全文获取类型
收费全文 | 412329篇 |
免费 | 4628篇 |
国内免费 | 1340篇 |
专业分类
化学 | 220264篇 |
晶体学 | 6271篇 |
力学 | 16796篇 |
综合类 | 5篇 |
数学 | 50098篇 |
物理学 | 124863篇 |
出版年
2020年 | 3364篇 |
2019年 | 3599篇 |
2018年 | 4483篇 |
2017年 | 4458篇 |
2016年 | 7323篇 |
2015年 | 4849篇 |
2014年 | 7212篇 |
2013年 | 19189篇 |
2012年 | 14012篇 |
2011年 | 17160篇 |
2010年 | 11523篇 |
2009年 | 11354篇 |
2008年 | 15745篇 |
2007年 | 15665篇 |
2006年 | 14590篇 |
2005年 | 13366篇 |
2004年 | 12060篇 |
2003年 | 10664篇 |
2002年 | 10460篇 |
2001年 | 11737篇 |
2000年 | 8886篇 |
1999年 | 6947篇 |
1998年 | 5853篇 |
1997年 | 5744篇 |
1996年 | 5559篇 |
1995年 | 5185篇 |
1994年 | 5032篇 |
1993年 | 5151篇 |
1992年 | 5567篇 |
1991年 | 5427篇 |
1990年 | 5188篇 |
1989年 | 5085篇 |
1988年 | 5157篇 |
1987年 | 4984篇 |
1986年 | 4775篇 |
1985年 | 6493篇 |
1984年 | 6656篇 |
1983年 | 5630篇 |
1982年 | 6040篇 |
1981年 | 5796篇 |
1980年 | 5666篇 |
1979年 | 5803篇 |
1978年 | 6070篇 |
1977年 | 5872篇 |
1976年 | 6043篇 |
1975年 | 5534篇 |
1974年 | 5673篇 |
1973年 | 6127篇 |
1972年 | 3846篇 |
1971年 | 3071篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
A. Bartnik H. Fiedorowicz R. Jarocki L. Juha J. Kostecki R. Rakowski M. Szczurek 《Applied physics. B, Lasers and optics》2006,82(4):529-532
The first results of experiments on direct photo-etching of heated PTFE using a 10 Hz X-ray source based on a laser-irradiated gas puff target are presented. X-ray radiation in the wavelength range from 6 to 20 nm was produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser pulses of energy 0.8 J and time duration 3 ns. The resulting X-ray pulses with energy of about 100–200 mJ were used to irradiate samples of PTFE to create microstructures by direct photo-etching. Strong enhancement of the photo-etching process was observed for samples heated up to 300 °C. PACS 52.38.Ph; 81.65.Cf; 61.82.Pv 相似文献
963.
M. R. Bedilov R. M. Bedilov A. R. Matnazarov M. M. Sabitov Zh. O. Kamalova 《Physics of the Solid State》2006,48(9):1629-1633
The effect of accumulation on the formation of multiply charged ions in optically opaque solids as a function of the number and the angle of incidence of laser pulses is investigated by mass spectrometry. It is revealed that the accumulation effect manifests itself at prethreshold power densities q = 108–109 W/cm2 irrespective of the angle of incidence of laser radiation α = 18°–85° and at subthreshold power densities q > 1010 W/cm2 in the case of grazing incidence of laser radiation at an angle α = 85°. The accumulation effect brings about an increase in the maximum charge multiplicity Z max of tungsten ions and a decrease in the number of impurity ions and in their intensity. No accumulation effect is observed at subthreshold power densities when laser radiation is incident at an angle α = 18°. 相似文献
964.
The impedance spectra of Pb5Ge3O11 single crystals are measured in the frequency range from 5 Hz to 13 MHz at temperatures of 600 to 800 K in dry air and in
a dry or wet nitrogen gas. It is found that the temperature and the gas composition significantly affect the electrical properties
of the compound. The data obtained are used to discuss the origin of crystal lattice defects and their influence on charge
transfer. It is concluded that the conduction is mixed in character (p-type electronic and ionic due to oxygen ions). The proton conduction is shown experimentally to be feasible. The possible
mechanisms of proton transport in Pb5Ge3O11 are discussed. 相似文献
965.
B. G. Sidharth 《Foundations of Physics Letters》2006,19(6):611-617
In this note we consider a variable G cosmology which is consistent with observation and which had successfully predicted an ever expanding accelerating universe
with a small cosmological constant amongst other things. Three further tests are proposed in this note: First, the inexplicable
anomalous accelerations of the Pioneer spacecrafts can be explained. It is then shown that the observed shortening of the
orbital periods of binary pulsars is in good agreement with this model. Finally, more general changes in orbital parameters
are deduced, which may be observed in the future. 相似文献
966.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献
967.
T. Rietmann S. Sohn M. Schröder D. Lipinsky H.F. Arlinghaus 《Applied Surface Science》2006,252(19):6640-6643
In order to improve quantification of high mass ions, the influence of cluster composition on detection efficiencies has been studied using a TOF-SIMS IV with the extended capability of postaccelerating ions up to 20 keV. In this experimental study, we focus on the comparison of detection efficiencies for three types of negatively charged secondary cluster ions: gold-alkanethiolate-clusters (AuxMy), gold-sulfur-clusters (AuxSy) and gold-clusters (Aux). The clusters were sputtered from self-assembled monolayers of hexadecanethiols on gold substrates using 10 keV Ar+ primary ions. The detection efficiencies were derived on the basis of a function for the secondary electron yield and a fourth-order approximated Poisson probability distribution for electron propagation and amplification within the microchannel plate.In addition to the well-known dependence of detection efficiencies on ion mass and energy, which has already been studied for positively charged ions, we were able to show a similar behaviour for the investigated negatively charged secondary ions. We have observed major variations among the three types of clusters at similar mass and energy as predicted in a theoretical approach. The observed differences are due to the different composition of the investigated clusters which has a major influence on the kinetic ion induced electron emission within the microchannel plate. For the first time it was possible to experimentally verify these predictions for detection efficiencies. 相似文献
968.
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into
nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm.
The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires
have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer
(VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated
domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices. 相似文献
969.
We investigate the electronic properties of multiwalled carbon nanotubes both before and after acid treatment with concentrated sulphuric and nitric acids. Magnetic susceptibility measurements were performed using a SQUID magnetometer and show that there is a considerable enhancement in the density of states at the Fermi level. The data shows that the diamagnetic influence from the graphitic nanotubes dominates. We experimentally observe, after acid treatment, that the diamagnetic susceptibility remains unchanged at 5 K but notably decreases at 77 K. We propose the acid treatment has increased the Van Vleck paramagnetic contribution lowering the diamagnetic response from the π-electron orbital magnetisation. The Van Vleck paramagnetic contribution is finite-temperature dependent with a diminishing contribution at higher fields. 相似文献
970.
This paper considers the general synchronization dynamics of coupled Van der Pol–Duffing oscillators. The linear and nonlinear stability analysis on the synchronization process is derived through the Whittaker method and the Floquet theory in addition to the multiple time scales method. A stability map displaying different dynamical states of the system is performed. Numerical simulation is carried out to support and to complement the accuracy of the analytical treatment. 相似文献