全文获取类型
收费全文 | 105629篇 |
免费 | 11285篇 |
国内免费 | 5926篇 |
专业分类
电工技术 | 7430篇 |
技术理论 | 6篇 |
综合类 | 7363篇 |
化学工业 | 22108篇 |
金属工艺 | 8529篇 |
机械仪表 | 4546篇 |
建筑科学 | 8629篇 |
矿业工程 | 4923篇 |
能源动力 | 3001篇 |
轻工业 | 12665篇 |
水利工程 | 2403篇 |
石油天然气 | 6972篇 |
武器工业 | 1339篇 |
无线电 | 8091篇 |
一般工业技术 | 10366篇 |
冶金工业 | 7307篇 |
原子能技术 | 1180篇 |
自动化技术 | 5982篇 |
出版年
2024年 | 436篇 |
2023年 | 1546篇 |
2022年 | 2825篇 |
2021年 | 3550篇 |
2020年 | 3701篇 |
2019年 | 3326篇 |
2018年 | 3121篇 |
2017年 | 3768篇 |
2016年 | 4044篇 |
2015年 | 4096篇 |
2014年 | 6486篇 |
2013年 | 6143篇 |
2012年 | 7759篇 |
2011年 | 7856篇 |
2010年 | 5650篇 |
2009年 | 5743篇 |
2008年 | 5140篇 |
2007年 | 6738篇 |
2006年 | 6344篇 |
2005年 | 5412篇 |
2004年 | 4782篇 |
2003年 | 4247篇 |
2002年 | 3654篇 |
2001年 | 3186篇 |
2000年 | 2713篇 |
1999年 | 2193篇 |
1998年 | 1609篇 |
1997年 | 1301篇 |
1996年 | 1088篇 |
1995年 | 904篇 |
1994年 | 770篇 |
1993年 | 546篇 |
1992年 | 491篇 |
1991年 | 361篇 |
1990年 | 266篇 |
1989年 | 212篇 |
1988年 | 164篇 |
1987年 | 115篇 |
1986年 | 77篇 |
1985年 | 95篇 |
1984年 | 63篇 |
1983年 | 27篇 |
1982年 | 53篇 |
1981年 | 40篇 |
1980年 | 45篇 |
1979年 | 17篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1964年 | 14篇 |
1959年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
991.
两种高压直流电源的比较及在铜冶炼烟气制酸装置电除雾器中的应用 总被引:2,自引:0,他引:2
论述恒压源与恒流源两种高压直流电源的工作原理和技术特点.对两种电源常见故障的原因进行分析,提出相应的解决方法。介绍两种电源在230kt/a诺兰达炉冶炼烟气和270kt/a转炉冶炼烟气制酸装置的电除雾器中的使用情况. 相似文献
992.
993.
994.
采用直接浸清一焙烧法,制备了SO4^2--TiO2/β-沸石催化剂。并以其催化苯乙酮和乙二醇合成了苯乙酮乙二醇缩酮、考察了催化剂的焙烧温度、TiO2负载量、催化剂用量、原料配比、带水剂的种类和用量、田流时间对反应的影响。最佳的反应条件为:催化剂焙烧温度500℃、TiO2负载量10%(质量分数)、催化剂用量1.1g、n(苯乙酮);n(乙二醇)=1:1.2、甲苯20mL、回流时间1.5h。在最佳反应条件下,苯乙酮乙二醇缩酮地度为99.6%,收率可达98.8%.SO4^2-TiO2/β-沸石催化剂制备简单、催化活性高、重复使用性好. 相似文献
995.
