全文获取类型
收费全文 | 233篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 182篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 22篇 |
物理学 | 33篇 |
出版年
2024年 | 8篇 |
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 30篇 |
2012年 | 15篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1978年 | 4篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 31 毫秒
61.
David Brardan Sylvain Franger Diana Dragoe Arun Kumar Meena Nita Dragoe 《固体物理学:研究快报》2016,10(4):328-333
Entropic contributions to the stability of solids are very well understood and the mixing entropy has been used for forming various solids, for instance such as inverse spinels, see Nawrotsky et al., J. Inorg. Nucl. Chem. 29 , 2701 (1967) [1]. A particular development was related to high entropy alloys by Yeh et al., Adv. Eng. Mater. 6 , 299 (2004) [2] and Cantor et al., Mater. Sci. Eng. A 375–377 , 213 (2004) [3] (for recent reviews see Zhang et al., Prog. Mater. Sci. 61 , 1 (2014) [4] and Tsai et al., Mater. Res. Lett. 2 , 107 (2014) [5]) in which the configurational disorder is responsible for forming simple solid solutions and which are thoroughly studied for various applications especially due to their mechanical properties, e.g. Gludovatz et al., Science 345 , 1153 (2014) [6] and Lu et al., Sci. Rep. 4 , 6200 (2014) [7], but also electrical properties, Kozelj et al., Phys. Rev. Lett. 113 , 107001 (2014) [8], hydrogen storage, Kao et al., Int. J. Hydrogen Energy 35 , 9046 (2010) [9], magnetic properties, Zhang et al., Sci. Rep. 3 , 1455 (2013) [10]. Many unexplored compositions and properties still remain for this class of materials due to their large phase space. In a recent report it has been shown that the configurational disorder can be used for stabilizing simple solid solutions of oxides, which should normally not form solid solutions, see Rost et al., Nature Commun. 6 , 8485 (2015) [11] these new materials were called ”entropy‐stabilized oxides”. In this pioneering report, it was shown that mixing five equimolar binary oxides yielded, after heating at high temperature and quenching, an unexpected rock salt structure compound with statistical distribution of the cations in a face centered cubic lattice. Following this seminal study, we show here that these high entropy oxides (named HEOx hereafter) can be substituted by aliovalent elements with a charge compensation mechanism. This possibility largely increases the potential development of new materials by widening their (already complex) phase space. As a first example, we report here that at least one HEOx composition exhibits colossal dielectric constants, which could make it very promising for applications as large‐k dielectric materials. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
62.
R. C. Mehrotra G. Srivastava P. N. Nagar 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-3):145-148
Abstract Dialkylphosphonates1 and -thiophosphonates2 are versatile ligands but except for a few brief reports3–9 the chemistry of their derivatives with group IV and V elements remains unexplored. The corresponding derivatives of cyclic phosphonates and thiophos-phonates10 are virtually unknown. 相似文献
63.
Parameterizing above Guaranteed Values: MaxSat and MaxCut 总被引:1,自引:0,他引:1
Meena Mahajan Venkatesh Raman 《Journal of Algorithms in Cognition, Informatics and Logic》1999,31(2):335
In this paper we investigate the parameterized complexity of the problems MaxSat and MaxCut using the framework developed by Downey and Fellows. LetGbe an arbitrary graph havingnvertices andmedges, and letfbe an arbitrary CNF formula withmclauses onnvariables. We improve Cai and Chen'sO(22ckcm) time algorithm for determining if at leastkclauses of ac-CNF formulafcan be satisfied; our algorithm runs inO(|f| + k2φk) time for arbitrary formulae and inO(cm + ckφk) time forc-CNF formulae, where φ is the golden ratio
. We also give an algorithm for finding a cut of size at leastk; our algorithm runs inO(m + n + k4k) time. We then argue that the standard parameterization of these problems is unsuitable, because nontrivial situations arise only for large parameter values (k ≥ m/2), in which range the fixed-parameter tractable algorithms are infeasible. A more meaningful question in the parameterized setting is to ask whether m/2 + kclauses can be satisfied, or m/2 + kedges can be placed in a cut. We show that these problems remain fixed-parameter tractable even under this parameterization. Furthermore, for up to logarithmic values of the parameter, our algorithms for these versions also run in polynomial time. 相似文献
64.
Reactions of bis(acetylacetonato)aluminum(III)‐di‐μ‐isopropoxo‐di‐isopropoxo aluminum(III), [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(OPri)2] with aminoalcohols, (HO R NR1R2) in 1:1 and 1:2 molar ratios in refluxing anhydrous benzene yielded binuclear complexes of the types [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(O R NR1R2)(OPri)] and [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(O R NR1R2)2] (R (CH2)3 , R1 = R2 = H; R = CH2C(CH3)2 , R1 = R2 = H; R = (CH2)2 , R1 = H, R2 = CH3; and R (CH2)2 , R1 = R2 = CH3), respectively. All these compounds are soluble in common organic solvents and exhibit sharp melting points. Molecular weight determinations reveal their binuclear nature in refluxing benzene. Plausible structures have been proposed on the basis of elemental analysis, molecular weight measurements, IR, NMR (1H, 13C, and 27Al), and FAB mass spectral studies. 27Al NMR spectra show the presence of both five‐ and six‐coordinated aluminum sites. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:518–522, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10184 相似文献
65.
