全文获取类型
收费全文 | 221篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 132篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 3篇 |
物理学 | 89篇 |
出版年
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 12篇 |
2011年 | 8篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1931年 | 3篇 |
1929年 | 2篇 |
1928年 | 2篇 |
1898年 | 1篇 |
1862年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
51.
Retention forces and drop parameters are investigated for drops on the verge of sliding on vertical and inclined surfaces. Using earlier observations of drop geometry, the retentive-force factor relating surface-tension forces to contact-angle hysteresis is reliably determined. The retention force for a drop is found to be insignificantly affected by the aspect ratio of its contour. The maximum size of a drop is predicted with good accuracy, based on the two-circle method for approximating shapes of drops. The Bond number of a critical drop is found to be constant for a given surface and liquid. A general relation is proposed between the characteristic advancing and receding contact angles. The relation is supported by a large set of contact-angle data. In the absence of theta R data, the relation allows estimating the receding contact angle and the critical drop size, using only the advancing angle. 相似文献
52.
Multiphase thermoplastic hybrid for controlled release of antimicrobial essential oils in active packaging film
下载免费PDF全文
![点击此处可从《先进技术聚合物》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Itan Moshe Orli Weizman Michal Natan Gila Jacobi Ehud Banin Ana Dotan Amos Ophir 《先进技术聚合物》2016,27(11):1476-1483
Active packaging, a new technology concept in the field of food packaging, has been introduced in recent years in order to provide quality and safety, as well as extend the shelf life of food products. Antimicrobial (AM) agents can be incorporated directly into the active packaging and migrate in a controlled manner to the headspace between the food and the package, inhibiting bacteria growth on the food surface. Naturally derived AM agent, such as essential oils (EOs), has received considerable attention for food preservation purposes, because of their effective AM activity against various bacteria and fungi. In the present study, AM active film systems based on polypropylene/polyamide blends, montmorillonite nanoclays, and thymol EO were produced to investigate the feasibility of controlling the release rate of thymol from food packaging systems. Selective localization of thymol in a specific phase in the system that derives from thermodynamic affinity was assumed to be useful in controlling its migration rate from the film to the headspace. EO retention in the film under two different time conditions was measured by spectroscopic analysis. The release rate of EO was determined using Gas chromatography technique and analyzed by diffusion model approach. Inhibition of bacterial growth was periodically tested for Listeria and Escherichia coli bacteria. This study confirms the thermodynamic affinity of polyamide phase with thymol that has a positive effect in retaining the EO. Results show controlled AM behavior of the active packaging films, based on various blend compositions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
53.
Prof. Barry M. Trost Mark J. Bartlett Dr. Andrew H. Weiss Dr. Axel Jacobi von Wangelin Dr. Vincent S. Chan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16498-16509
The development of a general and practical zinc‐catalyzed enantioselective alkyne addition methodology is reported. The commercially available ProPhenol ligand ( 1 ) has facilitated the addition of a wide range of zinc alkynylides to aryl, aliphatic, and α,β‐unsaturated aldehydes in high yield and enantioselectivity. New insights into the mechanism of this reaction have resulted in a significant reduction in reagent stoichiometry, enabling the use of precious alkynes and avoiding the use of excess dimethylzinc. The enantioenriched propargylic alcohols from this reaction serve as versatile synthetic intermediates and have enabled efficient syntheses of several complex natural products. 相似文献
54.
55.
An efficient synthesis of the title compound 1 has been achieved beginning with 3-methylglutaric anhydride. 相似文献
56.
Dori Gal Eli Sone R Cohen G Hodes J Libman A Shanzer H-W Schock David Cahen 《Journal of Chemical Sciences》1997,109(6):487-496
The electronic properties of semiconductor surfaces can be controlled by binding tailor-made ligands to them. Here we demonstrate
that deposition of a conducting phase on the treated surface enables control of the performance of the resulting device. We
describe the characteristics of the free surface of single crystals and of polycrystalline thin films of semiconductors that
serve as absorbers in thin film polycrystalline, heterojunction solar cells, and report first data for actual cell structures
obtained by chemical bath deposition of CdS as the window semiconductor. The trend of the characteristics observed by systematically
varying the ligands suggests changes in work function rather than in band bending at the free surface, and implies that changes
in band line-up, which appear to cause changes in band bending, rather than direct, ligand-induced band bending changes, dominate. 相似文献
57.
