全文获取类型
收费全文 | 299篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 259篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 18篇 |
物理学 | 24篇 |
出版年
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 15篇 |
2012年 | 15篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 23篇 |
2007年 | 28篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 15 毫秒
291.
A. L. Svistkov Lyudmila Andreevna Komar G. Heinrich B. Lauke 《Polymer Science Series A》2008,50(5):600-606
A theory to explain the appearance of oriented layers at the filler surface in polymer nanocomposites is proposed. The theory is based on the assumption that small oriented polymer regions have an effect on the state of neighboring regions and tend to orient polymer chains in these regions. As a result, the point-to-point transfer of this effect takes place, thereby causing the propagation of the oriented layer in the polymer nanocomposite over a considerable distance from the filler surface. The appearance of the polymer in the biaxially oriented state, which is transferred to the neighboring regions and leads to the formation of a layer with specific mechanical properties, is possible near the filler particles in this case. 相似文献
292.
This study compares the results of the general effective fragment potential (EFP2) method to the results of a previous combined coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] and symmetry-adapted perturbation theory (SAPT) study [Sinnokrot and Sherrill, J. Am. Chem. Soc., 2004, 126, 7690] on substituent effects in pi-pi interactions. EFP2 is found to accurately model the binding energies of the benzene-benzene, benzene-phenol, benzene-toluene, benzene-fluorobenzene, and benzene-benzonitrile dimers, as compared with high-level methods [Sinnokrot and Sherrill, J. Am. Chem. Soc., 2004, 126, 7690], but at a fraction of the computational cost of CCSD(T). In addition, an EFP-based Monte Carlo/simulated annealing study was undertaken to examine the potential energy surface of the substituted dimers. 相似文献
293.
Budgin AM Kabachii YA Shifrina ZB Valetsky PM Kochev SS Stein BD Malyutin A Bronstein LM 《Langmuir : the ACS journal of surfaces and colloids》2012,28(9):4142-4151
For the first time the four block copolymers derived from 1-alkyl[2-(acryloyloxy)ethyl]dimethylammonium bromides with hexyl (ADA) or cetyl (ADHA) groups and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) were synthesized and employed for functionalization of monodisperse iron oxide nanoparticles (NPs). The polyADA (pADA) or polyADHA (pADHA) block consists of long hydrophobic tails (C(6) or C(16)) connected to a positively charged quaternary ammonium group, making this block amphiphilic. The second block was either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). The dependence of the NP coating on the length of the hydrophobic tail in the amphiphilic block, the composition of the hydrophilic block, and the NP sizes have been studied. Unusual self-assembling of iron oxide NPs into well-defined composite submicrometer particles was observed for pADHA-b-pNIPAM in the wide range of concentrations (at the pADHA repeating unit concentrations of 0.065 × 10(-2)-2.91 × 10(-2) mmol/mL per 1 mg/mL NPs) but only two concentrations, 1.62 × 10(-2) and 1.94 × 10(-2) mmol/mL, led to regular spherical particles. The thermoresponsive behavior of these composite particles was tested using ζ-potential and dynamic light scattering measurements, while the morphology of particles was characterized by transmission electron microscopy. Coating of NPs with pADHA-b-pHEA results in the formation of individually coated NPs. The different composite particle morphologies are explained by different properties of pHEA and pNIPAM. It is demonstrated that the composite particles based on pADHA-b-pNIPAM are responsive to a magnetic field and can be recommended as magnetic stoppers in biorelated membrane separations. The incorporation of Pd species in submicrometer particles makes them promising candidates for catalytic applications as magnetically recoverable catalysts with a high magnetic response. 相似文献
294.
Cyclization of (non)‐methylated nitro‐o‐phenylenediamines with cyanogen bromide provided nitro‐substituted 2‐aminobenzimidazoles in good up to excellent yields. Catalytic hydrogenation of 2‐amino‐1‐methyl‐5‐nitrobenzimidazole yielded 2,5‐diamino‐1‐methylbenzimidazole, which on treatment with 1,1,3,3‐tetramethoxypropane in methanol and subsequently after removal of methanol in polyphosphoric acid afforded food‐borne carcinogen 2‐amino‐3‐methylimidazo[4,5‐f]quinoline (IQ) in 20% yield. J. Heterocyclic Chem.,(2011). 相似文献
295.
