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111.
Ulrike Mammel Manfred Brun Dieter Oelkrug 《Fresenius' Journal of Analytical Chemistry》1992,344(4-5):147-152
Summary The optical absorption and fluorescence of scattering samples is investigated theoretically and experimentally under the condition of steady-state and pulsed irradiation, taking into account inhomogeneous distribution of the absorbing species. Based on the Kubelka-Munk model, numerical iterative expressions for the steady-state and time-resolved light flues of excitation and emission are derived. The intensities of reflected, transmitted and forward or backward emitted radiation in layered samples with vertical concentration gradients are discussed. Modification of fluorescence spectra and decay curves due to self absorption, background absorption, secondary emission and time of flight dispersion are calculated and compared to experimental data of hydrocarbons adsorbed on polycrystalline silica gel. 相似文献
112.
113.
114.
Helge Hannebauer Thorsten Dullweber Ulrike Baumann Tom Falcon Rolf Brendel 《固体物理学:研究快报》2014,8(8):675-679
We evaluate industrial‐type PERC solar cells applying a 5 busbar front grid and fineline‐printed Ag fingers. We obtain finger widths down to 46 µm when using a stencil with 40 µm opening for the finger print, whereas the busbar is printed in a separate printing step with a different Ag paste (dual print). This compares to finger widths of 62 µm to 66 µm when applying print‐on‐print. The 5 busbar front grid with the best dual print process reduces the shadowing loss of the front grid to 4.0% compared to 5.8% for a conventional 3 busbar front grid printed with print‐on‐print. The 1.8% reduction in shadowing loss results in equal parts from the reduced finger width with dual print as well as from a reduced total busbar width of the 5 busbar design. The resulting PERC solar cells with 5 busbars demonstrate independently confirmed conversion efficiencies of 21.2% compared to 20.6% efficiency of the 3 busbar PERC solar cell. The increased conversion efficiency is primarily due to an increased short‐circuit current resulting from the reduced shadowing loss. To our knowledge, 21.2% conversion efficiency is the highest value reported so far for industry typical silicon solar cells with printed metal front and rear contacts. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
115.
Peter Krumbiegel Irina Lehmann Albin Alfreider Gisela J. Fritz David Boeckler Ulrike Rolle-Kampczyk 《Isotopes in environmental and health studies》2013,49(1):75-80
Background.?Studies conducted in Europe as well as in North and South America have tried to link Helicobacter pylori colonization with the drinking water supply, especially since H. pylori is known to survive quite well in water. Methods.?In 2000, a cohort of 1884 grade-two children from two rural counties surrounding the city of Leipzig, Germany (77.4% of the 1991/1992 birth cohort) were tested for H. pylori colonization using the [13C]urea breath test. A parent-completed questionnaire elicited details on living conditions and lifestyle habits including questions on the children's drinking water from sources other than public water supplies, swimming in natural waters, etc. In a second independent study, samples of well water, taken from 157 private wells still used in the two counties, were being tested for the presence of H. pylori, using polymerase chain reaction (PCR) method to determine relevant target DNA fragments of H. pylori. Results.?In county I, 5.7% of the children and in county II 6.6% tested H. pylori-positive. Cluster analyses of the questionnaire data in both counties pointed to ‘drinking water from other than municipal sources’, as the closest H. pylori-associated cluster variable. The cluster estimations were supported by odds ratio (OR) calculations with an OR?=?16.4 (95% confidence interval (CI) 3.1,…,88.5) for county I and OR?=?4.0 (95% CI 1.3,…,12.4) for county II. The PCR analyses showed H. pylori DNA fragments in 10.8% of the wells in county I and 9.2% in county II. The detection limit was set at 10 DNA copies corresponding to 125?bacteria/L, the average infestation of these wells was 931?bacteria/L. Conclusion.?Despite the fact that the microbiological and epidemiological data do not correspond except that both studies were conducted in the same geographical areas, the independent findings of H. pylori in well water in the same general areas where children do seem to drink water other than from the public water supply suggests that water may be an important source of H. pylori infection. 相似文献
116.
Thermodynamic functions of an electron–hole plasma in an optically excited semiconductor are derived in the nondegenerate region. The existence of excitons and the ionization equilibrium are discussed in the ne–T (electron density–temperature) plane. Above the Mott curve (r0 = 0.84 a0, r0 screening length, a0 Bohr's radius) excitons do not exist. Besides the well known electron–hole droplet phase transition the critical point of which lies above the Mott curve, a region of instability is found below the Mott curve which might correspond to a plasma phase transition (weakly ionized plasma → strongly ionized plasma). Outside of this instability region at the Mott curve a diffuse phase transition (Mott-transition) exists. 相似文献
117.
A theory of the exciton ionization by phonons is developed. A non static effective electron-hole interaction is derived from the Bethe-Salpeter equation in the ladder approximation. The imaginary part of the effective potential is related to the life time and to the level width of the excitons. An application of the theory to Ge shows, that the ionization of excitons by LO-phonons in comparison with the recombination is the dominating damping process, where KBT is or order of the effective binding energy of the excitons. 相似文献
118.
The thermodynamic stability of the optically excited electrons and holes in a semiconductor is investigated in a wide temperature—density range. In dependence on the position of the instability region with respect to the Mott curve the two coexisting phases (i), (ii) may have very different properties: e.g. (i) drops of degenerate electrons and holes and (ii) a partially ionized plasma of excitons, electrons, and holes. For Ge the region of instability is determined. For this purpose the chemical potential is calculated exactly at all temperatures in the ideal and Hartree-Fock contributions and approximately in the correlation part, using exact formulae for the highly degenerate and the non-degenerate cases. In the low density region the mass action law is taken into account. 相似文献
119.
The dependence of two-particle energies on plasma density is investigated using Green's functions. An effective exciton equation is derived taking into account dynamically screened potential and one-particle self-energies. A variational calculation shows that the bound state levels (exciton energies) remain practically constant whereas the continuum edge (band gap) shifts to lower energies with increasing density, which is in accordance with experimental observations. 相似文献
120.
G. Rupke K. Kilimann D. Kremp W. D. Kraeft R. Zimmermann 《physica status solidi b》1978,88(1):K59-K63