全文获取类型
收费全文 | 794篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 521篇 |
晶体学 | 8篇 |
力学 | 2篇 |
数学 | 14篇 |
物理学 | 260篇 |
出版年
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 29篇 |
2012年 | 28篇 |
2011年 | 33篇 |
2010年 | 18篇 |
2009年 | 10篇 |
2008年 | 47篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 33篇 |
2004年 | 40篇 |
2003年 | 24篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1970年 | 3篇 |
1968年 | 5篇 |
排序方式: 共有805条查询结果,搜索用时 15 毫秒
781.
Sugikawa K Numata M Kinoshita D Kaneko K Sada K Asano A Seki S Shinkai S 《Organic & biomolecular chemistry》2011,9(1):146-153
Creation of higher-ordered polymeric architectures composed of alternative assemblies of single-walled carbon nanotubes (SWNTs) and fibrous porphyrin J-aggregates can be easily achieved utilizing the cationic semi-artificial polysaccharide which can act not only as a tubular host for SWNTs but also as a one-dimensional template for porphyrin molecules. This new class of hierarchical polymer assembly is formed, for the first time, by the mutual template effect of two components, i.e., the cationic SWNT complexes and the anionic porphyrin supramolecular nanofibers. In the present system, the self-assembling behaviors of the SWNT complexes as well as the final properties of the SWNT nanoarchitectures are strongly affected by the packing mode of porphyrin molecules on the cationic semi-artificial polysaccharide. Furthermore, we have confirmed that the light energy captured by the porphyrin J-aggregates is effectively transferred to SWNTs. 相似文献
782.
Kinoshita K Minami H Tarutani Y Tajima K Okubo M Yanagimoto H 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4474-4480
Polystyrene (PS)/aluminum hydroxide (Al(OH)(3)) composite particles were successfully prepared by the sol-gel process of aluminum isopropoxide (Al(OPr(i))(3)) in a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) using ammonium hydroxide (NH(4)OH) as a catalyst in the presence of PS seed. Transmission electron microscopy observation of ultrathin cross-sections of the composite particles revealed that the composite particles had a core-shell morphology consisting of a PS core and a Al(OH)(3) shell having high crystallinity. The amount of secondary nucleated Al(OH)(3) could be reduced by dropwise addition of NH(4)OH. Moreover, PS/η-Al(2)O(3) composite particles were successfully prepared by heat treatment of PS/Al(OH)(3) at 300 °C in N(2) atmosphere, which is below the decomposition temperature of PS. 相似文献
783.
Yoshidome T Ito Y Ikeguchi M Kinoshita M 《Journal of the American Chemical Society》2011,133(11):4030-4039
We propose a novel picture of the rotation mechanism of F(1)-ATPase, a rotary-motor protein complex. Entropy, which originates from the translational displacement of water molecules, is treated as the key factor in the proposal. We calculate the water entropy gains upon formation of the α-β, α-γ, and β-γ subunit pairs. The gain is given as the difference between the hydration entropy of a subunit pair and the sum of the hydration entropies of the separate subunits forming the pair. The calculation is made using a hybrid of a statistical-mechanical theory for molecular liquids and morphometric approach. The water entropy gain is considered as a measure of tightness of the packing at each subunit interface. The results are highly correlated with the numbers of stable contacts at the subunit interfaces estimated by a molecular dynamics simulation. We also calculate the hydration entropies of three different subcomplexes comprising the γ subunit, one of the β subunits, and two α subunits adjacent to them. The major finding is that the packing in F(1)-ATPase is highly asymmetrical, and this asymmetry is ascribed to the water entropy effect. We discuss how the rotation of the γ subunit is induced by such chemical processes as ATP binding, ATP hydrolysis, and release of the products. In our picture, the asymmetrical packing plays crucially important roles, and the rotation is driven by the water entropy effect. 相似文献
784.
