全文获取类型
收费全文 | 7642篇 |
免费 | 1193篇 |
国内免费 | 349篇 |
专业分类
电工技术 | 181篇 |
综合类 | 414篇 |
化学工业 | 1416篇 |
金属工艺 | 1140篇 |
机械仪表 | 89篇 |
建筑科学 | 134篇 |
矿业工程 | 1865篇 |
能源动力 | 138篇 |
轻工业 | 154篇 |
水利工程 | 62篇 |
石油天然气 | 75篇 |
武器工业 | 21篇 |
无线电 | 112篇 |
一般工业技术 | 535篇 |
冶金工业 | 2675篇 |
原子能技术 | 114篇 |
自动化技术 | 59篇 |
出版年
2024年 | 24篇 |
2023年 | 162篇 |
2022年 | 305篇 |
2021年 | 341篇 |
2020年 | 320篇 |
2019年 | 272篇 |
2018年 | 227篇 |
2017年 | 294篇 |
2016年 | 343篇 |
2015年 | 332篇 |
2014年 | 447篇 |
2013年 | 488篇 |
2012年 | 547篇 |
2011年 | 562篇 |
2010年 | 392篇 |
2009年 | 369篇 |
2008年 | 310篇 |
2007年 | 430篇 |
2006年 | 429篇 |
2005年 | 326篇 |
2004年 | 285篇 |
2003年 | 299篇 |
2002年 | 254篇 |
2001年 | 230篇 |
2000年 | 234篇 |
1999年 | 194篇 |
1998年 | 135篇 |
1997年 | 119篇 |
1996年 | 92篇 |
1995年 | 75篇 |
1994年 | 57篇 |
1993年 | 74篇 |
1992年 | 48篇 |
1991年 | 47篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有9184条查询结果,搜索用时 15 毫秒
1.
2.
3.
《International Journal of Hydrogen Energy》2022,47(100):41994-42000
Hydrogen technology is widely considered a novel clean energy source, and electrolysis is an effective method for hydrogen evolution. Therefore, efficient hydrogen evolution reaction (HER) catalysts are urgently needed to replace precious metal catalysts and meet ecological and environmental protection standards. Herein, Ni–Mn–P electrocatalysts are synthesized using facile electrodeposition technology. The influence of the Mn addition on the catalytic behavior is studied by the comprehensive analysis of catalytic performance and morphology of the catalysts. Among them, the Ni–Mn–P0.01 catalyst exhibits small coral-like structures, greatly improving the adsorption and desorption of hydrogen ions and reducing the overpotential hydrogen evolution. Consequently, overpotential at 10 mA cm?2 electric current density is 113 mV, and the value of the Tafel slope achieves 74 mV/dec. Furthermore, the Ni–Mn–P catalyst shows long-time (20 h) stability at current densities of 10 and 60 mA/cm2. The results confirm that the synergistic effect of Ni, Mn, and P accelerates the electrochemical reaction. Meanwhile, the addition of manganese element can change the micromorphology of the catalyst, thereby exposing more active sites to participate in the reaction, enhancing water ionization, improving the catalytic performance. This study opens a new way toward improving the activity of the catalyst by adjusting Mn concentration during the electrodeposition process. 相似文献
4.
Liangtao Yang Liang-Yin Kuo Juan Miguel López del Amo Prasant Kumar Nayak Katherine A. Mazzio Sebastian Maletti Daria Mikhailova Lars Giebeler Payam Kaghazchi Teófilo Rojo Philipp Adelhelm 《Advanced functional materials》2021,31(38):2102939
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. 相似文献
5.
Mn4+激活红光荧光粉是白光半导体发光二极管(wLEDs)领域当前研究热点之一。Mn4+离子2E→4A2跃迁在铝酸盐中的最短发光波长是在MgAl2O4中实现的651 nm发光, 由于其结构中含有形成四面体或八面体配位的两种阳离子格位(Mg2+/Al3+), 易造成所掺杂锰元素存在多种价态(+2/+4/+3等)。本研究通过改变起始原料中Al2O3的晶型(γ/α比例)及退火处理来调控锰离子在MgAl2O4晶格中的占据格位, 对其主要存在价态实现调控。采用荧光光谱和紫外-可见-近红外漫反射光谱技术来表征所合成荧光粉中Mn离子的价态及其演变。研究发现, 高α/(α+γ)比铝源促进Mn2+形成, 而低α/(α+γ)比铝源促进Mn4+形成。通过使用高活性纳米γ-Al2O3为铝源, 有效抑制了锰离子在MgAl2O4中Mg2+格位的占据及Mn2+离子的形成, 经空气中1550 ℃保温5 h的一次高温热处理即可制备出在可见光区只有Mn4+红光发光的高纯高亮度MgAl2O4:Mn4+荧光粉。氧化铝晶型影响锰离子掺杂格位和掺杂价态的本质规律是: 氧化铝活性决定实际固溶掺杂反应步骤, 进而影响锰离子掺杂格位和价态。本研究提出的反应步骤调控作为反应气氛、电荷补偿剂、反应温度三种调控方法外的一种新方法, 为Mn4+激活铝酸盐荧光粉中锰离子掺杂价态调控提供了新思路。 相似文献
6.
