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1.
Melting and crystallization of n-decane embedded into porous glass with the mean pore size of about 6.4 nm were studied using acoustic and DSC methods. Smearing of the phase transitions, decrease of melting and freezing temperatures, pronounced hysteresis between melting and crystallization were revealed by both methods. In DSC measurements for the pore filling factors 70% and higher double peaks were observed upon cooling while only single peaks were present upon heating. Also a high reduction of the corresponding phase transition heats was revealed. Melting and freezing intervals determined by acoustic and DSC methods strongly differed from each other. A model which qualitatively explains the observed anomalies is proposed. It supposes the formation of liquid layers on the surface of the pores.  相似文献   
2.
Halogen-functionalized graphenes are utilized as electronic devices and energy materials. In the present paper, the effects of halogen-termination of graphene edge on the structures and electronic states of graphene flakes have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the halogen termination, while the excitation energy is red-shifted. The drastic change showed a possibility as electronic devices such as field-effect transistors. The change of electronic states caused by the halogen termination of graphene edge was discussed on the basis of the theoretical results.  相似文献   
3.
To meet the processing requirements of resin transfer moulding(RTM)technology,reactive diluent containing m-phenylene moiety was synthesized to physically mixed with phenylethynyl terminated cooligoimides with well-designed molecular weights of 1500-2500 g/mol derived from 4,4’-(hexafluoroisopropylidene)diphthalic anhydride(6 FDA),3,4’-oxydianiline(3,4’-ODA)and m-phenylenediamine(m-PDA).This blend shows low minimum melting viscosity(<1 Pa·s)and enlarged processing temperature window(260–361℃).FPI-R-1 stays below 1 Pa·s for2 h at 270℃.The relationship between the molecular weight of the blend and its melting stability was first explored.Blending oligoimides with lower molecular weights exhibit better melting stability.Upon curing at 380℃for 2 h,the thermosetting polyimide resin demonstrates superior heat resistance(Tg=420-426℃).  相似文献   
4.
This article presents a new model to simulate melting with natural convection of a phase change material. For the phase change problem, the enthalpy formulation is used. Energy equation is solved by a finite difference method, whereas the fluid flow is solved by the multiple relaxation time (MRT) lattice Boltzmann method. The model is first verified and validated using the data from the literature. Then, the model is applied to a tall brick filled with a fatty acid eutectic mixture and the results are presented. The main results are (1) the spatial convergence rate is of second order, (2) the new model is validated against data from the literature and (3) the natural convection plays an important role in the melting process of the fatty acid mixture considered in our work.  相似文献   
5.
Different types of 1-ethyl-3-methylimidazolium (EMIM) ionic liquid compounds, including halides, tetrafluoroborate, tribromide, diiodobromate, chloroaluminate, and bromine aluminate, have been investigated using quantum chemical calculations. First, geometry optimizations of the ion systems, including {[EMIM]Xn}(n-1)- (X = Cl, Br, I, BF4, AlCl4, AlBr4, Br3, IBrI, FHF; n = 2, 3) and {[EMIM]2Xn'}(n'-2)- (n' = 3, 4, 5), were performed using the density functional theory (DFT) B3LYP method together with the 6-311++G(d, p) (6-311G(d, p) for I) basis set. The vibrational spectra were also calculated for the EMIM halides and tetrafluoroborate. The obtained structures and vibrational spectra were consistent with experimental results. In addition, a linear correlation between melting point and interaction energy was obtained for the {[EMIM]2Xn'}(n'-2)- models of the compounds studied.  相似文献   
6.
Outdoor applications of composites raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The weathering resulted in considerable colour fading of the composites. Composites containing darker colour pigments had better colour stability. Scanning electron microscopy analysis revealed that surface cracks caused by weathering in a wood-polypropylene composite having a higher polypropylene content were less abundant, and the deterioration of the surface layer was lower compared to composites containing less polymer. Measurements of melting temperatures by differential scanning calorimetry gave a consistent picture of polypropylene degradation in the surface layer. After weathering, a decrease in Charpy impact strength was found for composites characterised by higher moisture absorption.  相似文献   
7.

In previous papers, one of the authors (K. K.) has observed the anomalous melting of the surface layer of deuteron implanted Al, containing so-called "tunnel structures", on the electron bombardment in transmission electron microscope. In the present paper, we intended to observe the evidence of the d-d nuclear reaction, expecting neutron emission, associated with the melting phenomenon. However, the result was rather unexpected. The melting phenomenon was certainly observed under the same experimental conditions as before. But, in spite of the melting, neutron emission associated with the nuclear reaction was not observed. And, more unexpectedly, X-ray emission of energy less than roughly 400 v keV was observed when specimens with a bubble structure, which never showed melting, were bombarded with electron beams. Several conceivable mechanisms are discussed which, however, are all not convincing to explain the melting. The melting is attributed to some excess energy generation. The error estimation of the radiation measurements was undertaken.  相似文献   
8.
9.
Shear-induced nonisothermal crystallization of two commercial polylactides (PLAs) differing in optical purity was studied. The molten polymers were sheared at selected temperatures (Ts) and subsequently cooled. The crystallization was followed by a light depolarization method, whereas the specimens were analysed ex-situ by DSC, 2D-WAXS and SEM after etching. It was found that the effect of shear, especially on the crystallinity developed during post-shearing cooling, intensified with a decrease of Ts from 160 to 146 °C, and with increasing shear rate and strain. Moreover, the effect of shear on PLA1.5 with d-lactide content of 1.5% was stronger than PLA2.8 with 2.8% of d-lactide, although maximum crystallinity of both polymers was practically the same. A decrease of cooling rate from 30 to 10 °C/min increased crystallinity of both PLAs, except for those shearing conditions which induced high crystallinity even during faster cooling. Although SEM examination revealed some row-nucleated forms, no significant crystal orientation was detected by 2D-WAXS, indicating that, under the experimental conditions, the shear induced predominantly point-like nuclei.  相似文献   
10.
为了确保晶硅太阳能电池在拥有较高光电转换效率的同时降低投入成本,本文研究了45wt%的低固相含量状态下不同粒径及振实密度的片状银粉对背面银浆性能的影响。将球形银粉经过不同时间的球磨得到不同粒径的片状银粉。用这四种银粉制成背面银浆并经过印刷烧结形成背电极,研究了粒径、振实密度对背电极烧结膜形态及电性能的影响。结果证明平均粒径为2.5μm的片状银粉具有最高的振实密度,由其制备背电极的烧结膜最为致密,焊接强度达到8.5 N,硅太阳能电池的光电转换效率达到18.09%,可以满足目前背面银浆的商业使用需要。  相似文献   
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