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   2027篇
  免费   330篇
  2023年   13篇
  2022年   2篇
  2021年   21篇
  2020年   34篇
  2019年   132篇
  2018年   111篇
  2017年   111篇
  2016年   151篇
  2015年   107篇
  2014年   107篇
  2013年   453篇
  2012年   112篇
  2011年   124篇
  2010年   103篇
  2009年   76篇
  2008年   93篇
  2007年   92篇
  2006年   63篇
  2005年   37篇
  2004年   51篇
  2003年   46篇
  2002年   30篇
  2001年   29篇
  2000年   39篇
  1999年   11篇
  1998年   19篇
  1997年   30篇
  1996年   23篇
  1995年   18篇
  1994年   16篇
  1993年   7篇
  1992年   10篇
  1991年   2篇
  1990年   6篇
  1989年   3篇
  1987年   5篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1983年   4篇
  1982年   9篇
  1980年   6篇
  1979年   7篇
  1978年   5篇
  1977年   8篇
  1976年   2篇
  1975年   5篇
  1974年   4篇
  1971年   2篇
  1968年   2篇
排序方式: 共有2357条查询结果,搜索用时 31 毫秒
51.
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   
52.
Bell, P.R., Burns, M.E. & Smith, E.T. October 2017. A probable ankylosaurian (Dinosauria, Thyreophora) from the Early Cretaceous of New South Wales, Australia. Alcheringa 42, 120–124. ISSN 0311-5518.

We describe an isolated osteoderm from the Albian Griman Creek Formation where it is exposed near the town of Lightning Ridge in central-northern New South Wales, Australia. Several lines of evidence allow referral of this element to the Ankylosauria—a group that epitomises body armour and ubiquitous osteodermal coverage among dinosaurs. Despite the abundant record of fossil vertebrates from this interval, ankylosaurians have not been previously reported, although, they have been described from penecontemporaneous deposits in western Queensland and Victoria. This discovery, therefore, provides an important link between the northerly faunas (including the Griman Creek Formation) that flourished at the edge of the epeiric Eromanga Sea, with those from the sub-polar rift-valley system of Victoria during the mid-Cretaceous.

Phil R. Bell [], School of Environmental and Rural Science, University of New England, Armidale 2351, NSW, Australia; Michael E. Burns [], Department of Biology, Jacksonville State University, 700 Pelham Rd N., Jacksonville, AL 36265-2138, USA; Elizabeth T. Smith [], Australian Opal Centre, Lightning Ridge 2834, NSW, Australia.  相似文献   

53.
Intensive farming is an increasing part of Australian agriculture, including in the multi‐functional landscapes at the edges of Australian cities. The example of intensive “broiler” poultry production reveals the tensions that arise when sites of hyper‐productivity conflict with social change in rural areas. Planning processes for intensive farming in the Australian state of Victoria are predicated on stability and consensus: on assumed static and uncontroversial ideas of agriculture, its place, and the primacy of agricultural productivity. Yet concerns about the industrialisation of agriculture are live political issues at the local level, especially in dynamic peri‐urban locations. This paper explores the emergence of a politics of place outside the bounds of planning consensus through an analysis of planning appeals and associated media relating to planning permits for intensive poultry developments in Victoria over 2011–2016. We highlight tensions that exist in relation to technical planning assessments and categorisations used to assert farming as the orthodox use of rural land, especially when new forms of farming look and feel demonstrably different. Using Mouffe's problematising of the negation of antagonism and Rancière's notion of the risks of a false consensus democracy, we argue that planning processes for intensive farming illustrate critical issues in participatory planning. While ostensibly post‐political decision‐making narrows the politics of place and food systems to decisions about policing the boundaries and buffer distances placed around intensive poultry developments, alternative representations of rural life persist. The certainty offered by code‐based planning does not negate the ongoing (if inconvenient) politics of intensive peri‐urban agriculture.  相似文献   
54.
55.
56.
57.
58.
Accurate simulation of multiphase flow in fractured porous media remains a challenge. An important problem is the representation of the discontinuous or near discontinuous behaviour of saturation in real geological formations. In the classical continuum approach, a refined mesh is required at the interface between fracture and porous media to capture the steep gradients in saturation and saturation‐dependent transport properties. This dramatically increases the computational load when large numbers of fractures are present in the numerical model. A discontinuous finite element method is reported here to model flow in fractured porous media. The governing multiphase porous media flow equations are solved in the adaptive mesh computational fluid dynamics code IC‐FERST on unstructured meshes. The method is based on a mixed control volume – discontinuous finite element formulation. This is combined with the PN+1DG‐PNDG element pair, which has discontinuous (order N+1) representation for velocity and discontinuous (order N) representation for pressure. A number of test cases are used to evaluate the method's ability to model fracture flow. The first is used to verify the performance of the element pair on structured and unstructured meshes of different resolution. Multiphase flow is then modelled in a range of idealised and simple fracture patterns. Solutions with sharp saturation fronts and computational economy in terms of mesh size are illustrated.  相似文献   
59.
This article explores everyday life among Guji children in southern Ethiopia and the place of children in an intergenerational social order. Based on data generated through ethnographic fieldwork among the Guji, we show that work, school and play are significant and intertwined social practices. Local knowledge and skills of importance for sustainable livelihood are acquired through children's participation in these different social practices. Oral tradition represents a key element of local knowledge and social practices in everyday life. However, political and social changes, such as settlement policies and the introduction of schools, affect the dynamic interconnectedness of these practices, as well as relations between different generations. These changes also have implications for local knowledge and local livelihoods.  相似文献   
60.
Home range is commonly understood to be the distance from home that children are allowed to go in the outdoor environment with the term being used within various academic disciplines. Different factors influence children's home range including traffic, age, parental fears and understandings of what it means to be a good parent. Research addressing home range over different generations has identified a context of changes in the built environment, demography and technology. This paper reports results from three generations of two families in Sheffield in the north of England and confirms a reduction in four major domains: home range, variety of outdoor spaces visited, range of activities undertaken and the number of companions.  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