全文获取类型
收费全文 | 2065篇 |
免费 | 39篇 |
国内免费 | 14篇 |
专业分类
化学 | 1152篇 |
晶体学 | 8篇 |
力学 | 81篇 |
数学 | 215篇 |
物理学 | 662篇 |
出版年
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 23篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2014年 | 25篇 |
2013年 | 83篇 |
2012年 | 70篇 |
2011年 | 92篇 |
2010年 | 49篇 |
2009年 | 28篇 |
2008年 | 74篇 |
2007年 | 81篇 |
2006年 | 94篇 |
2005年 | 82篇 |
2004年 | 73篇 |
2003年 | 74篇 |
2002年 | 58篇 |
2001年 | 62篇 |
2000年 | 61篇 |
1999年 | 38篇 |
1998年 | 33篇 |
1997年 | 36篇 |
1996年 | 37篇 |
1995年 | 41篇 |
1994年 | 46篇 |
1993年 | 59篇 |
1992年 | 35篇 |
1991年 | 35篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 35篇 |
1984年 | 23篇 |
1983年 | 32篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 19篇 |
1978年 | 24篇 |
1977年 | 35篇 |
1975年 | 30篇 |
1974年 | 23篇 |
1973年 | 18篇 |
1972年 | 24篇 |
1966年 | 12篇 |
排序方式: 共有2118条查询结果,搜索用时 15 毫秒
861.
862.
863.
864.
Edward B. Harris Douglas P. Johnson James C. Garland 《Czechoslovak Journal of Physics》1996,46(2):593-594
We report numerical simulations on the effect of disorder in parallel-biased series of arrays of overdamped Josephson junctions. Our arrays feature additional parallel-conected ‘shunt’ junctions which provide strong local coupling between pairs of junctions along the series-connected ‘backbone’. We find that series arrays of 20 junctions have phase-locked and phase-coherent dynamical modes which are tolerant of more than 50% spread in critical currents,I C , and plaquette area, S. The arrays, however, show moderate tolerance to (10% spread) disorder in bias currents,I B . This tolerance to disorder in array parameters implies that practical RF sources might be possible using these arrays. 相似文献
865.
Y Yoon R. -M. Ho F. Li B. Moon D. Kim J. -Y. Park F. W. Harris S. Z. D. Cheng V. Percec P. Chu 《Journal of Thermal Analysis and Calorimetry》1996,47(4):957-973
A series of polyethers have been synthesized from 1-(4-hydroxy-4-biphenyl)-2-(4-hydroxyphenyl)propane and , -dibromoalkanes having different numbers of methylene units [TPPs]. Both odd- and even-numbered TPPs [TPP(n=odd)s and TPP(n=even)s) exhibit multiple transitions during cooling and heating and they show little supercooling dependence, indicating close-to-equilibrium nature of these transitions. Combining the structural characterization obtainedvia wide angle X-ray diffraction powder and fiber patterns at different temperatures and the morphological observations from microscopy techniques, not only the nematic liquid crystalline phase but also highly ordered smecticF, smectic crystalG andH phases have been identified. The phase diagrams for both TPP(n=odd)s and TPP(n=even)s have been constructed [1–3]. Thermodynamic properties (enthalpy and entropy changes) during these transitions are studied based on differential scanning calorimetry experiments. The contributions of the mesogenic groups and methylene units to each ordering process can be separated and they indicate the characteristics of these processes thereby providing estimations of the transition types.This work was supported by the SZDC's Presidential Young Investigator Award from the National Science Foundation (DMR-9175538). The generous donation of a DSC-7 from Perkin Elmer Inc. is also greatly appreciated. 相似文献
866.
867.
868.
Coe BJ Jones LA Harris JA Brunschwig BS Asselberghs I Clays K Persoons A 《Journal of the American Chemical Society》2003,125(4):862-863
We have used several techniques, including hyper-Rayleigh scattering and Stark spectroscopy, to investigate the effects of polyene chain length on the optical properties of complexes containing ruthenium(II) electron donor groups and pyridinium electron acceptors. In marked contrast with all other known donor-acceptor polyenes, conjugation extension beyond a single double bond in the dipolar complexes studied leads to blue-shifting of the intramolecular charge-transfer absorptions. Furthermore, the static first hyperpolarizabilities beta0 become maximized with trans-1,3-butadienyl linkages and then decrease in complexes with three CH=CH bonds. Our results clearly demonstrate that the molecular engineering criteria for metal-containing nonlinear optical chromophores can differ dramatically from those for purely organic compounds. 相似文献
869.
Coe BJ Jones LA Harris JA Brunschwig BS Asselberghs I Clays K Persoons A Garín J Orduna J 《Journal of the American Chemical Society》2004,126(12):3880-3891
In this paper, we describe the extremely unusual optical properties of Ru(II)-based electron donor-acceptor (D-A) polyene and some closely related chromophores. For three different polyene series, the intense, visible d-->pi* metal-to-ligand charge-transfer bands unexpectedly blue-shift as the number of E-ethylene units (n) increases from 1 to 3, and the static first hyperpolarizabilities beta(0) determined via hyper-Rayleigh scattering and Stark spectroscopy maximize at n = 2, in marked contrast to other known D-A polyenes in which beta(0) increases steadily with n. Time-dependent density-functional theory and finite field calculations verify these empirical trends, which arise from the orbital structures of the complexes. This study illustrates that transition metal-based nonlinear optical chromophores can show very different behavior when compared with their more thoroughly studied purely organic counterparts. 相似文献
870.
Several polymethyl-1,10-phenanthrolines were synthesized by the use of 3-methyl-3-penten-2-one in Skraup reactions. The behavior of this ketone as well as that of 4-hydroxy-2-pentanone and 4-hydroxy-3-methyl-2-bulanone with various substituted anilines was studied. 相似文献