全文获取类型
收费全文 | 4970篇 |
免费 | 374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 | 3255篇 |
金属工艺 | 124篇 |
机械仪表 | 49篇 |
建筑科学 | 4篇 |
矿业工程 | 21篇 |
能源动力 | 131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 | 47篇 |
一般工业技术 | 148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 | 118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 | 207篇 |
2002年 | 190篇 |
2001年 | 132篇 |
2000年 | 150篇 |
1999年 | 117篇 |
1998年 | 107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5507条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(4):2187-2199
A superhydrophilic Ru-based 3D electrode, denoted as Ru-PA/NF, was fabricated under the assistance of phytic acid (PA) for electrocatalytic hydrogenation of p-Nitrophenol. PA serves as a multifunctional modulator to facilitate the dispersion of active Ru species in porous nickel foam (NF), meanwhile enhance the surface wettability as well as adjust the micromorphology. In alkaline media, the Ru-PA/NF electrode shows the PNP conversion of 94.68% and the PAP selectivity of 99% after 9 h, accompanied by the faraday efficiency (FE) of 73.15%. Over the superhydrophilic Ru-PA/NF the rate constant of PNP conversion into PAP is 2.62-times higher than that over the hydrophobic Ru/NF prepared without the aid of PA, and FE of Ru-PA/NF is 1.28-times higher than Ru/NF. This can be ascribed to intriguing features of Ru-PA/NF involving higher Ru loading, more exposed sites, superior electrolyte wetting along with faster charge transfer rate. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(64):27566-27578
Electrochemical hydrogenation is an environmentally favorable alternative to chemical reduction of indigo because it performs under ambient conditions using water as the donor of hydrogen. The purpose of this work is to fabricate electrocatalysts with high activity and durability for electrocatalytic hydrogenation of indigo. This work compares the performances of a series of Ni based catalysts (Ni, NiMo, NiP and NiMoP) on the substrate of carbon felt (CF) for electrolyzing water. Both the overpotential and Tafel slop are decreased as a function of the components as Ni > NiMo > NiP > NiMoP. Hence, NiMoP/CF shows the excellent performance based on the thermodynamics (η10 = 239 mV) and kinetics (Tafel slope = 89.7 mV·dec?1) for splitting water. Further, the electrode of NiMoP/CF was used for the electrocatalytic hydrogenation of indigo. The conversion efficiency and Faradic efficiency can be improved as 26.2% and 10.7% respectively. Furthermore, the dyeing behavior of the electrohydrogenated indigo is similar to that of conventional reduction methods. Thus, the present work offers foundational results and paves the way for the design of new catalytic materials for the reduction of vat dyes. 相似文献
3.
针对芳香硝基化合物的催化选择性加氢反应,开发可替代贵金属催化剂的低成本、高效非贵金属催化剂,对于芳香胺类化合物的绿色生产具有重要意义。利用简易、可规模化的制备方法,以镍—2,5-吡啶二羧酸金属有机框架为前驱体,热解制备了氮掺杂石墨碳包覆镍纳米催化材料(Ni@CN)。采用X射线衍射、扫描电镜、透射电镜、元素分析、N2吸脱附等检测手段对Ni@CN的物化性质进行了表征,并对其催化性能进行了评价。结果表明,Ni@CN可在温和条件下(85℃,1.0 MPa H2)高效加氢含取代官能团的芳香硝基化合物生成对应的芳香胺类化合物。对比试验表明,镍纳米颗粒是Ni@CN的加氢活性中心,而石墨碳壳的存在有利于优先吸附硝基官能团。此外,进一步考察了Ni@CN的循环使用性能以及抗硫化物中毒的特性。 相似文献
4.
