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81.
Electron spin resonance (ESR) measurements have been carried out on a 10Fe2O3 · 10Al2O3 · 80SiO2 gel heat-treated at different temperatures in air and under reducing conditions. ESR spectra were obtained at 300, 50 and 5 K. The effective g value (g = h/H), linewidth (Hpp) and ESR amplitude (A) depend on heat-treatment temperature of the gel-derived samples. ESR spectra exhibit different magnetic characteristics as a function of heat-treatment temperature and atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and a.c. susceptibility (a.c.) analyses were used to better understand the ESR results. The results show that in the samples heat-treated in air, up to 700°C, Fe3+ ions are incorporated in the glass network in tetrahedral and/or octahedral co-ordinations. In the samples heat-treated between 250 and 700°C was not detected, by ESR, the presence of iron oxide aggregates. However, the formation of hematite particles was observed by XRD and SEM. The presence of iron oxide aggregates was detected (by ESR) in the samples heat-treated at temperatures higher than 700°C. These aggregates are formed, at 1200 and 1300°C, by hematite and magnetite particles as proved by XRD. The ESR spectra and a.c. susceptibility, of the samples heat-treated at 250°C (under reducing conditions), show a behaviour characteristic of small magnetite particles presence. The sample heat-treated at 500°C (under reducing conditios) contains magnetite particles (XRD). In the ESR spectra of the sample heat-treated at 1000°C, under reducing conditions, was not detected any resonance signal. 相似文献
82.
Strontium Sorption on Hematite at Elevated Temperatures 总被引:1,自引:0,他引:1
Karasyova ON Ivanova LI Lakshtanov LZ Lövgren L 《Journal of colloid and interface science》1999,220(2):419-428
Acid–base reactions and surface complexation of Sr(II) at the hematite/water interface have been studied by means of potentiometric titrations at three different temperatures: 25, 50, and 75°C. Equilibrium measurements were performed in 0.1 M NaCl. In the evaluation of equilibrium models for the acid–base reactions and complexation reactions in the three-component system H+ ---(FeOH)---Sr2+, the constant capacitance model was applied. During the titrations with Sr, aliquots of the suspension were sampled at in several points. The aqueous concentrations of Sr were analyzed by atomic absorption spectrometry. Treatment of data included tests for formation of both inner-sphere and outer-sphere complexes of different stoichiometric composition. The proposed equilibrium model consists of the following surface complexes of inner sphere type: FeOHSr2+ and FeOSrOH. Besides the stability constants for the surface complexes, the thermodynamic parameters ΔH and ΔS were evaluated. The combined effect of a decrease in pHpzc with increasing temperature and positive enthalpies of surface complex formation favors adsorption of Sr at elevated temperatures. 相似文献
83.
Uniform diamond-shaped and spherical -Fe2O3 particles, prepared by a forced hydrolysis of FeCl3–HCl solutions, were characterized by various means. Electron microscope and x-ray diffraction measurements indicated that these particles are formed by recrystallization of -FeOOH to -Fe2O3 accompanying the dissolution of -FeOOH. Ultramicropores were formed in spherical particles with outgassing in vacuo above 150 °C by dehydration of inner OH groups, proving that the particles are polycrystalline. On the other hand, the highly crystallized diamond-shaped particles showed a less microporosity and were thermally stable against outgassing up to 400 °C. These results are compatible with those obtained for the monodispersed cubic and spherical -Fe2O3 particles reported in our previous paper [J Chem Soc Faraday Trans 87: 2241 (1991)]. 相似文献
84.
回流水热合成均分散纳米α-Fe2O3单晶粒子 总被引:6,自引:0,他引:6
系统地研究了以Fe(NO3)3为原料,回流水热合成均分散α-Fe2O3纳米粒子。实验结果显示:当pH=1时,随着水热时间的增加,由透射电镜测试可知,多孔性纺锤形α-Fe2O3单晶转变成粒径在45 nm左右的均分散菱形单晶;而Fe(NO3)3用氨水中和形成Fe(OH)3凝胶后,随着初始pH值的增加,完全转变成α-Fe2O3所需的时间增加、粒径减小,但产物的结构更为完整。另外通过实验发现,反应体系中存在的电解质对α-Fe2O3晶体的生成有促进作用。同时对初始pH值及电解质对α-Fe2O3生成速率的影响机理进行了分析。 相似文献
85.
Acid Treatment Enables Suppression of Electron–Hole Recombination in Hematite for Photoelectrochemical Water Splitting 下载免费PDF全文
Yi Yang Mark Forster Dr. Yichuan Ling Dr. Gongming Wang Dr. Teng Zhai Prof. Yexiang Tong Prof. Alexander J. Cowan Prof. Yat Li 《Angewandte Chemie (International ed. in English)》2016,55(10):3403-3407
We report a strategy for efficient suppression of electron–hole recombination in hematite photoanodes. Acid‐treated hematite showed a substantially enhanced photocurrent density compared to untreated samples. Electrochemical impedance spectroscopy studies revealed that the enhanced photocurrent is partly due to improved efficiency of charge separation. Transient absorption spectroscopic studies coupled to electrochemical measurements indicate that, in addition to improved bulk electrochemical properties, acid‐treated hematite has significantly decreased surface electron–hole recombination losses owing to a greater yield of the trapped photoelectrons being extracted to the external circuit. 相似文献
86.
