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51.
Analysis by synthesis is a method that has been successfully applied in many areas of scientific research. In speech research, it has proven to be an excellent tool for identifying perceptually relevant acoustical properties of sounds. This paper reports on some first attempts at synthesizing choir singing, the aim being to elucidate the importance of factors such as the frequency scatter in the fundamental and the formants. The presentation relies heavily on sound examples. 相似文献
52.
Ab initio LCAO-MO-SCF calculations using a double zeta basis set have been performed for the methyl esters of acetic acid, carbamic acid, methylcarbonic acid, and trifluoracetic acid, in order to model the corresponding choline esters. The systems have been compared by means of population analyses, electron density differences, electrostatic potentials and potential differences. The significance of the electrostatic potential in connection with crystal structure and packing has been studied. The differences in the proton affinity of the compounds have been correlated to differences in the potentials. 相似文献
53.
LSbOF is orthorhombic, space group Pnma, with a = 8.873, b = 4.099 and c = 5.483 Å. Four anions are bonded to Sb3+, all to one side, and such polyhedra form chains by edge sharing along c. Evidence is given for an ordered arrangement of fluorine and oxygen anions. The lone pair of electrons is described as taking a certain volume, the centre of which is derived. Relationships with other structures are discussed. 相似文献
54.
Based on the formalism developed in a recent note, we have worked out a program for CI calculations in molecules. In the present
note, the details of the program are discussed. The usefulness of the program has been illustrated using some calculations.
On leave from the Indian Institute of Technology, Bombay, India. 相似文献
55.
Liu YJ Persson P Karlsson HO Lunell S Kadi M Karlsson D Davidsson J 《The Journal of chemical physics》2004,120(14):6502-6509
Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C2v to Cs along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene. 相似文献
56.
An automated gas chromatographic subsystem for the provision of fast and reliable concentration profile data for distillation column control is presented. The subsystem consists of a gas chromatograph, equipment for sample conditioning and a PC/AT compatible computer communicating with the supervisory process computer. A fast separation time is obtained through the use of a liquid chromatographic packing material and a high pressure drop across the column. Preliminary results show separation times below 10 s for the water-methanol-isopropanol system. Peak areas are quantified by use of parameter estimation in the frequency domain, a method that does not demand complete peak separation. 相似文献
57.
Summary Proton isotropic hyperfine coupling constants have been calculated for three low-energy nuclear conformations on the ground state potential surface of the propane cation, using a multireference singles and doubles configuration interaction (MR-SDCI) wave function. The lowest point found on the potential surface hadC
2v
symmetry and the electronic wave function at this point had2B2 symmetry. At this point, the largest isotropic coupling constant is calculated to be 88.6 G, which is in fair agreement with the experimental value of 98 G obtained in an SF6 matrix at 4 K. No support is found for a long-bond ground state of lower symmetry thanC
2v
. AnotherC
2v
minimum on the ground state potential energy surface was found at which the wave function had2
B
1 symmetry. At this point, two large coupling constants of 198 G and 35 G were calculated. AC
2v
stationary point was also found on the ground state potential surface at which the wave function had2
A
1 symmetry. At this point, couplings of 86 G and 25 G were obtained. None of these agree closely with the other experimental result of couplings at both 100–110 G and 50–52.5 G which was obtained in freon matrices. It is suggested that the latter spectra might correspond to a dynamical average of two distorted2
A' states inC
s symmetry. 相似文献
58.
It is shown that the cusp conditions for the ordinary Hartree-Fock orbitals are not applicable in extended SCF methods, contrary to what has been stated in the literature. The correct cusp condition for a singlet state of a two-electron atom is given. 相似文献
59.
60.
Twinning on the unit cell level of the idealized cristobalite structure, using a mirror plane as the twin and composition plane, provides a simple relationship between 14 tetrahedral frameworks. Of these, 9 are found among the aluminosilicates with examples ranging from (stuffed) silicas to zeolites and include the framework types of nepheline hydrate I, zeolite LiA(BW), gismondine, phillipsite, merlinoite, tridymite, paracelsian, and monoclinic CaAl2Si2O8. Similar twinning relates the frameworks of natrolite, thomsonite, and edingtonite. 相似文献