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   380200篇
  免费   30283篇
  国内免费   15823篇
电工技术   22562篇
技术理论   58篇
综合类   24194篇
化学工业   61099篇
金属工艺   21681篇
机械仪表   25204篇
建筑科学   29743篇
矿业工程   12536篇
能源动力   11339篇
轻工业   22696篇
水利工程   6921篇
石油天然气   25210篇
武器工业   3402篇
无线电   42676篇
一般工业技术   43762篇
冶金工业   19723篇
原子能技术   3978篇
自动化技术   49522篇
  2024年   603篇
  2023年   5642篇
  2022年   8800篇
  2021年   14037篇
  2020年   11282篇
  2019年   9036篇
  2018年   10553篇
  2017年   11968篇
  2016年   10747篇
  2015年   14652篇
  2014年   18932篇
  2013年   22741篇
  2012年   24571篇
  2011年   27286篇
  2010年   23592篇
  2009年   22376篇
  2008年   22232篇
  2007年   21481篇
  2006年   21759篇
  2005年   18873篇
  2004年   12293篇
  2003年   10471篇
  2002年   9349篇
  2001年   8457篇
  2000年   8724篇
  1999年   10087篇
  1998年   8342篇
  1997年   6887篇
  1996年   6446篇
  1995年   5487篇
  1994年   4467篇
  1993年   3145篇
  1992年   2538篇
  1991年   1986篇
  1990年   1515篇
  1989年   1239篇
  1988年   1014篇
  1987年   650篇
  1986年   514篇
  1985年   329篇
  1984年   227篇
  1983年   193篇
  1982年   195篇
  1981年   129篇
  1980年   141篇
  1979年   77篇
  1978年   33篇
  1977年   39篇
  1976年   55篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone.  相似文献   
25.
26.
27.
Zhang  Qi  Wang  Yujing  Zhang  Xueling  Song  Jun  Li  Yinlei  Wu  Xuehong  Yuan  Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after...  相似文献   
28.
文章分析智能建造技术创新主体的特点,界定并划分智能建造技术协同创新主体互动关系的范畴和类别,建立智能建造协同创新的多方演化博弈模型,揭示智能建造技术协同创新主体互动关系。主要结论为:①智能建造技术协同创新呈现级联性、函数性、动态平衡性、不确定性和指数性特征;②智能建造技术协同创新主体互动关系分为同质性的内部主体互动和异质性的内部主体与外部主体互动,表现出利益共生、成长进化和共享协同的特征;③创新主体之间的互动行为有利于对创新资源进行有效配置,推动智能建造技术的应用。  相似文献   
29.

Digital currency price prediction is vital to both sellers and purchasers. Over these years, decomposition and integration models have been applied more and more to realize the goal of precise prediction, however, many of them tend to neglect the reconstruction of features or the residual series. Altogether, one of the biggest drawbacks of the decomposition and integration framework is the method applied requires manual parameter setting whether it is for decomposition or integration. Still, for the results, they are merely satisfied with the point prediction which brings high uncertainty. In this paper, an optimized feature reconstruction decomposition and two-step nonlinear integration method is proposed which gives consideration to feature reconstruction, nonlinear integration, optimization and interval prediction. The original data series is decomposed through improved variational mode decomposition based approximate entropy feature reconstruction system. Then, improved particle swarm optimization-gated recurrent unit (iPSO-GRU) is utilized in the first and second nonlinear integration part separately. Meanwhile, the residual series is given attention, if it is not a white noise series, the residual will be the input of iPSO-GRU whose result will be added back to the second integration result to form the point prediction result. Based on the point prediction result, interval prediction estimate will be generated as well via maximum likelihood function. This study chooses three kinds of digital currency as cases and the results show that the MAPE values of point prediction are all below 3.5%, and CP values of interval prediction are all 1 with suitable MWP. In addition, compared with other benchmark models, the proposed model shows better performance.

  相似文献   
30.
MgAl2O4 transparent ceramics were shaped by a commonly used polyacrylic acid (PAA), which acted as both dispersant and gelling agent. The spinel slurries were prepared by ball-milling MgAl2O4 powder, PAA, and water in an attrition mill. The gelling of slurries happened at room temperature in air atmosphere without any other organic additive. The gelling mechanism was the formation of chelates between Mg2+ and carboxyl groups (-COO) of PAA. The frequency-based testing method was applied to investigate the gelling process of the as-prepared slurry. In addition, a novel in situ characterization method based on a modified indentation testing was invented to better understand the strengthening of the wet green body with time and to guide when demolding could be carried out. After sintering, transparent MgAl2O4 ceramics with high in-line transmittance were resulted.  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