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排序方式: 共有199条查询结果,搜索用时 93 毫秒
191.
Some of the most significant discoveries and achievements concerning the mass spectra and gas phase ion chemistry of carbon clusters are reviewed. These include (1) nanosecond and femtosecond laser ionizations; (2) ion structures through ion/molecule reactions, ion chromatography, and computational methods; (3) carbon cluster cooling through radiative decay, dissociative decay, and thermionic emission; (4) mechanisms and energetics of fragmentation reactions; (5) endohedral fullerenes including recent data on ion beam implantation, and (6) ion chemistry as a function of the fullerene charge state. 相似文献
192.
Ulli Englert Frank Podewils Ingo Schiffers Albrecht Salzer 《Angewandte Chemie (International ed. in English)》1998,37(15):2134-2136
Air-stable, yellow crystals are formed by the first bis(metallabenzene) sandwich complex 1 . With regard to its properties, 1 shows many similarities to classical metallocenes, the syn-ecliptical arrangement of the metal atoms in the rings pointing to an additional interaction between the ring Ru atoms. 相似文献
193.
Prof. Dr. Peter B. Karadakov 《Chemphyschem》2023,24(9):e202300038
The spatial variations in the diamagnetic and paramagnetic contributions to the off-nucleus isotropic shielding, , and to the zz component of the off-nucleus shielding tensor, , around benzene (C6H6) and cyclobutadiene (C4H4) are investigated using complete-active-space self-consistent field wavefunctions. Despite the substantial differences between and around the aromatic C6H6 and the antiaromatic C4H4, the diamagnetic and paramagnetic contributions to these quantities, and , and and , are found to behave similarly in the two molecules, shielding and deshielding, respectively, each ring and its surroundings. The different signs of the most popular aromaticity criterion, the nucleus-independent chemical shift (NICS), in C6H6 and C4H4 are shown to follow from a change in the balance between the respective diamagnetic and paramagnetic contributions. Thus, the different NICS values for antiaromatic and antiaromatic molecules cannot be attributed to differences in the ease of access to excited states only; differences in the electron density, which determines the overall bonding picture, also play an important role. 相似文献
194.
Younghun Kim Heechan Kim Dr. Jung Bae Son Dr. Michael Filatov Prof. Dr. Cheol Ho Choi Prof. Dr. Nam Ki Lee Prof. Dr. Dongwhan Lee 《Angewandte Chemie (International ed. in English)》2023,62(20):e202302107
Molecular emitters simultaneously generating light at different wavelengths have wide applications. With a small molecule, however, it is challenging to realize two independent radiative pathways. We invented the first examples of dual-emissive single-benzene fluorophores (SBFs). Two emissive tautomers are generated by synthetic modulation of the hydrogen bond acidity, which opens up pathways for excited-state proton transfer. White light is produced by a delicate balance between the energy and intensity of the emission from each tautomer. We show that the excited-state antiaromaticity of the benzene core itself dictates the proton movements driving the tautomer equilibrium. Using this simple benzene platform, a fluorinated SBF was synthesized with a record high solubility in perfluorocarbon solvents. White light-emitting devices and multicolor imaging of perfluorocarbon nanodroplets in live cells demonstrate the practical utility of these molecules. 相似文献
195.
Binbin Ming Chuan Yan Shoudong Xie Si Liu Yingjian Ren Hao Zong Weinan Chen Gang Zhou 《中国化学》2023,41(1):13-20
S-fused heterocycles have become popular building blocks to construct functional polycyclic compounds. In contrast to the abundant synthetic methodologies for thiophene-fused aromatics, the synthesis of S-heterocycles containing six-membered thiopyran and seven-membered thiepine rings is much less reported owing to their unfavorable synthetic protocols and the thermal instabilities. Herein, a series of thiepine-containing polycyclic S-heterocycles have been successfully synthesized via different synthetic routes which involve initial construction of sulfur bridges and final ring-closure reactions. Therefore, the dilithium intermediates are excluded, which facilitates the fusion on the thiepine ring with different S-heterocycles, including thiophene and thiopyran derivatives. Typically, a S-fused multi-membered polycyclic compound simultaneously involving thiophen, thiopyran, and thiepine rings has been successfully prepared. Interestingly, nucleus-independent chemical shift calculations reveal that the incorporated thiopyran and thiepine rings demonstrate aromatic and nonaromatic characteristics, respectively. Moreover, the thermal stabilities of the thiepine derivatives have been tremendously improved after the fusion on the three vinyl groups in the thiepine unit, which is attributed to the enhancements of the activation energies for the S-extrusion reactions, as revealed by density functional theory calculations. Therefore, our findings not only provide a facile synthetic methodology for S-fused multi-membered polycyclic heterocycles, but also furnish a novel construction strategy towards thermally stable thiepine derivatives. 相似文献
196.
