全文获取类型
收费全文 | 205篇 |
免费 | 3篇 |
专业分类
化学 | 152篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 16篇 |
物理学 | 31篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有208条查询结果,搜索用时 11 毫秒
61.
Jonathan S. Schulze Timothy P. Lodge Christopher W. Macosko Jens Hepperle Helmut Münstedt Heike Bastian Dino Ferri David J. Groves Yong Hoon Kim Mike Lyon Thomas Schweizer Terry Virkler Erik Wassner Wim Zoetelief 《Rheologica Acta》2001,40(5):457-466
The transient uniaxial extensional viscosity η
e
of linear low density polyethylene (LLDPE) has been measured using the commercial Rheometric Scientific RME and the Münstedt
Tensile Rheometer in an effort to compare the performance of available extensional rheometers. The RME indicated a significant
strain hardening of the LLDPE, especially at a strain rate of 1 s−1. In contrast, the Münstedt rheometer showed the LLDPE to be only slightly strain hardening. This artificial strain hardening
effect in the RME resulted from the strain rate applied to the sample, determined from the sample deformation, being up to
20% less than the set strain rate. These results initiated a round-robin experiment in which the same LLDPE was tested on
several RMEs in various locations around the world. All but one of the RMEs indicated a deviation between set and applied
strain rates of at least 10%, especially at strain rates above 0.1 s−1. The strain rate deviation was found to depend strongly on the value of the basis length L
0
, and may result from the upper pair of belts not properly gripping the sample during extension. Thus visual inspection of
the sample deformation is necessary to determine the applied strain rate. The most accurate measurements of η
e
with respect to the strain rate deviation were obtained when the correct L
0
value and belt arrangement were used. A list of recommendations for running an RME test is provided. Future work focusing
on the fluid mechanics during the test may identify fully the cause of the strain rate deviation, but from a practical point
of view the problem can be corrected for in the determination of η
e
.
Received: 27 September 2000/Accepted: 5 February 2001 相似文献
62.
Lavinia de Ferri Pier Paolo Lottici Andrea Lorenzi Angelo Montenero Giovanna Vezzalini 《Journal of Sol-Gel Science and Technology》2013,66(2):253-263
Medieval glass is commonly attacked by atmospheric pollutants conveyed by water, triggering the corrosion process. Current conservation strategies aim to maintain window glass in its original context, and so it is necessary to protect it from further degradation. Sol–gel technology is very effective for the preparation of protective films, using Si-alkoxide precursors chemically similar to the substrate. The present work discusses water-repellent hybrid sol–gel coatings made from tetra-ethyl-ortho-silicate with different quantities of Si-alkoxides, functionalized with various alkyl groups. The coatings were deposited using the dip-coating technique and characterized by UV–VIS and FT-IR spectroscopy. Static and dynamic contact angle measurements showed an overall homogeneity of the coatings and indicated improved water-repellency when functionalized by long alkyl chains. The coatings with best performance in terms of transparency and contact angle, and with the lowest organic content, were selected and applied to medieval-like glass samples. Colorimetric characterization was carried out using a spectrophotometric scanner before and after application of the coatings and no significant color changes were found. The electron microscopy images revealed relatively even, crack-free coatings, especially with higher organic contents. Contact angle and colorimetric measurements were repeated after accelerated ageing by exposure to UV light and an SO2-saturated atmosphere. A significant decrease in the contact angle was observed only for the samples treated at the highest SO2 concentration. The silica-based materials did not give reaction by-products, were water-repellent, compatible with the substrate, colorless, transparent, and stable under exposure to chemicals and light, thereby satisfying the main requirements for the conservation of Cultural Heritage. 相似文献
63.
Marco Giannetto Elisabetta Maiolini Elida Nora Ferri Stefano Girotti Giovanni Mori Maria Careri 《Analytical and bioanalytical chemistry》2013,405(2-3):737-743
A new amperometric immunosensor for 2,4,6-trinitrotoluene based on the working principle of competitive enzyme-linked immunosorbent assay was developed and characterised. An electrodeposited nanogold substrate was functionalised by deposition of self-assembled monolayers of 2-aminoethanethiol as linkers for the subsequent immobilisation of polyamidoaminic dendrimers. Our approach makes use of those dendrimers to anchor a trinitrobenzene-ovalbumin conjugate on the electrode surface. The immunosensor was tested and validated for the determination of 2,4,6-trinitrotoluene showing high selectivity with respect to other nitroaromatic compounds, a limit of detection of 4.8 ng/mL and a limit of quantitation of 6 ng/mL. The immunosensor was tested for the quantification of the analyte in spiked soils and in a real sample of post-blast soil, evidencing a good recovery rate (113 %). Figure
Setup of sensor and immunoassay for TNT 相似文献
64.
