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21.
The incorporation of (±)-norcoclaurine, (±)-coclaurine, (±)-N-methylcoclaurine and dehydro-N-methylcoclaurine into nortiliacorinine A in Tiliacora racemosa colebr has been studied and specific utilisation of the (±)-coclaurine demonstrated. The evidence supports oxidative dimerization of two coclaurine units to give nortiliacorinine A. Experiments with (±)-N-methylcoclaurine and (±)-[1-3H, N-14CH3]N-methylcoclaurine established that only one N-methylcoclaurine unit is specifically utilised to constitute that “half” of the base which had phenolic OH group in the benzylic portion and further demonstrated that the H atom at the asymmetric centre in the 1-benzylisoquinoline precursor is retained in the bioconversion into nortiliacorinine A. Double labelling experiment with (±)-[1-3H, 6,0-14CH3]N-methylcoclaurine showed that O-Me function of the precursor is lost in the bioconversion into nortiliacorinine A. Parallel feedings of (+)-(S)- and (-)-(R)-N-methyl-coclaurines and (-)-(S)-, and ( + )-(R)-coclaurines revealed that the stereo-specificity is maintained in the biosynthesis of nortiliacorinine A from 1-benzylisoquinoline precursors and established ‘S,S’-configuration at the two asymmetric centres in nortiliacorinine A. 相似文献
22.
Underpotential deposition (UPD) of metals is analysed from the perspective of phenomeno-logical and statistical thermodynamic
considerations; the parameters influencing the UPD shift have been quantitatively indicated using a general formalism. The
manner in which the macroscopic properties pertaining to the depositing ions and solvent dipoles and the nature of the metallic
substrate influence the UPD process are highlighted; earlier correlations of the UPD shift with the work function differences
are rationalised. Anion-induced phase transitions which manifest as sharp peaks in experimental cyclic voltammograms are discussed
using statistical thermodynamic models. 相似文献
23.
J. D. Sudha C. K. S. Pillai 《Journal of polymer science. Part A, Polymer chemistry》2003,41(2):335-346
Hydrogen‐bonded aromatic–aliphatic polyester–amides (PEAs) were prepared by solution/melt polycondensation of aromatic–aliphatic amidodiols 1,4‐bis(4‐hydroxybutyramide)benzene (BHBB), 1,4‐bis(5‐hydroxy pentamide)benzene, 1,4‐bis(6‐hydroxyhexamide)benzene, 1,4‐bis(4‐hydroxybutyramidexylene), 1,4‐bis(5‐hydroxypentamidexylene, 1,4‐bis(4‐hydroxybutyramide)benzene, and 1,4‐bis(6‐hydroxyhexamidexylene) with terephthaloyl chloride/dimethyl terephthalate. Aromatic–aliphatic amido diols were prepared by the aminolysis of γ‐butyrolactone, δ‐valerolactone, and ?‐caprolactone with aromatic diamines such as paraphenylene diamine and paraxylene diamine. The monomers and polymers were characterized by chemical analysis (hydroxyl value and elemental analysis), Fourier transform infrared spectroscopy, 1H NMR, and 13C NMR. The thermal‐ and phase‐transition behaviors of the polymers were investigated by differential scanning calorimetry in combination with hot‐stage optical microscopy. Crystallinity of polymers was examined with wide‐angle X‐ray diffraction. The polymers exhibited liquid crystallinity with layered structures formed by self‐organization of the hetero intermolecular hydrogen‐bonded networks indicating smectic phases except for PEAs prepared from BHBB. The hydrogen atom of the phenyl‐substituent group forces the neighboring carbonyl groups out of plane of the rings preventing formation of layered structures in the case of BHBB. The PEAs retained intermolecular hydrogen bonding even in the mesomorphic state, and variations in the hydrogen‐bonded lamellae/micelles might be responsible for the variations from one smectic to another texture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 335–346, 2003 相似文献
24.
