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   8455篇
  免费   325篇
  2020年   109篇
  2019年   156篇
  2018年   188篇
  2017年   211篇
  2016年   267篇
  2015年   191篇
  2014年   173篇
  2013年   2548篇
  2012年   239篇
  2011年   258篇
  2010年   286篇
  2009年   250篇
  2008年   223篇
  2007年   241篇
  2006年   240篇
  2005年   119篇
  2004年   118篇
  2003年   108篇
  2002年   111篇
  2001年   124篇
  2000年   87篇
  1999年   108篇
  1998年   76篇
  1997年   61篇
  1996年   75篇
  1995年   85篇
  1994年   81篇
  1993年   86篇
  1992年   78篇
  1991年   64篇
  1990年   60篇
  1989年   76篇
  1988年   66篇
  1987年   78篇
  1986年   74篇
  1985年   88篇
  1984年   75篇
  1983年   99篇
  1982年   79篇
  1981年   83篇
  1980年   77篇
  1979年   73篇
  1978年   78篇
  1977年   67篇
  1976年   76篇
  1975年   72篇
  1974年   56篇
  1973年   59篇
  1972年   64篇
  1970年   49篇
排序方式: 共有8780条查询结果,搜索用时 234 毫秒
151.
Several samples of geological stones from statuary pedestals found in various archaeological sites in Cyprus have been characterized using non-contact laser infrared photothermal radiometry. Thermal diffusivities and effective optical absorption coefficients were calculated using a one-dimensional thermal-wave model. The mean values and standard deviations were tabulated and comparisons were made with lithographic and petrographic studies of the samples. Good correlations were found, thus demonstrating that laser photothermal archaeometry is a promising methodology for the accurate, potentially non-destructive and convenient characterization of the origins of ancient stones in Cyprus and other geological and archaeological sites.  相似文献   
152.
The study addresses the chemical variations for Roman Samian wares manufactured during various periods at different workshops within the Lezoux production centre. Instrumental neutron activation analysis and inductively coupled plasma spectrometry were used to determine the chemical constituents of the pottery. The two techniques were evaluated based on the capacity of each to identify the same compositional groups for Lezoux Samian with the use of multivariate statistics. The compositional analysis redefines and clarifies how potters used the clay sources at the site to produce fine wares. The results indicate that the majority of potters from different workshops at Lezoux shared the same clay source during the second century AD.  相似文献   
153.
Blue glass trade beads from well-dated late seventeenth- to early twentieth-century sites and collections have been analysed non-destructively by instrumental neutron activation analysis. The beads display enough variations in their elemental contents to allow us to characterize the different chemistries. The implication of these results is that similar chemical analyses of blue beads from undated archaeological sites may be used to help date the sites, since each bead chemistry has a specific earliest period.  相似文献   
154.
Fifty-three copper-based metal fragments, recovered from the Robitaille site in southcentral Ontario, were analysed by neutron activation to establish their chemical make-up and to sort them by their trace elemental chemistries. Three different European copper samples, one brassy copper and 48 brass samples with five different chemistries were found. As few as eight trading actions may account for all of the recovered European metal fragments.  相似文献   
155.
The possibility of lead isotope fractionation in ancient lead production is examined. Kinetic theory relating to isotopic fractionation in non-equilibrium evaporation is considered and the feasibility of the alteration of lead isotope abundance ratios in ore roasting and smelting is assessed. Previous experimental work is shown to have been inconclusive and conclusions are drawn on the need for further research to quantify the possible extent of fractionation in practice.  相似文献   
156.
157.
This article uses material from a series of case studies conducted in Latin America to analyse various aspects of the formalization of the informal sector. In particular, it examines the legal and bureaucratic barriers confronting informal sector micro-enterprises which seek to become part of the formal, legal circuit, and assesses the costs in time and money which are involved in the formalization process. The process itself is seen as consisting of two elements — achieving legality and retaining that status over time — each of which involves certain bureaucratic and financial demands. While recognizing that the requirements for formalization can represent a burden in some cases, the main finding of the article is that the procedures and related costs vary between countries to such a degree that it is impossible to claim, as some earlier studies have done, that disproportionate regulation and bureaucracy constitute an insurmountable obstacle to the legalization of informal sector enterprises.  相似文献   
158.
159.
160.
Current theoretical understanding of compliance with international law is based on an assumption that international law consists of a finite set of objective, compulsory rules. This image does not match reality but the two can be reconciled through theorising international law as ideology. Such an approach subsumes questions as to why states do or do not obey law and what influence international law has on foreign policy decision making. By placing the relationship of state behaviour to international law in a broader perspective it can account for previously identified determinants of compliance and provide a basis on which to assess their relative significance. At the same time, the research agenda regarding compliance is broadened by the introduction of fresh questions.  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