全文获取类型
收费全文 | 1543篇 |
免费 | 30篇 |
国内免费 | 4篇 |
专业分类
化学 | 1112篇 |
晶体学 | 16篇 |
力学 | 22篇 |
数学 | 104篇 |
物理学 | 323篇 |
出版年
2021年 | 7篇 |
2020年 | 12篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 13篇 |
2014年 | 33篇 |
2013年 | 66篇 |
2012年 | 47篇 |
2011年 | 64篇 |
2010年 | 34篇 |
2009年 | 45篇 |
2008年 | 98篇 |
2007年 | 70篇 |
2006年 | 76篇 |
2005年 | 83篇 |
2004年 | 89篇 |
2003年 | 66篇 |
2002年 | 67篇 |
2001年 | 33篇 |
2000年 | 57篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 24篇 |
1993年 | 10篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 41篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 29篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 9篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有1577条查询结果,搜索用时 140 毫秒
101.
Water content distribution in a polymer electrolyte membrane for advanced fuel cell system with liquid water supply 总被引:2,自引:0,他引:2
To better understand the operation of a new fuel cell design, we used magnetic resonance imaging (MRI) to measure the water content distribution in a polymer electrolyte membrane under fuel cell operation with and without a supply of liquid water. The supply of liquid water to the membrane improved the cell performance by increasing the water content in the membrane and thus reducing the electrical resistance of the membrane. The study also showed that MRI is a promising method to investigate the distribution of water in the membrane of a fuel cell under operating conditions. 相似文献
102.
We report inelastic neutron scattering measurements on polystyrene thin films in a glassy state in the meV region. We found in elastic scattering that the mean square displacement decreased with film thickness, and hence the corresponding force constant f increased. In inelastic and quasielastic scattering, we observed the so-called boson peak at around 1.5 meV and the picosecond fast process for the first time in thin films, both of which decreased in intensity with film thickness. These results were discussed in terms of the potential hardening due to the confinement of polymer chains and/or the interfacial dead layer. 相似文献
103.
Taniguchi J Yamaguchi A Ishimoto H Ikegami H Matsushita T Wada N Gatica SM Cole MW Ancilotto F Inagaki S Fukushima Y 《Physical review letters》2005,94(6):065301
Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D 3He fluid is indicated by a predominantly linear temperature dependence below about 30 mK. 相似文献
104.
Morita Y Nishida S Kobayashi T Fukui K Sato K Shiomi D Takui T Nakasuji K 《Organic letters》2004,6(9):1397-1400
[structure: see text] A bowl-shaped neutral radical with a corannulene system has been designed and synthesized for the first time as a stable solid in air. An unequivocal characterization of the electronic properties of the radical shows that an appreciable amount of spin delocalization extends onto the corannulene unit's curved surface. 相似文献
105.
Effects of disorder on the two competing phases, i.e., the ferromagnetic metal and the commensurate charge/lattice ordered insulator, are studied by Monte Carlo simulation. The disorder suppresses the charge/lattice ordering more strongly than the ferromagnetic order, driving the commensurate insulator to the ferromagnetic metal near the phase boundary in the pure case. Above the ferromagnetic transition temperature, on the contrary, the disorder makes the system more insulating, which might cause an enhanced colossal magnetoresistance as observed in the half-doped or Cr-substituted manganites. No indication of the percolation or the cluster formation is found, and there remains the charge/lattice fluctuations instead which are enhanced toward the transition temperature. 相似文献
106.
Two new tetranor-cycloartane glycosides (1, 2) were isolated from Cimicifuga Rhizome. Their structures were determined by spectroscopic analysis. These compounds suggested the existence of a biogenetic pathway into C-23 lactone-type cycloartane glycosides. 相似文献
107.
[reaction: see text] A concept for the development of practical glycosylation is presented and demonstrated by one-pot alpha-glycosylation applying Appel agents for 2-O-benzyl-1-OH hexoses in DMF. The reaction, in situ giving the equilibrium of glycosyl bromides and more reactive O-glycoside intermediates, accomplishes a near-quantitative alpha-glycosylation removing the water molecules. 相似文献
108.
Let R be a commutative Noetherian ring. Let P(R) (respectively,I(R)) be the category of all finite R-modules of finite projective(respectively, injective) dimension. Sharp [9] constructed acategory equivalence between I(R) and P(R) for certain CohenMacaulaylocal rings R. Thus many properties about finite modules offinite projective dimension can be connected with those of finiteinjective dimension through this equivalence. 相似文献
109.
Alexander Čeklovský Juraj Bujdák Adriana Czímerová Nobuo Iyi 《Central European Journal of Physics》2007,5(2):236-243
Tetracationic porphyrin dyes TMPyP and ZnPyP were intercalated into hydrophobized layered silicate films of three smectites.
The smectites represented the layered silicate specimens of high (Fluorohectorite, Corning; FHT), medium (Kunipia F montmorillonite;
KF) and low layer charge (Laponite, Laporte; LAP). The molecular orientations of the dye cations were studied by means of
linearly-polarized ultraviolet-visible (UV-VIS) spectroscopy. The spectral analysis and consequent calculations of tilting
angles of the transition moments at the wavelengths of Soret band transitions were in the range of 25°-35°. The determined
angles indicated molecular orientation of the dye cations being almost parallel to the surface of the silicates. Slightly
higher values (above 35°), determined for a FHT film, indicated either a slightly tilted orientation of the dye cations or
the change of molecular comformation after the intercalation of the dye.
Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia 相似文献
110.
We have developed the mechanically controllable break junction setup with an electrochemical cell (EC-MCBJ) to measure the electric conductance of metal nanowires under electrochemical potential control. The electric conductance of Au nanowires was investigated in 0.1 M Na2SO4 solution using EC-MCBJ. The conductance of the Au nanowires was quantized in units of G0 (=2e2/h), showing clear features in the conductance histogram. The atomic contact with a specific conductance value was kept for >5 s, indicating the relatively high stability of the present EC-MCBJ system. 相似文献