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51.
P. V. Shibaev Corresponding author V. Kopp A. Genack E. Hanelt 《Liquid crystals》2013,40(12):1391-1400
Glass-forming cholesteric liquid crystals were studied as promising dye-doped lasing materials at different pumping energies and temperatures. Cholesteric samples doped with laser dye pyrromethane 597 were pumped by Nd:YAG laser. Lasing was found to depend strongly on the vitrification rate of cholesteric samples, their temperature and multidomain structure. The lasing threshold and intensity as a function of thickness of cholesteric resonator are determined by two competing factors: narrowing of the band edge modes and increasing disorder. 相似文献
52.
Soňa Lisníková Josef Kopp Vlastimil Vrba Petr Novák 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(34):e202104331
This work explores the benefits of single-phase oxalate precursors for the preparation of spinel ferrites by thermal decomposition. A direct comparison between the genuine oxalate solid solution and the physical mixture of simple oxalates is presented using the case study of cobalt ferrite preparation. The mixing of metal cations within a single oxalate structure could be verified prior to its thermal decomposition by several non-destructive experimental techniques, namely Mössbauer spectroscopy, X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy. In situ XRD experiments were conducted to compare the decomposition processes of the solid solution and the physical mixture. Additionally, the decomposition products of the FeCo oxalate solid solution were studied ex situ by means of N2 adsorption, Mössbauer spectroscopy and XRD. The results obtained for different reaction temperatures demonstrate the possibilities to easily control the physical properties of the prepared oxides. 相似文献
53.
J. Kohoutek O. Adamovský M. Oravec Z. Šimek M. Palíková R. Kopp L. Bláha 《Analytical and bioanalytical chemistry》2010,398(3):1231-1237
Microcystins are cyclic peptide toxins with hepatotoxic and tumour-promoting properties which are produced in high quantities
in freshwater cyanobacterial water blooms, and several studies have reported microcystin accumulation in fish with possible
food transfer to humans. In this study, we provide the first comparison of liquid chromatography with single mass-spectrometric
and with tandem mass-spectrometric detection for analyses of microcystins in complex fish tissue samples. Use of traditional
single mass spectrometry (i.e. monitoring of ions with m/z 519.5 for microcystin-RR and m/z 995.5 for microcystin-LR) was found to provide false-positive responses, thus overestimating the concentrations of microcystins
in the tissue samples. More selective tandem mass spectrometry seems to provide more reliable results. The concentrations
of microcystins detected by tandem mass spectrometry in fish from controlled-exposure experiments were more than 50% lower
in comparison with concentrations obtained by single mass spectrometry. Extensive analyses of edible fish parts—muscles (148
fish specimens from eight different species from five natural reservoirs with dense cyanobacterial water blooms)—showed negligible
microcystin concentrations (all analyses below the limit of detection; limit of detection of 1.2–5.4 ng/g fresh weight for
microcystin-RR, microcystin-YR and microcystin-LR in multiple reaction monitoring mode). Our findings have practical consequences
for critical re-evaluation of the health risks of microcystins accumulated in fish. 相似文献
54.
Plastic nuclear track detectors were used to measure the contribution of High charge Z and energy E (HZE) particles to the radiation exposure of manned space missions. Results from numerous space missions in the orbit planned for the International Space Station are compared. The measurements cover the declining phase of the last solar cycle during the past 7 years and various shielding conditions inside the US Space Shuttle and the Russian MIR-station. 相似文献
55.
The reaction of various iodophenols with MeMgCl in presence of LiCl followed by the addition of i-PrMgCl provides the corresponding magnesiated magnesium phenolates as THF soluble reagents; this approach can be extended to heterocyclic compounds bearing a hydroxy group like pyridines and quinolines. 相似文献
56.
Sébastien Gottis Cyril Kopp Emmanuel Allard Robert Deschenaux 《Helvetica chimica acta》2007,90(5):957-962
A liquid‐crystalline mixed [5 : 1]hexa‐adduct of [60]fullerene was synthesized by addition of two different malonate derivatives onto C60. The hexa‐adduct derivative 2 was prepared by a stepwise synthetic procedure (fullerene→mono‐adduct of C60→hexa‐adduct of C60). Cyanobiphenyl and octyloxybiphenyl derivatives were selected as mesogens. The malonate derivatives showed either a monotropic nematic phase or a monotropic smectic A phase, and the hexa‐adduct derivative gave rise to an enantiotropic smectic A phase. 相似文献
57.
