全文获取类型
收费全文 | 1013篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
化学 | 636篇 |
晶体学 | 8篇 |
力学 | 23篇 |
数学 | 138篇 |
物理学 | 237篇 |
出版年
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 34篇 |
2012年 | 62篇 |
2011年 | 80篇 |
2010年 | 47篇 |
2009年 | 29篇 |
2008年 | 54篇 |
2007年 | 59篇 |
2006年 | 57篇 |
2005年 | 49篇 |
2004年 | 41篇 |
2003年 | 32篇 |
2002年 | 36篇 |
2001年 | 28篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1958年 | 5篇 |
1956年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有1042条查询结果,搜索用时 15 毫秒
41.
In Taylor-Couette flow the total energy dissipation rate and therefore the drag can be determined by measuring the torque on the system. We do so for Reynolds numbers between Re=7 x 10(4) and Re=10(6) after having injected (i) small bubbles (R=1 mm) up to a volume concentration of alpha=5% and (ii) buoyant particles (rhop/rhol=0.14) of comparable volume concentration. In case (i) we observe a crossover from little drag reduction at smaller Re to strong drag reduction up to 20% at Re=10(6). In case (ii) we observe at most little drag reduction throughout. Several theoretical models for bubbly drag reduction are discussed in view of our findings. 相似文献
42.
43.
The ultrafast dephasing of waveguide-plasmon polaritons in metallic photonic crystal slabs is investigated in the femtosecond regime by second-order nonlinear autocorrelation. We find a drastic modification of the dephasing rates due to interaction between localized particle plasmons and optical waveguide modes and subsequent modification of the photonic density of states. In the strong coupling regime our measurements give clear evidence for the appearance of ultrafast polaritonic beat phenomena. All experimental results agree well with theoretical simulations based on a coupled damped harmonic oscillator model. 相似文献
44.
45.
We classify the complete metrics of nonnegative sectional curvature on M
2 × 2, where M
2 is any compact 2-manifold. 相似文献
46.
We have achieved efficient simultaneous intracavity doubling of the signal frequency and sum-frequency generation between the signal and the pump in a periodically poled LiNbO(3) femtosecond optical parametric oscillator pumped by a Ti:sapphire laser. The responsible mechanisms are second-, third-, and fourth-order quasi-phase matching (QPM). An ~56% poling duty cycle permits efficient even-order QPM. Femtosecond pulses tunable in the visible were generated with a total efficiency of more than 8% for only 480-mW pump power at 80 MHz. Optimization of the poling duty cycle can improve the efficiency further. 相似文献
47.
Detlef Mü ller Zhenqiu Zhang 《Proceedings of the American Mathematical Society》2001,129(10):3101-3107
As one step in a program to understand local solvability of complex coefficient second order differential operators on the Heisenberg group in a complete way, solvability of operators of the form , where the leading term is a ``positive combination of generalized and degenerate generalized sub-Laplacians', has been studied in a recent article by M. Peloso, F. Ricci and the first-named author (J. Reine Angew Math. 513 (1999)). It was shown that there exists a discrete set of ``critical' values , such that solvability holds for . The case remained open, and it is the purpose of this note to close this gap. Our results extend corresponding results in another article by the above-mentioned authors (J. Funct. Anal. 148 (1997)), by means of an even simplified approach which should allow for further generalizations.
48.
Christiane Becker Michael Hodenius Gitta Blendinger Antonio Sechi Thomas Hieronymus Detlef Müller-Schulte Thomas Schmitz-Rode Martin Zenke 《Journal of magnetism and magnetic materials》2007
A challenge for future applications in nanotechnology is the functional integration of nano-sized materials into cellular structures. Here we investigated superparamagnetic Fe3O4 iron oxide nanoparticles coated with a lipid bilayer for uptake into cells and for targeting subcellular compartments. It was found that magnetic nanoparticles (MNPs) are effectively taken up into cells and make cells acquire magnetic activity. Biotin-conjugated MNPs were further functionalized by binding of the fluorescent tag streptavidin–fluorescein isothiocyanate (FITC) and, following uptake into cells, shown to confer magnetic activity and fluorescence labeling. Such FITC-MNPs were localized in the lysosomal compartment of cells which suggests a receptor-mediated uptake mechanism. 相似文献
49.
The mechanism of the copper-mediated disproportionation of aromatic imine disulfides to benzothiazoles in the gas phase is investigated by experimental and theoretical methods. Application of infrared multiphoton dissociation and hydrogen/deuterium exchange experiments combined with density functional theory (DFT) calculations of the relevant molecular structures and the associated infrared spectra allows the identification of the observed ionic intermediates. The theoretical investigation of the possible reaction pathways supported by collision-induced dissociation experiments provides a consistent mechanistic picture of the reaction catalyzed by a single copper(I) ion. Activation of the substrate proceeds via homolytic sulfur-sulfur bond cleavage, yielding metal complexes in the formal +3 oxidation state; carbon-sulfur coupling and hydrogen-atom transfer complete the transformation to the products. Exploratory studies demonstrate that in the gas phase, the disproportionation of the imine disulfide can also be mediated by other metal ions via different either homo- or heterolytic mechanisms without involving high-valent intermediates. 相似文献
50.