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   689篇
  免费   39篇
  2024年   4篇
  2023年   6篇
  2022年   5篇
  2021年   9篇
  2020年   12篇
  2019年   21篇
  2018年   43篇
  2017年   46篇
  2016年   37篇
  2015年   34篇
  2014年   26篇
  2013年   136篇
  2012年   22篇
  2011年   32篇
  2010年   21篇
  2009年   22篇
  2008年   22篇
  2007年   10篇
  2006年   7篇
  2005年   6篇
  2004年   9篇
  2003年   11篇
  2002年   6篇
  2001年   10篇
  2000年   13篇
  1999年   7篇
  1998年   4篇
  1997年   9篇
  1996年   6篇
  1995年   10篇
  1993年   8篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1986年   4篇
  1977年   10篇
  1976年   5篇
  1975年   4篇
  1972年   5篇
  1971年   4篇
  1969年   5篇
  1968年   3篇
  1967年   4篇
  1966年   4篇
  1965年   3篇
  1964年   3篇
  1961年   3篇
  1960年   3篇
  1959年   4篇
  1950年   3篇
排序方式: 共有728条查询结果,搜索用时 15 毫秒
31.
A lack of clear political commitment together with confusing rules and enforcement often characterize the institutional context of policy implementation and regulatory compliance in developing countries. By connecting such contextual features to existing models of policy implementation and regulatory compliance, we examine how regulatory factors are related to basic and proactive corporate environmental management practices in the Pearl River Delta region in China. Drawing on data derived from both a survey and in‐depth interviews, we show that a perception of clear political commitment to environmental protection across multiple government levels and units is positively associated with business efforts in basic environmental practices, regardless of the specific enforcement intensity. Nevertheless, a perception of clear political commitment is not related to proactive environmental practices. Conversely, a perception of policy ambiguity, in the form of confusing regulatory standards and enforcement, is negatively associated with corporate efforts in both basic and proactive environmental practices; yet, intensive inspections mitigate these negative associations with policy ambiguity.  相似文献   
32.
The aim of this work is to characterize the original concrete from Roman buildings for public spectacles, theatre and amphitheatre, from Emerita Augusta, Mérida, Spain. An advanced knowledge of the Roman concrete composition is required for a reliable restoration and preservation of these ancient monuments. The concrete was studied through mineralogical (optical polarized microscopy and X-ray diffraction) and petrophysical (bulk and real density, open porosity to water and Hg, mechanical strength and ultrasonic velocity) analyses. With this work, it is possible to fill the gap that exists in this field and the characterization of the materials used in the Roman concrete from these two buildings, never previously studied, despite the significance of this archaeological ensemble, declared a World Heritage Site by UNESCO in 1993. The results allowed us to determine the composition of the Roman concrete and to infer the provenance of the aggregates used in these monuments.  相似文献   
33.
Determining hand laterality during human evolution is important in order to identify brain hemispheric lateralization for motor tasks and, indirectly, to gain information on the complex cognitive functions of the human brain. In this paper, we present a new method for inferring handedness from lithic evidence. The study is based on an analysis of the scatter patterns of lithic remains from stone-knapping episodes. An experimental programme was carried out by 14 knappers (eight right-handed and six left-handed), ranging from individuals that had never even struck two pebbles together to individuals who were quite familiar with prehistoric tools and had some degree of practice. The results of the experiment show that the material scatter patterns of right- and left-handed knappers at group level are different, but they do overlap at certain intervals. At the individual level, the probability of falsely ascribing left- and right-handedness has also been estimated. In addition, we have adapted this method to be applied to the archaeological record. In this case, only well-preserved knapping events with no post-depositional alterations can be used to assign left- or right-handed knappers, with the former being more reliably detected than the latter.  相似文献   
34.
This article aims at presenting and discussing the strategies for updating the finite element numerical modeling of stone masonry arch bridges using operational modal analysis. The study comprehended three bridges: two old ones, the St. Lázaro and the Lagoncinha bridges, and a recently constructed bridge in Vila Fria, Portugal. Updating of the bridge models is performed by comparing the numerical and experimental modal parameters. Three-dimensional detailed numerical models are used to perform modal analysis of the bridges. Experimental modal identification of the bridges is based on the measurement of their acceleration responses during normal operation. The assigned material properties are also based on available results obtained from in situ and laboratory tests and on the results of visual inspection and historical research carried out for both old bridges.  相似文献   
35.
Abstract

This special issue addresses the influences of planning cultures and histories on the evolution of planning systems and spatial development. As well as providing an international comparative perspective on these issues, the collection of articles also engages in a search for new conceptual frameworks and alternative points of view to better understand and explain these differences. The articles focus on three main aspects: the change in planning systems and its impact on spatial development patterns; the interrelationship between planning cultures and histories from a path-dependency perspective; and the variations in physical development patterns resulting from different planning cultures and histories. Papers from different parts of the European continent present evidence at different scales to illustrate these aspects. In all cases, the specific combinations of political, ideological, social, economic and technological factors are important in determining urban and regional planning trajectories as well as spatial development patterns.  相似文献   
36.
37.
38.
Strengthening social, economic and territorial cohesion is a central objective of the European Union (EU) and the Structural Funds reflect the main financial effort of the EU to pursue this goal. So far we have gone through four programming periods; to what extent the EU Funds have become more effective in promoting growth and reducing the disparities between EU Member countries is a matter of concern. We investigate the existence (or not) of learning effects and efficiency improvements following the reforms of Regional Policy. The study is applied to data from EU regions (EU12) in the most recent programming periods where data are available. The results suggest an improvement of the Funds efficiency in growth in 2000–2006 when compared to the previous programming period. Moreover, the returns from investments of Funds tend to be higher in richer, higher-educated and more innovative regions. Finally, the Cohesion group has not been able to transform the large transfers received into additional growth.  相似文献   
39.
40.
We examine the relationship between individual commuting behavior and household responsibilities, with a focus on gender differences in that relationship. Using the Dutch Time Use Survey for the years 2000 and 2005, we analyze the relationship between commuting time, home production, and childcare. To deal with reverse causality, we use Propenstity Score Matching techniques to obtain imputed data for individuals. We find that the effect of home production on commuting time for women is more than double that for men, while childcare time has an effect on women's commuting behavior only. Our results shedding light on the Household Responsibility Hypothesis.  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