全文获取类型
收费全文 | 165篇 |
免费 | 4篇 |
专业分类
化学 | 100篇 |
晶体学 | 1篇 |
数学 | 14篇 |
物理学 | 54篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 7篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 3篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 12篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有169条查询结果,搜索用时 15 毫秒
161.
A. Cabral-Prieto I. Garc??a-Sosa N. Nava E. Camps Luis Escobar R. L??pez-Casta?arez O. Olea-Cardoso 《Hyperfine Interactions》2011,202(1-3):153-157
Amorphous alloy ribbons of Fe77Cr2B16Si5 were exposed to cold plasmas of N2 and Ar?CN2 at temperatures lower than Tx?=?808?K. The conversion X-ray M?ssbauer spectra of the plasma-exposed ribbons consist of a singlet and a broadened magnetic sextet. The singlet with isomer shift $\updelta = -0.11$ ?mm/s can be assigned to $\upgamma $ -Fe austenite phase. Minor bulk magnetic changes in the alloy were measured as a consequence of these treatments; e.g. the relative intensities A23 of the transmission M?ssbauer spectra of the untreated and treated samples, were 3.22 and 3.56, respectively, the Bhf values changed from 22.9?T (untreated sample) to 22.4?T (plasma treated samples). Unexpectedly, the $\upgamma $ -Fe phase can also be produced by simply heating the alloy ribbons under N2 flux at temperatures as low as 423?K. M?ssbauer data of the crystallized samples are also reported, and a qualitative assessment on the mechanical properties of the Fe77Cr2B16Si5 alloy associated with the plasma and/or temperature surface induced $\upgamma $ -Fe phase is given. 相似文献
162.
J. A. Wang A. Cuan J. Salmones N. Nava S. Castillo M. Morn-Pineda F. Rojas 《Applied Surface Science》2004,230(1-4):94-105
The textural properties, morphological features, surface basicity and oxygen reduction behaviours of titania and Pt supported titania catalysts synthesized via a sol–gel method were studied by means of N2 physisorption, SEM, TEM, CO2-TPD and H2-TPR techniques. Mesostructured TiO2 shows a very narrow pore size distribution that uniformly centred at about 4 nm. High resolution TEM images confirmed that most of Pt particles on Pt/TiO2-SG had a size smaller than 2 nm. Both the titania support and Pt loaded catalysts chiefly contained weak basic sites with small amount of strong basic sites. Loading Pt did not significantly alter the surface reduction characters of titania, indicating a weak interaction between Pt metals and titania support. Catalytic evaluation revealed that the selectivity of NO reduction over titania was insensitive to variation of textural property. On the bare titania, low NO conversion but high selectivity to N2O was obtained. However, the Pt/TiO2-SG catalysts exhibited high NO conversion and high selectivity to N2, which is assumed to relate to NO dissociation catalysed by the metallic Pt clusters. In addition, when the reaction temperature was above 200 °C, 3–11% NO2 was yielded over the Pt/TiO2-SG catalysts, which was discussed on a basis of reaction competition, metal-support interaction and NO dissociation. 相似文献
163.
A highly diastereoselective Diels-Alder reaction between cyclopentadiene and ethyl (Z)-2-N-Boc-amino-3-nitroacrylate in neat conditions affords the ethyl 2-t-butoxycarbonylamino-3-endo-nitro-bicyclo[2.2.1]hept-5-ene-2-exo-carboxylate: a new constrained carbocyclic amino acid. Catalytic hydrogenation of this cycloadduct gave the corresponding reduced norbornane derivative. A preliminary investigation into the chemistry of these two amino acids was performed. In particular, the epimerization to their corresponding 3-exo-nitro compounds by treatment both with acid and base was studied. From this study, valuable information on the endo/exo process at the C-3 carbon atom, as well as on the stability of the different stereomers, was obtained. The stability is closely related to the presence or the absence of the double bond in the ring and to the substitution pattern. Finally, deprotection of the amino acid function has been performed. 相似文献
164.
E. Carreto C. Piña H. Arriola A. Barahona N. Nava V. Castaño 《Journal of Radioanalytical and Nuclear Chemistry》2001,250(3):453-458
Iron-doped silicate (zircon), prepared by a ceramic method with the addition of LiF as mineralizer, was analyzed by X-ray powder diffraction (XRD) and 57Fe Mössbauer spectroscopy to obtain information on the solid solution formation. The results of X-ray diffraction and Mössbauer spectroscopy have shown that only a small fraction of iron, about 1.5 mol%, is incorporated in the zircon structure as paramagnetic Fe3+ species while the remaining Fe3+ cations form magnetic -Fe2O3 particles which are trapped within the zircon matrix. 相似文献
165.
