全文获取类型
收费全文 | 11112篇 |
免费 | 512篇 |
国内免费 | 74篇 |
专业分类
化学 | 7612篇 |
晶体学 | 127篇 |
力学 | 341篇 |
数学 | 957篇 |
物理学 | 2661篇 |
出版年
2023年 | 62篇 |
2022年 | 53篇 |
2021年 | 271篇 |
2020年 | 223篇 |
2019年 | 222篇 |
2018年 | 215篇 |
2017年 | 180篇 |
2016年 | 357篇 |
2015年 | 340篇 |
2014年 | 441篇 |
2013年 | 736篇 |
2012年 | 903篇 |
2011年 | 1031篇 |
2010年 | 564篇 |
2009年 | 504篇 |
2008年 | 759篇 |
2007年 | 705篇 |
2006年 | 635篇 |
2005年 | 601篇 |
2004年 | 493篇 |
2003年 | 389篇 |
2002年 | 387篇 |
2001年 | 248篇 |
2000年 | 216篇 |
1999年 | 153篇 |
1998年 | 86篇 |
1997年 | 93篇 |
1996年 | 88篇 |
1995年 | 88篇 |
1994年 | 87篇 |
1993年 | 64篇 |
1992年 | 65篇 |
1991年 | 56篇 |
1990年 | 57篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1972年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J.-H. Lee B.-H. Jun S.-D. Park B.J. Park S.C. Han S.H. Lee C.-J. Kim 《Physica C: Superconductivity and its Applications》2011,471(21-22):863-866
To suppress the samarium diffusion from a SmBa2Cu3O7?y (Sm123) seed into an YBa2Cu3O7?y (Y123) compact during a top seeded melt growth (TSMG) process, Y211 buffer disks of various thicknesses (t) were inserted at the seed/compact interface. The effectiveness of the Y211 buffer insert on the suppression of samarium diffusion was estimated from the susceptibility curve and composition analysis for the three top surface regions (region just below the seed/buffer, intermediate region between the buffer and compact edge and compact edge). The difference in the superconducting temperature (Tc) and the superconducting transition width (ΔT) in the three regions was large, when no buffer or thin buffers (t is smaller than 1 mm) were used. As a buffer disk of an appropriate thickness was inserted into the seed/compact interface, the difference in Tc and ΔT in the three regions was much reduced. The composition analysis across the seed/buffer/compact region clearly revealed that the Tc decrease was caused by the samarium diffusion from a seed, which led to the formation of Y1?xSmxBa2Cu3O7?y in the Y123 compact region. The buffer insert technique was demonstrated to insure the uniform superconducting properties of the top surface of TSMG processed Y123 superconductors. 相似文献
992.
S.D. Park H.J. Kim B.J. Park Y.H. Han B.-H. Jun J.S. Lee C.-J. Kim 《Physica C: Superconductivity and its Applications》2011,471(21-22):880-883
The effect of calcium doping on the superconducting properties of top seeded melt growth (TSMG) processed Y1.5Ba2?xCaxCu3Oy superconductors was studied in terms of calcium content (Xca). YBa2?xCaxCu3O7?δ (Xca = 0, 0.005, 0.01, 0.02, 0.04, 0.1, 0.3) powders were synthesized by the powder calcination method. YBa2?xCaxCu3O7?δ powders were mixed with 0.25 mole Y2O3 powder and 1 wt.% CeO2 as Y2BaCuO5 (Y211) refiner, and finally made into Y1.5Ba2?xCaxCu3Oy (Y1.5) + 1 wt.% CeO2 composition. The single Y123 growth on the top surface was observed up to Xca = 0.1, while the multiple Y123 growth was observed at Xca ? 0.1. The superconducting transition temperature (Tc) and critical current density (Jc) of TSMG processed Y1.5 samples were inversely proportional to Xca. The Y211 size increased with increasing Xca due to the enhancement of Y211 coarsening by calcium doping. No Y211 refining effect by CeO2 was observed in the calcium doped samples. The Tc and Jc decrease by calcium doping are likely to be due to the calcium incorporation with the Y123 lattice and formation of coarse Y211 particles. 相似文献
993.
Yong-Hee Park Jungwon Kim Hyoungjoon Kim Ilsoo Kim Ki-Young Lee Dongjea Seo Heon-Jin Choi Woochul Kim 《Applied Physics A: Materials Science & Processing》2011,104(1):7-14
In this paper, we synthesize VLS-grown rough Si nanowires using Mn as a catalyst with various surface roughnesses and diameters
and measured their thermal conductivities. We grew the nanowires by a combination vapor-liquid-solid and vapor-solid mechanism
for longitudinal and radial growth, respectively. The surface roughness was controlled from smooth up to about 37 nm by the
radial growth. Our measurements showed that the thermal conductivity of rough surface Si nanowires is significantly lower
than that of smooth surface nanowires and decreased with increasing surface roughness even though the diameter of the smooth
nanowire was lower than that of the rough nanowires. Considering both nanowires were grown via the same growth mechanism,
these outcomes clearly demonstrate that the rough surface induces phonon scattering and reduces thermal conductivity with
this nanoscale-hole-free nanowires. Control of roughness induced phonon scattering in Si nanowires holds promise for novel
thermoelectric devices with high figures of merit. 相似文献
994.
