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   308728篇
  免费   18458篇
  国内免费   9608篇
电工技术   13339篇
技术理论   24篇
综合类   16116篇
化学工业   49631篇
金属工艺   17811篇
机械仪表   17339篇
建筑科学   19758篇
矿业工程   8067篇
能源动力   7481篇
轻工业   16946篇
水利工程   4842篇
石油天然气   17006篇
武器工业   1660篇
无线电   33859篇
一般工业技术   42704篇
冶金工业   15374篇
原子能技术   2504篇
自动化技术   52333篇
  2024年   1011篇
  2023年   3840篇
  2022年   6551篇
  2021年   9220篇
  2020年   7147篇
  2019年   6064篇
  2018年   20125篇
  2017年   19967篇
  2016年   16008篇
  2015年   9487篇
  2014年   11556篇
  2013年   13527篇
  2012年   17282篇
  2011年   24422篇
  2010年   21343篇
  2009年   17941篇
  2008年   18855篇
  2007年   19348篇
  2006年   12523篇
  2005年   11940篇
  2004年   8342篇
  2003年   7371篇
  2002年   6020篇
  2001年   5003篇
  2000年   5633篇
  1999年   6529篇
  1998年   5499篇
  1997年   4493篇
  1996年   4247篇
  1995年   3517篇
  1994年   2834篇
  1993年   1976篇
  1992年   1554篇
  1991年   1249篇
  1990年   936篇
  1989年   743篇
  1988年   548篇
  1987年   338篇
  1986年   278篇
  1985年   198篇
  1984年   139篇
  1983年   114篇
  1982年   124篇
  1981年   99篇
  1980年   70篇
  1968年   47篇
  1966年   43篇
  1965年   48篇
  1955年   64篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
介绍了子午轮胎硫化的各种介质性能要求及介质供应工艺流程,分析了各种介质的质量要求.介绍了系统各参数的控制调节项目及运行技术管理的一些措施.  相似文献   
23.
介绍并分析了春光油田现代油藏经营管理模式的构建与运作及实施效果.  相似文献   
24.
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry  相似文献   
25.
Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO3/SrTiO3 (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO3 with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO3 films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress.  相似文献   
26.
Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the method employed for coprecipitation of the initial compounds, sintering of the samples at 950°C leads to the formation of lanthanum orthoferrite crystals up to 100 nm in size.  相似文献   
27.
28.
测试与分析了两种塑料管材的拉伸与弯曲性能、热变形温度、结晶性和化学组成,分析结果表明:管材B较管材A具有更高模量与热变形温度,但管材B较高的分子量与较小的分子量分布抑制管材产品内在的均匀性,且管材B中的α晶在高温下向β晶的转变可能会影响管材长期使用性能.  相似文献   
29.
Functionalized polyanilines containing biphenyl, terphenyl, carbazole, anthracene, and 4-n-hexylphenyl moieties were synthesized though the reaction of polyaniline in emeraldine base form with sodium salt of corresponding vinylketoaromatics with quantitative yields. Polymers were characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and thermogravimetry. The emission characteristics of these polymers in N-methyl-2-pyrrolidone solution were examined. The functionalized polyanilines exhibited an intense green emission.  相似文献   
30.
研究了富氧燃烧技术对梭式窑烧成的影响.研究结果表明,随着氧浓度从21%-30%的逐渐增加,CO总浓度和NO总浓度都先明显下降,后缓慢上升;节能效果在初始段较为明显,而后效果不明显;而实际烟气量与氧浓度成反比,与过剩空气系数成正比.  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