全文获取类型
收费全文 | 440篇 |
免费 | 15篇 |
国内免费 | 5篇 |
专业分类
化学 | 335篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 71篇 |
物理学 | 39篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 27篇 |
2012年 | 11篇 |
2011年 | 27篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 30篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 19篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 2篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有460条查询结果,搜索用时 0 毫秒
91.
Lucjan Strekowski J. Christian Mason Hyeran Lee Martial Say Gabor Patonay 《Journal of heterocyclic chemistry》2004,41(2):227-232
Three methods were used to synthesize a series of the title compounds. The ketones absorb in the visible region, and upon protonation (pH<6) they are converted to hydroxy‐substituted heptamethine cyanines that show an intense absorption in the near‐infrared region (>700 nm). The conversion is reversible and depends solely on pH conditions. 相似文献
92.
Song H Rioux RM Hoefelmeyer JD Komor R Niesz K Grass M Yang P Somorjai GA 《Journal of the American Chemical Society》2006,128(9):3027-3037
A novel high surface area heterogeneous catalyst based on solution phase colloidal nanoparticle chemistry has been developed. Monodisperse platinum nanoparticles of 1.7-7.1 nm have been synthesized by alcohol reduction methods and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis. Characterization of the Pt/SBA-15 catalysts suggests that Pt particles are located within the surfactant micelles during silica formation leading to their dispersion throughout the silica structure. After removal of the templating polymer from the nanoparticle surface, Pt particle sizes were determined from monolayer gas adsorption measurements. Infrared studies of CO adsorption revealed that CO exclusively adsorbs to atop sites and red-shifts as the particle size decreases suggesting surface roughness increases with decreasing particle size. Ethylene hydrogenation rates were invariant with particle size and consistent with a clean Pt surface. Ethane hydrogenolysis displayed significant structure sensitivity over the size range of 1-7 nm, while the apparent activation energy increased linearly up to a Pt particle size of approximately 4 nm and then remained constant. The observed rate dependence with particle size is attributed to a higher reactivity of coordinatively unsaturated surface atoms in small particles compared to low-index surface atoms prevalent in large particles. The most reactive of these unsaturated surface atoms are responsible for ethane decomposition to surface carbon. The ability to design catalytic structures with tunable properties by rational synthetic methods is a major advance in the field of catalyst synthesis and for the development of accurate structure-function relationships in heterogeneous reaction kinetics. 相似文献
93.
94.
Chemical‐Reaction‐Induced Hot Electron Flows on Platinum Colloid Nanoparticles under Hydrogen Oxidation: Impact of Nanoparticle Size 下载免费PDF全文
Hyosun Lee Ievgen I. Nedrygailov Changhwan Lee Prof. Gabor A. Somorjai Prof. Jeong Young Park 《Angewandte Chemie (International ed. in English)》2015,54(8):2340-2344
Generation of hot electron flows and the catalytic activity of Pt nanoparticles (NPs) with different sizes were investigated using catalytic nanodiodes. We show that smaller Pt NPs lead to higher chemicurrent yield, which is associated with the shorter travel length for the hot electrons, compared with their inelastic mean free path. We also show the impact of capping on charge carrier transfer between Pt NPs and their support. 相似文献
95.
The spectral features of the squarylium near-infrared (NIR) dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is λ=663 nm in methanol. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in methanol is λem=670 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, KSV, was calculated from the Stern–Volmer plot to be KSV=2.70×107 M−1 for Co(II) ion. The KSV value for Fe(III) ion could not be established due to the non-linearity of the Stern–Volmer plot and the modified Stern–Volmer plot for this ion. The detection limit is 6.24×10−8 M for Fe(III) ion and 1.55×10−5 M for Co(III) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, KS, of the metal–dye complex was calculated to be 3.14×106 M−1 for the Fe–dye complex and 2.64×105 M−1 for the Co–dye complex. 相似文献
96.
Kovacs J Joo F Benyei AC Laurenczy G 《Dalton transactions (Cambridge, England : 2003)》2004,(15):2336-2340
In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction. 相似文献
97.
Judit E. Puskas Yaohong Chen Kevin Kulbaba Gabor Kaszas Ali Soleymannezhad 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1770-1776
This article discusses the characterization of arborescent (hyperbranched) polyisobutylenes (arb‐PIBs) by size exclusion chromatography and differential scanning calorimetry, in comparison with linear PIB standards. The radius of gyration (〈r〉1/2 = Rz), measured from the angle dependence of light scattering of high‐molecular‐weight arb‐PIBs, was significantly larger than the hydrodynamic radius (Rh) from size exclusion chromatography/viscometry, and the Rh values were significantly smaller than Rh of linear PIBs. The glass‐transition temperature of arb‐PIBs having a branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total number‐average molecular weight and BR up to BR ~ 15. A modified Fox–Flory equation is proposed to describe the effect of architecture on the thermal transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1770–1776, 2006 相似文献
98.
Rebeka Torok Klaudia Horompoly Marton Szigeti Andras Guttman Marta Vitai Laszlo Koranyi Gabor Jarvas 《Molecules (Basel, Switzerland)》2021,26(21)
Currently, diagnosing type 2 diabetes (T2D) is a great challenge. Thus, there is a need to find rapid, simple, and reliable analytical methods that can detect the disease at an early stage. The aim of this work was to shed light on the importance of sample collection options, sample preparation conditions, and the applied capillary electrophoresis bioanalytical technique, for a high-resolution determination of the N-glycan profile in human blood samples of patients with type 2 diabetes (T2D). To achieve the profile information of these complex oligosaccharides, linked by asparagine to hIgG in the blood, the glycoproteins of the samples needed to be cleaved, labelled, and purified with sufficient yield and selectivity. The resulting samples were analyzed by capillary electrophoresis, with laser-induced fluorescence detection. After separation parameter optimization, the capillary electrophoresis technique was implemented for efficient N-glycan profiling of whole blood samples from the diabetic patients. Our results revealed that there were subtle differences between the N-glycan profiles of the diabetic and control samples; in particular, two N-glycan structures were identified as potential glycobiomarkers that could reveal significant changes between the untreated/treated type 2 diabetic and control samples. By analyzing the resulting oligosaccharide profiles, clinically relevant information was obtained, revealing the differences between the untreated and HMG-CoA reductase-inhibitor-treated diabetic patients on changes in the N-glycan profile in the blood. In addition, the information from specific IgG N-glycosylation profiles in T2D could shed light on underlying inflammatory pathophysiological processes and lead to drug targets. 相似文献
99.
100.
Judit E. Puskas Sam W. P. Chan Kimberley B. Mcauley Gabor Kaszas Sohel Shaikh 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1778-1787
The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl4 in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and Mn–conversion plots) were found, provided that the St concentration was above a critical value ([St]0 ~ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching Mw/Mn ~ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with Mn = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007 相似文献