全文获取类型
收费全文 | 9089篇 |
免费 | 911篇 |
国内免费 | 708篇 |
专业分类
化学 | 5090篇 |
晶体学 | 1156篇 |
力学 | 505篇 |
综合类 | 103篇 |
数学 | 1497篇 |
物理学 | 2357篇 |
出版年
2024年 | 23篇 |
2023年 | 218篇 |
2022年 | 174篇 |
2021年 | 217篇 |
2020年 | 258篇 |
2019年 | 252篇 |
2018年 | 248篇 |
2017年 | 249篇 |
2016年 | 327篇 |
2015年 | 252篇 |
2014年 | 508篇 |
2013年 | 599篇 |
2012年 | 448篇 |
2011年 | 675篇 |
2010年 | 566篇 |
2009年 | 589篇 |
2008年 | 626篇 |
2007年 | 648篇 |
2006年 | 630篇 |
2005年 | 548篇 |
2004年 | 549篇 |
2003年 | 310篇 |
2002年 | 215篇 |
2001年 | 190篇 |
2000年 | 204篇 |
1999年 | 210篇 |
1998年 | 211篇 |
1997年 | 158篇 |
1996年 | 92篇 |
1995年 | 74篇 |
1994年 | 73篇 |
1993年 | 57篇 |
1992年 | 52篇 |
1991年 | 54篇 |
1990年 | 38篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Here we report a metal induced nucleation to realize the growth of ReS2 flowers at controlled locations. The ordered arrays of ReS2 flowers have been successfully prepared on SiO2/Si substrate using Pt metal dots as nucleation sites and S, NH4ReO4 powders as precursors by a chemical vapor depostion method. The NH4ReO4 powders are used as the rhenium sources. The ReS2 flowers are grown above the pre-patterned Pt dots, Raman and transmission electron microscopy measurements indicated that the prepared ReS2 flowers have excellent crystalline quality. 相似文献
82.
We prepared in-situ Au contacts on high-quality epitaxial YBa2Cu3O7 (YBCO) films. Very high specific contact resistivity values up to ∼10−2 Ω cm2 at 4.2 K were obtained on 12×5 μm2 contact areas. This resistivity value decreased by two orders of magnitude as the temperature was raised to room temperature. In the temperature range T<200 K, the contacts showed non-ohmic behavior suggesting the presence of a well-defined insulating native Y-Ba-Cu-O barrier between the two electrodes. The electrical transport in this barrier layer was analyzed in the limit of high temperatures and high voltages to follow Mott's variable-range hopping conduction mechanism with physically reasonable parameters describing the localized states in the barrier. The high-resistivity contacts were tested successfully in quasiparticles injection experiments where the critical current Ic of the YBCO microbridge could be strongly suppressed on injection of an additional current through the contact into the superconducting channel. 相似文献
83.
We show how macroeconomic dynamics can be derived from asymmetric information. As an illustration of the utility of this approach we derive the equilibrium density, non-equilibrium densities and the equation of motion for the response to a demand shock for productivity in a simple economy. Novel consequences of this approach include a natural incorporation of time dependence into macroeconomics and a common information-theoretic basis for economics and other fields seeking to link micro-dynamics and macro-observables. 相似文献
84.
A. Hussain C.W. Ahn H.J. Lee I.W. Kim J.S. Lee S.J. Jeong S.K. Rout 《Current Applied Physics》2010,10(1):305-310
We have fabricated lead-free Bi0.5(Na0.75K0.25)0.5TiO3 (BNKT) ceramics by a conventional process (CP) and reactive templated grain growth (RTGG) methods. The effect of grain orientation on structure, dielectric, complex impedance and electrical properties was investigated. The phase formation and grain morphology of BNKT ceramics were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. High dielectric constant and low dielectric loss was observed for grain oriented (textured) BNKT ceramics. Complex impedance, temperature dependent ac and dc conductivity were performed to explore the conduction behavior of the prepared BNKT ceramics. 相似文献
85.
