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951.
Palladium-catalyzed cross-coupling of vinylic tellurides and potassium vinyltrifluoroborate salt: synthesis of 1,3-dienes 总被引:1,自引:0,他引:1
Here we report an ultrasound-assisted synthesis of stereodefined 1,3-dienes by Suzuki-Miyaura cross-coupling reactions of vinylic tellurides and potassium β-styryl trifluoroborate salt. 相似文献
952.
Froimowitz M Wu KM Rodrigo J George C 《Journal of computer-aided molecular design》2000,14(2):135-146
Molecular mechanics calculations using MM3-92 and ab initio quantum mechanical calculations using SPARTAN 5.0 were performed on the structurally similar PCP and BTCP, in which only the latter has a cocaine-like pharmacological profile as a dopamine reuptake blocker. Calculations were also performed on BTCP analogs with a methyl group in various positions of the cyclohexane ring. The results for the cis-2-methyl compound, which retains good pharmacological activity, allowed us to determine that an aryl-axial conformer is the biologically active form for at least some of the compounds in this series. However, an aryl-equatorial conformer presents the identical pharmacophore, as shown by superposition of the two conformers. X-ray crystallographic structures were also obtained for BTCP and related compounds with a 2-methyl group on the cyclohexane ring, with reasonable agreement between the computational and experimental results. Superposition studies were performed with two rigid analogs of cocaine which illustrate the optimal orientations of the ammonium hydrogen for monoamine transporters. There is excellent agreement between a `back-bridged' cocaine analog that is optimal as a dopamine reuptake blocker and the previously proposed biologically active conformer of methylphenidate. However, BTCP is found to be a better fit to the `front-bridged' cocaine analog that is optimal for a serotonin reuptake blocker. 相似文献
953.
Petoral RM Wermelin K Dahlstedt E Hellberg J Uvdal K 《Journal of colloid and interface science》2005,287(2):388-393
Tetrathiafulvalene (TTF) derivative substituted with two butyl- and two dodecylthiol chains is adsorbed on polycrystalline gold. The TTF-derived thiol adsorbates were characterized by ellipsometry, contact angle goniometry, infrared and X-ray photoelectron spectroscopy and cyclic voltammetry. The molecule is strongly anchored on the gold surface through the sulfur terminating the alkylthiol chains. On the average, the TTF moiety is oriented extended away from the gold surface. The topmost layer of the film containing the dibutyl chains is disordered with gauche defects. The molecule was organized with majority of the alkylthiol chains bound to the gold surface. There are indications of pinholes in the monolayer due to steric hindrance of the bulky TTF rings. The molecular systems consisting of an electroactive pi-system such as TTF, are promising for thin-film field effect transistor application. 相似文献
954.
Jairo Quiroga Braulio Insuasty Rodrigo Abonia Pedro Hernndez Justo Cobo Manuel Nogueras Adolfo Snchez John Nicolson Low 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1460-1461
The title compound, C25H19NO4S, (IV), was produced by a cyclocondensation reaction similar to that which had previously produced an unexpected product, thus giving a novel route for such reactions. The structure of (IV) contains two S(6) motifs formed by strong intramolecular O—H?O hydrogen bonds. Weak C—H?O hydrogen bonds form primary C(11), R(7) and R(8) motifs which combine to form a complex three‐dimensional network. 相似文献
955.
Rodrigo E Palacios Gerdenis Kodis Stephanie L Gould Linda de la Garza Alicia Brune Devens Gust Thomas A Moore Ana L Moore 《Chemphyschem》2005,6(11):2359-2370
An artificial photosynthetic reaction center consisting of a carotenoid (C), a dimesitylporphyrin (P), and a bis(heptafluoropropyl)porphyrin (P(F)), C-P-P(F) , and the related triad in which the central porphyrin has been metalated to give C-P(Zn)-P(F) have been synthesized and characterized by transient spectroscopy. These triads are models for amphipathic triads having a carboxylate group attached to the P(F) moiety; they are designed to carry out redox processes across lipid bilayers. Triad C-P-P(F) undergoes rapid singlet-singlet energy transfer between the porphyrin moieties, so that their excited states are in equilibrium. In benzonitrile, photoinduced electron transfer from the first excited singlet state of P and hole transfer from the first excited singlet state of P(F) yield the initial charge-separated state C-P(.) (+)-P(F) (.) (-). Subsequent hole transfer to the carotenoid moiety generates the final charge-separated state C(.) (+)-P-P(F) (.) (-), which has a lifetime of 1.1 mus and is formed with a quantum yield of 0.24. In triad C-P(Zn)-P(F) energy transfer from the P(Zn) excited singlet to the P(F) moiety yields C-P(Zn)-(1)P(F) . A series of electron-transfer reactions analogous to those observed in C-P-P(F) generates C(.) (+)-P(Zn)-P(F) (.) (-), which has a lifetime of 750 ns and is formed with a quantum yield of 0.25. Flash photolysis experiments in liposomes containing an amphipathic version of C-P(Zn)-P(F) demonstrate that the added driving force for photoinduced electron transfer in the metalated triad is useful for promoting electron transfer in the low-dielectric environment of artificial biological membranes. In argon-saturated toluene solutions of C-P-P(F) and C-P(Zn)-P(F) , charge separation is not observed and a considerable yield of triplet species is generated upon excitation of the porphyrin moieties. In both triads triplet energy localized in the P(F) moiety is channeled to the carotenoid chromophore by a triplet energy-transfer relay mechanism. Certain photophysical characteristics of these triads, including the sequential electron transfer and the triplet energy-transfer relay mechanism, are reminiscent of those observed in natural reaction centers of photosynthetic bacteria. 相似文献
956.
