全文获取类型
收费全文 | 226篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
化学 | 170篇 |
力学 | 4篇 |
数学 | 15篇 |
物理学 | 47篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 16篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 26篇 |
2007年 | 8篇 |
2006年 | 4篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 1篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1994年 | 3篇 |
1987年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有236条查询结果,搜索用时 921 毫秒
61.
Hania Hebbache Zakia Hank Sultana Boutamine M'hamed Meklati Christian Bruneau Jean-Luc Renaud 《Comptes Rendus Chimie》2008,11(6-7):612-619
The direct condensation of amines with β-ketoesters to produce functional enamine derivatives has been investigated with iron Lewis acid catalysts. FeCl3·6H2O shows good catalytic activity and makes possible the chemo- and stereoselective formations of (Z)-enamine derivatives from aliphatic and aromatic primary amines under mild conditions. 相似文献
62.
Choudhary MI Batool I Khan SN Sultana N Shah SA Ur-Rahman A 《Natural product research》2008,22(6):489-494
The biotransformation of a pentacyclic triterpene, oleanolic acid (1), with Fusarium lini afforded two oxidative metabolites, 2alpha,3beta-dihydroxyolean-12-en-28-oic acid (2), and 2alpha,3beta,11beta-trihydroxyolean-12-en-28-oic acid (3). Metabolite 3 was found to be a new compound. The structures were characterized on the basis of spectroscopic studies. These metabolites exhibited a potent inhibition of alpha-glucosidase enzyme. 相似文献
63.
Norbani Abdullah Zainudin Arifin Edward R. T. Tiekink Naima Sharmin Nur Syamimi Ahmad Tajidi Siti Amira Mat Hussin 《Journal of Coordination Chemistry》2016,69(5):862-878
A covalent mononuclear complex, [Cu(p–HOC6H4COO)2(cyclam)] (1), and two ionic mononuclear complexes, [Cu(cyclam)(H2O)2](p–CH3OC6H4COO)2 (2) and [Cu(cyclam)(H2O)2](p–CH3(CH2)15OC6H4COO)2·H2O (3), were formed from reaction of cyclam with [Cu2(p–HOC6H4COO)4(H2O)2], [Cu2(p–CH3OC6H4COO)4(H2O)2] and [Cu2(p-CH3(CH2)15OC6H4COO)4(H2O)2], respectively. These complexes were isolated as purple crystals with molecular structures showing distorted octahedral N4O2 geometry. Complexes 1 and 2 were irreversibly reduced to Cu(I) and oxidized to Cu(III), while 3 was redox inactive. Complex 2 reacted with N-(hexadecyl)isonicotinamide (L) to form [Cu(cyclam)(L)2](p–CH3OC6H4COO)2 (4). These complexes were thermally stable (Tdec > 200 °C for 1–3 and 174 °C for 4). Complexes 3 and 4 behaved as ionic liquids (melting temperatures lower than 100 °C) and exhibited mesomorphism. 相似文献
64.
Tahir Ali Khan Sultana Naseem Yasser Azim Shama Parveen Mohammad Shakir 《Transition Metal Chemistry》2007,32(6):706-710
A novel series of 16-membered binuclear complexes of octaazatetraimine ligand,
[M = MnII, CoII, NiII, CuII and ZnII; X = Cl or NO3] have been synthesized by metal template condensation reactions of o-phenylenediamine with N,N′-diacetylhydrazine in 1:1:1 molar ratio in methanol. The proposed stoichiometry and the bonding of the macrocyclic moiety
to metal ions along with the overall stereochemistry have been derived from the results of elemental analyses, magnetic susceptibility,
conductivity data and the spectral data revealed from FT-IR,
, ESI mass, UV–visible studies. An octahedral geometry has been envisaged for MnII, CoII, and NiII complexes while a slight distortion in octahedral geometry has been noticed for CuII complexes. The low conductivity data of all the complexes suggest their non-ionic nature. 相似文献
65.
MdNurnobi Rashed Abeda Sultana Touchy Chandan Chaudhari Jaewan Jeon S.M.A.Hakim Siddiki Takashi Toyao Ken-ichi Shimizu 《催化学报》2020,(6):970-976
本文报道了将市售CeO2作为一种高活性和可重复使用的催化剂用于无溶剂条件下氧化吲哚与醛的C3选择性烷基化反应.这种催化方法一般适用于不同的芳香族和脂肪族醛,得到3-烷基二烯-辛醇,产率高(87%–99%),立体选择性高(79%–93%为E-异构体).这是从氧化吲哚与各种脂肪族醛催化合成3-烯基氧化吲哚的首例.采用原位红外光谱研究了CeO2上Lewis酸位点与苯甲醛之间的Lewis酸-碱相互作用.不同粒径CeO2催化剂的构效关系研究表明,无缺陷CeO2表面是该反应的活性中心. 相似文献
66.
