全文获取类型
收费全文 | 1809篇 |
免费 | 84篇 |
国内免费 | 8篇 |
专业分类
化学 | 1247篇 |
晶体学 | 1篇 |
力学 | 27篇 |
数学 | 453篇 |
物理学 | 173篇 |
出版年
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 32篇 |
2020年 | 34篇 |
2019年 | 48篇 |
2018年 | 24篇 |
2017年 | 17篇 |
2016年 | 58篇 |
2015年 | 55篇 |
2014年 | 53篇 |
2013年 | 60篇 |
2012年 | 113篇 |
2011年 | 143篇 |
2010年 | 69篇 |
2009年 | 54篇 |
2008年 | 81篇 |
2007年 | 86篇 |
2006年 | 104篇 |
2005年 | 96篇 |
2004年 | 62篇 |
2003年 | 62篇 |
2002年 | 58篇 |
2001年 | 47篇 |
2000年 | 46篇 |
1999年 | 41篇 |
1998年 | 42篇 |
1997年 | 36篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 33篇 |
1993年 | 28篇 |
1992年 | 41篇 |
1991年 | 36篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 6篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1890年 | 2篇 |
1889年 | 2篇 |
排序方式: 共有1901条查询结果,搜索用时 15 毫秒
951.
Huseyin Tas Lon J. Mathias 《Journal of polymer science. Part A, Polymer chemistry》2008,46(23):7785-7793
New ether dimer (ED‐Od) and diester (ODE) derivatives of α‐hydroxymethylacrylate, each having two octadecyl side chains, were synthesized and (co)polymerized to evaluate the effects of differences in the structures of the monomers on final (co)polymer properties, particularly glass transition temperature. The free radical polymerizations of both monomers yielded high‐molecular weight polymers. Cyclopolymer formation of ED‐Od was confirmed by 13C NMR analysis and the cyclization efficiency (0.95 or greater) was found to be as high as the cyclization efficiencies of the cyclopolymerizations of ether dimers of various alkyl α‐hydroxymethylacrylates synthesized previously. Copolymers of both ED‐Od and ODE with methyl methacrylate (MMA) showed significant Tg decreases over PMMA due to octadecyl side groups causing “internal” plasticization. Comparison of the Tg's of the copolymers of octadecyl methacrylate, ED‐Od and ODE with MMA revealed that the impacts of these monomers on depression of Tg's are identical. That is, the magnitude of decrease in Tg's was quantitatively related to the number of the octadecyl side groups in the copolymers rather than their placement on the same or randomly incorporated repeat units. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7785–7793, 2008 相似文献
952.
Gabriela P. Aguiar Kamila A. L. Wakabayashi Guilherme F. Luz Vilma B. Oliveira Leda Mathias Ivo J. C. Vieira Raimundo Braz‐Filho Antonio E. M. Crotti 《Rapid communications in mass spectrometry : RCM》2010,24(3):295-308
The fragmentation of six plumeran indole alkaloids (PIAs) previously isolated from Aspidosperma spruceanum has been investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in the positive ion mode. The fragmentation pathways have been established on the basis of MS/MS experiments using fragment ions generated in‐source and deuterium‐labeled alkaloids as precursor ions and on the basis of accurate mass measurements. Our results demonstrated that the fragmentation routes observed for the protonated PIAs are essentially derived from a pericyclic reaction and from the opening of rings D and E, followed by 1,4‐hydrogen rearrangements. Product ions resulting from radical eliminations were also observed, contrary to the ‘even‐electron rule’. Our data reveals that some product ions from protonated PIAs provide crucial information for the characterization of the acyl substituent at N‐1, the methoxyl and hydroxyl groups at the aromatic moiety, and give evidence of an ether bridge between C‐18 and C‐21. The data reported here were used for the dereplication of these compounds in a stem bark methanolic extract of Aspidosperma spruceanum. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
953.
954.
Maximilian Mathias 《Mathematische Zeitschrift》1923,16(1):103-125
Ohne Zusammenfassung 相似文献
955.
956.
957.
958.
J M Mathias 《OR manager》1999,15(4):27, 29-30, 32
959.
The electronic structure of hydrogen adsorbate-induced states on Gd(0001) was investigated by means of photoelectron spectroscopy with linearly polarized radiation. The E vector of the incoming photon beam is rotatable. Clean and well-ordered rare-earth (0001) surfaces exhibit a highly localized surface state near the Fermi edge. After the adsorption of hydrogen, the surface state disappears and an additional sharp feature at about 4 eV binding energy is observed. For this latter
state, the ratio of the radial matrix elements as well as the relative phase shifts were determined to be R=Rp/Rf=2.4±0.3 and δf−δp=310±10°, respectively. The removal of the Gd surface state by hydrogen adsorption was investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS). The removal of the surface state exhibits domain-like behavior, with surface steps acting as domain boundaries. The tunneling spectra reveal that hydrogen adsorption causes a dramatic reduction in the differential conductivity near the Fermi level. 相似文献
960.
Angelina Leonardi Heather M. Ricker Ariel G. Gale Benjamin T. Ball Tuguldur T. Odbadrakh George C. Shields Juan G. Navea 《International journal of quantum chemistry》2020,120(20):e26350
Aerosols significantly influence atmospheric processes such as cloud nucleation, heterogeneous chemistry, and heavy-metal transport in the troposphere. The chemical and physical complexity of atmospheric aerosols results in large uncertainties in their climate and health effects. In this article, we review recent advances in scientific understanding of aerosol processes achieved by the application of quantum chemical calculations. In particular, we emphasize recent work in two areas: new particle formation and heterogeneous processes. Details in quantum chemical methods are provided, elaborating on computational models for prenucleation, secondary organic aerosol formation, and aerosol interface phenomena. Modeling of relative humidity effects, aerosol surfaces, and chemical kinetics of reaction pathways is discussed. Because of their relevance, quantum chemical calculations and field and laboratory experiments are compared. In addition to describing the atmospheric relevance of the computational models, this article also presents future challenges in quantum chemical calculations applied to aerosols. 相似文献