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21.
The stabilities of different isomers of C60Brn have been calculated for n = 2 to 12. A general stereochemical pattern which emerges is the tendency to form strings created by the edge sharing of C6Br2 hexagonal faces. Stable structures are formed if these strings form loops, thereby eliminating string ends, which may involve the creation of C6Br3 hexagonal faces. A particularly stable structure is formed at C60Br6 in which the loop forms a C10Br6 fragment with a pentagonal pyramidal arrangement of six bromine atoms. Two isomers of C60Br12 are also particularly stable. One isomer contains two of these Br6 pentagonal pyramids on opposite sides of the molecule, and the other isomer contains a single large loop wrapped around the middle of the molecule. 相似文献
22.
The products of hydrolysis of C60F48 (which contains six isolated double bonds) by either aq. acetone or aq. THF show that no more than twelve fluorines are replaced through nucleophilic substitution, as predicted by the recently identified S(N)2' mechanism. Subsequent HF elimination gives fragments containing a maximum of six epoxide oxygens. Calculated heats of formation of models for the possible initial hydroxy derivatives indicate that there is little energetic discrimination between them, so that a complex mixture is likely to be formed. Overall the data show that hydrolytic degradation of fluorofullerenes is less severe than believed previously, requires a specific motif, and explains the low susceptibility of C60F18 towards hydrolysis and the high stability of trannulenes. 相似文献
23.
Mary E. R. McHale Ann-Sofi M. Kauppila Joyce R. Powell Pablo Otero Jr. Melani Jayasekera William E. Acree Jr. 《Journal of solution chemistry》1996,25(3):295-302
Experimental solubilities are reported for benzil dissolved in six binary mixtures containing dibutyl ether with hexane, heptane, octane, cyclohexane, methylcyclohexane, and 2,2,4-trimethylpentane at 25°C. Results of these measurements are compared to the predictions of equations developed previously for solubility in systems of nonspecific interactions. The most successful equation in terms of goodness of fit involved a volume fraction average of the excess Gibbs energies relative to the Flory-Huggins model, and predicted the experimental solubilities in the six systems studied to within an overall average absolute deviation of 3.4% and with a maximum deviation of 6.0%. 相似文献
24.
Preparation and spectroscopic studies of some cyclic urea adducts of triphenyl-tin and -lead halides
1,3-Dimethyl-2-imidazolidinone (dimethylethylene urea, DMEU) and 1,3-di- methyl-3,4,5,6-tetrahydro-2(IH)-pyrimidinone (dimethylpropylene urea, DMPU) adducts of the type Ph3SnX·L (X = Cl, Br and I), Ph3PbX·L (X = Br, I), 3Ph3PbCl·2DMEU and 2Ph3PbCl · DMPU have been prepared and characterized. Assignments are made for ν(CO) and ν(CN) frequencies in the IR, and for skeletal frequencies observed in both the IR and Raman spectra in the range 400 to 100 cm?1 Infrared measurements show that the adducts are bound through the carbonyl oxygen, and are highly dissociated in dichloromethane solution. 1H and 119Sn or 207Pb NMR measurements reveal that ligand exchange, fast on the NMR time scale, occurs in solution. Coordination of the ligand causes a large upfield shift in the 119Sn or 207Pb resonances, but Ph3MI · L have shifts similar to those for the parent iodides, indicating almost complete dissociation. Thermodynamic parameters are reported for the dissociation of Ph3SnX · DMPU (X = Cl, Br) in CH2Cl2 solution. 相似文献
25.
A new procedure for simultaneous preconcentration, separation, and determination of permanganate, chromate and vanadate was developed for aqueous solutions containing p.p.b. levels of these anions (and molybdate). The presence of other (non-complexing) ions in p.p.m. concentrations did not interfere. The procedure consisted of reactive adsorption of all three anions as their reduced cations, on iron(II)-treated resin, followed by elution of vanadium(IV) with 0.01 M HNO3/H2O2, manganese(II) with 0.35 M HCl, and chromium(III) with 4M HCl. Concentration factors of 40 were obtained with 1-l “samples” 10 p.p.b. concentrations were determined with standard deviations of 4–5 % by a.a.s. and conventional spectrophotometry. 相似文献
26.
