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91.
Shea SL Jelínek T Perera SD Stíbr B Thornton-Pett M Kennedy JD 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1521-1523
Addition of PMe2Ph to fused-cluster syn-[(eta5-C5Me5)IrB18H20] 1 to give [(eta5-C5Me5)HIrB18H19(PMe2Ph)] 3 entails a diminution in the degree of intimacy of the intercluster fusion, rather than retention of inter-subcluster binding intimacy and a nido-->arachno conversion of the character of either of the subclusters. Reaction with MeNC gives [(eta5-C5Me5)HIrB18H19[C(NHMe)2]] 4 which has a similar structure, but with the ligand now being the carbene [:C(NHMe)2], resulting from a reductive assembly reaction involving two MeNC residues and the loss of a carbon atom. 相似文献
92.
Bohumil Docekal José A. C. Broekaert Thomas Graule Peter Tschöpel Günther Tölg 《Fresenius' Journal of Analytical Chemistry》1992,342(1-2):113-117
Summary The analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO3, HF and fuming H2SO4 in an autoclave at 240°C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1–1 g/g; those for Al, B, Fe, Ni, Ti and V are at the 1–5 g/g level. With a Babingtontype nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e.g. for Fe, are communicated.Part of this paper was presented at XI. International Symposium of Microtechniques, Wiesbaden, FRG, Aug. 28th–Sept. 1st 1989 相似文献
93.
[reaction: see text]. Diastereoselective syntheses of the endo- and exo-spirotetronates 1 and 2, corresponding to the galacto and agalacto fragments of quartromicins A3 and D3, are described. The key step of these syntheses are highly enantio- and diastereoselective Lewis acid catalyzed Diels-Alder reactions of the 1,1,3,4-tetrasubstituted diene 3. 相似文献
94.
Trace amounts (10-5–10-6% ) of Ca, Cr, Cu, Fe, Na and Pb in aluminium oxide can be determined by graphite-furnace a.a.s. with injection of stirred sample suspensions into the tube. Calibration is possible either with Al2O3 standards for peak height and peak area measurements, or with standard solutions containing no aluminium for peak area measurements (except for copper). The analytical signals do not depend on the quantity of applied sample (0.02–1 mg Al2O3). Relative standard deviations are 2–6%. 相似文献
95.
Bohumil tbr Francesc Teixidor Clara Vias Ji Fusek 《Journal of organometallic chemistry》1998,550(1-2)
An alternative route to the parent nido-5,6-C2B8H12 dicarbaborane is reported together with a convenient synthesis of its carbon-substituted derivatives. The method is based on reactions between 4-(Me2S)-arachno-B9H13 and alkynes R1R2C2 (where R1R2=H,H; Me, Me; Ph,H, and Ph,Ph) in toluene at reflux. The characteristic reaction mode is a dicarbon insertion into the 9-vertex arachno cluster to produce a series of the 5,6-R1R2-nido-5,6-C2B8H10 species combined with concomitant elimination of one {BH} vertex. The products were characterised by high-field 1H and 11B NMR spectroscopy and mass spectrometry associated with [11B–11B]-COSY and 1H{11B(selective)} measurements that permitted complete assignments of all resonances to individual cluster {BH} units. 相似文献
96.
Bohumil Proksa Stanislava Uhrínová Jana Adamcová Ján Fuska 《Monatshefte für Chemie / Chemical Monthly》1992,123(3):251-256
Summary Hydrogenation of vermistatin, a metabolite ofPenicillium vermiculatum, affordedcis- andtrans-3-(2-carboxy-4,6-dimethoxybenzyl)-6-propyltetrahydro-4H-pyran-4-one and 4,6-dimethoxy-3-(4-propylcyclopentanon-2-yl)phthalide. The latter compound was found to be the strongest inhibitor of RNA synthesis in P 388 leukemia cells of all compounds tested.
Hydrierung von Vermistatin
Zusammenfassung Bei der Hydrierung von Vermistatin, einem neuen sekundären Metabolit ausPenicillium vermiculatum, wurdencis- undtrans 3-(2-Carboxy-4,6-dimethoxybenzyl)-6-propyltetrahydro-4-pyran-4-on und 4,6-dimethoxy-3-(4-propylcyclopentanon-2-yl)phthalid erhalten und spektroskopisch charakterisiert. Die letztgenannte Verbindung zeigte von allen getesteten Verbindungen die stärkste Hemmwirkung auf die RNA Synthese in P 388 Leukämiezellen.相似文献
97.
