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   5567篇
  免费   199篇
  国内免费   8篇
电工技术   139篇
综合类   13篇
化学工业   1425篇
金属工艺   117篇
机械仪表   104篇
建筑科学   431篇
矿业工程   10篇
能源动力   122篇
轻工业   751篇
水利工程   36篇
石油天然气   13篇
无线电   287篇
一般工业技术   920篇
冶金工业   637篇
原子能技术   58篇
自动化技术   711篇
  2022年   44篇
  2021年   70篇
  2020年   55篇
  2019年   58篇
  2018年   66篇
  2017年   85篇
  2016年   114篇
  2015年   137篇
  2014年   149篇
  2013年   249篇
  2012年   227篇
  2011年   242篇
  2010年   208篇
  2009年   224篇
  2008年   217篇
  2007年   250篇
  2006年   202篇
  2005年   203篇
  2004年   183篇
  2003年   125篇
  2002年   135篇
  2001年   111篇
  2000年   99篇
  1999年   77篇
  1998年   87篇
  1997年   85篇
  1996年   82篇
  1995年   75篇
  1994年   55篇
  1993年   78篇
  1992年   80篇
  1991年   53篇
  1990年   62篇
  1989年   61篇
  1987年   71篇
  1986年   58篇
  1985年   72篇
  1984年   65篇
  1983年   61篇
  1982年   63篇
  1981年   68篇
  1980年   67篇
  1979年   68篇
  1978年   51篇
  1977年   54篇
  1976年   57篇
  1975年   56篇
  1974年   67篇
  1973年   49篇
  1970年   41篇
排序方式: 共有5774条查询结果,搜索用时 31 毫秒
991.
Implementation of the European Landscape Convention requires new tools that link ecological, social and cultural dimensions in practical planning. Here, we propose connectivity as a conceptual tool to include different dimensions into landscape and spatial planning. We present a short review of the connectivity concept in relation to ecological, social and cultural dimensions and illustrate it by examples from a real landscape planning case.  相似文献   
992.
Research in the field of construction management and economics (CME) can be characterized as a multidisciplinary design science. Results from the sciences and humanities are necessary inputs for this field of research that deals with design, production and operation of the built environment. The output of CME research as multidisciplinary design science consists of three types of solution concepts: empirical generalizations based on statistical data analysis (technological laws), concepts that specify what to do, if a certain result is to be attained under given circumstances (functional rules), and insights in the interrelationship between design, production and operation of the built environment and social practice (socio‐technological understanding). Scientific justification of these solution concepts is obtained through testing them in the specific context of the built environment.  相似文献   
993.
To provide a background for the other articles in this issue the author summarizes some of the studies that have identified key variables affecting urban growth patterns. The most consistent factor related to land use distribution is sheer distance, and especially distance from the CBD. In Philadelphia and Toronto urban density patterns have followed almost identical patterns over the past half-century, giving support to the “crest of the wave” theory of urban growth. Both residential and employment densities exhibit a consistently regular pattern that follows concentric rings out from the CBD. The observations reveal strong regularities of metropolitan land use patterns and hence raise the intriguing question posed in the title of this article.  相似文献   
994.
The objective of this study is to show that the core competence approach has validity when applied to construction. The focus is on the analysis of the fit between market strategies of firms in the building industry and their core capabilities. Certain strategies require specific core capabilities and key external and internal conditions supporting these capabilities. The resource-based approach focuses on the conditions in a firm, the internal capabilities, and supports a core capability that is demanded. The network literature will be related to external conditions that support a core capability of a firm active in a certain market. In a multiple case study, firms are analysed that are involved in different stages of the building process. The case studies demonstrate firms with consistent patterns of market strategies, core capabilities, and supporting internal and external conditions. The specific core capability of the firm under investigation determines the types of external and internal conditions that are critical.  相似文献   
995.
Many architecture, engineering and construction (AEC) professionals would like to use real option (RO) and decision analysis (DA) to evaluate alternatives in investment in the face of uncertainty. However, they have difficulty deciding which one to use and many are not aware of the subtle differences in assumptions and techniques between the two methodologies. We explain how DA and RO can be applied in complete and incomplete markets and what implicit assumptions we need to be aware of in each scenario. Through a toll road example, it is shown that, in a complete market, DA and RO give the same valuation regardless of the choice of the utility function. A formula is provided for pricing any investment in a complete market. The paper also discusses why the values calculated using DA and RO differ in an incomplete market and when DA is more appropriate than RO and vice versa.  相似文献   
996.
Design and construction of a new bridge for the Berlin underground to replace an old structure under high time pressure. This paper is about the design and construction of a new bridge for the underground in Berlin. A new structure was necessary due to insufficient stability and serviceability of the old one. The project had to be carried out under high time pressure to avoid a decommissioning of the underground traffic. As a result of this the planning and execution phases were significantly reduced. Besides, the client provided the construction firm with the structural steel to be used for the superstructure, a potential for conflict that would need to be tackled. The project will be described from the design point of view.  相似文献   
997.
998.
Flexible barriers are increasingly used for the protection from debris flow in mountainous terrain due to their low cost and environmental impact. However, the development of a numerical tool for the rational design of such structures is still a challenge. In this work, a hybrid computational framework is presented, using a total Lagrangian formulation of the finite element method to represent a flexible barrier. The actions exerted on the structure by a debris flow are obtained from simultaneous simulations of the flow of a fluid‐grain mixture, using two conveniently coupled solvers: the discrete element method governs the motion of the grains, while the free‐surface non‐Newtonian fluid phase is solved using the lattice Boltzmann method. Simulations on realistic geometries show the dependence of the momentum transfer on the barrier on the composition of the debris flow, challenging typical assumptions made during the design process today. In particular, we demonstrate that both grains and fluid contribute in a nonnegligible way to the momentum transfer. Moreover, we show how the flexibility of the barrier reduces its vulnerability to structural collapse, and how the stress is distributed on its fabric, highlighting potential weak points.  相似文献   
999.
1000.
Methods for analyzing the fracture behavior of high‐strength steel fiber‐reinforced concretes High‐strength and ultra‐high strength fiber‐reinforced concretes are most suitable for applications with extreme mechanical loads. These extreme conditions require a ductile behavior under tensile loading, which is obtained solely by the addition of steel fibers and their working mechanism. Profound know ledge on the working mechanism of the steel fibers is necessary for optimizing this material. Usually, this knowledge is obtained by means of classical measuring techniques of destructive tests. Adopting measuring techniques from non‐destructive material testing helps to analyze and to identify the different stages of the fracture mechanism of high‐strength and ultra‐high strength fiber‐reinforced concretes in detail. The application of different non‐destructive measuring techniques is shown exemplary on tensile tests conducted on an ultra‐high strength fiber‐reinforced concrete and its applicability for analyzing the fracture behavior is discussed. The main focus is on the characterization of the relevant failure modes under tensile loading by the different measuring techniques and the comparison with classical measuring techniques (e. g. extensometer). The tensile tests have been analyzed by optical deformation measurements using digital image correlation (DIC), acoustic emission analysis (AE), and 3D computed tomography (CT).  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