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排序方式: 共有947条查询结果,搜索用时 953 毫秒
941.
Hatem M. Titi Israel Goldberg 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(12):o639-o644
The structure of 1‐benzofuran‐2,3‐dicarboxylic acid (BFDC), C10H6O5, (I), exhibits an intramolecular hydrogen bond between one –COOH group and the other, while the second carboxyl function is involved in intermolecular hydrogen bonding to neighbouring species. The latter results in the formation of flat one‐dimensional hydrogen‐bonded chains in the crystal structure, which are π–π stacked along the normal to the plane of the molecular framework, forming a layered structure. 1:1 Cocrystallization of BFDC with pyridine, phenazine and 1,4‐phenylenediamine is associated with H‐atom transfer from BFDC to the base and charge‐assisted hydrogen bonding between the BFDC− monoanion and the corresponding ammonium species, while preserving, in all cases, the intramolecular hydrogen bond between the carboxyl and carboxylate functions. The pyridinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C5H6N+·C10H5O5−, (II), and phenazinium 3‐carboxylato‐1‐benzofuran‐2‐carboxylic acid, C12H9N2+·C10H5O5−, (III), adducts form discrete hydrogen‐bonded ion‐pair entities. In the corresponding crystal structures, the two components are arranged in either segregated or mixed π–π stacks, respectively. On the other hand, the structure of 4‐aminoanilinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C6H9N2+·C10H5O5−, (IV), exhibits an intermolecular hydrogen‐bonding network with three‐dimensional connectivity. Moreover, this fourth structure exhibits induction of supramolecular chirality by the extended hydrogen bonding, leading to a helical arrangement of the interacting moieties around 21 screw axes. The significance of this study is that it presents the first crystallographic characterization of pure BFDC, and manifestation of its cocrystallization with a variety of weakly basic amine molecules. It confirms the tendency of BFDC to preserve its intramolecular hydrogen bond and to prefer a monoanionic form in supramolecular association with other components. The aromaticity of the flat benzofuran residue plays an important role in directing either homo‐ or heteromolecular π–π stacking in the first three structures, while the occurrence of a chiral architecture directed by multiple hydrogen bonding is the dominant feature in the fourth. 相似文献
942.
943.
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
944.
Francis Ignatious Yadollah Delaviz Israel Cabasso Johannes Smid 《Macromolecular Symposia》1992,60(1):247-257
Styryl- and α-methylstyryldiphenylbismuth (I and II, respectively), and styryl and α-methylstyryltriphenyllead and the two corresponding tin-containing monomers (III, IV, V and VI, respectively) were synthesized. Compounds III through VI were obtained pure, but I and II contain substantial quantities of Ph3Bi and di- and tri-vinyl derivatives. Homopolymers of I, III and V, as well as copolymers with methyl acrylate were synthesized radically. Monomers III, V, and VI yielded narrow MWD polymers with anionic initiators such as the potassium salt of the α-methylstyrene dimer carbanion in THF at −80°C, while I gave a broad, bimodal MWD. Monomers II and IV did not polymerize under these conditions due to side reactions with the initiator. Glass transition temperatures, thermal stabilities and radiopacities of a number of the polymers were determined. 相似文献
945.
Archiv der Mathematik - It is known that every finite group can be represented as the full group of automorphisms of a suitable compact origami. In this paper, we provide a short argument to note... 相似文献
946.
Kathleen Fuchs Dr. Samara Medina Rivero Anna Weidlich Dr. Frank Rominger Noel Israel Dr. Alexey A. Popov Prof. Dr. Andreas Dreuw Dr. Jan Freudenberg Prof. Juan Casado Prof. Dr. Uwe H. F. Bunz 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305712
Two series of regioisomeric dicyanomethylene substituted dithienodiazatetracenes with formal para- or ortho-quinodimethane subunits were synthesized and characterized. Whereas the para-isomers (p-n, diradical index y0=0.01) are stable and isolable, the ortho-isomer (y0=0.98) dimerizes into a covalent azaacene cage. Four elongated σ-CC bonds are formed and the former triisopropylsilyl(TIPS) -ethynylene groups transformed into cumulene units. The azaacene cage dimer (o-1)2 was characterized by X-ray single crystal structure analysis and temperature-dependent infrared (IR), electron paramagnetic resonance (EPR, solid-state), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV/Vis) spectroscopies (solution) indicating reformation of o-1. 相似文献
947.