花生是一种重要的植物油脂和蛋白资源,水酶法处理花生能够同时得到油脂和具有特定功能的水解蛋白。为提高花生水解蛋白的纯度,在酶解前设计了酸浸过程,以除去花生体系中的可溶性糖和盐类等杂质。在单因素试验的基础上,通过正交试验优化酸浸工艺条件。结果表明,料液比和温度对蛋白质损失率及可溶性糖脱除率都有极显著或显著影响。酸浸工艺的最佳条件为料液比1∶6,处理时间30 min,pH 5,温度50℃。在最佳条件下,可溶性糖脱除率为(83. 11±0. 33)%,蛋白质损失率为(6. 19±0. 13)%。酸浸处理花生后可显著减少花生蛋白中糖的含量,但同时也伴有少量蛋白质损失。 相似文献
7.
Kamalesh Pal Amitava Mukherjee Md. Motin Seikh Parthasarathi Bera Arup Gayen 《Ceramics International》2021,47(10):14798-14808
Synthesis of nanocrystalline pristine and Mn-doped calcium copper titanate quadruple perovskites, CaCu3?xMnxTi4?xMnxO12 (x = 0, 0.5, and 1.0) by modified citrate solution combustion method has been reported. Powder X-ray diffraction patterns attest the phase purity of the perovskite materials. Average particle sizes of all the materials obtained from the Scherrer's formula are in the range of 55–70 nm. The specific surface areas for all the perovskites obtained from BET isotherms are found to be low as expected for the condensed oxide systems and fall in the range of 13–17 m2 g?1. Transmission electron microscopy studies show a reduction in particle size of CaCu3Ti4O12 with increase in Mn doping. Ca and Ti are present in +2 and +4 oxidation states in all the materials as demonstrated by X-ray photoelectron spectroscopy analyses. Cu2+ gets reduced in CaCu3Ti4O12 with higher Mn content. Mn is observed to be present only in +3 oxidation state. All the materials have been examined to be active in CO oxidation as well as H2 production from methanol steam reforming. CaCu3Ti4O12 with ~14 at.% Mn is found to show best catalytic activities among these materials. A comprehensive analysis of the catalytic activities of these perovskites toward CO oxidation and H2 production from MSR reveal the cooperative activity of copper-manganese in the doped perovskites and it is more effective at lower manganese content. 相似文献
8.
9.
湿法炼锌流程中钴渣浸出液中含有高浓度的Fe2+和Mn2+,用分光光度法测定Co2+和Ni2+时,Fe2+-EDTA会严重干扰Co2+和Ni2+的测定;在用光度滴定法测定Zn2+和Co2+合量时,Ni2+对二甲酚橙指示剂具有封闭作用,Mn2+亦与EDTA螯合,导致滴定结果偏高。为消除Fe2+和Mn2+对Zn2+、Co2+和Ni2+测定的干扰,实验进行氧化分离Fe2+和Mn2+预处理,在NaAc/Hac缓冲体系下,以EDTA作显色剂用分光光度法测定Co2+、Ni2+。在波长466nm处,Co2+的线性范围为50~500mg/L时与吸光度呈线性,相关系数R2为0.9992;在384nm处,Ni2+的线性范围为50~500mg/L时与吸光度呈线性,相关系数R2为0.9998。根据分光光度法测出Ni2+物质的量,加入1.1倍的丁二酮肟以除去Ni2+,用二甲酚橙为指示剂,EDTA鳌合-光度滴定法测定Zn2+、Co2+合量,扣减Co2+含量得出Zn2+含量。选取4个锌湿法炼锌流程中钴渣浸出液实际样品,按照实验方法中的分光光度法测定Co2+和Ni2+,光度滴定法测定Zn2+、Co2+合量,Zn2+、Co2+和Ni2+测定结果的相对标准偏差(RSD,n=6)均不大于0.70%,加标回收率分别为99.59%~100.41%、99.69%~100.64%、99.92%~100.08%。 相似文献
10.
针对湖南柿竹园铋精矿火法冶炼过程中存在的成本高、低浓度SO2和散烟排放污染环境、有价金属综合回收率低等问题, 以柿竹园铋精矿为原料, 提出了加压氧化氨浸分离铋与铜、硫的新工艺, 研究了氨水加入量、浸出温度、浸出时间、浸出压力及浸出液固比等因素对铜、硫、铋浸出率的影响。在氨水用量1.8 mL/g铋精矿、液固比4∶1、釜压2.8 MPa、浸出温度160 ℃、浸出时间5 h、搅拌速度600 r/min的优化工艺条件下, 铜、硫浸出率分别达93.57%和92.87%, 铋不浸出并以氧化铋形态全部入渣, 实现了铜、硫与铋的高效分离。 相似文献