全文获取类型
收费全文 | 182篇 |
免费 | 3篇 |
专业分类
化学 | 103篇 |
晶体学 | 14篇 |
力学 | 8篇 |
数学 | 30篇 |
物理学 | 30篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 23篇 |
2012年 | 18篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 2篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有185条查询结果,搜索用时 15 毫秒
101.
Berhal F Esseiva O Martin CH Tone H Genet JP Ayad T Ratovelomanana-Vidal V 《Organic letters》2011,13(11):2806-2809
Two new atropisomeric electron-poor chiral diphosphine ligand analogues of SYNPHOS were prepared, and their electronic properties are described. These two ligands afforded high performance for the Rh-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds at room temperature. 相似文献
102.
ABSTRACTWe investigated the alignment director of a frustrated cholesteric liquid crystal (CLC) confined in a planar cell. Three cells with different confinement ratio (c?=?d/p) (where p is the pitch and d is the cell thickness) are prepared. Under an electric field, the CLC planar texture is transformed into a cholesteric fingerprint (CF). The results showed that CF contrast depends on c. When c?≈?2, CLC stripes are formed by a periodic CF, with a period equal to the CLC pitch. The CF is developed and slowly extended to the whole cell surface along the rubbing direction and the contrast of the grating stripes keeps unchangeable. Yet, the CLC finger borders have a different light intensity. However, when c?≈?1, the CF contrast increases with time. When c?1, an isolated CF is obtained whose borders contrast change by varying the angle θ between the polarizer and the CFs. 相似文献
103.
Imen Ben Naceur Moez Guettari Ghazi Kassab Tahar Tajouri 《Journal of Macromolecular Science: Physics》2013,52(11):2171-2182
The aim of this work was to study the rheological behavior of water in-oil microemulsion formulated with AOT (sodium bis(2-ethylhexyl) sulfoccinate) in isooctane over a temperature range from 25°C to 55°C for the oil/AOT volume fraction φ m =0.1 and various AOT and H2O molar ratios, W0, ranging from 0 to 45. The apparent viscosity was measured vs. shear rate by a rotational concentric cylinder viscometer. It was shown that above s?1, the solutions utilized behaved as Newtonian liquids. The absolute viscosities were deduced from the shear stress- shear rate rheograms. For W0 < 17, the solutions behaved as simple fluids, where the viscosities decrease as the temperature increases. However, an opposite behavior was observed for W0 > 17; the viscosity remained constant and then increased above a critical temperature, Tc, depending on W0. For the molar ratio W0,c = 17; the studied viscosity remained constant, η(W0,c) = (1.17 ± 0.04) cP, for the temperature range studied. Thus, a simple–complex fluid transition was evident in the studied system. For the simple fluids, W0 < W0,c, the total activation energy vs. W0 showed three linear parts. The different slopes were attributed to the change of the microscopic structure of the formed micelles. For the critical molar ratio W0,c = 17, the total activation energy vanished. So, according to the Eyring lattice model, the jump of the formed micelles from one site to another was not permitted and the entire molecular groups were in vibration and rotation motions. For W0 > W0,c, where the formed micelles were fully hydrated, the relative viscosity of the studied solutions vs. temperature was fitted according a polynomial law, where the exponent was found to be dependent on W0. 相似文献
104.
Sami Soukrata Mohamed Belhouchet Joen Josep Suñol Tahar Mhiri 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):422-431
Abstract A new adduct bis-(2-amino-3-benzyloxypyridinium) selenate monohydrate, [C12H13N2O]2SeO4.H2O, has been synthesized by slow evaporation at room temperature using 2-amino-3-benzyloxypyridine as the structure-directing agent. The structure, determined by single-crystal X-ray diffraction at 298 K, can be described as organic-inorganic tunnels with different forms built by infinite inorganic chains parallel to the c axis and connected to the organic cations. In this atomic arrangement, hydrogen bonds and van der Waals interactions between the different species play an important role in the tri-dimensional network cohesion. Solid-state 13C and 77Se MAS NMR spectroscopy results are in agreement with the X-ray structure. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional figures and tables.] 相似文献
105.
106.
The paper deals with the existence of weak positive solutions for a new class of quasilinear singular elliptic systems involving critical Caffarelli–Kohn–Nirenberg exponent with sign-changing weight functions using the method of sub-super solutions. Our results are natural extensions from the previous ones in [3]. 相似文献
107.
K3Sb4BO13, Mr = 823.11 g.mol–1, crystallizes in the triclinic system, space group P
, Z = 2. The lattice parameters are a = 7.133(1) Å, b = 7.232(1) Å, c = 13.259(2) Å, = 82.00 (1)°, = 99.77(1)° and = 117.08(1)°, V = 598.7(2) Å3, Dx = 4.566 Mg m–3. The final R index and weighted Rw index are 0.0251 and 0.0623, respectively. The three-dimensional network of the title compound is constituted by layers (Sb3O9)n, similar to that of hexagonal bronze of Magneli. These layers are linked together, in the c direction, alternatively by edge-sharing pairs of SbO6 octahedra and BO3 triangles. This framework has interconnected tunnels, running approximately along the a and b directions, in which the K+ ions are located. 相似文献
108.
A variational formulation for a vibroacoustic problem of a membrane and a viscothermal fluid is investigated in this paper. The formulation combines a variational formulation by integral equations of the fluid, that takes into account the acoustic and entropic waves coupling, with a variational formulation of the membrane. The formulation has been implemented numerically for the problems with axisymmetric geometry. The numerical results are compared to the analytical solution for a circular membrane coupled to a cylindrical cavity filled with air. These results show the validity of numerical implementation and illustrate the thermal effects of air on the membrane-cavity system modes in the micro cavities cases. 相似文献
109.
Mohamed Tahar Kadaoui Abbassi Noura Amri Giovanni Calvaruso 《Mathematische Nachrichten》2020,293(10):1873-1887
The study of symmetries is a well known research topic in differential geometry with relevant physical interpretations. Given a Riemannian manifold , we consider pseudo-Riemannian g-natural metrics G on its tangent bundle and characterize conformal, homothetic and Killing vector fields of obtained from natural lifts of vector fields of M. 相似文献
110.
Salem Saïd Noureddine Mhadhbi Fadhel Hajlaoui Samia Yahyaoui Alexander J. Norquist Tahar Mhiri 《Phase Transitions》2013,86(1):71-84
Single crystals of [(R)-C5H14N2][Cu(SO4)2(H2O)4]·2H2O (1) were grown through the slow evaporation of a solution containing H2SO4, (R)-C5H12N2 and CuSO4·5H2O. These crystals spontaneously transform to [(R)-C5H14N2]2[Cu(H2O)6](SO4)3 (2) over the course of four days at room temperature. The same single crystal on the same mounting was used for the determination of the structure of (1) and the unit cell determination of (2). A second single crystal of the transformed batch has served for the structural determination of (2). Compound 1 crystallizes in the noncentrosymmetric space group P21 (No. 4) and consists of trimeric [Cu(SO4)2(H2O)4]2? anions, [(R)-C5H14N2]2+ cations and occluded water molecules. Compound 2 crystallizes in P21212 (No. 18) and contains [Cu(H2O)6]2+ cations, [SO4]2? anions and occluded water molecules. The thermal decompositions of compounds 1 and 2 were studied by thermogravimetric analyses and temperature-dependent X-ray diffraction. 相似文献