Bhagwant S. Despande Sudha S. Ambedkar Jaiprakash G. Shewale 《Applied biochemistry and biotechnology》1996,60(3):245-250
A simple method based on Schiff’s base formation betweenp-dimethylaminobenzaldehyde and cephalosporin C is developed for estimation of cephalosporin C. The calibration curve was linear
up to 500 μg of cephalosporin C. The application of the method in monitoring bioconversion of cephalosporin C to glutaryl-7-amino
cephalosporanic acid is described. 相似文献
25.
A. Reginiv R. Kaur N. Sudha S. C. Menon H. B. Singh 《Journal of Chemical Sciences》1995,107(4):431-442
A range of novel bi-, tri- and multidentate organotellurium ligands containing Te and N donor atoms and their derivatives
have been synthesised. The synthetic strategy involves telluration of orthochelating, monoanionic substrates derived from
the following arylamines: N,N-dimethylbenzylamine, (S)-(-)-N,Ndimethyl-1-phenethylamine, N,N-dimethylnaphthylamine, (N,N-di-methylaminomethy
l) ferrocene, tricarbony1(N, N-dimethylbenzenemethanamine) chromium and 2-(3-thienyl)-pyridine. In addition novel chiral hybrid
Schiff base ligands have been prepared by the condensation reaction of bis(o-formylphenyl) telluride ando-butyltellurobenzaldehyde with (R)-(+)-l-phenethylamine and (1R, 2S)-(-)-norephedrine. 相似文献
26.
Specific incorporation of didehydroreticuline and reticuline into (±)- (+)-, and (-)-tetrahydropalmatines in Cocculus laurifolius and of (R)- and (S)-reticulines into (R)- and (S)-tetrahydropalmatines respectively has been demonstrated. Feeding of[l-3H, 4'-methoxy-14C]reticuline suggested that reticuline was not converted in the plants into didehydroreticuline and racemisation of optically active forms of tetrahydropalmatine did not take place via dehydrotetrahydropalmatine 相似文献
27.
The incorporation of (±)-norlaudanosoline, norprotosinomenine, nororientaline, norlaudanidine, reticuline and laudanosine into tetrahydropalmatine and palmatine has been studied, and specific utilization of reticuline demonstrated. Feeding of (±)-[N-methyl-14C] reticuline showed that C atom 8 of tetrahydropalmatine and palmatine are formed by oxidative cyclisation of the N-Me group of reticuline. Parallel experiments with (R)-; and (S)-, reticulines demonstrated specific incorporation of (R)- isomer into these bases. Feeding experiments also revealed that the plants can convert tetrahydropalmatine into palmatine with high efficiency. 相似文献
28.
Dattatray J. Late Soumen Karmakar Mahendra A. More Sudha V. Bhoraskar Dilip S. Joag 《Journal of nanoparticle research》2010,12(7):2393-2403
Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show
that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim
plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling
phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and
also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic
devices. 相似文献
29.
The solubility of a water molecule in a binary mixture of nonpolar cyclohexane and quadrupolar benzene is studied with the ab initio method. A novel self-consistent reaction field theory that properly accounts for benzene quadrupole moments in the continuum solvent framework is used to describe the solvation effects of the solvent mixture. The free energy of transfer from pure cyclohexane to the mixture solvent is obtained with the neglect of nonelectrostatic contributions. A reasonable agreement with experiments indicates that the theoretical method presented here provides a promising approach to electronic structure calculations in quadrupolar solvents and their mixtures with nonpolar solvents. 相似文献
30.
Results are reported of measurements of the glass transition temperature (Tg), conductivity and density (d) for glasses of the AsSbSe system, with compositions (As, Sb)40Se60 and AsxSb15Se85?x. The results are compared with glasses of similar compositions of the AsxSe100?x about compositions in the GexSb15Se85?x and AsxSe100?x glasses, in the case of AsxSb15Se85?x glasses, the As-rich compositions exhibit higher values of Tg and d compared to the stoichiometric composition As25Sb15Se60. These results are discussed in the light of a chemically ordered structural arrangement in these glasses. 相似文献