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   7618篇
  免费   273篇
  2020年   96篇
  2019年   121篇
  2018年   173篇
  2017年   174篇
  2016年   236篇
  2015年   150篇
  2014年   151篇
  2013年   2197篇
  2012年   216篇
  2011年   266篇
  2010年   242篇
  2009年   198篇
  2008年   177篇
  2007年   163篇
  2006年   155篇
  2005年   117篇
  2004年   98篇
  2003年   81篇
  2002年   92篇
  2001年   120篇
  2000年   105篇
  1999年   127篇
  1998年   84篇
  1997年   78篇
  1996年   66篇
  1995年   70篇
  1994年   65篇
  1993年   78篇
  1992年   70篇
  1991年   67篇
  1990年   67篇
  1989年   71篇
  1988年   61篇
  1987年   82篇
  1986年   68篇
  1985年   91篇
  1984年   87篇
  1983年   109篇
  1982年   86篇
  1981年   93篇
  1980年   90篇
  1979年   73篇
  1978年   75篇
  1977年   87篇
  1976年   66篇
  1975年   65篇
  1974年   56篇
  1973年   56篇
  1972年   52篇
  1971年   51篇
排序方式: 共有7891条查询结果,搜索用时 15 毫秒
991.
ABSTRACT The twenty‐first century will be one of intensified urbanization, on a scale never before experienced. How do urban systems and individual cities change and develop? The social sciences have many different approaches to analyzing the economic, social, and spatial dimensions of urban change. We inventory some of these approaches and their implications for public policy toward cities, urban change, and economic development.  相似文献   
992.
ABSTRACT On a sample of U.S. urbanized areas in 2000, we test theoretical hypotheses of the effect of land‐use controls on the spatial size of urban areas. We find that minimum lot‐size zoning and maximum FAR restrictions expand the urban area, while maximum lot‐size zoning, urban growth boundaries, minimum square footage limits, maximum building permit restrictions, minimum person per room controls, and impact fees contract the urban area. All of these findings are consistent with theoretical predictions although the effect of urban growth boundaries and minimum square footage limits are not statistically significant.  相似文献   
993.
Cultural landscapes were prominent during the Early Roman period when agronomic knowledge allowed the spread of intensive land exploitation in most of the available land. The aim of this contribution is to explore whether for the Campania region (Southern Italy) archaeoenvironmental data would support continuity or change in the cultural landscape of Roman tradition in the 4th and 5th centuries. To do so, new data from two sites located on the northern slopes of the Vesuvius, both buried by the AD 472 eruption have been investigated. Charcoal analysis, 14C dating, and chemical analysis of organic residues were carried out in order to study the landscape and the food production at these sites. The results suggest the persistence of the Roman cultural landscape until the 4th and 5th centuries in this area. The landscape is in fact strongly marked both in agriculture and woodland exploitation and management, being characterized by managed chestnut forests as well as valuable cultivations of walnut, large vineyards, olive groves, and probably orchards and crops. The integrated approach with archaeobotanical and archaeometric analyses proves to be a powerful method for the study of the past landscapes, providing a good insight into the environment. Furthermore, this study provided the most ancient evidence of chestnut silviculture for wood.  相似文献   
994.
Integrating portable X-ray fluorescence (pXRF) instrumentation into archaeological investigations has generated as much interest as skepticism because several characteristics of the technique limit analytical accuracy and precision. This paper seeks to explore inter-instrument performance in order to assess the potential pXRF instrumentation has in examining the elemental composition of lithic raw materials. Two pXRF instruments, Delta and Omega models both manufactured by Olympus Innov-X Systems, were utilized to obtain the trace element signatures of five fine-grained volcanic sources and four obsidian sources in the Great Basin. We compared the two portable instruments to a wavelength-dispersive instrument extensively calibrated with geologic standards and to a commercial benchtop energy-dispersive system. Our results suggest that the relationships between the data produced by these different instruments are complex, and as we look to the future of pXRF use in archaeological analysis we argue that that the same strict protocols applied in laboratory-based XRF analyses, involving instrument calibration, evaluation of inter-instrument performance, and comparison to accepted geologic standards, need to be applied in pXRF analysis.  相似文献   
995.
Uranium-series age estimates for rock art in southwest China   总被引:1,自引:0,他引:1  
We report the first uranium-series age estimates for rock art in China. Calcite bracketing a paint layer was used to constrain the age of a naturalistic outline hunter-gatherer painting in the Jinsha River area of northwest Yunnan Province (southwest China). The rock paintings in this region are unique in style and content compared with other bodies of rock art in China, which are dominated by Neolithic subject matter. The minimum and maximum ages were determined using isochron techniques on multiple samples of calcite from above and beneath the paint layer. A large painted deer head was dated to between 5738 and 2050 years. This painting and underlying flowstone are superimposed on older paintings that suggest the older paintings are at least 3400 years old, if not older than 5738 years. The results indicate for the first time that Jinsha River rock art is older than other forms of rock art in the region and show that rock art likely extends back to at least the transition from the Palaeolithic to Neolithic in this part of China.  相似文献   
996.
