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   203篇
  免费   8篇
  2022年   3篇
  2021年   1篇
  2020年   5篇
  2019年   4篇
  2018年   5篇
  2017年   4篇
  2016年   8篇
  2015年   6篇
  2014年   4篇
  2013年   39篇
  2012年   6篇
  2011年   11篇
  2010年   19篇
  2009年   12篇
  2008年   8篇
  2007年   14篇
  2006年   12篇
  2005年   9篇
  2004年   4篇
  2003年   6篇
  2002年   3篇
  2001年   9篇
  2000年   2篇
  1999年   3篇
  1998年   1篇
  1996年   1篇
  1995年   3篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1985年   1篇
  1983年   1篇
  1978年   1篇
  1976年   1篇
  1973年   1篇
排序方式: 共有211条查询结果,搜索用时 140 毫秒
1.
浑仪、简仪(以下简称两仪)在高PH、大气污染和日晒雨淋环境中的腐蚀是一种动态加速腐蚀过程。采用合成的双唑胺铜缓蚀剂和有机硅改性的甲基丙烯酸树脂,并分别复配成协同缓蚀剂群和含有增效稳定剂的封护剂。采用这两种材料和脱水后再防护的工艺,使带锈防护后的浑仪、简仪的腐蚀低于无污染大气中的速率。用电化学方法评价了防护技术的可行性,根据腐蚀与人工老化试验结果讨论了防护材料性能与腐蚀环境和带锈防护的关系,采用XPS分析方法探索了双唑胺比BTA更适用于两仪防护的原因。  相似文献   
2.
3.
ABSTRACT

A remote archipelago, Hawai'i, offers a plethora of sought after coastal and marine tourism experiences. The same unique marine fauna that draws tourists also makes Hawai'i a major player in the international ornamental aquarium trade. For many residents of Hawai'i, the marine realm is part of their island home and interactions with tourists and tourism activities are a part of everyday life. For many residents, the ocean is an important resource and for some a staple source of livelihood, be it through tourism, fisheries, or the aquarium trade. This variance between extractive and non-extractive marine resource use creates conflicts between stakeholder groups in Hawai'i. This study thematically analyzes public testimony records, which included 1652 individual testimonies, from proposed legislation aimed to establish ‘an aquatic life conservation program in the Division of Aquatic Resources to implement conservation measures, including limited entry areas and certification requirements, to regulate the collection of fish and other aquatic life for aquarium purposes. Public opinions evident in individual testimonies are representative of the disagreement in the literature regarding the stability and health of reef fishes populations in Hawai'i and broader resource-user conflicts. This study aims to better describe the user conflict between stakeholder groups in the marine resources of Hawai'i by exposing themes concerning change in natural environments.  相似文献   
4.
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   
5.
卢梭的“自然美”思想丰赡深邃,精远宏阔.从美育目标、理念、重点三个层面梳理了卢梭自然主义美育思想的核心内容,将其教育特点归纳为整体性、平民性、情感性和自然性,并着重阐述了这一思想对新时期我国美育工作的四个重要启示:即注重美育工作的辩证性;尊重美育实践的主体性;激励美育过程的情感性;倡导美育内容的生态性.  相似文献   
6.
Abstract

The social insurrection of May 1968 in France continues to provoke strong political debate. Compared to most French politicians and social commentators who dismiss or condemn it as an excessive adolescent rebellion, French anarchists contend that it was a substantial political rupture because participants challenged the legitimacy of all hierarchy and domination in every realm of society. Research into a wide range of French anarchist books and articles from 1988 to the present reveals several distinct approaches to May 68. Beyond narratives of the events themselves, anarchists emphasised the rapid spread and delight with horizontalist social relations of mutual aid and respect on campuses and in workplaces and neighbourhoods as 10 million French people went on strike for several weeks. This liberating experience, they contend, transformed the social consciousness of large numbers and led to the great surge of anarchic autonomous social movements in different realms in the 1970s. These writings also reveal important debate among anarchists themselves on whether May 68 was a revolution, whether revolution is even possible and how to organise a revolutionary movement.  相似文献   
7.
新中国土地改革后新富农产生的规模与分布研究   总被引:1,自引:0,他引:1  
从土地改革结束到农业集体化高潮前夕,新富农的出现从全国范围来看是稀少而缓慢的。在各省之间,农民的富裕程度与新富农比重大小关系不明显,但在同一地区内来看,两者呈现正相关关系。同时,在农业合作化程度较高亦即是较早对新富农采取限制政策的地区,新富农的比重并不一定低于甚至高于其他地区。这说明多种因素对新富农的产生、发展发生作用,单因素的分析不能解释清楚新富农这个复杂的社会经济问题。  相似文献   
8.
国民经济恢复时期,面对失业和人才需求关系的矛盾,城市失业知识分子受到党和政府的高度关注。北京市的失业知识分子虽人数不多,但呈现出一定程度的复杂性。为此,北京市根据党和国家的政策,从首都社会秩序的稳定和首都建设的人才需求出发,在较短的时间内,有计划有步骤地对失业知识分子进行了必要的社会救济,达到了预期的目标。同时,实际操作中也遇到了一些不容回避的问题。  相似文献   
9.
The femur remains an important bone in palaeoanthropology and this paper reports various analyses of measurements taken from long-cassette radiographs of adult femurs of a reference population from the south of England (n=81, males 33, females 48). Discriminant analysis confirmed that the male femur is usually larger than the female femur, and that a femur may be sexed with some confidence. Discriminant scores have been derived to permit estimates to be made, from the whole or a part of a femur, of the probability of the male gender. Outcomes from a principal component analysis suggest: that the female proximal femur is a morphological unit; that neck length and shaft length are dissociated and there is no common factor representing linearity; and that the male bicondylar width is anomalous, a finding that is confirmed by other analyses. An estimate of the robusticity of the complete female, but not male, bone may sometimes be made from a proximal fragment. The robusticity of the complete bone may be made confidently from the shaft for both genders. The two width variables relating to a distal fragment cannot be used to predict the robusticity of the complete bone for either gender. A method of defining the position of the waist in terms of displacement in deciles down the shaft is described. The position of the waist seems to have a bimodal distribution. The positive association between age and distal displacement may be due to remoulding of the shaft with age or to a cohort (generational) effect. There is a weak correlation between a small neck–shaft angle and the distal displacement of the waist, two archaic phenotypic traits. Ten statements in the literature relating to the femur have been examined and tested; six are confirmed and four are unconfirmed, and it is suggested that there is a need for further studies relating to the morphology of the femur.  相似文献   
10.
Higher dimensional algebra frees mathematics from the restriction to a purely linear notation, in order to improve the modelling of geometry and so obtain more understanding and more modes of computation. It gives new tools for noncommutative, higher dimensional, local to global problems, through the notion of «algebraic inverse to subdivision». We explain the way these ideas arose for the writters, in extending first the classical notion of abstract group to abstract groupoid, in which composition is only partially defined, as in composing journeys, and which brings a spatial component to the usual group theory: An example from knot theory is used to explain how such algebra can be used to describe some structure of a space. The extension to dimension 2 uses compositions of squares in two directions, and the richness of the resulting algebra is shown by some 2-dimensional calculations. The difficulty of the jump from dimension 1 to dimension 2 is also illustrated by the comparison of the commutative square with the commutative cube-discussion of the latter requires new ideas. The importance of category theory is explained, and a range of current and potential applications of higher dimensional algebra indicated.  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