全文获取类型
收费全文 | 245819篇 |
免费 | 2331篇 |
国内免费 | 1089篇 |
专业分类
化学 | 114817篇 |
晶体学 | 3201篇 |
力学 | 14154篇 |
综合类 | 7篇 |
数学 | 48628篇 |
物理学 | 68432篇 |
出版年
2021年 | 991篇 |
2020年 | 1112篇 |
2019年 | 1127篇 |
2018年 | 11332篇 |
2017年 | 11135篇 |
2016年 | 8204篇 |
2015年 | 2707篇 |
2014年 | 2744篇 |
2013年 | 7949篇 |
2012年 | 9883篇 |
2011年 | 18012篇 |
2010年 | 10302篇 |
2009年 | 10853篇 |
2008年 | 13605篇 |
2007年 | 15658篇 |
2006年 | 7170篇 |
2005年 | 7759篇 |
2004年 | 7302篇 |
2003年 | 6919篇 |
2002年 | 5900篇 |
2001年 | 6233篇 |
2000年 | 4801篇 |
1999年 | 3597篇 |
1998年 | 2780篇 |
1997年 | 2733篇 |
1996年 | 2755篇 |
1995年 | 2388篇 |
1994年 | 2233篇 |
1993年 | 2116篇 |
1992年 | 2393篇 |
1991年 | 2369篇 |
1990年 | 2066篇 |
1989年 | 2063篇 |
1988年 | 2082篇 |
1987年 | 2015篇 |
1986年 | 1928篇 |
1985年 | 2819篇 |
1984年 | 2792篇 |
1983年 | 2242篇 |
1982年 | 2431篇 |
1981年 | 2308篇 |
1980年 | 2269篇 |
1979年 | 2215篇 |
1978年 | 2277篇 |
1977年 | 2217篇 |
1976年 | 2144篇 |
1975年 | 2134篇 |
1974年 | 2032篇 |
1973年 | 2128篇 |
1972年 | 1215篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
11.
12.
13.
14.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
15.
David S. McGuinness Edward L. Marshall Vernon C. Gibson Jonathan W. Steed 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3798-3803
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003 相似文献
16.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
17.
G. C. Psarras 《Journal of Polymer Science.Polymer Physics》2007,45(18):2535-2545
The charge transport properties of polymer matrix–carbon black composites are investigated in this study. Direct current conductivity is examined with varying parameters: the temperature and the conductive filler content. Conductivity data are analyzed by means of percolation theory, and both percolation threshold and critical exponent are determined at each of the examined temperatures. The temperature dependence of conductivity and the agreement of experimental results with the variable range hopping model reveal hopping conduction as the predominant transport mechanism, below and in the vicinity of the critical concentration of carbon black particles. At higher concentrations, the contribution of hopping transport to the overall conductivity is reduced and a balance between hopping and conduction via geometrical contact occurs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2535–2545, 2007 相似文献
18.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
19.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
20.