全文获取类型
收费全文 | 49838篇 |
免费 | 617篇 |
国内免费 | 975篇 |
专业分类
电工技术 | 950篇 |
技术理论 | 1篇 |
综合类 | 662篇 |
化学工业 | 4997篇 |
金属工艺 | 1156篇 |
机械仪表 | 2873篇 |
建筑科学 | 3112篇 |
矿业工程 | 1808篇 |
能源动力 | 302篇 |
轻工业 | 8939篇 |
水利工程 | 1031篇 |
石油天然气 | 1333篇 |
武器工业 | 201篇 |
无线电 | 6406篇 |
一般工业技术 | 13382篇 |
冶金工业 | 1015篇 |
原子能技术 | 521篇 |
自动化技术 | 2741篇 |
出版年
2023年 | 246篇 |
2022年 | 285篇 |
2021年 | 264篇 |
2018年 | 261篇 |
2015年 | 282篇 |
2014年 | 692篇 |
2013年 | 531篇 |
2012年 | 4272篇 |
2011年 | 5123篇 |
2010年 | 1220篇 |
2009年 | 921篇 |
2008年 | 3793篇 |
2007年 | 3606篇 |
2006年 | 3125篇 |
2005年 | 2752篇 |
2004年 | 2258篇 |
2003年 | 1978篇 |
2002年 | 1783篇 |
2001年 | 1560篇 |
2000年 | 1446篇 |
1999年 | 947篇 |
1998年 | 618篇 |
1997年 | 566篇 |
1996年 | 563篇 |
1995年 | 578篇 |
1994年 | 558篇 |
1993年 | 419篇 |
1992年 | 510篇 |
1991年 | 537篇 |
1990年 | 540篇 |
1989年 | 492篇 |
1988年 | 416篇 |
1987年 | 488篇 |
1986年 | 459篇 |
1985年 | 472篇 |
1984年 | 420篇 |
1983年 | 389篇 |
1982年 | 388篇 |
1981年 | 384篇 |
1980年 | 293篇 |
1979年 | 250篇 |
1977年 | 268篇 |
1976年 | 279篇 |
1975年 | 309篇 |
1974年 | 309篇 |
1972年 | 278篇 |
1971年 | 268篇 |
1970年 | 261篇 |
1967年 | 358篇 |
1965年 | 344篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
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
2.
3.
随着当前社会经济的进步,近年来我国工业发展极为迅速,轧钢机械设备作为工业生产的关键机械设备,其质量性能以及运行过程稳定性,决定了整个工业行业整体经济效益;但在实际实践期间轧钢机械设备轴瓦作为设备的关键部位,由于目前所存在的对其检修维护不足会直接使得整个轧钢机械设备运行稳定性无法得到保障,一定程度上对我国工业发展造成不利影响,因此注重轧钢机械设备轴瓦的检修与维护措施设置,也是保障我国工业发展能够高效、稳定发展下去的必要条件。 相似文献
4.
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
6.
又到了“十一”长假,除了计划着外出旅游,对于数码玩家,可千万别忘了给自己留点时间,好好地清理一下手中的数码设备。数码相机、数码摄像机、掌上电脑,哦!还有身边的笔记本电脑。这些功臣们跟随自己在这几个月里又立下了不少汗马功劳,如今过节,该好好地“慰劳”一下它们,给它们的屏幕做一下“皮肤护理”了。 相似文献
7.
8.
9.
1 Introduction High power laser diode arrays (LDA) have many advan- tages such as small volume, long working life, high slope efficiency and high optical density, so they have many applications in medical treatment, material pro- cessing, and for the pumping source of solid laser and etc. But unfortunately, the LDA can not be easy to use directly in these fields because of their poor beam quality and extremely asymmetric divergent beams (!x≈ 5°~10°and !y≈20°~35°, for example), so it … 相似文献
10.