全文获取类型
收费全文 | 224篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 138篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 50篇 |
物理学 | 43篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 17篇 |
2012年 | 14篇 |
2011年 | 7篇 |
2010年 | 15篇 |
2009年 | 7篇 |
2008年 | 16篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有237条查询结果,搜索用时 15 毫秒
131.
Ramn Artiaga Jorge Lpez‐Beceiro Javier Tarrío‐Saavedra Carlos Gracia‐Fernndez Salvador Naya Jos L. Mier 《Journal of Chemometrics》2011,25(6):287-294
A mathematical model for the total heat flow obtained in differential scanning calorimetry (DSC) experiments from polymers with enthalpic relaxation is proposed. It is limited to the glass transition and enthalpic relaxation range of temperature and to the cases where the enthalpic relaxation is the only non‐reversing process taking place. The model consists of a mixture of functions representing the heat capacity heat flow of the glassy and non‐glassy fractions, the glass transition progress and the enthalpic relaxation heat flow. Optimal fittings of the model were performed on the experimental total heat flow data, obtained from two thermoplastics with different aging times. Considering which functions of the mixture represent reversing and non‐reversing processes, the reversing and non‐reversing heat flows were also estimated. The estimated reversing and non‐reversing signals were compared with the ones obtained by modulation. On the whole a good match was found, which was even better considering that the estimates are not affected by the frequency effect of the modulated temperature DSC (MTDSC) measurements. The model assumes linear trends for the heat capacity heat flow of the glassy and non‐glassy structures. The glass transition progress is represented by a generalized logistic function and the enthalpic relaxation heat flow by the first derivative of another generalized logistic. It brings about a new approach to these phenomena, where the parameters of these functions represent the temperature at which each event is centered, the change of heat capacity (Cp) at the glass transition and the energy involved in the enthalpic recovery. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
132.
Wang H Wang B Quek XY Wei L Zhao J Li LJ Chan-Park MB Yang Y Chen Y 《Journal of the American Chemical Society》2010,132(47):16747-16749
Selective synthesis of single walled carbon nanotubes (SWCNTs) with specific (n,m) structures is desired for many potential applications. Current chirality control growth has only achieved at small diameter (6,5) and (7,5) nanotubes. Each (n,m) species is a distinct molecule with structure-dependent properties; therefore it is essential to extend chirality control to various (n,m) species. In this communication, we demonstrate the highly selective synthesis of (9,8) nanotubes on a cobalt incorporated TUD-1 catalyst are (Co-TUD-1). When catalysts were prereduced in H(2) at the optimized temperature of 500 °C, 59.1% of semiconducting nanotubes have the (9,8) structure. The uniqueness of Co-TUD-1 relies on its low reduction temperature (483 °C), large surface area, and strong metal-support interaction, which stabilizes Co clusters responsible for the growth of (9,8) nanotubes. SWCNT thin film field effect transistors fabricated using (9,8) nanotubes from our synthesis process have higher average device mobility and a higher fraction of semiconducting devices than those using (6,5) nanotubes. Combining with further postsynthetic sorting techniques, our selective synthesis method brings us closer to the ultimate goal of producing (n,m) specific nanotube materials. 相似文献
133.
In this work a system of two parabolic singularly perturbed equations of reaction–diffusion type is considered. The asymptotic behaviour of the solution and its partial derivatives is given. A decomposition of the solution in its regular and singular parts has been used for the asymptotic analysis of the spatial derivatives. To approximate the solution we consider the implicit Euler method for time stepping and the central difference scheme for spatial discretization on a special piecewise uniform Shishkin mesh. We prove that this scheme is uniformly convergent, with respect to the diffusion parameters, having first-order convergence in time and almost second-order convergence in space, in the discrete maximum norm. Numerical experiments illustrate the order of convergence proved theoretically. 相似文献
134.
J. R. Gancedo M. Gracia A. Martínez-Alonso J. L. Miranda J. M. D. Tascón 《Hyperfine Interactions》1992,71(1-4):1403-1406
Mössbauer spectroscopy was used to determine the iron-containing minerals that remained in two different Spanish subbituminous coals after acidic treatments. Spectra were taken before and after treatments of both coals with HCl and HCl followed by HF. Pyrite, jarosite and Fe2+-clay were the main iron mineral constituents of the untreated samples. After the treatments significant changes in the relative concentration of these species were noticed. The weakness of the used demineralization procedures is discussed. 相似文献
135.
