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排序方式: 共有711条查询结果,搜索用时 640 毫秒
91.
Eunkeu Oh Fredrik K. Fatemi Marc Currie James B. Delehanty Thomas Pons Alexandra Fragola Sandrine Lévêque‐Fort Ramasis Goswami Kimihiro Susumu Alan L. Huston Igor L. Medintz 《Particle & Particle Systems Characterization》2013,30(5):453-466
Biocompatible, near‐infrared luminescent gold nanoclusters (AuNCs) are synthesized directly in water using poly(ethylene glycol)‐dithiolane ligands terminating in either a carboxyl, amine, azide, or methoxy group. The ≈1.5 nm diameter AuNCs fluoresce at ≈820 nm with quantum yields that range from 4–8%, depending on the terminal functional group present, and display average luminescence lifetimes approaching 1.5 μs. The two‐photon absorption (TPA) cross‐section and two‐photon excited fluorescence (TPEF) properties are also measured. Long‐term testing shows the poly(ethylene glycol) stabilized AuNCs maintain colloidal stability in a variety of media ranging from saline to tissue culture growth medium along with tolerating storage of up to 2 years. DNA and dye‐conjugation reactions confirm that the carboxyl, amine, and azide groups can be utilized on the AuNCs for carbodiimide, succinimidyl ester, and CuI‐assisted cycloaddition chemistry, respectively. High signal‐to‐noise one‐ and two‐photon cellular imaging is demonstrated. The AuNCs exhibit outstanding photophysical stability during continuous‐extended imaging. Concomitant cellular viability testing shows that the AuNCs also elicit minimal cytotoxicity. Further biological applications for these luminescent nanoclustered materials are discussed. 相似文献
92.
Tanya M RamondGustavo E Davico Fredrik HellbergFredrik Svedberg Peter SalénPatrick Söderqvist W.Carl Lineberger 《Journal of Molecular Spectroscopy》2002,216(1):1-14
The 364-nm negative ion photoelectron spectra of XO and OXO molecules (X=Ni, Pd, and Pt) are reported. The spectra yield the electron affinities (EAs): EA(NiO)=1.455±0.005 eV; EA(PdO)=1.672±0.005 eV; EA(PtO)=2.172±0.005 eV; EA(ONiO)=3.043±0.005 eV; EA(OPdO)=3.086±0.005 eV; EA(OPtO)=2.677±0.005 eV. In addition, for the diatomics, transitions from the anion X?2Π3/2 and X?′2Π1/2 states into neutral X?3Σ−, 3Π, and for NiO and PdO, 1Π, are assigned. Several states have been reassigned from those in the existing literature. Anion 2Π3/2-2Π1/2 spin-orbit splittings are measured, as are neutral 3Π2-3Π1 spin-orbit splittings: the XO 3Π 2-3Π1 splittings increase from 405±30 cm−1 (NiO) to 805±30 cm−1 (PdO) to 3580±40 cm−1 (PtO). A bond length shortening of 0.03±0.01 Å is measured upon electron detachment from NiO−, resulting in an anion bond length of 1.66±0.01 Å. The bond length does not change upon electron detachment from PdO− using 3.4-eV photons. The Pt-O bond length decreases by 0.035±0.010 Å in the 3Π1←2Π3/2 transition. The spectrum of OPtO displays a significantly more extended vibrational progression than those of ONiO or OPdO, and the O-Pt bond length is found to decrease by 0.07±0.01 Å upon electron detachment. The spectra support the view that the Ni-O bond is largely ionic, the Pd-O bond is somewhat less so, and the Pt-O bond displays a substantial covalent character. 相似文献
93.
Radical cations of the 1,2,3-trimethylcyclohexane isomers stabilized in various γ-irradiated solute/halocarbon matrices have been investigated by means of ESR in the temperature range 4–77K. At 4 K the ESR spectra are dominated by contributions from an asymmetrically distorted structure with the unpaired electron localized to the C1-C2 bond. On increasing the temperature a reversible change occurs in the ESR line-shape of the cations of the two symmetrical isomers. Using a two-site jump model to reproduce the temperature dependent line-shape, the phenomenon is explained in terms of an interconversion between two such distorted structures, each being the mirror image of the other. The Arrhenius plot associated with the process is markedly nonlinear towards the low temperature region. The experimental data are also modelled by postulating that another (different) electronic ground state, having higher symmetry, becomes populated with the increase of temperature. In this way, the spectral changes can be simulated using a three-site jump model which couple the thermally activated two-site jump process (E a ca. 0.137 kcal/mol) with a dynamical equilibrium between the asymmetrical ground state and a symmetrical structure 0.058 kcal/mol higher in energy. The energy barrier to pass from the distorted to the symmetrical structure was evaluated to be 0.085 kcal/mol. 相似文献
94.
