全文获取类型
收费全文 | 254篇 |
免费 | 5篇 |
专业分类
化学 | 165篇 |
晶体学 | 5篇 |
力学 | 16篇 |
数学 | 24篇 |
物理学 | 49篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 4篇 |
2013年 | 38篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 15篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有259条查询结果,搜索用时 15 毫秒
61.
62.
Hypervalent iodine oxidation of ketoximes (1) using iodosobenzene diacetate leads to cleavage of 1 with the formation of corresponding ketones (2) under neutral conditions in good yields. The scope and limitations of the reaction are discussed as well as the mechanism. 相似文献
63.
K. Vyas A. Sivalakshmidevi G. Om Reddy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):e572-e573
Lansoprazole, 2‐({[3‐methyl‐4‐(2,2,2‐trifluroethoxy)pyridin‐2‐yl]methyl}sulfinyl)‐1H‐benzimidazole, C16H14F3N3O2S, is an antiulcerative agent. The molecules in the lattice are held together by intermolecular hydrogen bonds between the NH group of benzimidazole and the sulfinyl O atom. 相似文献
64.
Cook GA Pajewski R Aburi M Smith PE Prakash O Tomich JM Gokel GW 《Journal of the American Chemical Society》2006,128(5):1633-1638
The synthetic peptide (C(18)H(37))(2)NCOCH(2)OCH(2)CON-(Gly)(3)-Pro-(Gly)(3)-OCH(2)Ph forms chloride-selective channels in liposomes and exhibits voltage-gating properties in planar phospholipid bilayers. The peptide fragment of the channel is based on a conserved motif in naturally occurring chloride transporters. Membrane-anchoring residues at the N- and C-terminal ends augment the peptide. NMR spectra (1D and 2D) of the channel in CDCl(3) showed significant variation in the absence and presence of stoichiometric tetrabutylammonium chloride (Bu(4)NCl). One-dimensional solution-state NMR titration studies combined with computational molecular simulation studies indicate that the peptide interacts with the salt as an ion pair and H-bonds chloride. To our knowledge, this is the first structural analysis of any synthetic anion-channel salt complex. 相似文献
65.
Om V SinghHyunsoo Han 《Tetrahedron letters》2003,44(11):2387-2391
A general methodology for the stereoselective synthesis of 1-deoxymannojirimycin and its three other stereoisomers is described. The achiral olefin 6 was converted through the common olefin intermediate 12 to the target compounds in a highly stereocontrolled manner. The regioselective asymmetric aminohydroxylation (AA) and diastereoselective dihydroxylation reactions were used for the introduction of all four stereocenters in the targets, and the ring-closing metathesis (RCM) reaction was utilized for the construction of the required six-membered ring. 相似文献
66.
Several newSchiff base derivatives of antimony(III) have been synthesized by the reaction of antimony(III) isopropoxide with theSchiff bases having the donor system, O–N–O. The reactions in 1:1 and 2:3 molar ratios [Sb(O-i-C3H7)3: :Schiff base] have yielded Sb(O-i-C3H7) (SB) and Sb2 (SB)3 type of derivatives (whereSB represents the anion of theSchiff base andSBH2=o-hydroxyacetophenone-2-hydroxy-1-propylimine, o-hydroxycetophenone-3-hydroxy-1-propylimine, salicylidene-2-hydroxyethylamine, salicylidene-2-hydroxy-1-propylamine and 2-hydroxy-1-naphthylidene-2-hydroxyethylamine) resp. In the resultingSchiff base derivatives, the central antimony atom appears to be tetracoordinated as indicated by their monomeric state determined ebullioscopically. The infrared spectra of the resulting complexes have been recorded and tentative structures indicated. The thermogravimetric analysis of antimony-monoisopropoxysalicylidene-2-hydroxy-1-propylamine has also been carried out.With 1 Figure 相似文献
67.
An amperometric titration of cobalt(II) with hexacyanoferrate(III) in aqueous ammonium citrate or aqueous glycine solution at pH 9.8 or pH 8.0 respectively, is reported. Cobalt concentrations of 2-30 mg/l were successfully determined. In citrate solutions cerium(III) and iron(III) interfered, and in glycine solutions, copper(II) and vanadium(V). 相似文献
68.
Linnea Lindh Olga Gordivska Samuel Persson Hannes Michaels Hao Fan Pavel Chbera Nils W. Rosemann Arvind Kumar Gupta Iacopo Benesperi Jens Uhlig Om Prakash Esmaeil Sheibani Kasper S. Kjaer Gerrit Boschloo Arkady Yartsev Marina Freitag Reiner Lomoth Petter Persson Kenneth Wrnmark 《Chemical science》2021,12(48):16035
A new generation of octahedral iron(ii)–N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push–pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push–pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I−/I3− redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO2. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO2. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO2 back to the oxidized dye, leaving only 5–10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 μs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6–8 μs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.Iron-based photosensitizers for dye-sensitized solar cells with a rod-like push–pull design. Solar cell performance was limited by ultrafast (sub-ps) recombination, but yielded better performance than the homoleptic parent photosensitizer. 相似文献
69.
70.
Om P. Agrawal 《Journal of Mathematical Analysis and Applications》2008,337(1):1-12
This paper presents a general finite element formulation for a class of Fractional Variational Problems (FVPs). The fractional derivative is defined in the Riemann-Liouville sense. For FVPs the Euler-Lagrange and the transversality conditions are developed. In the Fractional Finite Element Formulation (FFEF) presented here, the domain of the equations is divided into several elements, and the functional is approximated in terms of nodal variables. Minimization of this functional leads to a set of algebraic equations which are solved using a numerical scheme. Three examples are considered to show the performance of the algorithm. Results show that as the number of discretization is increased, the numerical solutions approach the analytical solutions, and as the order of the derivative approaches an integer value, the solution for the integer order system is recovered. For unspecified boundary conditions, the numerical solutions satisfy the transversality conditions. This indicates that for the class of problems considered, the numerical solutions can be obtained directly from the functional, and there is no need to solve the fractional Euler-Lagrange equations. Thus, the formulation extends the traditional finite element approach to FVPs. 相似文献