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141.
A Sarkar M Chakrabarti D Sanyal D Bhowmick S Dechoudhury A Chakrabarti T Rakshit SK Ray 《J Phys Condens Matter》2012,24(32):325503, 1-325503, 9
Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6?MeV H(+) ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378?eV (10?K). The irradiation creates an intense and narrow emission at 3.368?eV (10?K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368?eV emission indicate its origin as a 'hydrogen at oxygen vacancy' type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164?±?1?ps) and irradiated crystal (175?±?1?ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ~4?×?10(17)?cm(-3) (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ~175?ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed. 相似文献
142.
Functionalization of edge reconstructed graphene nanoribbons by H and Fe: A density functional study
Soumyajyoti Haldar Sumanta Bhandary Satadeep Bhattacharjee Olle Eriksson Dilip Kanhere Biplab Sanyal 《Solid State Communications》2012,152(18):1719-1724
In this paper, we have studied functionalization of 5–7 edge-reconstructed graphene nanoribbons by ab initio density functional calculations. Our studies show that hydrogenation at the reconstructed edges is favorable in contrast to the case of unreconstructed 6–6 zigzag edges, in agreement with previous theoretical results. Thermodynamical calculations reveal the relative stability of single and dihydrogenated edges under different temperatures and chemical potential of hydrogen gas. From phonon calculations, we find that the lowest optical phonon modes are hardened due to 5–7 edge reconstruction compared to the 6–6 unreconstructed hydrogenated edges. Finally, edge functionalization by Fe atoms reveals a dimerized Fe chain structure along the edges. The magnetic exchange coupling across the edges varies between ferromagnetic and antiferromagnetic ones with the variation of the width of the nanoribbons. 相似文献
143.
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145.
A. Mishra A. Kumar S. Sanyal V. Dexheimer S. Schramm 《The European Physical Journal A - Hadrons and Nuclei》2010,45(2):169-177
The modification of kaon and antikaon properties in the interior of (proto-)neutron stars is investigated using a chiral SU(3) model. The parameters of the model are fitted to nuclear-matter saturation properties, baryon octet vacuum masses, hyperon
optical potentials and low-energy kaon-nucleon scattering lengths. We study the kaon/antikaon medium modification and explore
the possibility of antikaon condensation in (proto-)neutron star matter at zero as well as finite temperature/entropy and
neutrino content. The effect of hyperons on kaon and antikaon optical potentials is also investigated at different stages
of the neutron star evolution. 相似文献
146.
147.
Sanyal A Norsten TB Uzun O Rotello VM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5958-5964
Diblock copolymers containing recognition units designed to participate in specific three-point hydrogen bonding were adsorbed onto modified gold surfaces. Self-assembled monolayers (SAMs) containing complementary recognition units were used to direct the adsorption process. The polymer-modified surfaces obtained were characterized using X-ray photoelectron spectroscopy, water contact angle, and ellipsometry. The role of individual block lengths on the adsorption process was followed by observing frequency changes of thymine-SAM-modified quartz crystal microbalance chips during adsorption of diamidopyridine-functionalized polymers from a nonpolar solvent. The renewable nature of these recognition unit functionalized surfaces was demonstrated by reversible binding of polymers. Adsorption onto fresh surfaces, followed by desorption and subsequent readsorption of monoblock and diblock copolymers was also investigated. 相似文献
148.
We have investigated the structural and electronic properties of monophospides of thorium, uranium and neptunium. The total energy as a function of volume is obtained by means of the self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). From the present study with the help of total energy calculations it is found that ThP, UP and NpP are stable in NaCl-type structure at ambient pressure. The structural stability of ThP, UP and NpP changes under the application of pressure. We predict a structural phase transition from NaCl-type (B1-phase) structure to CsCl-type (B2-phase) structure for these phospides in the pressure range of 37.0-24.0 GPa (ThP-NpP). We also calculate lattice parameter (a0), bulk modulus (B0), band structure and density of states. From energy band diagram it is observed that ThP, UP and NpP exhibit metallic behavior. The calculated equilibrium lattice parameters and bulk modulus are in good agreement with experimental and theoretical work. 相似文献
149.
150.
Tacchi S Gr?n?s O Stollo A Madami M Gubbiotti G Carlotti G Marangolo M Eddrief M Etgens VH Yadav MK Nordstr?m L Sanyal B 《J Phys Condens Matter》2012,24(23):236006
It is well known that Fe films deposited on a c(2 × 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 × 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 × 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 × 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 × 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings. 相似文献