Eu3+-, Tb3+- and Er3+-cored dendrimer complexes were prepared by self-assembly of three fluorinated dendrons, each with a carboxylate anion focal point, around the lanthanide ion. Energy transfer from the peripheral fluorinated phenyl moieties of the dendrons to the lanthanide cation was evidenced spectroscopically for Eu3+- and Tb3+-cored dendrimer complexes in solution. The excitation of perfluorinated aromatic groups was found to decay with ca. 0.7 ns and a longer decay time 10-13 ns was related to the coordination at the Ln3+ focal point. Luminescence from the lanthanide core decays with lifetime in the range 1-1.5 ms over a wide concentration range (μM-mM), similar to the luminescence decay time of the corresponding acetate ion complexes in D2O. The main quenching mechanism of the lanthanide emission appears to be due to vibrations among surrounding C-H bonds of the intermediate shell of the flexible dendrimer scaffold. Antenna effect and energy harvesting from the surface of the dendrimer and transfer to the core was the main mechanism for luminescecnce in the dendrimer complexes with lanthanide cations. 相似文献
95.
The electric field gradient at111Cd in Antimony was studied at hydrostatic pressures up to 7 kbar at 150 K, 293 K and 473 K. The logarithmic pressure derivatives, dlnq/dP, were found to be –67, –37 and –26 Mbar–1 respectively. The isotropic volume dependence derived from these values was found to be positive and largely responsible for the anomalous temperature dependence, previously observed. 相似文献
96.
97.
S. Garpman I. Lindgren J. Lindgren J. Morrison 《Zeitschrift für Physik A Hadrons and Nuclei》1976,276(3):167-177
A non-relativistic perturbation method of Brueckner-Goldstone type is used to calculate the hyperfine interactions in the lowest2 S and2 P states of the Li-like systems, Li, Be+, B2+, C3+, N4+, O5+ and F6+. The effect of the polarization of the closed shell is treated to all orders of perturbation, while the correlation effect is calculated in the lowest order, i.e. in the third order of the perturbation expansion. Experimental data are at present available only for Li, Be+ and F6+, and the agreement with the calculated values is in these cases very good, usually within the experimental uncertainties. This implies that the predictions made in the remaining cases should be quite reliable, which may simplify the experimental determination of these quantities. Theoretical values are also given for the quadrupole interaction, which can be used to determine the nuclear quadrupole moments, when accurate experimental information becomes available. 相似文献
98.
The potential profile for positive muons on the body diagonal in Al and Cu, are calculated using a molecular cluster model within the framework of the Hartree — Fock — Slater theory. The effects of substitutional Ag and Mn impurities are investigated. The extension of the muon wavefunction in a non-spherical potential is compared to the result obtained in a spherically averaged one. 相似文献
99.
100.
A many-body calculation of the hyperfine interaction in the lowest2S and2P states of li-like systems
S. Garpman I. Lindgren J. Lindgren J. Morrison 《Zeitschrift für Physik A Hadrons and Nuclei》1976,99(4):167-177
A non-relativistic perturbation method of Brueckner-Goldstone type is used to calculate the hyperfine interactions in the lowest2
S and2
P states of the Li-like systems, Li, Be+, B2+, C3+, N4+, O5+ and F6+. The effect of the polarization of the closed shell is treated to all orders of perturbation, while the correlation effect is calculated in the lowest order, i.e. in the third order of the perturbation expansion. Experimental data are at present available only for Li, Be+ and F6+, and the agreement with the calculated values is in these cases very good, usually within the experimental uncertainties. This implies that the predictions made in the remaining cases should be quite reliable, which may simplify the experimental determination of these quantities. Theoretical values are also given for the quadrupole interaction, which can be used to determine the nuclear quadrupole moments, when accurate experimental information becomes available. 相似文献