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91.
Two 1-aryl-3-cyclohexylurea and two 1-aryl-3-cyclohexylurethane with and without alkyl tail in aryl fragments were synthesized and their variable-temperature 1H NMR spectra in chloroform, DMSO and DMF were recorded. The temperature dependences of chemical shift of NH protons for all compounds have been observed. The type of dependence has been explained by the aggregation of molecules and formation of ionic structures. The formation of intermolecular complexes leads to possible formation of symmetrical N1 … … H ……N3 intramolecular hydrogen bond in urea fragment. As a result,4hJH1H3 trans-hydrogen bond scalar coupling constants have been observed for the first time in low molecular weight compounds using a simple one-dimensional 1H NMR experiment. The formation of strong intramolecular H-bond leads to π-conjugation not only with spacer but with phenyl ring too. It support the Gilli conception that RAHB formation is a result of π-electron delocalization. The presence in urea fragment of such kind interaction leads to formation of ionic structure, which has been detected by NMR and UV spectroscopies. The formation of ionic structure can explain the catalytic activity of such compounds and the mechanism of transformation in organic and bioorganic reactions in which involved the urea compounds. 相似文献
92.
Thermoresponsive covalent adaptive networks (CANs) have attracted increasing research attention because of their temperature-dependent reversibility, which endows the materials with versatile smart functionalities including intrinsic self-healability not available for traditional thermosets. Nevertheless, the associated reduction in creep resistance of this type of CANs limits their practical application. Here in this work, we demonstrate that the reversibility and dimensional stability can be combined via interlocking the thermoresponsive network with an ultraviolet-responsive network. The two types of networks are, respectively, crosslinked by orthogonal reversible Diels-Alder (DA) bonds and coumarin. Owing to the interlocked architecture, the latter single network can be uniformly distributed in the former, restricting the chain movement and enhancing the creep resistance even when the former is decrosslinked at elevated temperature as a result of retro-DA reaction. Meanwhile, the ultraviolet-responsive network plays the role of a photo-reversible switch. Its decrosslinking on exposure to 254 nm ultraviolet (UV) light and recrosslinking under a UV irradiation of 350 nm lead to repeated releasing and reimposing of the restraints on the neighboring thermoresponsive network. By using this smart habit, the material can either be conditionally self-healed with moderate healing efficiency or completely self-healed depending on whether only DA bonds or both DA bonds and coumarin are triggered. More importantly, the conflicting properties, that is, creep resistance and reversibility of the CANs are thus united. The proposed strategy provides a facile way for overcoming the weaknesses of CANs while maintaining the advantage. 相似文献
93.
An in-situ remediation procedure is proposed to remove Volatile Organic Compounds (VOCs) dissolved in groundwater. This is accomplished by injecton of air into a well, using a combined technique of air-lift pumping with a form of vapor stripping. When air is injected into a well, it causes water to be lifted and forces groundwater flow towards the well, creating a recirculating cleanup zone. During this process, VOCs are transferred from the contaminated water to the rising air bubbles inside the well. The air bubbles are separated from the liquid near the top of the well, and the VOC vapor is collected and treated. In this system, water is not permitted to be lifted to the ground surface. Rather, the water is diverted into the unsaturated zone through a series of drains that are installed beneath the root-zone. The water then, free of a portion of VOCs, infiltrates back to the water table. As water continues to circulate, the VOC concentrations are gradually reduced.The feasibility of the proposed method was analyzed using concepts of mass transfer of VOCs from water to air-bubbles. Calculations indicate that the method has promise because equilibrium partitioning between the contaminated liquid and the gas bubbles is rapidly established. 相似文献
94.
