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排序方式: 共有213条查询结果,搜索用时 0 毫秒
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Komamiya S Abrams GS Adolphsen CE Averill D Ballam J Barish BC Barklow T Barnett BA Bartelt J Bethke S Blockus D Bonvicini G Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan DE Dorfan JM Drewer DC Elia R Feldman GJ Fernandes D Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gatto C Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Grindhammer G Grosse-Wiesmann P Hanson G Harr R 《Physical review letters》1990,64(24):2881-2884
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Virgil Percec Hildeberto Nava Hkan Jonsson 《Journal of polymer science. Part A, Polymer chemistry》1987,25(7):1943-1965
The influence of molecular weight on thermal transitions and on their thermodynamic parameters is discussed for a random thermotropic liquid crystalline copolyether based on the reaction of a 1:1 molar mixture of 1,5-dibromopentane and 1,7-dibromoheptane with 4,4′-dihydroxy-α-methylstilbene. Optimum phase transfer catalyzed polyetherification reaction conditions were established for the synthesis of polymers containing bromoalkane chain ends only over a wide variety of molecular weights. All these copolyethers present a crystalline and an enantiotropic nematic mesophase over the entire range of molecular weights studied. Both the thermal transitions and their thermodynamic parameters are strongly molecular weight-dependent up to M n = 10,000–12,000, after which they remain constant. The enthalpies and entropies of isotropization of the copolyethers are higher than those of melting. This is in contrast to the same thermodynamic parameters of the corresponding homopolyethers. The enthalpies and entropies of isotropization of both homopolymers and copolymers present similar values, suggesting that copolymerization does decrease the degree of order in the crystalline phase but does not significantly change the alignment degree of the mesogenic units in the nematic mesophase. 相似文献
25.
Eurydice Arroyo Diana Tentori Alfonso Garcia Ricardo Valdez Miguel A. Armenta Osvaldo J. Nava Roberto Machorro Amelia Olivas 《Particle & Particle Systems Characterization》2023,40(6):2200200
Carbon quantum dots (CQD) have received significant attention in recent years due to their potential applications in optics and sensing. In this study, the authors report on the first characterization of the optical activity and broad absorption spectrum covering from short-wave ultraviolet, at 200 nm, to mid-infrared, at 1600 nm, of CQD synthesized using the “low-molecular-weight alcohols electrochemical carbonization” method. The CQD are analyzed using spectroscopic techniques, optical activity in the infrared, and high-resolution transmission electron microscopy. Results show a CQD size distribution of 5±3 nm and spherical morphology. The absorption spectra show increased absorption at both, high and low frequency. Additionally, the specific rotation of the CQD solution is significantly higher than that of pure ethanol, by three orders of magnitude. These findings suggest that CQD may have potential applications in polarized infrared filters and/or sensors due to their ability to rotate the polarization state of light at 1550 nm. The results of this study provide valuable insights into the optical properties of CQD and their potential for infiltration into hollow core photonic crystal fibers, making them a promising material for future research and development in the field of optics and sensing. 相似文献
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Michael Esseling Annamaria Zaltron Nicola Argiolas Giovanni Nava Jörg Imbrock Ilaria Cristiani Cinzia Sada Cornelia Denz 《Applied physics. B, Lasers and optics》2013,113(2):191-197
We investigate the applicability of highly reduced lithium niobate samples doped with iron for the use as optoelectronic tweezers. Increasing the reduction degree of Fe-doped lithium niobate is well known to increase the photoconductivity and reduce the writing time of internal space-charge fields. Based on our measurements of the photorefractive properties, we determine the optimal conditions for dielectrophoretic trapping and present the application of Fe-doped lithium niobate as optoelectronic tweezers. For higher reduction degrees, an unexpected decrease in the photovoltaic current density and the saturation space-charge field is reported. 相似文献
28.
Calcium tin silicate, CaSnSiO5, called Malayaite is synthesized with equimolecular quantities of calcium oxide, silica and stannic oxide followed by a thermic
process. In this work, the synthesis of Malayaite and the structure of a Malayaite-based pigment, Sn/Co pink, is investigated
by X-ray diffraction and Mossbauer spectroscopy. The results indicate Malayaite and Cassiterite formation, but the ion cobalt
incorporated in the Malayaite structure, diminishes the Cassiterite proportion and causes larger asymmetry in the environment
of the tin atom. 相似文献
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Giorgio Abbiati Alessandro Contini Donatella Nava Elisabetta Rossi 《Tetrahedron》2009,65(24):4664-3418
The cycloaddition reactions of ‘all-carbon’ 1,3-diazabuta-1,3-dienes with a few conjugated and unconjugated alkynyl ketenes are described. The reactions provide some interesting azetidinones and dihydropyrimidinones bearing an alkynyl moiety. The regiochemistry of cycloadduct is related with the degree of conjugation of the alkynyl ketene. Moreover, two alternative approaches to ‘all-carbon’ 1,3-diazabuta-1,3-dienes are reported. 相似文献