全文获取类型
收费全文 | 256篇 |
免费 | 16篇 |
国内免费 | 3篇 |
专业分类
化学 | 191篇 |
力学 | 5篇 |
数学 | 40篇 |
物理学 | 39篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 21篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 15篇 |
2009年 | 9篇 |
2008年 | 17篇 |
2007年 | 19篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1940年 | 2篇 |
1933年 | 1篇 |
排序方式: 共有275条查询结果,搜索用时 15 毫秒
71.
J. Pens P. E. Winkler R. G. Myers E. Pache C. W. Anderson und I. E. Rikkert 《Fresenius' Journal of Analytical Chemistry》1940,120(7-8):259-262
Ohne Zusammenfassung 相似文献
72.
David Elbaz Sophia Buhbut Benjamin Zeev Kupfer Arie Zaban Zeev Zalevsky 《Optics Communications》2012,285(10-11):2746-2749
In this paper we present a new type of optical fiber aiming to radially polarize the electrical field. This special device is composed of a tapered fiber having a classical core while on top of its external surface, radially oriented nanorods are disposed. The tails of the propagated wave are interacting with those radially oriented nanorods. This interaction performs the polarization of the propagated mode into a radial polarization. 相似文献
73.
Dr. Heiko Geisler Dr. Sophia Harringer Dominik Wenisch Richard Urban Dr. Michael A. Jakupec Dr. Wolfgang Kandioller Prof. Dr. Dr. Bernhard K. Keppler 《ChemistryOpen》2022,11(7):e202200019
The cytotoxicities of seven dimeric metal species of the general formula [M(arene)Cl2]2, commonly used as precursors for complex synthesis and deemed biologically inactive, are investigated in seven commonly employed human cancer cell lines. Four of these complexes featured a ruthenium(II) core, where p-cymene, toluene, benzene and indane were used as arenes. Furthermore, the osmium(II) p-cymene dimer, as well as the Cp* dimers of rhodium(III) and its heavier analogue iridium(III) were included in this work (Cp*=1,2,3,4,5-pentamethylcyclopentadienide). While the cytotoxic potencies of the ruthenium(II) and osmium(II) dimers are very low (or not even detectable at applicable concentrations), surprising activity, especially in cells from ovarian malignancies (with one or two-digit micromolar IC50 values), have been found for the rhodium(III) and iridium(III) representatives. This publication is aimed at all researchers using synthetic procedures based on functionalization of these dimeric starting materials to rationalize changes in biological properties, especially cytotoxicity in cancer cells. 相似文献
74.
Demetrius G. Themelis Sophia C. Karastogianni Paraskevas D. Tzanavaras 《Analytica chimica acta》2009,632(1):93-116
A highly selective sequential injection (SI) method for the automated determination of weak-acid-dissociable cyanides is reported. The analytical procedure is based on the on-line reaction of the analyte with ninhydrin in carbonate medium to form a coloured product (λmax = 510 nm). Cyanides are removed from sample matrix by acidification through a gas-diffusion step incorporated in the SI manifold. The effect of instrumental and chemical variables was studied. By adopting an on-line standard addition protocol, the sensitivity of the proposed method was enhanced drastically, without affecting the determination range. The assay was validated in terms of linearity (up to 200 μg L−1), limit of detection (cL = 2.5 μg L−1), limit of quantitation (cQ = 7.5 μg L−1), precision (sr < 2.5% at 100 μg L−1) and selectivity. High tolerance against critical species such as sulfides and thiocyanates was achieved. The applicability of the method was demonstrated by analyzing tap and mineral water samples at levels below the limits established by international E.U. and U.S. organizations. The percent recoveries were satisfactory in all cases, ranging between 94.2 and 103.6%. 相似文献
75.
Sophia S. Michaelidou 《Tetrahedron》2010,66(3):685-3845
Anthranilonitrile 3a, 4,5-dimethoxyanthranilonitrile 3b and 5-nitroanthranilonitrile 3c, react with paraformaldehyde, KCN and ZnCl2 in acetic acid under acid catalysis (H2SO4) in a sealed tube at ca. 55 °C to give the corresponding 2-(cyanomethylamino)benzonitriles 4a-c in 96, 86 and 57% yields, respectively. Thorpe-Ziegler cyclisation of the N-unprotected 2-(cyanomethylamino)benzonitriles 4a-c with K2CO3 in EtOH at elevated temperatures and pressures using either microwave heating or conventional heating in a sealed tube gives 3-amino, 3-amino-5,6-dimethoxy, and 3-amino-5-nitroindole-2-carbonitriles 2a-c in moderate to good yields. All new compounds are fully characterised. 相似文献
76.
