全文获取类型
收费全文 | 224篇 |
免费 | 7篇 |
专业分类
化学 | 161篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 24篇 |
物理学 | 42篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 2篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1964年 | 3篇 |
1963年 | 3篇 |
1932年 | 2篇 |
1928年 | 1篇 |
1914年 | 1篇 |
排序方式: 共有231条查询结果,搜索用时 15 毫秒
1.
Summary Methods are described for the preparation of monodisperse polystyrene latices using as initiators, 2-azo-bis-(2-methylpropamidinium) dichloride and 2-azo-bis-(2-isopropyliminazolium) dichloride. The preparations were carried out in the absence of any added surface active agents. The effect on particle size of varying initiator concentration, monomer concentration, temperature and ionic strength was examined and the conditions defined for preparing monodisperse latices, with particles in the size range 0.2 to 1m. Electrophoretic measurements confirmed that the latex particles were cationic. The evidence obtained suggested that the charged sites on the particle surface were amidinium groupings. The latices were not stable at pH values greater than 11 and prolonged heating at 90° also caused coagulation.
With 6 figures and 9 tables 相似文献
Zusammenfassung Es wurden Methoden zur Darstellung monodisperser Polystyrol-Latices unter Verwendung von 2-azo-bis-(2-methylpropamidinium)-dichlorid und 2-azo-bis-(2-isopropyliminazolium)-dichlorid als Initiator beschrieben. Die Darstellung erfolgte in Abwesenheit von grenzflächenaktiven Verbindungen. Der Einfluß unterschiedlicher Initiator- und Monomerkonzentrationen, der Temperatur und der lonenstärke auf die Teilchengröße wurde untersucht und die Bedingungen festgelegt, unter denen monodisperse Latices mit Teilchen im Größenbereich von 0,2-1m erhalten werden. Elektrophoretische Messungen bestätigten, daß die Latexteilchen kationisch sind. Die Ladungen auf der Teilchenoberfläche sind Amidiniumgruppen. Die Latices waren bei pH-Werten über 11 nicht stabil; längeres Erhitzen auf 90° führte ebenfalls zur Koagulation.
With 6 figures and 9 tables 相似文献
2.
Alan Rigter Jan PM Langeveld Drophatie Timmers-Parohi Jorg G Jacobs Peter LJM Moonen Alex Bossers 《BMC biochemistry》2007,8(1):6
Background
The common event in transmissible spongiform encephalopathies (TSEs) or prion diseases is the conversion of host-encoded protease sensitive cellular prion protein (PrPC) into strain dependent isoforms of scrapie associated protease resistant isoform (PrPSc) of prion protein (PrP). These processes are determined by similarities as well as strain dependent variations in the PrP structure. Selective self-interaction between PrP molecules is the most probable basis for initiation of these processes, potentially influenced by chaperone molecules, however the mechanisms behind these processes are far from understood. We previously determined that polymorphisms do not affect initial PrPC to PrPSc binding but rather modulate a subsequent step in the conversion process. Determining possible sites of self-interaction could elucidate which amino acid(s) or amino acid sequences contribute to binding and further conversion into other isoforms. To this end, ovine – and bovine PrP peptide-arrays consisting of 15-mer overlapping peptides were probed with recombinant sheep PrPC fused to maltose binding protein (MBP-PrP). 相似文献3.
4.
Tresa Nesbitt Aubrey Lemley Jeff Davis Michael J Yost Richard L Goodwin Jay D Potts 《Microscopy and microanalysis》2006,12(5):390-398
Development of the epicardium is critical to proper heart formation. It provides all of the precursor cells that form the coronary system and supplies signals that stimulate cardiac myocyte proliferation. The epicardium forms from mesothelial cells associated with the septum transversum and is referred to as the proepicardium (PE). Two different methods by which these PE cells colonize the developing heart have been described. In avians, PE cells form a bridge to the heart over which PE cells migrate onto the heart. In fish and mammals, PE cells form vesicles of cells that detach from the mesothelium, float through the pericardial cavity, and attach to the heart. A previous study of rat PE development investigated this process at the histological level. Protein markers have been developed since this study. Thus, we investigated this important developmental process coupled with these new markers using other visualization techniques such as scanning electron microscopy (SEM) and confocal microscopy. Finally, a novel, three-dimensional (3-D) culture system was used to confirm the identity of the PE cells. In this study, we found convincing evidence that the rat PE cells directly attach to the heart in a manner similar to that observed in avians. 相似文献
5.
