全文获取类型
收费全文 | 503篇 |
免费 | 17篇 |
出版年
2020年 | 5篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 20篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 207篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 3篇 |
2001年 | 8篇 |
1998年 | 6篇 |
1995年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1964年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有520条查询结果,搜索用时 171 毫秒
51.
52.
53.
Urban Growth in the 1990s: Is City Living Back? 总被引:3,自引:0,他引:3
The 1990s were an unusually good decade for the largest American cities and, in particular, for the cities of the Midwest. However, fundamentally urban growth in the 1990s looked extremely similar to urban growth during prior post–war decades. The growth of cities was determined by three main trends: (1) cities with strong human capital bases grew faster than cities without skills, (2) people moved to warmer, drier places, and (3) cities built around the automobile replaced cities that rely on public transportation. Although the negative impact of population density diminished slightly in the 1990s, there is no real evidence for a return to large, dense cities. 相似文献
54.
ABSTRACT There is a strong connection between per‐worker productivity and metropolitan area population, which is commonly interpreted as evidence for the existence of agglomeration economies. This correlation is particularly strong in cities with higher levels of skill and virtually nonexistent in less skilled metropolitan areas. This fact is particularly compatible with the view that urban density is important because proximity spreads knowledge, which either makes workers more skilled or entrepreneurs more productive. Bigger cities certainly attract more skilled workers, and there is some evidence suggesting that human capital accumulates more quickly in urban areas. 相似文献
55.
56.
The Nene Valley, in eastern central England, was a major pottery production centre in the Roman period. Many kiln sites have been identified in the Lower Nene Valley region and, although comparatively less is known about production in the Upper Nene Valley, substantial amounts of mortaria and other coarse wares have been recovered during excavations at Roman sites in the area, and much of it is thought to be locally made. However mortaria made in the Upper and Lower Nene Valley can be difficult to tell apart, and many also have similar forms and fabrics to mortaria produced in Mancetter–Hartshill, Warwickshire. Therefore ICP analysis was used in an attempt to identify the products of different regions. 相似文献
57.
Andrew A. Meharg Kevin J. Edwards J. Edward Schofield Andrea Raab Joerg Feldmann Annette Moran Charlotte L. Bryant Barry Thornton Julian J.C. Dawson 《Journal of archaeological science》2012,39(3):717-727
Tin, as a constituent of bronze, was central to the technological development of early societies, but cassiterite (SnO2) deposits were scarce and located distantly from the centres of Mediterranean civilizations. As Britain had the largest workable ore deposits in the ancient Western world, this has led to much historical speculation and myth regarding the long-distance trading of tin from the Bronze Age onwards. Here we establish the first detailed chronology for tin, along with lead and copper deposition, into undisturbed ombrotrophic (rain-fed) peat bogs located at Bodmin Moor and Dartmoor in the centre of the British tin ore fields. Sustained elevated tin deposition is demonstrated clearly, with peaks occurring at 100–400 and 700–1000 calendar years AD – contemporaneous with the Roman and Anglo-Saxon periods respectively. While pre-Roman Iron Age tin exploitation undoubtedly took place, it was on a scale that did not result in convincingly enhanced deposition of the metal. The deposition of lead in the peat record provides evidence of a pre-Roman metal-based economy in southwest Britain. Emerging in the 4th century BC, this was centred on copper and lead ore processing that expanded exponentially and then collapsed upon Roman colonization during the 1st century AD. 相似文献
58.
Magnetometry has been little used on Arctic archaeological sites, but has great potential to help us understand site structure by identifying buried features and providing additional detail about the construction and use of visible surface features. In the Arctic environment, magnetometer surveys have to deal with the effects of permafrost activity on soils and the potential influence of glacial erratics of varying geological composition. Here, we present the results of magnetometer surveys of a non-cultural site with periglacial features and two archaeological sites located in the Canadian low Arctic. Despite considerable “noise” apparently caused by igneous erratics, the surveys successfully identified several frost features and a range of archaeological feature types. They also appear to have located buried archaeological features and identified activity areas within some dwellings. These preliminary results suggest that the technique is worth pursuing on northern sites. 相似文献
59.
60.
Gordon Morgan Holmes, MD, MRCP was an Irish born neurologist who received his medical education at Trinity College, Dublin, Ireland. He was trained in neuroanatomy and neuropathology at the Senckenberg Institute, Frankfort-Am-Main by Ludwig Edinger. He then returned to serve as a Registrar (House Officer) mentored by Richard Gowers and John Hughlings Jackson at the National Hospital, Queen Square, London. He collaborated with Thomas Granger Stewart in describing the loss of recoil in patients with cerebellar hemispheric tumors in 1904. Volunteering in 1914 for frontline hospital duty, he examined soldiers who had injuries to their occipital area causing hypotonia, dysmetria, staggering gait, and falling to the side ipsilateral to their injured cerebellar hemisphere. Holmes discovered that increasing the pace of the finger-nose manuever and applying slight resistance to a moving limb attenuated the dysmetria. Continuing observation of these patients afforded him to describe the evolution of their injuries to include increasing tremor and decreasing hypotonia. Holmes first attached levers to the limbs of hispatients to record their movements on a moving smoked paper kymograph. In 1939 he published photograh tracings made by low mass minature light bulbs attached to ataxic limbs that showed thehpometira and hypometria of their movements ipsilateral to their damaged cerebellar lobes. Holmes made sigficant contributions to understanding of the physiology of the human cerebellum. 相似文献