全文获取类型
收费全文 | 216篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 176篇 |
力学 | 5篇 |
数学 | 11篇 |
物理学 | 29篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 18篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 2篇 |
2008年 | 9篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 14篇 |
2001年 | 2篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 422 毫秒
61.
Sachi Morinaga Takashi Nishiyama Takashi Kajiwara Kunihito Nagayama 《Applied Physics A: Materials Science & Processing》2010,101(4):743-746
A compositionally graded thin film of FeSi2 was fabricated by a gravity-assisted pulsed laser ablation (GAPLA) system. By this method, a compositionally graded structure
was successfully produced under a gravity field of 5400 G. We demonstrate that the atomic fraction of Fe, the heavier component
of the thin film measured by scanning electron microscope/energy dispersive X-ray (SEM-EDX), showed increasing spatial distribution
with the direction of gravity. We found that optimal laser fluence exists to give a thin film having the largest possible
spatial compositional gradient. We found that surface energy density on the substrate surface is the key parameter to control
the composition distribution. Furthermore, the ratio of Fe/Si of the film did not match that of the target. This result shows
that the Si component is selectively etched during the film-forming process. Relatively high laser fluence as well as a very
narrow space between the target and the substrate are essential to etch the film once it is deposited, in order to re-ionize
and etch Si selectively while gravity accelerates both Fe and Si particles to the direction of gravity. We hypothesize that
this process accounts for both the change in the stoichiometry and the formation of composition distribution. 相似文献
62.
Yuji Utsunomiya Takashi Kajiwara Takashi Nishiyama Kunihito Nagayama Shiro Kubota Motonao Nakahara 《Applied Physics A: Materials Science & Processing》2010,101(1):137-141
The pulse laser ablation of a liquid surface in air when induced by laser irradiation through a liquid medium has been experimentally
investigated. A supersonic liquid jet is observed at the liquid–air interface. The liquid surface layer is driven by a plasma
plume that is produced by laser ablation at the layer, resulting in a liquid jet. This phenomenon occurs only when an Nd:YAG
laser pulse (wavelength: 1064 nm) is focused from the liquid onto air at a low fluence of 20 J/cm2. In this case, as Fresnel’s law shows, the incident and reflected electric fields near the liquid surface layer are superposed
constructively. In contrast, when the incident laser is focused from air onto the liquid, a liquid jet is produced only at
an extremely high fluence, several times larger than that in the former case. The similarities and differences in the liquid
jets and atomization processes are studied for several liquid samples, including water, ethanol, and vacuum oil. The laser
ablation of the liquid surface is found to depend on the incident laser energy and laser fluence. A pulse laser light source
and high-resolution film are required to observe the detailed structure of a liquid jet. 相似文献
63.
Takashi Kajiwara Takashi Nishiyama Sachi Morinaga Kunihito Nagayama 《Applied Physics A: Materials Science & Processing》2010,101(4):739-742
We carried out the thin film deposition of iron silicide by pulsed laser ablation (PLA) on a sapphire substrate, which was
placed on a high-speed rotating titanium disk. The deposited thin film exhibited a continuous composition gradient. We investigated
how the continuous composition gradient was attained, because the strength of the gravity field in our experiment was far
below that in the experiment on bulk crystalline compounds. In the present study, we obtain the spatial distribution of several
species in the PLA plume of FeSi2 by using an intensified charge-coupled device (ICCD) camera. 相似文献
64.
Kajiwara Y Santander PJ Roessner CA Pérez LM Scott AI 《Journal of the American Chemical Society》2006,128(30):9971-9978
Two new cobalt corrinoid intermediates, cobalt-precorrin 5A and cobalt-precorrin 5B, have been synthesized with the aid of overexpressed enzymes of the vitamin B(12) pathway of Salmonella entericaserovar typhimurium. These compounds were made in several regioselectively (13)C-labeled forms, and their structures have been established by multidimensional NMR spectroscopy. The addition of CbiF to the enzymes known to synthesize cobalt-precorrin 4 resulted in the formation of cobalt-precorrin 5A, and the inclusion of CbiG with CbiF produced cobalt-precorrin 5B, which has allowed us to define the role of these enzymes in the anaerobic biosynthetic pathway. CbiF is the C-11 methylase, and CbiG, an enzyme which shows homology with CobE of the aerobic pathway, is the gene product responsible for the opening of the ring A delta-lactone and extrusion of the "C(2)" unit. The discovery of these long-sought intermediates paves the way for defining the final stages of the anaerobic pathway. It is of considerable evolutionary interest that nature uses two distinct pathways to vitamin B(12), both conserved over several billion years and featuring completely different mechanisms for ring-contraction of the porphyrinoid to the corrinoid ring system. Thus the aerobic pathway utilizes molecular oxygen to trigger the events at C-20 leading to contraction and expulsion of the "C(2)" unit as acetic acid from a metal-free intermediate, whereas the anaerobic route features internal delivery of oxygen from a carboxylic acid terminus to C-20 followed by extrusion of the "C(2)" unit as acetaldehyde, using cobalt complexes as substrates. 相似文献
65.