Crystals of the complexes of (+)-catechin (CA) of non-galloylated catechin and (-)-catechin-3-O-gallate (Cg) of galloylated catechin with caffeine were prepared, and their stereochemical structures and intermolecular interactions were determined by X-ray crystallographic analysis. CA formed a 1 : 1 complex with caffeine by intermolecular hydrogen bonds, whereas Cg formed a 1 : 2 complex with caffeine, which was formed by face-to-face and offset π-π interactions and intermolecular hydrogen bonds. A solution of two kinds of non-galloylated catechin, CA and (-)-epicatechin (EC), and caffeine (molar ratio 1 : 1 : 2) in water afforded a 1 : 1 : 2 complex, the crystal structure of which had two layers, one layer in which CA and caffeine formed alternate lines and an other layer in which EC and caffeine formed alternate lines. The 1 : 1 : 2 complex was formed by offset π-π and CH-π interactions and intermolecular hydrogen bonds. 相似文献
785.
Bhardwaj V Trabelsi K Singh JB Choi SK Olsen SL Adachi I Adamczyk K Asner DM Aulchenko V Aushev T Aziz T Bakich AM Barberio E Belous K Bhuyan B Bischofberger M Bondar A Bračko M Brodzicka J Browder TE Chen A Chen P Cheon BG Cho K Choi Y Dalseno J Doležal Z Eidelman S Epifanov D Gaur V Gabyshev N Golob B Haba J Hayasaka K Hayashii H Horii Y Hoshi Y Hou WS Hsiung YB Hyun HJ Iijima T Inami K Ishikawa A Iwabuchi M Iwasaki Y Iwashita T Joshi NJ Julius T Kang JH Kawasaki T Kiesling C Kim HO Kim JB 《Physical review letters》2011,107(9):091803
We report a study of B→(J/ψγ)K and B→(ψ'γ)K decay modes using 772×10? B ?B events collected at the Υ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We observe X(3872)→J/ψγ and report the first evidence for χ(c2)→J/ψγ in B→(X_{c ?cγ)K decays, while in a search for X(3872)→ψ'γ no significant signal is found. We measure the branching fractions, B(B(±)→X(3872)K(±))B(X(3872)→J/ψγ)=(1.78(-0.44)(+0.48)±0.12)×10(-6), B(B(±)→χ(c2)K(±))=(1.11(-0.34)(+0.36)±0.09)×10(-5), B(B(±)→X(3872)K(±))B(X(3872)→ψ'γ)<3.45×10? (upper limit at 90% C.L.), and also provide upper limits for other searches. 相似文献
786.
Hitoshi Tamiaki Nobuo Kosaka Yusuke Kinoshita 《Research on Chemical Intermediates》2013,39(1):221-232
A cyclic chlorophyll hetero-dyad 1-H2H2, prepared by double ester linking of two structurally different pyropheophorbide-a moieties through 3-CH2OCO-132′ and 172-COOCH2-3′, was metallated with zinc and copper to give mono and di-metallated complexes 1-MH2 or 1-H2M and 1-MM. The metallation proceeded stepwise and regioselectively, with predominant synthesis of one of the two mono-metallated complexes 1-MH2 as intermediate. The di-zinc complex produced, 1-ZnZn, was demetallated exclusively via the same mono-zinc complex 1-ZnH2 as was the major intermediate during metallation. Visible and/or circular dichroism spectra of 1-H2H2, 1-MH2, 1-H2M, and 1-MM (M = Ni, Cu, or Zn) were measured in organic solvents. Intramolecular interaction of chlorin chromophores is discussed and compared with that of the corresponding monomeric species. 相似文献
787.
