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排序方式: 共有209条查询结果,搜索用时 31 毫秒
31.
The current research was undertaken to investigate the structural, electrical, and optical properties of C20 fullerene decorated with different numbers of lithium (Li) atoms on its surface. The stability of the structure increased as the number of lithium atoms increased. Increasing the number of lithium atoms around C20 from one to four slightly increased the Eg (energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital). Increasing the number to five or six narrowed the Eg. The electrical properties such as ionization potential (I), electron affinity (A), chemical potential (μ), global hardness (η), global softness (γ), global electrophilicity (ω), and electronegativity (χ) were also calculated. The polarizability (α) and first hyperpolarizability (β0), which correspond to the linear optical and nonlinear optical properties, respectively, were also calculated. An intense increase in β0 was recorded as the effect of five Li atoms adsorbed onto the C20 surface. The results of this study can be used to design and fabricate nanomaterials with adjustable electro-optical properties. 相似文献
32.
Mohammad Ali Amrollahi Zohreh Kheilkordi 《Journal of the Iranian Chemical Society》2016,13(5):925-929
A convenient and direct approach has been developed for the preparation of bis(indole) derivatives by one-pot four-component condensing of indole, aldehydes and active methylene compounds in the presence of 12-tungstophosphoric acid in aqueous media under silent and ultrasound methods. The remarkable advantages are the simplicity of the experimental procedures, short reaction times and high yields with the green aspects by avoiding toxic catalysts and solvents. 相似文献
33.
The changes in stabilization energy upon the formation of intermolecular hydrogen, dihydrogen and lithium bond complexes between C2B3H7, LiH and HF have been investigated using MP2 method with aug-cc-pVDZ basis set. The interaction of HF with nido-C2B3H7 could occur through the formation of B–H?δ···+δH–F, C–H+δ···F?δ–H and B–C···H–F classical and non-classical hydrogen bonds. The B–C bonds in backbone of the C2B3H7 as electron donor interact with σ* orbital of HF as electron acceptor. Also interaction of LiH with nido-C2B3H7 resulted in B–C···Li–H and B–H···LiH lithium bonds as well as C–H···H–Li dihydrogen bond complexes. In some of these complexes, LiH interacts with B–C bonds. Results are indicating that more stable complexes belong to interaction of HF and LiH with backbone of the nido-C2B3H7. The AIM and NBO methods were used to analyze the intermolecular interactions; also the electron density at the bond critical point and the charge transfer of obtained complexes were studied. 相似文献
34.
Hodgson M Steininger G Razavi Z 《The Journal of the Acoustical Society of America》2007,121(4):2023-2033
Measurements made of the acoustical characteristics of, and occupied noise levels in, ten eating establishments are described. Levels to which diners and employees were exposed varied from 45 to 82 dB(A). From these levels and diner questionnaire responses, the number of customers present and average noise levels to which individual diners were exposed during their visits were estimated. These data, assumptions about the number of talkers per customer, and classical room-acoustical theory were used to deduce talker voice output levels. These varied from slightly above "casual" to "loud." An iterative model for predicting speech and noise levels in eating establishments, including the Lombard effect as described by a new, proposed model, was developed. With the measured noise levels as the target for prediction, optimization techniques were used to find best estimates of unknown prediction parameters--such as those defining the Lombard effect, the number of talkers per customer, and the average absorption per customer--with highly credible results. The prediction algorithm and optimal parameters constitute a novel model for predicting speech and noise levels--and thus speech intelligibility--in eating establishments, as a function of the number of customers, including a proven, realistic model of the Lombard effect. 相似文献
35.
