全文获取类型
收费全文 | 1723篇 |
免费 | 69篇 |
国内免费 | 27篇 |
专业分类
化学 | 1173篇 |
晶体学 | 11篇 |
力学 | 75篇 |
数学 | 273篇 |
物理学 | 287篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 46篇 |
2021年 | 64篇 |
2020年 | 100篇 |
2019年 | 66篇 |
2018年 | 91篇 |
2017年 | 59篇 |
2016年 | 133篇 |
2015年 | 92篇 |
2014年 | 113篇 |
2013年 | 181篇 |
2012年 | 144篇 |
2011年 | 114篇 |
2010年 | 98篇 |
2009年 | 62篇 |
2008年 | 84篇 |
2007年 | 54篇 |
2006年 | 52篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 25篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 15篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1981年 | 5篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有1819条查询结果,搜索用时 15 毫秒
31.
32.
Optical Review - Both Fabry–Pérot interferometry and the DC electrochemical method have been simultaneously used for the first time to measure in situ the anodic current density (J) of... 相似文献
33.
There is a high overvoltage in the oxidation of methanol in fuel cells,and so modified electrodes are used to decrease it.A modified electrode that used Ni(II) loaded analcime zeolite to catalyze the electrooxidation of methanol in alkaline solution was proposed.Analcime zeolite was synthesized by hydrothermal synthesis,and Ni(II) ions were incorporated into the analcime structure,which was then mixed with carbon paste to prepare modified electrode.The electrocatalytic oxidation of methanol on the surface of the modified electrode in alkaline solution was investigated by cyclic voltammetry and chronoamperometry.The effects of the scan rate of the potential,concentration of methanol,and amount of zeolite were investigated.The rate constant for the catalytic reaction of methanol was 6 × 103 cm3 mol-1 s-1 from measurements using chronoamperometry.The proposed electrode significantly improved the electron transfer rate and decreased the overpotential for methanol oxidation. 相似文献
34.
Song and Mason equation of state (EOS) with a simple modification has been extended to modelling PVT properties of ionic liquids (ILs). The considered ILs are [C1mim][MeSO4], [C1mim][CH3OC2H5SO4], [C1mim][(CH3)2PO4], [C2mim][MeSO4], [C2mim][BF4], [C2mim][SCN], [C2eim][NTf2], [C4mim][C(CN)3], [C4mim][CF3SO3], [C4mim][SCN], [C5mim][NTf2], [C8mim][NTf2], [(C6H13)3P(C14H29)][Cl], [(C6H13)3P(C14H29)][NTf2], [(C6H13)3P(C14H29)][Ac], [C3mpyr][NTf2], [C4mpyr][NTf2] and [Py][C2H5OC2H4SO4]. Three temperature-dependent parameters in the proposed EOS have been scaled as functions of reduced temperature with the use of the law of corresponding states. It is shown that the knowledge of just critical temperature and critical density is sufficient to predict the PVT properties of these ILs. The overall average absolute deviation of calculated densities from literature values for 1347 data points of 18 ILs was found to be 0.58%. The predicted density of ILs from proposed EOS has been compared with those obtained by other literature work. Moreover, we indicate that the Zeno line regularity can well be predicted by proposed model for ILs. 相似文献
35.
Mohammad Ali Karimi Zarchi Seyed Shahab Addin Darbandizadeh Mohammad Abadi 《Journal of the Iranian Chemical Society》2018,15(4):915-929
A novel method for the synthesis of pyrazines and quinoxalines has been developed using α-hydroxyketones and 1,2-diamines in the presence of cross-linked poly(4-vinylpyridine)-stabilized Pd(0) nanoparticles, [P4-VP]-PdNPs. The catalyst was easily prepared and characterized using various techniques such as FT-IR and UV–Vis spectroscopy, AAS, TEM, FESEM, EDX analysis and XRD. The results confirm a good dispersion of palladium nanoparticles on the polymer support. The catalyst displayed good catalytic activity when applied to the synthesis of quinoxalines via condensation of α-hydroxyketones with 1,2-diamines. A few pyrazine derivatives and various quinoxalines are prepared via coupling reaction of α-hydroxyketones and 1,2-diamines in high–excellent yields (81–99%) with short reaction times. The quinoxalines products were characterized by FT-IR, 1H and 13C NMR spectroscopy, and the physical properties were compared to the literature values of known compounds. The advantages of the present method over conventional classical methods are rapid and very simple work-up, and the catalyst is reusable many times without a significant loss in its activity. 相似文献
36.
Zahra Shokri Behzad Zeynizadeh Seyed Ali Hosseini Behrooz Azizi 《Journal of the Iranian Chemical Society》2017,14(1):101-109
Magnetically separable nano core–shell Fe3O4@Cu(OH)x with 22 % Cu content was prepared by the addition of sodium hydroxide to a mixture of CuCl2·2H2O and nano Fe3O4 in water. Characterization of the impregnated copper hydroxide was carried out by X-ray fluorescence (XRF), X-ray diffraction (XRD) atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), value stream mapping (VSM) and Brunauer–Emmett–Teller (BET) analysis. The core–shell nanocatalyst exhibited the excellent catalytic activity toward reduction of various nitro compounds to the corresponding amines with NaBH4. All reactions were carried out in H2O (55–60 °C) within 3–15 min to afford amines in high to excellent yields. Reusability of core–shell Cu(OH)x catalyst was examined 9 times without significant loss of its catalytic activity. 相似文献
37.
38.
39.
40.