Jiajing Wang Danxia Chen Zhao Chen Guorong Fan Yutian Wu 《Journal of separation science》2010,33(8):1099-1108
A rapid CEC method with poly(butyl methacrylate‐co‐ethylene dimethacrylate‐co‐[2‐(methacryloyloxy)ethyl] trimethylammonium chloride) monolithic column has been developed for separation and determination of four coumarins (isopimpinelline, bergapten, imperatorin, and osthole) in Fructus cnidii extracts. The effect of polymerization condition including the monomers ratio and the porogens ratio were studied. The mobile‐phase composition, such as the composition of organic solvent, the concentration and pH of buffer, was also optimized. Under the same condition (50% ACN and 50% of a 10 mM sodium dihydrogen phosphate electrolyte at pH 4.95), in contrast to 25 min of analysis time in HPLC and 10 min of analysis time in pCEC, a fast separation of these analytes was achieved in less than 5 min in CEC. Method validation was developed in accordance with the analytical procedures. Intra‐ and interday precisions (RSD) for relative retention time and peak area were less than 1.69 and 4.63%, and LODs were lower than 0.5 μg/mL. Calibration curves of four compounds also showed good linearity (r2>0.995). The mean recoveries ranged between 93.91 and 98.65%. With this CEC system, the quality of F. cnidii extracts from various resources was evaluated by determining the contents of the four coumarins. 相似文献
95.
Konstantin A. Brylev Nikolay G. Naumov Alexander V. Virovets Sung-Jin Kim Vladimir E. Fedorov 《Journal of Cluster Science》2009,20(1):165-176
Three novel coordination polymers K5[MnMo6Se8(CN)6] · 8H2O (1), (Me4N)4[{Mn(H2O)2}1.5Mo6Se8(CN)6] · 4H2O (2), and K3[{Mn2(H2O)4}Mo6Se8(CN)6] · 7H2O (3) have been synthesized by layering of a methanol solution of [Mn(salen)]CH3COO (salen–N,N′-bis(salicylidene)ethylenediamine) on an aqueous solution of K7[Mo6Se8(CN)6] · 8H2O. The compounds have been characterized by single-crystal X-ray diffraction analysis. All structures are based on negatively
charged porous polymer frameworks where CN groups of [Mo6Se8(CN)6]7− cluster complexes are coordinated to Mn2+ cations. Cavities in the frameworks are filled by additional cations and solvate water molecules. 相似文献
96.
Vadim V. Negrebetsky Peter G. Taylor Sergey Yu. Bylikin Alexander G. Shipov Yuri I. Baukov 《Journal of organometallic chemistry》2006,691(19):3976-3988
Eleven new silicon-substituted N-(dimethylsilylmethyl)- and N-(methylphenylsilylmethyl)amides and -lactams bearing a chiral carbon in the amide or lactam fragment, and containing the OSiC3X (X = Hal, OTf) coordination fragment have been synthesized and their structures determined in solution by spectroscopic means. These structures are consistent with the hypervalency model. Quantum chemical calculations adequately reflect correlations between the type of monodentate ligand X and the geometric parameters of the N-C-O-Si-X fragments.The activation parameters for enantiomerization and diastereomerization in these new compounds and the other related compounds were determined by the dynamic NMR (DNMR) method using full line-shape analysis. The free activation energy values in the absence of external nucleophiles vary from 9 to 27 kcal mol−1. The entropies of activation (ΔS#) are negative (−20 to −50 cal mol−1 K−1) in all cases except for the chloride derivatives of 4-phenyl-2-pyrrolidone and 4-oxazolidinone that have weaker intramolecular O → Si coordination. Irregular mechanisms of permutational isomerization were proposed on the basis of the DNMR data and the results of quantum-chemical calculations carried out by ab initio (HF) and DFT (PBE, B3PW91, 6-311++G(d,p)). Depending on the coordination environment at silicon, the mechanisms proposed involve either the dissociation of the Si-X bond followed by the Berry pseudorotation or similar in the intermediate or the cleavage of intramolecular O-Si bond with subsequent inversion at the silicon atom. The apparently simple pseudorotation mechanism involving only the pentacoordinate structures 1-21 does not appear to be favoured in any of the examples studied. 相似文献
97.
