全文获取类型
收费全文 | 968篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
化学 | 691篇 |
晶体学 | 9篇 |
力学 | 13篇 |
数学 | 63篇 |
物理学 | 225篇 |
出版年
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 23篇 |
2019年 | 20篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 29篇 |
2013年 | 44篇 |
2012年 | 43篇 |
2011年 | 56篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 38篇 |
2007年 | 53篇 |
2006年 | 56篇 |
2005年 | 30篇 |
2004年 | 33篇 |
2003年 | 34篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1968年 | 5篇 |
1958年 | 23篇 |
排序方式: 共有1001条查询结果,搜索用时 0 毫秒
61.
We report on the photoelectrochemical and terahertz measurements, of the charge transport properties of 1 μm thick self‐organized TiO2 nanotube layers, prepared by the anodization of titanium. We provide evidence regarding the complexity of electron transport, and dynamics in the nanotubes. Shortly after photoexcitation, charge mobilites in amorphous and crystalline nanotubes are similar, but still lower compared to the bulk anatase. The mobility subsequently decreases due to trapping‐detrapping processes. The recombination rate in anatase nanotubes is much slower than in the amorphous ones, enabling the material to reach an internal photon to electron conversion efficiency exceeding 60%. 相似文献
62.
63.
Third-order nonlinear optical susceptibility, χ(3) of symmetrically octa-substituted metal-free phthalocyanine thin films measured by the third-harmonic generation technique are reported. The metal-free phthalocyanine has been found to show a χ(3) (−3ω; ω,ω, ω) value as large as 7.73×10−12 esu at 1.80 μm. The figure of merit, χ(3)/α, was estimated to be 4.17×1017 esu cm at 1.05 μm and 6.97×1016 esu cm at 1.65 μm. Both linear and third-order optical properties of liquid-crystalline metal-free phthalocyanines are discussed 相似文献
64.
MR imaging findings in recurrent primary osseous Ewing sarcoma 总被引:1,自引:0,他引:1
William M. Kauffman Barry D. Fletcher Soheil L. Hanna William H. Meyer 《Magnetic resonance imaging》1994,12(8):1147-1153
The objective of this study was to determine the value of magnetic resonance (MR) imaging in diagnosing local recurrence of Ewing sarcoma. We retrospectively reviewed radiographs, Tc99m-methylene diphosphonate (MDP) skeletal scintigraphy, computed tomography scans, and MR studies of 11 patients who had local recurrences of osseous Ewing sarcoma following initial responses to chemotherapy and local radiation. The MR images were compared to those of a control group of nine patients who had no evidence of relapse. T1- and T2-weighted MR images identified 9 of the 11 recurrences. Computed tomography was diagnostic in 4 of 6 cases evaluated, Tc99m-MDP bone scintigraphy in 4 of 11 cases, and plain radiographs in 2 of 10. MR findings at relapse included changes in signal intensity, increased extent of abnormal marrow signal on T1- and T2-weighted images, and identification of a new soft tissue mass. These findings suggest that MR imaging is valuable in the routine follow-up of parimary osseous Ewing sarcoma. 相似文献
65.
Xiaoheng Yan John Mason Gila Hanna 《International Journal of Mathematical Education in Science & Technology》2019,50(2):244-259
This study investigates an exploratory teaching style used in an undergraduate geometry course to help students identify an ellipse. We attempt to probe beneath the surface of exploration to understand how the actions of teachers can contribute to developing students’ competence in justifying an ellipse. We analyse the complex interactions between student, content, and teacher, and discuss explicit pedagogical strategies that help students develop a higher level of geometric reasoning. The findings indicate that students engaged in guided explorations by the teacher and in group discussions with peers were able to identify an ellipse and justify their reasoning. 相似文献
66.
Optical parametric oscillation in periodically poled lithium niobate driven by a diode-pumped Q-switched erbium fiber laser 总被引:2,自引:0,他引:2
Britton PE Taverner D Puech K Richardson DJ Smith PG Ross GW Hanna DC 《Optics letters》1998,23(8):582-584
We describe what is to our knowledge the first nanosecond periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) driven by a fiber laser. The source was frequency doubled by a PPLN sample before pumping a second, 20-mm-long, PPLN crystal. The OPO threshold was <10muJ, with pump depletions of as much as 45% and a tunable signal range of 945-1450 nm (1690-4450-nm idler range). We demonstrated 130-nm signal tuning by varying the pump wavelength and doubling crystal's temperature. Also, we achieved 15-nm tuning with all crystals at a constant temperature. The results demonstrate the potential of the fiber laser:PPLN combination for practical, versatile, and tunable sources. 相似文献
67.
Krauter H Muschik CA Jensen K Wasilewski W Petersen JM Cirac JI Polzik ES 《Physical review letters》2011,107(8):080503
Entanglement is a striking feature of quantum mechanics and an essential ingredient in most applications in quantum information. Typically, coupling of a system to an environment inhibits entanglement, particularly in macroscopic systems. Here we report on an experiment where dissipation continuously generates entanglement between two macroscopic objects. This is achieved by engineering the dissipation using laser and magnetic fields, and leads to robust event-ready entanglement maintained for 0.04 s at room temperature. Our system consists of two ensembles containing about 10(12) atoms and separated by 0.5 m coupled to the environment composed of the vacuum modes of the electromagnetic field. By combining the dissipative mechanism with a continuous measurement, steady state entanglement is continuously generated and observed for up to 1 h. 相似文献
68.
Stretcher-free high energy nonlinear amplification of femtosecond pulses in rod-type fibers 总被引:3,自引:0,他引:3
Zaouter Y Papadopoulos DN Hanna M Boullet J Huang L Aguergaray C Druon F Mottay E Georges P Cormier E 《Optics letters》2008,33(2):107-109
We report on the study of direct amplification of femtosecond pulses in an 80 mum core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a 1250 line/mm (l/mm) grating-based compressor, pulses as short as 49 fs with 870 nJ pulse energy and 12 MW peak power are obtained. Alternatively, the use of a 1740 l/mm grating allows the production of higher quality pulses of 70 fs, 1.25 microJ pulse energy, and 16 MW peak power. 相似文献
69.
70.
Hanna K Beurroies I Denoyel R Desplantier-Giscard D Galarneau A Di Renzo F 《Journal of colloid and interface science》2002,252(2):276-283
During the synthesis of micelle-templated silica an intermediate inorganic/organic mesostructure is obtained with an hexagonal arrangement of channels filled by surfactant molecules. The ability of such a mesostructure to solubilize organic molecules from an aqueous solution was investigated. To that end, silica/cationic surfactant mesostructures were prepared under various conditions and their stability toward surfactant release in water was first compared in order to select materials as stable as possible. Swelled mesostructures were also used. The sorption from solution of hydrophobic molecules was then studied. The affinity of the molecules for the mesostructures is directly related to their hydrophobic character as it is derived from their octanol/water partition coefficient. A cooperative effect between hydrophobic molecules and the cationic surfactant that stabilizes the surfactant inside the mesostructure was observed. Interaction energies between the solutes and the mesostructures were determined by microcalorimetry. They varied in accordance with the hydrophobic character of the molecule and, at low sorption amounts, they were of the same order of magnitude as the solubilization enthalpies in bulk micelles. When the sorption increases, the surfactant layer in the mesostructure is not allowed to swell as the free micelle does, and steric limitations in the headgroup area render sorption less favorable. 相似文献