全文获取类型
收费全文 | 32841篇 |
免费 | 3349篇 |
国内免费 | 4095篇 |
专业分类
化学 | 27315篇 |
晶体学 | 503篇 |
力学 | 1608篇 |
综合类 | 218篇 |
数学 | 3200篇 |
物理学 | 7441篇 |
出版年
2024年 | 52篇 |
2023年 | 366篇 |
2022年 | 842篇 |
2021年 | 923篇 |
2020年 | 1166篇 |
2019年 | 1122篇 |
2018年 | 993篇 |
2017年 | 1211篇 |
2016年 | 1322篇 |
2015年 | 1199篇 |
2014年 | 1468篇 |
2013年 | 2272篇 |
2012年 | 1849篇 |
2011年 | 2089篇 |
2010年 | 1705篇 |
2009年 | 2165篇 |
2008年 | 1966篇 |
2007年 | 2019篇 |
2006年 | 1786篇 |
2005年 | 1617篇 |
2004年 | 1662篇 |
2003年 | 1280篇 |
2002年 | 1595篇 |
2001年 | 969篇 |
2000年 | 792篇 |
1999年 | 638篇 |
1998年 | 565篇 |
1997年 | 511篇 |
1996年 | 553篇 |
1995年 | 519篇 |
1994年 | 482篇 |
1993年 | 340篇 |
1992年 | 345篇 |
1991年 | 212篇 |
1990年 | 172篇 |
1989年 | 159篇 |
1988年 | 172篇 |
1987年 | 126篇 |
1986年 | 98篇 |
1985年 | 82篇 |
1984年 | 85篇 |
1983年 | 32篇 |
1982年 | 77篇 |
1981年 | 104篇 |
1980年 | 116篇 |
1979年 | 119篇 |
1978年 | 99篇 |
1977年 | 71篇 |
1976年 | 65篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
101.
Pál Sohár Gábor Bernáth Géza Stájer Angela E. Szabo 《Magnetic resonance in chemistry : MRC》1989,27(9):872-876
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments. 相似文献
102.
103.
Morphological and chemical properties of both the surface and interface of poly(vinylidene fluoride)/poly(methyl methacrylate)-co-poly(ethyl acrylate) (PVDF/PMMA-co-PEA) blend films have been investigated before and after the samples were exposed to ultraviolet (UV) irradiation using a xenon arc lamp at 50 °C and 9% relative humidity (RH) for 7 months. Surface and interfacial morphologies were studied by atomic force microscopy (AFM). Chemical composition information was obtained by confocal Raman microscopy, attenuated total reflection-FTIR spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Results show an enrichment of the PVDF material at the air surface, while the acrylic copolymer enriches the interface. Blends having greater than 50% mass fraction of PVDF show little change in the surface morphology after UV exposure for 7 months. However, for a lower PVDF content, blends exhibit significant degradation of PMMA-co-PEA copolymer and a much rougher surface after UV exposure. Microstructural changes in the PVDF spherulites are also observed after UV degradation. It is found that the surface and interfacial morphologies are correlated with the chemical properties. 相似文献
104.
105.
1 Introduction Inrecentyears,boththetheoreticalandexperimentalinvestigationsonlasercoolingandtrappinghavebecomeoneofthemajorfieldsinatomic,molecularandoptical physics[1~ 8] .Thedevelopmentoflasercoolingandtrappingtechnologyisimportantfortheapplicationssu… 相似文献
106.
M. I. Pech-Canul F. Ortega-Celaya M. A. Pech-Canul 《Mechanics of Composite Materials》2006,42(3):283-296
The effect of SiO2 in SiCp and the following processing parameters on the microstructure and impact strength of Al/SiCp composites fabricated by pressureless infiltration was investigated: Mg content in the aluminum alloy, SiC particle size,
and holding time. Preforms of SiCp in the form of rectangular bars (10 × 1 × 1 cm) were infiltrated at 1150°C in an argon→nitrogen atmosphere for 45 and 60
min by utilizing two aluminum alloys (Al-6 Mg-11 Si and Al-9 Mg-11 Si, wt.%). The results obtained show that the presence
of SiO2 in SiC affects the microstructure and impact strength of the composites significantly. When Al4C3 is formed, the impact strength decreases. However, a high proportion of SiC to SiO2 limits the formation of the unwanted Al4C3 phase in the composites. Also, a higher content of Mg in the Al alloy lowers the residual porosity and, consequently, increases
the composite strength. The impact strength grows with decrease in SiC particle size and increases considerably when the residual
porosity is less than 1%.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 401–418, May–June, 2006. 相似文献
107.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献
108.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
109.
110.
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