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   491652篇
  免费   13311篇
  国内免费   5894篇
电工技术   12727篇
技术理论   10篇
综合类   9632篇
化学工业   76358篇
金属工艺   26356篇
机械仪表   21434篇
建筑科学   17778篇
矿业工程   5658篇
能源动力   9640篇
轻工业   35515篇
水利工程   6641篇
石油天然气   13768篇
武器工业   1010篇
无线电   51094篇
一般工业技术   91568篇
冶金工业   59649篇
原子能技术   8465篇
自动化技术   63554篇
  2022年   4091篇
  2021年   6114篇
  2020年   4544篇
  2019年   4570篇
  2018年   24946篇
  2017年   24925篇
  2016年   18519篇
  2015年   7421篇
  2014年   9419篇
  2013年   17205篇
  2012年   18351篇
  2011年   30911篇
  2010年   26639篇
  2009年   24173篇
  2008年   25322篇
  2007年   27721篇
  2006年   13820篇
  2005年   16031篇
  2004年   12365篇
  2003年   11399篇
  2002年   10032篇
  2001年   8994篇
  2000年   8703篇
  1999年   8749篇
  1998年   15141篇
  1997年   11418篇
  1996年   9226篇
  1995年   7110篇
  1994年   6389篇
  1993年   5930篇
  1992年   4773篇
  1991年   4478篇
  1990年   4372篇
  1989年   4264篇
  1988年   3968篇
  1987年   3359篇
  1986年   3353篇
  1985年   3675篇
  1984年   3569篇
  1983年   3303篇
  1982年   2938篇
  1981年   3117篇
  1980年   2855篇
  1979年   3055篇
  1978年   3011篇
  1977年   3097篇
  1976年   3951篇
  1975年   2711篇
  1974年   2583篇
  1973年   2587篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
High Temperature - The temperature dependences of the viscosity of liquid Fe90B x Si(10 − x) alloys are studied in the mode of heating and subsequent cooling. The temperature dependences of...  相似文献   
113.
Russian Engineering Research - Formulas are derived for the most important parameters of channel extrusion.  相似文献   
114.
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.  相似文献   
115.
An automated system for integrated electrophysical and optical studies of semiconductor nanoheterostructures, which operates in a wide temperature range from 15 to 475 K, is designed. The setup is intended to measure the temperature and frequency admittance and electroluminescence spectra of light-emitting diode and laser chips formed on substrates of diameter up to 50.2 mm, and the distribution of parameters over the wafer. The setup includes the closed-cycle helium cryogenic station, LCR meter, and temperature controller. The characterization results of nanoheterostructures with InGaN/GaN multiple quantum wells, which are used for creating highly efficient white and blue light-emitting diodes, are presented.  相似文献   
116.
The influence of the thermal cycling conditions on the thermal-cycling creep of a TN-1 alloy and the related irreversible deformations is studied. The conditions under which an anomalous increase in the irreversible deformations begins are determined. The structural mechanism of the irreversible deformations of an equiatomic alloy is shown to be analogous to the structural mechanism of metal creep at high temperatures: it predominantly has a dislocation character. It is proposed to use the effect of anomalous increase in the deformation of materials with reversible martensitic transformations for forming parts made of these materials at low temperatures.  相似文献   
117.
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs.  相似文献   
118.
119.
120.
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