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   1748篇
  免费   111篇
  国内免费   75篇
电工技术   18篇
综合类   99篇
化学工业   801篇
金属工艺   127篇
机械仪表   11篇
建筑科学   43篇
矿业工程   50篇
能源动力   79篇
轻工业   186篇
水利工程   20篇
石油天然气   173篇
武器工业   21篇
无线电   53篇
一般工业技术   163篇
冶金工业   45篇
原子能技术   20篇
自动化技术   25篇
  2024年   9篇
  2023年   30篇
  2022年   23篇
  2021年   45篇
  2020年   41篇
  2019年   37篇
  2018年   39篇
  2017年   73篇
  2016年   65篇
  2015年   63篇
  2014年   73篇
  2013年   115篇
  2012年   80篇
  2011年   136篇
  2010年   92篇
  2009年   96篇
  2008年   81篇
  2007年   105篇
  2006年   93篇
  2005年   81篇
  2004年   67篇
  2003年   59篇
  2002年   50篇
  2001年   36篇
  2000年   44篇
  1999年   40篇
  1998年   43篇
  1997年   44篇
  1996年   21篇
  1995年   28篇
  1994年   18篇
  1993年   21篇
  1992年   17篇
  1991年   11篇
  1990年   9篇
  1989年   6篇
  1988年   4篇
  1987年   8篇
  1986年   5篇
  1985年   2篇
  1984年   7篇
  1983年   3篇
  1982年   10篇
  1980年   2篇
  1977年   1篇
  1975年   1篇
排序方式: 共有1934条查询结果,搜索用时 15 毫秒
131.
A series of novel carbamate group-containing quaternary ammonium salts (QASs) have been synthesized, which were subsequently used as antimicrobial agent and incorporated into polyurethane coatings through crosslinking with terpene-based polyol and polyisocyanate. The chemical structures of QASs were characterized by FT-IR, 1H NMR, and 13C NMR. The effects of QASs on the properties of coatings were investigated. The results showed that the resulting coatings exhibited significant antimicrobial activity against both Staphylococcus aureus and Escherichia coli by introducing QASs into the polyurethane networks. Furthermore, with the increasing of QAS content, the antimicrobial activity and adhesion of the coatings were enhanced, while the pencil hardness, water resistance and thermal stability of the coatings were decreased.  相似文献   
132.
杨铃  徐运欢  毛桃嫣  林璟  郑成 《精细化工》2015,32(2):139-143
含氟季铵盐表面活性剂是一类具有高表面活性、高耐热稳定性、高化学稳定性和憎水、憎油等特殊性能的表面活性剂。该文通过测定不同时间、不同种类的油相、不同质量分数的表面活性剂以及不同无机盐添加比例对油水界面张力的影响以及不同浓度的含氟季铵盐表面活性剂水溶液在石蜡、金属铁等不同固体表面上的接触角,对其动态界面张力以及润湿铺展性能进行了研究。结果表明:界面张力值通常在10 min后基本达到平衡,且用渤61#油做油相时,界面张力值较低,效果比较好;随着表面活性剂质量分数的增加,界面张力先减小,达到一个最低值后渐渐趋于平缓;无机盐的加入使得界面张力先降后升,在Na Cl质量浓度为50~80 g/L内均降至低界面张力,最低值达到0.053 1 m N/m;同时,在典型的具有强疏水性的低能表面石蜡上的铺展性能优良。该研究为其在水溶性场合的应用提供了实验数据。  相似文献   
133.
稠油污水处理对硅含量有严格要求。作者针对污水中不同类型的硅酸存在形态,研究了硫酸铝的加量以及反应体系所处的pH范围对各形态硅酸的去除效果。实验结果表明,6mmol/L的硫酸铝加量能将污水中总硅降到50mg/L以下。硫酸铝对高聚硅酸的处理效果要优于对单体硅酸和二聚硅酸。在pH=5时硫酸铝的除硅效果最好,在中性和强碱性条件下效果较差。分析了硫酸铝在稠油污水中对各形态硅酸的去除机制,硫酸铝作为除硅剂的同时也具有一定的混凝作用,可用于稠油污水的处理。  相似文献   
134.
New alkyl hydroxyethyl imidazoline salts were synthesized via a high pressure process with imidazoline and dimethyl carbonate, and their chemical structure were confirmed using mass spectral fragmentation and FTIR spectroscopic analysis. In addition, several quaternary ammonium salts with new counterions (formic acid, acetic acid and lactic acid) were also synthesized by ion exchange reaction of methyl carbonate quaternary ammoniums with the corresponding acids. These new compounds reduced the surface tension of water to a minimum value of approximately 27 mN m?1 at a concentration of 8.72 × 10?5 mol L?1. They also show efficient corrosion inhibition performances and could significantly inhibit the corrosion of mild steel in acid solutions. It was also found that the biological degradation of these imidazoline surfactants was greater than 98 % after 7 days.  相似文献   
135.
Copper salts, which are abundant, relatively inexpensive and possess low toxicity, have long been used as versatile catalysts for various reactions in organic synthesis. Recently, the development of Cu‐catalyzed or ‐mediated C H functionalization reactions has gained significant attention. Since the pioneering work of Daugulis on the introduction of 8‐aminoquinoline and picolinic acid auxiliaries as removable directing groups in transition metal‐catalyzed C H bond activations, the combination of copper salts with these bidentate directing groups has emerged as an innovative strategy for the construction of carbon‐carbon or carbon‐heteroatom bonds through C H bond cleavage. In addition to the 8‐aminoquinoline and picolinamide systems, several other bidentate directing groups including the 2‐aminophenyloxazoline group by Yu and Dai and the PIP system by Shi, have been developed as well. This review intends to cover most of the recent advances on copper‐catalyzed or ‐mediated direct sp2 and sp3 C H bond functionalizations assisted by these bidentate directing groups. The major achievements in this area are discussed and catalogued by the type of bonds formed (C C, C O, C N, C S, C P etc.). Special attention is paid to the reaction mechanisms. Selected examples of substrates are listed as well. In addition, a personal outlook is given at the end.