The sonochemical formation of Au seeds and their autocatalytic growth to Au nanorods were investigated in a one-pot as a function of concentration of HAuCl4, AgNO3, and ascorbic acid (AA). The effects of ultrasonic power and irradiation time were also investigated. In addition, the formation rate of Au nanorods was analyzed by monitoring the extinction at 400 nm by UV–Vis spectroscopy and compared with the growth behavior of Au seeds to nanorods. Most of the reaction conditions affected the yield, size, and shape of Au nanorods formed. It was confirmed that the concentration balance between HAuCl4 and AA was important to proceed the formation of Au seeds and nanorods effectively. The formation rate became faster with increasing AA concentration and dog-bone shaped nanorods were formed at high AA concentration. It was also confirmed a unique phenomenon that the shape of Au nanorods changed even after the completion of the reduction of Au(I) in the case of short-time ultrasonic irradiation for Au seed formation. 相似文献
86.
The liquid to solid transformation of ternary Ag42.4Cu21.6Sb36 eutectic alloy was accomplished in an ultrasonic field with a frequency of 35 kHz, and the growth mechanism of this ternary eutectic was examined. Theoretical calculations predict that the sound intensity in the liquid phase at the solidification interface increases gradually as the interface moves up from the sample bottom to its top. The growth mode of (ε θ Sb) ternary eutectic exhibits a transition of "divorced eutectic- mixture of anomalous and regular structures-regular eutectic" along the sample axis due to the inhomogeneity of sound field distribution. In the top zone with the highest sound intensity, the cavitation effect promotes the three eutectic phases to nucleate independently, while the acoustic streaming efficiently suppresses the coupled growth of eutectic phases. In the meantime, the ultrasonic field accelerates the solute transportation at the solid-liquid interface, which reduces the solute solubility of eutectic phases. 相似文献
87.
The formation of Ag nanoparticles synthesized by homogeneous nucleation, stabilized by polymers (PVA and PVP) was monitored
by UV–Vis spectrophotometry and transmission electron microscopy. Our aim was to differentiate between the two main phases
of particle formation, i.e. nucleation and growth and to characterize their rates with the help of appropriate kinetic equations.
Time resolved spectrophotometric measurements revealed that particle formation is an autocatalytic process: a slow, continuous
nucleation phase (3–5 min) is followed by a rapid, autocatalytic growth phase where the maximal particle size is 5–7 nm. By
freezing the reaction mixture, the process of particle growth can be followed from 5 to 40 min on TEM pictures. The first
order rate constants were calculated and they are strongly depend on the polymer concentration. If the growing particles are
attached by PEI to the surface of a solid support, the formation of silver nanoparticles can also be followed by atomic force
microscopy (AFM) and we can control the particle growth on mica surface. The cross section analysis of the pictures show,
that the particle growing process can be also monitored at solid–liquid interface. 相似文献
88.
V.Yu. Argonov 《Physics letters. A》2011,375(7):1116-1119
The motion of an atomic wave packet in a standing light wave can be described in terms of two periodic potentials. Single atom may perform Landau-Zener (LZ) transitions between these two energy states. In this Letter we have found regimes when atom is localized in the momentum space in the vicinity of its initial momentum. We argue that this localization is caused by the asymmetry of LZ transitions (i.e. probability of tunneling depends on its direction) due to the interference. 相似文献
89.
A mesoporous La-doped nano-TiO2 was prepared by the sol-gel method using polyethylene glycol as the template. A combination of surface photovoltaic (SPV) and photoacoustic technologies, aided by laser Raman technology, was used to probe the photoexcited charge transfer transition behaviors in the surface space charge region of the sample. The results confirm that the lanthanum doping was responsible for inhibiting the transformation from the anatase to rutile form and grain growth, thus strengthening the microstructure that was formed after removal of the template clearly. The experiment reveals that appropriate La-doping resulted in an obvious increase in the SPV response. By contrast, the remainder of the template had a somewhat negative effect on the SPV response of the samples. The effect of both the La-doping and the removal of the template on the nonradiative de-excitation process of the main band-gap can be negligible, in spite of the nonradiative de-excitation processes of the sub-band-gap of the La-undoped sample, in which the surface states possessed the donor characteristic, being more obvious than that of the La-doped samples. The results showed that the electron-phonon interactions on the surfaces resulting from the nonradiative de-excitation process were closely dependent on the effect of quantum confinement of the mesoporous nano-TiO2. 相似文献
90.
The aim of this note is two-fold. First, we investigate the relations between the volume growth of a submanifold and its second fundamental form. In the second part, we discuss the relations between the index of some Schrödinger operators and the structure of a submanifold, and prove some one-end theorems. 相似文献