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排序方式: 共有140条查询结果,搜索用时 15 毫秒
1.
K.P.B. Moosad P. Krishnakumar G. Chandrashekar R.M.R. Vishnubhatla 《Applied Acoustics》2007,68(10):1280-1285
Class IV flextensional transducers (FTs) are the best-known FTs in literature. These are light-weight projectors (compared to the conventional Tonpilz designs) with capability for high power delivery at low frequencies. The resonance frequencies of this type of transducers are known to be dominantly dependent on the characteristics of the outer shell than on the driver stack. Consequently, the method of achieving fine-tuning of the transducer by modifying the characteristics of the stack, as practiced in the case of Tonpilz designs, is not very effective. This paper describes a method for fine-tuning of the frequency of a Class IV FT, which involves only a modification of a pair of small components used for coupling the stack to the transducer. The effectiveness of the method is examined by finite element modelling using the package ATILA, in the case of a 3 kHz aluminium shell transducer. Experimental results are also presented. 相似文献
2.
Yu JQ Wu HC Ramarao C Spencer JB Ley SV 《Chemical communications (Cambridge, England)》2003,(6):678-679
A robust and recyclable palladium catalyst [Pd0EnCat] has been prepared by ligand exchange of polyurea-encapsulated palladium(II) acetate with formic acid, resulting in deposition of Pd(0) in the support material; Pd0EnCat is shown to be a highly efficient transfer hydrogenation catalyst for chemoselective reduction of a wide range of aryl ketones to benzyl alcohols. 相似文献
3.
[reaction: see text] Pd nanoparticles (approximately 2 nm in size) microencapsulated in polyurea is an efficient and recyclable catalyst for reductive ring-opening hydrogenolysis of epoxides, using either HCOOH/Et(3)N or H(2) as a hydrogen donor. 相似文献
4.
S Chandrasekhar G Chandrashekar B Nagendra Babu K Vijeender K Venkatram Reddy 《Tetrahedron letters》2004,45(28):5497-5499
A facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes. This reaction is performed using inert polymethylhydrosiloxane as the hydride source and B(C6F5)3 as the catalytic activator of the PMHS. 相似文献
5.
Sridevi B Narayanan SJ Chandrashekar TK Englich U Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(14):2554-2563
A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the alpha-alpha coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Nil(II), Cu(II), and Co(II) with the participation of all heteroatoms in the coordination. However, Rh(I) ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni(II) and Rh(I) complexes reveal square planar geometry completed by two CO molecules for Rh(I). The EPR spectra of the paramagnetic that Cu(II) and Col(II) complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the Cu(II) complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO. 相似文献
6.
Venkatraman S Anand VG Pushpan SK Sankar J Chandrashekar TK 《Chemical communications (Cambridge, England)》2002,(5):462-463
Successful syntheses of two new aromatic core modified oxybenziporphyrins by a simple '3 + 1' methodology and the first aromatic core modified oxybenziporphyrin palladium complex are reported. 相似文献
7.
Anand VG Venkatraman S Rath H Chandrashekar TK Teng W Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2282-2290
Modified octaphyrins with 34pi electrons have been synthesized and characterized following a simple synthetic methodology. An acid-catalyzed alpha,alpha coupling of tetrapyrranes containing furan, thiophene and selenophene rings resulted in the formation of the respective octaphyrins in relatively good yield. Solution studies by (1)H NMR and 2D NMR methods and single crystal Xray structural characterization reveal an almost flat structure with two heterocyclic rings inverted. Specifically, in 14 two selenophene rings (one on each biselenophene unit) are inverted while in 15 two furan rings (one on each bifuran unit) are inverted when the meso substituent are mesityl groups. On changing the mesityl substituent to m-xylyl group as in 19, the location of ring inversion shifts to pyrrole rings (one on each bipyrrole unit) indicating the dependence of structure on the meso substituents. UV/Vis studies, both in freebase and protonated forms reveal typical porphyrinic character and the aromatic nature of the octaphyrins. The Deltadelta values evaluated by (1)H NMR spectroscopy also support their aromatic nature. The protonated forms of octaphyrins bind TFA anion in a 1:2 ratio. The TFA anions are located one above and below the plane of the octaphyrin macrocycle and they are held by weak electrostatic NH-O interactions similar to that observed for protonated rubyrins. However, in the present case, there is an additional non-electrostatic CH-O interaction involving beta-CH of the inverted heterocyclic ring and the carbonyl oxygen of the TFA. Furthermore, inter molecular interactions between the Cbond;H of the meso-mesityl group and the fluorine of CF(3) group of bound TFA leads to the formation of one-dimensional supramolecular arrays with interplanar distance of 13 A between two octaphyrins. 相似文献
8.
