全文获取类型
收费全文 | 469篇 |
免费 | 25篇 |
国内免费 | 6篇 |
专业分类
化学 | 321篇 |
晶体学 | 5篇 |
力学 | 16篇 |
综合类 | 2篇 |
数学 | 56篇 |
物理学 | 100篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 18篇 |
2011年 | 17篇 |
2010年 | 14篇 |
2009年 | 27篇 |
2008年 | 26篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 26篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1989年 | 6篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 6篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1940年 | 2篇 |
1927年 | 2篇 |
1913年 | 2篇 |
排序方式: 共有500条查询结果,搜索用时 156 毫秒
61.
The technique of Doppler free two photon absorption is used to measure the fine structure interval in the 2D states of potassium for principal quantum numbers from 8 to 19. 相似文献
62.
Jeffrey A. Jackson Howard S. Derman Richard L. Harper M.Robert Willcott Joseph J. Ford Nicholas J. Schneiders John A. McCrary Anne Kelly R.Nick Bryan 《Magnetic resonance imaging》1984,2(3):227-233
A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T2 (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients. 相似文献
63.
The application of digital phase shift holographic interferometry to flow-visualization and flow temperature measurement of a 2D thermal flow field was experimentally investigated. An improved recording system for two reference beam phase shift holographic interferometry is set up for this experiment, and details of this experimental technique are described. The phase distribution obtained by this technique presents an excellent picture of flow visualization. From this phase image, temperature distribution of the 2D thermal flow field is also calculated and compared with some measured values obtained using thermocouple probes. 相似文献
64.
An opto-thermal molecular beam study has been carried out to investigate the multiple-photon laser excitation of SF6 and CF3Br. The molecular beam was produced by means of a supersonic expansion through a nozzle at variable temperature. The opto-thermal signal was measured by means of a high-sensitivity superconducting bolometer. The multiple-photon excitation of SF6 has been measured as a function of the initial ro-vibrational population of the molecule. The experimental results have been compared with both previously published data of molecular beam and gas cell experiments and theoretical calculations. A satisfactory agreement has been found between some of our experimental results and the theoretical spectra obtained by means of the heat-bath feed-back model. 相似文献
65.
Ground state rotation and quartic distortion constants were obtained for 11B2D6 from the analysis of high resolution (~0.05 cm?1) Fourier transform infrared spectra. The bands studied comprised the ν17, ν18 type A, and ν14, ν9 + ν15 type C bands of 11B2H6 and the ν16, ν17, ν18 type A, ν8 type B, and ν14 type C bands of 11B2D6. In the case of 11B2H6, the authors' ground state data were combined with those of Lafferty et al. obtained from a previous study (J. Mol. Spectrosc.33, 345–367 (1970)) at comparable resolution of the ν16 type A and ν8 type B fundamentals. Information on the ground state rotational energy manifold of 11B2H6 was accumulated up to J = 23, Ka = 18, and of 11B2D6 up to J = 32, Ka = 22. This permitted rather precise determination of the distortion constants ΔJ0, ΔJK0, ΔK0, although δJ0 and δK0 proved to be too small (< 10?7 cm?1) and were constrained to values calculated from the force field. Sets of upper state parameters were determined for all vibrational levels studied. Although these appear to be essentially unperturbed globally, several localized perturbations were observed and identified. 相似文献
66.
Further experiments in doped InSb are reported on the anomalous NMR relaxation peak, the B-peak, first reported by Bridges and Clark. Data on the peak now extends up to donor concentrations of 8 × 1021 m?3 and permits a sharp reduction in the number of possible explanations of the peak which remain plausible.The peak occurs well above the critical field required for magnetic freeze-out, and appears to follow a dependence of magnetic field at the peak, BB, against density, nD, of BB ∝ n0.60±0.01D at constant temperature. The possibility that the peak is due to the tuning of the ESR frequency through the typical electron hopping frequency ωH in the crystal is explored; a consequence of this model is that ωH must be dominated by nearest-neighbour hops, involving only a very small minority of the donor centres. 相似文献
67.
68.
A rate process model is developed to interpret the experimental results of Smith, Schmid, Tablas and Kompa on the time and intensity dependence of the infrared absorption of SF6. In this model incoherent excitation of the λ3 molecular mode by the processes of absorption and stimulated emission is followed by radiationless energy transfer from a maximum level to an inactive mode heatbath. This achieves control of the level population by an empirical transfer rate parameter. Good theoretical fits of the experiment absorption decays are obtained with values of approximately 0.1 ns. 相似文献
69.
70.
Menard LD Gao SP Xu H Twesten RD Harper AS Song Y Wang G Douglas AD Yang JC Frenkel AI Nuzzo RG Murray RW 《The journal of physical chemistry. B》2006,110(26):12874-12883
The synthesis and characterization of the clusters Au13[PPh3]4[S(CH2)11CH3]2Cl2 (1) and Au13[PPh3]4[S(CH2)11CH3]4 (2) are described. These mixed-ligand, sub-nanometer clusters, prepared via exchange of dodecanethiol onto phosphine-halide gold clusters, show enhanced stability relative to the parent. The characterization of these clusters features the precise determination of the number of gold atoms in the cluster cores using high-angle annular dark-field scanning transmission electron microscopy, allowing the assignment of 13 gold atoms (+/-3 atoms) to the composition of both cluster molecules. Electrochemical and optical measurements reveal discrete molecular orbital levels and apparent energy gaps of 1.6-1.7 eV for the two cluster molecules. The electrochemical measurements further indicate that the Au13[PPh3]4[S(CH2)11CH3]2Cl2 cluster undergoes an overall two-electron reduction. The electrochemical and spectroscopic properties of the two Au13 cluster molecules are compared with those of a secondary synthetic product, which proved to be larger Au thiolate-derivatized monolayer-protected clusters with an average core of Au180. The latter shows behavior fully consistent with the adoption of metallic-like properties. 相似文献