Zohreh Khani Gilles Taillades Deborah J. Jones Jacques Rozière 《Journal of solid state chemistry》2009,182(4):790-208
Low temperature routes have been developed for the preparation of BaCe0.9Y0.1O2.95 (BCY10) and BaZr0.9Y0.1O2.95 (BZY10) in the form of nanoparticulate powders for use after densification as ceramic membranes for a proton ceramic fuel cell. These methods make use on the one hand of the chelation of metal (II), (III) and (IV) ions by acrylates (hydrogelation route) and on the other of the destabilisation and precipitation of micro-emulsions. Both routes lead to single phase yttrium doped barium cerate or zirconate perovskites, as observed by X-ray diffraction, after thermal treatment at 900 °C for 4 h for BCY10 and 800 °C for BZY10. These temperatures, lower than those usually used for preparation of barium cerate or zirconate, lead to oxide nanoparticles of size <40 nm. Dense ceramics (?95%) are obtained by sintering BCY10 pellets at 1350 °C and BZY10 pellets at 1500 °C for 10 h. The water uptake of compacted samples at 500 °C is 0.14 wt% for BCY10 and 0.26 wt% for BZY10. Total conductivities in the range 300-600 °C were determined using impedance spectroscopy in a humidified nitrogen atmosphere. The total conductivity was 1.8×10−2 S/cm for BCY10 and 2×10−3 S/cm for BZY10 at 600 °C. The smallest perovskite nanoparticles and highest conductivities were obtained by hydrogelation of precursor barium, zirconium, cerium and yttrium acrylates. 相似文献
36.
Hojati Z Milne C Harvey B Gordon L Borg M Flett F Wilkinson B Sidebottom PJ Rudd BA Hayes MA Smith CP Micklefield J 《Chemistry & biology》2002,9(11):1175-1187
The calcium-dependent antibiotic (CDA), from Streptomyces coelicolor, is an acidic lipopeptide comprising an N-terminal 2,3-epoxyhexanoyl fatty acid side chain and several nonproteinogenic amino acid residues. S. coelicolor grown on solid media was shown to produce several previously uncharacterized peptides with C-terminal Z-dehydrotryptophan residues. The CDA biosynthetic gene cluster contains open reading frames encoding nonribosomal peptide synthetases, fatty acid synthases, and enzymes involved in precursor supply and tailoring of the nascent peptide. On the basis of protein sequence similarity and chemical reasoning, the biosynthesis of CDA is rationalized. Deletion of SCO3229 (hmaS), a putative 4-hydroxymandelic acid synthase-encoding gene, abolishes CDA production. The exogenous supply of 4-hydroxymandelate, 4-hydroxyphenylglyoxylate, or 4-hydroxyphenylglycine re-establishes CDA production by the DeltahmaS mutant. Feeding analogs of these precursors to the mutant resulted in the directed biosynthesis of novel lipopeptides with modified arylglycine residues. 相似文献
37.
Reza Yousefi Sadaf Aghevlian Fatemeh Mokhtari Hamidreza Samouei Mehdi Rashidi S. Masoud Nabavizadeh Zohreh Tavaf Zahra Pouryasin Ali Niazi Reza Faghihi Mohammad Mehdi Papari 《Applied biochemistry and biotechnology》2012,167(4):861-872
The development of resistance and unwanted harmful interaction with other biomolecules instead of DNA are the major drawbacks for application of platinum (Pt) complexes in cancer chemotherapy. To conquer these problems, much works have been done so far to discover innovative Pt complexes. The objective of the current study was to evaluate the anti cancer activities of a series of four and five-coordinated Pt(II) complexes, having deprotonated 2-phenyl pyridine (abbreviated as C^N), biphosphine moieties, i.e., dppm?=?bis(diphenylphosphino) methane (Ph2PCH2PPh2) and dppa?=?bis(diphenylphosphino)amine (Ph2PNHPPh2), as the non-leaving carrier groups. The growth inhibitory effect of the Pt complexes [Pt(C^N)(dppm)]PF6: C 1 , [Pt(C^N)(dppa)]PF6: C 2 , and [Pt(C^N)I(dppa)]: C 3 , toward the cancer cell lines was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. In addition, the florescence quenching experiments of the interaction between human serum albumin (HSA) and the Pt complexes were performed in order to obtain the binding parameters and to evaluate the denaturing properties of these complexes upon binding to the general carrier protein of blood stream. The structure?Cactivity relationship studies reveal that four-coordinated Pt complexes C 1 and C 2 with both significant hydrophobic and charge characteristics, not only exhibit strong antiproliferation activity toward the cancer cell lines, but also they display lower denaturing effect against carrier protein HSA. On the other hand, five-coordinated C 3 complex with the unusual intermolecular NH??Pt hydrogen binding and the intrinsic ability for oligomerization, exhibits poor anticancer activity and strong denaturing property. The current study reveals that the balance between charge and hydrophobicity of the Pt complexes, also their hydrogen binding abilities and coordination mode are important for their anticancer activities. Moreover, this study may suggest C 1 and C 2 as the potential template structures for synthesis of new generation of four-coordinated Pt complexes with strong anticancer activities and weak denaturing effects against proteins. 相似文献
38.
