全文获取类型
收费全文 | 1384篇 |
免费 | 55篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 24篇 |
2019年 | 45篇 |
2018年 | 44篇 |
2017年 | 60篇 |
2016年 | 50篇 |
2015年 | 23篇 |
2014年 | 42篇 |
2013年 | 433篇 |
2012年 | 36篇 |
2011年 | 40篇 |
2010年 | 35篇 |
2009年 | 33篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 24篇 |
2005年 | 23篇 |
2004年 | 29篇 |
2003年 | 33篇 |
2002年 | 25篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有1439条查询结果,搜索用时 31 毫秒
991.
Timber output, the major commodity use of the National Forests, was tracked from 1981 to 1993, to assess changes that have occurred in the amount of timber offered, sold, and harvested. In addition, changes in the method of harvest used on the National Forests were examined to view trends in the management practices of the Forest Service. Although trends regarding changes in timber harvest methods varied from region to region, data on timber offered, sold, and harvested showed a dramatic decrease both nationally and in important timber-producing regions since the late 1980s. This reduction, when seen in the light of other recent studies, suggests that the Forest Service is changing the emphasis of its management practices, placing less priority on the traditional high level of timber output. 相似文献
992.
The Zone Definition Problem in Location-Allocation Modeling 总被引:1,自引:0,他引:1
Location-allocation modeling is a frequently used set of techniques for solving a variety of locational problems, some of which can be politically sensitive. The typical application of a location-allocation model involves locating facilities by selecting a set of sites from a larger set of candidate sites, with the selection procedure being a function of “optimality” in terms of the allocation of demand to the selected sites. In this paper we examine the sensitivity of one particular type of location-allocation model, the p-median procedure, to the definition of spatial units for which demand is measured. We show that a p-median solution is optimal only for a particular definition of spatial units and that variations in the definition of spatial units can cause large deviations in optimal facility locations. The broad implication of these findings is that the outcome of any location-allocation procedure using aggregate data should not be relied upon for planning purposes. This has important implications for a large variety of applications. 相似文献
993.
Paul Richard Blum 《Berichte zur Wissenschaftsgeschichte》1994,17(2):144-144
994.
Narrative policy analysis and policy change theory rarely intersect in the literature. This research proposes an integration of these approaches through an empirical analysis of the narrative political strategies of two interest groups involved in policy debate and change over an eight‐year period in the Greater Yellowstone Area. Three research questions are explored: (i) Is it possible to reconcile these seemingly disparate approaches? (ii) Do policy narrative strategies explain how interest groups expand or contain policy issues despite divergent core policy beliefs? (3) How does this new method of analysis add to the literature? One hundred and five documents from the Greater Yellowstone Coalition and the Blue Ribbon Coalition were content analyzed for policy narrative strategies: identification of winners and losers, diffusion or concentration of costs and benefits, and use of condensation symbols, policy surrogates, and science. Five of seven hypotheses were confirmed while controlling for presidential administration and technical expertise. The results indicate that interest groups do use distinctive narrative strategies in the turbulent policy environment. 相似文献
995.
996.
Paul F. Steinberg 《政策研究杂志》2007,35(2):181-204
The identification of cause‐and‐effect relationships plays an indispensable role in policy research, both for applied problem solving and for building theories of policy processes. Historical process tracing has emerged as a promising method for revealing causal mechanisms at a level of precision unattainable through statistical techniques. Yet historical analyses often produce dauntingly complex causal explanations, with numerous factors emerging as necessary but insufficient causes of an outcome. This article describes an approach that renders complex causal narratives more analytically tractable by establishing measurement criteria for ranking the relative importance of component causes. By focusing on subjectively useful measurement attributes, the approach is well suited to the policy sciences' unique combination of explicitly normative aspirations and a commitment to the systematic assessment of causal claims. 相似文献
997.
Paul Widmer 《Indo-Iranian Journal》2007,50(3):215-228
Young Avestan nāuuiia-, Old Persian nāviyā, Sanskrit nāvyà-, all descending from Indo-Iranian *nāu̯ii̯a-, are usually glossed by ‘passable (only) by boat, not to be crossed without the help of a boat’. A closer examination of
the contexts they occur in reveals that the meaning ‘streaming, raging’ is much more appropriate. In consequence, *nāu̯ii̯a- can not be a secondary derivative of Indo-Iranian *nāu̯- ‘ship, boat’, which is improbable for other reasons as well. It is suggested that *nāu̯ii̯a- rather represents a primary formation derived from the Indo-Iranian root *nāu̯- ‘to flow’.
相似文献
998.
THE IMPACTS OF TRANSPORTATION INFRASTRUCTURE ON PROPERTY VALUES: A HIGHER-ORDER SPATIAL ECONOMETRICS APPROACH 总被引:3,自引:0,他引:3
ABSTRACT. We evaluate the impacts of enhanced transportation systems on property values for U.S. manufacturing firms, allowing for higher-order spatial error correlation. We use a state-level model of production cost and input demand that recognizes the productive contribution of public transportation infrastructure stocks. Our findings include significant impacts on property shadow values and input composition from both public highway and airport investment. We also find that these effects have a spatial dimension that depends on the proximity of the transport system; at least one and as many as three spatial error lags are significant in our estimating equations. Further, recognizing production growth from transportation system improvements augments the associated incentives for private capital investment. 相似文献
999.
1000.
Patrizia Pernter Paul Gostner Eduard Egarter Vigl Frank Jakobus Rühli 《Journal of archaeological science》2007
A possible cause of death of the Iceman – a ca. 5’300 BP natural human glacier mummy from the Tyrolean Alps – is an intrathoracic stone arrowhead. The aim of this study was to prove radiologically his enigmatic cause of death. In August 2005, the Iceman underwent his first multislice computed tomography examination. As the main pathologic finding, the left dorsal subclavian artery contures shows a 13 mm-long part where the vessel wall is damaged and a 3 mm-long irregular pseudo-aneurysm – a typical complication of a laceration of the subclavian artery. In the surrounding soft tissue a large haematoma is visible. Historic records highlight the fatal destiny of subclavian artery injuries e.g. due to massive active bleeding and shock-related cardiac arrest. Therefore, the Iceman's cause of death by an arrowhead lacerating among others the left subclavian artery and leading to a deadly hemorrhagic shock can be now postulated with almost complete certainty, especially when taking the environmental (3’210 meters above sea level) and historic (5’300 BP) settings into account. 相似文献