全文获取类型
收费全文 | 547篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 293篇 |
晶体学 | 7篇 |
力学 | 15篇 |
数学 | 78篇 |
物理学 | 166篇 |
出版年
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 31篇 |
2012年 | 30篇 |
2011年 | 29篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 20篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 23篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1984年 | 6篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 9篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1963年 | 3篇 |
排序方式: 共有559条查询结果,搜索用时 0 毫秒
1.
2.
Denis W. Clack Leon A. P. Kane-Maguire David H. Knight Peter A. Williams 《Transition Metal Chemistry》1980,5(1):376-378
Summary Molecular orbital calculations using-, the INDO method have been carried out fm the [FeL(CN)4]2 and [FeLH(CN)4] complexes, as well as for the tree ligands, with L 2 × pyridine, 1,10-phenanthroline.2,2-bipyridyl. 2,2-rimidine, 2, 3,3-bipyridazine and 4.4-bipyrimidine. Calculations of residual charge at carbon atoms in the ligand rings. correlating with relative nucleophilicity of the compounds, corresponds with observed differences of rate of reaction of the complex [FeI;]2 With nucleophiles. 相似文献
3.
Nizkorodov SA Ziemkiewicz M Nesbitt DJ Knight AE 《The Journal of chemical physics》2005,122(19):194316
Spectroscopy and predissociation dynamics of (H2O)2 and Ar-H2O are investigated with vibrationally mediated dissociation (VMD) techniques, wherein upsilon(OH) = 2 overtones of the complexes are selectively prepared with direct infrared pumping, followed by 193 nm photolysis of the excited H2O molecules. As a function of relative laser timing, the photolysis breaks H2O into OH and H fragments either (i) directly inside the complex or (ii) after the complex undergoes vibrational predissociation, with the nascent quantum state distribution of the OH photofragment probed via laser-induced fluorescence. This capability provides the first rotationally resolved spectroscopic analysis of (H2O)2 in the first overtone region and vibrational predissociation dynamics of water dimer and Ar-water clusters. The sensitivity of the VMD approach permits several upsilon(OH) = 2 overtone bands to be observed, the spectroscopic assignment of which is discussed in the context of recent anharmonic theoretical calculations. 相似文献
4.
Knight JS Petrie SA Freeman CG McEwan MJ McLean AD DeFrees DJ 《Journal of the American Chemical Society》1988,110(16):5286-5290
Reactivities of the structural isomers CCN+ and CNC+ were examined in a selected-ion flow tube at 300 +/- 5 K. The less reactive CNC+ isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC+ can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN+ and CNC+; a saddle point for the reaction CCN+ --> CNC+ is calculated to be 195 kJ mol-1 above the CNC+. The results provide evidence that the more reactive CCN+ isomer is unlikely to be present in measurable densities in interstellar clouds. 相似文献
5.
Beam depletion spectroscopy has been used to measure absolute total inelastic electron-sodium cluster collision cross sections in the energy range fromE0.1 toE6 eV. The investigation focused on the closed shell clusters Na8, Na20, and Na40. The measured cross sections show an increase for the lowest collision energies where electron attachment is the primary scattering channel. The electron attachment cross section can be understood in terms of Langevin scattering, connecting this measurement with the polarizability of the cluster. For energies above the dissociation energy the measured electron-cluster cross section is energy independent, thus defining an electron-cluster interaction range. This interaction range increases with the cluster size. 相似文献
6.
Silvin P. Knight Louise Newman John D. OConnor James Davis Rose Anne Kenny Roman Romero-Ortuno 《Entropy (Basel, Switzerland)》2021,23(1)
In this cross-sectional study, the relationship between noninvasively measured neurocardiovascular signal entropy and physical frailty was explored in a sample of community-dwelling older adults from The Irish Longitudinal Study on Ageing (TILDA). The hypothesis under investigation was that dysfunction in the neurovascular and cardiovascular systems, as quantified by short-length signal complexity during a lying-to-stand test (active stand), could provide a marker for frailty. Frailty status (i.e., “non-frail”, “pre-frail”, and “frail”) was based on Fried’s criteria (i.e., exhaustion, unexplained weight loss, weakness, slowness, and low physical activity). Approximate entropy (ApEn) and sample entropy (SampEn) were calculated during resting (lying down), active standing, and recovery phases. There was continuously measured blood pressure/heart rate data from 2645 individuals (53.0% female) and frontal lobe tissue oxygenation data from 2225 participants (52.3% female); both samples had a mean (SD) age of 64.3 (7.7) years. Results revealed statistically significant associations between neurocardiovascular signal entropy and frailty status. Entropy differences between non-frail and pre-frail/frail were greater during resting state compared with standing and recovery phases. Compared with ApEn, SampEn seemed to have better discriminating power between non-frail and pre-frail/frail individuals. The quantification of entropy in short length neurocardiovascular signals could provide a clinically useful marker of the multiple physiological dysregulations that underlie physical frailty. 相似文献
7.
Abstract The infrared spectra (700–100 cm?1) of the complexes [M(ox)2(H2O)2] (ox = 8-hydroxyquinolinate anion, M = Mn, Fe, Co, Ni, Cu, Zn) are discussed. For the purposes of assignment of the metal ligand modes, deuterated 8-hydroxyquinoline-d 7 was prepared by the Skraup synthesis and the spectra of the deuterated complexes were compared with those of the unlabelled species. Furthermore, [64Zn(ox)2(H2O)2] and [68Zn(ox)2(H2O)2] were prepared by reaction of 64ZnSO4 and 68ZnSO4 with 8-hydroxyquinoline and the effects of metal isotope labelling on the spectra were examined and compared with earlier isotopic data on the nickel and zinc complexes. 相似文献
8.
9.
Using cross-correlation frequency-resolved optical gating, we observe the phase-sensitive resonance in the interaction of a soliton with a continuous wave in a photonic crystal fiber. This interaction strongly depends on the difference in the phase velocities of the orthogonally polarized fiber modes and leads to generation of a new spectral peak. The spectral and temporal structure of this signal is revealed in our measurements, which are supported by analytical theory and numerical simulations. 相似文献
10.
Selective mode excitation in hollow-core photonic crystal fiber 总被引:2,自引:0,他引:2
Galea AD Couny F Coupland S Roberts PJ Sabert H Knight JC Birks TA Russell PS 《Optics letters》2005,30(7):717-719
Modes are selectively excited by launching light through the cladding from the side into a hollow-core photonic crystal fiber. Measuring the total output power at the end of the fiber as a function of the angle of incidence of the exciting laser beam provides a powerful diagnostic for characterizing the cladding bandgap. Furthermore, various types of modes on either side of the bandgap are excited individually, and their nearfield images are obtained. 相似文献