296.
Alexander V. Martynov Lyudmila I. Larina Svetlana V. Amosova 《Tetrahedron letters》2012,53(10):1218-1221
An efficient synthesis of novel bis[(E)-1-(halomethyl)-2-chlorovinyl] sulfides and selenides via regio- and stereoselective electrophilic addition of SCl2 and SeCl2 to propargyl halides has been developed. The bis(2-chlorovinyl) chalcogenides prepared represent reagents for the synthesis of chalcogen-containing heterocycles and have been used for the synthesis of novel bis(E-chloromethylidene) derivatives of 1,4-dichalcogenanes with various combinations of sulfur and selenium atoms in the ring. 相似文献
297.
Sergey E. Lyubimov Vadim A. Davankov Lyudmila N. Popova Petr M. Valetskii 《Journal of organometallic chemistry》2006,691(26):5980-5983
Novel chiral monodentate phosphite ligands bearing cymantrene fragment have been prepared. Phosphite 4 with PPh3, instead of CO-ligand, in cymantrene moiety provided higher enantioselectivity than its unsubstituted analogue 3 in hydrogenation of (Z)-methyl-2-acetamido-3-phenylacrylate. 相似文献
298.
In the dehydro-m-xylylene (DMX) anion [Munsch; et al. J. Org. Chem. 2004, 69, 5735], three nearly degenerate orbitals host four electrons, which results in a large number of nearly-degenerate electronic states. By using this challenging example, we assess the performance of the multireference "brute force" approach and the two-step schemes based on single-reference methods for calculating accurate energy differences. Different schemes for calculating adiabatic ionization potential (IP) of DMX- are also investigated. IP calculated by single-reference based schemes is in excellent agreement with experiment. 相似文献
299.
Boris A. Trofimov Anastasiya G. Mal'kina Olesya A. Shemyakina Lyudmila I. Larina Grigorii G. Alexandrov 《Tetrahedron》2010,66(9):1699-3203
Adenine (9H-purin-6-amine) adds readily to available α,β-acetylenic γ-hydroxy nitriles under mild conditions (molar ratio 1:1, K2CO3, DMF, rt, 10 min) to afford chemo-, regio- and stereospecifically (Z)-3-(6-amino-9H-purin-9-yl)-4-hydroxy-4-alkyl-2-alkenenitriles, novel functionalized acyclic nucleoside analogues (95-98% yield). Under similar conditions (K2CO3, DMF, rt, 1 h), 8-azaadenine (3H-[1,2,3]triazolo[4,5-d]pyrimidin-7-amine) reacts with 4-hydroxy-4-methyl-2-pentynenitrile nonselectively at the 7-, 8- and 9-positions to give the corresponding adducts in a 1:10.5:9 ratio, the total yield being 81%. Chemo-, regio- and stereospecific addition of 8-azaadenine to the above α,β-acetylenic γ-hydroxy nitriles leading to (Z)-3-(7-amino-2H-[1,2,3]triazolo[4,5-d]pyrimidin-2-yl)-4-hydroxy-4-alkyl-2-alkenenitriles in 44-90% yield is attained when the reaction is carried out without solvent in the presence of Et3N (30 mol %), the molar ratio of 8-azaadenine:α,β-acetylenic nitriles being 1:2.0 (rt, 12-38 h). 相似文献
300.
Alexei Lukin Mikhail Chudinov Tatiana Vedekhina Elizaveta Rogacheva Lyudmila Kraeva Olga Bakulina Mikhail Krasavin 《Molecules (Basel, Switzerland)》2022,27(15)
The previously reported as well as newly synthesized derivatives of the 1-oxa-9-azaspiro[5.5]undecane were employed in the synthesis of thirty-six derivatives of ciprofloxacin using commercially available 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid and the literature protocol involving the preparation of boron chelate complex to facilitate nucleophilic aromatic substitution. All new fluoroquinolone derivatives were tested against two gram-positive as well as three gram-negative strains of bacteria. With the activity spectrum of the new derivatives being substantially narrower than that of ciprofloxacin, compounds were distinctly active against two of the five strains: gram-negative Acinetobacter baumannii 987® and gram-positive Bacillus cereus 138®. Towards these two strains, a large group of compounds displayed equal or higher potency than ciprofloxacin. 相似文献