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51.
Nakamura H. Imai H. Shiga M. Mekata M. Nishiyama K. Nagamine K. 《Hyperfine Interactions》1999,120(1-8):633-637
Positive muon spin relaxation measurements were performed on a spin-1/2 system BaVS3, which shows a metal-insulator transition at TMI= 70 K. We found a marked muon-spin depolarization below TX= 30 K without appreciable critical divergence. The possibility of muonium formation in the insulating state rather than electron
spin freezing is discussed taking into account the quenching of V spins evidenced by 51V NMR and NQR measurements.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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The composition of the dopant for the analysis of polycyclic aromatic hydrocarbons (PAHs) by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry under reversed-phase conditions was optimized to enhance the ionization efficiency for PAHs. The most suitable dopant was a toluene/anisole mixture (99.5:0.5, v/v) and it could improve limit of detections (LODs) to 0.79-168 ng mL(-1) (signal-to-noise (S/N)=3) for 16 common PAHs. The LODs are 3.8-40 times lower than those obtained with toluene alone and are comparable to those obtained using gas chromatography/mass spectrometry. 相似文献
55.
Shiga T Okawa H Kitagawa S Ohba M 《Journal of the American Chemical Society》2006,128(51):16426-16427
Integration of mononuclear [Cr(CN)6]3- and preorganized trinuclear [Co2Ln(L)2]3+ complexes provides novel trimetallic magnets having a 3-D pillared-layer framework with an alternate array of 2-D layer extended by Cr(III)-CN-Co(II) linkages and Ln(III) ion. The overall magnetic nature can be systematically controlled by Ln(III) ions inserted between the 2-D ferromagnetic layers. 相似文献
56.
Yamamoto C Nishikawa H Nihei M Shiga T Hedo M Uwatoko Y Sawa H Kitagawa H Taguchi Y Iwasa Y Oshio H 《Inorganic chemistry》2006,45(25):10270-10276
Reactions of K1.62[Pt(ox)2].2H2O and [Cu(bpy)(H2O)3](NO3)2 yielded partially oxidized one-dimensional (1D) bis(oxalato)platinates of [Cu(bpy)(H2O)n]6[Pt(ox)2]7.7H2O (n = 2, 3, or 4) (1) and [Cu(bpy)(H2O)n]8[Pt(ox)2]10.8H2O (n = 3 or 4) (2). The average oxidation numbers of the platinum ions in 1 and 2 are +2.29 and +2.40, respectively. Complexes 1 and 2 crystallize in the triclinic P and monoclinic C2/c space groups, respectively, and the [Pt(ox)2]n- anions are stacked along the crystallographic b axis with 7-fold periodicity for 1 and 10-fold periodicity for 2. In 1, an oxalato ligand in the platinum chain directly coordinates to a paramagnetic [Cu(bpy)(H2O)3]2+ ion, whereas no such direct coordination was observed for 2. The electrical conductivity of 2 at room temperature along the platinum chain is approximately 3 orders of magnitude smaller (sigma||= 1.3 x 10(-3) S cm(-1)) than that of 1 (sigma|| = 0.9-0.5 S cm(-1)), and the activation energies of 1 and 2 are 29 and 67 meV, respectively. The longest inter-platinum distances in 1 and 2 are 2.762 and 3.0082 A, respectively, and this is responsible for the lower electrical conductivity of 2. An X-ray oscillation photograph taken along the b axis of 1 reveals the 7-fold periodicity in the 1D chain, consistent with the period of the Peierls distortion estimated from the degree of partial oxidation. The semiconducting state of 1 can therefore be regarded as a commensurate Peierls state. The magnetoresistance of 1 at ambient pressure indicates no interaction between conduction electrons in the platinum chain and local spins of the paramagnetic CuII ions. Application of hydrostatic pressures of up to 3 GPa enhances electrical conduction, as is often seen as the usual pressure effect on the electrical conductivity, which is due to enhanced orbital (Pt-5dz2) overlap by pressure application. 相似文献
57.
As an application of atomistic simulation methods to heat capacities, path-integral molecular dynamics has been used to calculate the constant-volume heat capacities of light and heavy water in the gas, liquid, and solid phases. While the classical simulation based on conventional molecular dynamics has estimated the heat capacities too high, the quantum simulation based on path-integral molecular dynamics has given reasonable results based on the simple point-charge/flexible potential model. The calculated heat capacities (divided by the Boltzmann constant) in the quantum simulation are 3.1 in the vapor H2O at 300 K, 6.9 in the liquid H2O at 300 K, and 4.1 in the ice Ih H2O at 250 K, respectively, which are comparable to the experimental data of 3.04, 8.9, and 4.1, respectively. The quantum simulation also reproduces the isotope effect. The heat capacity in the liquid D2O has been calculated to be 10% higher than that of H2O, while it is 13% higher in the experiment. The results demonstrate that the path-integral simulation is a promising approach to quantitatively evaluate the heat capacities for molecular systems, taking account of quantum-mechanical vibrations as well as strongly anharmonic motions. 相似文献
58.
Kenshu Fujiwara Yu-ichi Aki Fuyuki Yamamoto Mariko Kawamura Masanori Kobayashi Azusa Okano Daisuke Awakura Shunsuke Shiga Akio Murai Hidetoshi Kawai Takanori Suzuki 《Tetrahedron letters》2007,48(26):4523-4527
In this study, we synthesized the C8-C20 and C21-C30 segments of the diarrhetic shellfish toxin pectenotoxin 2. The C8-C20 segment was assembled from a phosphonate corresponding to the C8-C15 segment (prepared from l-malic acid in 19 steps) and an aldehyde corresponding to the C16-C20 segment (synthesized from 3-methyl-3-butenol in nine steps) by a twelve-step process including the Horner-Wadsworth-Emmons reaction, regio- and stereoselective reduction of the resulting enone, diastereoselective epoxidation, and 5-exo epoxide cleavage forming the C-ring. The C21-C30 segment was constructed in 13 steps from (S)-glycidol via a route involving E-ring formation by 5-exo epoxide cleavage and stereoselective methylation at C27 by the Evans method. 相似文献
59.
By means of facing target dc sputtering, an amorphous phase has been produced for immiscible Fe---Cu---Ag alloys at around the central concentration of the ternary phase diagram. The radial distribution function estimated from X-ray diffraction measurements indicates that a tetrahedron is the dominant structure unit and that the average coordination number is about 11. In the extended X-ray absorption fine structure radial structure function, a clear peak is detected at the nearest neighbor distance, but the peak intensity is weaker than those for binary crystalline Fe---Cu and Fe---Ag alloys and no clear peak is detectable at larger distances. A hard or soft sphere dense random packing model is appropriate for the amorphous structure in these immiscible alloys. 相似文献
60.