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   90866篇
  免费   8519篇
  国内免费   5977篇
电工技术   2899篇
技术理论   1篇
综合类   5560篇
化学工业   22763篇
金属工艺   7452篇
机械仪表   4733篇
建筑科学   3237篇
矿业工程   2338篇
能源动力   2243篇
轻工业   5511篇
水利工程   1322篇
石油天然气   2975篇
武器工业   699篇
无线电   11177篇
一般工业技术   15766篇
冶金工业   3347篇
原子能技术   1164篇
自动化技术   12175篇
  2024年   227篇
  2023年   1691篇
  2022年   2204篇
  2021年   3392篇
  2020年   2941篇
  2019年   2743篇
  2018年   2435篇
  2017年   2968篇
  2016年   3319篇
  2015年   3505篇
  2014年   4825篇
  2013年   5153篇
  2012年   5721篇
  2011年   7621篇
  2010年   5700篇
  2009年   6389篇
  2008年   5471篇
  2007年   6138篇
  2006年   5380篇
  2005年   4796篇
  2004年   3934篇
  2003年   3568篇
  2002年   3028篇
  2001年   1983篇
  2000年   1904篇
  1999年   1548篇
  1998年   1212篇
  1997年   958篇
  1996年   899篇
  1995年   687篇
  1994年   654篇
  1993年   483篇
  1992年   381篇
  1991年   307篇
  1990年   228篇
  1989年   199篇
  1988年   128篇
  1987年   108篇
  1986年   121篇
  1985年   67篇
  1984年   45篇
  1983年   47篇
  1982年   53篇
  1981年   31篇
  1980年   42篇
  1979年   32篇
  1978年   12篇
  1977年   18篇
  1976年   17篇
  1974年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
通过对液态染料溶解性、稳定性、耐水解程度等的测试,综合考察了添加剂的种类及用量对高浓度液态活性艳蓝P-3R性能的影响,结果表明:在所考察的四种有机共溶剂中,N-甲基吡咯烷酮(NMP)的效果最好,且其最佳用量为10%;缓冲溶液中Na2HPO4/NaH2PO4的效果较好,最佳用量为3%.  相似文献   
992.
用NaOH熔融样品,向标准溶液中加入同样量的KOH基体,建立工作曲线,试样酸化后,直接用ICP-AES法测定。  相似文献   
993.
1-环丙基-7-氯-6-(1-哌嗪基)-4-氧-1,4-二氢-3-喹啉羧酸盐酸盐为环丙沙星合成中主要的杂质之一,研究其物化性质对于改善环丙沙星的结晶分离提纯具有重要意义。本文研究了1-环丙基-7-氯-6-(1-哌嗪基)-4-氧-1,4-二氢-3-喹啉羧酸盐酸盐的熔化,分解特性,溶解度与离子强度,温度和pH值的关系,并测定了该物质的离解常数,估算了该物质在水溶液中的活度积。  相似文献   
994.
对不锈钢缓蚀剂2-炔丙基巯基苯并咪唑的合成工艺进行了研究。先由邻苯二胺和二硫化碳合成2-巯基苯并咪唑,炔丙醇和三氯化磷合成3-氯丙炔;再由2-巯基苯并咪唑和3-氯丙炔在丙酮溶剂中合成2-炔丙基巯基苯并咪唑。对是否使用相转移催化剂进行了探讨,认为无相转移催化剂可使操作简便,适合于工业化生产。  相似文献   
995.
S Cui  R Canet  M Couzi 《Carbon》2003,41(4):797-809
Carbon nanotubes prepared by a classical CVD method with a nickel catalyst have been characterized, then used as conducting anisometric objects dispersed into a polymeric matrix. In a first part, these nanotubes are structurally characterized before and after heat treatments (HTT=1500, 2000, 2500 °C). Diffusion Raman experiments and diamagnetic susceptibility experiments demonstrated their limited graphitized structures.Then, in a second step, a well defined processing way to prepare nanocomposites with a standard epoxy resin is presented. In particular, the use or not of a non-ionic surfactant (Tergitol) to disperse these nanotubes is analyzed. The influence of nanotube contents is examined on the bulk nanocomposite density, the glass transition temperature of the nanocomposites, and the d.c. electrical conductivity behavior. These results demonstrated that the interfacial properties are playing a fundamental role. On one hand, the glass transition temperature is increasing with the nanotube content, and on the other hand, the percolation threshold is found for a rather high critical volumic concentration. Finally, it is demonstrated that a pure geometrical model is not sufficient to explain these behaviors and that a wrapping effect of the organic matrix around the nanotubes has to be considered.  相似文献   
996.