Mössbauer spectroscopy has been used extensively in surface studies. The different experimental approaches to derive surface information from this technique are reviewed. 相似文献
136.
Jorge?López-BeceiroEmail author Ramón?Artiaga Carlos?Gracia Javier?Tarrío-Saavedra Salvador?Naya José?Luis?Mier 《Journal of Thermal Analysis and Calorimetry》2011,104(1):169-175
Vegetable oils of different types and qualities are widely used in homemade cooking and food industry. Most of the safety
concerns were related to possible oxidation processes produced at the relatively high temperatures used when frying. Thus,
the thermal stability to oxidation is an important parameter for edible oils. Oils from the Arbequina, Picual, Hojiblanca
and Cornicabra olive varieties, corn, soybean and sunflower are studied in this work by means of pressure differential scanning
calorimetry (PDSC). The general aim of this work is to evaluate the thermooxidative stability of these vegetable oils by the
ASTM onset oxidation temperature (OOT) method. In addition, the ability of some parameters to identify different oils and
some relations between the chemical composition and the OOT results are investigated. 相似文献
137.
An element g in a group G is called a left Engel element of G, if for each x ∈ G, there is a positive integer n = n(g, x) such that [x, n g] = 1. In this article, we will study a generalization of the left Engel elements and its connections with the generalized Hirsch–Plotkin and Baer radical. 相似文献
138.
Mbaz Gracia It Mwad Parani Sundararajan Oluwafemi Oluwatobi Samuel 《Journal of fluorescence》2022,32(5):1769-1777
Journal of Fluorescence - Quantum dots (QDs) have attracted much attention over the past decades due to their outstanding properties. However, obtaining QDs with excellent photoluminescence and... 相似文献
139.
Marija Prosheva Mohammad Ali Aboudzadeh Gracia Patricia Leal Jadranka Blazhevska Gilev Radmila Tomovska 《Particle & Particle Systems Characterization》2019,36(7)
Ultraviolet (UV) degradation is one of the most important challenges of waterborne coatings in exterior applications. One of the ways to address this issue is addition of radical scavenging species within the polymer matrix. Herein, hybrids of graphene (G) and multiwall carbon nanotubes (CNTs) in different ratios are used as radical scavenging species. Evaluated by electron paramagnetic resonance spectroscopy, it is found that the hybrid made of G/CNTs in ratio of 10:1 efficiently captures and quenches the free radicals. The waterborne polymer composites containing 1 wt% of hybrid G/CNT are synthesized by in situ miniemulsion free radical polymerization using a water soluble initiator. However, due to excellent efficiency to capture free radicals, the polymerization performed using water soluble initiators in the presence of 10:1 G/CNT filler is hindered. This is resolved by physical separation of the free radicals and the scavenging materials within different phases by use of oil soluble initiator. The resulting polymer composites, beside having excellent mechanical resistance, present exceptional stability under accelerated aging conditions during 400 h, suppressing almost completely the UV photodegradation. This is attributed to the efficient radical scavenging of the G/CNTs hybrid filler distributed within polymer matrix, resulting in high‐performance UV protective waterborne composite coatings. 相似文献
140.
Nikolai L. Yakovlev Hou Chin Quek Karol M. Dąbrowski William R. Birch 《Surface and interface analysis : SIA》2019,51(7):697-702
On the basis of a miniature polarisation modulator, a precision ellipsometry system has been made, enabling real-time measurement of subnanometre thin layers on reflecting substrates. This system monitored the kinetics of adsorption and desorption of propanol, or ethanol, or methanol on oxidised Si substrates. While adsorption of propanol and ethanol increased the thickness, adsorption of methanol showed surprising kinetics: the thickness first increased, then decreased. To explain this, a model of substitutional (or competitive) adsorption has been used, where the target molecule is adsorbed only when it substitutes another one leaving an adsorption site. The model fits the experimental data quantitatively and can predict processes involving several components on solid surfaces. Precision ellipsometry demonstrated its high analytical potential in investigation of surfaces at molecular level. 相似文献