全文获取类型
收费全文 | 135篇 |
免费 | 0篇 |
国内免费 | 6篇 |
专业分类
化学 | 73篇 |
力学 | 3篇 |
数学 | 43篇 |
物理学 | 22篇 |
出版年
2021年 | 1篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 8篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1994年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1969年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有141条查询结果,搜索用时 4 毫秒
131.
132.
133.
A. R. Shultz A. L. Bridgman E. M. Hadsell C. R. McCullough 《Journal of Polymer Science.Polymer Physics》1972,10(2):273-282
Ten unfractionated poly(2,6-diphenyl-1,4-phenylene oxide) samples were examined by gel permeation chromatography (GPC) and intrinsic viscosity [η] at 50°C in benzene, by intrinsic viscosity at 25°C in chloroform, and by light scattering at 30°C in chloroform. The GPC column was calibrated with ten narrow-distribution polystyrenes and styrene monomer to yield a “universal” relation of log ([η]M) versus elution volume. GPC-average molecular weights, defined as M?gpc = \documentclass{article}\pagestyle{empty}\begin{document}$\Sigma w_i [\eta ]_i M_i /\Sigma w_i [\eta ]_i$\end{document}, wi denoting the weight fraction of polymer of molecular weight Mi, were computed from the GPC and [η] data on the polyethers. The M?GPC were then compared with the weight-average M?w from light scattering. The intrinsic viscosity (dl/g) versus molecular weight relations for the unfractionated poly(2,6-diphenyl-1,4-phenylene oxides) determined over the molecular weight range 14,000 ≤ M?w ≤ 1,145,000 are log [η] = ?3.494 + 0.609 log M?w (chloroform, 25°C) and log [η] = ?3.705 + 0.638 log M?w (benzene, 50°C). The M?w(GPC)/M?n(GPC) ratios for the polymers in the molecular weight range 14,000 ≤ M?w ≤ 123,000 approximate 1.5 according to computer integrations of the GPC curves with the use of the “universal” calibration and the measured log [η] versus log M?w relation. The higher molecular weight polymers (326,000 ≤ M?w ≤ 1,145,000) show slightly broadened distributions. 相似文献
134.
135.
Monoozonolyses of dienes 2 in methanol gave in each case the corresponding unsaturated alpha-methoxy hydroperoxides 3. Capture of 2-alkyl-substituted cyclohexanone oxides by methanol was highly diastereoselective, thereby providing exclusively the hydroperoxides derived from attack by methanol from the less hindered face of the carbonyl oxide intermediates. Halonium ion-mediated reactions of the hydroperoxides 3 gave the novel methoxy- or hydroxy-migrated products, together with the expected halogen-substituted 1, 2-dioxanes and/or 1,2-dioxepanes, the composition of the product mixture being a function of the halogenating agent utilized and the structure of 3. 相似文献
136.
137.
J. William?Helton Scott A.?McCullough Mihai?PutinarEmail author 《Mathematische Zeitschrift》2005,250(3):515-522
We prove a non-negative-stellensatz and a null-stellensatz for a class of polynomials called hereditary polynomials in a free *-algebra.Partially supported by NSF, DARPA and Ford Motor Co.Partially supported by NSF grant DMS-0140112Partially supported by NSF grant DMS-0100367 相似文献
138.
Kowalewski T McCullough RD Matyjaszewski K 《The European physical journal. E, Soft matter》2003,10(1):5-16
The development of new controlled/living radical polymerization processes, such as Atom Transfer Radical Polymerization (ATRP)
and other techniques such as nitroxide mediated polymerization and degenerative transfer processes, including RAFT, opened
the way to the use of radical polymerization for the synthesis of well-defined, complex functional nanostructures. The development
of such nanostructures is primarily dependent on self-assembly of well-defined segmented copolymers. This article describes
the fundamentals of ATRP, relevant to the synthesis of such systems. The self-assembly of block copolymers prepared by ATRP
is illustrated by three examples. In the first, block copolymers of poly(butyl acrylate) with polyacrylonitrile phase separate,
leading to spherical, cylindrical or lamellar morphologies, depending on the block copolymer composition. At a higher temperature,
polyacrylonitrile block converts to nanostructured carbon clusters, whereas poly(butyl acrylate) block serves as a sacrificial
block, aiding the development of designed nanostructures. In the second example, conductive nanoribbons of poly(n-hexylthiophene)
surrounded by a matrix of organic polymers are formed from block copolymers prepared by ATRP. The third example describes
an inorganic-organic hybrid system consisting of hard nanocolloidal silica particles (20 nm) grafted by ATRP with well-defined
polystyrene-poly(benzyl acrylate) block copolymer chains (1000 chains per particle). Silica cores in this system are surrounded
by a rigid polystyrene inner shell and softer polyacrylate outer shell.
Received 9 July 2002 Published online: 11 March 2003 相似文献
139.
Jaruga P Jabil R McCullough AK Rodriguez H Dizdaroglu M Lloyd RS 《Photochemistry and photobiology》2002,75(2):85-91
A DNA glycosylase specific for UV radiation-induced pyrimidine dimers has been identified from the Chlorella virus Paramecium Bursaria Chlorella virus-1. This enzyme (Chlorella virus pyrimidine dimer glycosylase [cv-pdg]) exhibits a 41% amino acid identity with endonuclease V from bacteriophage T4 (T4 pyrimidine dimer glycosylase [T4-pdg]), which is also specific for pyrimidine dimers. However, cv-pdg possesses a higher catalytic efficiency and broader substrate specificity than T4-pdg. The latter excises 4,6-diamino-5-formamidopyrimidine (FapyAde), a UV radiation- and hydroxyl radical-induced monomeric product of adenine in DNA. Using gas chromatography-isotope-dilution mass spectrometry and y-irradiated DNA, we show in this work that cv-pdg also displays a catalytic activity for excision of FapyAde and, in addition, it excises 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua). Kinetic data show that FapyAde is a better substrate for cv-pdg than FapyGua. On the other hand, cv-pdg possesses a greater efficiency for the extension of FapyAde than T4-pdg. These two enzymes exhibit different substrate specificities despite substantial structural similarities. 相似文献
140.
Super-reltron theory and experiments 总被引:1,自引:0,他引:1
Miller R.B. McCullough W.F. Lancaster K.T. Muehlenweg C.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(3):332-343
A highly efficient, high-power microwave tube called super-reltron is reported. The authors have achieved operation at >400 MW with ~50% efficiency at 1 GHz, and 250 MW with 40% efficiency at 3 GHz. The RF pulse durations are typically a few hundred nanoseconds. These compact lightweight tubes do not require an external magnetic field. The RF output coupling is straightforward and delivers the power directly via the fundamental TE10 wave in a rectangular waveguide without a mode converter. The key features of the tube include (i) generation of a well-modulated electron beam by periodic virtual cathode formation, (ii) postacceleration of the modulated beam to reduce the relative electron energy spread, and (iii) a multicavity output section that efficiently extracts power without RF breakdown. Various theoretical aspects of the device are discussed and the experimental results are summarized 相似文献