In this study, waste biological sludge is converted to an adsorbent by chemical activation with sulphuric acid. The adsorbent obtained is then applied to the aerated vessel of an activated sludge process treating glucose and phenol to improve the quality of the treated effluent. The sludge-based carbonaceous adsorbent was found to be mesoporous in nature, with a good adsorption capacity for large molecular weight compounds and limited removal efficiency for smaller molecules such as phenol. The addition of carbon, either sludge-based or commercial, enhanced phenol removal from 58% to 98.7% and from 87% to 93% the organic matter removal as measured by the chemical oxygen demand (COD) when operated with feed concentrations of 100 mg phenol/l and 2500 mg COD/l. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based adsorbents in spite of the higher adsorption capacity of the former. It is suggested that powdered adsorbent bioregeneration in the combined AS-PAC system may be impaired by the obstruction of pores due to bacterial growth, the effect being more important for the commercial activated carbon with a narrower pore size distribution.  相似文献   
997.
The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH3-TPD and TPR techniques were used for catalysts characterization. Results of NH3-SCO were compared with those of selective catalytic reduction of NO with NH3 (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR) and activity tests with a various contact time. Catalytic performance of the studied samples depends on both kind and loading of transition metals in the mixed metal oxide system. The Cu-containing samples have been found to be the most active catalysts of the NH3-SCO process. Transition metal loading strongly influences distribution of ammonia oxidation products. The highest selectivity to N2 was measured for the catalysts with the lowest transition metal content.  相似文献   
998.
以3-氨基-4-氯苯甲酸和正十六醇为原料,二甲苯为溶剂,对甲苯磺酸为催化剂酯化合成3-氨基-4-氯苯甲酸十六酯。采用傅里叶红外光谱(FTIR)、核磁共振光谱(NMR)的方法对产品的结构进行表征。考察了醇酸摩尔比、催化剂加量、反应物浓度对酯化率的影响。结果表明:醇酸摩尔比1.2:1,催化剂用量为总质量5%,反应物浓度65%,反应时间7 h,酯化率达96.20%,单程收率为73.91%。研究确立了产物提纯、提高单程收率和滤液去除催化剂后回收、重复使用的最佳系统工艺路线,单程收率提至78.90%,总收率为82.62%,产品的纯度高于使用标准。  相似文献   
999.
酸性气流脱除物是净化天然气、合成气、煤气时脱除的物质,STW-3#是由该物质制成的样品之一。就STW-3#对NR硫化性能的影响进行了研究。结果表明,STW-3#对NR有较好的硫化促进特性和一定的软化增塑作用;其用量3.0份以下时,硫化特性较差,3.0份以上时硫化特性较好,但超过4.0份时有粘辊和喷霜现象。它与促进剂M并用时,硫化特性与促进剂D相似。  相似文献   
1000.
Systems of Pd supported on various La2O3-modified -Al2O3 and CeO2–Al2O3 catalysts were tested for catalytic methanol decomposition and characterized by means of XRD, BET, TPR, H2-chemisorption and CO–FTIR. The addition of lanthanum significantly improved the selectivity of CO and H2 for all the catalysts but showed a different influence on the catalytic activity in two systems. Methanol conversion decreased on La2O3-modified Pd/-Al2O3 catalysts, in line with the reduction of Pd dispersion, while the addition of La2O3 improved the dispersion of Pd and reinforced Pd–CeO2 interaction for La2O3-modified Pd/CeO2–Al2O3 catalysts, which resulted in a high production rate of CO and H2. Thus, a synergistic effect between CeO2 and La2O3 was observed on -Al2O3-supported Pd catalyst for methanol decomposition.  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