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   6854篇
  免费   230篇
  国内免费   87篇
电工技术   86篇
综合类   131篇
化学工业   638篇
金属工艺   258篇
机械仪表   153篇
建筑科学   389篇
矿业工程   27篇
能源动力   76篇
轻工业   358篇
水利工程   41篇
石油天然气   45篇
武器工业   24篇
无线电   441篇
一般工业技术   818篇
冶金工业   3189篇
原子能技术   100篇
自动化技术   397篇
  2023年   37篇
  2022年   52篇
  2021年   89篇
  2020年   62篇
  2019年   88篇
  2018年   96篇
  2017年   81篇
  2016年   87篇
  2015年   90篇
  2014年   119篇
  2013年   207篇
  2012年   180篇
  2011年   206篇
  2010年   169篇
  2009年   169篇
  2008年   157篇
  2007年   195篇
  2006年   208篇
  2005年   150篇
  2004年   146篇
  2003年   132篇
  2002年   129篇
  2001年   87篇
  2000年   121篇
  1999年   198篇
  1998年   906篇
  1997年   581篇
  1996年   400篇
  1995年   234篇
  1994年   200篇
  1993年   247篇
  1992年   67篇
  1991年   70篇
  1990年   66篇
  1989年   74篇
  1988年   58篇
  1987年   70篇
  1986年   44篇
  1985年   41篇
  1984年   33篇
  1983年   34篇
  1982年   35篇
  1981年   32篇
  1980年   50篇
  1979年   30篇
  1978年   36篇
  1977年   108篇
  1976年   213篇
  1975年   26篇
  1974年   27篇
排序方式: 共有7171条查询结果,搜索用时 93 毫秒
1.
ABSTRACT

The digital age of the future is ‘not out there to be discovered’, but it needs to be ‘designed’. The design challenge has to address questions about how we want to live, work, and learn (as individuals and as communities) and what we value and appreciate, e.g.: reflecting on quality of life and creating inclusive societies. An overriding design trade-off for the digital age is whether new developments will increase the digital divide or will create more inclusive societies. Sustaining inclusive societies means allowing people of all ages and all abilities to exploit information technologies for personally meaningful activities. Meta-design fosters the design of socio-technical environments that end-user developers can modify and evolve at use time to improve their quality of life and favour their inclusion in the society. This paper describes three case studies in the domain of assistive technologies in which end users themselves cannot act as end-user developers, but someone else (e.g.: a caregiver or a clinician) must accept this role requiring multi-tiered architectures. The design trade-offs and requirements for meta-design identified in the context of the case studies and other researchers’ projects are described to inform the development of future socio-technical environments focused on social inclusion.  相似文献   
2.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant.  相似文献   
3.
The enzymatic conversion of lignins, possibly in combination with electrochemical oxidation, makes aromatics such as syringol, guaiacol, vanillin and catechol available in the qualities required by the fragrance industry. The lignins were obtained by soda digestion from wheat straw and Miscanthus, characterized and then converted with laccases. The overall yield amounted up to 9 wt % with a product spectrum confined to four substances. Catechol was the major product, with a fraction of ≈75 %. It can easily be isolated by extraction with acetone.  相似文献   
4.
5.
近年来澜沧江公司对安全生产工作采取了强有力手段,安全生产基础不断夯实。如何将安全工作推进更深的层次,如何把控"准入关",将信用评价纳入安全生产不失为一个行之有效的方式。安全信用评价是建立水电工程施工安全信用体系的重要手段,能够促进整体行业安全管理水平的提升。  相似文献   
6.
Primary care physicians can easily incorporate efforts toward the primary and secondary prevention of family violence into their practices. By designing a preventive effort using the phases of the family life cycle, a developmentally appropriate system of prevention is created. The anticipatory guidance at each (annual) visit acknowledges family transitions and assures the family that abuse is a health issue and that the physician is a resource for issues of violence prevention. Using the FLC, the first phase is Coupling, when there is a risk of partner violence that continues as long as there is a partnership. Pregnancy and childbirth bring concerns of child neglect and battery. Older children are at additional risk for child sexual abuse. As families age, risks develop for elder abuse, too. The regular discussion of these issues raises the awareness that the potential for family violence continues over the life span and allows the physician opportunities to assess the risk of violence in that family and make appropriate preventive referrals. Primary care physicians are optimally positioned to address violence and its prevention in the office: they know and care for family units over time. Physicians are respected and trusted advisors who can become effective in preventing violence.  相似文献   
7.
水蒸汽喷射泵系统实用设计软件的开发   总被引:3,自引:0,他引:3  
本文在Turboc环境下开发了多级蒸汽喷射泵系统的设计软件,该软件包括了压缩比优化分配、单级喷射泵结构尺寸设计和冷凝器的结构尺寸设计等内容,使设计人员能够根据具体的工艺条件,快速地完成多级喷射泵系统的设计,对于提高多级喷射泵系统的工作稳定性、节省能源具有实际意义。  相似文献   
8.
抽油机减速箱的润滑和漏失问题已经严重影响了抽油机的正常运转,引起了人们的重视。为了解决这个问题,中原油田分公司采油一厂应用了由燕化集团生产的半流体润滑脂,先后应用于20台抽油机减速箱的润滑保养,通过6个月应用与监测,发现该半流体脂的润滑及防漏效果良好。  相似文献   
9.
In this paper, new homogeneous hot-electron injection data at 300 K and 77 K is provided covering applied voltages from well below to well above the Si-SiO2 barrier height, and a wide range of oxide fields. We found that, in contrast to the MOSFET case, homogeneous injection shows two different regimes for accelerating voltages below and above the barrier height. A simple interpretation of the data is proposed, and supported by Monte Carlo (MC) simulations of the injection experiment. Essentially, the two regimes are the signature of a marked transition between an electron population mostly heated by the electric field, and a tail population created by additional but less efficient energy gain mechanisms, leading to a sharp transition in the carrier distribution function. The details of the bias and temperature dependence of injection are then interpreted as the combined effect of tunneling and carrier distribution. Furthermore, possible implications on MOSFET gate currents are briefly discussed  相似文献   
10.
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