全文获取类型
收费全文 | 817篇 |
免费 | 36篇 |
国内免费 | 8篇 |
专业分类
化学 | 585篇 |
晶体学 | 6篇 |
力学 | 60篇 |
数学 | 97篇 |
物理学 | 113篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 54篇 |
2019年 | 42篇 |
2018年 | 40篇 |
2017年 | 37篇 |
2016年 | 50篇 |
2015年 | 48篇 |
2014年 | 49篇 |
2013年 | 89篇 |
2012年 | 66篇 |
2011年 | 70篇 |
2010年 | 43篇 |
2009年 | 53篇 |
2008年 | 33篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有861条查询结果,搜索用时 78 毫秒
141.
Rozita Zoghi Majid M. Heravi Naser Montazeri Masoud Mohammadi Zeydi Tayebeh Hosseinnejad 《应用有机金属化学》2020,34(4):e5435
A novel polymer supported [poly (styrene-co-maleic imide) (SMI)]Cu(I) nano-particles was prepared via in situ reaction of 4-amino-5-methyl-4H-1,2,4-triazole-3-thione with [poly (styrene-co-maleic anhydride)] (SMA) along with immobilization of CuI. These nano-particles were fully characterized by using scanning electron microscopy (SEM), energy dispersive spectroscopy analysis, Xray (EDAX), inductively coupled plasma (ICP) analysis, 1H NMR and FT-IR techniques. Moreover, the structural and electronic features of metal–ligand interactions in the complex model of polymer-supported copper nanocatalyst were assessed using density functional theory calculations. The catalytic activity of these supported Cu(I) nonoparticles was examined in one of the classiest name reaction so–called “click reaction” which is coined K. B Sharpless for the regioselective synthesis of 1,2,3-triazole derivatives using a multicomponent reaction (MCR) involving benzyl halides, sodium azide and terminal alkynes in water as a green solvent. This heterogeneous catalyst showed excellent catalytic activity and was separated by simple filtration and was used at least in five consecutive runs without a significant decrease in its activity. 相似文献
142.
Ghorbani Bahram Ebrahimi Armin Skandarzadeh Fatemeh Ziabasharhagh Masoud 《Journal of Thermal Analysis and Calorimetry》2021,145(3):925-953
Journal of Thermal Analysis and Calorimetry - The natural gas entering the liquefaction cycle usually consists of nitrogen, ethane, propane and also heavier hydrocarbons which are economically... 相似文献
143.
Effects of Zr addition on solidification characteristics of Al–Zn–Mg–Cu alloy using thermal analysis
Saman Mostafapoor Mehdi Malekan Masoud Emamy 《Journal of Thermal Analysis and Calorimetry》2018,134(3):1457-1469
The effect of Zr as a grain refiner on the solidification behavior, micro- and macrostructure of a new Al–Zn–Mg–Cu aluminum super-high strength alloy containing high Zn content was studied. The addition of 2 mass% Zr reduced the grain size from 1500 to 190 μm. Moreover, the dendritic structure of the alloy altered from a coarse, elongated and non-uniform morphology to a rosette-like shape and more uniform one. The parameters of liquidus region of cooling curve obtained from thermal analysis were in a good correlation with grain size results. The maximum of first derivative in the liquidus region was introduced beside recalescence undercooling which could predict the grain refinement level even after disappearing of recalescence in the cooling curve. Furthermore, the addition of 1 mass% Zr enhanced fraction of solid in dendrite coherency point from 21 to 31% and lessened the amounts of porosity from 2.3 to 1.4%. 相似文献
144.
Banazadeh Alireza Williamson Seth Zabet Masoud Hussien Ahmed Mechref Yehia 《Analytical and bioanalytical chemistry》2018,410(28):7395-7404
Analytical and Bioanalytical Chemistry - More than 50% of all known proteins are glycosylated, which is critical for many biological processes such as protein folding and signal transduction.... 相似文献
145.
Judit Éva Fleischer Radu Levente Novak John F. Hartmann Neda Beheshti Anna-Lena Kjøniksen Bo Nyström János Borbély 《Colloid and polymer science》2008,286(4):365-376
This work describes the formation of water-soluble hydrophilic nanoparticles from biosynthetic poly-γ-glutamic acid (PGA).
Nanoparticles were formed by cross-linking using 2,2′-(ethylenedioxy) diethylamine in the presence of water-soluble carbodiimide.