The results of a minero-petrographic and isotopic study carried out on the marbles of statues and architectural elements belonging to several buildings on the “Hadrian's Villa” site (the so-called Canopus, the Peschiera, the Sala dei Pilastri Dorici and the Serapeum) are presented here as part of an ongoing archaeometric project which considers the determination of the provenance of all the marble decorations of the Villa complex. Analytical data indicate the prevailing presence of marmor lunense and the use of Pentelic and Thasian marbles for architectural elements in a few parts of the Sala dei Pilastri Dorici, the Peschiera and the Serapeum; no significant use is made of Proconnesian marble, probably the most inexpensive of the time. Analysis of sculptures from the Canopus showed that those of the Tiber and Nile gods were made of Parian marble, the Caryatids and Telamons of Pentelic marble and the Amazons of the precious white Dokymaean marble.  相似文献   
997.
The early medieval period marks an important turning point in the history of glassmaking, since it comprises the transition period between the mineral-based silica-soda-lime glass of the Roman tradition and the plant ash-based glass. With the aim of expanding the knowledge on the glass recipes and technologies of this period, 37 glass samples were analyzed, originating from the archaeological excavations of San Genesio (Tuscany) and dated from the fourth to the eleventh century. The major and minor element concentrations were measured with SEM-EDX, while the trace elements were quantified with LA-ICP-MS. The results were compared with published compositions of glass samples of similar age in order to highlight differences and similarities. The results offer a very interesting view on the glass circulation in the religious/residential/manufacturing center of San Genesio in the early medieval period. Most of the glass has a typical late-Roman composition, but some glass fragments are identified as soda ash glass. These are among the earliest medieval ash-fluxed glasses ever found in the Italian peninsula.  相似文献   
998.
M. KUHLE  S. KUHLE 《Archaeometry》2012,54(3):591-601
For a long time now, historians have considered the way across the Col de Clapier as the most likely invasion route of Hannibal's army across the Alps. Mahaney et al. challenge this view by introducing a two‐tier rockfall into the discussion, which they believe is mentioned in the ancient texts and has gone unnoticed by modern scholars. Since a deposit of this kind can only be found at the Col de la Traversette—and there alone—Hannibal's crossing of the Alps, so they reason, must have followed this alternative route. However, a critical reassessment of the ancient texts and a closer look at the geomorphological situation clearly show that this interpretation is unwarranted.  相似文献   
999.
This study presents the first ever lead isotope ratio data for copper ore samples (malachite and azurite) from the Sierra El Aramo (Asturias, northwestern Spain). The aim of this study was to supplement information in the existing reference database on the lead isotopic composition of Spanish ores. The Sierra El Aramo is particularly important because, while no data for the Asturian ores have been published so far, this northern province of Spain has played a significant role in terms of copper exploitation and metallurgy since the Copper Age.  相似文献   
1000.
Intra‐tooth sequential analysis of enamel δ18O is currently used to investigate birth seasonality in past animal populations, offering new insights into seasonal availability of animal resources, herd management and seasonality of site occupation. Reference data sets are still required to address two major difficulties: (1) that inter‐individual variability in the record of the seasonal cycle is affected by tooth size; and (2) that the season of birth cannot be directly estimated from the timing of tooth growth, because of a delay in enamel mineralization. We present a data set acquired on the lower second molar of 10 modern sheep from Rousay (Orkney) born within a few weeks of each other in April/May and submitted to the same environmental conditions until death. All sheep have recorded a sinusoidal pattern of δ18O variation spanning approximately a year. From the difference between the expected and the measured time sequence, the delay of enamel mineralization is estimated to be 5–6 months. The data set is then described using a model mainly based on a cosine function. The period, corresponding to the length of the M2 crown formed over a year, averaged 35.8 mm. A very slight variation of tooth growth rate with time and no attenuation of the isotopic signal towards the cervical margin of the crown could be detected in this data set. The lowest δ18O values, corresponding to the sheep's first winter, were tracked at a distance from the enamel/root junction that varied between 23.0 and 30.3 mm (xmin mean = 27.6 mm); the highest δ18O values, corresponding to the sheep's second summer, were between 6.3 and 11.6 mm (xmax mean = 9.9 mm). Most of the variability can be attributed to tooth size. When normalized on the period, xmin and xmax are 0.28 (± 0.05) and 0.78 (± 0.05) on average, meaning that the Rousay sheep have recorded the minimum and maximum δ18O values on average at 78% and 28%, respectively, of the end of the periodic cycle recorded in the second molar.  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