全文获取类型
收费全文 | 706篇 |
免费 | 3篇 |
国内免费 | 13篇 |
专业分类
化学 | 563篇 |
晶体学 | 2篇 |
力学 | 23篇 |
数学 | 61篇 |
物理学 | 73篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 27篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 28篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 62篇 |
2013年 | 107篇 |
2012年 | 38篇 |
2011年 | 49篇 |
2010年 | 45篇 |
2009年 | 51篇 |
2008年 | 39篇 |
2007年 | 45篇 |
2006年 | 24篇 |
2005年 | 20篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 8篇 |
2001年 | 14篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1989年 | 1篇 |
排序方式: 共有722条查询结果,搜索用时 31 毫秒
71.
Excess molar volumes, VE123V^{\mathrm{E}}_{123} of 1,3-dioxolane or 1,4-dioxane (1) + benzene or toluene (2) + formamide or + N,N-dimethylformamide (3) ternary mixtures at 308.15 K and at atmospheric pressure have been determined dilatometrically over
the entire composition range. The excess molar volumes data of these ternary systems were fitted to the Redlich–Kister equation.
The data have been analyzed in terms of Graph theory (model) to understand the nature and strength of molecular interactions
existing in these mixtures. It has been observed that VE123V^{\mathrm{E}}_{123} values predicted by Graph theory compare well with their corresponding experimental values. 相似文献
72.
Abbas Afkhami Tayyebeh Madrakian Ali Shirzadmehr Hasan Bagheri Masoumeh Tabatabaee 《Ionics》2011,18(9):881-889
An effective potentiometric sensor had been fabricated for the rapid determination of Pb2+ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb2+ carbon paste electrode for the successfully determination of Pb2+ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF6, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade?1) toward Pb2+ ions in the range of 5?×?10?9?C1.0?×?10?1 mol L?1 with a detection limit of 2.51?×?10?9 mol L?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions. 相似文献
73.
Densities, viscosities and refractive indices have been determined for mixtures of acetophenone with N,N-dimethylethanolamine
or with N,N-diethylethanolamine over the entire composition range at temperatures of (303.15, 313.15 and 323.15) K. The viscosity
values were fitted to the Krishnan-Laddha and McAllister models. The thermophysical properties under study were also fitted
to the Jouyban-Acree model. The excess values were correlated using the Redlich-Kister polynomial equation. It was found that,
in all cases, the obtained data were correlated very well by the corresponding models. The molecular interactions existing
between the components are also discussed. 相似文献
74.
75.
76.
Mohammad Ali Zolfigol Mojtaba Bagherzadeh Shadpour Mallakpour Gholamabbas Chehardoli Arash Ghorbani-Choghamarani Nadiya Koukabi Mina Dehghanian Mahmoudreza Doroudgar 《Journal of molecular catalysis. A, Chemical》2007,270(1-2):219-224
A combination of periodic acid or oxone® and a catalytic amount of KBr in the presence of few drops of water, were used for the catalytic oxidation of urazoles and bis-urazoles to their corresponding triazolinediones under mild and heterogeneous conditions with moderate to excellent yields. 相似文献
77.
78.
An efficient ionic liquid with both Brønsted acidic and Lewis basic sites, namely 1,4-dimethyl-1-(4-sulphobutyl)piperazinium hydrogen sulphate (IL1), was synthesised and characterised. IL1 is a “green”, homogeneous and reusable catalyst for: i) the synthesis of pyranopyrazoles (Va-Vj)and benzopyrans (VIa-VIj and VIIa-VIIf) at ambient temperature under solvent-free conditions and ii) the synthesis of amino-2-chromenes (VIIIa-VIIIi and IXa-IXi) and dihyropyrano[c]chromenes (Xa-Xi) at 80 °C under solvent-free conditions. The reactions were rapid with excellent product yields. In addition, the double Brønsted acid, 1,4-dimethyl-1,4-bis(4-sulphobutyl)piperazinium hydrogen sulphate (IL2), was prepared to evaluate the cooperation efficiency of their Brønsted acidic and Lewis basic sites as compared with the double Brønsted acidic sites in IL1. 相似文献
79.
Mahtab HejazifarSaeid Azizian Hassan SarikhaniQiang Li Dongyuan Zhao 《Journal of Analytical and Applied Pyrolysis》2011,92(1):258-266
Grapevine rhytidome (the outer layer of bark on trunk), as an abundant and low-cost precursor, was used to prepare granular activated carbon with high surface area for the removal of methyl violet from aqueous solution. Microwave heating source was used to reduce the treatment time and energy consumption. To optimize the preparation, the effects of the different parameters, such as phosphoric acid concentration, acid/precursor weight ratio, impregnation time, microwave power, radiation time, and oven heating time on the ability of the samples for removal of methyl violet were studied. The obtained activated carbon was characterized by N2 adsorption/desorption, SAXS, TEM and SEM methods. The adsorption of methyl violet onto the activated carbon was studied from both equilibrium and kinetic point of view and the results were compared with the commercial granular activated carbon. The rate of adsorption onto the prepared activated carbon was faster than commercial activated carbon. Different kinetic models were used to analyze the experimental kinetic data. The obtained activated carbon showed higher adsorption capacity (more than twice) for the adsorption of methyl violet in comparison with the commercial one. The equilibrium data were analyzed using different isotherm models. Adsorption was found to be maximum in the pH range 7-9. 相似文献
80.
Ramin Ghorbani-Vaghei Rahman Karimi-NamiZahra Toghraei-Semiromi Mostafa AmiriMehdi Ghavidel 《Tetrahedron》2011,67(10):1930-1937
N, N, N′, N′-Tetrabromobenzene-1,3-disulfonamide and poly(N-bromo-N-ethylbenzene-1,3-disulfonamide) were used as efficient catalysts for the one-pot synthesis of aliphatic and aromatic 2H-indazolo[2,1-b]phthalazine-triones in excellent yields from aldehydes, phthalhydrazide, and dimedone at 80-100 °C under solvent-free conditions. 相似文献