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51.
52.
A. Del Guerra A. Giazotto M.A. Giorgi A. Stefanini D.R. Botterill D.W. Braden P.R. Norton 《Physics letters. [Part B]》1973,45(4):409-410
The azimuthal angle dependence of the process ep → enπ+ has been measured by detecting the electron and neutron in coincidence. Data are presented for momentum transfers (?k2) between 0.08 and 0.32 and at energies close to threshold. Fixed-t dispersion relation models give predictionsin good qualitative agreement with the data. 相似文献
53.
Benzoyl bromide (2-nitrophenyl) hydrazone (2) was treated with sodium ethoxide and ethyl cyanoacetate and two unexpected products were obtained. These products were ultimately shown to be 6-bromo-3-phenyl-1,2,4-benzotriazine (32) and 5-bromo-2-phenylbenzoxazole (38), by comparison with authentic samples which were synthesized. A mechanism is presented for the formation of these two heterocyclic systems (32 and 38) from 2. 相似文献
54.
Two newly discovered phases on the Pt(100) surface produced by the adsorption of oxygen have been investigated using Rutherford baekscattering (RBS), nuclear microanalysis (NMA), work function changes (Δφ) and LEED. One phase is associated with the oxygensaturated surface (0.63 ± 0.03 monolayers0.81 × 1015 O atoms cm?2), where a very complex LEED pattern is observed; the other is observed at an average coverage of 0.44 ± 0.05 monolayers and gives rise to a (3 × 1) LEED pattern (when observed at room temperature). For both surfaces, RBS measurements indicate large (? 0.025 nm) Pt atom displacements. Also discussed is a new method for preparing the “clean” (1 × 1)-Pt(100) surface without the need for NO adsorption/decomposition. 相似文献
55.
56.
Using dynamic LEED measurements of spot intensities and profiles, together with thermal desorption data, we have investigated the oxidation of CO on Pt(100)?(1 × 1). At T = 355 K, either CO or O was preadsorbed and reacted off with the other species. Results from both titration sequences point to the following conclusions: Titration of preadsorbed oxygen with COg leads to rapid reaction, with a reaction probability of unity for each chemisorbed CO. Adsorbed CO does not accumulate on the surface until θo ? 0.05, i.e. an intermediate, rather clean (1 × 1) Pt surface is obtained. Further evidence for this clean intermediate is provided by the fact that characteristics of the diffraction spots of the c(2 × 2) of CO develop identically during this reaction sequence and during adsorption of CO on a clean (1 × 1) Pt surface. In the reverse case, titration of preadsorbed CO with O2,g, the reaction rate is slower than the oxygen adsorption rate, leading to a pressure-dependent development of coexisting Oad and COad domains, which we observe directly with LEED. The stable phases coexisting are the c(2 × 2) of CO and the oxygen-related (3 × 1). Thermal desorption peak shapes, together with LEED observations, indicate that the CO in this case is held in c(2 × 2) islands by a matrix of surrounding oxygen atoms. In no case do mixed structures form, nor is an existing structure compressed by subsequent adsorption of the second species. Starting from a Langmuir-Hinshelwood mechanism, the differences between the two reaction sequences are discussed in terms of different activation barriers for reaction and different sticking coefficients of the adsorbing species. Special attention is given to the mobilities of the adsorbed reactants. 相似文献
57.
The structural, solvent and temperature effects on the PMR spectra of several alkyl alkanesulfinates and arenesulfinates are discussed. A low order intrinsic nonequivalence was observed in substituents alpha to the sulfinate sulfur atom, the nonequivalence being significantly less than in sulfoxides, and solvent and temperature dependent. Nonequivalence of diastereotopic substituents on the ester oxygen exceeded nonequivalence in similar sulfoxides and is largely insensitive to temperatures from 25° to 120°C. Benzene complexes with sulfinates greatly enhancing the proton nonequivalence of alpha substituents apparently by causing a further shielding of the already more shielded nonequivalent protons. 相似文献
58.
The absolute coverage (θ) of deuterium adsorbed on Pt(111) in the ranges 180< T<440 K and 5 × 10?6 < P < 5 × 10?2 Pa D2 has been determined by nuclear microanalysis using the D(3He, p)4He reaction. From these data, the isosteric heat of adsorption (Ea) has been determined to be 67 ± 7 kJ mol?1 at θ ? 0.3. This heat of adsorption yields values of the pre-exponential for desorption (10?5 to 10?2 cm2 atom?1 s?1) that lie much closer to the normal range for a second order process than those determined from previous isosteric heat measurements. The Ea versus θ relationship indicates that the adsorbed D atoms are mobile and that there is a repulsive interaction of 6–8 kJ mol?1 at nearest neighbour distances. At 300 K the coverage decreases to ? 0.05 monolayer (? 8 × 1013 D atoms cm?2) as P→ 0, apparently invalidating a recent model of site exchange in the adsorbed layer. 相似文献
59.
The (p, t) reactions on isotopic targets of 178, 180Hf and all the stable isotopes of Yb and on natural targets of Gd, Dy, Er, Hf, Ta, W, Os and Au were studied at a beam energy of 19 MeV with an average resolution of 12 keV. A split-pole magnetic spectrometer was used to measure (p, t) Q-values and absolute differential cross sections. On the basis of angular distribution shapes definite 0+ and tentative 2+ assignments were made. Rotational bands were identified assuming an I(I+1) spacing. The (p, t) reaction populates excited 0+ states strongly in 174Yb, 176Hf, 166Yb and several Gd, Dy and Er isotopes. The 174Yb and 176Hf 0+ states are discussed in terms of the pairing phase transition and in terms of Nilsson orbitals with unequal (p, t) reaction amplitudes. Members of gamma and octupole vibrational bands were observed in the even-N nuclei. The lowest L = 0 transfers to states in 169, 171Yb were found to have less than 55% of the strength to ground states in adjacent even-N nuclei. A strong L = 0 transfer to a state at 1513 keV in 171Yb indicates the presence of a possible K = 0 core vibration coupled to the unpaired [512] neutron. The natural targets have furnished information on trends in cross sections for members of ground bands, gamma bandheads, 3? octupole states, and strongly excited 0+ states. 相似文献
60.
D.R. Botterill D.W. Braben R. Kikuchi P.R. Norton A. Del Guerra A. Giazotto M.A. Giorgi A. Steffanini 《Physics letters. [Part B]》1973,45(4):405-408
The total cross section for the reaction ep → enπ+ at momentum transfers |k2| between 0.08 and 0.32 ()2 and for centre of mass energies between threshold, at W = 1.078 GeV, and W = 1.106 GeV has been measured by detecting the electron and neutron in coincidence. Comparisons are made with both current algebra and dispersion relation theoretical models. 相似文献