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   52263篇
  免费   4768篇
  国内免费   1987篇
电工技术   8599篇
技术理论   1篇
综合类   5692篇
化学工业   1515篇
金属工艺   733篇
机械仪表   2357篇
建筑科学   23821篇
矿业工程   1361篇
能源动力   2027篇
轻工业   396篇
水利工程   1428篇
石油天然气   735篇
武器工业   293篇
无线电   1650篇
一般工业技术   3061篇
冶金工业   989篇
原子能技术   188篇
自动化技术   4172篇
  2024年   193篇
  2023年   504篇
  2022年   1154篇
  2021年   1229篇
  2020年   1371篇
  2019年   1096篇
  2018年   1041篇
  2017年   1423篇
  2016年   1547篇
  2015年   1838篇
  2014年   4964篇
  2013年   3061篇
  2012年   3997篇
  2011年   4237篇
  2010年   3418篇
  2009年   3623篇
  2008年   3309篇
  2007年   3858篇
  2006年   3059篇
  2005年   2628篇
  2004年   2107篇
  2003年   1807篇
  2002年   1443篇
  2001年   1294篇
  2000年   1013篇
  1999年   910篇
  1998年   566篇
  1997年   495篇
  1996年   430篇
  1995年   308篇
  1994年   255篇
  1993年   187篇
  1992年   128篇
  1991年   96篇
  1990年   89篇
  1989年   70篇
  1988年   69篇
  1987年   45篇
  1986年   21篇
  1985年   28篇
  1984年   21篇
  1983年   20篇
  1982年   17篇
  1981年   7篇
  1980年   26篇
  1979年   6篇
  1957年   1篇
  1955年   1篇
  1954年   1篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
41.
42.
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves.  相似文献   
43.
冯明光  谢安国 《冶金能源》2004,23(1):6-8,26
利用寿命周期评价的思想,计算了炼铁生产过程中的环境负荷,并分析了各因素对环境负荷的影响,运用神经网络对炼铁生产过程环境负荷进行了预测。  相似文献   
44.
随着VLSI工艺技术的发展和芯片规模的不断增加,尤其是在SOC设计中,原有的那种供电压焊块只能位于芯片边缘的确定益的模式已经不能够满足整个电路性能的需要。在很多情况下,依靠在电源线的拓扑结构确定后的线宽优化,还是无法保证在有限的布线资源下为电路提供可靠的高性能的供电需求。由此,出现了在芯片边缘上浮动放置压焊块及在芯片的顶部放置供电压焊块阵列的方法。文中提出了一种用于SOC设计中新的基于树型结构的浮动压焊块的电源/地线网络优化算法,经过MCNC电路实例测试后得到明显的优化结果。  相似文献   
45.
We study the stressed state of an inhomogeneous welded joint containing an interlayer of a more high-strength material under the action of tensile loads. It is assumed that the contact boundary has a cracklike defect. We deduce analytic dependences of the fracture load on the mechanical inhomogeneity of the joint, thickness of the interlayer, and depth of the defect. The maximum depth of the defect to which the joint is insensitive is established. The proposed theoretical results are innovative and agree with the experimental data obtained for specimens cut out from a pipe of 14KhGS steel.  相似文献   
46.
静态EPS及其在建筑工程中的应用   总被引:2,自引:0,他引:2  
董家业 《低压电器》2003,(2):20-21,44
一级负荷中特别重要的负荷,除由两个电源供电外,尚应增设应急电源。在供电条件比较差的地区,取得第二个电源供给一级负荷有困难时,也需要增设应急备用电源。以往经常用自备柴油发电机组、蓄电池、干电池和镍锦电池应急灯作为应急备用电源。本文通过对目前常用的各种应急电源的分析比较,推荐一种新颖的、静态、无公害、免维护无人值守的、供电质量好、安全可靠的集中供电式EPS装置。  相似文献   
47.
董世坚 《电力电容器》2003,(2):41-42,48
就我公司动力厂给水车间155kW水泵电机无功就地补偿的可行性及经济效益进行了分析和研究,对工厂用电如何节能降耗有一定的参考价值。  相似文献   
48.
An increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints.  相似文献   
49.
A method for constructing an approximation of the critical excitation that drives an elastoplastic system from rest to a target threshold at a specified time instant, referred to as the “suboptimal excitation,” is presented in this paper. It is based on the observations gained from study of the critical excitations in the companion paper. Essentially, for the usual case of interest where the failure time is not small compared to the natural period, the duration of the positive and negative pulses of the critical excitation are roughly equal to half of the natural period. This consideration allows for a simple intuitive approximation of the critical excitation. The amplitudes of the positive and negative pulses are obtained in closed forms using energy balance. Numerical investigations show that the critical excitations are well approximated by the suboptimal excitations.  相似文献   
50.
提出一种金属圆锥弹簧与橡胶圆锥弹簧复合而成的弹簧.分析表明:它可以应用于弹性耦合激励振动筛和座式直线振动筛。  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