全文获取类型
收费全文 | 660篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 382篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 46篇 |
物理学 | 192篇 |
综合类 | 49篇 |
出版年
2020年 | 7篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 21篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 32篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 29篇 |
2007年 | 27篇 |
2006年 | 26篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 28篇 |
2001年 | 18篇 |
2000年 | 25篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 25篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 15篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1970年 | 8篇 |
1968年 | 3篇 |
1965年 | 3篇 |
1909年 | 3篇 |
排序方式: 共有680条查询结果,搜索用时 15 毫秒
71.
Matthew Myers Eric F. Connor Thierry Glauser Andreas Mck Gregory Nyce James L. Hedrick 《Journal of polymer science. Part A, Polymer chemistry》2002,40(7):844-851
A new metal‐free synthetic approach to the controlled ring‐opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)3, PhPMe2, Ph2PMe, PPh3, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α‐end group upon ROP. A likely polymerization pathway is through a monomer‐activated mechanism, with minimal active species, facilitating narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 844–851, 2002; DOI 10.1002/pola.10168 相似文献
72.
The two-photon-resonant first hyperpolarizabilities associated with hyper-Rayleigh and hyper-Raman scattering are reported for 4-dimethylamino-4-nitrostilbene in 1,4-dioxane, dichloromethane, acetonitrile, and methanol, and for an ionic analog, 4-N,N-bis(6-(N,N,N-trimethylammonium)-hexyl)amino-4-nitrostilbene dibromide in methanol and water. Resonance Raman and hyper-Raman excitation profiles are also measured and modeled. The resonance Raman and hyper-Raman spectra show very similar relative intensities which do not vary much as the excitation frequency is tuned across the lowest-energy strong linear absorption band, suggesting that a single resonant electronic state dominates the one- and two-photon absorptions in this region. The absorption, resonance Raman, and hyper-Raman profiles can be simulated reasonably well with a common set of parameters. The peak resonant (absolute value of beta)2, measured by hyper-Rayleigh scattering, varies by about 50% over the range of solvents examined and shows a weak correlation with the linear absorption maximum, with the redder-absorbing systems exhibiting larger peak hyperpolarizabilities. The experimental hyper-Rayleigh intensities are higher than those calculated, possibly reflecting contributions from nonresonant electronic states. 相似文献
73.
74.
75.
Regulacio MD Pablico MH Vasquez JA Myers PN Gentry S Prushan M Tam-Chang SW Stoll SL 《Inorganic chemistry》2008,47(5):1512-1523
We have discovered room temperature photoluminescence in Sm3+ and Pr3+ dithiocarbamate complexes. Surprisingly, these complexes exhibit more intense emission than those of the Eu3+, Tb3+, and Dy3+ analogues. The electronic absorption, excitation, and emission spectra are reported for the complexes [Ln(S2CNR2)3L] and NH2Et2[Ln(S2CNEt2)4], where Ln = Sm, Pr; R = ethyl, ibutyl, benzyl; and L = 1,10-phenanthroline, 2,2'-bipyridine, and 5-chloro-1,10-phenanthroline. The lowest ligand-localized triplet energy level (T1) of the complexes are determined from the phosphorescence spectra of analogous La3+ and Gd3+ chelates. The luminescence decay curves were measured to determine the excited-state lifetimes for the Pr3+ and Sm3+ complexes. X-ray crystal structures of Sm(S2CNiBu2)3phen, Pr(S2CNEt2)3phen, and Pr(S2CNiBu2)3phen are also reported. 相似文献
76.
77.
78.
Manea S. AlKhalifah Chunhong Lei Steven A. Myers Stuart P. Kitney 《Liquid crystals》2013,40(3):402-417
The cross-linking of polymerisable liquid crystalline semiconductors is a promising approach to solution-processable, multilayer, organic photovoltaics. Here we demonstrate an organic bilayer photovoltaic with an insoluble electron-donating layer formed by cross-linking a nematic reactive mesogen. We investigate a range of perylene diimide (PDI) materials, some of which are liquid crystalline, as the overlying electron acceptor layer. We find that carrier mobility of the acceptor materials is enhanced by liquid crystallinity and that mobility limits the performance of photovoltaic devices. 相似文献
79.
Jakub Kołacz Henry G. Gotjen Robel Y. Bekele Jason D. Myers Jesse A. Frantz Michael Ziemkiewicz 《Liquid crystals》2020,47(4):531-539
ABSTRACTIn a planar dielectric waveguide, weak confinement of a propagating mode in a high index core leads to a measurable evanescent interaction with the cladding. In this work, we study the effect of a reorientable anisotropic cladding on the behaviour of Transverse Electric (TE) and Transverse Magnetic (TM) mode polarisations using a liquid crystal (LC)-clad waveguide architecture. The polarised evanescent field of a guided mode interacts with a voltage-tunable birefringent LC cladding to deflect an out-coupled beam. Experimental measurements are coupled with a theoretical framework and show good consistency with simulation results. We isolate the effect of mode confinement by changing the thickness of the high index core. Interactions between the LC index ellipsoid and the mode polarisation are probed by changing the initial alignment of the LC. Finally, we examine the difference in deflection between TE and TM modes, which incorporates both a change in mode confinement and a difference in LC index components. 相似文献
80.
Lancaster M Goodall DM Bergström ET McCrossen S Myers P 《Journal of chromatography. A》2005,1090(1-2):165-171
This paper presents the first study of imaging of spots on thin-layer chromatographic plates whilst still wet with solvent. Imaging and quantification of Sudan II after development with dichloromethane was carried out in both reflectance and transmission modes, using a charge coupled device (CCD) camera. The relationship between peak area and sample loading was established at low sample loading, and found to be linear over an order of magnitude for both wet and dry modes with r2-values > 0.99. All data processing was carried out using the Beer-Lambert equation. Curvature at high loadings in the plots of integrated absorbance as a function of sample loading was accounted for using an empirical expression designed for use with the Kubelka-Munk treatment and apparent absorbance of the stationary phase due to scattering. Results are consistent with an effective pathlength significantly longer than the thickness of the sorbent layer. The limit of detection on a dry plate (0.5 ng) was found to be lower than on a wetted plate (2 ng). Precision was found to be 1-4% RSD intra-plate and 8-14% RSD inter-plate. Results are compared with quantification of the same analyte on dried plates. 相似文献