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   7744篇
  免费   251篇
  2020年   82篇
  2019年   132篇
  2018年   171篇
  2017年   181篇
  2016年   208篇
  2015年   151篇
  2014年   142篇
  2013年   2259篇
  2012年   220篇
  2011年   228篇
  2010年   239篇
  2009年   219篇
  2008年   175篇
  2007年   169篇
  2006年   151篇
  2005年   110篇
  2004年   99篇
  2003年   79篇
  2002年   88篇
  2001年   124篇
  2000年   94篇
  1999年   110篇
  1998年   97篇
  1997年   86篇
  1996年   93篇
  1995年   72篇
  1994年   76篇
  1993年   82篇
  1992年   80篇
  1991年   65篇
  1990年   51篇
  1989年   76篇
  1988年   68篇
  1987年   91篇
  1986年   65篇
  1985年   83篇
  1984年   85篇
  1983年   104篇
  1982年   78篇
  1981年   95篇
  1980年   100篇
  1979年   77篇
  1978年   65篇
  1977年   103篇
  1976年   75篇
  1975年   77篇
  1974年   50篇
  1973年   45篇
  1972年   49篇
  1971年   51篇
排序方式: 共有7995条查询结果,搜索用时 0 毫秒
161.
Discriminant analyses of distances and angles obtained from 25 coins struck by P. Crepusius in 82 BC permitted the correct chronology for five groups of closely-related dies to be obtained by the method of Carter and Frurip. Twenty distances and 15 angles were measured on 10 x projections of the coins which represented five groups of dies separated in time from each other. The use of all or many variables gave poorer results than the use of five to ten variables having a high ‘figure of merit’, defined as the maximum range of mean values for a given variable in the five groups of dies divided by the mean standard deviation of the variable in the five groups. It is recommended that chronologies of ancient coins be determined from Mahalanobis distances by using only variables of relatively high figure of merit.  相似文献   
162.
Limestone from quarries known to medieval craftsmen and from the monuments they built and embellished, as well as from carvings now in museum collections, has been characterized by neutron activation analysis. Specimens from 38 quarries in the Lutetian and Jurassic limestone formations of France and from sculptures in American and French museums have been tested, and the results have been compiled in a data base to which art historians may refer when attempting to determine provenance for sculptures. Multivariate statistical analysis of concentration data shows stone from a particular quarry in the Paris basin to be compositionally homogeneous and distinguishable from other quarries in the same formation. The same approach to data related to quarries near the Burgundian abbey of Cluny finds general agreement between classifications based on compositional and on petrographic data, but the number of samples available for analysis at the time of writing was insufficient to achieve the finer distinctions reported for the Paris basin.  相似文献   
163.
ABSTRACT. This paper analyzes 1954–1987 state manufacturing employment growth in 19 two-digit industries. Markets were found to be the strongest influence in 18 industries. Labor was the second strongest, followed by a threshold variable. Weaker influences were resources, taxes, and amenities. Regional values for the market, labor, and threshold variables corresponded well with regional employment change in the Manufacturing Belt and all other regions of the U.S.  相似文献   
164.
The conventional model of the relationship between welfare incentives and poverty rates holds that welfare payments produce an income-enhancement effect that removes families from poverty until some threshold. Beyond this point increased payments engender a work-disincentive effect resulting in increased rates of poverty. We challenge the model's assumption that poverty levels are a simple and spatially invariant response to welfare incentives, contending instead that local employment conditions may substantially alter the relation. Our reformulation of the conventional modeling approach is based on the expansion method. Specifically, we extend the model to include the effects of local labor-market conditions on the response of poverty levels to welfare incentives. In contesting the invariance assumption, the expansion method allows us to determine where and in what contexts welfare is “work discouraging.” The empirical analysis, which is undertaken at the county level, indicates that welfare payments vary in their influence on poverty rates across different employment contexts. A national map portraying this parameter instability demonstrates that female-family poverty rates are most responsive to welfare assistance in the rural South and least responsive in the metropolitan Northeast. Finally, we examine two sharply contrasting locales to illustrate how poverty is governed by specific employment and welfare characteristics.  相似文献   
165.
Innovation by "groping along," in which appointed public officials experiment during program implementation after little, if any, initial planning and analysis, has been promoted as a more accurate model of policy innovation than the rational comprehensive model of policy change. Analysis of two cases of environmental regulatory policy innovation suggests that administrative agencies may be more likely to follow the conventional model of the policy cycle when high levels of conflict are likely to accompany policy initiatives. The cases also suggest, however, that public officials will experiment during the innovation process when they are uncertain about the nature of the problem and the probable impacts of alternative solutions.  相似文献   
166.
167.
168.
169.
170.
As social constructions of reality, maps embody the values, truth-claims and power-structures of the cultures that make them. Using a variety of interpretive methodologies, geographers and cartographers have developed the thesis that, through selective 're-presentation', maps 'work' at a discursive, symbolic level. In focusing on the artifact itself, however, they have tended to forget that maps are made by someone. Indeed, as part of a wider institutional network, organized and reified by people in pursuit of certain goals, maps serve to create and sustain territories. In a colonial context, moreover, maps arrest and de-legitimize the territorialization of some cultural groups even as they enfranchise and legitimize that of others. Maps are, in this view, ideological weapons. In this paper I use a materialist hermeneutic to investigate the way in which maps helped to actualize the territorial dispossession of the original inhabitants of what is now British Columbia. Beginning with the charts of George Vancouver and Alexander MacKenzie, and ending with the Indian Reserve maps of the 1916 Royal Commission, I illustrate this thesis by tracing the cartographic encirclement of the Nuxalk and Ts'ilhqot'in First Nations. As an essential adjunct in the Euro-Canadian colonization of the region, the analysis has implications for our understanding of the social, political, and juridical function of maps within contemporary land claims discourse.  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