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991.
The adsorption of Na on a Ge(100)-(2 × 1) surface has been studied by means of AES, LEED, EELS, TPD and work-function measurements. In the submonolayer coverage region the coverage dependencies of the desorption activation energy E(Θ) and desorption frequency v(Θ) have been determined using the threshold TPD method. Our experimental data show that after the completion of the first Na layer, 3D crystallites develop on the Na/Ge(100) surface (Stranski-Krastanov growth mode). For Θ > 1 ML, formation, followed by decomposition of a certain Na---Ge surface compound occurs in the temperature range 410–550 K. 相似文献
992.
The growth of Co on thin Al2O3 layers on Ni3Al(1 0 0) was investigated by Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), and scanning tunneling microscopy. At 300 K, Co grows in three-dimensional clusters on top of the Al2O3 layer. A defect structure of the alumina layer plays a crucial role during the early stage of Co growth. After deposition of 10 Å of Co, a complete screening of the dipoles of the Al2O3 layer due to the Co film is found in the EELS measurements. Annealing the Co film reveals a process of coalescence of Co clusters and, above 700 K, diffusion of the Co atoms through the oxide film into the substrate takes place. 相似文献
993.
The O-bridge atoms on a stoichiometric RuO2(1 1 0) surface were removed by reaction with CO. The resulting reduced surface was then further exposed to CO. By means of thermal desorption spectroscopy and high-resolution electron energy-loss spectroscopy three adsorbed CO states were identified on bridge sites and assigned to double-bonded, single-bonded, and single-bonded species in the vicinity of O-bridge residues, respectively. 相似文献
994.
Desorption of metastable particles from layered and mixed films, composed of N2 and Kr, is induced by the impact of 6–50 eV monoenergetic electrons. From yield functions and time-of-flight analysis of the metastable particles emanating from these films, N*2 and Kr* are identified as the desorbing species. Basic mechanisms responsible for their desorption are discussed. It is suggested that the desorption of Kr* arises from dissociation of transitory [Kr·N2]* excimers. The desorption of N*2 can arise from cavity expulsion, intramolecular vibrational energy transfer (with or without prior electronic excitation energy transfer from Kr excitions to N2) and the dissociation of [Kr·N2]* excimers. 相似文献
995.
The effect of the physisorbed hydrogen molecules on the electron stimulated desorption of metastables from the surface of solid Kr was investigated. At the clean surface of solid Kr, the desorption of Kr metastables occurs only through an excimer dissociation mechanism. Physisorption of hydrogen molecules causes the following effects: (1) the total desorption yield of the metastable species increased by an order of magnitude or more; (2) metastable Kr, which is probably desorbed through the cavity ejection mechanism, emerges; (3) metastable Kr by excimer dissociation is also enhanced; and (4) a new metastable species, which seems to be composed of metastable hydrogen molecule, appears. 相似文献
996.
In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O+ ions through discontinuous Au films adsorbed on TiO2(110). A low energy (< 10 eV) O+ ion beam is generated via electron stimulated desorption when an Au-dosed TiO2(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO2(110). As the Au coverage increases, the formation of Au clusters on TiO2(110) blocks a fraction of the TiO2 surface and the O+ yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O+ signal decreases at a faster rate than the TiO2 open area fraction. We attribute the attenuation of the O+ yield for high Au coverages mainly to blocking of O+ by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O+ and neighboring Au clusters. 相似文献
997.
Photodesorption and photofragmentation of disilane adsorbed on a hydrogen terminated Si(100) surface
The photochemical mechanisms leading to the desorption and fragmentation of Si2H6 adsorbed on a hydrogen terminated Si(100) surface have been explored by recording the time-of-flight distributions of products escaping from the surface and by using electron energy loss spectroscopy to probe possible electronic excitations. Photodesorption of intact Si2H6 involves hot electrons that lose energy and move to the conduction band edge before initiating desorption. When the wavelength of the incident light is 193 nm, Si2H6 fragments give mostly Si, SiH2, H2 and SiH4, but this pathway is quenched at longer wavelengths. This is consistent with direct excitation, but we also show that a negative ion resonance is accessible to substrate electrons that have been excited by 193 nm light. 相似文献
998.
Hirofumi Maekawa 《Tetrahedron letters》2004,45(20):3869-3872
Mg-promoted reduction of a mixture of aromatic ketones (or imines) and aliphatic carbonyl compounds in N,N-dimethylformamide (DMF) brought about unique mixed pinacol type of cross coupling to give unsymmetrical vicinal diols (or amino alcohols) or α-hydroxyketones in good to moderate yields. The reaction may be initiated by electron transfer from magnesium metal to an aromatic carbonyl compound possessing a less negative reduction potential. The difference of reduction potential between aromatic ketones (or imines) and aliphatic carbonyl compounds was found to be one of the important key factors in this selective cross coupling. 相似文献
999.
We have developed a new electron energy analyzer with a large solid angle of 0.14π, which is comparable to that of cylindrical mirror analyzer. Typical energy resolution was ΔE/E0 ∼ 0.016 for the aperture of 1 mm and central radius of 100 mm, and typical angular resolution was less than 0.5°. 相似文献
1000.
We have used scanning tunneling microscopy (STM) to explore the details of single and multiple H atom desorption from the H-Si(1 0 0)-2 × 1 surface induced by the inelastic scattering of electrons from an STM tip. The desorption of pairs of H atoms from individual Si dimers is rarely observed. Two-H atom desorption most often involves pairs of dimers, in the same or adjacent rows. This suggests that recombinative H2 desorption via an interdimer reaction pathway, like that observed recently under nanosecond laser heating, may also be operative for electron-induced excitation using STM. Repeatable fabrication of desired size-selected dangling bond (DB) clusters is also achieved. The single atomic precision of the fabrication is a result of the intrinsically unfavorable paired H atom desorption from a single dimer, but does not result from the spatial localization of excitation energy of the Si-H bond under the STM tip as suggested in previous studies. 相似文献