全文获取类型
收费全文 | 24410篇 |
免费 | 2644篇 |
国内免费 | 1368篇 |
专业分类
电工技术 | 963篇 |
技术理论 | 2篇 |
综合类 | 2025篇 |
化学工业 | 5412篇 |
金属工艺 | 806篇 |
机械仪表 | 1092篇 |
建筑科学 | 1638篇 |
矿业工程 | 792篇 |
能源动力 | 398篇 |
轻工业 | 5224篇 |
水利工程 | 335篇 |
石油天然气 | 1459篇 |
武器工业 | 204篇 |
无线电 | 1343篇 |
一般工业技术 | 2481篇 |
冶金工业 | 1188篇 |
原子能技术 | 361篇 |
自动化技术 | 2699篇 |
出版年
2024年 | 129篇 |
2023年 | 449篇 |
2022年 | 716篇 |
2021年 | 1070篇 |
2020年 | 976篇 |
2019年 | 828篇 |
2018年 | 771篇 |
2017年 | 892篇 |
2016年 | 934篇 |
2015年 | 967篇 |
2014年 | 1510篇 |
2013年 | 1794篇 |
2012年 | 1840篇 |
2011年 | 1807篇 |
2010年 | 1348篇 |
2009年 | 1376篇 |
2008年 | 1178篇 |
2007年 | 1394篇 |
2006年 | 1260篇 |
2005年 | 1088篇 |
2004年 | 934篇 |
2003年 | 875篇 |
2002年 | 707篇 |
2001年 | 622篇 |
2000年 | 495篇 |
1999年 | 421篇 |
1998年 | 333篇 |
1997年 | 336篇 |
1996年 | 225篇 |
1995年 | 224篇 |
1994年 | 175篇 |
1993年 | 126篇 |
1992年 | 134篇 |
1991年 | 81篇 |
1990年 | 78篇 |
1989年 | 55篇 |
1988年 | 34篇 |
1987年 | 44篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1966年 | 3篇 |
1961年 | 5篇 |
1959年 | 3篇 |
1958年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Methylated-β-cyclodextrin (Me-β-CD) was used to complex the photoinitiator, 2,2-dimethoxy-2-phenyl acetophenone (DMPA), yielding a water-soluble host/guest complex. The comparative studies demonstrated that the Me-β-CD complexed DMPA exhibited a high photoreactivity identical to the uncomplexed DMPA, while the CD complex obviously influenced the products of primary photolysis of DMPA and the photopolymerization kinetics due to the steric effect of CD on the subsequent initiation reactions. The photopolymerization rate of acrylamide can be described by the equation: Rp=K[2a]0.62[M]1.37[I]0.5[Me-β-CD]0. The mechanism of polymerization was also discussed. 相似文献
62.
通过优化工艺条件,严控进料质量、改造循环氢压缩机油系统、调整二甲苯塔操作等措施,使催化剂在运行末期,也能发挥出良好的催化性能,并延长催化剂使用寿命;提高了催化剂处理C10芳烃的能力,降低重芳烃产率,提高经济效益。为催化剂运行末期操作和正常操作提供有益的探索。 相似文献
63.
本文应用NOPD技术设计了一种复合多层板,按照四边固定薄板结构的模态振型,对不同的NOPD填充形式,进行声学实验,来评价不同填充形式在降低板类结构声辐射方面的效果,分析了该类板结构声振耦合的关系并验证了NOPD技术对声辐射控制的作用。 相似文献
64.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
65.
66.
Anumberoflanthanideternarycomplexescon tainingheterocyclicamineshavebeenreportedsince1960 [1] .Inrecentyearsmuchattentionhasbeenpaidtoquaternarycomplexesoflanthanidesbecauseofin terestingstructure ,coordinationmode ,competitionre actionandproperty[2~ 9] .ESRcane… 相似文献
67.
68.
以燕化集团公司炼油事业部用大庆原油生产的HVI350、HVI650、HVI120BS为基础油,研制出YL-1043柴油机油复合剂。以YL-10434.0%的剂量可调配CC30及CC40油品,以YL-10436.73%的剂量另补加0.27%的添加剂A可调配CD40油品,其性能达到了GB11122-1997柴油机油标准。以该复合剂调配CC、CD级油品,与燕化公司原用配方相比,分别降低添加剂剂量1.46%及1.5%,每吨油可节约添加剂费用183.3元及207.3元 相似文献
69.
化学反应和气相色谱法联合测定含烯汽油中共轭二烯烃含量 总被引:3,自引:0,他引:3
建立了利用共轭二烯烃与马来酸酐的Diels-Alder特性反应和1m×1.7mm(id)非极性固定液SE-30填充柱气相色谱法联合分析含烯汽油中的共轭二烯烃含量的方法。该柱能用低碳数的正构烷烃如正十一烷作内标物,内标物与油样组份分离很好,色谱分析一次4min,油样的相对标准偏差为1.7%。在一定的化学反应条件下,用I2和AlCl3作催化剂,当I2、AlCl3与共轭二烯烃的物质的量比分别为0.8×10-5和(1~2)×10-3时,异戊二烯有最高的转化率分别为68.51%和98.18%,回流反应装置的挥发损失率为0.28%。 相似文献
70.
The interaction of different metal oxides such as Co3O4, NiO, Al2O3, Cr2O3, Fe2O3 and SiO2 with Na2SO4 at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were
carried out as a function of Na2SO4 in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis
and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM).
The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study
of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined
quantitatively using atomic absorption spectrophotometry.
The high temperature interaction products usually contain a 3-phase structure namely, Na2O·M2O
x
, M2O
x
and metal sulphide and/or metal sulphate. The formation of Na2O·M2O
x
depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility
conditions Na2O·M2O
x
is invariably formed, but as soon as this condition is relaxed the oxide. M2O
x
, precipitates and forms a separate phase. 相似文献