全文获取类型
收费全文 | 170篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学 | 118篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 15篇 |
物理学 | 34篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 2篇 |
2011年 | 12篇 |
2010年 | 3篇 |
2009年 | 11篇 |
2008年 | 3篇 |
2007年 | 7篇 |
2006年 | 2篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有171条查询结果,搜索用时 15 毫秒
71.
72.
Yoshiro Kobayashi Kosuke Kawada Akira Ando Itsumaro Kumadaki 《Tetrahedron letters》1984,25(18):1917-1920
The photolysis of 2,3-bis(trifluoromethyl)thiophene gave an equilibrium mixture of 2,3- and 3,4-bis(trifluoromethyl)Dewar thiophenes, while that of 2,5-bis(trifluoromethyl)thiophene gave 2,4-bis(trifluoromethyl)-thiophene, which seemed to be formed through an intermediate other than the Dewar form. 相似文献
73.
Y. Bando M. Saeki M. Onoda I. Kawada M. Nakahira 《Journal of solid state chemistry》1980,34(3):381-384
A superstructure of TiS1.62 is determined by 100 kV high-resolution electron microscopy, in which the arrangement of metal vacancies is obtained from structure images. The crystal has monoclinic symmetry (pseudo-hexagonal) with lattice parameters a = 11.9, b = 6.85, c = 11.5Å, β = 90°. The space group is considered as . Metal vacancies are confined to every second metal layer and ordered within the partly filled metal layer, resulting in formation of a (2H)22C type of superstructure. The ordered metal vacancy layers are arranged in 2C-type stacking sequence along the c axis, while sulfur atoms are arranged in 2H-type stacking sequence along the c axis. 相似文献
74.
Hayashi K Sushko PV Shluger AL Hirano M Hosono H 《The journal of physical chemistry. B》2005,109(50):23836-23842
The 12CaO.7Al2O3 (C12A7) crystal with a nanoporous lattice framework exhibits high electrical conductivity with an activation energy of approximately 1.5 eV when equilibrated in a hydrogen atmosphere above approximately 800 degrees C. The high conductivity is preserved in a quenched state below approximately 600 degrees C with a reduced activation energy of approximately 0.8 eV. Such complex behavior in electrical conductivity is associated with incorporation of hydride ions (H-) in cages of the lattice framework. Electromotive force measurements reveal that the major carrier for the conductivity is electron with a small contribution by proton (H+), ruling out the possibility of direct intercage migration of the H- ion. A combination of these observations with the ab initio calculations leads to the conclusion that the electrons are thermally generated from the H- ion by the dissociation into two electrons and an proton, which is further converted to an OH- ion via reaction with an extraframework oxide ion (O2-). The energy difference between the initial (H- + O2-) and the final (2e- + OH-) states as evaluated by the theoretical calculation is as small as approximately 1 eV, which agrees well with an experimentally obtained enthalpy change, approximately 1.4 eV. Thus, internal equilibration between the extraframework hydrogen and the oxygen species is responsible for the thermal generation of the carrier electron. It is also suggested that the same conductive (2e- + OH-) state is reached by the photoirradiation of H- -containing C12A7. In this case the photoionization of H- forms an electron and an Ho atom, which then forms an OH- ion and another electron with thermal assistance. The persistence of photoinduced conductivity is explained by the slow kinetics of the reverse process at room temperature. 相似文献
75.
The substitution of the siloxy group in silyl enol ethers with Grignard reagents to form olefins is accomplished by use of nickel acetylacetonate or phosphine-nickel complexes as catalysts, the stereo- and regiochemistry of coupled olefins depending upon the nature of the catalyst and reaction conditions employed. 相似文献
76.
Noboru Kimizuka Motohiko Ishii Isao Kawada Masanobu Saeki Mitsuoki Nakahira 《Journal of solid state chemistry》1974,9(1):69-77
The effects of nonstoichiometry upon the behavior of vanadium dioxide single crystals in the vicinity of the semiconductor/metal transition temperature (Tc) were experimentally investigated. According to the electrical and thermal measurements, more stoichiometric vanadium dioxide exhibited the less electrical conductivity gap, the larger thermal and electrical hysteresis, and the lower transition temperature than the increased nonstoichiometric one near transition. Infrared absorptions and X-ray observations indicated the local and overall lattice distortion in the nonstoichiometric crystal due to the existence of V5+ ions. Furthermore, an intermediate phase between the low-temperature monoclinic and the high-temperature tetragonal phases was found in the nonstoichiometric VO2. On the other hand, no evidence for this intermediate phase was found in the stoichiometric one. Finally, some comparisons and discussions of our present data with the previously published ones were made. 相似文献
77.