Quantum chemical CNDO /2 calculations for the conformational preference of the side chain of thioridazine as a function of angle indicated the crystallographically determined structure gave the lowest energy. There is also a small region of conformational flexibility within the first 90° of rotation of the side chain. This is commensurate with the results which we had obtained previously for our similar calculations for promazine and its Cl and CF3 derivatives, perazine and its Cl and CF3 derivatives, and for the hypothetical hitherto unknown N-piperidinopromazine and its Cl and CF3 derivatives. The conformational profile of thioridazine resembles that of the perazines. The calculated gross atomic populations on the alkyl nitrogen in thioridazine was within the range we had previously found necessary for neuroleptic activity. 相似文献
27.
W.Franklin Smyth Clare Joyce Venkataraman N. Ramachandran Edmund O’Kane Danny Coulter 《Analytica chimica acta》2004,506(2):203-214
The electrospray ionisation-ion trap mass spectrometry (ESI-MSn) of selected hypnotic drugs, i.e. zopiclone, zolpidem, flunitrazepam and their metabolites have been investigated. Sequential product ion fragmentation experiments (MSn) have been performed in order to elucidate the degradation pathways for the [M+H]+ ions and their predominant fragment ions. These MSn experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as neutral molecules such as H2O, CO, CO2, NO2, amines and HF. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with zopiclone and its N-desmethyl metabolite fragmentation initially occurs at the latter ring with the former being resistant to fragmentation. The structures of fragment ions proposed for ESI-MSn can be supported by electrospray ionisation-quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS).These molecules can be identified and determined in mixtures at low ng/ml concentrations by the application of liquid chromatography (LC)-ESI-MSn which can be used for their analysis in saliva samples.This paper includes a tabulation of mass losses/signals at low m/z values for these hypnotic drugs and many others in recent publications which will be of value in the characterisation of drug metabolites of unknown structure and also natural product pharmaceuticals isolated from plants, etc. 相似文献
28.
Peter D. Battle Jonathan C. Burley Clare P. Grey 《Journal of solid state chemistry》2004,177(1):119-125
Polycrystalline samples of the n=2 Ruddlesden-Popper phase La3LiMnO7 have been prepared and characterized. X-ray and neutron diffraction suggest that the structure is tetragonal with a disordered distribution of Li and Mn cations over the octahedral sites, but 6Li MAS NMR shows that the Li and Mn are 1:1 ordered locally. Electron microscopy shows that the stacking of the cation-ordered, perovskite-like bilayers along the crystallographic z-axis is disordered on the distance scale sampled by X-ray and neutron diffraction. Magnetometry data and neutron diffraction data collected at 2 K together suggest that the Mn cations within each structural domain order antiferromagnetically at 14 K, but that the disorder along z prevents the establishment of long-range magnetic order. 相似文献
29.
We apply an operator splitting method to develop a simulation algorithm that has complete analytical solutions for the Gaussian thermostated SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] for a system under shear. This leads to a homogeneous algorithm for performing both equilibrium and nonequilibrium isokinetic molecular dynamics simulation. The resulting algorithm is computationally efficient. In particular, larger integration time steps can be used compared to simulations with regular Gaussian thermostated SLLOD equations of motion. The utility and accuracy of the algorithm are demonstrated through application to the Weeks-Chandler-Anderson fluid. Although strict conservation of the kinetic energy suppresses thermal fluctuations in the system, this algorithm does not allow simulations at lower shear rates than those normally afforded by older nonequilibrium molecular dynamics simulations. 相似文献
30.
Determination of lead in phosphate ore and phosphogypsum 总被引:2,自引:0,他引:2
Laser induced breakdown spectroscopy (LIBS) is applied to analyze aqueous solutions of Li(+), Na(+), Ca(2+), Ba(2+), Pb(2+), Cd(2+), Hg(2+) and Er(3+) and suspensions of ErBa(2)Cu(3)O(x) particles (d=0.2 microm). An excimer (308 nm) pumped dye laser with laser pulse at 500 nm and pulse energy at 22+/-2 mJ is used to produce plasma in aqueous solution. Plasma emission lines of the elements are detected by a photodiode array detector. Detection limits of the metal ions are 500 mg/l for Cd(2+), 12.5 mg/l for Pb(2+), 6.8 mg/l for Ba(2+), 0.13 mg/l for Ca(2+), 13 microg/l for Li(+) and 7.5 microg/l for Na(+). No mercury and erbium emission can be detected, even at Hg(2+) and Er(3+) concentrations of up to the g/l range. On the other side, for Er in suspensions of ErBa(2)Cu(3)O(x) particles a more than 10(3) times higher sensitivity is found than for dissolved Er(3+). This result gives a possibility to analyze colloid-borne metal ions with an increased sensitivity. 相似文献