全文获取类型
收费全文 | 622篇 |
免费 | 58篇 |
国内免费 | 107篇 |
专业分类
化学 | 559篇 |
晶体学 | 6篇 |
力学 | 22篇 |
综合类 | 1篇 |
数学 | 35篇 |
物理学 | 164篇 |
出版年
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 18篇 |
2020年 | 45篇 |
2019年 | 41篇 |
2018年 | 29篇 |
2017年 | 17篇 |
2016年 | 38篇 |
2015年 | 30篇 |
2014年 | 22篇 |
2013年 | 34篇 |
2012年 | 50篇 |
2011年 | 59篇 |
2010年 | 39篇 |
2009年 | 32篇 |
2008年 | 45篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 27篇 |
2004年 | 33篇 |
2003年 | 15篇 |
2002年 | 19篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有787条查询结果,搜索用时 203 毫秒
31.
32.
Dr. Shengliang Hu Ruixue Tian Lingling Wu Qing Zhao Prof. Jinlong Yang Prof. Jun Liu Shirui Cao 《化学:亚洲杂志》2013,8(5):1035-1041
Carbon quantum dots (CQDs) were synthesized by heating various carbon sources in HNO3 solution at reflux, and the effects of HNO3 concentration on the size of the CQDs were investigated. Furthermore, the oxygen‐containing surface groups of as‐prepared CQDs were selectively reduced by NaBH4, leading to new surface states. The experimental results show that the sizes of CQDs can be tuned by HNO3 concentration and then influence their photoluminescent behaviors; the photoluminescent properties are related to both the size and surface state of the CQDs, but the photocatalytic activities are determined by surface states alone. The different oxygen‐containing groups on the surface of the CQDs can induce different degrees of the band bending upward, which determine the separation and combination of the electron–hole pairs. The high upward band bending, which is induced by C?O and COOH groups, facilitates separation of the electron–hole pairs and then enhances high photocatalytic activity. In contrast, the low upward band bending induced by C? OH groups hardly prevents the electron–hole pairs from surface recombination and then exhibits strong photoluminescence. Therefore, both the photocatalytic activities and optical properties of CQDs can be tuned by their surface states. 相似文献
33.
Tetrachloro-1, 2-benzoquinone and 2, 3-dichloro-1, 4-naphthoquinone react with a series of aryl and alkyl selenolate, generated either by the reaction of Grignard reagents and selenium powder or by the reduction of diselenides with NaBH4, to give 3, 6-diarylseleno-2, 5-dichloro-1, 4-benzoquinones 3 and 2, 3-diarylseleno-1, 4-naphthoquinones 4 in good yields. 相似文献
34.
One‐pot Wittig reactions of ethyl bromoacetate and bromoacetonitrile with aldehydes in the presence of PPh3 and LiOH in water were investigated. Most of the olefination reactions completed within 5–120 min in refluxing water containing 1.2 M LiCl to afford the olefin products in 71–97% yields with 100:0–55:45 ratios of E:Z isomers. 相似文献
35.
Song Wang Liqiang Tan Jinlong Jiang Jing Chen Liangdong Feng 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):1305-1312
In this research TiO2 sample was synthesized by a simple sol–gel method and was characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) techniques. The XRD result indicated that the obtained product was anatase titanium dioxide with high purity, the TEM image clearly showed that the particle sizes of TiO2 nanoparticles were in the range of 30–70 nm, and the measured BET surface area of the heated TiO2 nanoparticles was 147.14 m2/g. In this work, the prepared TiO2 sample was used as a new adsorbent for the adsorption of radionuclide Co(II) ions from aqueous solutions, and the influence of pH, contact time, ionic strength and temperature in the presence or absence of humic acid/fulvic acid (HA/FA) were also investigated. The experimental results indicated that the adsorption of Co(II) ions onto TiO2 was strongly pH-dependent. Based on the surface complexation, the presence of HSs enhanced the adsorption of Co(II) ions and the influence of Co(II) adsorption onto FA–TiO2 hybrids was much stronger than that of HA–TiO2 at pH values of 2.0–9.0. Adsorption of Co(II) ions onto TiO2 powder was strongly dependent on ionic strength. The adsorption process mainly occured in the first contact time of 2 h and could be fitted by a pseudo-second-order rate model. The calculated thermodynamic data indicated that the adsorption of Co(II) ions onto TiO2 was a spontaneous process and favorable at high temperatures. 相似文献
36.