Elia J.L. Stoffman 《Tetrahedron》2010,66(25):4452-4461
4-Chloro-, 4-bromo- and 4-iodoserotonin derivatives were synthesized from 4-halo-5-oxyindoles, themselves derived from coumarins. Synthesis of the 4-iodoserotonins involved conjugate addition of an allyl group to a 5-iodocoumarin, followed by conversion of the allyl group into an aminoethyl unit. One of the iodoserotonin derivatives was converted into the toad alkaloid dehydrobufotenine, which was isolated as its hydroiodide. 相似文献
98.
Summary A number of coumarins, furocoumarins and pyranocoumarins were investigated using HPTLC and HPLC systems consisting of silica gel and binary and ternary solvents containing a polar modifier (acetonitrile, dioxane, diisopropyl ether, methyl ethyl ketone, ethyl acetate, 2-propanol or tetrahydrofuran) and a non-polar or weakly polar diluent (n-heptane or dichloromethane). The experimental results obtained on thin layers, under isocratic conditions, showed a linear relationship between the RM values and the log of the concentration of the polar modifier.The influence of the modifier and the individual substituents in the solute molecule on retention is presented as chromatographic spectra by plotting the RM and logk values against the mobile phase used.Preliminary communication of this work was presented at the 46th International Congress of Pharmaceutical Sciences, in Helsinki, Finland, 1–5 September, 1986. 相似文献
99.
The results of ab initio calculations at the MP2/6-31G(d) level of molecules of the series ClPXX′ (X, X′=C2H5, N(CH3)2, OCH3) and ClP(M)XX′ (M=O, S; X=CH3, ?CH3; X′=C2H5, OCH3) with total optimization of their geometry were presented. They were compared with the obtained earlier results of such calculations at the RHF/6-31G(d) level and with experimental 35Cl nuclear quadrupole resonance (NQR) spectra for these compounds. MP2/6-31G(d) calculations confirm non-inductive influence of heteroatoms on the geminal Cl atom in the non-linear three-atomic Cl–P–M groups. They agree to the conclusion that the abnormal correlation of the 35Cl NQR frequencies for the compounds studied at different X, X′ and M is caused, in general, by the P–Cl bond polarization under the action of the geminal atom partial charges directly through the field. The satisfactory conformity between the experimental 35Cl NQR frequencies and those estimated from 3p-components of the Cl atom valence p-orbitals calculated at the MP2/6-31G(d) level was obtained. 相似文献
100.
Anita Müller Matthias Krieger Bernhard Neumüller Kurt Dehnicke Jrg Magull 《无机化学与普通化学杂志》1997,623(7):1081-1087
Phosphaneimine and Phosphoraneiminato Complexes of Magnesium. The Crystal Structures of [MgBr1,25I0,75(Me3SiNPMe3)(OEt2)], [MgI2(Me3SiNPMe3)2], [Mg2I2(Me3SiNPMe2CH2)(Me3SiNPMe2CH2CH(Me)O)(OEt2)], and [MgBr(NPMe3)]4 · C7H8 By reactions of the silylated phosphaneimine Me3SiNPMe3 with the Grignard reagents EtMgBr and MeMgI, respectively, the carbanionic phosphoraneiminato derivatives [XMg(CH2PMe2NSiMe3)]n (X ? Br, I) can be isolated as main products. The by-products of these reactions, [MgBr1.25I0.75(Me3SiNPMe3)(OEt2)], [MgI2(Me3SiNPMe3)2] and [Mg2I2(CH2PMe2NSiMe3)(O(Me)CHCH2PMe2NSiMe3)(OEt2)] were identified by crystal structure determinations. The phosphoraneiminato complex [MgBr(NPMe3)]4 · C7H8 with hetero cubane structure is formed by a metathesis reaction of [ZnBr(NPMe3)]4 with RMgBr (R ? Ph. Mes). 相似文献