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111.
J. A. Ramos M. Larrañaga I. Mondragon W. Salgueiro A. Somoza S. Goyanes G. H. Rubiolo 《先进技术聚合物》2009,20(1):35-38
A set of diglycidylether of bisphenol‐A (DGEBA)/4,4′‐diaminodiphenylmethane (DDM) epoxy matrix modified with poly(ethylene oxide) (PEO), pre‐cured at two different temperatures, was examined by positron annihilation lifetime spectroscopy (PALS). The aim was to investigate the correlation between local free volume and mechanical properties. A negative deviation from the linear additivity rule of the local free volume is observed at both cure schedules. Using together the local free volume and mechanical results allows to conclude that the cure temperature makes small contribution to the flexural strength and modulus of blends but is responsible for the composition‐dependent rise of the fracture toughness. It is proposed that this behavior is a consequence of the nearest‐neighbor intrachain contacts or self‐association of the epoxy‐OH groups during cure leading to a non‐uniform space distribution of the DGEBA–PEO contacts, which causes the deflection of the crack path. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
112.
L. C. Mendes R. E. R. Abrigo V. D. Ramos P. S. C. Pereira 《Journal of Thermal Analysis and Calorimetry》2010,99(2):545-549
The influence of PC melt flow rate (MFR) on phase behavior, thermal and rheological properties of catalysed and non-catalysed
poly(ethylene terephthalate)/polycarbonate (PET/PC) (80/20 wt%) reactive blending were investigated. Two types of PC named
PC1 and PC2 with MFR 3.1 and 10.8 g/10 min, respectively, were used. Each PC and the catalyst showed significant influence
on calorimetric properties, thermal stability and WAXS patterns of the blends. Regarding to TG/DTG, the blends degraded in
two steps which were attributed to PET rich phase and PC one and permit to infer that a partially miscible blends were produced. 相似文献
113.
Felipe Avalos‐Belmontes Ivan Zapata‐Gonzalez Luis F. Ramos‐De Valle Roberto Zitzumbo‐Guzman Sergio Alonso‐Romero 《Journal of Polymer Science.Polymer Physics》2009,47(19):1906-1915
The composition, the thermal properties, and the kinetics of the thermo‐oxidative degradation of high‐density polyethylene (HDPE) were studied as a function of the increasing crystalline fraction, which resulted from the selective extraction of the amorphous part, through digestion by immersion in fuming nitric acid (HNO3) for different periods of time. The chemical and thermodynamic changes in HDPE, brought about by digestion in nitric acid for different periods of time, are discussed. Changes in the chemistry and microstructure of the HDPE, as a function of acid treatment for different periods of time, were studied using infra‐red spectroscopy (FTIR), gel permeation chromatography (GPC), and thermal analysis (DSC and TGA), as well as scanning electron microscopy (SEM). These studies were carried out as a function of the extracted amorphous fraction of HDPE samples via digestion in HNO3. These studies showed that in the first stages of the acid chemical attack, the amorphous part first undergoes a chemical modification and then dissolves into the strong acid medium. The total crystalline fraction apparently decreases during the first stages of the chemical attack and then increases as the amorphous part is extracted. TGA results show that as the selective extraction of the amorphous part occurs, there is a displacement of the thermo‐oxidative degradation toward higher temperatures. The kinetics of the thermo‐oxidative degradation as a function of the extraction of the amorphous part was followed according to the Horowitz‐Metzger method, and it was found that as the concentration of the crystalline fraction increases, the activation energy for the thermo‐oxidative degradation increases. SEM studies show that the extraction of the amorphous part does not affect the size of the crystalline lamellar thickness of HDPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1906–1915, 2009 相似文献
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116.
Lobo AO Corat MA Ramos SC Matsushima JT Granato AE Pacheco-Soares C Corat EJ 《Langmuir : the ACS journal of surfaces and colloids》2010,26(23):18308-18314
A method for the electrodeposition of hydroxyapatite films on superhydrophilic vertically aligned multiwalled carbon nanotubes is presented. The formation of a thin homogeneous film with high crystallinity was observed without any thermal treatment and with bioactivity properties that accelerate the in vitro biomineralization process and osteoblast adhesion. 相似文献
117.
Juliana S Luz Celso RR Ramos Márcia CT Santos Patricia P Coltri Fernando L Palhano Debora Foguel Nilson IT Zanchin Carla C Oliveira 《BMC biochemistry》2010,11(1):22
Background
The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors. 相似文献118.
Paula Gonçalves Fenga Nelson Ramos Stradiotto Maria Isabel Pividori 《Electroanalysis》2010,22(24):2979-2984
The growth of zinc hexacyanoferrate (ZnHCF) hybrid film on the surface of graphite‐epoxy composite (GEC) electrodes was demonstrated by cyclic voltammetry. Surface morphology of the hybrid film was investigated by using scanning electron microscopy. The effect of the type of monovalent cations on the redox behaviour of hybrid film was also studied. This effect indicated that the radius of the hydrated cation mainly determines the ion permeability of the film. 相似文献
119.
B.G. Oliveira R.C.M.U. Araújo A.B. Carvalho M.N. Ramos 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(2):563-566
B3LYP/6-311++G(d,p) calculations were used to predict some molecular properties of the C2H6N+?BeH2, C2H6N+?MgH2, C3H8N+?BeH2 and C3H8N+?MgH2 dihydrogen-bonded complexes. In these systems, it was demonstrated that the C2H6N+ and C3H8N+ protonated rings are potential candidates to bind with protonic hydrogens derived from alkaline earth metal compounds, BeH2 and MgH2. In terms of structural parameters and quantification of the dihydrogen bond energies, we should mention that the C2H6N+ three-membered ring provides the formation of stronger bound systems, which are 4.0 kJ mol?1 more stables than C3H8N+ four-membered ones. As complement, the analysis of the infrared spectrum indicated that red-shifts and blue-shifts are occurring in the N–H bonds of both C2H6N+ and C3H8N+ cationic rings. However, these two vibrational shifts were also verified on BeH2 and MgH2, what lead us to affirm that cationic compounds derived from small nitrogen rings and earth alkaline molecules are able to form unusual dihydrogen-bonded complexes by means of distinct spectroscopic phenomena, the red-shits and blue-shifts. 相似文献
120.