全文获取类型
收费全文 | 1862篇 |
免费 | 109篇 |
国内免费 | 49篇 |
专业分类
化学 | 1374篇 |
晶体学 | 20篇 |
力学 | 89篇 |
数学 | 144篇 |
物理学 | 393篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 34篇 |
2021年 | 89篇 |
2020年 | 81篇 |
2019年 | 88篇 |
2018年 | 106篇 |
2017年 | 72篇 |
2016年 | 104篇 |
2015年 | 88篇 |
2014年 | 114篇 |
2013年 | 226篇 |
2012年 | 126篇 |
2011年 | 131篇 |
2010年 | 103篇 |
2009年 | 90篇 |
2008年 | 100篇 |
2007年 | 81篇 |
2006年 | 59篇 |
2005年 | 35篇 |
2004年 | 39篇 |
2003年 | 17篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有2020条查询结果,搜索用时 531 毫秒
981.
Mehdi Shakourian-Fard Mohammadreza Nasiri Alireza Fattahi Majid Vafaeezadeh 《Structural chemistry》2012,23(3):857-865
Influence of the addition of water molecules (n = 1–6) on the interaction energy between Li+, Na+, K+ cations and indole molecule as tryptophan amino acid residue is considered at MP2(FULL)/6-311++G(d,p)//B3LYP/6-311++G(d,p)
levels of theory. The calculations suggest that the size of cation and the number of water molecules are two important factors
that affect the interaction energy between the hydrated metal cation and indole molecule. The strength of cation–π interactions
get substantially reduced when the metal ion is solvated or the size of metal cation increases. Quantum theory of atoms in
molecules analysis of cation–π interaction indicates that there is a correlation between the electron density (ρ(r)) in the cage critical points generated upon complexation and the distance between metal cation and centroid of phenyl ring
in indole molecule. 相似文献
982.
This work proposes a novel biomimetic sensor for the potentiometric transduction of rivastigmine based on molecularly imprinted polymer (MIP). Using the Taguchi method, this study analyzed the optimum conditions for preparing the MIP‐based membranes. The rank order of each controllable factor was also determined. MIP‐based membranes exhibited a Nernstian response (30.7±1.1 mV decade?1) in a concentration range from 1.0×10?5 to 1.0×10?2 mol L?1 with a LOD of 6.3×10?6 mol L?1. The sensor was successfully applied to the determination of rivastigmine concentrations in human serum, plasma, urine, rat brain and tablets. 相似文献
983.
Mehdi Vahidi Naser Seyed Matin Mahdi Goharrokhi Masih Hosseini Jenab Majid Abedinzadegan Abdi Seyed Hesam Najibi 《The Journal of chemical thermodynamics》2009,41(11):1272-1278
Solubility data of CO2 in aqueous N-methyldiethanolamine (MDEA) solutions of concentration (2.52, 3.36, and 4.28) kmol/m3 were obtained at temperatures (313, 323, and 343) K and partial pressures ranging from about (30 to 5000) kPa. A thermodynamic model based on extended Debye–Hückel theory was applied to predict and correlate of CO2 solubility in various aqueous amine solutions. The effect of piperazine (PZ) concentration on CO2 loading in MDEA solutions was determined at PZ concentration (0.36, 0.86, and 1.36) kmol/m3. Using experimental data in various temperatures the interaction parameters of activity coefficient model for these systems were determined. The results show the model consistency with experimental and literature data and PZ is beneficial to the CO2 loading. The comparison of results of this study with previous data work shows the wide range of CO2 loading considered in this work and the better agreement of model with experimental data. The average absolute relative deviation percent (δAAD) for all data points were 8.11%. 相似文献
984.
Majid M. Heravi Samaheh Sadjadi Hossein A. Oskooie Fatemeh F. Bamoharram 《Tetrahedron letters》2009,50(8):943-17
A new multi-component synthesis of 4-arylaminoquinazolines from the reaction of 2-aminobenzamide, orthoesters, and substituted anilines in the presence of catalytic amounts of Keggin-type heteropolyacids is reported. The effects of reaction conditions and different heteropolyacids have been studied. 相似文献
985.
