全文获取类型
收费全文 | 383篇 |
免费 | 2篇 |
专业分类
化学 | 228篇 |
晶体学 | 17篇 |
力学 | 7篇 |
数学 | 3篇 |
物理学 | 130篇 |
出版年
2021年 | 2篇 |
2016年 | 8篇 |
2014年 | 4篇 |
2013年 | 23篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 18篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1968年 | 16篇 |
1967年 | 28篇 |
1966年 | 25篇 |
1965年 | 11篇 |
1961年 | 2篇 |
1940年 | 2篇 |
1935年 | 2篇 |
1913年 | 7篇 |
1912年 | 11篇 |
1895年 | 1篇 |
排序方式: 共有385条查询结果,搜索用时 15 毫秒
1.
Mary E. Neubert DAVID G. ABDALLAH Jr Sandra S. Keast Julie M. Kim Soonnam Lee Ryan M. Stayshich Margaret E. Walsh Rolfe G. Petschek Shin-Tson Wu 《Liquid crystals》2003,30(6):711-731
New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1-4; and X = C n H 2n + 1 , F, CF 3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF 3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices.
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
2.
E. E. Roper W. P. White H. P. Brown O. A. Sliskonskaja F. Lieneweg I. Schrodt M. Benedict und P. Neubert 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):17-18
Ohne Zusammenfassung 相似文献
3.
4.
5.
6.
7.
Dynamic light scattering experiments have been performed at various concentrations, of pharmaceutical oil-in-water microemulsions
consisting of Eutanol G as oil, a blend of a high (Tagat O2) and a low (Poloxamer 331) hydrophilic–lipophilic balance surfactant,
and a hydrophilic phase (propylene glycol/water). We probe the dynamics of these microemulsions by dynamic light scattering.
In the measured concentration range, two modes of relaxation were observed. The faster decaying mode is ascribed classically
to the collective diffusion D
c (total droplet number density fluctuation). We show that the slow mode is also diffusive and suggest that its possible origin
is the relaxation of polydispersity fluctuations. The diffusion coefficient associated with this mode is then the self-diffusion
D
s of the droplets. It was found that D
c and D
s had opposite volume fractions of oil plus surfactants (ϕ) dependence and a common limiting value D
0 for ϕ=0. Average hydrodynamic radius (R
h=10.5 nm) of droplets was calculated from D
0. R
h is supposed to compose the inner core, a surfactant film including possible solvent molecules, which migrate with the droplet.
The concentration dependence of diffusion coefficients reflects the effect of hard sphere and the supplementary repulsive
interactions which arises due to loss of entropy, when absorbed chains of surfactant intermingle on the close approach of
the two droplets. This mechanism could also explain the observed stability of our systems. The estimated extent of polydispersity
is 0.22 from the amplitude of slower decaying mode. The polydispersity in microemulsion systems is dynamic in origin. Results
indicate that the time scale for local polydispersity fluctuations is at least three orders of magnitude longer than the estimated
time between droplet collisions. 相似文献
8.
Determination of isotopic composition of lithium by neutron activation analysis; comparison with mass spectrometry 总被引:1,自引:0,他引:1
An activation analysis method is described for routine determination of6Li-abundances in various lithium compounds on the basis of the reaction sequence6Li(n,α)T and16O(t, n)18F and the measurement of18F. Irradiations of diluted equeous solutions of samples containing CrO3 as internal flux monitor were carried out at a thermal neutron flux density of ϕ≤1011 n·cm−2·sec−1. Interferences from variations in neutron self-shielding oxygen concentration and triton range do not exceed 0.5% when using
the dilution technique. The results for6Li abundances from 3.52 to 7.60% with standard deviations of 1 to 2.5% were confirmed by mass spectrometric measurements. 相似文献
9.
10.
J. N. Spencer S. K. Berger C. R. Powell B. D. Henning G. S. Furman W. M. Loffredo E. M. Rydberg R. A. Neubert C. E. Shoop D. N. Blauch 《Journal of solution chemistry》1981,10(7):501-509
Enthalpies of solution and of transfer of amides for the solvents chloroform (CHCl3), methylenechloride (CH2Cl2), carbontetrachloride (CCl4), cyclohexane (C6H12), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and ethylacetate (EtOAc) have been used to isolate and quantify the solvation interactions of amides in chlorinated solvents. Specific interactions at the aminde carbonyl and N–H groups have been identified. An analysis of the transfer enthalpies of pyrrole and methylpyrrole from cyclohexane to the chlorinated solvents shows that specific interactions between the pyrroles and these solvents are similar in nature. A means of calculating differences in the transfers of different solutes between the same solvent pair is given.Work done at Lebanon Valley College. 相似文献