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   4476篇
  免费   169篇
  2020年   35篇
  2019年   64篇
  2018年   362篇
  2017年   267篇
  2016年   358篇
  2015年   85篇
  2014年   79篇
  2013年   792篇
  2012年   116篇
  2011年   265篇
  2010年   261篇
  2009年   140篇
  2008年   145篇
  2007年   155篇
  2006年   86篇
  2005年   72篇
  2004年   52篇
  2003年   54篇
  2002年   36篇
  2001年   63篇
  2000年   50篇
  1999年   58篇
  1998年   49篇
  1997年   44篇
  1996年   39篇
  1995年   32篇
  1994年   20篇
  1993年   46篇
  1992年   33篇
  1991年   23篇
  1990年   32篇
  1989年   36篇
  1988年   27篇
  1987年   35篇
  1986年   29篇
  1985年   32篇
  1984年   25篇
  1983年   48篇
  1982年   36篇
  1981年   33篇
  1980年   33篇
  1979年   28篇
  1978年   34篇
  1977年   37篇
  1976年   32篇
  1975年   30篇
  1974年   27篇
  1973年   25篇
  1972年   29篇
  1971年   24篇
排序方式: 共有4645条查询结果,搜索用时 15 毫秒
81.
82.
ABSTRACT. This paper uses new estimates of metropolitan factor demand and output supply functions to study how federal, state, and local fiscal policies affect metropolitan economies. We illustrate our work with findings for ten metropolitan areas in five states for changes in state corporate income taxes, local property taxes, the federal corporate income tax, an investment tax credit, interest rates, public capital stocks, output prices, and tax and regulatory policies affecting gross wages. It is clear from these simulations that a policy that is nominally the same everywhere will have repercussions that vary widely across regions and cities.  相似文献   
83.
The recent application by Burton and Krinsley (1987) of back-scattered electron (BSE) petrography to obsidians from sources located in the south-western United States established that this method can effectively resolve and characterize included micro-crystalline phases that have proven difficult to analyse by optical thin-section microscopy. In the first extension of their original study, we have examined, using BSE petrography, obsidians from island sources located in the Mediterranean, including sources known to have been exploited in prehistory. Because of the kinetic contrasts on their crystallization, these microcrystalline phases reflect the magmatic history of the obsidian, providing information about superheating, supercooling, sub-solidus processes, and other phenomena. This information is of significance for the chemical analysis of Mediterranean obsidians and also as the basis for a powerful alternative to existing non-destructive analytical methods for the sourcing of archaeological and art-historical obsidian.  相似文献   
84.
Classifying coins found during excavation is a challenging task for the archaeologist. This paper describes a multimedia system designed to assist the archaeologist by enabling him either to classify coins based on a pre-existing catalogue or to draw up his own catalogue for specific purposes. The system can also be used to train novices in the field: following an initial screening, the archaeologist only has to examine coins specifically requiring his expertise. A case study uses coins minted in Salerno 800–1200 AD, but the system has been designed to classify any set of coins by simply changing the underlying knowledge base. Very little training is required to operate the user-friendly system, which runs on multimedia PCs, as it is written using the C++ language and makes full use of the advanced features of Windows 3.11.  相似文献   
85.
86.
Ancient mortars from northern Italy, dating from the fifth to the seventeenth century AD, were examined in order to formulate an hypothesis regarding the origin of the white lumps often observed in these mortars and in other samples of the same geographical provenance. Various characterization techniques were employed, including scanning electron microscopy, X-ray powder diffraction and Fourier transform infrared (FTIR) and micro-FTIR spectroscopy.  相似文献   
87.
88.
89.
90.
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