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71.
Ohne Zusammenfassung 相似文献
72.
T. Vogel T. Neuhaus M. Bachmann W. Janke 《The European physical journal. E, Soft matter》2009,30(1):7-18
In this work we investigate the structural properties of native states of a simple model for short flexible homopolymers,
where the steric influence of monomeric side chains is effectively introduced by a thickness constraint. This geometric constraint
is implemented through the concept of the global radius of curvature and affects the conformational topology of ground-state
structures. A systematic analysis allows for a thickness-dependent classification of the dominant ground-state topologies.
It turns out that helical structures, strands, rings, and coils are natural, intrinsic geometries of such tubelike objects. 相似文献
73.
Rainer Bachmann Clemens Burda Fabian Gerson Markus Scholz Hans-Jürgen Hansen 《Helvetica chimica acta》1994,77(5):1458-1465
Proton-hyperfine data are reported for the radical anions generated from azulene ( 1 ) and its alkyl derivatives 2 – 11 in 1,2-dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3-dimethyl- ( 2 ), 5,7-dimethyl- ( 3 ), 1,3,5,7-tetramethyl- ( 4 ), 2-methyl- ( 5 ), 4,6,8-trimethyl- ( 6 ), 2,4,6,8-tetramethyl-( 7 ), 1,3,4,6,8-pentamethyl- ( 8 ), 1,3,4,8-tetramethyl-6-propyl- ( 9 ), 6-(tert-butyl)-1,3,4,8-tetramethyl- ( 10 ), and 1,2,3,4,6,8-hexamethylazulene ( 11 ). Alkyl substituents at the odd-numbered centers μ = 1, 3, 5, and 7 partly shift the π-spin population from the seven- to the five-membered ring, whereas those at the even-numbered centers μ = 4, 6, and 8 exert an opposite effect on the π-spin distribution. 相似文献
74.
Silva CR Bachmann S Schefer RR Albert K Jardim IC Airoldi C 《Journal of chromatography. A》2002,948(1-2):85-95
A new C18 urea stationary phase was prepared by a single-step modification process through the reaction of ProntoSil spherical silica (3 microm, Bischoff) with the trifunctional alkoxysilane (CH3CH2O)3-Si-(CH2)3-NH-C(O)-NH-(CH2)17-CH3, prepared in our laboratory. The phase was characterized by elemental analysis and solid-state 29Si and 13C nuclear mangnetic resonance spectrometry. Chromatographic evaluations of the new phase in 150 x 3.9 mm HPLC columns involving the separation of different test mixtures, indicate good performance for both polar and basic mixtures and also show promising results for further applications. 相似文献
75.
A. Jesih K. Lutar B.
emva B. Bachmann St. Becker B. G. Müller R. Hoppe 《无机化学与普通化学杂志》1990,588(1):77-83
Single Crystal Investigation on AgF2 For the first time single crystals of AgF2 (black, metalic bright) have been obtained by heating AgF2 powder under a mixture of HF and F2 in autoclaves at 400°C. It crystallizes orthorhombic in the space group Pbca – D (Nr. 61) – with a = 556.8(1), b = 583.1(1) and c = 510.1(1) pm; Z = 4. The Madelung Part of Lattice Energy, MAPLE, and the Effective Coordination Number, ECoN, via the Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. 相似文献
76.
The synthesis, electronic structure, and oxidation-reduction chemistry of a homologous series of Zn(II) porphyrinogens are presented. The fully reduced member of the series, [LZn](2-), was prepared in two steps from pyrrole and acetone. The compound undergoes consecutive two-electron, ligand-based, oxidations at +0.21 and +0.63 V vs NHE to yield [L(Delta)Zn] and [L(Delta Delta)Zn](2+), which also have been independently prepared by chemical means. X-ray diffraction analysis of the redox intermediary, [L(Delta)Zn], shows that the partly oxidized macrocycle is composed of a methylene-bridged dipyrrole that is doubly strapped to a two-electron oxidized dipyrrole bridged by a cyclopropane ring (L(Delta)). The localization of two hole equivalents on the oxidized side of the porphyrinogen framework is consistent with a two-electron mixed valency formulation for the [L(Delta)Zn] species. Electronic structure calculations and electronic spectroscopy support this formalism. Density functional theory computations identify the HOMO to be localized on the reduced half of the macrocycle and the LUMO to be localized on its oxidized half. As implicated by the energy level diagram, the lowest energy transition in the absorption spectrum of [L(Delta)Zn] exhibits charge-transfer character. Taken together, these results establish the viability of using a ligand framework as a two- and four-electron/hole reservoir in the design of multielectron redox schemes. 相似文献
77.