Hong?ZhangEmail author Lars?Saaby?Pedersen Dorther?Kristensen Jens?Adler-Nissen Hans?Christian Holm 《Journal of the American Oil Chemists' Society》2004,81(7):653-658
Lipozyme TL IM-catalyzed interesterification for the modification of margarine fats was carried out in a batch reactor at
70°C with a lipase dosage of 4%. Solid fat content (SFC) was used to monitor the reaction progress. Lipase-catalyzed interesterification,
which led to changes in the SFC, was assumed to be a first-order reversible reaction. Accordingly, the change in SFC vs. reaction
time was described by an exponential model. The model contained three parameters, each with a particular physical or chemical
meaning: (i) the initial SFC (SFC0), (ii) the change in SFC (ΔSFC) from the initial to the equilibrium state, and (iii) the reaction rate constant value (k). SFCo and ΔSFC were related to only the types of blends and the blend ratios. The rate constant k was related to lipase activity on a given oil blend. Evaluation of the model was carried out with two groups of oil blends,
i.e., palm stearin/coconut oil in weight ratios of 90∶10, 80∶20, and 70∶30, and soybean oil/fully hydrogenated soybean oil
in weight ratios of 80∶20, 65∶35, and 50∶50. Correlation coefficients higher than 0.99 between the experimental and predicted
values were observed for SFC at temperatures above 30°C. The model is useful for predicting changes in the SFC during lipase-catalyzed
interesterification with a selected group of oil blends. It also can be used to control the process when particular SFC values
are targeted. 相似文献
996.
997.
The three-way catalyst promoters (Ce-Zr)O2, (Pr-Ce-Zr)O2 and (Pr-Zr)O2 were prepared by the sol-gel method. The reduction/oxidation behavior of these mixed oxides was compared. It is shown that the formation of (Pr-Zr)O2 cubic solid solution at high temperature up to 800 °C makes it more reducible, and that the ternary solid solution that formed in (Pr-Ce-Zr)O2 mixed oxides plays an important role in the reduction process. The catalytic performance tests reveal that the introduction of a small amount of praseodymium into (Ce-Zr)O2 favors the light-off temperature of C3H6 and NO and the effectiveness for NO conversion at the lean region. 相似文献
998.
Approximate migration coefficient of interfacial transition zone and the effect of aggregate content on the migration coefficient of mortar 总被引:3,自引:0,他引:3
In this study, the electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. In order to investigate the effect of aggregate content on the chloride migration coefficient of mortar, specimens with different fine aggregate volume fractions were cast and tested. The chloride migration coefficient of mortar was determined experimentally as a function of the volume fraction of aggregate. The chloride migration coefficient of mortar is used to assess the dilution, tortuosity and interfacial transition zone (ITZ) effects of aggregate in the cement-based composites. A model modified from the Bruggeman theory for the migration coefficient of mortar is used, and the regression analysis is used to determine the approximate chloride migration coefficient of ITZ. Based on the experimental and regression analytical results, the approximate ITZ migration coefficient is 2.83, 1.76 and 1.55 times of the matrix migration coefficient for the ITZ with the thickness of 20, 40 and 50 μm, respectively. 相似文献
999.
A method of electrical conductivity and an analysis of recovered explosion products are used to study interaction of aluminum
with detonation products of condensed high explosives. The electrical conductivity of HMX/Al and RDX/Al mixtures is inhomogeneous;
a region with the maximum electrical conductivity is adjacent to the detonation front, whereas the electrical conductivity
decreases with distance from the front. If the wave is incident onto a wall, the electrical resistance of the composite high
explosive increases, which indicates that the high-conducting zone disappears. The electrical conductivity, resistance of
the conducting zone, and the time of resistance growth are found as functions of the particle size of the additive. The results
obtained confirm the reaction of the metal additive with detonation products in a microsecond range of time. An analysis of
condensed explosion products shows that the reaction of aluminum with detonation products proceeds on the particle surface.
The amount of reacted aluminum and the oxide-layer thickness are estimated.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 120–129, Jnuary–February, 2006. 相似文献
1000.
固相微萃取/气相色谱-质谱法分析小茴香挥发性成分 总被引:2,自引:3,他引:2
考察了萃取样品温度、萃取纤维吸附时间及解吸时间对于固相微萃取的影响,确定了固相微萃取小茴香挥发性成分较佳的实验条件为:萃取样品温度60℃,萃取纤维吸附时间40min,脱附温度250℃,脱附时间5min。用计算机谱库检索结合气相色谱保留指数二维定性方法,从小茴香的固相微萃取/气相色谱-质谱联用分析谱图中,鉴定出反式-茴香脑、顺式-茴香脑、爱草脑、葑酮、p-茴香醛、1,8-桉树脑、樟脑等35种小茴香挥发性成分,总质量分数98·70%。 相似文献