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31.
A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 m CO2 laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 m amplifier using low-power pulses from a 4.3 m probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 m amplifier. Optimization of the gain is discussed. 相似文献
32.
O'Hair RA Androutsopoulos NK Reid GE 《Rapid communications in mass spectrometry : RCM》2000,14(18):1707-1716
The proposal that protonated peptides react with NH(3) in the gas phase via transacylation reactions (Tabet et al., Spectros. Int. J. 5: 253 1987) has been investigated by studying the reactions of the fixed charge derivatives [RC(O)NMe(2)CH(2)CO(2)H](+) (R=Me and Ph) with pyridine and triethylamine and the reactions of protonated glycine oligomers and leucine enkenphalin with butylamine. Under the near thermal conditions of the quadrupole ion trap, both the fixed charge derivatives as well as the protonated peptides react with the amines via either proton transfer or proton bound dimer formation. Collision induced dissociation of protonated peptides in the presence of butylamine yields b(n) and y(n) sequence ions as well as [b(n) + BuNH(2)](+) and [y(n) + BuNH(2)](+) ions. MS(3) experiments reveal that a major route to these [b(n) + BuNH(2)](+) and [y(n) + BuNH(2)](+) ions involves ion-molecule reactions between the b(n) and y(n) sequence ions and butylamine. MS(4) experiments, carried out to determine the nature of the [b(n) + BuNH(2)](+) ions, reveal that they correspond to a mixture of hydrogen bonded (i.e. proton bound dimer) and covalent amide bond structures. 相似文献
33.
Milanesi L Reid GD Beddard GS Hunter CA Waltho JP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(7):1705-1710
A new series of photocleavable protein cross-linking reagents based on bis(maleimide) derivatives of diaryl disulfides have been synthesised. They have been functionalised with cysteine and transient absorption spectra for the photolysis reaction have been recorded by using the pump-probe technique with a time resolution of 100 femtoseconds. Photolysis of the disulfide bond yields the corresponding thiyl radicals in less than a picosecond. There is a significant amount of geminate recombination, but some of the radicals escape the solvent cage and the quantum yield for photocleavage is 30 % in water. 相似文献
34.
Levason W Matthews ML Reid G Webster M 《Dalton transactions (Cambridge, England : 2003)》2004,(1):51-58
High yield syntheses for 1,2-, 1,3-, and 1,4-xylyl distibines (1,2-C6H4(CH2SbMe2)2, 1,3-C6H4(CH2SbMe2)2, 1,4-C6H4(CH2SbMe2)2, respectively) from Me2SbCl (conveniently made in situ from Me2PhSb and HClgas) and the appropriate di-Grignard are reported. The 1,3- and 1,4-phenylene distibines, 1,3-C6H4(SbMe2)2 and 1,4-C6H4(SbMe2)2, were made similarly. The new ligands have been characterised by mass spectrometry, 1H and 13C[1H] NMR spectroscopy, and by the preparation of methiodide derivatives. The crystal structures of 1,4-C6H4(CH2SbMe2)2 and [1,3-C6H4(CH2SbMe3)2]I2 have been determined. The synthesis of 1,2-C6H4(CH2SbPh2)2 has been achieved similarly in modest yield and the distibine converted into the tetra-iodo-derivative 1,2-C6H4(CH2SbPh2I2)2. The coordination modes available to these ligands have been probed by the synthesis and characterisation of complexes with nickel, iron and tungsten carbonyls. The crystal structure of [[Fe(CO)4]2[micro-1,3-C6H4(CH2SbMe2)2]] has been determined. The spectroscopic properties of these carbonyl derivatives have been compared with those of complexes of other antimony ligands, and in some cases with diphosphine and diarsine complexes, to probe the electronic properties of the new ligands. 相似文献
35.
Charles E. Reid 《International journal of quantum chemistry》1972,6(2):383-386
It is a standard theorem of group representation theory that the dimension of an irreducible representation is a divisor of the order of the group. This paper gives a new, relatively simple proof, intended to make the theorem understandable to readers unfamiliar with algebraic integers. 相似文献
36.
Tyler GW 《The Journal of the Operational Research Society》1984,35(3):257-259
McClean's model is applied to an analysis of Consultant Staff in the Royal Infirmary of Edinburgh from 1801 to 1968. 相似文献
37.
Intramolecular energy migration and trapping by acceptor species which are an integral part of a macromolecule have been studied in three polymer systems using the techniques of fluorescence depolarization. The effect of energy migration produces depolarization of both donor and acceptor emissions. Copolymers of styrene with 1-vinylaphthalene or 2-phenyl-5-(p-vinyl)phenyloxazole have been studied. In addition, energy transfer to a terminal anthracene species has been studied in a polyvinyltoluene sample. When energy transfer occurs with unit efficiency, the depolarization of acceptor emission reflects the path length available to the migrating exciton. In cases of lesser transfer efficiency, the acceptor emission exhibits depolarization characteristics which reflect the distribution of migration lengths from the site of energy absorption. 相似文献
38.
The Mössbauer spectra of 57Fe3+ substituted in 0.2 to 0.4 atom % of the octahedral sites in the host lattices Na0.9Mg0.45Ti1.55O4, TiO2, Sc2O3, LiScO2 and MgAl2O4 have been examined. Hyperfine splittings of the spectra were observed for all cases except Sc2O3. In all cases the electron spin resonance spectrum was found, or has been shown to be highly anisotropic as a result of the presence of strong axial or rhombic fields and consequent splitting of the 3d5 ground state energy levels. In several cases resolution of the and Mössbauer spectra was observed. Mössbauer spectra of the solid solutions Na0.9Mg0.45Ti1.55O4Na0.9Fe0.9Ti1.1O4, LiScO2LiFeO2 and TiO2FeNbO4 have also been examined. 相似文献
39.
Matthew HesfordWilliam Levason Simon D. OrchardGillian Reid 《Journal of organometallic chemistry》2002,649(2):214-218
The syntheses and spectroscopic characterisation of the new facultative tridentate tellurium containing ligands MeS(CH2)3Te(CH2)3SMe (S2Te) and H2N(CH2)3Te(CH2)3NH2 are described. The complexes of the former, fac-[Mn(CO)3(S2Te)]CF3SO3, [Rh(Cp*)(S2Te)][PF6]2, [MCl(S2Te)]PF6 (M=Pd or Pt), [Cu(S2Te)]BF4 and [Ag(S2Te)]CF3SO3 have been prepared and characterised by analysis, IR, 1H-, 13C{1H}-, 125Te- and 195Pt-NMR spectroscopy and mass spectrometry. The X-ray crystal structures of [Rh(Cp*)(S2Te)][PF6]2 and [PtCl(S2Te)]PF6 are described. The results are compared with those obtained from complexes of the related tridentates Te{(CH2)3TeR}2, Se{(CH2)3SeMe}2 and S{(CH2)3SR}2. 相似文献
40.
Rebecca J. Hopkins Rachel Symes Robert M. Sayer Jonathan P. Reid 《Chemical physics letters》2003,380(5-6):665-672
Cavity-enhanced Raman scattering is used to determine the size and composition of multicomponent ethanol/water droplets in the concentration range 7.5–19% ethanol by volume. Under the experimental conditions presented here, the integrated CERS signal from ethanol shows an exponential increase with increase in ethanol concentration when compared with the integrated intensity of the water band. The calibration is shown to be invariant with particle size over the droplet radius range 20–35 μm. In addition to providing a method for determining particle size and composition, initial studies show that the evaporation dynamics of these multicomponent droplets can be probed by CERS. 相似文献