全文获取类型
收费全文 | 10933篇 |
免费 | 2010篇 |
国内免费 | 2588篇 |
专业分类
化学 | 12313篇 |
晶体学 | 156篇 |
力学 | 326篇 |
综合类 | 62篇 |
数学 | 195篇 |
物理学 | 2479篇 |
出版年
2024年 | 54篇 |
2023年 | 197篇 |
2022年 | 542篇 |
2021年 | 510篇 |
2020年 | 733篇 |
2019年 | 537篇 |
2018年 | 482篇 |
2017年 | 546篇 |
2016年 | 686篇 |
2015年 | 657篇 |
2014年 | 735篇 |
2013年 | 1252篇 |
2012年 | 858篇 |
2011年 | 868篇 |
2010年 | 705篇 |
2009年 | 717篇 |
2008年 | 716篇 |
2007年 | 682篇 |
2006年 | 591篇 |
2005年 | 550篇 |
2004年 | 539篇 |
2003年 | 434篇 |
2002年 | 326篇 |
2001年 | 272篇 |
2000年 | 215篇 |
1999年 | 193篇 |
1998年 | 174篇 |
1997年 | 133篇 |
1996年 | 109篇 |
1995年 | 117篇 |
1994年 | 85篇 |
1993年 | 88篇 |
1992年 | 38篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1972年 | 4篇 |
1971年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
《Mendeleev Communications》2020,30(2):192-194
- Download : Download high-res image (135KB)
- Download : Download full-size image
133.
以互通多孔碳(IPC)为载体,水热条件下在碳表面原位反应生成纳米结构的二氧化锰(MnO2),制备互通多孔碳/二氧化锰纳米(IPC/MnO2)复合电极材料. 采用扫描电镜(SEM),透射电镜(TEM),X射线衍射(XRD),热重分析(TGA)对其结构进行表征;采用循环伏安法、恒流充放电和交流阻抗对其电化学性能进行研究. 结果表明:生成的MnO2均匀地负载在碳的表面,形成多层次结构,并且随着温度的升高IPC表面负载的MnO2由纳米颗粒变为纳米片状结构;MnO2纳米片具有典型的K-Birnessite 型晶体结构;复合物中MnO2的含量约为34%(w). 在100 ℃制备的IPC/MnO2复合材料在三电极系统中最高比电容达到了411 F·g-1;随着反应温度的升高,比容量先增长后基本保持不变. 以IPC/MnO2为正极,活性炭(AC)为负极,1 mol·L-1 Na2SO4溶液为电解液组装成IPC/MnO2//AC 混合超级电容器,发现IPC/MnO2电极的电容器其电位窗口从1 V扩展到1.8 V,容量可达86F·g-1,且表现出良好的电容特性和大电流放电性能. 相似文献
134.
缓慢炭化部分氧化对制备煤质活性炭的影响 总被引:5,自引:0,他引:5
研究了炭化升温速度、炭化低温区引入空气部分氧化对活性炭制备过程中炭化阶段、炭化物结构、活性炭性能等的影响。结果表明,炭化时低温部分氧化可提高炭化物得率,使炭化物微晶的d002值升高和Lc值减小;而较慢的炭化升温速度有利于制备优质活性炭。缓慢炭化、部分氧化可以在一定程度上控制炭化路径,使炭化向生成取向性差、难石墨化、各向同性、呒定形炭多的炭化物的方向进行;并讨论了它们控制炭化的作用机理。以此为指导, 相似文献
135.
提出了一种测定安乃近新法。由于安乃近没有电活性,故将安乃近和盐酸在100℃共热后生成电活性产物,用玻碳电极在0.1mol/LNaOH中得一良好的阳极氧化伏安峰,Ep+0.35V(vs·Ag/AgCl)左右,峰电流与安乃近浓度在0.1~100mg/L之间呈线性关系,分析了制剂安乃近的含量,实验证实电极反应属于扩散控制的不可逆过程。 相似文献
136.
