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951.
Georg Gescheidt Axel Lamprecht Christoph Rüchardt Michael Schmittel 《Helvetica chimica acta》1991,74(8):2094-2099
The radical mono-ions of three azoalkanes in which the azo group is connected to the polycyclic alkane moieties at the bridgehead C-atoms, i. e. 1,1′-azonorbornane ( 1 ), 1,1′-azotwistane ( 2 ), and 1,1′-azobi-cyclo[3.2.1]octane ( 3 ), were studied in fluid solution by ESR spectroscopy. According to the ESR parameters and MO models, the radical cations of 1 – 3 should be considered as σ radicals, whereas the corresponding radical anions are π radicals. INDO calculations point to a remarkable dependence of the l4N-coupling constants on the geometry at the N-atoms in the radical cations of aliphatic azo compounds. 相似文献
952.
Lin Zhu Ali Al-Sakeeri Filip Lenrick Oskar Darselius Berg Per Sjödin Alexei A. Zakharov Axel Knutsson Anders Mikkelsen 《Surface and interface analysis : SIA》2022,54(2):99-108
Removal of the native surface oxide from steel is an important initial step during vacuum brazing. Trace and alloying elements in steel, such as Mn, Si, and Ni, can diffuse to the surface and influence the deoxidation process. The detailed surface chemical composition and grain morphology of the common stainless-steel grade 316L is imaged and spectroscopically analyzed at several stages of in-vacuum annealing from room temperature up to 850°C. Measurements are performed using synchrotron-based X-ray photoemission and low-energy electron microscopy (XPEEM/LEEM). The initial native Cr surface oxide is amorphous and unaffected by the underlying Fe grain morphology. After annealing to ~700°C, the grain morphology is seen at the surface, persisting also after the complete oxygen removal at 850°C. The surface concentration of first Mn and then Si increases significantly when annealing to 500°C and 700°C, respectively, while Ni and Cr concentrations do not change. Mn and Si are not located only in grain boundaries or clusters but are distributed across over the surface. Both Mn and Si appear as oxides, while Cr oxide becomes metallic Cr. Annealing from 500°C up to 850°C leads to the removal of first the Mn and then Si oxides from the surface, while Cr and Fe are completely reduced to metals. Deoxidation of Cr occurs faster at the grain boundaries, and the final Cr metal surface content varies between the grains. The findings are summarized in a general qualitative model, relevant for austenite steels. 相似文献
953.
Xianqiao Liu Michael D. Kaminski Yueping Guan Haitao Chen Huizhou Liu Axel J. Rosengart 《Journal of magnetism and magnetic materials》2006
The present study describes the preparation and analysis of a highly concentrated hydrophobic oleic acid-coated magnetite gel. By contrast to conventional techniques to prepare magnetic fluids, herein the oleic acid was introduced as a reactant during the initial crystallization phase of magnetite that was obtained by the co-precipitation of Fe(II) and Fe(III) salts by addition of ammonium hydroxide. The resulting gelatinous hydrophobic magnetite was characterized in terms of morphology, particle size, magnetic properties, crystal structure, and hydrophobicity/hydrophilicity. This magnetic gel exhibited superparamagnetism with a saturation magnetization of 46.0 emu/g at room temperature and could be well dispersed both in polar and nonpolar carrier liquids. This protocol produced highly concentrated hydrophobic magnetic gel for biopolymer encapsulations. 相似文献
954.
Axel Ruhe 《BIT Numerical Mathematics》2007,47(4):697-697
955.
The partial oxidation of methanol to formaldehyde on oxygen-precovered Cu(1 1 0) has been studied using kinetic Monte Carlo simulations. The rates entering the simulation have been derived from density functional theory calculations within the generalized gradient approximation using transition state theory. We demonstrate that kinetic Monte Carlo simulations are a powerful tool to elucidate the microscopic details of the reaction kinetics on surfaces. Furthermore, the comparison of calculated and measured temperature programmed desorption rates allows a genuine assessment of the calculated barrier heights. We find that some of the calculated barriers and adsorption energies have to be adjusted by up to 0.5 eV in order to reproduce the measured desorption spectra. Possible reasons for the discrepancies between experiment and theory are discussed. 相似文献
956.
Chinmei Liu Seok-Hwan Chung Qiaoling Jin April Sutton Funing Yan Axel Hoffmann Brian K. Kay Samuel D. Bader Lee Makowski Liaohai Chen 《Journal of magnetism and magnetic materials》2006
Biological templating of inorganic nanoparticles provides promising opportunities to address the grand challenge in nanoscience of realizing the full potential of self-assembled materials. We implement such biotemplating to create magnetic nanoparticles by utilizing native protein capsid shells derived in high yield from the T7 bacteriophage virus. The magnetic nanoparticles are grown via bio-mineralization reactions inside of hollowed-out capsids that retain their original chemical recognition properties. The resultant “magnetic viruses” are uniform in geometry, physical properties, and biochemical functionality. We first coax the DNA out of the T7 virus by means of an alkaline treatment, and then grow magnetic cobalt particles inside the remaining hollow capsid shell. Related methods of fabricating bio-functional magnetic nanoparticles have utilized either recombinant, single-protein-type capsids, or involve coating previously synthesized inorganic particles with bio-ligands. Given the richness of the protein types that form the native T7 capsid, our magnetic viruses can be tailored to tune the bio-functionality and/or bio-tagging of a sample. As an example, we consider a nano-biomagnetic sensing scheme that would utilize the T7 capsid to control the magnetic nanoparticle size distribution. 相似文献
957.
958.
In this paper, the authors introduce a robust numerical technique for radiation–conduction heat transfer in the high temperature
fields of gas turbine combustors. The conduction and radiation effects are analyzed by a differential and an integral equation,
respectively. Using discrete ordinates for the angular discretization of the integral equation for the radiation effects and
a Galerkin discretization for the heat equation, the authors propose a fast multilevel algorithm to solve the fully discretized
problem. The algorithm uses the same mesh hierarchy for both radiation and conduction effects, but with two different smoothing
operators. Numerical results are shown for test problems in three space dimensions, and comparisons to other methods are also
given. 相似文献
959.
Michael Willmann Axel Glahn Sigmar Wittig 《Particle & Particle Systems Characterization》1997,14(3):122-128
A promising optical layout for standard phase-Doppler particle sizing instruments for use in two-phase flows with extremely limited optical access is presented. When applied to turbine oil of variable temperature and therefore refractive index (1.40< n < 1.46), the layout procedure leads to several suitable off-axis configurations. From these, a backscatter angle of ? = 125° is chosen owing to several geometrical restrictions. Although this angle lies in Alexander's darkband and therefore the intensities are low, the theoretical analysis indicates that this configuration is extremely insensitive to Gaussian-beam defects, which usually aggravate backscatter applications. Monosized droplet experiments confirmed the application of the configuration and showed an acceptable accuracy of the measurements. Experiments in a bearing chamber test rig gave reliable results and for the first time allowed an insight into the flow phenomena of this highly complex technical two-phase flow. 相似文献
960.