Pierre Mathey Frédéric Lirette Prof. Dr. Israel Fernández Lukas Renn Prof. Dr. R. Thomas Weitz Prof. Dr. Jean-François Morin 《Angewandte Chemie (International ed. in English)》2023,62(11):e202216281
Non-alternant non-benzenoid hydrocarbons exhibit very different optical and electronic properties than their well-studied benzenoid analogues. However, preparing such structures with extended conjugation length, remains challenging. Herein, we report the synthesis and properties of azuleno[2,1,8-ija]azulene derivatives using a two-step sequence involving a four-fold aldol condensation between aromatic dialdehydes and readily available tetrahydropentalene-2,5-(1H,3H)-dione. Molecules with band gap values ranging from 1.69 to 2.14 eV and molar extinction coefficients (ϵ) of nearly 3×105 M−1 cm−1 have been prepared. These annulene-like structures exhibit significant diatropic ring currents (aromatic), as supported by 1H NMR spectroscopy and DFT calculations. Field-effect transistors (OFETs) using azuleno[2,1,8-ija]azulene derivatives as semiconductors exhibit charge mobility values of up to 0.05 cm2 V−1 s−1. 相似文献
197.
Jiping Hao Akihide Nishiyama Dr. Shigeki Mori Prof. Dr. Ko Furukawa Prof. Dr. Soji Shimizu 《Angewandte Chemie (International ed. in English)》2023,62(34):e202307862
5,15-Dioxaporphyrin ( DOP ) is a novel meso-oxaporphyrin analogue and exhibits unique 20π-antiaromaticity, unlike its mother congener of 18π-aromatic 5-oxaporphyrin, commonly known as its cationic iron complex called verdohem, which is a key intermediate of heme catabolism. To reveal its reactivities and properties as an oxaporphyrin analogue, the oxidation of tetra-β-arylated DOP ( DOP-Ar4 ) was explored in this study. Stepwise oxidation from the 20π-electron neutral state was achieved, and the corresponding 19π-electron radical cation and 18π-electron dication were characterized. Further oxidation of the 18π-aromatic dication resulted in the formation of a ring-opened dipyrrindione product by hydrolysis. Considering a similar reaction of verdoheme to ring-opened biliverdin in the heme degradation in nature, the current result consolidates the ring-opening reactivity of oxaporphyrinium cation species. 相似文献
198.
M.Sc. Steffen Maier M.Sc. Nikolai Hippchen Fabian Jester Marcus Dodds Michel Weber Leon Skarjan Dr. Frank Rominger Dr. Jan Freudenberg Prof. Uwe H. F. Bunz 《Angewandte Chemie (International ed. in English)》2023,62(5):e202214031
Cyclopentannulation was explored as a strategy to access large, stable azaarenes. Buchwald–Hartwig coupling of previously reported di- and tetrabrominated cyclopentannulated N,N′-dihydrotetraazapentacenes furnished stable azaarenes with up to 13 six-membered rings in a row and a length of 3.1 nm. Their optoelectronic and semi-conducting properties as well as their aromaticity were investigated. 相似文献
199.
Takahiro Sakurai Yuya Hiraoka Dr. Hisaaki Tanaka Prof. Dr. Yoshihiro Miyake Prof. Dr. Norihito Fukui Prof. Dr. Hiroshi Shinokubo 《Angewandte Chemie (International ed. in English)》2023,62(12):e202300437
NiII 3,7,13,17-tetrapyridyl-5,15-diazaporphyrin serves as a double tridentate ligand to PdII ions to provide a pincer-type bispalladium complex. Electrochemical analysis revealed that the bispalladium complex shows excellent ability to accept electrons and reversible redox properties due to the coordination of the two cationic PdII centers to the meso-nitrogen atoms. We isolated and characterized one- and two-electron reduction species of the bispalladium complex. The 20π antiaromatic nature of the two-electron reduction species was confirmed by 1H NMR spectroscopy, UV/Vis-near-IR (NIR) absorption spectra, and density functional theory (DFT) calculations. X-ray diffraction revealed highly twisted structures for the bispalladium complexes regardless of the oxidation state. 相似文献