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   3388篇
  免费   149篇
  2023年   20篇
  2020年   60篇
  2019年   65篇
  2018年   104篇
  2017年   97篇
  2016年   114篇
  2015年   78篇
  2014年   92篇
  2013年   1022篇
  2012年   81篇
  2011年   110篇
  2010年   84篇
  2009年   80篇
  2008年   76篇
  2007年   84篇
  2006年   52篇
  2005年   53篇
  2004年   48篇
  2003年   36篇
  2002年   43篇
  2001年   41篇
  2000年   50篇
  1999年   50篇
  1998年   32篇
  1997年   31篇
  1996年   33篇
  1995年   30篇
  1993年   22篇
  1992年   20篇
  1991年   28篇
  1990年   21篇
  1989年   35篇
  1988年   27篇
  1987年   27篇
  1986年   36篇
  1985年   42篇
  1984年   29篇
  1983年   37篇
  1982年   25篇
  1981年   38篇
  1980年   35篇
  1979年   35篇
  1978年   36篇
  1977年   28篇
  1976年   32篇
  1975年   25篇
  1974年   19篇
  1973年   28篇
  1972年   24篇
  1969年   22篇
排序方式: 共有3537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.
84.
85.
K. B. PERSSON 《Archaeometry》1997,39(2):441-443
A new method for soil phosphate analysis has been developed for field measurement which will increase the applicability of phosphate mapping in archaeological prospection.  相似文献   
86.
Some 630 Roman silver coins excavated at Augusta Raurica (Switzerland) have been analysed by non-destructive X-ray fluorescence and X-ray diffraction. Furthermore, the density and the weight have been determined. The measured average density of plated and massive depletion-silvered coins is lower than the density calculated from the chemical composition, whereas massive coins display equal values for both of the densities. Based on experimental X-ray investigations of modern silver (tempering, acid treatment, production of corrosion layers), the nature of corrosion products on silver, their impact on surface analysis, and aspects of wearing-off by circulation are briefly discussed.  相似文献   
87.
Senator George Sigerson (1836-1925), Dublin's first neurologist, was also a significant contributor to Anglo-Irish literature. His medical career and literary accomplishments are outlined, the focus of the article being Sigerson's friendly relationship with Charcot (with whom he corresponded), and whose Le?ons sur les maladies du système nerveux he translated.  相似文献   
88.
This paper describes the use of electron spin resonance spectroscopy to estimate the degree of heating of quartzite cobbles from hearths on the floor of the archaeological remains of an eighteenth-century Dutch colonial slave lodge. A novel technique based on the comparison of line intensities for the E’and O-2 centres in quartz distinguished successfully between cobbles which had been heated to estimated temperatures ranging from 300 °C to 450° C and controls from an adjacent stream bed. This inexpensive and simple technique could be applied to a wide range of archaeological problems involving the thermal history of objects consisting of or containing quartz.  相似文献   
89.
The levels of ten elements (phosphorus, calcium, magnesium, strontium, barium, potassium, sodium, zinc, iron, and aluminium) have been measured in the femurs and humeri of laboratory rats grown on test diets as a model for palaeodietary studies of excavated human skeletons. High levels of dietary fibre correlate with lower Ca and higher Sr and Ba in the bone. High values of the dietary Sr/Ca ratio correlate with high Sr levels in the bone. High levels of dietary protein correlate with lower Sr and higher Zn. High values of the ratio Ba/Ca and lower levels of Fe correlate with higher levels of Ba. Because bone levels typically are controlled by several dietary components, variation of the levels of a given element in the diet does not necessarily translate into analogous variations in bone. Only K and Fe in bone correlate highly with their levels in diet. The failure of bone Sr, Ba, and Zn to correlate positively with dietary levels is fully explicable in terms of their interdependence on other dietary components, such as Ca, P, Fe, protein, and fibre.  相似文献   
90.
ABSTRACT. A multi-plant producer has sole access to a region, and each of the plants processes a raw material which is drawn from its own exclusive supply area. Under these conditions what spatial structure of production (in terms of plant scale, plant frequency, supply-area size and supply-area shape) will enable region-wide or multi-plant profit to be maximized? The form of this optimal structure is shown to vary with prevailing level of price, which is exogenously determined.  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