全文获取类型
收费全文 | 510806篇 |
免费 | 5514篇 |
国内免费 | 1249篇 |
专业分类
化学 | 257514篇 |
晶体学 | 7561篇 |
力学 | 24217篇 |
综合类 | 13篇 |
数学 | 70333篇 |
物理学 | 157931篇 |
出版年
2021年 | 3764篇 |
2020年 | 4185篇 |
2019年 | 4521篇 |
2018年 | 12403篇 |
2017年 | 12933篇 |
2016年 | 11902篇 |
2015年 | 6201篇 |
2014年 | 8641篇 |
2013年 | 20280篇 |
2012年 | 18925篇 |
2011年 | 28659篇 |
2010年 | 19068篇 |
2009年 | 18979篇 |
2008年 | 25863篇 |
2007年 | 28380篇 |
2006年 | 16406篇 |
2005年 | 19814篇 |
2004年 | 16188篇 |
2003年 | 14597篇 |
2002年 | 12873篇 |
2001年 | 13562篇 |
2000年 | 10330篇 |
1999年 | 7944篇 |
1998年 | 6602篇 |
1997年 | 6332篇 |
1996年 | 6225篇 |
1995年 | 5554篇 |
1994年 | 5473篇 |
1993年 | 5271篇 |
1992年 | 5888篇 |
1991年 | 5996篇 |
1990年 | 5725篇 |
1989年 | 5542篇 |
1988年 | 5571篇 |
1987年 | 5453篇 |
1986年 | 5161篇 |
1985年 | 6641篇 |
1984年 | 6789篇 |
1983年 | 5384篇 |
1982年 | 5467篇 |
1981年 | 5444篇 |
1980年 | 5038篇 |
1979年 | 5444篇 |
1978年 | 5587篇 |
1977年 | 5413篇 |
1976年 | 5388篇 |
1975年 | 4960篇 |
1974年 | 4932篇 |
1973年 | 4964篇 |
1972年 | 3492篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
A. Ferreira da Silva I. Pepe S.A. Tomás W.M. de Azevedo R. Ahuja 《Applied Surface Science》2006,252(15):5365-5367
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed. 相似文献
982.
High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi3 and Ti2Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes. 相似文献
983.
984.
The discovery of the neutrino oscillation pattern with solar and atmospheric neutrinos has stimulated systematic studies with long-baseline accelerator experiments. Precise neutrino beamline calculations have demonstrated the importance and paucity of existing hadroproduction data needed to shape the primary meson production in targets and tune available Monte Carlo codes for hadronic shower simulation. After a brief introduction to the physics of neutrino beams, available hadron production data will be reviewed with regards to their parametrization. Fast simulations based on such parameterizations and full Monte Carlo simulations of neutrino beamlines will then be illustrated. The prospective impact of new hadroproduction experiments, such as HARP at CERN and MIPP at Fermilab, will be shown together with some neutrino beamline simulations. 相似文献
985.
986.
Ultraviolet and blue-green photoluminescence (PL) was investigated on multicrystalline silicon (mc-Si) samples chemically etched by Secco and Yang solutions. The samples were characterized by dislocation density (105-106 cm−2). The form of etched pits is triangular with Yang etch and like a honeycomb with Secco etch as observed with a scanning electron microscope (SEM). These textures of mc-Si wafers give a PL activity similar to that obtained with nanostructures of porous silicon (PS) as reported in the literature. The ultraviolet PL spectra observed with Yang etch shift to the blue-green spectrum range when applying Secco etch. In our experiments we have observed 3-5 μm diameter macro pores separated by a high density of nanowalls. These observations suggest that the origin of the PL activity are quantum dots resulting from the silicon nanocrystallites obtained after few minutes of chemical etching. 相似文献
987.
In this contribution we present new data resulting from the analysis of concentration patterns of mixed juvenile fragments ejected by a highly explosive volcanic eruption that occurred on Salina Island (Aeolian Islands, Italy) and our aim is to identify the fluid-dynamic regime characterizing the magma mixing process. Concentration patterns are studied by calculating the power spectrum of concentration variability along transects crossing the magma mixing structures. Results indicate that the slope of power spectrum has an average value of about −5/3, according to Kolmogorov law of turbulence, and suggest that the magma mixing process, in the studied conditions, can be approximated by considering the passive scalar mixing hypothesis in homogeneous isotropic turbulent flow. These results represent a first step towards a better understanding of magma mixing processes associated to highly explosive volcanic eruptions and this first step is taken by studying concentration patterns in volcanic rocks by coupling petrological and non-linear dynamics methods. 相似文献
988.
989.
In this paper, we study an evasion problem in systems described by equations of parabolic type. We consider four versions of constraints on the control parameters. 相似文献
990.
I. P. Dobrovol’skaya M. V. Mokeev Yu. N. Sazanov A. V. Gribanov T. E. Sukhanova 《Russian Journal of Applied Chemistry》2006,79(8):1312-1315
Variation of the supramolecular structure of heat-resistant polymide films in the course of high-temperature treatment was studied by X-ray diffraction analysis and NMR spectroscopy in solids. 相似文献