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   431篇
  免费   22篇
  2020年   7篇
  2019年   11篇
  2018年   11篇
  2017年   19篇
  2016年   14篇
  2015年   15篇
  2014年   10篇
  2013年   91篇
  2012年   13篇
  2011年   12篇
  2010年   19篇
  2009年   13篇
  2008年   6篇
  2007年   11篇
  2006年   7篇
  2005年   5篇
  2004年   9篇
  2003年   11篇
  2002年   11篇
  2001年   6篇
  2000年   9篇
  1999年   9篇
  1998年   5篇
  1997年   3篇
  1996年   5篇
  1995年   8篇
  1994年   6篇
  1991年   3篇
  1990年   5篇
  1989年   5篇
  1988年   6篇
  1987年   6篇
  1986年   8篇
  1985年   5篇
  1984年   6篇
  1983年   5篇
  1982年   4篇
  1981年   2篇
  1980年   3篇
  1979年   7篇
  1978年   3篇
  1977年   2篇
  1975年   3篇
  1974年   6篇
  1973年   5篇
  1972年   2篇
  1971年   4篇
  1970年   2篇
  1966年   2篇
  1957年   2篇
排序方式: 共有453条查询结果,搜索用时 15 毫秒
61.
62.
63.
While much recent thinking about city administration suggests tinkering with attitudes of administrators, it will be useful to review how administrators and officials encounter deeper social forces: the continuing inequalities and separations of race and class. Cases of "progressive government" experience—in Chicago; Boston; Berkeley; Santa Monica; Burlington, Vermont; and elsewhere—and of community development institutions spread more broadly through US. cities, suggest the outlines of new challenges and response by urban administrators and politicians.  相似文献   
64.
The objective of this paper is to assess whether establishments' innovation performance and innovation strategies differ by the size of the city in which they are located. Using the Canadian 1999 Survey of Innovation database (establishment-based), it was found that the rate of innovation is not correlated with city-size, but when the innovation measure takes into account the importance of innovation, then the size of the city does matter. The results show that establishments belonging to smaller cities (with populations of less than 50,000) are less likely to be associated with a world-first innovation than those located in larger cities. Four innovation strategies have been retained—Private Source, R&D, Collaboration and Public Science Base paths—and the results show that the R&D path leads to the greatest increase in the estimated probability to be associated with a world-first innovation, for almost all sectors and all city sizes.  相似文献   
65.
The objective of this paper is to compare fractal‐based parameters calculated by different fractal methods for urban built‐up areas and to link the observed spatial variations to variables commonly used in urban geography, urban economics, or land‐use planning. Computations are performed on Brussels, Belgium. Two fractal methods (correlation and dilation) are systematically applied for evaluating the fractal dimension of built‐up surfaces; correlation is used to evaluate the fractal dimension of the borders (lines). Analyses show that while fractal dimension is ideal for distinguishing the morphology of Brussels, each estimation technique leads to slightly different results. Interesting associations are to be found between the fractal dimensions and rent, distance, income, and planning rules. Despite its limitations, fractal analysis seems to be a promising tool for describing the morphology of the city and for simulating its genesis and planning. The model is robust: it replicates the urban spatial regularities and patterns, and could hence fruitfully be integrated into intra‐urban simulation processes.  相似文献   
66.
67.
Le Grand Abri aux Puces (GAP), located on the right bank of the Ouvèze River of southern France, has been known to contain well-preserved stone tools and faunal remains, but our work in 2008 was the first professional, controlled excavation at the site and has exposed at least 1 archaeological layer with a very rich and diverse faunal assemblage (23 macrofaunal species, as many for the microfauna, 27 land snail species), abundant charcoals (fragments are large and preserve small twigs with their pith and bark still intact), and stone tools with immaculate surface preservation (retaining their original freshness and preserving microscopic use wear). The information issuing from paleontology, micropaleontology, malacology, and anthracology all place the principle GAP human occupation unambiguously in a temperate climatic phase. Different biometric and biochronological characters of the fauna converge to place the layers found thus far from before the last glacial, and most likely in MIS 5e (127–117 kya). The lithic elements, mainly composed of tools of superior quality, demonstrating particular technical investment, and made from widely distributed raw material sources, lead us to hypothesize brief passages of hunting groups in the cave focused around an anticipated activity. This hypothesis will be refined and tested during further excavations.  相似文献   
68.
The 9th‐century‐AD Belitung wreck was discovered in 1998 in the Java Sea. Construction techniques rapidly confirmed that it was unlike any known Chinese or Southeast Asian vessel. The uncertainty about its origins was resolved in 2008 by timber identifications: it was constructed in the Middle East (probably Oman or Yemen). This paper, on the characterization of a dammar resin lump collected in the vicinity of the wreck, supplies additional evidence confirming the probable re‐stitching of the vessel somewhere in Asia. © 2010 The Authors  相似文献   
69.
Mineralised fruits and seeds are frequently found in archaeological sediments but their chemical nature has not been often examined. The nature and the origin of these archaeobotanical remains have to be investigated to understand their taphonomic history. Fruits or seeds can be mineralised not only by replacement mineralisation but also by biomineralisation during the plant life. The mineral components of three fossil fruits sampled on the Pleistocene site of Dmanisi were analysed and compared with their modern analogues. Analyses were carried out by means of an environmental scanning electron microscope, equipped with an energy dispersive X-ray device and by means of a Fourier transform infrared spectrometer. Biogenic carbonates and/or biogenic silica were identified in the fossil and modern fruits of some taxa. Comparison between fossil and modern specimens has shown that molecular reorganisation occurred in carbonate and in biogenic silica during fossilisation, through diagenetic processes. The resulting stable mineral structures confer an exceptional preservation to fruits in sediments. Taking into account these taphonomic specificities (transformation and differential preservation), the chronological and palaeoenvironmental aspects of the mineralised fruits are discussed.  相似文献   
70.
Weatherliness is widely considered to have been an important ability for ancient sailing vessels, yet little firm experimental or theoretical data on the matter is available. However, by drawing on a variety of sources of model-test data and trials of full-scale replicas, it is possible to establish a general picture of what might have been possible. It appears that while ancient sailing vessels may have been capable of modest windward performance in moderate conditions and with a freshly-cleaned hull, this capability quickly disappeared as the hull became fouled and/or the wind and sea conditions deteriorated.
© 2008 The Author  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