The application of reversed-phase high-performance liquid chromatography to the analytical- and preparative-scale separation of sterols has been evaluated. The capacity factors, k', for a number of compounds chromatographed on a muBondapak C18 (LESS THAN 10 MUM) COLUMN ARE PRESENTED. C27, C28 and C29 sterols and also sterols differing in degree of unsaturation could be readily separated as their acetates in this system. The present reversed-phase chromatographic method is apparently not as selective as silver nitrate-silica gel thin-layer chromatography for the position of unsaturation in the sterol molecule. 相似文献
6.
Abstract— Treatment of etiolated pea seedlings with a short exposure to red light caused a stimulation of growth (size and dry wt production) and carotenoid synthesis during the following 48 hr compared with seedlings kept entirely in darkness.The effect is nullified by a following dose of far red light and thus the phenomenon is probably phytochrome-controlled.
Similar treatment with red light one hour before continuous illumination with white light tended to reduce the lag period for chlorophyll synthesis.Again a following dose of far red light reversed this response. 相似文献
Similar treatment with red light one hour before continuous illumination with white light tended to reduce the lag period for chlorophyll synthesis.Again a following dose of far red light reversed this response. 相似文献
7.
J rg Enderlein Peter M. Goodwin Alan Van Orden W. Patrick Ambrose Rainer Erdmann Richard A. Keller 《Chemical physics letters》1997,270(5-6):464-470
We have developed a maximum likelihood estimator to distinguish between similar molecules at the single molecule level based upon fluorescence decay measurements. Time resolved fluorescence measurements for single Rhodamine 6G and tetramethylrhodamine isothiocyanate molecules in fluid flow are derived from time-correlated single photon counting. A maximum likelihood estimator is developed and applied to data from a mixture of molecules. Single molecules are identified and distinguished by their fluorescence time decays. Comparison is made between identification error rates and theoretical predictions. To our knowledge, this is the first reported example of single molecule identification by fluorescence decay in a mixture. 相似文献
8.
The 57Fe Mössbauer effect in [Fe(pythiaz)2] (BF4)2 (I) and [Fe(pythiaz)2] (C&O4)2 (II) has been studied between 298 and 4.2°K (pythiaz = 2,4-bis(2-pyridyl)thiazole). At 298°K compound I shows a doublet with ΔEQ(5T2) = 1.29 mm sec?1 and δ1S(5T2) = +0.93 mm sec?1 characteristic of a 5T2 ground state. At 236°K, a second doublet, typical for a 1A1 ground state appears. The transition 5T2 å 1A1 progresses as the temperature is lowered but levels off below ≈ 120°K. At 4.2°K, 59% of the intensity is due to the 1A1 state, and ΔEQ(1A1) = 1.59 mm sec?1 and δ1S(1A1) = +0.26 mm sec?1. In an applied magnetic field, Vzz(1A1) < 0 has been determined Similar results have been obtained with compound II.Debye-Waller factors f5T2 and f1A1. were determined from the Mössbauer spectra under the assumption of Curie-Weiss dependence of the magnetism for the 5T2 and constant μeff for the 1A1 ground state. The resulting temperature dependence of f1A1 is highly unusual thus suggesting complicated magnetic behaviour of both ground states in the transition region. Two mechanisms for the nature of the transition are discussed, a “spin-flip” mechanism being the physically more reasonable one. The assumption of a simple Boltzmann distribution (“spin equilibrium”) may be ruled out for the solid but could be encountered in solutions. 相似文献
9.
α-Oxo-carboxylic acids undergo photo-oxidative decarboxylation from both C-1 and C-2 positions, and reaction does not involve singlet oxygen: a mechanism involving an electron transfer reaction is postulated. 相似文献
10.
R. Mercadé-Prieto R. Allen D. York J. A. Preece T. E. Goodwin Z. Zhang 《Experimental Mechanics》2012,52(9):1435-1445
The encapsulation of liquids within an external wall or shell is an important technology often utilized in the production of many commercial products. The mechanical characterization of such microcapsules is paramount in order to fully understand their performance in their target environment. Some microcapsules, with wall materials such as inorganic based compounds, rupture at small deformations, commonly near the elastic regime. The study herein presents a general methodology that enables calculation of the failure stresses leading to the elastic-like rupture of microcapsules under parallel compression testing. Two scenarios of failure, brittle and ductile, were considered. Analyses of the critical stresses present within the microcapsule wall during different degrees of fractional deformation were obtained using finite element modelling, resulting in similar values for both the brittle and ductile scenarios. The correlations presented were used to determine the failure stresses of tetraethoxyorthosilane-methyltrimethoxysilane (TEOS-MTMS) microcapsules with a model core oil, which are 11?C14?±?10?MPa. The data were further analyzed using Weibull distributions. 相似文献