全文获取类型
收费全文 | 258篇 |
免费 | 2篇 |
专业分类
化学 | 88篇 |
晶体学 | 9篇 |
力学 | 11篇 |
数学 | 55篇 |
物理学 | 77篇 |
无线电 | 20篇 |
出版年
2019年 | 2篇 |
2014年 | 2篇 |
2013年 | 9篇 |
2012年 | 8篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 9篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 15篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1907年 | 1篇 |
1890年 | 1篇 |
排序方式: 共有260条查询结果,搜索用时 20 毫秒
101.
Experimental studies of interface behavior when a gas flow, confined in a vertical tube, flows past a stationary body of liquid are presented. Critical conditions necessary for the interface to become unstable or break up are investigated. Specific phenomena studied include: penetration of liquid from a reservoir into the top open end of a vertical tube from which gas is emerging, flow of gas past a liquid ring maintained on the inside wall of the tube, conditions for the support of a “hanging film” on the tube wall, formation of droplets and establishment of a continuous upwards-flowing liquid film. A general mathematical formulation of this problem is presented and used to derive the set of relevant dimensionless parameters. Solutions are obtained to certain simple cases and are shown to be consistent with experiment in the limits in which one or more of the variables exerts negligible influence. 相似文献
102.
Michael D. Wallis 《Polymer Degradation and Stability》2007,92(9):1721-1729
The thermal degradation of high density polyethylene was conducted in a reactive extruder at various screw speeds with reaction temperatures of 400 °C and 425 °C. The residence time of the extruder was estimated and the molecular weight distribution of the fed plastic and reaction products was analysed using gel permeation chromatography. A continuous kinetic model was used to describe the degradation of the high density polyethylene in the reactive extruder. The breakage kernel and the scission rate model parameters were estimated from the experimental data for a variety of cases. It was found that purely random breakage and a scission rate which had a power law dependence on molecular size of 0.474 best described the experimental data. 相似文献
103.
In the crystal structure of the title compound at 98 K the dimethylamino group has pyramidal geometry. The nitrogenlone pair is not directed towards the triple bond; instead, one N? CH3 bond lies almost in the plane of the disubstituted ring, directed away from the triple bond, while the other N? CH3 bond and the lone pair are directed to opposite sides of the plane, nearer to the acetylene. There is a remarkably short intramolecular contact (2.39 Å) between a methyl H- and an acetylenic C-atom. The Taft σI parameter of the arylethynyl substituent appears to be similar to that of a carboxylic ester, judging from the bond-angle deformation at the ipso-C-atom. 相似文献
104.
The time constant for the collisional deactivation of the υ = 1 vibrational level of N2 is found to be 1.5 ± 0.5 s in liquid nitrogen of 99.9995% purity of 78 K. This result is consistent with a simple binary collision theory of vibrational relaxation for liquids. 相似文献
105.
Michael Wallis 《Polymer Degradation and Stability》2006,91(7):1476-1483
The thermal degradation of high density polyethylene has been modelled by the random breakage of polymer bonds, using a set of population balance equations. A model was proposed in which the population balances were lumped into representative sizes so that the experimentally determined molecular weight distribution of the original polymer could be used as the initial condition. This model was then compared to two different cases of the unlumped population balance which assumed unimolecular initial distributions of 100 and 500 monomer units, respectively. The model that utilised the experimentally determined molecular weight distribution was found to best describe the experimental data. The model fits suggested a second mechanism in addition to random breakage at slow reaction rates. 相似文献
106.
Salts of Halogenophosphoric Acids. XVII. Preparation and Crystal Structure of Copper(II) Monofluorophosphate Dihydrate CuPO3F · 2H2O Copper(II) monofluorophosphate dihydrate, CuPO3F · 2H2O 1 was obtained by the reaction of aqueous NH4HPO3F and acid (NH4)2PO3F solutions, respectively, using acetone or ethanol as precipitating agents. The thermal dehydration of 1 gives the water-free copper monofluorophosphate CuPO3F ( 2 ). 1 crystallizes in the monoclinic space group P21/c with a = 761,44, b = 780,97, c = 921,02 pm, β = 112,94° and Z = 4. 相似文献
107.
108.
109.
Megan Hogan Juliet Cotter James Claffey Brendan Gleeson Denise Wallis Donal O'Shea Matthias Tacke 《Helvetica chimica acta》2008,91(9):1787-1797
From the carbolithiation of 1‐(cyclopenta‐2,4‐dien‐1‐ylidene)‐N,N‐dimethylmethanamine (=6‐(dimethylamino)fulvene; 3 ) and different lithiated azaindoles 2 (1‐methyl‐7‐azaindol‐2‐yl, 1‐[(diethylamino)methyl]‐7‐azaindol‐2‐yl, and 1‐(methoxymethyl)‐7‐azaindol‐2‐yl), the corresponding lithium cyclopentadienide intermediates 4a – 4c were formed (7‐azaindole=1H‐pyrrolo[2,3‐b]pyridine). The latter underwent a transmetallation reaction with TiCl4 resulting in the (dimethylamino)‐functionalised ‘titanocenes’ 5a – 5c . When the ‘titanocenes’ 5a – 5c were tested against LLC‐PK cells, the IC50 values obtained were of 8.8, 12, and 87 μM , respectively. The most cytotoxic ‘titanocene’, 5a , with an IC50 value of 8.8 μM is nearly as cytotoxic as cis‐platin, which showed an IC50 value of 3.3 μM when tested on the epithelial pig kidney LLC‐PK cell line, and ca. 200 times better than ‘titanocene dichloride’ itself. 相似文献
110.
Structural studies of peri-interactions with dimethylamino groups in naphthalene systems indicate that the N-phenylcarboxamide group has a through-space electron attracting power closer to that of a carboxylic ester than a N,N-dialkylcarboxamide, while 2-nitroalkenyl groups have a lower through-space electron attracting power. However, addition of a benzoyl group to the 2-position of the nitroethenyl group leads to cyclisation to give a zwitterion, in which the carbanion is stabilised by full conjugation with the nitro group and partial conjugation with the carbonyl group. An interesting case where a steric interaction overrides an electrophile/nucleophile attraction is also described. The limitations to the interpretation of short contact distances from crystallographic measurements are discussed. 相似文献