Majid Kolahdoozan Roozbeh Javad Kalbasi Zohreh S. Shahzeidi 《Monatshefte für Chemie / Chemical Monthly》2012,38(2):325-334
Abstract
Poly(4-vinylpyridine)/SBA-15 (P4VP/SBA-15) composites with various amounts of SBA-15 were prepared and characterized. The physical and chemical properties of P4VP/SBA-15 were investigated by XRD, BET, FT-IR, TGA, and SEM techniques. The catalytic performance of each material was determined for the Knoevenagel condensation reaction between carbonyl compounds and ethyl cyanoacetate in the presence of water as a solvent. The effects of reaction temperature, the amount of catalyst, amount of support, solvent, and the amount of benzoyl peroxide during the synthesis of P4VP/SBA-15 were investigated, as well as the recyclability of the heterogeneous composite. The catalyst used for this synthetically useful transformation showed a considerable level of reusability as well as very good activity. This reaction occurred rapidly when water was used as a solvent, so we assume it to be a green reaction. 相似文献39.
Zohreh Hamnabard Zahra Khalkhali Shamsi Sadat Alavi Qazvini Saeid Baghshahi Amir Maghsoudipour 《Journal of luminescence》2012,132(5):1126-1132
Four glasses in ZnO–SiO2–B2O3 ternary system were prepared by the melt quenching method with the objective of optimizing sub-nanosecond emission over the UV region of zinc borosilicate glasses used in superfast scintillators. The effect of vanadium addition and heat treatment on phase formation, microstructure and photoluminescence properties of the glasses was characterized by means of DTA, XRD, SEM and fluorescence spectrophotometer. Vanadium contributed to the near-band-edge emission in two ways, by introducing donor levels in the energy band of ZnO particles and by facilitating the precipitation of ZnO and willemite crystals. Furthermore, nucleation of willemite and zinc oxide phases, which are both the origins of the intense emission bands in the UV region, was facilitated with increasing either the time or temperature of heat treatments. Photoluminescence spectra showed the elimination of the visible emission band which is favorable in scintillating glasses. 相似文献
40.
Akbar Mohebbi Zohreh Asgari Mehdi Dehghan 《Communications in Nonlinear Science & Numerical Simulation》2012,17(12):4602-4610
In this work we investigate the numerical solution of Jaulent–Miodek (JM) and Whitham–Broer–Kaup (WBK) equations. The proposed numerical schemes are based on the fourth-order time-stepping schemes in combination with discrete Fourier transform. We discretize the original partial differential equations (PDEs) with discrete Fourier transform in space and obtain a system of ordinary differential equations (ODEs) in Fourier space which will be solved with fourth order time-stepping methods. After transforming the equations to a system of ODEs, the linear operator in JM equation is diagonal but in WBK equation is not diagonal. However for WBK equation we can also implement the methods such as diagonal case which reduces the CPU time. Comparing numerical solutions with analytical solutions demonstrates that those methods are accurate and readily implemented. 相似文献