全文获取类型
收费全文 | 69840篇 |
免费 | 1512篇 |
国内免费 | 1773篇 |
专业分类
电工技术 | 2388篇 |
综合类 | 1965篇 |
化学工业 | 7150篇 |
金属工艺 | 2070篇 |
机械仪表 | 4406篇 |
建筑科学 | 4787篇 |
矿业工程 | 3017篇 |
能源动力 | 773篇 |
轻工业 | 11526篇 |
水利工程 | 1970篇 |
石油天然气 | 2422篇 |
武器工业 | 384篇 |
无线电 | 8223篇 |
一般工业技术 | 14591篇 |
冶金工业 | 1945篇 |
原子能技术 | 905篇 |
自动化技术 | 4603篇 |
出版年
2023年 | 425篇 |
2022年 | 546篇 |
2021年 | 501篇 |
2020年 | 446篇 |
2019年 | 539篇 |
2018年 | 574篇 |
2016年 | 377篇 |
2015年 | 561篇 |
2014年 | 1292篇 |
2013年 | 1016篇 |
2012年 | 4952篇 |
2011年 | 5781篇 |
2010年 | 1959篇 |
2009年 | 1736篇 |
2008年 | 4628篇 |
2007年 | 4401篇 |
2006年 | 4012篇 |
2005年 | 3605篇 |
2004年 | 3162篇 |
2003年 | 2864篇 |
2002年 | 2596篇 |
2001年 | 2210篇 |
2000年 | 2158篇 |
1999年 | 1613篇 |
1998年 | 1210篇 |
1997年 | 1168篇 |
1996年 | 1191篇 |
1995年 | 1203篇 |
1994年 | 1209篇 |
1993年 | 944篇 |
1992年 | 1065篇 |
1991年 | 1032篇 |
1990年 | 1055篇 |
1989年 | 890篇 |
1988年 | 648篇 |
1987年 | 720篇 |
1986年 | 666篇 |
1985年 | 648篇 |
1984年 | 616篇 |
1983年 | 569篇 |
1982年 | 563篇 |
1981年 | 528篇 |
1980年 | 378篇 |
1979年 | 309篇 |
1977年 | 285篇 |
1976年 | 293篇 |
1975年 | 320篇 |
1974年 | 325篇 |
1967年 | 360篇 |
1965年 | 360篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
采用X射线荧光分析仪、X射线衍射仪、N2物理吸附仪、场发射扫描电子显微镜等仪器表征了苏州、广西和美国佐治亚州3个产地的高岭土,并以此3种高岭土为原料制备了模型催化裂化(FCC)催化剂,在ACE评价装置上对比了模型催化剂的反应性能。结果表明:苏州及广西高岭土主要组分为高岭石,佐治亚高岭土主要组分为地开石及珍珠陶土;苏州高岭土呈片状,还含有少量棒状颗粒;广西高岭土呈多层片状,晶粒粒径较大;佐治亚高岭土呈薄片状,晶粒粒径较小;3种高岭土制备的模型催化剂反应活性、Na2O及RE2O3质量分数相近;广西高岭土制备的模型催化剂具有最大的孔体积和磨损指数,但比表面积最小,具有较强的重油转化能力,其目标产物(液化气+汽油)和副产物(干气+焦炭)收率都高于苏州、佐治亚高岭土制备的催化剂的。 相似文献
2.
3.
4.
Mohamed A.El-Nemr Ibrahim M.A.Ismail Nabil M.Abdelmonem Ahmed El Nemr Safaa Ragab 《中国化学工程学报》2021,36(8):199-222
Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars, Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, were made from watermelon peel via dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH_2 or Triethylenetetramine(TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET, BJH,SEM, FT-IR, TGA, DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B,98% for Melon-BO-NH_2 and 99% for Melon-BO-TETA biochars of 100 mg·L~(-1) Cr(VI) ions initial concentration and 1.0 g·L~(-1) adsorbents dose. The unmodified biochar(Melon-B) and modified biochars(Melon-BO-NH_2 and Melon-BO-TETA) had maximum adsorption capacities(Qm) of 72.46, 123.46, and 333.33 mg·g~(-1), respectively.The amination of biochar reduced the pore size of modified biochar, whereas the surface area was enhanced.The obtained data of isotherm models were tested using different error function equations. The Freundlich,Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, respectively. The adsorption rate was primarily controlled by pseudo-second–order rate model. Conclusively, the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B, Melon-BO-NH_2 and Melon-BO-TETA could be explained for acid–base interaction and hydrogen bonding interaction. 相似文献
5.
9.
Covalent triazine frameworks (CTFs) have been recently employed for visible light-driven photocatalysis due to their unique optical and electronic properties. However, the usually highly hydrophobic nature of CTFs, which originates from their overall aromatic backbone, leads to limitations of CTFs for applications in aqueous media. In this study, we aim to extend the range of the application media of CTFs and design hybrid material of a CTF and mesoporous silica (SBA-15) for efficient photocatalysis in aqueous medium. A thiophene-containing CTF was directly synthesized in mesopores of SBA-15. Due to the high surface area and the added hydrophilic properties by silica, the hybrid material demonstrated excellent adsorption of organic molecules in water. This leads not only to high photocatalytic performance of the hybrid material for the degradation of organic dyes in water, but also for efficient photocatalysis in solvent-free and solid state. Furthermore, the reusability, stability and easy recovery of the hybrid material offers promising metal-free heterogeneous photocatalyst for broader applications in different reaction media. 相似文献
10.