Christopher Glidewell John N. Low Justo Cobo Manuel Nogueras Adolfo Snchez Emerson Rengifo Rodrigo Abonia 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(6):o314-o317
In the title compound, C20H22N6, the molecules are linked into a chain of rings by N—H?N [H?N 2.16 Å, N?N 2.950 (3) Å and N—H?N 149°] and C—H?N [H?N 2.55 Å, C?N 3.481 (3) Å and C—H?N 165°] hydrogen bonds, and these chains are linked into sheets by means of C—H?π(pyrazole) interactions. 相似文献
957.
Guilherme M.O Barra Rodrigo L Oréfice Jose R.G Carneiro 《European Polymer Journal》2004,40(9):2017-2023
Incorporation of polyaniline (PAni) into thermoplastic elastomers can be used to produce materials that potentially combine the good mechanical properties and processability of thermoplastic elastomers with electrical, magnetic and optical characteristics of PAni. In this work, a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene copolymer (SEBS) was chemically modified by grafting a sulfonic group onto the chain backbone in order to promote higher levels of compatibility between the thermoplastic elastomer and polyaniline. The sulfonation process was performed by reacting SEBS with acetyl sulfate. Infrared spectroscopy and titration were used to monitor the amount of sulfonic groups successfully grafted on SEBS. Mechanical tests performed in sulfonated SEBS showed that sulfonation levels lower than 15% did not reduce substantially the mechanical properties of SEBS. PAni doped with dodecylbenzenesulfonic acid (PAni·DBSA), used in the preparation of the blends, was prepared by the “in situ doping polymerization” method. PAni·DBSA was then blended in solution with SEBS having different levels of sulfonation. The introduction of sulfonic group into the structure of SEBS improved coulombic interactions between the phases in the blend and enhanced compatibility. As a consequence, higher values of electrical conductivity (measured by the four-probe method) were achieved in blends with sulfonic groups grafted onto polymer chains. Concentrations as low as 20 wt% of PAni were able to lead to electrical conductivities of PAni·DBSA/sulfonated SEBS blends close to 1.2 S/cm. Optical micrographs of the blends showed that PAni·DBSA/sulfonated SEBS microstructure is composed of a very disperse group of small conducting particles. This type of microstructure would then be responsible for the enhanced electrical conductivity and low percolation threshold of PAni·DBSA/sulfonated SEBS, when compared to PAni·DBSA/SEBS blends. 相似文献
958.
[reaction: see text] o-Toluate anions generated via transmetalation from the corresponding tributyl stannane underwent a Michael addition-Dieckmann condensation sequence with various cyclohexenones. This protocol provides an efficient entry into complex polycyclic systems without the use of beta-alkoxy enones hitherto required for the reaction. 相似文献
959.
Reinaldo Calixto de Campos Rodrigo Araújo Gonalves Gisele Birman Tonietto Jos Marcus Godoy Geisamanda Pedrini Brando 《Microchemical Journal》2006,84(1-2):26-30
A new procedure for the speciation analysis of hydride forming elements using GFAAS as detector is proposed. The separation of the species is performed by HPLC and the eluent flow is merged with HCl and NaBH4 solutions moved by peristaltic pumps controlled by a flow injection apparatus. As the species emerges from the column, its respective hydride is formed and carried through the autosampler capillary to an Ir treated graphite tube pre-heated at 300 °C, where it is trapped. After the hydride collection, the autosampler arm is moved from the tube and atomization takes place. The sequence is repeated for the next emerging species. The feasibility of the system was evaluated for the speciation of As (III) and As (V) in waste water samples. The retention times were previously determined using a more concentrated mixed analytical solution and a quartz tube as atomizer. The analytical curves obtained by the proposed procedure showed similar slopes for both species as well as coefficient of regression better than 0.99. Limits of detection were 0.2 ng/mL for both species, 50 times better then the same assembly using a quartz tube atomizer. In the analysis of certified reference materials the sum of the As (III) and As (V) species concentrations were in close agreement with the arsenic concentration certified for total arsenic. 相似文献
960.
Rodrigo A. A. Munoz Cíntia S. Silva Paulo R. M. Correia Pedro V. Oliveira Lúcio Angnes 《Mikrochimica acta》2005,149(3-4):199-204
The determination of metals in lubricating oil has been used as an important means of preventing components failures, to provide environmental information, and to solve criminal issues. In this study derivative potentiometric stripping analysis (DPSA) was used for the simultaneous determination of copper and lead in lubricating oils of vehicular engines. The samples were completely digested in a focused microwave-assisted oven using a powerful oxidant mixture (HNO3, H2SO4, H2O2). The optimized heating program to digest about 1mL of lubricating oil takes 45minutes. The residual carbon content after digestion was below 0.3%m/m for all samples. Copper and lead were also determined by graphite furnace atomic absorption spectrometry (GFAAS), and the results obtained were in good agreement with those obtained by electrochemical measurements. Recoveries of 94–109 and 93–103%, for copper and lead, respectively, were obtained for new and used lubricating oil samples. 相似文献