S. Nagel 《Journal of Physics and Chemistry of Solids》1985,46(8):905-919
The MSXα cluster technique has been used to study the electronic structure of hematite α-Fe2O3, where iron is formally in a 3d56S state. The calculated energy levels are compared with X-ray emission and photoelectron spectra. The wave functions have been used to compute the charge distribution, as well as hyperfine parameters such as quadrupole coupling constant, isomer shift and magnetic hyperfine field. The results indicate a considerable influence of chemical bonding on these parameters due to charge transfer and covalency. From the calculated field gradient and the measured quadrupole coupling constant a nuclear quadrupole moment for 57mTe of about 0.11b is deduced. This value is smaller than the most recent estimates of 0.15b based on the ionic model but not as small as the value of 0.082b obtained from first principles calculations on iron dihalides. 相似文献
87.
Gunnlaugsson H. P. Merrison J. P. Mossin L. A. NØrnberg P. Sanden J. UggerhØj E. Weyer G. 《Hyperfine Interactions》2002,144(1-4):365-370
Hyperfine Interactions - The rare occurrence of magnetic soil in Denmark is normally explained by the hypothesis that the site has been burned. However, at some sites formation by means of organic... 相似文献
88.
聚合氯化铁的制备及其絮凝效果 总被引:1,自引:0,他引:1
以赤铁矿和工业盐酸为原料,采用盐酸酸浸和加碱聚合等方法制取聚合氯化铁絮凝剂(PFC),将其用来处理造纸废水,并与市售聚合氯化铁和碱式氯化铝絮凝剂进行比较.结果表明,在碱化度为2∶1、聚合温度为40℃、陈化时间为24h时,自制聚合氯化铁絮凝剂对造纸废水具有较好的处理效果;投加量为1.4mL/L时,造纸废水的浊度降低了99%,化学需氧量(COD)降低了69.55%,优于市售絮凝剂对造纸废水的处理效果;且三种絮凝剂用量相同时,自制的聚合氯化铁絮凝剂形成絮体的速率和沉降速率都较快. 相似文献
89.
Dawid Lupa Magdalena Oćwieja Zbigniew Adamczyk 《Particle & Particle Systems Characterization》2021,38(2):2000239
Among the methods utilized for the preparation of raspberry-like microcomposites, due to its simplicity and universality, the electrostatically-driven deposition of nanoparticles at the surface of microparticles is especially attractive. This process, leading to the formation of a single nanoparticle monolayer, is widely reported. On the other hand, no data concerning the electrostatically-driven formation of nanoparticle bilayers at the surface of microparticles are reported. To fill this gap, the detailed investigation of the formation of silver/hematite nanoparticle bilayers at the surface of polystyrene microparticles is reported. First, the hematite/polystyrene raspberry-like microcomposites are obtained by immobilization of hematite nanoparticles under an electrostatically-driven process. The stability of hematite/polystyrene microcomposites at elevated temperatures up to 323 K is monitored using microelectrophoresis. No significant changes in the hematite nanoparticle layer coverage are observed after prolonged time of incubation. This proves the irreversible character of nanoparticle immobilization. Next, the hematite/polystyrene microcomposites are utilized as the interfaces for immobilization of negatively charged silver nanoparticles. This process is quantitatively described using electrokinetic measurements. The changes in the hydrodynamic diameter of microcomposites are also determined. Finally, the validity of the electrokinetic model used in this work for predicting the zeta potential of the silver/hematite/polystyrene microcomposites is confirmed. 相似文献
90.
Akira Satoh 《Molecular physics》2014,112(7):1002-1011
We have investigated various problems that arise in applying the Brownian dynamics method to a suspension composed of rod-like hematite particles, which have a magnetic moment normal to the particle axis direction. The accuracy and the deviation of simulation results from theoretical solutions have been discussed by comparison with the theoretical solutions that were obtained by solving the basic equations of the orientational distribution function. The characteristics of the negative viscosity are not observed to be dependent on a time interval unless a sufficiently short time interval is used. The present simulation results can satisfactorily reproduce the qualitative characteristics of the negative magneto-rheological effect that was predicted by the previous theoretical investigation. Good quantitative agreement is obtained in the range of small-applied magnetic fields, but agreement is not significantly good in the large magnetic field region. The deviation of the negative viscosity from the theoretical prediction cannot be improved by using a more accurate numerical algorithm such as moving from Euler to second-order or fourth-order Runge–Kutta. The results of the orientational distribution can well reproduce the characteristic features that the distribution has a gradual shape with low linear-like peak, which is in significant contrast to the sharp single-peak distribution of a ferromagnetic rod-like particle dispersion. The present orientational distributions are in significantly good agreement with those of the theoretical prediction in regard to the position and the height of a peak and the general shape of the overall profile. Good agreement of the present magnetisation curves with the theoretical prediction verifies that the spin rotational Brownian motion is activated at a physically reasonable level in the present simulations. 相似文献