The small angle X-ray scattering of molecular fluids contains information on particular aspects of their orientational order. Examples are given for the case of the isotropic, nematic and cholesteric phases of mesogenic molecules. It is shown that the distribution of the molecular centers relative to the direction defined by the molecular long axes can be analysed by means of small angle X-ray scattering. An approximate expression for the circulation correlation function is given. 相似文献
58.
Knochel P Dohle W Gommermann N Kneisel FF Kopp F Korn T Sapountzis I Vu VA 《Angewandte Chemie (International ed. in English)》2003,42(36):4302-4320
Organomagnesium reagents occupy a central position in synthetic organic and organometallic chemistry. Recently, the halogen-magnesium exchange has considerably extended the range of functionalized Grignard reagents available for synthetic purposes. Functional groups such as esters, nitriles, iodides, imines, or even nitro groups can be present in a wide range of aromatic and heterocyclic organomagnesium reagents. Also various highly functionalized alkenyl magnesium species can be prepared. These recent developments as well as new applications of organomagnesium reagents in cross-coupling reactions and amination reactions will be covered in this Review. 相似文献
59.
CsF as Fluoridation Agent for Organometal Compounds of the Elements of Group 13 Cs[i-Bu3AlF] ( 1 ) can be obtained by the reaction of Al(i-Bu)3 with CsF in toluene. In a halide exchange reaction of Mes*GaCl2 with CsF in acetonitrile not the desired product Mes*GaF2 (Mes* = 2,4,6-(t-Bu)3C6H2) was isolated but the metalate Cs[Mes*GaF3] ( 2 ), formed by the addition of a third unit CsF. A ligand distribution was observed by the treatment of [(PhCH2)2GaTe(t-Bu)]2 with CsF in THF. The triorganofluoro gallate [Cs{(PhCH2)3GaF}]2 ( 3 ) was isolated. The triorganofluoro gallate Cs[Me3GaF] does not react with dry O2 in THF. With S8 in THF a reaction was achieved and the diorganodifluoro gallate [Cs(THF)0,5(Me2GaF2)] ( 4 ) could be characterized. The treatment of MesInBr2 with CsF in acetonitrile gives as only identified compound the indate Cs[MesInBr3] ( 5 ). 相似文献
60.
Perfluoromethyl Element Ligands. XLIII [1] Novel Synthetic Routes to Binuclear Complexes of the Type MM′(CO)8ER2X (M/M′ = Mn/Mn, Mn/Re, Re/Re; E = P, As; R = CF3, Me; X = Hal, ) Mn(CO)5I reacts with compounds of the type (CF3)2EAsMe2 (E = P, As) as with the symmetric E2(CF3)4 ligands in the first step with cleavage of the E‐As bond to yield the pro ducts (CO)5MnE(CF3)2 and Me2AsI. Reaction of the mononuclear complexes with excess of Mn(CO)5I leads in good yields to the known dinuclear compounds (CO)4Mn[E(CF3)2, I]Mn(CO)4 and CO. Me2AsI, the second product of the EAs cleavage, attacks the starting compound Mn(CO)5I giving cis‐Mn(CO)4I(AsMe2I) and CO. This result encouraged us to thoroughly investigate the preparation of cis‐M(CO)4X(EMe2Y) complexes with most of the possible combinations of M = Mn, Re; E = P, As and X, Y = Cl, Br, I. An alternative route to these compounds was opened by the cleavage of the dinuclear manganese or rhenium halides M2(CO)8X2 with the halophosphanes or ‐arsanes Me2EY. This route was found to be especially advantageous for the preparation of the rheniumcarbonyl precursors, since milder conditions than for the CO‐substitution in Re(CO)5X compounds are sufficient for the halogen‐bridged dinuclear complexes. Cis‐M(CO)4X(EMe2Y) complexes were used as precursors for the synthesis of novel homo‐ and heterodinuclear complexes of the type (CO)4M(EMe2, X)M′(CO)4 by reacting the EY function with transition metal carbonylates Kat[M′(CO)5] (Kat = Na, Bu4N, Ph4As). Thus the preparation of a wide range of complexes was possible, which before had been successfully prepared by the direct reaction of Mn2(CO)10 with Me2EX only in few cases, e. g. with Me2AsI. Spectroscopic investigations, using the CO valence frequencies and the 1H‐NMR data of the ligands EMe2Y or of the Me2E bridges, were applied to study the influence of the variables M, M′, E, X, Y and Kat on the reactivity of the mononuclear complexes and the bonding situation in both the mono‐ and the dinuclear systems. The new compounds were characterized by spectroscopic (IR, NMR, MS) and analytic methods (C, H). 相似文献