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511.
Basudeb Achari Soumitra Bandyopadhyay Krishnakali Basu Satyesh C. Pakrashi 《Tetrahedron》1985,41(1):107-110
Aristolindiquinone () , the first naturally occurring 8-methyl-juglone earlier isolated from has been synthesised from -allyl--cresol in 7% overall yield. 相似文献
512.
Straight SD Andréasson J Kodis G Bandyopadhyay S Mitchell RH Moore TA Moore AL Gust D 《Journal of the American Chemical Society》2005,127(26):9403-9409
A molecular triad consisting of a porphyrin (P) covalently linked to two photochromes-one from the dihydroindolizine family (DHI) and one from the dihydropyrene family (DHP)-has been synthesized and found to act as either a molecular AND logic gate or an INHIBIT gate, depending on the inputs and initial state of the photochromes. The basis of these functions is quenching of porphyrin fluorescence (output of the gates) by the photochromes. The spiro form of DHI does not quench porphyrin fluorescence, whereas its betaine isomer strongly quenches by photoinduced electron transfer. DHP also quenches porphyrin fluorescence, but its cyclophanediene isomer does not. The triad has been designed using suitable energetics and electronic interactions, so that although these quenching phenomena may be observed, independent isomerization of the attached photochromes still occurs. This makes it possible to switch porphyrin fluorescence on or off by isomerization of the photochromes using various combinations of inputs such as UV light, red light, and heat. 相似文献
513.
Preparation of pyridine derivatives of ReCl3(NO) viz. (pyH)2ReCl5(NO), pyH[ReCl4py(NO)], H[ReCl4py(NO)], K[ReCl4py(NO)], Ag[ReCl4py(NO)] and [ReCl3py2(NO)] are described. All these compounds are stable solids. They are characterised by their analytical composition, spectral data, conductance and magnetic moment values. 相似文献
514.
Avijit Banerji Debasish Bandyopadhyay Bidyut Basak Alain Neuman 《Tetrahedron letters》2006,47(23):3827-3830
A series of cycloadducts possessing unusual flipping modes have been isolated from the 1,3-dipolar cycloaddition of 3,4,5,6-tetrahydropyridine N-oxide to piperidides of cinnamic acid and para-substituted cinnamic acids and these were analyzed by X-ray crystallography to reveal novel solid-state structures. The presence of two different flippomers arising due to flipping of the six/five bicyclic ring was confirmed both in solid state and in solution. This is the first observation of 1,3-dipolar cycloadducts having two different flippomers arising due to flipping of the isoxazolidine ring. 相似文献
515.
516.
P.L. Majumder S. Joardar B.N. Dinda D. Bandyopadhyay S. Joardar A. Basu 《Tetrahedron》1981,37(6):1243-1248
19-Epi-(+)-echitoveniline, a new indole alkaloid of the leaves ofAlstonia venenata R.Br., has been shown to possess the structure and absolute stereochemistry represented by 5b on the basis of spectral and chemical evidence. A mechanistic rationale for the dependence of the mode of LAH reduction of the δ-lactone 11 on its configuration at C-19 has been offered. The influence of the C-19 configuration on the chemical shift values of the C-16 carbomethoxy protons in the 19-aroyloxy-(+)-and (?)-vincadifformine alkaloids has been discussed. 相似文献
517.
K. Bandyopadhyay K. Bhattacharyya A. K. Bhattacharya 《International journal of quantum chemistry》2002,88(6):691-700
We exploit the interrelation among the parameters embedded in the maximum entropy ansatz to develop a scheme for obtaining accurate estimates of the ground‐state energy and wave function of systems for which the potential is represented by a rational function. Our scheme reduces an N‐parameter optimization problem to a two‐parameter one, leading to considerable simplification of the prevalent strategy. An indirect route for the study of excited states is also sketched. Test calculations on hydrogenic systems subject to strong or superstrong radial magnetic fields with and without electric field reveal the advantages of our approach. Additional studies on 1‐D anharmonic oscillators affirm its workability and generality. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
518.
Mitchell RH Blunden R Hollett G Bandyopadhyay S Williams RV Twamley B 《The Journal of organic chemistry》2005,70(2):675-680
Ground state energies (DFT) and 1H and 13C NMR chemical shifts are calculated for the conformers of 13-methyl-2,6-dithia[7]metacyclophane (1), and the results are compared with X-ray structural data and variable-temperature NMR data, including the determination of the activation barrier. Calculations predict the correct low energy conformer with good agreement with chemical shifts, bond distances, and angles. VT NMR data for the 10-tert-butyl-substituted derivative 2 indicate that it undergoes the same conformational equilibria as 1. This paper should enhance the confidence that organic chemists have in calculations to satisfactorily predict conformer energies. 相似文献
519.
Aravinda S Shamala N Bandyopadhyay A Balaram P 《Journal of the American Chemical Society》2003,125(49):15065-15075
The structural characterization in crystals of three designed decapeptides containing a double d-segment at the C-terminus is described. The crystal structures of the peptides Boc-Leu-Aib-Val-Xxx-Leu-Aib-Val-(D)Ala-(D)Leu-Aib-OMe, (Xxx = Gly 2, (D)Ala 3, Aib 4) have been determined and compared with those reported earlier for peptide 1 (Xxx = Ala) and the all l analogue Boc-Leu-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe, which yielded a perfect right-handed alpha-helical structure. Peptides 1 and 2 reveal a right-handed helical segment spanning residues 1 to 7, ending in a Schellman motif with (D)Ala(8) functioning as the terminating residue. Polypeptide chain reversal occurs at residue 9, a novel feature that appears to be the consequence of a C-H.O hydrogen bond between residue 4 C(alpha)H and residue 9 CO groups. The structures of peptides 3 and 4, which lack the pro R hydrogen at the C(alpha) atom of residue 4, are dramatically different. Peptide 3 adopts a right-handed helical conformation over the 1 to 7 segment. Residues 8 and 9 adopt alpha(L) conformations forming a C-terminus type I' beta-turn, corresponding to an incipient left-handed twist of the polypeptide chain. In peptide 4, helix termination occurs at Aib(6), with residues 6 to 9 forming a left-handed helix, resulting in a structure that accommodates direct fusion of two helical segments of opposite twist. Peptides 3 and 4 provide examples of chiral residues occurring in the less favored sense of helical twist; (D)Ala(4) in peptide 3 adopts an alpha(R) conformation, while (L)Val(7) in 4 adopts an alpha(L) conformation. The structural comparison of the decapeptides reported here provides evidence for the role of specific C-H.O hydrogen bonds in stabilizing chain reversals at helix termini, which may be relevant in aligning contiguous helical and strand segments in polypeptide structures. 相似文献
520.
The compounds BaxLn1?xCoO3 (Ln = La, Nd, Sm and Dy) were prepared by ceramic technique. They were characterised for oxygen non-stoichiometry using isothermal DTA under varying oxygen partial pressure and TG in air. Isothermal DTA was also employed to study the catalytic activity of the compounds towards CO oxidation. For a given compound, the oxygen deficiency increases with increasing temperature and decreasing oxygen partial pressure. For a given BaxLn1?xCoO3 series, in general barium-rich compounds were more oxygen deficient. Isothermal DTA study of CO oxidation over BaxLa1?xCoO3 compounds at 600 K suggested that the carbon monoxide takes up lattice-labile oxygen from the sample and is oxidised to CO2, the percent CO conversion being higher for barium-rich samples. 相似文献