The Bowman-Birk inhibitors (BBIs) are a family of proteins that share a canonical loop structure whose presence in a conserved conformation is linked to their inhibitory activity. We study the conformational properties of the canonical loop using a graph theoretical approach as implemented in the floppy inclusions and rigid substructure topography (FIRST). We find that the canonical loop is an independent rigid cluster in the natural inhibitors. We have further used this technique to identify residues that play an important role in the structural rigidity of the protein by quantifying their contribution to the overall rigidity of the inhibitor. We find that the conserved elements among the natural and synthetic peptides are the ones that contribute the most to rigidity, even if they are located far from the active site, as rigidity effects are nonlinear and hence nonlocal. The results help to elucidate why certain mutations in the loop of the BBI produce peptides that fail to have the designed inhibitory activity. 相似文献
77.
Gullick J Taylor S Ryan D McMorn P Coogan M Bethell D Bulman Page PC Hancock FE King F Hutchings GJ 《Chemical communications (Cambridge, England)》2003,(22):2808-2809
During the aziridination of styrene using copper bis(oxazoline) complexes the ee increases with conversion due to further reactions of the product. 相似文献
78.
Sankar Muniappan Sophia Liptsman Israel Goldberg 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(4):m140-m143
Tetrakis(4‐methoxycarbonylphenyl)porphyrin, or tetramethyl 4,4′,4′′,4′′′‐porphyrin‐5,10,15,20‐tetrabenzoate, crystallizes as a nitrobenzene 1.9‐solvate, C52H38N4O8·1.9C6H5NO2, (I). The solvent molecules are contained in extended channels which propagate through the host lattice between parallel screw/glide‐related columns of offset‐stacked porphyrin entities. Side packing of these columns involves π–π interactions between the methoxycarbonylphenyl residues. Molecules of the porphyrin host lie on crystallographic inversion centres. The zinc(II)–pyridine derivative pyridine(tetramethyl 4,4′,4′′,4′′′‐porphyrin‐5,10,15,20‐tetrabenzoato)zinc(II), [Zn(C52H36N4O8)(C5H5N)], (II), is a square‐pyramidal five‐coordinate complex with pyridine as an apical ligand, which crystallizes as a chloroform–pyridine solvate. The metalloporphyrin–pyridine units form an open layered arrangement, occluding the non‐coordinated solvent moieties within the intralayer interporphyrin voids. Within such arrays, the host porphyrin molecules are in contact with one another through the peripheral methoxycarbonyl substituents. The crystal packing consists of a bilayered arrangement of inversion‐related porphyrin layers, with the axial ligands mutually penetrating into the voids of neighbouring arrays and tight offset stacking of these bilayers. 相似文献
79.
Sophia Demoulini David M. A. Stuart Athanasios E. Tzavaras 《Archive for Rational Mechanics and Analysis》2001,157(4):325-344
We construct a variational approximation scheme for the equations of three-dimensional elastodynamics with polyconvex stored
energy. The scheme is motivated by some recently discovered geometric identities (Qin [18]) for the null Lagrangians (the determinant and cofactor matrix), and by an associated embedding of the equations of
elastodynamics into an enlarged system which is endowed with a convex entropy. The scheme decreases the energy, and its solvability
is reduced to the solution of a constrained convex minimization problem. We prove that the approximating process admits regular
weak solutions, which in the limit produce a measure-valued solution for polyconvex elastodynamics that satisfies the classical
weak form of the geometric identities. This latter property is related to the weak continuity properties of minors of Jacobian
matrices, here exploited in a time-dependent setting.
Accepted November 18, 2000?Published online April 23, 2001 相似文献
80.
John Erik Fornæ ss Nils Ø vrelid Sophia Vassiliadou 《Proceedings of the American Mathematical Society》2005,133(8):2377-2386
We obtain some -results for the operator on forms that vanish to high order on the singular set of a complex space.