Characterization of mitochondria isolated from normal and ischemic hearts in rats utilizing atomic force microscopy 总被引:1,自引:0,他引:1
Lee GJ Chae SJ Jeong JH Lee SR Ha SJ Pak YK Kim W Park HK 《Micron (Oxford, England : 1993)》2011,42(3):299-304
Mitochondria play critical roles in both the life and the death of cardiac myocytes. Various factors, such as the loss of ATP synthesis and increase of ATP hydrolysis, impairment in ionic homeostasis, formation of reactive oxygen species (ROS), and release of proapoptotic proteins are related to the generation of irreversible damage. It has been proposed that the release of cytochrome c is caused by a swelling of the mitochondrial matrix triggered by the apoptotic stimuli. However, there is a controversy about whether or not the mitochondria, indeed, swell during apoptosis. The major advantages of atomic force microscopy (AFM) over conventional optical and electron microscopes for bio-imaging include the fact that no special coating and vacuum are required and imaging can be done in all environments--air, vacuum or aqueous conditions. In addition, AFM force-distance curve measurements have become a fundamental tool in the fields of surface chemistry, biochemistry, and material science. In this study, we used AFM to observe the morphological and property changes in heart mitochondria that were isolated from a rat myocardial infarction model. From the shape parameters of the mitochondria in the AFM topographic image, it seemed that myocardial infarction caused the mitochondrial swelling. Also, the results of force-distance measurements showed that the adhesion force of heart mitochondria was significantly decreased by myocardial in infarction. Therefore, we suggested that myocardial infarction might be the cause of mitochondrial swelling and the changes in outer membrane of heart mitochondria. 相似文献
995.
A single-mode fiber (SMF) acousto-optic tunable filter (AOTF) with a tuning range of more than 300 nm is demonstrated. The SMF used in the experiment has a ring of symmetric holes within the cladding, which causes a larger mode-index difference between the first and the second higher-order antisymmetric modes than those of a conventional SMF. As a result, the difference in beatlengths between the core mode and the higher-order modes is highly increased, which makes it possible for the SMF AOTF to exhibit a single resonance peak in the transmission spectrum over the wavelength range of 1.3-1.6 μm for given acoustic frequencies of 3.1-3.8 MHz. 相似文献
996.
We propose and experimentally demonstrate a novel design for temporal integration of microwave and optical intensity waveforms with combined high processing speed and a long operation time window. It is based on concatenating in series a discrete-time (low-speed) photonic integrator and a high-speed analog time-limited intensity integrator. This scheme is demonstrated here using a cascaded fiber-based interferometers' system (as a passive eight-point discrete-time integrator) and an analog time-limited intensity integrator. The latter is based on temporal intensity modulation of the input waveform with a rectangular-like incoherent energy spectrum followed by linear dispersion. Using this setup, we experimentally achieve accurate time integration of intensity signals with ~36 GHz bandwidths over an operation time window of ~4 ns, corresponding to a processing time-bandwidth product of >144. 相似文献
997.
We report on efficient single-pass, high-power second-harmonic generation in a periodically poled MgO-doped LiNbO3 planar waveguide using a distributed Bragg reflector tapered diode laser as a pump source. A coupling efficiency into the planar waveguide of 73% was realized, and 1.07 W of visible laser light at 532 nm was generated. Corresponding optical and electro-optical conversion efficiencies of 26% and 8.4%, respectively, were achieved. Good agreement between the experimental data and the theoretical predictions was observed. 相似文献
998.
γ-Fe2O3 has a spinel structure with cation vacancy and is expected to perform as a favorable electrode material for secondary lithium-ion battery. When lithium is inserted electrochemically into γ-Fe2O3, prolonged potential change is observed after the insertion. In this study, we inserted various amount of Li into γ-Fe2O3 (x = 0.66, 1.1, 1.5 in terms of LiXFe2O3), then made the circuit open, measured X-ray diffraction (XRD) patterns at various elapsed time, and analyzed the crystal structure change of γ-Fe2O3 with time by the Rietveld method. The X-ray Rietveld analysis revealed that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and after lithium insertion, the iron occupancy of 8a site increased and that of 16c site decreased gradually with relaxation time. It is indicated that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically. 相似文献
999.
Beom-Ki ShinTae-Il Lee Ji-Hyeon ParkKang-Il Park Kyung-Jun AhnSung-Kee Park Woong LeeJae-Min Myoung 《Applied Surface Science》2011,258(2):834-838
Applicability of Ga-doped ZnO (GZO) films for thin film solar cells (TFSCs) was investigated by preparing GZO films via pulsed dc magnetron sputtering (PDMS) with rotating target. The GZO films showed improved crystallinity and increasing degree of Ga doping with increasing thickness to a limit of 1000 nm. The films also fulfilled requirements for the transparent electrodes of TFSCs in terms of electrical and optical properties. Moreover, the films exhibited good texturing potential based on etching studies with diluted HCl, which yielded an improved light trapping capability without significant degradation in electrical propreties. It is therefore suggested that the surface-textured GZO films prepared via PDMS and etching are promising candidates for indium-free transparent electrodes for TFSCs. 相似文献
1000.