全文获取类型
收费全文 | 354篇 |
免费 | 17篇 |
专业分类
化学 | 297篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 18篇 |
物理学 | 48篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 17篇 |
2012年 | 38篇 |
2011年 | 35篇 |
2010年 | 19篇 |
2009年 | 13篇 |
2008年 | 33篇 |
2007年 | 24篇 |
2006年 | 25篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有371条查询结果,搜索用时 16 毫秒
81.
To expand the repertoire of our benzyl-protection strategy for solid-phase glycopeptide synthesis, an O-sulfated glycopeptide was chosen as the synthetic target. Trisaccharyl serine derivatives (Galβ1-4-GlcNAcβ1-2-Manα1-3-Ser) carrying (4-methoxyphenyl)methyl (MPM) groups at either 3-O or 6-O of the Gal residue were prepared through three stereoselective glycosylations. Cleavage of MPM followed by reaction with Me3N·SO3 efficiently afforded 3-O- and 6-O-sulfo-glycoserines, respectively. A preliminary debenzylation study using the sulfated glycoserines revealed that the sulfate groups persisted under ‘low-acidity TfOH’ conditions, when using a limited amount of TfOH and extending the reaction period. The 3-O-sulfo-glycoserine was then introduced into an icosapeptide modeled after an α-dystroglycan fragment by a combination of automated and manual solid-phase peptide synthesis procedures. The synthesized glycopeptide was successfully debenzylated by the low-acidity TfOH cocktail with slight damage to the sulfate functionality. 相似文献
82.
Yasuhiro Morisaki Keita Ohashi Hai‐Sub Na Yoshiki Chujo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(16):4857-4863
We successfully synthesized the first conjugated polymer containing a bismuth atom in the conjugated main chain by incorporating a bismuth atom into the cyclopentadiene framework (bismole), which was constructed by a polymer reaction. A synthetic procedure and characterization of the obtained polymers were discussed. This bismole‐containing conjugated polymer exhibited moderate bluish green photoluminescence in solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4857–4863, 2006 相似文献
83.
Bassil BS Kortz U Tigan AS Clemente-Juan JM Keita B de Oliveira P Nadjo L 《Inorganic chemistry》2005,44(25):9360-9368
The 6-cobalt-substituted [{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2]22- has been characterized by IR and UV-vis spectroscopy, elemental analysis, magnetic studies, electrochemistry, and gel filtration chromatography. A single-crystal X-ray analysis was carried out on K10Na12[{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2].49H2O (KNa-1), which crystallizes in the monoclinic system, space group P2(1)/n, with a=19.9466(8) A, b=24.6607(10) A, c=34.0978(13) A, beta=102.175(1) degrees, and Z=2. Polyanion 1 represents a novel class of asymmetric sandwich-type polyanions. It contains three cobalt ions, which are encapsulated between an unprecedented (B-beta-SiW9O34) fragment and a (B-beta-SiW8O31) unit. Polyanion 1 is composed of two sandwich species via two Co-O-W bridges in the solid state and almost certainly in solution as well based on gel filtration chromatography. UV-visible spectroscopy and cyclic voltammetry also confirmed its stability. Two well-separated groups of waves appeared in the voltammetric pattern: the wave observed in the negative potential range versus a saturated calomel electrode features the redox processes of WVI centers; the two reversible redox couples observed in the positive potential domain are attributed to the redox processes of Co2+ centers and indicated that the two types of Co2+ centers in the structure are oxidized in separate waves. Such reversibility of Co2+ centers within multi-Co-substituted polyoxometalates is uncommon. The magnetic properties of KNa-1 are also discussed. The ferromagnetic ground state has been studied by magnetic susceptibility and magnetization measurements and fitted according to an anisotropic exchange model. 相似文献
84.
85.
Kengo Oka Shunsuke Fuchi Dr. Keita Komine Dr. Hayato Fukuda Prof. Dr. Susumi Hatakeyama Prof. Dr. Jun Ishihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(56):12862-12867
The catalytic asymmetric total synthesis of (−)-exiguolide, a complex 20-membered macrolide embedded with a bis(tetrahydropyran) motif, is reported. The convergent synthesis involves the construction of the C1–C11 tetrahydropyran segment via catalytic asymmetric allylation and Prins cyclization, and the formation of the C12–C21 phosphonate segment via catalytic asymmetric cyclocondensation reaction and Johnson–Claisen rearrangement. The synthesis of 15-epi-exiguolide is also described. 相似文献
86.
