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   1139篇
  免费   77篇
  2023年   7篇
  2022年   4篇
  2021年   4篇
  2020年   25篇
  2019年   47篇
  2018年   59篇
  2017年   66篇
  2016年   62篇
  2015年   45篇
  2014年   30篇
  2013年   274篇
  2012年   35篇
  2011年   43篇
  2010年   39篇
  2009年   31篇
  2008年   40篇
  2007年   30篇
  2006年   21篇
  2005年   18篇
  2004年   23篇
  2003年   22篇
  2002年   27篇
  2001年   19篇
  2000年   15篇
  1999年   13篇
  1998年   16篇
  1997年   16篇
  1996年   4篇
  1995年   9篇
  1994年   9篇
  1993年   12篇
  1992年   7篇
  1991年   7篇
  1990年   10篇
  1989年   5篇
  1988年   11篇
  1987年   12篇
  1986年   4篇
  1985年   10篇
  1984年   6篇
  1983年   10篇
  1982年   11篇
  1981年   5篇
  1980年   8篇
  1979年   7篇
  1978年   5篇
  1977年   7篇
  1976年   5篇
  1975年   9篇
  1974年   3篇
排序方式: 共有1216条查询结果,搜索用时 15 毫秒
141.
142.
143.
Mark J. White 《外交史》1999,23(3):565-570
Book reviewed in this article:
Ernest R. May and Philip D. Zelikow (eds.), The Kennedy Tapes: Inside the White House during the Cuban Missile Crisis  相似文献   
144.
It has been difficult to infer behaviours related to anterior tooth use in fossil hominids owing to a lack of broad‐based comparative studies of the relationships between front tooth use and craniodental features in modern humans. In this study, we seek to establish such a neontological baseline by exploring aspects of craniodental form among populations of recent humans that are inferred to have differed in habitual levels of ingestive and paramasticatory processing using the incisors. Morphometric data are compared among samples from three human populations: Aleutian Islanders (n=25); Arikara from the Mobridge Site, SD (n=19); and a late Woodland Bluff group from Jersey County, IL (n=24). Data for various biomechanically relevant dimensions were collected using standard callipers, while three‐dimensional (3D) coordinate data for 28 cranial landmarks were recorded using a video‐based image analysis system. These data indicate that several aspects of cranial form thought to influence the efficiency of force production on the incisors differ among the examined groups, including the positions and size of the primary masticatory muscles and the position of the dentition. For most dimensions, the Aleut sample exhibits the most mechanically advantageous configuration, the Illinois Bluff group the least advantageous configuration, while the Arikara are intermediate in form. This pattern corresponds to differences in the intensity of incisor loading among these groups, as inferred from both ethnographic reports and incisor microwear data. These results, therefore, suggest that cranial form in humans varies with subsistence‐related differences in masticatory force production and that quantitative studies of masticatory system configuration may provide useful information for studies of hominid palaeobiology. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   
145.
Spatial clusters contain biases and artifacts, whether they are defined via statistical algorithms or via expert judgment. Graph-based partitioning of spatial data and associated heuristics gained popularity due to their scalability but can define suboptimal regions due to algorithmic biases such as chaining. Despite the broad literature on deterministic regionalization methods, approaches that quantify regionalization probability are sparse. In this article, we propose a local method to quantify regionalization probabilities for regions defined via graph-based cuts and expert-defined regions. We conceptualize spatial regions as consisting of two types of spatial elements: core and swing. We define three distinct types of regionalization biases that occur in graph-based methods and showcase the use of the proposed method to capture these types of biases. Additionally, we propose an efficient solution to the probabilistic graph-based regionalization problem via performing optimal tree cuts along random spanning trees within an evidence accumulation framework. We perform statistical tests on synthetic data to assess resulting probability maps for varying distinctness of underlying regions and regionalization parameters. Lastly, we showcase the application of our method to define probabilistic ecoregions using climatic and remotely sensed vegetation indicators and apply our method to assign probabilities to the expert-defined Bailey's ecoregions.  相似文献   
146.
The paper compares the abundance of domestic fowl bones with those of sheep/goat and pig from published and unpublished reports on Romano-British animal bones assemblages. The samples are drawn from 68 urban, military, nucleated, villa and unromanized rural settlements. Variations in abundance of domestic fowl within and between these settlement types are noted. Some methodological problems encountered in this survey are discussed and suggestions are made about how more reliable results could be achieved. © 1997 John Wiley & Sons, Ltd.  相似文献   
147.
Since at least the 1960s, the importance of the tremendous territorial expansion under Qing role to the modem history of China has been generally acknowledged. Indeed, one can say that the frontier story is one of the things that makes the Qing "Qing." However, only in the last twenty years has the study of what is now termed the "borderlands" come into its own as a sub-field. This essay begins by describing some key concepts and terms in the study of the Qing frontier, including the Manchu wordjecen. It then raises the problem of narrative fiameworks, asking how we might best contextualize the growth of the empire, before going on to explore the implications of the discursive shift represented by the "New Qing History" and the extensive research on Qing borderlands associated therewith. A poem by the Mongol poet Na-xun Lan-bao provides the focus for a concluding discussion of a distinctive Qing frontier sensibility.  相似文献   
148.
149.
This article presents a new spatial modeling approach that deals with interactions between individual geographic entities. The developed model represents a generalization of the transportation problem and the classical assignment problem and is termed the hierarchical assignment problem (HAP). The HAP optimizes the spatial flow pattern between individual origin and destination locations, given that some grouping, or aggregation of individual origins and destinations is permitted to occur. The level of aggregation is user specified, and the aggregation step is endogenous to the model itself. This allows for the direct accounting of aggregation costs in pursuit of optimal problem solutions. The HAP is formulated and solved with several sample data sets using commercial optimization software. Trials illustrate how HAP solutions respond to changes in levels of aggregation, as well as reveal the diverse network designs and allocation schemes obtainable with the HAP. Connections between the HAP and the literature on the p-median problem, cluster analysis, and hub-and-spoke networks are discussed and suggestions for future research are made.  相似文献   
150.
A Genetic Approach to Detecting Clusters in Point Data Sets   总被引:1,自引:0,他引:1  
Spatial analysis techniques are widely used throughout geography. However, as the size of geographic data sets increases exponentially, limitations to the traditional methods of spatial analysis become apparent. To overcome some of these limitations, many algorithms for exploratory spatial analysis have been developed. This article presents both a new cluster detection method based on a genetic algorithm, and Programs for Cluster Detection, a toolkit application containing the new method as well as implementations of three established methods: Openshaw's Geographical Analysis Machine (GAM), case point-centered searching (proposed by Besag and Newell), and randomized GAM (proposed by Fotheringham and Zhan). We compare the effectiveness of cluster detection and the runtime performance of these four methods and Kulldorf's spatial scan statistic on a synthetic point data set simulating incidence of a rare disease among a spatially variable background population. The proposed method has faster average running times than the other methods and significantly reduces overreporting of the underlying clusters, thus reducing the user's postprocessing burden. Therefore, the proposed method improves upon previous methods for automated cluster detection. The results of our method are also compared with those of Map Explorer (MAPEX), a previous attempt to develop a genetic algorithm for cluster detection. The results of these comparisons indicate that our method overcomes many of the problems faced by MAPEX, thus, we believe, establishing that genetic algorithms can indeed offer a viable approach to cluster detection.  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