S Kataoka J Imai N Yamaji M Kato T Kawada S Imai 《Chemical & pharmaceutical bulletin》1990,38(6):1596-1600
The alkylation of adenosine-3',5'-cyclic phosphate (cAMP, 1) with alkyl bromides was investigated and various new alkylated cAMP derivatives, N6,N6,2'-O-trialkyl cAMPs (2), N6,2'-O-dialkyl cAMPs (3) and 2'-O-alkyl cAMPs (4), were prepared by a one step reaction without the introduction of a protecting group into 1. Compounds (2) were synthesized from 1 by treatment with alkyl bromides in the presence of NaH or potassium tert-butoxide in dimethyl sulfoxide. Compounds (3) were also synthesized from 1 under conditions similar to those of the synthesis of 2 except for the use of MeONa as a base. Compounds (4) were prepared from 1 by treatment with alkyl bromides in the presence of 18-crown-6 in dioxane-aqueous KOH solution. N6,2'-O-Dibenzyl cAMP (3e) was obtained from 1 by the same method as the preparation of 4. These new alkylated derivatives were evaluated for cardiotonic activity in vitro. Some of them showed weak positive inotropic effects and strong negative chronotropic effects. Thus, the presence of the 2'-hydroxyl group seemed to be essential for the appearance of potent positive inotropic activity caused by cAMP derivatives. 相似文献
78.
A new, highly sensitive method for quantitative separation and determination of capsaicin and dihydrocapsaicin by high-performance liquid chromatography with electrochemical detection is elaborated. The method employs a Cosmosil 5Ph column eluted with 100 mM potassium dihydrogenphosphate containing 45% acetonitrile (pH 5.0) at a flow-rate of 1.0 ml/min, and an electrochemical detector (at a potential of +750 mV versus the Ag/AgCl electrode). The detection limits for both capsaicin and dihydrocapsaicin were 12 pg (39 fmol) at a signal-to-noise ratio of 3:1. By applying this method, the biological half-life of capsaicin in the rat was investigated. 相似文献
79.
Yoshiro Kobayashi Akira Ando Kosuke Kawada Itsumaro Kumadaki 《Journal of fluorine chemistry》1980,16(6):505
Tetrakis(trifluoromethyl)Dewar thiophene () is found to be a good dipolarophile and dienophile. Therefore, reacts with any kind of azides to give 1,3-dipolar cycloadducts, which are transformed to tetrakis(trifluoromethyl)Dewar pyrroles (), compounds of a new cyclic ring system. Further, reacts with cyclic or acyclic dienes to give Diels-Alder adducts. The adduct () of with butadiene was transformed to tetrakis(trifluoromethyl)cyclooctatetraene () by desulfurization, bromination and dehydrobromination, stepwise. Valence-bond isomerisation of will be presented. 相似文献
80.
Shouhei Kawada Eri Kodama Keisuke Sato Shuhei Ogawa Masaya Watanabe Hikaru Okubo Shinya Sasaki 《Surface and interface analysis : SIA》2019,51(1):17-20
The interfacial structures of cyano-based room-temperature ionic liquids play a very important role in reducing friction. However, the presence of water impairs their tribological performance. The interfacial structures and friction forces of 1-ethyl-3-methylimidazolium dicyanamide, [EMIM][DCN], and the effect of water on these structures and forces were investigated using atomic force microscopy. In addition, the interaction of water and [EMIM][DCN] was evaluated using Fourier-transform infrared (FT-IR) spectroscopy. Multiple repulsive layers were observed in the [EMIM][DCN] solution. This solution showed low friction force because these repulsive layers worked as protective layers against friction. On the other hand, the specific repulsive layer characteristics of [EMIM][DCN] could not be observed in a [EMIM][DCN] + 2 wt% H2O solution. FT-IR results indicated that the layer structure of [EMIM][DCN] was disturbed by the addition of H2O. Therefore, the solution containing water exhibited a high friction force. 相似文献