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   584866篇
  免费   93534篇
  国内免费   58384篇
电工技术   49042篇
技术理论   62篇
综合类   46322篇
化学工业   90613篇
金属工艺   44517篇
机械仪表   31980篇
建筑科学   43693篇
矿业工程   25496篇
能源动力   19753篇
轻工业   46672篇
水利工程   14178篇
石油天然气   37109篇
武器工业   6888篇
无线电   71806篇
一般工业技术   75541篇
冶金工业   28089篇
原子能技术   5254篇
自动化技术   99769篇
  2024年   4050篇
  2023年   10204篇
  2022年   15554篇
  2021年   20532篇
  2020年   20006篇
  2019年   26706篇
  2018年   29356篇
  2017年   31638篇
  2016年   30444篇
  2015年   33376篇
  2014年   36785篇
  2013年   39939篇
  2012年   40685篇
  2011年   40233篇
  2010年   35724篇
  2009年   31433篇
  2008年   29643篇
  2007年   28191篇
  2006年   27911篇
  2005年   24659篇
  2004年   20304篇
  2003年   17726篇
  2002年   16879篇
  2001年   15069篇
  2000年   14456篇
  1999年   15289篇
  1998年   12867篇
  1997年   10867篇
  1996年   10374篇
  1995年   9132篇
  1994年   7478篇
  1993年   5914篇
  1992年   5143篇
  1991年   3900篇
  1990年   3030篇
  1989年   2683篇
  1988年   2183篇
  1987年   1063篇
  1986年   834篇
  1985年   563篇
  1984年   396篇
  1983年   310篇
  1982年   350篇
  1981年   266篇
  1980年   241篇
  1976年   284篇
  1975年   225篇
  1972年   249篇
  1971年   138篇
  1960年   206篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
实验研究了以工业硫酸亚铁及废硫酸为原料,分别采用NaClo_3、KClO_3、H_2O_2及(o_2+NaNO_2)为氧化剂成聚硫酸铁的条件。在以(O_2+NaNO_2)为氧化剂的合成过程中,发现添加微量助催化剂(型号为HG-1、HG-2和HG-3),对提高合成速度及反应过程的稳定性具有重大作用。  相似文献   
22.
A CEC-funded project has been performed to tackle the problem of producing an advanced Life Monitoring System (LMS) which would calculate the creep and fatigue damage experienced by high temperature pipework components. Four areas were identified where existing Life Monitoring System technology could be improved:
1. 1. the inclusion of creep relaxation
2. 2. the inclusion of external loads on components
3. 3. a more accurate method of calculating thermal stresses due to temperature transients
4. 4. the inclusion of high cycle fatigue terms.

The creep relaxation problem was solved using stress reduction factors in an analytical in-elastic stress calculation. The stress reduction factors were produced for a number of common geometries and materials by means of non-linear finite element analysis. External loads were catered for by producing influence coefficients from in-elastic analysis of the particular piping system and using them to calculate bending moments at critical positions on the pipework from load and displacement measurements made at the convenient points at the pipework. The thermal stress problem was solved by producing a completely new solution based on Green's Function and Fast Fourier transforms. This allowed the thermal stress in a complex component to be calculated from simple non-intrusive thermocouple measurements made on the outside of the component. The high-cycle fatigue problem was dealt with precalculating the fatigue damage associated with standard transients and adding this damage to cumulative total when a transient occurred.

The site testing provided good practical experience and showed up problems which would not otherwise have been detected.  相似文献   

23.
Among the photocathodes used for particle identification based on the Cherenkov Ring Imaging technique, the TMAE molecule is still the best in terms of quantum efficiency. Despite the fact that TMAE gaseous photocathodes have already been used in a number of large experiments, one still seeks answers to many detailed questions. We present a systematic study of gaseous photocathodes based on TMAE mixed with helium, hydrocarbon and CF4-based gases at normal pressure. The study includes a measurement of the electron drift velocity, gas quenching properties, single electron pulse height spectra and anode wire aging. The paper makes recommendations for carrier gas mixtures to obtain the best quenching, and suggests how to manage TMAE wire aging. This study was motivated by a specific particle identification detector proposal, the Fast Drift CRID proposed for the B-factory at SLAC.  相似文献   
24.
25.
Introduction   Owing to long-time running, more facilities including stations, pipelines, vessels have become corrosive and aged ,some process has grown old, it has exert more burden for the maintenance and repair.Simultaneously, the fluid production rate, oil production rate and water injection rate has changed greatly so that the inflicts and problems from the established surface systems will become more obvious. Energy cost of production and running has increasing continuously. Capacity has been unbalance in systems and areas.   ……  相似文献   
26.
The objective of this study is to evaluate the potential for recovering fluorocarbons as measures for the abatement of global warming. In this study, we focused on the three different kinds of fluorocarbons: CFCs, HCFCs and HFCs, and targeted refrigerant use because of the availability of relevant data. We first estimated future fluorocarbon emissions from the targeted appliances; we next compared those emissions in the units of CO2 equivalent to the level of CO2 emissions in 1990 from a quantitative point of view. As the result of this study, it was found that fluorocarbon emissions in 1999 and 2010 would be equal to approximately 7 and 3% of the level of CO2 emissions in 1990 respectively. Moreover, if we implement a 100% recovery rate in every recovery route, we can reduce a large amount of emissions which correspond to approximately 2–5% of the level of CO2 emissions in 1990, even if we take into account the energy-related CO2 emissions by the transportation and decomposition of fluorocarbons.  相似文献   
27.
28.
29.
30.
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