全文获取类型
收费全文 | 227篇 |
免费 | 16篇 |
国内免费 | 1篇 |
学科分类
数理化 | 244篇 |
出版年
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 3篇 |
2018年 | 10篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 13篇 |
2012年 | 23篇 |
2011年 | 15篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有244条查询结果,搜索用时 562 毫秒
61.
Nobuko Yoshimoto Osamu Shimamura Takuya Nishimura Minato Egashira Maiko Nishioka Masayuki Morita 《Electrochemistry communications》2009,11(2):481-483
A novel polymeric electrolyte based on a self-assembled copolymer moiety has been prepared by a simple method of photo-induced radical polymerization of a mixture consisting of stearylmethacrylate (SMA) and poly(ethylene glycol)-monomethacrylate (PEM) that dissolves LiBF4 as the electrolytic salt. The SMA moiety work as mechanically stable backbone and the PEM unit dissolving the salts serves as ion-conducting path in the polymeric composite. Solid-state NMR measurements indicated that the resulting polymer composite consists of PEM-rich and SMA-rich phases, each of which exists within several nanometers apart. The ionic conductivity of the polymer electrolyte with the composition of PEM/SMA = 7/3 (by mass ratio) was 2.8 × 10?5 S cm?1 at 50 °C, which was significantly higher than that of the polymer electrolyte based on cross-linked PEM copolymer without SMA. 相似文献
62.
63.
Junko Okamoto Shinichi Yamabe Tsutomu Minato Toshio Hasegawa Takahisa Machiguchi 《Helvetica chimica acta》2005,88(6):1519-1539
Tropone ( 1 ) reacts with ketenes 2 to yield [8+2] cycloadducts, the γ‐lactones 3 . The concerted [8+2] cycloaddition path is formally symmetry‐allowed, but we established that it is unfavorable. Careful low‐temperature NMR (1H, 13C, and 19F) spectroscopies of the reaction of diphenyl ketene ( 2b ) or bis(trifluoromethyl) ketene ( 2c ) with tropone ( 1 ) allowed the direct detection of a β‐lactone intermediates 5b , c and novel norcaradiene species 6b , c in head‐to‐head configurations. The [2+2] cycloadducts 5b , c equilibrated with the norcaradienes 6b , c . The β‐lactones 5b and 5c were converted to the γ‐lactones 3b and 3c , respectively, in quantitative yields. The DFT calculations showed that the concerted [8+2] cycloaddition is unfavorable. The first step of the calculated reaction 1 + 2c is a cycloaddition which leads to a dioxetane intermediate. This initial [2+2] cycloadduct is isomerized to the β‐lactone 5c via the first zwitterionic intermediate. The β‐lactone 5c is further isomerized to the product γ‐lactone 3c via the second zwitterion intermediate. Thus, 3c is not formed via the well‐established two‐step mechanism including zwitterionic intermediates but via a five‐step mechanism composed of a [2+2] cycloaddition and subsequent isomerization (Scheme 12). 相似文献
64.
Makoto Minato Susumu Hiratsuka Takashi Ito 《Journal of organometallic chemistry》2004,689(6):1025-1028
The reaction of Cp2MoH2 (Cp=η5-C5H5) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η3-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η3-crotyl complex. 相似文献
65.
Toshifumi Takeuchi Yuji Minato Masayoshi Takase Hideyuki Shinmori 《Tetrahedron letters》2005,46(52):9025-9027
Molecular recognition materials bearing halogen bonding-based binding sites were synthesized by a non-covalent imprinting technique using a 2,3,5,6-tetrafluoro-4-iodostyrene (TFIS) as the functional monomer. The binding sites were generated by co-polymerizing TFIS, styrene and divinylbenzene in the presence of the template molecule (4-dimethylaminopyridine—DMAP). The imprinted polymer preferentially adsorbed aminopyridine derivatives, suggesting that halogen bonding may play a role in the selective recognition of analytes by the synthesized synthetic receptor. 相似文献
66.
Daisuke Sawai Kazuhiko Nagai Minato Kubota Toshio Ohama Tetsuo Kanamoto 《Journal of Polymer Science.Polymer Physics》2006,44(1):153-161
The effects of molecular weight (MW) and MW distribution on the maximum tensile properties of polyethylene (PE), achieved by the uniaxial drawing of solution‐grown crystal (SGC) mats, were studied. The linear‐PE samples used had wide ranges of weight‐average (Mw = 1.5–65 × 105) and number‐average MWs (Mn = 2.0–100 × 104), and MW distribution (Mw/Mn = 2.3–14). The SGC mats of these samples were drawn by a two‐stage draw technique, which consists of a first‐stage solid‐state coextrusion followed by a second‐stage tensile drawing, under controlled conditions. The optimum temperature for the second‐stage draw and the resulting maximum‐achieved total draw ratio (DRt) increased with the MW. For a given PE, both the tensile modulus and strength increased steadily with the DRt and reached constant values that are characteristic for the sample MW. The tensile modulus at a given DRt was not significantly affected by the MW in the lower DRt range (DRt < 50). However, both the maximum achieved tensile modulus (80–225 GPa) and strength (1.0–5.6 GPa), as well as those at higher DRts > 50, were significantly higher for a higher MW. Although the maximum modulus reached 225 ± 5 for Mn ≥ 4 × 105, the maximum strength continued to increase with Mn even for Mn > 4 × 105, showing that strength is more strongly dependent on the Mn, even at higher Mn. Furthermore, it was found that each of the maximum tensile modulus and strength achieved could be expressed by a unique function of the Mn, independently of the wide variations of the sample MW and MW distribution. These results provide an experimental evidence that the Mn has a crucial effect on the tensile properties of extremely drawn and chain‐extended PE fibers, because the structural continuity along the fiber axis increases with the chain length, and hence with the Mn. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 153–161, 2006 相似文献
67.
Counterion binding in Na poly(acrylate) gel immersed in water/organic solvent [ethanol (EtOH), acetonitrile (AcN), or tetrahydrofuran (THF)] mixtures was investigated by 23Na‐NMR spectroscopy. With an increase in the content of an organic solvent (~40–50 vol %), the 23Na chemical shift significantly moved downfield on a gel collapse. This downfield shift strongly suggests that the gel collapse was induced by contact ion‐pair formation between the counterion and the carboxyl anion on the polymer. With a further increase in the solvent content (~90 vol %), the chemical shift for an EtOH system showed a slight upfield shift, while THF and AcN systems maintained downfield shifts. The contrasting behaviors for EtOH and the latter two solvent systems were interpreted as being caused by desolvation and resolvation of bound Na+ counterions because of deswelling and reswelling of the respective gels in the pertinent solvent concentration regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4412–4420, 2004 相似文献
68.
69.
S Minato 《Radioisotopes》1990,39(4):170-173
This note describes a method of direct measurement of airborne gamma-rays primarily from 222Rn daughters using a NaI(Tl) scintillation spectrometer with lead shields. This method has the advantage of being able to maintain the system easily compared to other usual systems including a pump. The pulse-height distributions are successively fed to a floppy disk in a personal computer every unit time. The gain shifts can be corrected automatically by a computer program. This technique would be applicable to the estimation of 222Rn daughters concentration and to examination of disequilibrium between 214Pb(RaB) and 214Bi(RaC) and of those height distribution up to about 200 m. The accuracy for estimating the concentration is as good as that of the filter method. 相似文献
70.