the sampled plasters can be placed into two groups based on the aggregate composition and classified as marmorino or intonachino. However, a similar aggregate composition did not induce superimposable thermal behaviour, thus suggesting that the samples underwent different ageing/weathering processes, with a consequent change of the ratio among the components.  相似文献   
27.
    
Radon (Rn) is a potentially toxic gas in soil which may affect human health. Assessing Rn levels in soil gas usually requires enormous efforts in terms of time and costs, since the sampling protocol is very complex. In most cases, the variable under study is sparsely sampled over the domain and this could affect the reliability of the spatial predictions. For this reason, it is useful to incorporate, into the estimation procedure, some auxiliary variables, correlated with the in soil gas Rn concentrations (primary variable) and more densely available over the domain. On the basis of this latter aspect, it is even better if the covariates are derived from a geographical information system (GIS). In this article, the Rn sampling protocol used during a measurement campaign planned over a risk area is described and the process of deriving GIS covariates considered as secondary information for predicting the primary variable is clarified. Then, multivariate modeling and prediction of the Rn concentrations over the domain of interest are discussed and a comparative study regarding the performance of the prediction procedures is presented. Rn prone areas are also analyzed with respect to urban and school density. All these aspects can clearly support decisions on environmental and human safeguard.  相似文献   
28.
    
Particle-induced X-ray emission (PIXE), X-ray diffraction (XRD), electron microprobe analysis (EDS) and scanning electron microscopy (SEM) analytical techniques were used to characterize surface paints in pre- and post-fired Aguada Portezuelo decorated pottery. Surface paintings in black, white, red, brown, burgundy and ochre were analysed. Major, minor and trace elements were detected by PIXE, whereas XRD and SEM-EDS gave information on the main mineral phases and the characteristic morphology for each analysed pigment. The results obtained indicate that the main colour groups can be easily discriminated by PIXE, and they are characterized by only one pigment for each colour: hematite (red) and manganese mineral oxides (black), respectively, whereas white pigments are characterized by calcite, ghelenite and gypsum.  相似文献   
29.
Aspects of Roman pottery production at the workshops of Kontich, Tienen, Rumst, Grobbendonk and Clavier-Vervoz in the Civitas Tungrorum of central Belgium are explored. A total of 150 wasters from five sites were studied macroscopically, as well as via a combination of thin-section petrography, geochemistry and scanning electron microscopy, in order to gain insights into ceramic technology and aspects of the organization of production. Particular emphasis was given to the individual technological sequences and shared strategies of raw material selection, paste preparation and firing employed at the five adjacent sites. The integration of petrographic and geochemical data permitted the establishment of compositional reference groups for the Roman kiln sites of Civitas Tungrorum, which can be used to track their products within the surrounding landscape.  相似文献   
30.
In north-western Patagonia, obsidian was used during the entire Holocene, and its importance increased with time. Recent fieldwork discovered a new obsidian source located in the Río Grande, which was called ‘Coche Quemado' (CQ). The results indicate that the CQ source has a different geochemical signal than all other sources in the region. Its use is spatially restricted to piedmont and, to a lesser extent, the plains. Chronologically, CQ was exploited in the middle and late Holocene, and its use accounts for a range of spatial distribution between 150 and 200 km.  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