全文获取类型
收费全文 | 151篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 117篇 |
晶体学 | 3篇 |
力学 | 2篇 |
数学 | 15篇 |
物理学 | 22篇 |
出版年
2022年 | 1篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 1篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 4篇 |
2004年 | 17篇 |
2003年 | 3篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 4篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有159条查询结果,搜索用时 0 毫秒
61.
Bazzicalupi C Bencini A Berni E Bianchi A Borsari L Giorgi C Valtancoli B Lodeiro C Lima JC Parola AJ Pina F 《Dalton transactions (Cambridge, England : 2003)》2004,(4):591-597
Protonation and Zn(II), Cd(II) and Hg(II) coordination with the ligand 5-aminoethyl-2,5,8-triaza-[9]-10,23-phenanthrolinophane (L2), which contains an aminoethyl pendant attached to a phenanthroline-containing macrocycle, have been investigated by means of potentiometric, 1H NMR and spectrofluorimetric titrations in aqueous solutions. The coordination properties of L2 are compared with those of the ligand 2,5,8-triaza-[9]-10,23-phenanthrolinophane (L1). Ligand protonation occurs on the aliphatic amine groups and does not involve directly the heteroaromatic nitrogens. The fluorescence emission properties of L2 are controlled by the protonation state of the benzylic nitrogens: when not protonated, their lone pairs are available for an electron transfer process to the excited phenanthroline, quenching the emission. As a consequence, the ligand is emissive only in the highly charged [H3L2]3+ and [H4L2]4+ species, where the benzylic nitrogens are protonated. Considering metal complexation, both [ML1]2+ and [ML2]2+ complexes (M = Zn(II) and Cd(II)) are not emissive, since the benzylic nitrogens are weakly involved in metal coordination, and, once again, they are available for quenching the fluorescence emission. Protonation of the L2 complexes to give [MHL2]3+ species, instead, leads to a recovery of the fluorescence emission. Complex protonation, in fact, occurs on the ethylamino group and gives a marked change of the coordination sphere of the metals, with a stronger involvement in metal coordination of the benzylic nitrogens; consequently, their lone pairs are not available for the process of emission quenching. 相似文献
62.
J. Pina J. Seixas de Melo H.D. Burrows A.P. Monkman S. Navaratnam 《Chemical physics letters》2004,400(4-6):441-445
Triplet state properties including transient triplet absorption spectrum, intersystem crossing yields in solution at room temperature and phosphorescence spectra, quantum yields and lifetimes at low temperature as well as singlet oxygen yields were obtained for poly(N-vinylcarbazole) (PVK) in 2-methyl-tetrahydrofuran (2-MeTHF), cyclohexane or benzene. The results allow the determination of the energy value for the lowest lying triplet state and also show that triplet formation and deactivation is a minor route for relaxation of the lowest excited singlet state of PVK. In addition, they show the triplet state is at higher energy than reported heavy metal dopants used for electrophosphorescent devices, such that if this is used as a host it will not quench their luminescence. 相似文献
63.
64.
Torsten W. Bünnagel Benjamin S. Nehls Frank Galbrecht Kristina Schottler Christof J. Kudla Markus Volk João Pina João S. Seixas de Melo Hugh D. Burrows Ullrich SCherf 《Journal of polymer science. Part A, Polymer chemistry》2008,46(22):7342-7353
A series of step‐ladder copolymers based on thiophene–phenylene–thiophene SL1 ‐ SL3 and thiophene–naphthylene–thiophene SL4 repeat units with varying lengths of the oligothiophene segment has been designed and synthesized via a microwave‐assisted Stille‐type cross‐coupling reaction followed by a polymer‐analogous cyclization reaction. The optical properties of the step‐ladder copolymers have been investigated in detail, in particular at low temperature and in the solid‐state. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7342–7353, 2008 相似文献
65.
The catalytic activity of "naked" gold particles 总被引:2,自引:0,他引:2
Comotti M Della Pina C Matarrese R Rossi M 《Angewandte Chemie (International ed. in English)》2004,43(43):5812-5815
66.
67.
