全文获取类型
收费全文 | 5032篇 |
免费 | 364篇 |
国内免费 | 163篇 |
专业分类
电工技术 | 5篇 |
综合类 | 167篇 |
化学工业 | 3302篇 |
金属工艺 | 124篇 |
机械仪表 | 51篇 |
建筑科学 | 4篇 |
矿业工程 | 21篇 |
能源动力 | 132篇 |
轻工业 | 101篇 |
水利工程 | 2篇 |
石油天然气 | 1379篇 |
武器工业 | 3篇 |
无线电 | 48篇 |
一般工业技术 | 149篇 |
冶金工业 | 47篇 |
原子能技术 | 9篇 |
自动化技术 | 15篇 |
出版年
2024年 | 5篇 |
2023年 | 61篇 |
2022年 | 129篇 |
2021年 | 176篇 |
2020年 | 119篇 |
2019年 | 143篇 |
2018年 | 119篇 |
2017年 | 129篇 |
2016年 | 173篇 |
2015年 | 166篇 |
2014年 | 254篇 |
2013年 | 240篇 |
2012年 | 301篇 |
2011年 | 290篇 |
2010年 | 229篇 |
2009年 | 245篇 |
2008年 | 239篇 |
2007年 | 276篇 |
2006年 | 249篇 |
2005年 | 280篇 |
2004年 | 234篇 |
2003年 | 214篇 |
2002年 | 201篇 |
2001年 | 146篇 |
2000年 | 156篇 |
1999年 | 122篇 |
1998年 | 115篇 |
1997年 | 70篇 |
1996年 | 59篇 |
1995年 | 70篇 |
1994年 | 82篇 |
1993年 | 54篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 23篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 28篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有5559条查询结果,搜索用时 15 毫秒
41.
42.
The influence of alloying of Pt with 20 at.% of Ni, Co and Fe has been studied in the hydrogenation of 1,3 butadiene. Iron induces the more important modifications, with both higher activity and selectivity. The results are discussed in terms of the surface segregation, the local order in surface and the electronic properties measured by photoemission of core levels. 相似文献
43.
裂解汽油加氢一段催化剂失活原因分析 总被引:1,自引:0,他引:1
介绍了中国石油辽阳石化分公司烯烃厂裂解汽油加氢装置一段全馏分镍系加氢催化剂失活情况及原因分析。通过对酸性硫来源的分析及酸性硫对催化剂影响的评价,总结了处理酸性硫的对策及方法。 相似文献
44.
J. D. Parry J. M. Winterbottom 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1991,50(1):67-80
Silica-supported Ni-Ag catalysts with a loading of 2·1·0.6% (w/w) total metal have been prepared using the precursors nickel dimethylglyoxime and silver nitrate by means of a simple impregnation method. The resulting catalysts were activated by calcination at 260°C in air, followed by hydrogen reduction at 450°C. They were then employed for soyabean oil hydrogenation at 1 bar H2 pressure and 160°C in a stirred batch reactor. Characterisation of the catalysts using temperature-programmed reduction and electron microscopy indicated that alloying of nickel and silver had occurred, but metal particle composition, for a given overall composition, varied with metal particle size and smaller metal particles were nickel rich. The hydrogenation activity and selectivity measurements revealed that the catalysts were more active and selective than a commercial nickel catalyst. Furthermore, the specific activities of the alloy catalysts were a maximum for alloys in the range 70–90 at. % Ni. However, the supported alloy catalysts also gave rise to greater trans isomerisation than the commercial catalyst. This is attributed to hydrogen deficiency caused by large triglyceride molecules blocking hydrogen chemisorption on small nickel particles (10–50 Å in diameter), leading to enhanced cis-trans isomerisation. 相似文献
45.
Shufang Wang Yuanhui Ma Yanji Wang Wei Xue Xinqiang Zhao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(11):1466-1471
BACKGROUND: A single‐step conversion of nitrobenzene (NB) to p‐aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S2O82?/ZrO2 (PSZ) solid acid and Pt‐S2O82?/ZrO2 (Pt‐PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non‐acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single‐step reaction of nitrobenzene over Pt‐PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO2 and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt‐PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. Copyright © 2008 Society of Chemical Industry 相似文献
46.
丁辛醇装置丁醛加氢催化剂在装置扩能投产以后热点上移 (失活 )的速率较快 ,针对催化剂老化的原因进行分析、判断 ,找出原因 ,采用相应的解决措施 ,可延长催化剂使用寿命 ,增加装置效益 相似文献
47.
48.
The effects of H2O and NH3 on the kinetics of the liquid phase hydrogenation of tetralin to decalin at 6.9 MPa and 330°C over commercial P---Ni---Mo/alumina catalysts in the presence of H2S have been investigated. H2O functioned as a mild kinetic inhibitor to an extent sensitive to the H2S level. Quasi in situ XPS was used to investigate the catalyst structure after exposure to H20/H2S. 相似文献
49.
A. Martin D. Gutschick N. I. Jaeger G. Schulz-Ekloff H. Miessner B. Lücke 《Catalysis Letters》1994,27(1-2):119-130
In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol. 相似文献
50.
5-氯-2-[2-羟基-3-叔丁基-5-(3-丙酸甲酯基)苯基]-2H-苯并三唑的合成 总被引:1,自引:0,他引:1
通过重氮偶合、还原环化和酯化反应合成了5-氯2-[2-羟基-3-叔丁基-5-(3-丙酸甲酯基)苯基]-2H-苯并三唑,并进行了工业放大实验,收率53.0%~55.0%。偶合反应时,以十二烷基苯磺酸钠为乳化试剂,pH=5~8,收率为73.7%;采用n(偶合物):n(保险粉):n(NaOH)=1.0:3.5:15.8进行还原反应,收率81.0%。用MS和~1H NMR谱图表征了产物的结构,测定了产物的紫外吸收和透光率。 相似文献