The structure was determined by nuclear magnetic resonance spectroscopy and the particle size by transmission electron microscopy
(TEM), size exclusion chromatography (SEC), and dynamic light-scattering (DLS) measurements. The results from TEM, SEC, and
DLS reveal that the particle size depends on the ratio of cross-linking. Particle size values measured by TEM were between
20 and 90 nm. Formation of cross-linked nanoparticles results in a dramatic viscosity drop compared to the viscosity of the
corresponding solution of the parent PGA. The viscosity and DLS experiments disclose an intriguing interplay between intrachain
and interchain cross-linking of the polymer chains, depending on the cross-linker density and polymer concentration. The SEC
measurements show that the retention time of the major portion of particles increase because of the higher cross-linking ratio.
At moderate cross-linker concentration, intramolecular cross-linking is the dominant process, whereas at higher cross-linker
densities, the interpolymer cross-linking plays an important role. As a result, large clusters are also formed. 相似文献
146.
Masoud Salavati-Niasari Seyed Nezamoddin Mirsattari Mehdi Bazarganipour 《Polyhedron》2008,27(18):3653-3661
The chemical modification of multi-wall carbon nanotubes (MWNTs) is an emerging area in material science. In the present study, an hydroxyl functionalized manganese(II) Schiff-base has been covalently anchored on modified MWNTs. The new modified MWNTs have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron (XPS), thermal analysis, UV–Vis, diffuse reflectance (DRS), FT-IR spectroscopy and elemental analysis. The results suggest that the symmetrical Schiff-base; N,N-bis(4-hydroxysalicylidene)-ethylene-1,2-diamine; H2[(OH)2-salen]; is a bivalent anion with tetradentate N2O2 donors derived from the phenolic oxygens and azomethine nitrogens. The formulae was found to be [Mn((OH)2-salen)] for the 1:1 non-electrolytic complex. The multi-wall carbon nanotubes covalently anchored manganese(II) complex ([Mn((OH)2-salen)]@MWNTs) catalyze the oxidation of cyclohexene with TBHP. Oxidation of cyclohexene catalyzed by this complex gave 2-cyclohexene-1-ol, 2-cyclohexene-1-one and 1-(tert-butylperoxy)-2-cyclohexene as the major products. The manganese(II) complex covalently anchored on MWNTs shows significantly higher catalytic activity than [Mn((OH)2-salen)]. The activity of the immobilized catalyst remains nearly the same after three cycles, suggesting the true heterogeneous nature of the catalyst. This catalyst is more selective towards 2-cyclohexene-1-one. 相似文献
147.
Ni(II) complexes of [14]aneN4: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN4: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo2[14]aneN4: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo2[16]aneN4: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)nickel(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Ni(N–N)2]2+–NaY; in the nanopores of the zeolite-Y, and (ii) in situ condensation of the nickel(II) precursor complex with ethylcinnamate. The new host–guest nanocomposite materials (HGNM) were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/Vis, XRD and DRS) and the BET technique. These complexes were used for oxidation of cyclohexene with molecular oxygen. 相似文献
148.
Hassan Ali Zamani Mohammad Reza Ganjali Masoud Salavati-Niasari 《Transition Metal Chemistry》2008,33(8):995-1001
A Fe3+ ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing bis-bidentate Schiff
base (BBS) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as anionic excluder, and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH, and additive
anionic influence on the response properties were investigated. The best performance was obtained with a membrane containing
32% PVC, 62.5% NPOE, 3% BBS, and 2.5% NaTPB. The electrode shows a Nernstian behavior (slope of 19.3 ± 0.6) over a very wide
iron ion concentration range (1.0 × 10−7–1.0 × 10−2 M) and has a low detection limit (7.4 × 10−8 M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 1.9–5.1. The proposed
sensor has a very low response time (<15 s) and a good selectivity relative to a wide variety of other metal ions including
common alkali, alkaline earth, heavy, and transition metal ions. The electrode can be used for at least 60 days without any
considerable divergence in potentials. The proposed sensor was successfully applied as an indicator electrode for the potentiometric
titration of 1.0 × 10−2 M Fe3+ ions with a 1.0 × 10−4 M EDTA and the direct determination of Fe3+ in mineral water and wastewater samples. 相似文献
149.
150.
Masoud Bakhshi Hamid Arab Mohammad K. Amini 《Journal of the Iranian Chemical Society》2016,13(9):1673-1681
Several sample preparation methods were evaluated for determination of free carbon in boron carbide powders by quantitative X-ray diffraction method, including ultrasonication, wet ball milling and dry ball milling–wet mixing. Quantitation was based on measuring the integral peak area ratio of the diffraction lines of graphite (002) to boron carbide (012) in samples spiked with pure graphite. The dry milling–wet mixing method provided the best precision and accuracy in all the measurements as well as in determination of free carbon in a boron carbide reference material. There was a linear relationship between the integral peak area ratios and graphite added to boron carbide samples which were purified from their free carbon content. The method provided a low detection limit of 0.05 wt% free carbon. 相似文献