Noémi Jordão Dr. Luis Cabrita Prof. Dr. Fernando Pina Dr. Luís C. Branco 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3982-3988
Novel mono and dialkylbipyridinium (viologens) cations combined with iodide, bromide, or bis(trifluoromethanesulfonyl)imide [NTf2] as anions were developed. Selective alkylation synthetic methodologies were optimized in order to obtain the desired salts in moderate to high yields and higher purities. All prepared mono‐ and dialkylbipyridinium salts were completely characterized by 1H, 13C, and 19F NMR spectroscopy, Fourier‐transform IR spectroscopy, and elemental analysis (in the case of NTf2 salts). Melting points, glass transition temperatures by differential scanning calorimetry (DSC) studies, and decomposition temperatures were also checked for different prepared organic salts. Viscosities at specific temperatures and activation energies were determined by rheological studies (including viscosity dependence with temperature in heating and cooling processes). Electrochemical studies based on cyclic voltammetry (CV), differential pulsed voltammetry (DPV), and square‐wave voltammetry (SWV) were performed in order to determine the redox potential as well as evaluate reversibility behavior of the novel bipyridinium salts. As proof of concept, we developed a reversible liquid electrochromic device in the form of a U‐tube system, the most promising dialkylbipyridinium‐NTf2 ionic liquid being used as the electrochromic material and the room‐temperature ionic liquid (RTIL), 1‐ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)‐imide [EMIM][NTf2], as a stable and efficient electrolyte. 相似文献
68.
Jernimo Abujas‐Pereira Ignacio Martin‐Bragado Carlos M. Pina Joaquín Pizarro Pedro L. Galindo 《Crystal Research and Technology》2016,51(10):575-585
This work presents a parallel approach of the Kinetic Monte Carlo (KMC) algorithm using a distributed memory architecture. The resulting computer software was tested by conducting crystal growth simulations on barite (001) face. Execution times, simulated times and crystallization velocities are compared with a shared memory parallel KMC software (MMonCa). Finally, a ≈ 1 μm2 crystal growth simulation is performed and compared with atomic force microscopy crystal growth experiments. The capability of this approach is demonstrated: a) a significant reduction of parallel overhead is achieved when comparing to the shared memory parallel version of the software, b) a distributed memory approach achieves an increase in memory resources enough to perform simulations with lattice sizes about 1 μm2, allowing the study of larger structures than those in shared memory or sequential implementations, c) this approach should be used only with large scale simulations to take advantage of the distributed memory architecture, d) further improvements are needed for parallel KMC to be faster than serial KMC in small scale simulations, e) the KMC algorithm used is able to adequately simulate two‐dimensional nucleation on large areas of barite (001) faces. 相似文献
69.
A new photochromic fused benzopyran presenting a bridge between the pyran double bond and the benzenic ring was prepared. While the UV irradiation of usual benzopyrans leads to the formation of two colored photoisomers with very different thermal stabilities, studies by laser flash photolysis showed that the presence of this particular bridge prevents the formation of the undesirable long-lived colored TT isomer and therefore after laser irradiation the colored solution fades following a fast monoexponential decay. 相似文献
70.
Romildo Pina Keti Tenenblat 《Proceedings of the American Mathematical Society》2004,132(12):3715-3724
We consider tensors on the unit sphere , where , is the standard metric and is a differentiable function on . For such tensors, we consider the problems of existence of a Riemannian metric , conformal to , such that , and the existence of such a metric that satisfies , where is the scalar curvature of . We find the restrictions on the Ricci candidate for solvability, and we construct the solutions when they exist. We show that these metrics are unique up to homothety, and we characterize those defined on the whole sphere. As a consequence of these results, we determine the tensors that are rotationally symmetric. Moreover, we obtain the well-known result that a tensor , 0 $">, has no solution on if and only metrics homothetic to admit as a Ricci tensor. We also show that if , then equation has no solution , conformal to on , and only metrics homothetic to are solutions to this equation when . Infinitely many solutions, globally defined on , are obtained for the equation
where . The geometric interpretation of these solutions is given in terms of existence of complete metrics, globally defined on and conformal to the Euclidean metric, for certain bounded scalar curvature functions that vanish at infinity.
where . The geometric interpretation of these solutions is given in terms of existence of complete metrics, globally defined on and conformal to the Euclidean metric, for certain bounded scalar curvature functions that vanish at infinity.