Parmeswaran D Pushpan SK Srinivasan A Ravi Kumar M Chandrashekar TK Ganesan S 《Photochemistry and photobiology》2003,78(5):487-495
The core modification of expanded porphyrins has been proved to have better photochemical properties, which are favorable for photodynamic therapy (PDT) applications. In this context, this study was aimed to investigate the in vitro and in vivo photodynamic activity of one such core-modified expanded porphyrin, namely, ammonium salt of 5,10,15,20-tetrakis-(meso-p-sulfonato phenyl)-25,27,29-trithia sapphyrin. For the in vitro studies, human erythrocytes were used as a membrane semimodel system to investigate the partitioning ability and drug-uptake characteristics. The partition studies on the membrane semimodel system revealed that maximum partitioning occurs at 12 microgm/mL concentration, and from the drug-uptake studies it is observed that maximum amount of the sensitizer is bound to the erythrocyte membranes during a 45 min incubation period. Photohemolysis studies at different concentrations of the sensitizer and exposure time showed maximum damage at 5 microgm/mL and 30 min exposure time. In vivo studies were performed on 7,12-dimethylbenz(a)nthracene-induced superficial squamous cell carcinoma on mouse skin. The sensitizer at a concentration of 2.5% in 2.0% dimethyl sulfoxide was applied topically on the tumor spot. After 1 h incubation the tumor spot was exposed to laser irradiation from Nd-YAG laser at its second harmonic wavelength of 532 nm. The photodynamic efficacy was estimated by tumor volume measurements at regular intervals after the treatment. One month after PDT exposure a 3.9-fold decrease in the tumor volume was observed with respect to the tumor volume before treatment. The treatment efficacy was further confirmed by histological and fluorescence spectroscopic evaluations of the tissue biopsy sample from the treated area. The results of our study suggest that the ammonium salt of 5,10,15,20-tetrakis-(meso-p-sulfonato phenyl)-25,27,29-trithia sapphyrin may find possible applications in the new modality of cancer treatment. 相似文献
9.
The automatic optimization of flow control devices is a delicate issue because of the drastic computational time related to unsteady high‐fidelity flow analyses and the possible multimodality of the objective function. Thus, we experiment in this article the use of kriging‐based algorithms to optimize flow control parameters because these methods have shown their efficiency for global optimization at moderate cost. Navier–Stokes simulations, carried out for different control parameters, are used to build iteratively a kriging model. At each step, a statistical analysis is performed to enrich the model with new simulation results by exploring the most promising areas, until optimal flow control parameters are found. This approach is validated and demonstrated on two problems, including comparisons with similar studies: the control of the flow around an oscillatory rotating cylinder and the reduction of the intensity of a shock wave for a transonic airfoil by adding a bump to the airfoil profile. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
Chandrashekar Ramarao Ramadevi Nandipati Rajasekhar Navakoti Ramanjaneyulu Kottamasu 《Tetrahedron letters》2012,53(6):637-640
1,2-Dihydroxy benzenes have been protected as cyclic diacetals using 2,3-butane dione. These diacetals are extremely robust and can be further chemically diversified and resolved with chirality embedded in the 1,4-dioxane ring attached to the aromatic back bone as a result of the anomeric effect. These systems can serve as ligands, auxiliaries or organocatalysts for asymmetric synthesis. 相似文献