Fan Yang Hongmei Yang Baozhu Tian Jinlong Zhang Dannong He 《Research on Chemical Intermediates》2013,39(4):1685-1699
Mo and C co-doped TiO2 photocatalysts were successfully prepared by a calcination–hydrothermal method. The catalysts were characterized by XRD, XPS, DRS, FTIR, and Raman spectroscopy. Results from photocatalysis showed that 1%Mo–C4/TiO2 had excellent visible light photocatalytic activity. This may be ascribed not only to the Mo and C doping but also to synergism between the Mo and C. 相似文献
37.
Jinlong Jiang Hao Huang Qiong Wang Weijun Zhu Junying Hao Weimin Liu 《Surface and interface analysis : SIA》2014,46(3):139-144
The titanium/silicon mono‐ and co‐doped amorphous carbon films were deposited by mid‐frequency magnetron sputtering Ti target, Si target, and Ti80S20 alloy target, respectively. The effects of doped elements on the composition, surface morphology, microstructure, and mechanical and tribological properties of the films were investigated. The results reveal that the ratio of sp3 and sp2 carbon bonds of the films is regulated between 0.28 and 0.62 by a combination of Ti and Si dopant. The addition of small amounts of silicon leads to an increase in sp3 bonds and disorder degree of the sp2 carbon. The co‐doped film exhibits significantly superior friction performance than the mono‐doped films. The ultra‐low friction (μ < 0.01) was achieved under a load of 2 N in ambient air with 40% RH. By comparing to the mono‐and co‐doped films, it is thought that the sp3/sp2 ratio of the films may play a key role for the superlow friction. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
38.
The passive film of iron showed n‐type semiconductor characteristic in borate buffer solution, and its donor concentration increased slightly after tensile strain in the present study. However, comparing with solution‐annealed sample, the anodic passive film formed on tensile‐strained one was highly protective. The more dislocations on tensile‐strained sample promoted the diffusion of iron and oxygen vacancy. Moreover, more donor density (mainly oxygen vacancies) promoted the diffusion of oxygen. They all facilitated tensile‐strained sample to form Fe2O3 and thicker passive film on the surface. More Fe2O3 and thicker passive film on the surface of tensile‐strained iron could improve corrosion resistance. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
39.
A general method for accessing 5-alkyl-5-aryl-1-pyrroline N-oxides (AAPOs) has been established using readily available aryl bromides, nitroalkanes, and acrolein as the starting materials. The palladium-catalyzed arylation of nitroalkanes gave the 1-aryl-substituted nitroalkanes, which underwent the Et3N-catalyzed Michael addition with acrolein at room temperature to afford the 4-aryl-4-nitroaldehydes. The latter were then subjected to the nitro reductive cyclization using Zn–HOAc in EtOH at 0 °C followed by warming the reaction mixture to room temperature for 24 h, furnishing the 5-alkyl-5-aryl-1-pyrroline N-oxides in good overall yields. Selected examples of 1,3-dipolar cycloaddition of the cyclic nitrones with methyl methacrylate were also described. 相似文献
40.
油气混相过程的界面传质特性对气驱提高原油采收率技术非常重要。本文针对吉林某油田的实际油组分,采用分子动力学模拟研究了气驱油过程,分析了不同气体和驱替压力下油气两相的状态变化以及界面特性,获得不同驱替气体的最小混相压力(MMP)。结果表明,随着驱替气体压力的升高,气相的密度逐渐增大,油相膨胀密度降低,气相与油相的混合程度增强,油气两相界面厚度增加,界面张力随之减小。同时发现,驱替相中二氧化碳浓度越高,在同等气体压力下,油气界面更厚,油气混合程度更高。纯CO2驱油得到的MMP远远小于纯N2驱油,当这两种气体摩尔比为1 : 1混合时MMP介于两种纯气体之间,说明要达到同样的驱油效果二氧化碳需要的压力更小。最后,本文从分子微观作用力角度解释了驱替气体不同时影响油气混相程度的机制,通过分子平均作用势曲线发现油相分子对CO2的吸引力要大于N2分子,因此CO2分子更容易与油相混合,驱替效果更明显。 相似文献