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281.
Magnetic measurements were made using pure YBCO and Zn doped YBa2(Cu1?xZnx)3O7?σ. Single crystals with Zn concentration of 0.5%, 1.5%, 3.0% and 4.3%. The magnetic hysteresis loops for these samples were measured in the temperature range 0.1 ? T/Tc ? 0.96 under magnetic fields of 5 T using SQUID. It was found that the critical current density Jc increased for low Zn content samples up to 3% Zn concentration compared to pure YBCO sample and decreased for the higher Zn content samples. These values varied consistently when compared at magnetic fields of 1 T and 3 T. Moreover Zn doped samples showed significant values of Jc in the temperature range of 0.7–0.9Tc, close to critical temperature compared to pure YBCO sample. The irreversibility field Hirr was also enhanced in this temperature range showing consistent decrease with increase of Zn concentration. The peak field Hp above Hc1 and irreversibility field Hirr, both show power law dependence of the form H = m1(1 ? T/Tc)m2 in the temperature range of 0.75–0.96Tc. The values of parameter m2 increased from 1.44 to 1.95 for the samples up to 3% Zn content and decreased to 1.37 for higher Zn contents. The ratio Hirr/Hp was found to be 3–4 for the lower Zn content samples and was 7–8 for the sample with high Zn content indicating more disorder for higher Zn content samples. The region between peak field Hp and irreversibility field Hirr was broadened with the increase of Zn concentration. The strong effect of Zn substitution in modifying behavior of these samples even at elevated temperatures is possibly due to the changes in the anisotropy of our samples with the increase of Zn concentration and also due to the locally induced changes in magnetic moments by Zn substitution. 相似文献
282.
L. Miu I. Ivan P. Badica G. Jakob D. Miu P. Mele K. Matsumoto M. Mukaida Y. Yoshida T. Horide A. Ichinose S. Horii 《Physica C: Superconductivity and its Applications》2010,470(20):1126-1129
The temperature T variation of the normalized magnetization relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster relaxation at low T appearing in standard magnetization relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the low-T range is also evidenced. The collective (elastic) creep regime is generated by the T dependent macroscopic currents induced in the sample during standard magnetization measurements. 相似文献
283.
Koki Fujimura Dr. Yoshihiro Ueda Dr. Yousuke Yamaoka Prof. Kiyosei Takasu Prof. Takeo Kawabata 《Angewandte Chemie (International ed. in English)》2023,62(30):e202303078
A method for rotaxane synthesis by enlargement of the size of the terminal phenol group of the axle component by aromatic bromination has been developed. This method may be regarded as an end-capping strategy involving the swelling of the phenol group at the axle terminal. The advantages of the present strategy include: ready availability of axle components with a variety of swelling precursors, wide product scope (19 examples given including a [3]rotaxane), mild conditions for the swelling process, rich potential for the derivatization of the brominated rotaxanes, and possible release of the axle component by degradative dethreading of the thermally stable brominated rotaxanes under the basic conditions. 相似文献
284.
Dr. Koki Ikemoto Kanato Takahashi Prof. Dr. Takeaki Ozawa Prof. Dr. Hiroyuki Isobe 《Angewandte Chemie (International ed. in English)》2023,62(14):e202219059
“How do we decide the stoichiometry of host–guest complexes?” This question has long been answered by the Job plot since its first report in 1928. However, as the Job plot was claimed to be misleading in 2016, the question became an open question again and called for renewed investigations. An information-theoretic approach, called Akaike's information criterion, is introduced in this study to select the best model of host–guest complexes, which can rank the models with weight of evidence. A few test cases with unique cylindrical hosts were examined to demonstrate the applicability of the information-theoretic method. Consequently, reasonable views over the thermodynamic behaviors of dumbbell-and-cylinder complexes were obtained. Akaike's information criterion can be a useful and superior alternative to statistical null hypothesis testing, which was proposed as a remedy in place of the Job plot. 相似文献
285.
Koki Yoshizawa Dr. Keisuke Hirata Prof. Shun-ichi Ishiuchi Prof. Masaaki Fujii Dr. Anne Zehnacker 《Chemphyschem》2023,24(18):e202300172
Alkali metal complexes of cyclic dipeptide cyclo Tyr-Tyr have been studied under cryogenic ion trap conditions. Their structure was obtained by combining Infra-Red Photo-Dissociation (IRPD) and quantum chemical calculations. The structural motif strongly depends on the relative chirality of the tyrosine residues. For residues of identical chirality, the cation interacts with one amide oxygen and one of the aromatic rings only; the distance between the aromatic rings does not change with the nature of the metal. In contrast, for residues of opposite chirality, the metal cation is located in between the two aromatic rings and interacts with both of them. The distance between the two aromatic rings strongly depends on the metal. Electronic spectra obtained by Ultra Violet Photodissociation (UVPD) spectroscopy and analysis of the UV photo-fragments shed light on the excited state deactivation processes, which depend on both the chirality of the residue and that of the metal ion core. Na+ stands out by the presence of low-lying charge transfer states resulting in the broadening of the electronic spectrum. 相似文献
286.
287.
Hirotaka Nakajima Kaiji Uchida Dr. Takefumi Yoshida Dr. Yoji Horii Dr. Tetsu Sato Zhang Luming Dr. Satoshi Yamashita Dr. Yasuhiro Nakazawa Dr. Verdad C. Agulto Dr. Makoto Nakajima Dr. Brian K. Breedlove Dr. Masahiro Yamashita Dr. Hiroaki Iguchi Dr. Shinya Takaishi 《Chemphyschem》2023,24(4):e202200618
We report the water adsorption/desorption behavior and dynamic magnetic properties of the Pt−Cl chain complex [{[Pt(en)2][PtCl2(en)2]}3][{(MnCl5)Cl3}2] ⋅ 12H2O ( 1 ). Upon heating 1 in a vacuum, we obtained the dehydrated form [{[Pt(en)2][PtCl2(en)2]}3][{(MnCl5)Cl3}2] ( 1DH ). The framework structures of 1 and 1DH are identical, and both complexes underwent slow magnetic relaxation. However, the magnetic relaxation times for 1DH were shorter than those for 1 , meaning that the dynamic magnetic properties were controlled upon water vapor adsorption/desorption. From detailed analyses of the dynamic magnetic behavior, a phonon-bottleneck effect contributes to the magnetic relaxation processes. We discuss the mechanism for the changes in the magnetic relaxation processes upon dehydration in terms of the heat capacity and thermal conductivity. 相似文献