Tomohiko Hirano Shinya Kitagawa Hajime Ohtani Takehiko Kinoshita Yuzo Ishigaki Nobuyuki Shibata Susumu Nii 《Analytical and bioanalytical chemistry》2013,405(25):8319-8326
A method for evaluating the interactions between metal ions and nonionic surfactants in aqueous solutions containing high-concentration HCl, using gas pressure-driven low-pressure high-performance liquid chromatography (LP-HPLC) as a highly acid-resistant HPLC system, was developed. To construct the LP-HPLC for this purpose, poly(styrene-co-divinylbenzene)-based low-flow-resistance monolithic columns tolerant to highly acidic conditions were prepared using low-conversion thermal polymerization. Thermal polymerization at 65 °C for 1.5 h (monomer conversions, 33 % for styrene and 59 % for divinylbenzene) allowed preparation of a column with both high separation efficiency (around 60,000 plates m?1 for alkylbenzenes) and a quite low back pressure of 0.14 MPa at a linear flow rate of 1 mm s?1 (2.8?×?10?13 m2 in permeability). The base column prepared under the above conditions was coated with a nonionic surfactant, polyoxyethylene nonylphenyl ether (PONPE, average oxyethylene unit numbers (n)?=?3, 7.5, 15, and 20), and used for evaluation of the interactions between PONPEs and metal ions in 6 M HCl. The interactions between PONPEs and Au(III), Ga(III), Fe(III), Zn(II), and Cu(II) were successfully evaluated using both breakthrough and chromatographic methods. Furthermore, a study of the effect of the polyoxyethylene (POE) chain length revealed that the use of PONPE with the longer POE moiety enhanced the magnitude of the interaction together with the increase in the amount of oxyethylene (OE) units coated on the monolith. Moreover, the interactions of metal ions with a single OE unit were almost constant in the range of n?=?7.5–20, whereas the suppression of the interaction between Au(III) with the shortest PONPE chain (n?=?3) was also observed. Figure
Acid-resistive gas pressure-driven low-pressure high-performance liquid chromatography was developed and applied to the evaluation of interactions between metal ions and nonionic surfactants in high-concentration HCl, in particular for the effect of polyoxyethylene length on the interaction. 相似文献
788.
Masayuki Kirihara Sayuri NaitoYuki Nishimura Yuki IshizukaToshiaki Iwai Haruka TakeuchiTomomi Ogata Honoka HanaiYukari Kinoshita Mari KishidaKento Yamazaki Takuya NoguchiShiro Yamashoji 《Tetrahedron》2014
The reaction of aromatic or benzylic disulfides with 2.5 equiv of Selectfluor™ in acetonitrile/water (10:1) at room temperature efficiently produced the corresponding thiosulfonates. Conversely, the reaction of disulfides with 6.5 equiv of Selectfluor™ or thiosulfonates with 4.5 equiv of Selectfluor™ in refluxing acetonitrile/water (10:1) provided sulfonyl fluorides in high yields. Accufluor™ and FP-T300™ are also effective in preparing sulfonyl fluorides from disulfides under the similar reaction conditions. Sulfonyl chlorides or sulfonyl bromides were effectively obtained from the reaction of disulfides with 6 equiv of either N-chlorosuccinimide or N-bromosuccinimide in acetonitrile/water (10:1) at room temperature. Some other electrophilic chlorinating or brominating reagents are also able to be used instead of N-chlorosuccinimide or N-bromosuccinimide for the syntheses of sulfonyl halides from disulfides. These reactions of disulfides with electrophilic halogenating reagents are convenient methods to prepare thiosulfonates and sulfonyl halides. 相似文献
789.
Yamaguchi T Yamamoto Y Kinoshita D Akiba KY Zhang Y Reed CA Hashizume D Iwasaki F 《Journal of the American Chemical Society》2008,130(22):6894-6895
In an exploration of six coordination and hypervalence in carbon compounds, steric constraints have been employed to bring four ether O atoms in close proximity to an allenic carbon atom. The dimethylated dication 2 is confirmed to have hexacoordinate carbon by experimental charge density analysis and DFT calculations and is arguably hypervalent. 相似文献
790.
Total syntheses of (+)-coronarin A (1), (+)-coronarin E (2), (+)-austrochaparol (3) and (+)-pacovatinin A (4) were achieved from the synthetic (+)-albicanyl acetate (6). Dess-Martin oxidation of (+)-albicanol (5) derived from the chemoenzymatic product (6) gave an aldehyde (7), which was subjected to Julia one-pot olefination using beta-furylmethyl-heteroaromatic sulfones (8 or 9 ) gave (+)-trans coronarin E (2) and (+)-cis coronarin E (12) with high cis-selectivity. The synthesis of (+)-coronarin A (1) from (+)-trans coronarin E (2) was achiev-ed, while (+)-cis coronarin E (12) was converted to the natural products (+)-(5S,9S,10S)-15,16-epoxy-8(17),13(16),14-labdatriene (13) and (+)-austrochaparol (3). By the asymmetric synthesis of (+)-3, the absolute structure of (+)-3 was determined to be 5S, 7R, 9R, 10S configurations. Homologation of (+)-albicanol (5) followed by allylic oxidation gave (7 alpha)-hydroxy nitrile (17), which was finally converted to the natural (+)-pacovatinin A (4) in 8 steps from (+)-albicanol (5). 相似文献