On Complex Fluorides of Divalent Palladium For the first time single crystals of the new compounds RbPdPdF5, KPdPdF5, and K2CsPdF5 have been obtained. Orange brown RbPdPdF5 crystallizes orthorhombic, space group Imma–D2h28 (No. 74) with a = 633.6(1) pm, b = 765.5.(1) pm, c = 1067.5(1) pm and Z = 4 and is isotypic with CsPdPdF5 [1]. Structure related KPdPdF5 (also orange brown) crystallizes orthorhombic too, but in space group Pnma–D2h16 (No. 62) with a 614.12(9) pm, b = 748.7(1) pm, c = 1065.0(2) pm and Z = 4. K2CsPdF5, light yellow, crystallizes tetragonal with a = 736.3(1) pm, c = 628.0(1) pm, Z = 2, and is isotypic with Rb2CsPdF5 (space group P4/mbm? D4h5 Nr. 127), an ordered structure variant of the Rb3PdF5-Type [1]. 相似文献
78.
Frank Bachmann Joachim Reimer Marcus Ruppenstein Joachim Thiem 《Macromolecular rapid communications》1998,19(1):21-26
Starting from 1,4:3,6-dianhydrosorbitol (DAS, 1 ), a five step monomer synthesis led to 2-deoxy-1,4:3,6-dianhydro-2-isocyanato-L -iditol, 9 , which by catalytic polyaddition gave polyurethane 13 . A second route required the synthesis of 2-azido-5-O-chloroformyl-2-deoxy-1,4:3,6-dianhydro-L -iditol, 11 . During catalytic hydrogenation, the intermediate 2-aminochloroformyl derivative 12 underwent spontaneous polycondensation. The structure of 13 was characterized by 1H and 13C NMR, IR spectroscopy and elemental analyses. Gel-permeation chromatography showed M̄n = 8 000–12 000 corresponding to a degree of polymerisation up to 70. Differential scanning calorimetry revealed the polyadduct to be semicrystalline with a glass transition at Tg = 118°C and a melting range of 190–200°C. The polycondensation product was found to be crystalline with a melting range of 140–180°C. 相似文献
79.
To study the stereoselectivity of enzymatic cleavage of poly(3-hydroxybutyrates) (PHB) in a well-defined system (purified depolymerase and monodisperse substrate of specific relative configuration), linear and cyclic oligomers of HB (OHBs) containing (R)- and (S)-3-hydroxybutanoate residues were synthesized. The starting material (R)-HB was prepared from natural sPHB, and (S)-HB by enantioselective reduction of 3-oxobutanoate with yeast or with H2/Noyori-Taber catalyst (Scheme 2). The HB building blocks were then protected (O-benzyl/tert-butyl ester; Scheme 3) and coupled to give dimers 3 , 4 , tetramers 5 – 9 , and octamers 10 – 18 ; for analytical comparison, a 3mer, 5mer, 6mer, and 7mer ( 19 – 22 ) were also prepared. Two of the tetramers were subjected to macrolactonization conditions (Yamaguchi) to give the cyclic tetramers 23 and 25 and octamers 24 and 26 . All new compounds were fully characterized (m.p., [α]D, CD, IR, 1H- and 13C-NMR, MS, elemental analysis). Single-crystal X-ray structure analyses were performed with oligolides 24 and 25 (Figs. 2 and 4), and the structures, as well as the crystal packing, were compared with those of analogs containing only (R)-HB units or consisting of 3-amino- instead of 3-hydroxybutanoic-acid moieties. 相似文献
80.
Development of a dipstick immunoassay for quantitative determination of 2,4-dichlorophenoxyacetic acid in water, fruit and urine samples 总被引:1,自引:0,他引:1
N. V. Cuong T. T. Bachmann R. D. Schmid 《Fresenius' Journal of Analytical Chemistry》1999,364(6):584-589
A sensitive dipstick assay for 2,4-dichlorophenoxyacetic acid (2,4-D) detection was developed. The assay was based on the
competitive reaction of 2,4-D and enzyme tracer with monoclonal antibodies immobilised on an Ultrabind? membrane. The binding of enzyme tracer on the test strip was determined by a simple, portable reflectometer as remission
at 657 nm. Using this technique, 2,4-D could be detected in a concentration range of 0.5 μg/L to 100 μg/L. The center point
of the 2,4-D test was found at a concentration of 6 μg/L. Cross-reactivity with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)
as determined by this dipstick assay was 2.5% and 3% by standard ELISA technique using microtiter plates. The assay was applied
in the detection of 2,4-D in real water samples, and sensitivity was comparable to spiked water samples. If combined with
an effective extraction procedure that results in recovery rates of 90%, the dipstick assay can be used to monitor human exposure
to 2,4-D from contamination in water, from oranges and in testing urine samples.
Received: 2 September 1998 / Revised: 29 January 1999 / Accepted: 31 January 1999 相似文献