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171.
Brian B. Frank Berta Camafort Blanco Samuel Jakob Fiammetta Ferroni Silvia Pieraccini Dr. Alberta Ferrarini Prof. Dr. Corinne Boudon Prof. Dr. Jean‐Paul Gisselbrecht Dr. Paul Seiler Gian Piero Spada Prof. Dr. François Diederich Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):9005-9016
Axially chiral, N‐arylated 3,5‐dihydro‐4H‐dinaphtho[2,1‐c:1′,2′‐e]azepines have been prepared by short synthetic protocols from enantiopure 1,1′‐bi(2,2′‐naphthol) (BINOL) and anilines. Alkynes substituted with two N‐phenyldinaphthazepine donors readily undergo a formal [2+2] cycloaddition, followed by retro‐electrocyclization, with tetracyanoethene (TCNE) to yield donor‐substituted 1,1,4,4‐tetracyanobuta‐1,3‐dienes (TCBDs) featuring intense intramolecular charge‐transfer (CT) interactions. A dicyanovinyl derivative substituted with one N‐phenyldinaphthazepine donor was obtained by a “one‐pot” oxidation/Knoevenagel condensation from the corresponding propargylic alcohol. Comparative electrochemical, X‐ray crystallographic, and UV/Vis studies show that the electron‐donor qualities of N‐phenyldinaphthazepine are similar to those of N,N‐dimethylanilino residues. The circular dichroism (CD) spectrum of a push–pull chromophore incorporating the chiral donor moiety features Cotton effects of exceptional intensity. With their elongated shape and the rigidity of the chiral N‐aryldinaphthazepine donors, these chromophores are effective inducers of twist distortion in nematic liquid crystals (LCs). Thus, a series of the dinaphthazepine derivatives was used as dopants in the nematic LC E7 (Merck) and high helical twisting powers (β) of the order of hundreds of μm?1 were measured. Theoretical calculations were employed to elucidate the relation between the structure of the dopants and their helical twisting power. For the derivatives with two dinaphthazepine moieties, a strong dependence of the β‐values on the structure and conformation of the linker between them was found. 相似文献
172.
Anke Flemming Martin Köckerling Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(14):2605-2608
Complete exchange : [M6X12] type cluster compounds with an octahedral M6 metal atom arrangement, which is completely surrounded by alcoholato ligands, were unknown until now. The first representatives are prepared containing a [Nb6(OR)12]4+ unit (R=CH3 or C2H5). They are accessible at elevated temperatures from strongly basic alcoholate solutions of [Nb6Cl12]2+‐containing precursors. C gray, H white, K turquoise, Nb blue, O red.
173.
Roncucci P Pirondini L Paderni G Massera C Dalcanale E Azov VA Diederich F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(18):4775-4784
The controllable switching of suitably bridged resorcin[4]arene cavitands between a "vase" conformation, with a cavity capable of guest inclusion, and a "kite" conformation, featuring an extended flattened surface, provides the basis for ongoing developments of dynamic molecular receptors, sensors, and molecular machines. This paper describes the synthesis, X-ray crystallographic characterization, and NMR analysis of the "vase-kite" switching behavior of a fully pyrazine-bridged cavitand and five other mixed-bridged quinoxaline-bridged cavitands with one methylene, phosphonate, or phosphate bridge. The pyrazine-bridged resorcin[4]arene cavitand displayed an unexpectedly high preference for the kite conformation in nonpolar solvents, relative to the quinoxaline-bridged analogue. This observation led to extensive solvent-dependent switching studies that provide a detailed picture of how solvent affects the thermal vase-kite equilibration. As for any thermodynamic process in the liquid phase, the conformational equilibrium is affected by how the solvent stabilizes the two individual states. Suitably sized solvents (benzene and derivatives) solvate the cavity of the vase form and reduce the propensity for the vase-to-kite transition. Correspondingly, the kite geometry becomes preferred in bulky solvents such as mesitylene, incapable of penetrating the vase cavity. As proposed earlier by Cram, the kite form is preferred at low temperatures due to the more favorable enthalpy of solvation of the enlarged surface. Furthermore, the kite conformation is more preferred in solvents with substantial hydrogen-bonding acidity: weak hydrogen-bonding interactions between the mildly basic quinoxaline and pyrazine nitrogen atoms and solvent molecules are more efficient in the open kite than in the closed vase form. Vase-to-kite conversion is entirely absent in dipolar aprotic solvents lacking any H-bonding acidity. Thermal vase-kite switching requires fully quinoxaline- or pyrazine-bridged cavitands, whereas pH-controlled switching is also applicable to systems incorporating only two or three such bridges. 相似文献
174.
Holz J Zayas O Jiao H Baumann W Spannenberg A Monsees A Riermeier TH Almena J Kadyrov R Börner A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(19):5001-5013
A set of 16 new and closely related bisphospholane ligands have been prepared by using a highly flexible and convergent approach. Each synthesis can be performed on an industrially relevant scale. The bisphosphines differ in the nature of the bridge connecting both phospholane units. Bridges are formed by three-, four-, five- and six-membered heterocyclic or alicyclic rings. Bisphospholanes and their Rh-precatalysts have been investigated by using results of theoretical calculations (DFT) and analytic measurements ((31)P and (103)Rh NMR spectroscopy, X-ray structure analysis). The studies showed that catalysts based on ligands with maleic anhydride or maleimide bridges give constantly superior enantioselectivities in methanol as the solvent. This may account for optimised steric and electronic effects. However, by changing the solvent catalysts with other backbones can give rise to excellent results. This gives proof that simple correlations between steric and electronic properties and results in the enantioselective hydrogenation frequently claimed in literature are not general. 相似文献
175.