An exact solution of a four part mixed boundary value problem representing a three colinear crack system connected with specified crack opening displacements between the cracks is obtained. The three cracks thus become one with pressure and/or opening displacement prescribed on the crack face. From considerations of dual symmetry and a formulation based on Papkovich-Neuber harmonic functions, the boundary value problem is reduced to solving a quadruple set of integral equations. An exact solution of these equations is derived using a modified finite Hilbert transform technique. The closed form results for the stress distributions and the crack-tip stress intensity factors are presented. Limiting cases of the solution yield results which agree with well known solutions. 相似文献
66.
Hydrolysis of pure Sb(OPri)3 by sol–gel method followed by sintering at 500 °C yields microcrystallites of Sb2O3 (senarmonite phase). Under similar conditions bimetallic alkoxide, [NaSb(OPri)4], yields a mixture of binary oxides Sb2O3 and Sb2O4. Chemical modification of Sb(OPri)3 with oximes forms monomeric products of the type [Sb(OPri)3−n
{ON=C(CH3)R}
n
] {where R = CH3, n = 1 [1]; n = 2 [2]; n = 3 [3]; R = 2-C5H4N, n = 1 [4]; n = 2 [5]; n = 3 [6]; R = 2-C4H3O, n = 1 [7]; n = 2 [8]; n = 3 [9]; R = 2-C4H3S, n = 1 [10]; n = 2 [11]; n = 3 [12]}. The liquid products [1–3, 7
&
10] were purified by distillation while the solids by recrystallization. All these products were characterized by elemental
analyses, IR, NMR (1H and 13C{1H}) and representative derivatives [1], [2] and [3] by FAB mass studies. On the basis of these studies, a distorted pyramidal structure for all the derivatives may be assumed
in the solution state containing an end-on coordination of oximes with the metal atom. Hydrolysis of the distilled precursors
[1], [2] and [3] under sol–gel conditions yields pure nano-sized α-Sb2O4. All the oxides were characterized by XRD, SEM and EDX analysis exhibiting minimum particle size for the oxide obtained from
the precursor [3]. 相似文献
67.
Complex permittivity, permeability and microwave absorbing properties of a U-type hexaferrite series Ba4Mn(2−x)ZnxFe36O60 (with 0≤x≤2 in step of 0.5) have been examined in the X-band (8.2-12.4 GHz) frequency range. The series have been prepared using conventional solid state reaction route. Microstructural variations with composition have been found with X-ray diffraction (XRD) and scanning electron microgram (SEM). The complex permittivity (ε?=ε′−jε″) and permeability (μ?=μ′−jμ″) were measured using vector network analyzer (Agilient Make model PNA E8364B). These parameters were then used for calculating the reflection loss for determination of microwave absorbing properties. Addition of Zn resulted in an increase in reflection loss from −4 dB (or 60 % absorption) in sample with x= 0 to −32 dB (99.92% absorption) in sample with x=1 when the sample thickness was 1.7 mm. Multiple peaks of resonance were obtained in the dielectric and magnetic loss spectra for all samples with x>0. The result indicates that the sample with composition Ba4MnZnFe36O60, i.e., x=1, can be used effectively for microwave absorption and suppression of electromagnetic interference. 相似文献
68.
Shakya Anshul Chikhale Rupesh V. Bhat Hans Raj Alasmary Fatmah Ali Almutairi Tahani Mazyad Ghosh Surajit Kumar Alhajri Hassna Mohammed Alissa Siham A. Nagar Shuchi Islam Md Ataul 《Molecular diversity》2022,26(1):265-278
Molecular Diversity - Transmembrane protease serine-2 (TMPRSS2) is a cell-surface protein expressed by epithelial cells of specific tissues including those in the aerodigestive tract. It helps the... 相似文献
69.
Nagar V. Kar R. Pansare-Godambe L. Chand N. Bute A. Bhale D. Rao A. V. S. S. N. Shashidhar R. Maiti Namita 《Plasma Chemistry and Plasma Processing》2022,42(5):1115-1126
Plasma Chemistry and Plasma Processing - Traditional disinfection methods against pathogens have numerous shortcomings, and inventive methods like cold plasma are required for virus inactivation.... 相似文献
70.
Student Perceptions of Interest,Learning, and Engagement from an Informal Traveling Science Museum 下载免费PDF全文
Laura B. Sample McMeeking Andrea E. Weinberg Kathryn J. Boyd Meena M. Balgopal 《School science and mathematics》2016,116(5):253-264
Informal Science Education (ISE) programs have been increasing in popularity in recent years. The National Research Council has laid out six strands that ISE programs should try to address, including increasing interest, knowledge, and allowing participants to engage in scientific activities. Past research suggests that informal settings can increase interest in science and may lead to knowledge gains. This study examined the impact of a unique ISE program that resembles a traveling museum and offers small‐scale, interactive experiences. Affective outcomes and self‐reported learning outcomes of the students who participated in the program were examined. In general, students reported increases in science interest and some knowledge gains. Students also reported they thought the program allowed them to engage in science. There were differences in student responses based on grade level, with intermediate elementary students more likely to report greater knowledge gains and more likely to see the educational value of the experience. Interestingly, middle school students were more likely to value the social aspects of the experience, another important aspect of ISE. This study provides some insight into the connections between the different ISE strands of informal science education and offers suggestions for future research. 相似文献