Md Anisur Rahman Yujin Cha Liang Yuan Parasmani Pageni Tianyu Zhu Moumita Sharmin Jui Chuanbing Tang 《Journal of polymer science. Part A, Polymer chemistry》2020,58(1):77-83
Cobaltocenium-containing polyelectrolyte block copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using aqueous dispersion RAFT polymerization. The cationic steric stabilizer was a macromolecular chain-transfer agent (macro-CTA) based on poly(2-cobaltocenium amidoethyl methacrylate chloride) (PCoAEMACl), and the core-forming block was poly(2-hydroxypropyl methacrylate) (PHPMA). Stable cationic spherical nanoparticles were formed in aqueous solution with low dispersity without adding any salts. The chain extension of macro-CTA with HPMA was efficient and fast. The effects of block copolymer compositions, solid content, charge density, and addition of salts were studied. It was found that the degree of polymerization of both the stabilizer PCoAEMACl and the core-forming PHPMA had a strong influence on the size of nanoparticles. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 77–83 相似文献
67.
A theoretical study on heavier group‐14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group‐14 analogues of formamide (YHONH2, Y = Si, Ge and Sn), the nN–πY=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H‐bond donors to form FYO–H2O complexes to being H‐bond acceptors to form FYH–H2O complexes. The NEDA analysis indicates that H‐bond energies of FYO–H2O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H2O complexes H‐bond strengths are similar. The model of CTs from FYO to H2O differs from that at FYH–H2O complexes, which are contributed not only by aligning lone‐pair orbital of O but also by another lone‐pair orbital. At two lowest lying excited states (the triplet and S1 excited states), formamide and its heavier analogues form double H‐bonds with H2O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/cc‐pVTZ level. NBO analysis indicates that the barrier does not only come from the nN→π*YO conjugation, and for heavier analogues of formamide, the nN→σ*YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
68.
Poly J Ibarboure E Le Meins JF Rodriguez-Hernandez J Taton D Papon E 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4290-4295
The use of poly(vinyl acetate) (PVAc) nanogels for the fabrication of patterned porous surfaces is described. These nanogels were synthesized by controlled radical cross-linking copolymerization (CRCC) involving a xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) mechanism. This synthesis methodology allowed for the preparation of nanogels based on PVAc with a controlled constitutive chain length and average numbers of chains and cross-links. Solutions of these branched polymers were prepared in THF with a fixed amount of water and spin coated onto a surface of graphite. The surface porosity of corresponding films was observed by atomic force microscopy (AFM). Compared with linear PVAc homologues with a degree of polymerization (DP) sufficiently high to favor the formation of porous structures (DP = 50), a sharper and better defined porosity was observed with nanogels, the constitutive chains of which had the same DP. For nanogels differing only in their cross-link density, the pores were smaller and better defined in the case of the higher cross-link density, suggesting an enhanced stabilization of the water droplets during film formation. To explain these observations, it is postulated that PVAc nanogels can behave as compact particles providing steric stabilization of water droplets, which is referred to as a Pickering effect. The coalescence of water droplets would be better prevented as the cross-link density of the nanogels increases, resulting in a smaller size pore. 相似文献
69.
Nousin Akter Ruhul A. Khan Stephane Salmieri Nusrat Sharmin Dominic Dussault Monique Lacroix 《Radiation Physics and Chemistry》2012,81(8):995-998
Chitosan (1 wt%, in 2% aqueous acetic acid solution) and starch (1 wt%, in deionised water) were dissolved and mixed in different proportions (20–80 wt% chitosan) then films were prepared by casting. Tensile strength and elongation at break of the 50% chitosan containing starch-based films were found to be 47 MPa and 16%, respectively. It was revealed that with the increase of chitosan in starch, the values of TS improved significantly. Monomer, 2-butane diol-diacrylate (BDDA) was added into the film forming solutions (50% starch-based), then casted films. The BDDA containing films were irradiated under gamma radiation (5–25 kGy) and it was found that strength of the films improved significantly. On the other hand, synthetic petroleum-based polymeric films (polycaprolactone, polyethylene and polypropylene) were prepared by compression moulding. Mechanical and barrier properties of the films were evaluated. The gamma irradiated (25 kGy) films showed higher strength and better barrier properties. 相似文献
70.
Nusrat Sharmin Ruhul A. Khan Dominic Dussault Stephane Salmieri Nousin Akter Monique Lacroix 《Radiation Physics and Chemistry》2012,81(8):932-935
Chitosan films were prepared by casting from its 1% (w/w) solution. Tensile strength (TS) and tensile modulus (TM) of chitosan films were found to be 30 MPa and 450 MPa, respectively. Silane monomer (3-aminopropyl tri-methoxysilane) (0.25%, w/w) was added into the chitosan solution (1%, w/w) and films were casted. Then films were exposed to gamma radiation (5–25 kGy) and mechanical properties were investigated. It was found that at 10 kGy, the values of TS and TM were improved significantly. Silane grafted chitosan film reinforced poly(caprolactone) (PCL)-based tri-layer composites were prepared by compression molding. Silane improved interfacial adhesion between chitosan and PCL in composites. Surface of the films was investigated by scanning electron microscope (SEM) and found better morphology for silane grafted films. 相似文献