Anke Rückert 《Tetrahedron letters》2006,47(45):7977-7981
A concise, enantioselective synthesis of (+)-dumetorine is described, giving the natural product in six steps and a 27% overall yield from a readily available precursor. Among the key steps used, the synthesis entails a high-yielding ring-rearrangement metathesis (RRM), using the commercially available first generation Grubbs catalyst 2 in combination with Ti(Oi-Pr)4 as a co-catalyst. This constitutes the first enantioselective total synthesis of the alkaloid from a known chiral intermediate, and hence a confirmation of its absolute stereochemistry. 相似文献
176.
Gärtner F Denurra S Losse S Neubauer A Boddien A Gopinathan A Spannenberg A Junge H Lochbrunner S Blug M Hoch S Busse J Gladiali S Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(11):3220-3225
Novel phenylazole ligands were applied successfully in the synthesis of cyclometalated iridium(III) complexes of the general formula [Ir(phenylazole)(2)(bpy)]PF(6) (bpy=2,2'-bipyridine). All complexes were fully characterized by NMR, IR, and MS spectroscopic studies as well as by cyclic voltammetry. Three crystal structures obtained by X-ray analysis complemented the spectroscopic investigations. The excited-state lifetimes of the iridium complexes were determined and showed to be in the range of several hundred ns to multiple μs. All obtained iridium complexes were active as photosensitizers in catalytic hydrogen evolution from water in the presence of triethylamine as a sacrificial reducing agent. Applying an in situ formed iron-based water reduction catalyst derived from [HNEt(3)](+) [HFe(3)(CO)(11)](-) and tris[3,5-tris-(trifluoromethyl)-phenyl]phosphine as the ligand, [Ir(2-phenylbenz-oxazole)(2)-(bpy)]PF(6) proved to be the most efficient complex giving a quantum yield of 16% at 440 nm light irradiation. 相似文献
177.
Dierckx A Miannay FA Ben Gaied N Preus S Björck M Brown T Wilhelmsson LM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5987-5997
Fluorescent-base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base-pairing properties of a new environment-sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid-phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B-form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2-aminopurine, and the recently developed triazole adenine, qA shows highly specific base-pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300?nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8?% with an emission maximum at 456?nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2-aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid-containing systems. 相似文献
178.
P Rivera-Fuentes Mv Rekowski WB Schweizer JP Gisselbrecht C Boudon F Diederich 《Organic letters》2012,14(16):4066-4069
A carbopalladation cascade reaction of easily accessible gem-dibromoolefins and alkynes furnishes monobenzo- and mononaphthopentalenes. The new chromophores accessed by this short route exhibit small HOMO-LUMO gaps and redox amphoteric behavior with tunable redox potentials. 相似文献
179.
Chiu M Jaun B Beels MT Biaggio I Gisselbrecht JP Boudon C Schweizer WB Kivala M Diederich F 《Organic letters》2012,14(1):54-57
A formal [2 + 2] cycloaddition-cycloreversion (CA-CR) between N,N'-dicyanoquinone diimides (DCNQIs) and electron-rich alkynes was explored, providing a new class of π-conjugated donor-acceptor chromophores. These DCNQI adducts exist in the solid state as single diastereoisomers, but as two interconverting diastereoisomers in solution. Solid- and solution-state evidence for intramolecular charge transfer (CT) was obtained; additionally, the DCNQI adducts exhibit positive solvatochromism and significant solution-state third-order polarizabilities. 相似文献
180.
Weisel M Bitter HM Diederich F So WV Kondru R 《Journal of chemical information and modeling》2012,52(6):1450-1461
A central problem in structure-based drug design is understanding protein-ligand interactions quantitatively and qualitatively. Several recent studies have highlighted from a qualitative perspective the nature of these interactions and their utility in drug discovery. However, a common limitation is a lack of adequate tools to mine these interactions comprehensively, since exhaustive searches of the protein data bank are time-consuming and difficult to perform. Consequently, fundamental questions remain unanswered: How unique or how common are the protein-ligand interactions observed in a given drug design project when compared to all complexed structures in the protein data bank? Which interaction patterns might explain the affinity of a tool compound toward unwanted targets? To answer these questions and to enable the systematic and comprehensive study of protein-ligand interactions, we introduce PROLIX (Protein Ligand Interaction Explorer), a tool that uses sophisticated fingerprint representations of protein-ligand interaction patterns for rapid data mining in large crystal structure databases. Our implementation strategy pursues a branch-and-bound technique that enables mining against thousands of complexes within a few seconds. Key elements of PROLIX include (i) an intuitive interface that enables users to formulate complex queries easily, (ii) exceptional speed for results retrieval, and (iii) a sophisticated results summarization. Herein we describe the algorithms developed to enable complex queries and fast retrieval of search results, as well as the intuitive aspects of the user interface and summarization viewer. 相似文献