Dr. Masanori Shigeno Kazuya Hanasaka Keita Sasaki Dr. Kanako Nozawa-Kumada Prof. Dr. Yoshinori Kondo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3235-3239
We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C−H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species. 相似文献
87.
88.
Takahito Itoh Keita Hirai Masashi Tamura Takahiro Uno Masataka Kubo Yuichi Aihara 《Journal of Solid State Electrochemistry》2010,14(12):2179-2189
Two different molecular weight hyperbranched polymers (HBP(L)-(PA)2 and HBP(H)-(PA)2) with two phosphonic acid groups as a functional group at the periphery and a low molecular weight hyperbranched polymer (HBP(L)-(PA)2-Ac) with both two phosphonic acid groups and an acryloyl group as a cross-linker at the periphery were successfully synthesized as thermally stable proton-conducting electrolytes. A cross-linked electrolyte membrane (CL-HBP(L)-(PA)2) was prepared by thermal polymerization of the HBP(L)-(PA)2-Ac using benzoyl peroxide. Ionic conductivities of the HBP(L)-(PA)2, the HBP(H)-(PA)2, and the CL-HBP(L)-(PA)2 under dry condition and their thermal properties were investigated, and also, the effect of the phosphonic acid group number on them was discussed. Ionic conductivities of the HBP(L)-(PA)2 and the HBP(H)-(PA)2 were found to be 1.5?×?10?5 S cm?1 at 150 °C and 3.6?×?10?6 S cm?1 at 143 °C, respectively, under dry condition, and showed the Vogel–Tamman–Fulcher type temperature dependence. The hyperbranched polymers and the cross-linked electrolyte membrane were thermally stable up to 300 °C, and the cross-linked electrolyte membrane (CL-HBP-(PA)2) had suitable thermal stability as an electrolyte membrane for the high-temperature fuel cells under dry condition. Fuel cell measurement using a single membrane electrode assembly cell with the cross-linked membrane was performed. 相似文献
89.
Bineta Keita Israel Martyr Mbomekalle Pedro de Oliveira Alireza Ranjbari Yves Justum Louis Nadjo Denis Pompon 《Journal of Cluster Science》2006,17(2):221-233
Three polyoxometalates (POMs),
(X=P or As) and
, in their oxidized and reduced forms, were selected for direct reaction or electrocatalytic reaction with L-cysteine, because they have the most negative formal potentials among those POMs active for the desired reaction. The good linearity of the UV–Visible calibration curve obtained for the reaction of α2-[P2VVW17O62]7− with L-cysteine indicates both a simple 1:1 stoichiometry for the process and the possibility to select a wavelength domain in which the one-electron reduced forms of this POM is the only strongly absorbing species in the mixture. Another general result among the three selected POMs is the existence, in each example, of a sharp isosbestic point during the recording of individual spectrakinetics using a photodiode array system. The kinetics could be fitted accuretely to a mono-exponential rate equation and the rate constants were determined. Electrocatalysis of the oxidation of L-cysteine was carried out in the presence of α2-[H4P VIVW17O62]9− as an example. The rate constant measured by chronocoulometry for this system compares favourably with that extracted from stopped flow experiments.Dedicated in honor of Professor Michael T. Pope on the occasion of his retirement. 相似文献
90.
Keita Emura Goichiro Hanaoka Koji Nuida Go Ohtake Takahiro Matsuda Shota Yamada 《Designs, Codes and Cryptography》2018,86(8):1623-1683
In homomorphic encryption schemes, anyone can perform homomorphic operations, and therefore, it is difficult to manage when, where and by whom they are performed. In addition, the property that anyone can “freely” perform the operation inevitably means that ciphertexts are malleable, and it is well-known that adaptive chosen ciphertext (CCA) security and the homomorphic property can never be achieved simultaneously. In this paper, we show that CCA security and the homomorphic property can be simultaneously handled in situations that the user(s) who can perform homomorphic operations on encrypted data should be controlled/limited, and propose a new concept of homomorphic public-key encryption, which we call keyed-homomorphic public-key encryption (KH-PKE). By introducing a secret key for homomorphic operations, we can control who is allowed to perform the homomorphic operation. To construct KH-PKE schemes, we introduce a new concept, transitional universal property, and present a practical KH-PKE scheme with multiplicative homomorphic operations from the decisional Diffie-Hellman (DDH) assumption. For \(\ell \)-bit security, our DDH-based KH-PKE scheme yields only \(\ell \)-bit longer ciphertext size than that of the Cramer–Shoup PKE scheme. Finally, we consider an identity-based analogue of KH-PKE, called keyed-homomorphic identity-based encryption and give its concrete construction from the Gentry IBE scheme. 相似文献