  相似文献   

136.
An unexpected reaction of cinnamylanilines was achieved through the radical cation salt‐induced aerobic oxidation of sp3 C H bonds, providing a series of 2‐arylquinolines. The mechanistic study shows that the cinnamylaniline was oxidized to an imine, which was attacked by the aniline generated through decomposition of the corresponding imine. After further intramolecular cyclization and aromatization, 2‐arylquinolines were obtained. This reaction provides a new method to construct 2‐arylquinolines from readily accessible starting materials.

  相似文献   

137.
In this work, we obtain the highest reported power conversion efficiency (13.3%) for sulfur‐free CIGSe solar cells by solution processing. Intentional sodium incorporation is achieved directly by dissolving sodium salts in the ink. The effect on solar cell properties of three sodium sources is investigated: NaCl, NaHCO2, and NaSCN. A comparison is made with absorbers grown on soda‐lime glass substrates and in the absence of sodium sources. The incorporation via sodium salts yields significantly better results, which is attributed to enhanced‐sodium availability. A comparison with identically annealed sputtered metal precursor layers capable of delivering 15.1% module efficiency suggests that the cell results are limited by the selenization procedure. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
138.
快速浅层床离子交换技术在胺液净化中的应用   总被引:1,自引:0,他引:1  
张莉霞 《广州化工》2010,38(7):209-211
控制和脱除溶剂中的杂质和降解产物是保持溶剂清洁的关键。胺液在线净化设备脱除热稳态盐是溶剂过滤的有益补充。浅层床离子交换工艺具有树脂细、床层矮、压缩填充、逆流再生、周期短、树脂用量小等优点,克服了传统离子交换技术设备体积大、树脂利用效率低的缺陷。该技术已应用于胺液净化,在镇海炼化取得了良好的应用成果。  相似文献   
139.
本文综述了国内外氨基葡萄糖硫酸盐及其复盐制备方法的研究进展,并对各种制备方法的做了对比和评价。  相似文献   
140.
铜盐对RDX-CMDB推进剂燃烧性能的影响   总被引:2,自引:0,他引:2  
研究了6种铜盐(DBC、CNI、NT-Cu、B-Cu、S-Cu、A-Cu)以及铜盐/炭黑复配体系对RDX-CMDB推进剂燃烧性能的影响,用扫描电镜和元素分析测试了推进剂的熄火表面.结果表明,铜盐可降低RDX-CMDB推进剂在16~22 MPa的压强指数;在10~22 MPa,铜盐和铜/炭黑混合物对RDX-CMDB推进剂燃烧特性的影响不显著.铜盐催化剂以及铜盐和炭黑复配催化剂对推进剂的燃烧反应有一定的促进作用.  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