全文获取类型
收费全文 | 1408篇 |
免费 | 39篇 |
国内免费 | 7篇 |
专业分类
化学 | 1048篇 |
晶体学 | 12篇 |
力学 | 22篇 |
数学 | 147篇 |
物理学 | 225篇 |
出版年
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 15篇 |
2017年 | 4篇 |
2016年 | 31篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 66篇 |
2012年 | 58篇 |
2011年 | 83篇 |
2010年 | 56篇 |
2009年 | 43篇 |
2008年 | 100篇 |
2007年 | 104篇 |
2006年 | 71篇 |
2005年 | 110篇 |
2004年 | 76篇 |
2003年 | 75篇 |
2002年 | 65篇 |
2001年 | 38篇 |
2000年 | 28篇 |
1999年 | 26篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 7篇 |
1969年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1454条查询结果,搜索用时 906 毫秒
91.
92.
Abstract The non-linear dielectric relaxation spectroscopy has been recently developed and applied to soft materials such as polymers. We have applied this new method to the S*C phases of some ferroelectric liquid crystals. Under a weak AC electric field, the original and third order harmonic frequency components of electric displacement are proportional to the first and third powers of the applied electric field, respectively. The linear spectrum obtained from the original frequency component shows the relaxation of Debye type and the third order non-linear spectrum shows the relaxation with an extended form of Debye type to the non-linear case. The third order non-linear dielectric increment is found to be negative, which implies that the dielectric non-linearity of the liquid crystal in the S*C phase is due to the saturation of molecular dipole moments induced by the applied electric field. The temperature dependence of the linear and third order non-linear spectra in the S*C phase are also studied. Both spectra do not change their forms much through the whole temperature range of the S*C phase. In the vicinity of the SA–S*C transition temperature, the critical behaviour is more remarkable in the third order spectrum than in the linear one. 相似文献
93.
Polymerizations of cyclooctene, 5-methyl, 5-chloro-, and 5-methoxycyclooctenes were studied. Cyclooctene (CO) and 5-methylcyclooctene (MCO) provided high polymers in 80% yield with the use of WCl6/AlEti.B Clu5 or WCl6/AlEtCl2 catalyst. 5-Chlorocyclooctene gave oligomer in 50% yield with WCl6/AlEt2Cl catalyst. Neither polymer nor oligomer was produced from 5-methoxycyclooctene. These polymers were found to be produced through a ring-opening mechanism. The ratio of cis to trans structure in poly(CO) and poly(MCO) was determined by measurements of the decoupled ′H-NMR spectrum. Poly(CO) containing more than 50% trans structure was a crystalline solid at room temperature, while the polymer containing 30% of trans structure did not crystallize at room temperature. Poly(MCO) was amorphous, regardless of the content of trans structure. Poly(CO) and poly(MCO) obtained with MoCU/AlEtaCl or MoCU/AlEtCb catalyst contained no carbon-carbon double bond, and a vinyl polymerization mechanism was expected for this system. 相似文献
94.
Yan Li Dr. Kazuki Fukushima Dr. Daniel J. Coady Dr. Amanda C. Engler Dr. Shaoqiong Liu Yuan Huang Dr. John S. Cho Dr. Yi Guo Dr. Lloyd S. Miller Dr. Jeremy P. K. Tan Dr. Pui Lai Rachel Ee Dr. Weimin Fan Prof. Yi Yan Yang Dr. James L. Hedrick 《Angewandte Chemie (International ed. in English)》2013,52(2):674-678
95.
Hideaki Iizuka Shoko Watanabe Mayuko Koshikawa Yurie Matsumoto Yuki Aoyama Hideaki Ichiba Toshitaka Nabeshima Takeshi Fukushima 《Analytical and bioanalytical chemistry》2013,405(25):8137-8141
It has been reported that repeated phencyclidine (PCP) treatment induces schizophrenia-like behavior in mice. l-Tryptophan (Trp) concentrations in brain tissues of control (n?=?8) and PCP-treated mice (10 mg/kg/day, s.c., 14 days, n?=?10) were determined using high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC method involved pre-column fluorescence derivatization with (R)-(?)-4-(N,N-dimethylaminosulfonyl)-7-(3-isothiocyanatopyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-PyNCS). Eight different parts of the brain, namely, the frontal cortex, nucleus accumbens, striatum, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum, of both groups were investigated. A significant decrease in the l-Trp concentration in the nucleus accumbens (p?=?0.024) and hippocampus (p?=?0.027) was observed in PCP-treated mice, suggesting that alteration of the l-Trp metabolism might occur in these brain parts. 相似文献
96.