M. Arshad K. Masud M. Arif S. Rehman M. Arif J. H. Zaidi Z. H. Chohan A. Saeed A. H. Qureshi 《Journal of Thermal Analysis and Calorimetry》2009,96(3):873-881
The thermal behavior of poly(methyl methacrylate) (PMMA) was studied in the presence of AlBr3 using TG-DTA-DTG, IR and Py-GC-MS techniques. Degradation products were identified. It was found that PMMA started degrading
at a lower temperature due to the generation of free radicals (Br•), being the product of decomposition of AlBr3. Despite early destabilization of the system, stabilization zone was also highlighted. Flammability test was conducted to
check the affectivity of AlBr3. Degradation mechanism has been proposed. Pyrolysis of the system (PMMA–AlBr3) was also monitored by heating it at different temperatures. 相似文献
986.
Thomas Cadenbach Christian Gemel Dr. Rochus Schmid Dr. Markus Halbherr Kirill Yusenko Dr. Mirza Cokoja Dr. Roland A. Fischer Prof. 《Angewandte Chemie (International ed. in English)》2009,48(21):3872-3876
All change : Complete ligand exchange through the hydrogenation of [Ru(η4‐cod)(η6‐cot)] in the presence of GaCp* under mild conditions leads to the title complex featuring a “naked” gallium atom bridging two ruthenium centers (see structure: C white, Ga blue, Ru red). This cluster can be considered as a trapped intermediate on the way to mixed‐metal nanoparticles; cot=1,3,5‐cyclooctatriene; cod=1,5‐cyclooctadiene, Cp*=C5Me5.
987.
Thomas Cadenbach Christian Gemel Dr. Rochus Schmid Dr. Markus Halbherr Kirill Yusenko Dr. Mirza Cokoja Dr. Roland A. Fischer Prof. 《Angewandte Chemie (International ed. in English)》2009,48(21):3713-3713
Soft skin, hard core …? is the basic principle for the formation of a nano‐alloy from molecular precursors. The co‐hydrogenolysis of ruthenium complexes in presence of GaCp* gives the isolable key intermediate [Ru2(Ga)(GaCp*)7(H)3] featuring a substituent‐free bridging gallium atom. From this “embryonic” species Ru/Ga phases are formed by complete cleavage of the protective Cp* shell (depicted as an eggshell in the Cover picture), as described by R. A. Fischer et al. in their Communication on page 3872 ff.
988.
Imprinted polymer particles for iron uptake: Synthesis, characterization and analytical applications
Mostafa Khajeh Massoud Kaykhaii Hossein Hashemi Majid Mirmoghaddam 《Polymer Science Series B》2009,51(9-10):344-351
This work reports the preparation of molecularly imprinted polymer particles for selective extraction and determination of iron ions from aqueous media. The polymer particles were synthesized from Fe(NO3)3, morin, 4-vinylpyridine, ethyleneglycoldimethacrylate, and 2,2′-azobisisobutyronitrile and characterized by IR and DSC both prior to and after removing the Fe-morin complex by leaching with HCl. The effect of different parameters, such as pH, adsorption and desorption time, type and minimum amount of eluent for removing the complex from polymer was evaluated and optimized. The proposed method is characterized by the detection limit of 3.1 µg l?1 anddynamic linear range of 25 to 200 µg l?1, with the relative standard deviation less than 8.8%. The method was applied to the recovery and determination of iron ions in a few real samples. 相似文献
989.
Synthesis and characterization of UV-irradiated silver/montmorillonite nanocomposites 总被引:1,自引:0,他引:1
Majid Darroudi Mansor Bin Ahmad Kamyar Shameli Abdul Halim Abdullah Nor Azowa Ibrahim 《Solid State Sciences》2009,11(9):1621-1624
We have successfully developed a simple method for preparing silver nanoparticles (Ag NPs) using UV irradiation of AgNO3 in the interlamellar space of a montmorillonite (MMT) without any reducing agent or heat treatment. The properties of Ag/MMT nanocomposites were studied as a function of the UV irradiation period. UV irradiation disintegrated the Ag NPs into smaller size until a relatively stable size and size distribution were achieved. The results from UV–vis spectroscopy show that particles size of Ag NPs decrease with the increase of irradiation period. The crystalline structure of Ag NPs was determined by powder X-ray diffraction (PXRD). 相似文献
990.
Hassan Keypour Nasibeh Rahpeyma Parisa Arzhangi Majid Rezaeivala Yalcin Elerman Orhan Buyukgungor Laura Valencia 《Polyhedron》2010
Two macrocyclic Schiff base ligands, L1 [1+1] and L2 [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L1 and L2) and the appropriate metal ions only [CoL1(NO3)]ClO4, [NiL1](ClO4)2, [CuL1](ClO4)2 and [ZnL1(NO3)]ClO4 complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL1(NO3)]ClO4 complex with NMR spectroscopy. 相似文献