First the analytical tools, preparation methods and surface crystallography of clean GaAs surfaces are briefly reviewed. Besides the usual methods of cleaving, ion bombardment and annealing, molecular beam epitaxy is mainly used as a growth method under UHV conditions, and has brought a manifold of differently reconstructed structures on the same crystallographic surface, depending on the exact experimental conditions during growth. Quantitative analysis of the surface composition by AES gives the result that these structures differ only in the amount of As in the topmost layer. From the combination of theoretical LEED analysis, UPS results and arguments considering the different physicochemical nature of Ga and As atoms, rehybridisation of the surface atomic bonds emerges as the driving force for reconstruction: the surface Ga atoms try to assume a trivalent planarsp2 and the As atoms a trivalentp3 configuration with three mutually perpendicularp-bonds. The better this rehybridised configuration can be achieved, the better is the chemical stability of the respective structure. The sticking coefficient for oxygen, although generally low, thus varies between ~10-4 and <10-9, depending on the crystallographic surface and, on the same surface, on the degree of surface bond saturation given by the respective structure. However, it emerges that, at least on As-depleted polar surfaces, adsorption proceeds via a mechanism of removal of Ga atoms during exposure and adsorption on the defect sites created in this way. The existence of such a complicated mechanism is consistent with the difficulties arising with the preparation of thick stoichiometric oxide layers, the preparation methods and properties of which are reviewed briefly in the last section. 相似文献
58.
Ch. Berger M. Fröhlich H. Mönch R. Nisius F. Raupach Y. Benadjal D. Blum C. Bourdarios B. Dudelzak P. Eschstruth S. Jullian D. Lalanne F. Laplanche C. Longuemare C. Paulot O. Perdereau Ph. Roy G. Szklarz L. Behr B. Degrange Y. Minet U. Nguyen-Khac S. Tisserant C. Arpesella P. Bareyre R. Barloutaud A. Borg G. Chardin J. Ernwein J. F. Glicenstein L. Mosca L. Moscoso J. Becker K. H. Becker H. J. Daum B. Jacobi B. Kuznik H. Meyer R. Möller M. Schubnell Y. Wei Fréjus Collaboration 《Zeitschrift fur Physik C Particles and Fields》1990,48(2):221-226
With the Fréjus detector we studied four astrophysical point-like sources by using \(v_e (\bar v_e )\) and \(v_\mu (\bar v_\mu )\) interactions in the detector and \(v_\mu (\bar v_\mu )\) interactions in the surrounding rock. No excess of events was found. Therefore upper limits of neutrino fluxes and source luminositics are quoted. These limits confirm results from other experiments. In addition new limits are presented for spectral indices above 3. 相似文献
59.
Berger C Fröhlich M Mönch H Nisius R Raupach F Schleper P Benadjal Y Blum D Bourdarios C Dudelzak B Eschstruth P Jullian S Lalanne D Laplanche F Longuemare C Paulot C Perdereau O Roy P Szklarz G Behr L Degrange B Minet Y Nguyen-Khac U Serri P Tisserant S Tripp RD Arpesella C Bareyre P Barloutaud R Borg A Chardin G Ernwein J Glicenstein JF Mosca L Moscoso L Becker J Becker KH Daum HJ Demski S Jacobi B Kuznik B Mayer R Meyer H Möller R Schubnell M Seyffert B Wei Y Wintgen P 《Physical review D: Particles and fields》1989,40(7):2163-2171
60.
Jacobi PA DeSimone RW Ghosh I Guo J Leung SH Pippin D 《The Journal of organic chemistry》2000,65(25):8478-8489
Pyrromethenone 7, the C,D-ring segment of phytochrome (Pr, 4), has been prepared in an efficient fashion employing three new strategies. Each of these has potential advantages for the synthesis of labeled material. Our first approach is related to the Gossauer synthesis, with the difference that strong alkali is avoided in the condensation of the C- and D-ring components 8 and 17. The key silyloxypyrrole 17 was readily prepared on multigram scales beginning with inexpensive butyrolactone (10). A second synthesis began with 2-acetylbutyrolactone (41). The key steps involved conversion of 41 to the Z-enoltriflate 42, followed by Pd(0)-catalyzed coupling with trimethylsilylacetylene, p-chlorophenylselenide ring opening, and finally, amidation to afford the ring-D synthon 45 having the proper geometry and oxidation state for conversion to 7. Sonogashira coupling of 45 with the iodopyrrole 22, followed by oxidative elimination, and F(-)-induced 5-exo-dig cyclization of the resultant pyrroloalkyne 47, then completed the synthesis. In similar fashion, we have also prepared pyrromethenone 6, the C,D-ring segment of phycocyanin (2). 相似文献