全文获取类型
收费全文 | 49975篇 |
免费 | 4963篇 |
国内免费 | 1995篇 |
专业分类
电工技术 | 1420篇 |
技术理论 | 1篇 |
综合类 | 2278篇 |
化学工业 | 13281篇 |
金属工艺 | 5640篇 |
机械仪表 | 853篇 |
建筑科学 | 1217篇 |
矿业工程 | 6314篇 |
能源动力 | 4002篇 |
轻工业 | 1344篇 |
水利工程 | 133篇 |
石油天然气 | 973篇 |
武器工业 | 83篇 |
无线电 | 2460篇 |
一般工业技术 | 7043篇 |
冶金工业 | 8871篇 |
原子能技术 | 466篇 |
自动化技术 | 554篇 |
出版年
2024年 | 180篇 |
2023年 | 881篇 |
2022年 | 1539篇 |
2021年 | 1913篇 |
2020年 | 1841篇 |
2019年 | 1694篇 |
2018年 | 1590篇 |
2017年 | 1737篇 |
2016年 | 1930篇 |
2015年 | 1768篇 |
2014年 | 2751篇 |
2013年 | 2934篇 |
2012年 | 3272篇 |
2011年 | 3975篇 |
2010年 | 2937篇 |
2009年 | 2719篇 |
2008年 | 2289篇 |
2007年 | 2804篇 |
2006年 | 2479篇 |
2005年 | 2077篇 |
2004年 | 1855篇 |
2003年 | 1732篇 |
2002年 | 1527篇 |
2001年 | 1324篇 |
2000年 | 1245篇 |
1999年 | 970篇 |
1998年 | 812篇 |
1997年 | 699篇 |
1996年 | 629篇 |
1995年 | 546篇 |
1994年 | 450篇 |
1993年 | 334篇 |
1992年 | 338篇 |
1991年 | 234篇 |
1990年 | 233篇 |
1989年 | 196篇 |
1988年 | 131篇 |
1987年 | 75篇 |
1986年 | 44篇 |
1985年 | 49篇 |
1984年 | 43篇 |
1983年 | 21篇 |
1982年 | 42篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1959年 | 5篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
91.
Summary In flow through porous media, solutions of poly(ethylene oxide) (PEO) exhibit extension thickening, whereas hydroxypropyl
guar (HPG) solutions are shear-thinning at high concentrations. The results show that the extension-thickening exhibited by
PEO solutions becomes less critical with increasing flow rate as the concentration of HPG in the solution is increased. At
high concentrations of HPG, the presence of PEO inhibits the shear-thinning behaviour, without increasing the apparent viscosity
of the solution. The presence of HPG reduces the rate and extent of degradation of PEO in the flowing solution. 相似文献
92.
天等锰矿石属高硅、低磷贫氧化锰矿石,矿物结晶粒度微细。选矿试验中进行了洗矿、强磁和重选流程研究,试验结果表明,洗矿效果较好,当原矿含锰16.85%,经一段洗矿后,可获得含锰29.77%,锰回收率为86.27%的锰净矿。 相似文献
93.
The conversion of chromite ore from iskenderun region into chromate was investigated. Firstly, the chromite ore was analysed using conventional chemical methods. Then, the effect of some parameters such as roasting time, temperature and the amount of additives on the conversion efficiency to the chromate was examined. The optimum roasting conditions were determined as 300°C, 2 hours, 10 times the stoichiometrically required amounts of NaClO3 and 6 times the stoichiometrically required amounts of KOH. Under these conditions, the maximum recovery of chromate was found to be 100%. The product obtained from the roasting process was leached with water to produce a clean chromate solution. The effect of temperature and solid/liquid (S/L) ratio was investigated in the water leaching experiments. The optimum experimental results obtained were 100% at a 1:5 solid to water ratio at 25°C and 20 min leaching period. The chromate solution was purified using conventional purification processes. 相似文献
94.
The current-voltage (I-V) characteristics of metal-oxide-semiconductor (MOS) structures with hafnium oxide as the gate dielectric film were studied. Sharp shifts from a low-voltage ohmic regime to a tunneling conduction were observed in the high-voltage range. The paper demonstrates that this behavior can be described very well with a double-layer dielectric model. Excellent fittings of the experimental curves were obtained and the related key structural and physical parameters were obtained. The model fitting further suggests the optimal annealing conditions for preparing the hafnium oxide films. 相似文献
95.
96.
Low carbon steel was oxidized over the temperature range 1000‐1250°C in O2‐CO2‐H2O‐N2, O2‐H2O‐N2, and O2‐CO2‐N2 gas mixtures. Oxidation times were 12‐120 min. and the scales were 50‐2000 μm thick. The variations of these parameters were chosen to elucidate the phase composition of oxide scales under conditions similar to those of reheating furnaces in hot strip mills, using either thin slab casting or conventional casting and rolling technology. Two types of scales have been observed which are influenced by the furnace atmosphere, oxidation time, and temperature. The first type is a crystalline scale with an irregular outer surface, composed mostly of wustite (FeO), and a negligible amount of magnetite (Fe3O4). The second type is the classical three‐layer scale, composed of wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3). In general, the experiments showed that an increase in oxidation time decreased the percentage of wustite while the percentages of magnetite and hematite increased. A rise in oxygen concentration in the gas mixture increased the percentages of magnetite and hematite, confirming earlier experimental findings. In water vapour‐free atmospheres O2‐CO2‐N2, the oxide scales had a low percentage of wustite, and high percentage of magnetite and hematite. Carbon dioxide showed a small influence at 1100°C, and a negligible one at 1250°C. 相似文献
97.
The role of gas phase CH3 radicals in the oxidative coupling of CH4 over 1 wt% Sr/La2O3 is supported by the observations that (i) this is a very effective catalyst for the generation of CH3 · radicals and (ii) the concentration of CH3 · radicals increases with temperature over the range of 450 °C–800 °C. 相似文献
98.
99.
Ying‐Hung So 《Polymer International》2006,55(2):127-138
Poly(2,4‐dimethyl‐1,4‐phenylene oxide) (PPO), poly(benzo[1,2‐d:5,4‐d′]bisoxazole‐2,6‐diyl‐1,4‐phenylene) (PBO) and poly(benzo[1,2‐d:4,5‐d′]bisthiazole‐2,6‐diyl‐1,4‐phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self‐sensitized photo‐induced electron‐transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo‐induced electron‐transfer mechanism. Methods to stabilize these polymers against photo‐oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry 相似文献
100.