全文获取类型
收费全文 | 239篇 |
免费 | 12篇 |
专业分类
化学 | 165篇 |
晶体学 | 1篇 |
力学 | 13篇 |
数学 | 35篇 |
物理学 | 37篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 18篇 |
2011年 | 14篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1978年 | 1篇 |
1965年 | 2篇 |
1928年 | 1篇 |
1925年 | 1篇 |
1903年 | 1篇 |
1900年 | 2篇 |
1869年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 437 毫秒
121.
Raffaella Puliti Carlo A. Mattia Alessia De Fazio Maria R. Ghiara Lelio Mazzarella 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1447-1449
The title compound, (3R,4S,8R,9S)-cinchoninium (2R,3R)-tartrate tetrahydrate, C19H23N2O+·C4H5O6−·4H2O, is a hydrated salt of cinchonine. In the cinchoninium cation, the geometry around the quinuclidinic N atom is typical of a protonated N atom, and the bond lengths and angles in the tartrate moiety clearly indicate the mono-ionized form. The relative orientation of the quinoline and quinuclidine systems is that most frequently observed in structures of cinchona salts and corresponds to one of the energy minima calculated for this type of molecule in the gas phase. An extended network of intermolecular hydrogen bonds spreads parallel to the bc plane separating apolar layers. 相似文献
122.
We investigate the morphology of a pentacene (C22H14) film adsorbed on the Cu(1 1 9) vicinal surface by scanning tunnelling microscopy (STM). Thermal treatment of a thick film of molecules generates a long-range ordered structure. Series of molecular rows are alternated with areas where the molecules assume two equivalent orientations. STM data analysis suggests that the ordered structure can be described by a rippled morphology. The behaviour of the film at different annealing temperatures suggests a possible explanation of the film structure as due to an adsorbate-induced modification of the substrate. 相似文献
123.
124.
125.
126.
Mattia Gazzola Philippe Chatelain Wim M. van Rees Petros Koumoutsakos 《Journal of computational physics》2011,230(19):7093-7114
We present a vortex particle method coupled with a penalization technique to simulate single and multiple swimmers in an incompressible, viscous flow in two and three dimensions. The proposed algorithm can handle arbitrarily deforming bodies and their corresponding non-divergence free deformation velocity fields. The method is validated on a number of benchmark problems with stationary and moving boundaries. Results include flows of tumbling objects and single and multiple self-propelled swimmers. 相似文献
127.
C.?ManninoEmail author S.?Mattia A.?Sassano 《Computational Optimization and Applications》2011,48(3):533-551
Transmitters and receivers are the basic elements of wireless networks and are characterized by a number of radio-electrical
parameters. The generic planning problem consists of establishing suitable values for these parameters so as to optimize some
network performance indicator. The version here addressed, namely the Power Assignment Problem (pap), is the problem of assigning transmission powers to the transmitters of a wireless network so as to maximize the satisfied
demand. This problem has relevant practical applications both in radio-broadcasting and in mobile telephony. Typical solution
approaches make use of mixed integer linear programs with huge coefficients in the constraint matrix yielding numerical inaccuracy
and poor bounds, and so cannot be exploited to solve large instances of practical interest. In order to overcome these inconveniences,
we developed a two-phase heuristic to solve large instances of pap, namely a constructive heuristic followed by an improving local search. Both phases are based on successive shortest path
computations on suitable directed graphs. Computational tests on a number of instances arising in the design of the national
Italian Digital Video Broadcasting (DVB) network are presented. 相似文献
128.
Elisabetta Canè Mattia Villa Riccardo Tarroni Andrea Pietropolli Charmet Nicola Tasinato 《Molecular physics》2014,112(14):1899-1909
The v4 fundamental band of CF379Br and CF381Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm?1, 1208.0–1210.1 cm?1 and 1212.5–1214.5 cm?1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm?1. A Fourier transform infrared spectrum covering the entire spectral region of the v4 band, between 1190 and 1220 cm?1, was recorded at 298 K with a resolution of 0.004 cm?1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v4. In total, 4651 transitions were assigned to CF379Br, 4047 to CF381Br, with J″max? = K″max?=80; of these, 3171 for CF379Br and 2755 for CF381Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C3v symmetry. The v4 band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v4 = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v4 = 1 for CF379Br and CF381Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10?3 cm?1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional. 相似文献
129.
130.