全文获取类型
收费全文 | 323篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 201篇 |
力学 | 8篇 |
数学 | 38篇 |
物理学 | 84篇 |
出版年
2019年 | 3篇 |
2018年 | 2篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 49篇 |
2012年 | 3篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 16篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 6篇 |
1968年 | 5篇 |
1961年 | 4篇 |
1933年 | 2篇 |
1927年 | 2篇 |
排序方式: 共有331条查询结果,搜索用时 46 毫秒
251.
E. A. Boucher D. J. Langdon R. J. Manning 《Journal of Polymer Science.Polymer Physics》1972,10(7):1285-1296
As part of a study of chemical and physical changes accompanying the formation of carbons by the pyrolysis of polymers, conventional electron microscopy, electron diffraction, and scanning electron microscopy techniques have been used to examine structural and morphological features of polyacrylonitrile (PAN) crystals, powder, and fibers, and of Saran and poly(vinylidene chloride) (PVDC) powder. Changes accompanying the heating of these polymers in air and in nitrogen have been investigated. PAN crystals grown from propylene carbonate were similar to those obtained by Klement and Geil. When heated in air at 220°C they retained their morphology, and electron diffraction gave the same reflections as PAN. On further heating to 400°C in nitrogen the morphology was retained, but the diffraction was lost. Crystals treated in nitrogen alone at 200°C showed morphology similar to that of the polymer. PAN powders and fibers retained discernable external features of their morphology on heating to 800°C. These results are discussed with reference to changes which take place when poly(vinylidene chloride) and Saran are heated in the range 150–180°C, which results in the loss of one hydrogen chloride per monomer unit, and are subsequently carbonized at 800°C. The development of pore structure and the adsorptive properties of Saran carbons are also discussed. 相似文献
252.
Naphtho[1,2-c:5,6-c]difuran has been isolated in a 9-step synthesis from 2,6-dimethylnaphthalene. It is a highly reactive diene similar in nature to the related isobenzofuran. In Diels-Alder reactions, its intermediate monoadducts are actually less reactive that the parent difuran making possible sequential Diels-Alder reactions with different dienophiles. Reaction with a tethered bis(dienophile) leads to the production of a naphthalenic cyclophane. 相似文献
253.
Barry SJ Carr RM Lane SJ Leavens WJ Manning CO Monté S Waterhouse I 《Rapid communications in mass spectrometry : RCM》2003,17(5):484-497
The synthesis of S-pentafluorophenyl tris(2,4,6-trimethoxyphenyl)phosphonium acetate bromide (TMPP-AcPFP) and the novel compound (4-hydrazino-4-oxobutyl) [tris(2,4,6-trimethoxyphenyl)phosphonium bromide (TMPP-PrG) is described and the use of these compounds as derivatizing reagents for alcohols, aldehydes and ketones evaluated. Methods have been developed for the pre-column derivatization of alcohols using TMPP-AcPFP and for aldehydes and ketones using TMPP-PrG. The reactions were investigated by the use of a variety of individual test compounds containing the target functional groups. The TMPP acetyl ester and TMPP propyl hydrazone derivatives formed with their respective target analytes produced an enhanced response in electrospray ionization mass spectrometry (ESI-MS), and reproducible chromatography. The use of these two reagents to derivatize and facilitate detection of alcohols (including sugars and steroids), aldehydes and ketones (including steroids) by LC/ESI-MS was investigated. 相似文献
254.
Rajganesh B. Selvaraj P. T. Manning F. S. Sublette K. L. Camp Carl 《Applied biochemistry and biotechnology》1995,51(1):735-746
Applied Biochemistry and Biotechnology - Water coproduced with petroleum may contain sulfides and organic constituents that give the water an aquatic toxicity preventing surface discharge. A... 相似文献
255.
R.M. Flynn R.G. Manning R.M. Kessler D.J. Burton S.W. Hansen 《Journal of fluorine chemistry》1981,18(4):525-531
Hydrolysis of [Ph3CF2Br]Br? afforded a high yield of bromodifluoromethane and triphenylphosphine oxide. Hydrolysis in the presence of a radioactive isotope of bromine or sodium iodide gave unequivocal evidence that the mechanism for this reaction proceeds through a difluorocarbene intermediate. 相似文献
256.
We have made the determination of V conform to the requirements of the modern (stabilized temperature) furnace technology where the integrated absorbance (A·s) signals are used to quantitate analyte volatilized into a chamber whose temperature is relatively constant during the period when the analyte peak is measured. Graphite tubes with good pyrolytic coating and fast (maximum power) heating are required. We explored the advantages of specially designed tubes, of a cool-down procedure between the char and atomization steps and of very thin platforms. We found that Mg(NO3)2 was advantageous as a matrix modifier. With these conditions we found no problems with several matrices reported by earlier workers to be troublesome, for example HNO3, phosphate, Fe, Mg and Ca. However metals that form very refractory carbides, such as La, Mo, W and Zr may remain troublesome for V, probably because mixed carbides result which include VC. A group of geological samples was analysed for V. Our recommendation is the use of wall atomization from tubes with good pyrolytic coatings, Mg(NO3)2 as a matrix modifier and the cool-down procedure to establish a nearly constant temperature along the tube. 相似文献
257.
258.
259.
The regiochemistry of the cyclization reations of some ω-lithioepoxides as a function of chain length and substitution pattern has been examined. Striking changes in regiochemistry have been observed in the presence of certain Lewis acids and metal halides. 相似文献
260.
The determination of aluminum in the presence of perchloric acid is shown to depend upon the quality of the pyrolytic coating of furnace tubes. With new pyrolytically coated tubes, no interference was found from 0.5 M HClO4 on 0.5 ng Al and no decrease in signal or deterioration of the pyrolytic coating was found after more than 150 firings. Very little interference was found in the determination of thallium in perchloric acid. In both cases the literature reported severe interferences. The determination of thallium and aluminum in perchloric acid appears to be more sensitive to the quality of the pyrolytic graphite coating than any of the materials studied previously here. 相似文献