全文获取类型
收费全文 | 764篇 |
免费 | 13篇 |
国内免费 | 5篇 |
专业分类
化学 | 606篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 46篇 |
物理学 | 113篇 |
出版年
2022年 | 4篇 |
2019年 | 5篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 8篇 |
2013年 | 52篇 |
2012年 | 41篇 |
2011年 | 35篇 |
2010年 | 22篇 |
2009年 | 21篇 |
2008年 | 34篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 35篇 |
2004年 | 40篇 |
2003年 | 29篇 |
2002年 | 27篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 6篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1970年 | 3篇 |
1967年 | 4篇 |
1960年 | 3篇 |
1930年 | 4篇 |
排序方式: 共有782条查询结果,搜索用时 9 毫秒
701.
The photoreactivating enzyme (PRE) is concerned with mainly two kinds of light wavelength. The PRE splits UVC (254 nm)-induced pyrimidine dimer by absorbing UVA (320–380 nm) or visible light in its chromophore. The present paper demonstrates that the phr gene expression was efficiently induced in an excision defective strain (uvrA∼) after irradiation by UVC and UVB (290-320 nm), but not by UVA and visible light. In addition, the induced activity was significantly depressed by irradiation with UVA and visible light. Therefore we conclude that the phr gene expression can be induced by pyrimidine dimers. 相似文献
702.
Takeo Taguchi Satoshi Mitsuhashi Akiko Yamanouchi Yoshiro Kobayashi Hiroshi Sai Nobuo Ikekawa 《Tetrahedron letters》1984,25(43):4933-4936
23,23-Difluoro-25-hydroxyvitamin D3 was synthesized from 6β-methoxy-3α,5-cyclo-23,24-dinor-5α-cholan-22-ol. 相似文献
703.
Benzylzirconocene intermediate, which was readily prepared by a reaction of o-alkoxymethylstyrene with `Cp2Zr' under mild conditions, reacted with acyl chlorides in the presence of a catalytic amount of CuBr-SMe2 to give ketone derivatives in moderate to good yields. 相似文献
704.
Hidefumi Hirai Katsuma Hiraki Isamu Noguchi Takeo Inoue Shoji Makishima 《Journal of polymer science. Part A, Polymer chemistry》1970,8(9):2393-2405
Polymerizations of butadiene, penta-1,3-diene, and isoprene with n-butyl titanate–triethylaluminum catalyst are examined by ESR measurements on the polymerization state. At Al/Ti molar ratios greater than 2.9 where the conjugated dienes are polymerized, the polymerization system of butadiene always gives an ESR signal with a g value of 1.983 and with a hyperfine structure of about 19 components. This signal does not appear at all, even in the presence of the monomer, at Al/Ti molar ratios smaller than two where butadiene is not polymerized. The absorption intensity of the signal coincides fairly well with the concentration of polymer chain calculated from polymer yield and the molecular weight. On the basis of these facts, the signal is assigned to the growing end of polybutadiene with this catalyst. The structure of the growing end is proposed to have both two substituted π-allyl groups and an alkoxy group in coordination to titanium (III), by analysis of the hyperfine structure. The polymerization system of penta-1,3-diene and that of isoprene respectively, give a new signal with a g value of 1.983, although the signal for the former monomer has a hyperfine structure of 11 components and that for the latter monomer has no hyperfine structure. A structure for the growing end in the polymerization of each of these two monomers analogous to that of the growing end of polybutadiene is proposed. 相似文献
705.
Takeshi Toru Kenzo Watanabe Takeo Oba Toshio Tanaka Noriaki Okamura Kiyoshi Bannai Seizi Kurozumi 《Tetrahedron letters》1980,21(26):2539-2542
Several phenyl sulfides including stable 5- and 7-phenylthioprostacyclins were obtained by the reaction of the vinyl ether () and prostacyclin methyl ester () with PhSCl. 相似文献
706.