66.
Dysidiolide (1), a novel sesterterpenoid previously isolated from the Caribbean sponge Dysidea etheria de Laubenfels, inhibits the action of the protein phosphatase, cdc25A. The authors establish a novel total synthesis of natural dysidiolide (1) using intramolecular Diels-Alder reaction as the key step from optically active cyclohexenone 3. Decalin, the core structure of 1, was constructed by intramolecular Diels-Alder reaction of the diene ester generated by elimination of the phenyl sulfoxide group from sulfoxide ester 6 prepared from cyclohexenone 3. Diastereoselective methylation at C-7, alkylation at C-6, and deoxygenation of C-12 and C-24 positions gave the fully substituted bicyclic core of 1. The two side chains of the bicyclic core were further extended so as to afford natural dysidiolide (1). The total yield of this synthesis exceeds that of previous syntheses of 1. 相似文献
67.
M Kajiwara K Kurumaya Y Kohno K Tomita A T Carpenter 《Chemical & pharmaceutical bulletin》1989,37(12):3386-3389
The oxidation of tyrosine by monophenol monooxygenase (tyrosinase: EC 1.10.3.1) to melanin has been studied by a combination of ultraviolet, circular dichroism, and nuclear magnetic resonance techniques. It is demonstrated that the chiral intermediate (dopachrome) is generated stereoselectively in this enzymic reaction. 相似文献
68.
Hideo Sawada Tamikazu Narumi Atsushi Kajiwara Katsuya Ueno Kazuo Hamazaki 《Colloid and polymer science》2006,284(5):551-555
Fluoroalkyl end-capped oligomers reacted with tetraethoxysilane and silica/nanoparticles under alkaline conditions to afford
fluoroalkyl end-capped oligomers/silica nanoparticles (mean diameters: 31–54 nm) with a good dispersibility and stability
in organic media. Interestingly, the isolated fluorinated particle powders were found to afford nanometer size-controlled
colloidal particles with a good redispersibility and stability in these media. In addition, fluoroalkyl end-capped oligomers/silica
nanoparticles-encapsulated guest molecules such as stable organic radicals and ionic liquids were prepared under similar conditions.
These fluorinated nanoparticles-encapsulated guest molecules were applied to a new type of surface-modification agent, and
these particles were able to disperse well above the poly (methyl methacrylate) films. 相似文献
69.
Norihiro Tokitoh Hiroyuki Suzuki Nobuhiro Takeda Takashi Kajiwara Takahiro Sasamori Renji Okazaki 《Silicon Chemistry》2002,1(5-6):313-319
In this paper, we present the reaction of an overcrowded silylene bearing a 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) group with pivalonitrile and t-butylphosphaalkyne to give the corresponding [1+2] cycloadducts, 2H-azasilirene and 2H-phosphasilirene derivatives. This is the first exampleof the isolation of a stable 2H-azasilirene derivative, and the X-ray crystallographic analysis unambiguously revealed its three-membered ring structure in the solid state. In addition, DFT calculations supported three-membered ring character in the structures of the 2H-azasilirene and 2H-phosphasilirene. 相似文献
70.
Hexakis(4-(4'-heptyloxy)biphenoxy)cyclotriphosphazene (HHCP) was synthesized from hexachlorocyclotriphosphazene and 4-heptyloxy-4'-hydroxybiphenyl. The mesogenicity of HHCP was studied by DSC, FTIR spectroscopy and polarizing microscopy. Enantiotropic smectic C and nematic phases were observed between 450 and 455 K and 455 and 456 K, respectively, on heating, and between 456 and 455 K (nematic) and 455 and 440 K (smectic C) on cooling from the isotropic liquid phase. The introduction of the heptyloxybiphenoxy groups as side chains into cyclotriphosphazene has generated the liquid crystalline phase. FTIR spectroscopy showed that the P=N and P-O-(C) stretching vibrations converted to lower frequencies from 1224 to 1210 cm-1 and from 920 to 910cm-1, respectively, at the crystalline (C)-Sc phase transition. This result suggests that the state of the cyclotriphosphazene ring dramatically changes near the C-Sc phase transition. 相似文献