Shiro Matsumoto Yasuyuki Sugiyama Seizou Sakata Takayoshi Hayashi 《Liquid crystals》2013,40(5):649-655
Polymers containing droplets of liquid crystal smaller than 100 nm, which have good transparency and easily form films, were prepared under various conditions to evaluate their potential as electro-optic materials for waveguide-type devices. By varying the liquid crystal concentration and the strength of the UV irradiation causing photo-induced phase separation of the droplets, we were able to control the droplet size and density. We have clarified how the birefringence generated in an applied electric field, switching speed, and optical loss of light propagating in the film depend on droplet size and density. Polymer materials having a large electro-optic effect (δn = 0.001 at 8 V μm-1), low propagation loss (~2.5 dB cm-1), and fast response time (~10 μs) have been developed. 相似文献
97.
A series of liquid crystalline compounds having the difluoropropyleneoxy moiety (–OCF2C2H4–) as a linking group has been synthesized. The physical properties, i.e. dielectric anisotropy, birefringence, viscosity and phase transition temperatures, have been measured. This novel class of compounds shows a larger negative dielectric anisotropy than the corresponding compounds having a propyleneoxy (–OC3H6–) linking group. Their dielectric properties may be explained by the combined effect of fluorine atoms with large electron negativities and the electron donating feature of an oxygen atom substituted on the same carbon atom. The semi‐empirical quantum calculation method (AM1) also confirmed this dielectric behaviour of the difluoropropyleneoxy linkage group. 相似文献
98.
Mari Iizuka Shoju Fukushima Yuki Goto Masaaki Okazaki Hideo Sawada Masato Yoshida 《Colloid and polymer science》2013,291(3):595-601
Head-to-head-type styrene and substituted styrene dimers bearing two fluoroalkyl end-groups have been efficiently synthesized by a simple reaction of perfluoroalkyl iodide with styrene under radical conditions as a mixture of meso and racemic forms. The meso form obtained from the mixture by recrystallization gave a crystal suitable for X-ray diffraction study and the crystal structure was found to be based on π-stacking of benzene rings and aggregation of fluoroalkyl chains. Dynamic light scattering measurements showed that meso-styrene dimers bearing two fluoroalkyl end-groups can form the nanometer size-controlled self-assemblies through the intermolecular π-stacking of benzene rings and aggregation of end-capped fluoroalkyl groups in methanol. Figure
Self-assembled meso-perfluorohexylated styrene dimer [C6F13–CH2CHPh–CHPh–CH2–C6F13] based on π-stacking of benzene rings and aggregation of fluoroalkyl chains: Fluorous domains are constructed by self-assembly of fluoroalkyl chains. 相似文献
99.
Nobutaka Yamaoka Kohei Sumida Itsuki Itani Hiroko Kubo Yusuke Ohnishi Sho Sekiguchi Dr. Toshifumi Dohi Prof. Dr. Yasuyuki Kita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):15004-15011
Metal‐free oxidative C? C coupling by using polyalkoxybenzene‐derived diaryliodonium(III) salts as both the oxidant and aryl source has been developed. These salts can induce single‐electron‐transfer (SET) oxidation to yield electron‐rich arenes and subsequently transfer the polyalkoxyphenyl group into in situ generated aromatic radical cations to produce biaryl products. The reaction is promoted by a Lewis acid that activates the iodonium salts. It has been revealed that the reactivity of the salts under acidic conditions is quite different to their known behavior under basic conditions. The reactivity preference of a series of iodonium salts in the SET oxidation and their ligand transfer abilities have been systematically investigated and the results are summarized in this report. 相似文献
100.