Theoretical investigation of solvent effects on the selective hydrogenation of furfural over Pt(111)
Jian Wang Cun-Qin Lv Jian-Hong Liu Rong-Rong Ren Gui-Chang Wang 《International Journal of Hydrogen Energy》2021,46(2):1592-1604
It was well known that solvent effect plays a very important role in the catalytic reaction. There are many theoretical studies on the solvent effect in homogeneous catalysis while there are few theoretical studies on the solvent effect in the heterogeneous catalytic reaction and there has been no work to investigate the solvent effect on furfural transformation in heterogeneous catalysis. In the present work, both the density functional calculations and the microkinetic analysis were performed to study the selective hydrogenation of furfural over Pt(111) in the presence of methanol as well as toluene and compared with that in the gas condition. The present results indicated that the methanol can enhance the adsorption strength of furfural and other oxygen-containing reaction species due to its relatively strong polarity properties and this can be a main reason for solvent-induced high activity and selectivity. Another reason is that reaction paths study showed that the presence of methanol solvent makes the dehydrogenation of furfural less thermochemical due to the fact that furfural is more stabilized than that of dehydrogenation species, and methanol also has an inhibition effect on the dehydrogenation of furfural in the kinetic aspect, and further energetic span theory proves highest activity and selectivity for hydrogenation in methanol solvent of vapor, methanol and toluene. Moreover, microkinetic model simulation demonstrated that the activity and selectivity of hydrogenation in methanol is both higher than that in vapor and toluene. The much higher activity in methanol is due to the stabilized adsorbed reactants in the surface, which leads to a higher surface coverage of furfural. It might be proposed based on the present work that a solvent with relatively strong polarity may be favorable for the high selective hydrogenation of furfural. 相似文献
5.
6.
Kai Li Tengteng Lyu Junyi He Ben W. L. Jang 《Frontiers of Chemical Science and Engineering》2020,14(6):929
Five hundred ppm Pd/CeO2 catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction. Pd/CeO2 catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction. Excellent ethylene selectivity of ~100% was obtained in the whole reaction temperature range of 50°C–200°C for samples calcined at temperatures of 600°C and 800°C. This could be ascribed to the formation of PdxCe1−xO2−y or Pd-O-Ce surface species based on the X-ray diffraction and X-ray photoelectron spectroscopy results, indicating the strong interaction between palladium and ceria. 相似文献
7.
Carina Heisig Jelka Diedenhoven Christopher Jensen Helmut Gehrke Thomas Turek 《化学工程与技术》2020,43(3):484-492
The conversion of bio-based succinic acid (SA) to the value-added chemicals 1,4-butanediol (BDO), γ-butyrolactone (GBL), and tetrahydrofuran (THF) can replace the corresponding petrochemical production routes to achieve a sustainable process. The reaction network for aqueous-phase catalytic hydrogenation of succinic acid over a supported Re-Pd catalyst was identified and the reaction kinetics was determined. With the developed kinetic model, the composition of the product mixture regarding the desired products (BDO, GBL, THF) can be described as a function of educt concentration, temperature, and pressure. The maximum BDO yield was achieved at high pressure and low temperature, while low pressure and high temperature favored GBL and THF production. 相似文献
8.
以废弃的流化催化裂化催化剂(简称SFCC)为载体、β-环糊精为金属络合剂、硝酸镍为镍源,采用湿法浸渍法制备β-环糊精修饰的Ni/SFCC催化剂(简称Ni/SFCC-CD催化剂),考察其对C9石油树脂的催化加氢性能。通过BET比表面积测试、H2程序升温还原、X射线光电子能谱等手段对催化剂的物相结构进行表征,研究β-环糊精的作用机理及其对催化剂加氢性能的影响。研究结果表明:在反应温度为260 ℃、反应压力为7 MPa、反应时间为2.0 h的最优条件下,采用Ni/SFCC-CD催化C9石油树脂加氢,可制得溴值为1.45 gBr/(100 g)、色号(加纳德)小于1的水白色氢化C9石油树脂,催化剂循环使用4次后仍保持良好活性;β-环糊精的作用机理是:β-环糊精与硝酸镍产生络合作用,抑制硝酸镍的分解、控制NiO的结晶过程和增强活性组分Ni与载体之间的相互作用力,从而提高了Ni/SFCC-CD的催化活性和稳定性。 相似文献
9.
10.
K. I. Baskakova O. V. Sedelnikova E. V. Lobiak P. E. Plyusnin L. G. Bulusheva A. V. Okotrub 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(4):342-347
AbstractIn the present work, we compare the structure and transport properties of carbon nanohorns (CNHs) synthesized by arc evaporation of graphite alone and with the addition of some portion of toluene. The materials have been investigated using transmission electron microscopy, Raman and infrared spectroscopies, thermogravimetric and BET analyses. The addition of a small amount of toluene during the evaporation of graphitic rod increases the length of CNHs, affects their hierarchical arrangement in aggregates and results in surface functionalization. All these features significantly enhance the conductivity of CNHs obtained with toluene additive in comparison with the pristine CNHs. 相似文献