Ten international reference samples have been analysed for thallium content by differential pulse anodic-stripping voltammetry. Two separation techniques, solvent extraction and ion-exchange, were employed to preconcentrate the thallium: the results were critically compared to establish which was the better separation technique. The values found were quite satisfactory and confirmed the wide scope for application (not yet fully investigated) of voltammetry in geochemical studies. 相似文献
65.
The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts 下载免费PDF全文
Adrian Marberger Dr. Davide Ferri Martin Elsener Prof. Oliver Kröcher 《Angewandte Chemie (International ed. in English)》2016,55(39):11989-11994
The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH3) on vanadium‐based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time‐resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH3 coordinated to Lewis sites on vanadia on tungsta–titania (V2O5‐WO3‐TiO2), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono‐oxo vanadyl group that reduces only in the presence of both nitric oxide and NH3. We were also able to verify the formation of the nitrosamide (NH2NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance. 相似文献
66.
A digital representation of a semigroup (S,⋅) is a family 〈F
t
〉
t∈I
, where I is a linearly ordered set, each F
t
is a finite non-empty subset of S and every element of S is uniquely representable in the form Π
t∈H
x
t
where H is a finite subset of I, each x
t
∈F
t
and products are taken in increasing order of indices. (If S has an identity 1, then Π
t∈∅
x
t
=1.) A strong digital representation of a group G is a digital representation of G with the additional property that for each t∈I,
for some x
t
∈G and some m
t
>1 in ℕ where m
t
=2 if the order of x
t
is infinite, while, if the order of x
t
is finite, then m
t
is a prime and the order of x
t
is a power of m
t
. We show that any free semigroup has a digital representation with each |
F
t
|=1 and that each Abelian group has a strong digital representation. We investigate the problem of whether all groups, or even
all finite groups have strong digital representations, obtaining several partial results. Finally, we give applications to
the algebra of the Stone-Čech compactification of a discrete group and the weakly almost periodic compactification of a discrete
semigroup.
Dedicated to Karl Heinrich Hofmann on the occasion of his 75th birthday.
Stefano Ferri was partially supported by a research grant of the Faculty of Sciences of Universidad de los Andes. The support is gratefully acknowledged.
Neil Hindman acknowledges support received from the National Science Foundation via Grant DMS-0554803. 相似文献
67.
68.
A chemoselective synthesis of the macrocyclic core of leucascandrolide A has been achieved, utilizing highly enantioselective allylmetalations, an enantioselective Noyori reduction of a propargylic ketone and olefin metatheses as the key steps. 相似文献
69.
Pau Ferri Chengeng Li Reisel Millán Dr. Joaquín Martínez-Triguero Dr. Manuel Moliner Dr. Mercedes Boronat Dr. Avelino Corma 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19876-19883
The methanol-to-olefins reaction catalyzed by small-pore cage-based acid zeolites and zeotypes produces a mixture of short chain olefins, whose selectivity to ethene, propene and butene varies with the cavity architecture and with the framework composition. The product distribution of aluminosilicates and silicoaluminophosphates with the CHA and AEI structures (H-SSZ-13, H-SAPO-34, H-SSZ-39 and H-SAPO-18) has been experimentally determined, and the impact of acidity and framework flexibility on the stability of the key cationic intermediates involved in the mechanism and on the diffusion of the olefin products through the 8r windows of the catalysts has been evaluated by means of periodic DFT calculations and ab initio molecular dynamics simulations. The preferential stabilization by confinement of fully methylated hydrocarbon pool intermediates favoring the paring pathway is the main factor controlling the final olefin product distribution. 相似文献
70.
Kato S Borgschulte A Ferri D Bielmann M Crivello JC Wiedenmann D Parlinska-Wojtan M Rossbach P Lu Y Remhof A Züttel A 《Physical chemistry chemical physics : PCCP》2012,14(16):5518-5526
The catalytic hydrogenation of CO(2) at the surface of a metal hydride and the corresponding surface segregation were investigated. The surface processes on Mg(2)NiH(4) were analyzed by in situ X-ray photoelectron spectroscopy (XPS) combined with thermal desorption spectroscopy (TDS) and mass spectrometry (MS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). CO(2) hydrogenation on the hydride surface during hydrogen desorption was analyzed by catalytic activity measurement with a flow reactor, a gas chromatograph (GC) and MS. We conclude that for the CO(2) methanation reaction, the dissociation of H(2) molecules at the surface is not the rate controlling step but the dissociative adsorption of CO(2) molecules on the hydride surface. 相似文献