M. García Hernández F. de J. Carrillo Romo A. García Murillo D. Jaramillo Vigueras M. A. Meneses Nava P. Bartolo Pérez G. Chadeyron 《Journal of Sol-Gel Science and Technology》2010,53(2):246-254
Erbium (Er3+) 0.5% mol doped barium titanate (BaTiO3) thin films were elaborated via sol–gel method and dip-coating technique using titanium alkoxide and barium pentanedionate.
Two syntheses were performed [with and without polyvinylpyrrolidone (PVP)] in order to obtain thick films. The BaTiO3:Er3+ thin films prepared from the sol with PVP were elaborated with 1 layer and those without PVP and were elaborated with 17 layers. In both cases, the films
were deposited on silica quartz substrates. Both BaTiO3:Er3+ films presented a cubic phase, as determined by X-ray diffraction. BaTiO3:Er3+ films elaborated with PVP via single-step dip coating produced crack-free films with thicknesses of ~800 nm. SEM micrographs
for the obtained BaTiO3:Er3+ films revealed high homogeneity and density. Mapping images obtained from BaTiO3:Er3+ revealed homogeneous distribution of Er3+ ions on the surface. XPS analyses of the chemical state and chemical environment of the constituent elements in the compositions
showed that Er3+ ions in (Ba1−x
Er
x
)TiO3 are in mixed valence of Er3+/Er2+. The BaTiO3:Er3+-PVP film exhibited luminescent properties under near-infrared excitation, as revealed by green emissions. The BaTiO3:Er3+-PVP film has good potential for optical applications. 相似文献
166.
Assembling OX40 aptamers on a molecular scaffold to create a receptor-activating aptamer 总被引:1,自引:0,他引:1
Dollins CM Nair S Boczkowski D Lee J Layzer JM Gilboa E Sullenger BA 《Chemistry & biology》2008,15(7):675-682
We show that a molecular scaffold can be utilized to convert a receptor binding aptamer into a receptor agonist. Many receptors (including tumor necrosis receptor family members) are activated when they are multimerized on the cell surface. Molecular scaffolds have been utilized to assemble multiple receptor binding peptide ligands to generate activators of such receptors. We demonstrate that an RNA aptamer that recognizes OX40, a member of the tumor necrosis factor receptor superfamily, can be converted into a receptor-activating aptamer by assembling two copies on an olignucleotide-based scaffold. The OX40 receptor-activating aptamer is able to induce nuclear localization of nuclear factor-kappaB, cytokine production, and cell proliferation, as well as enhance the potency of dendritic cell-based tumor vaccines when systemically delivered to mice. 相似文献
167.
J. A. Ascencio M. Mendoza T. Santamaria M. Perez I. Nava C. Gutierrez-Wing M. Jose-Yacaman 《Journal of Cluster Science》2002,13(2):189-197
In the new nanotechnology devices design, the stability of the systems is very important, in the present work we report evidences of internal and external changes of nanoparticles passivated by thiol molecules when they are irradiated under a high flux of an electron beam in the transmission electron microscope. High Resolution images were digitized and processed in order to identify the contrast changes produced by the atomic inside the nanoparticles. Fcc and decahedral nanoparticles cases are shown. Molecular dynamics calculations are also included in order to compare the experimental evidences with the cluster conditions of stabilities. Both theoretical and experimental results imply the occurrence of atomic and twining movements, and indicate that the n-alkyl thiol molecules prevent atomic movement and changes on the particle structure are not observed. 相似文献
168.
Pellegrino S Contini A Clerici F Gori A Nava D Gelmi ML 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8705-8715
A very efficient synthesis of orthogonally protected 1H-azepine-4-amino-4-carboxylic acid, abbreviated as Azn, a conformationally restricted analogue of ornithine, was realized. It was obtained on a gram scale in good overall yield in five steps, three of which did not require isolation of the intermediates, starting from the readily available 1-amino-4-oxo-cyclohexane-4-carboxylic acid. Both enantiomers were used for the preparation of pentapeptide models containing Ala, Aib, and Azn. Conformational studies using both spectroscopic techniques (NMR, CD) and molecular dynamics on model 5-mer peptides showed that the (R)-Azn isomer possesses a marked helicogenic effect. 相似文献
169.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献