The water gas shift reaction (CO + H2O = CO2+ H2) is catalyzed by aqueous metal carbonyl systems derived from simple mononuclear carbonyls such as Fe(CO)5 and M(CO)6 (M = Cr, Mo, and W) and bases in the 140–200 °C temperature range. The water gas shift reaction in a basic methanol-water solution containing Fe(CO)5 is first order in [Fe(CO)5], zero order in [CO], and essentially independent of base concentration and appears to involve an associative mechanism with a metallocarboxylate intermediate [(CO)4Fe-CO2H]–. The water gas shift reactions using M(CO)6 as catalyst precursors are first order in [M(CO)6], inverse first order in [CO], and first order in [HCO2
–] and appear to involve a dissociative mechanism with formatometallate intermediates [(CO)5M-OCHO]–.The Reppe hydroformylation of ethylene to produce propionaldehyde and 1-propanol in basic solutions containing Fe(CO)5 occurs at 110–140 °C. This reaction is second order in [Fe(CO)5], first order in [C2H4] up to a saturation pressure >1.5 MPa, and inhibited by [CO]. These experimental results suggest a mechanism where the rate-determining step involves a binuclear iron carbonyl intermediate. The substitution of Et3N for NaOH as the base facilitates the reduction of propionaldehyde to 1-propanol but results in a slower rate for the overall reaction.The homogeneous photocatalytic decomposition of the formate ion to H2 and CO2 in the presence of Cr(CO)6 appears to be closely related to the water gas shift reaction. The rate of H2 production from the formate ion exhibits saturation kinetics in the formate ion and is inhibited by added pyridine. The infrared spectra of the catalyst solutions indicate an LCr(CO)5 intermediate. Photolysis of the Cr(CO)6/formate system in aqueous methanol in the presence of an aldehyde RCHO (R =n-heptyl,p-tolyl, andp-anisyl) results in catalytic hydrogenation of the aldehyde to the corresponding alcohol RCH2OH by the formate ion. Detailed kinetic studies onp-tolualdehyde hydrogenation by this method indicates saturation kinetics in formate ion, autoinhibition by thep-tolualdehyde, and a threshold effect for Cr(CO)6 at concentrations >0.004 mol L–1. The presence of an aldehyde can interrupt the water gas shift catalytic cycle by interception of an HCr(CO)5
– intermediate by the aldehyde.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1533–1539, September, 1994. 相似文献
137.
《Mendeleev Communications》2020,30(3):285-287
- Download : Download high-res image (158KB)
- Download : Download full-size image
138.
《Mendeleev Communications》2020,30(5):679-682
- Download : Download high-res image (153KB)
- Download : Download full-size image
139.
A beta-iron oxyhydroxide (FeOOH) was synthesized via a hydrolyzing route and investigated as a lithium intercalation host.
It delivers a capacity of about 170 mAh/g and exhibits good cycling performance when charged/discharged in the voltage range
from 1.6 V to 3.3 V. For the first time we have confirmed that FeOOH is suitable for using it as a negative electrode for
hybrid electrochemical supercapacitor assembled with an activated carbon positive electrode in 1.0 M LiPF6 ethylene carbonate/dimethyl carbonate (EC/DMC, 1:2 in volume) solution. The cell reveals a slightly sloping voltage profile
from 0 V to 2.8 V and gives an estimated specific energy of 45 Wh/kg based on the total weight of two electrode materials,
approximately two times of carbon/carbon electrochemical double layer capacitors. The hybrid supercapacitor shows a good cycling
performance, it remains approximately 96% of initial capacity after 800 cycles at a charge/discharge rate of 4 C. The capacitor
also shows a desirable rate capability, even at 10 C discharge rate, it holds 80% of capacity compared with that at 1 C discharge
rate. 相似文献
140.
LiNi0.8Co0.2O2 / MWNTs复合物超级电容器电极材料的研究 总被引:2,自引:0,他引:2
Multiwalled carbon nanotubes (MWNTs) were used as the conductive additive in the electrode materials. The electrochemical properties of supercapacitors based on LiNi0.8Co0.2O2 / MWNTs composite and LiNi0.8Co0.2O2/acetylene black composite and MWNTs in 1.0 mol·L-1 LiClO4 / EC+DEC [V(EC)∶V(DEC)=1∶1] electrolyte were investigated by means of constant charge/discharge current tests, respectively. The experimental results show that the LiNi0.8Co0.2O2 / MWNTs composite has better performance than that of others, and the maximum specific capacitance of the supercapacitor can reach 271.6 F·g-1, while the energy density is up to 339.5 Wh·kg-1. Furthermore, it is remarkable that the performance of MWNTs is better than that of acetylene black as the conductive additive. 相似文献