全文获取类型
收费全文 | 748篇 |
免费 | 10篇 |
专业分类
化学 | 405篇 |
晶体学 | 9篇 |
力学 | 10篇 |
数学 | 65篇 |
物理学 | 269篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 58篇 |
2012年 | 17篇 |
2011年 | 38篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 35篇 |
2007年 | 27篇 |
2006年 | 46篇 |
2005年 | 27篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 16篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1974年 | 13篇 |
1973年 | 13篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1969年 | 7篇 |
排序方式: 共有758条查询结果,搜索用时 62 毫秒
61.
62.
QSAR modeling of flotation collectors using principal components extracted from topological indices 总被引:1,自引:0,他引:1
Natarajan R Nirdosh I Basak SC Mills DR 《Journal of chemical information and computer sciences》2002,42(6):1425-1430
Several topological indices were calculated for substituted-cupferrons that were tested as collectors for the froth flotation of uranium. The principal component analysis (PCA) was used for data reduction. Seven principal components (PC) were found to account for 98.6% of the variance among the computed indices. The principal components thus extracted were used in stepwise regression analyses to construct regression models for the prediction of separation efficiencies (Es) of the collectors. A two-parameter model with a correlation coefficient of 0.889 and a three-parameter model with a correlation coefficient of 0.913 were formed. PCs were found to be better than partition coefficient to form regression equations, and inclusion of an electronic parameter such as Hammett sigma or quantum mechanically derived electronic charges on the chelating atoms did not improve the correlation coefficient significantly. The method was extended to model the separation efficiencies of mercaptobenzothiazoles (MBT) and aminothiophenols (ATP) used in the flotation of lead and zinc ores, respectively. Five principal components were found to explain 99% of the data variability in each series. A three-parameter equation with correlation coefficient of 0.985 and a two-parameter equation with correlation coefficient of 0.926 were obtained for MBT and ATP, respectively. The amenability of separation efficiencies of chelating collectors to QSAR modeling using PCs based on topological indices might lead to the selection of collectors for synthesis and testing from a virtual database. 相似文献
63.
64.
Schmidt KS Filippov DV Meeuwenoord NJ van Der Marel GA van Boom JH Lippert B Reedijk J 《Angewandte Chemie (International ed. in English)》2000,39(2):375-377
Cross-linking ability is possible with the oligonucleotide-tethered, monofunctional trans-Pt(II) complex shown. It was synthesized by a novel solid-phase approach comprising conjugation of immobilized tetrathymidylic acid with a trans-a(2)Pt(II) building unit, ammonolysis, and transformation of the resulting complex (R=1-N-cyclohexylmethylthyminate) into the chloro derivative (R=Cl). a=NH(2)CH(3), T=thymine. 相似文献
65.
Psychometric functions for gap detection in noise measured from young and aged subjects. 总被引:3,自引:0,他引:3
N J He A R Horwitz J R Dubno J H Mills 《The Journal of the Acoustical Society of America》1999,106(2):966-978
Psychometric functions for gap detection of temporal gaps in wideband noise were measured in a "yes/no" paradigm from normal-hearing young and aged subjects with closely matched audiograms. The effects of noise-burst duration, gap location, and uncertainty of gap location were tested. A typical psychometric function obtained in this study featured a steep slope, which was independent of most experimental conditions as well as age. However, gap thresholds were generally improved with increasing duration of the noise burst for both young and aged subjects. Gap location and uncertainty had no significant effects on the thresholds for the young subjects. For the aged subjects, whenever the gap was sufficiently away from the onset or offset of the noise burst, detectability was robust despite uncertainty about the gap location. Significant differences between young and aged subjects could be observed only when the gap was very close to the signal onset and offset. 相似文献
66.
67.
Talat S. Rahman D.L. Mills J.E. Black 《Journal of Electron Spectroscopy and Related Phenomena》1983,29(1):199-212
Electron energy loss spectroscopy has proved a powerful probe of vibrational modes of a wide variety of adsorbed species. Here the primary focus has been on modes with frequency well above the maximum phonon frequency of the substrate. Examples are internal vibration modes of adsorbed molecules, possibly shifted significantly in frequency from their gas phase analogues, and high frequency vibrations of an adsorbed molecule or atom against the substrate. Recent experiments explore features in the energy loss spectrum with frequency below the maximum phonon frequency of the substrate, for ordered overlayers of atoms adsorbed on low index metal surfaces. We shall summarize our theoretical studies of such spectra for several adsorbate/substrate combinations, with emphasis oh the physical origin of the features which appear in the calculations. We obtain a good account of the existing data, within the framework of a rather simple lattice dynamical model, and the calculations show that the features which appear are quite sensitive to the symmetry of the adsorption sits, and other details of the surface geometry. We shall illustrate this with several specific examples. 相似文献
68.
A recently developed soft-mode theory of surface reconstruction1 is used to calculate the surface Debye-Waller factor (SDWF) as a function of temperature near a supposed transition temperature (T0) between two reconstruction patterns. The soft surface mode gives rise to a sharp decrease in the SDWF as T0 is approached, suggesting that an examination the LEED Bragg intensities may help verify the soft mode theory. 相似文献
69.
Newly observed data on the rotational constants of carbon su?ide in excited vibrational states of the low-wavenumber bending vibration ν7 have been successfully interpreted in terms of the two-dimensional anharmonic oscillator wavefunctions associated with this vibration. By combining these results with published infrared and Raman spectra the vibrational assignment has been extended and a refined bending potential for ν7 has been derived: this has a minimum at a bending angle of about 24° at the central C atom, with an energy maximum at the linear configuration some 23 cm?1 above the minimum. From similar data on the combination and hot bands of ν7 with ν4 (1587 cm?1) and ν2 (786 cm?1) the effective ν7 bending potential has also been determined in the one-quantum excited states of ν4 and ν2. The effective ν7 potential shows significant changes from the ground vibrational state; the central hump in the ν7 potential surface is increased to about 50 cm?1 in the v4 = 1 state, and decreased to about 1 cm?1 in the v2 = 1 state. In the light of these results vibrational assignments are suggested for most of the observed bands in the infrared and Raman spectra of C3O2. 相似文献
70.