Takanobu Aoyagi Takeo Araki Hisaya Tani 《Journal of polymer science. Part A, Polymer chemistry》1972,10(8):2325-2334
The catalytic behavior of binary systems derived from AIR3 and alkali metal hydroxide in a molar ratio of 1 to 0.5 in situ for stereospecific polymerization of acetaldehyde was studied for the purpose of preparation of isotactic polyacetal. The polymer obtained can be readily stretched to a film. The polymerization proceeds slowly (in ~20 hr). The polymer yield and stereospecificity of the polymerization by AlEt3–LiOH (1:0.5) catalyst were not significantly changed by the nature of solvent or dilution as far as studied. AlEt3–NaOH, AlEt3–KOH, AlEt3–CsOH, AliBu3–LiOH and AlMe3–LiOH in molar ratios of 1 to 0.5 behaved similarly. AlMe3–NaOH, AlMe3–KOH and AliBu3–NaOH also gave isotactic polymer of high stereoregularity but in lower yields. 相似文献
707.
Takeo Saegusa 《Angewandte Chemie (International ed. in English)》1977,16(12):826-835
This article describes a new concept of copolymerization which occurs spontaneously without any added catalyst. A nucleophilic monomer (MN) combines with an electrophilic one (ME) to generate a zwitterion [+]MN—M, which is responsible for the initiation and propagation of copolymerization. Twenty-three novel copolymerizations have been explored on the basis of the new concept. MN monomers which have been investigated are five- and six-membered cyclic imino ethers, dihydro-2(3H)-furanimine, an azetidine, a cyclic phosphinic acid ester and a Schiff base; the ME monomers include β-propiolactone, a cyclic dicarboxylic acid anhydride, a sultone, acrylic acid, acrylamide, a β-hydroxyalkyl acrylate and ethylenesulfonamide. In most combinations, alternating 1 : 1 copolymers were produced. In addition to the above-mentioned combinations, the alternating 1 : 1 copolymerization of cyclic phosphite with α-keto acid was discovered. 相似文献
708.
Reactions of o-(alkoxymethyl)styrene derivatives with a stoichiometric amount of zirconocene-butene complex (zirconocene equivalent, "Cp(2)Zr") brought about an insertion of the zirconocene species into a benzylic carbon-oxygen bond. The oxidative insertion of Cp(2)Zr to the benzylic carbon-oxygen bond is a result of sequential reactions: (i) formation of zirconacyclopropane by the ligand exchange with o-(alkoxymethyl)styrene, (ii) elimination of the alkoxy group through an aromatic conjugate system giving metalated o-quinodimethane species, and (iii) transfer of zirconium metal to the benzylic position. Through use of a catalytic amount of "Cp(2)Zr", however, unprecedented homo-coupling reactions (dimerization) of o-(alkoxymethyl)styrene derivatives occurred to give a tetracyclic compound. On the other hand, reactions of o-(1-alkoxyisopropyl)styrene derivatives gave rise to the analogous tetracyclic compounds regardless of the amount of "Cp(2)Zr" (stoichiometric or catalytic). Heterocoupling product between o-(1-alkoxyisopropyl)styrene and styrene congeners was obtained in high cis stereo- and regioselectivity by treating o-(1-alkoxyisopropyl)styrene derivatives with "Cp(2)Zr" in the presence of an excess amount of styrene derivatives. 相似文献
709.
Two-electron reduction of [(eta5-C5H4Me)4Fe4(mu3-CH)2(mu3-CO)2](PF6)2 (1) results in the coupling of two methylidyne ligands to form (eta5-C5H4Me)4Fe4(HCCH)(mu3-CO)2 (2), the two-electron oxidation of which reproduces 1. Structures of 1 and 2 were determined by X-ray diffraction analysis. 相似文献
710.
Soo-Gil Park Jong-Eun Park Eun-In Cho Jin-Hee Hwang Takeo Ohsaka 《Research on Chemical Intermediates》2006,32(5):595-601
The electrochemical oxidation of ascorbic acid (AA) and serotonin (5-HT) at a boron-doped diamond (BDD) electrode modified
with poly(N,N-dimethylaniline) (PDMA) has been studied. The oxidation potentials of 5-HT and AA overlapped after mixing of the two chemicals,
due to interference of AA at the bare BDD electrode. However, after modifying the BDD electrode with a cationic polymer (PDMA),
the oxidation peaks of 5-HT and AA were separated. PDMA-coated BDD electrodes can be used for simultaneous detection of these
species. 相似文献