Macías R Bould J Holub J Stíbr B Kennedy JD 《Dalton transactions (Cambridge, England : 2003)》2008,(35):4776-4783
Reaction of the [arachno-4-NB(8)H(12)](-) anion with [RhCl(2)(eta(5)-C(5)Me(5))](2) in CH(2)Cl(2) at room temperature affords a mixture of red '6,9' isomer [9-(eta(5)-C(5)Me(5))-nido-6,9-NRhB(8)H(11)] () and its yellow '6,8' isomer, [8-(eta(5)-C(5)Me(5))-nido-6,8-NRhB(8)H(11)] (). Under the same conditions, reactions of with [IrCl(2)(eta(5)-C(5)Me(5))](2) and [RuCl(2)(eta(6)-MeC(6)H(4)-4-(iso)Pr)](2) give the '6,8' isomers, yellow [8-(eta(5)-C(5)Me(5))-nido-6,8-NIrB(8)H(11)] () and red [8-(eta(6)-MeC(6)H(4)-4-(iso)Pr)-nido-6,8-NRuB(8)H(11)] (), respectively. In contrast, [IrCl(PPh(3))(3)] yields orange [9,9-(PPh(3))(2)-9-H-nido-6,9-NIrB(8)H(11)] (), which exhibits the '6,9' configuration. Compound isomerizes quantitatively in solution to give . At high temperatures, compound gives the yellow '6,8' species, [8,8-(PPh(3))(2)-8-H-nido-6,8-NIrB(8)H(11)] (), in low yields. Possible mechanisms for the unprecedented 6,9 --> 6,8 isomerization are discussed. 相似文献
98.
Kovaríková V Docekalová H Docekal B Podborská M 《Analytical and bioanalytical chemistry》2007,389(7-8):2303-2311
The diffusive gradients in thin film technique (DGT) was used for characterization of South Moravian arable soils (sampling
sites Zlín, Tuřany, and Chrlice) amended by sewage sludge in the 1980s. Two types of polyacrylamide diffusive gel with different
pore size (APA gels—cross-linked with agarose and RG gels—cross-linked with bis-acrylamide) were employed. The (bio)available
parts of Cd, Cu, and Ni and the proportions of inorganically and organically complexed species of these metals were assessed.
The degree of metal resupply from the soil solid phase to the soil solution was also determined. Metal concentrations obtained
by the DGT technique were lower by almost 4 to 5 orders of magnitude in comparison with those obtained by extraction with
aqua regia. DGT concentrations of metals were also lower by approximately 1 to 2 orders of magnitude in comparison with those
obtained by extraction with sodium nitrate (commonly used for assessment of the (bio)available part of metals). Results obtained
by DGT measurement were expected to be closer to the actual content of available metal species than results obtained by extraction
with sodium nitrate. Using RG gels together with APA gels provided resolution of inorganically and organically complexed metal
species and their proportional representation. Inorganic metal species (particles smaller than 1 nm) formed a predominant
part of assessed metal content in all studied soil samples and horizons. However, there was the exception of the cadmium content
in the middle profile of Chrlice sandy soil sample. Ratio R values indicated that resupply of Cd, Cu, and Ni from the solid phase to the soil solution varied for individual soil samples
and individual depth profiles. Mobile and labile species of Cd, Cu, and Ni were much more closely related to upper rather
than deeper horizons. This observation correlates very well with the mechanical treatment and amendment of the studied soils. 相似文献
99.
Grüner B Holub J Plesek J Stíbr B Thornton-Pett M Kennedy JD 《Dalton transactions (Cambridge, England : 2003)》2007,(42):4859-4865
Oxidative coupling by FeCl(3) of the [nido-7,8-C(2)B(9)H(11)-9-Me](-) anion 1a with SMe(2) yields a mixture of four isomers of 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-X-Me, where X = 1, 2, 3 and 4 (compounds 2a, 2b, 2c and 2d respectively). On high dilution of the reaction mixture, the 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-10-Me 2e isomer is also isolated in a low yield. The isomers are separated by HPLC, and are identified and characterised by NMR spectroscopy and by single-crystal X-ray diffraction analyses of 2c and 2d. The formation of the products implies an unexpected cluster rearrangement, which is discussed in terms of dsd and vertex-flip reaction pathways. Two additional isomers, 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-5-Me 2f and 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-6-Me 2g occur when [nido-7,8-C(2)B(9)H(11)-5-Me](-) 1b is used as the starting substrate, in a reaction in which no cluster rerarrangement is observed. The corresponding bromide, [nido-7,8-C(2)B(9)H(11)-5-Br](-) 1c, behaves similarly, forming only 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-5-Br 2h and 9-(SMe(2))-nido-7,8-C(2)B(9)H(10)-6-Br 2i. 相似文献
100.
Jelínek T Císarová I Stíbr B Kennedy JD 《Dalton transactions (Cambridge, England : 2003)》2007,(42):4766-4768
[9-((ter)BuNH(2))-(anti)-9-CB(18)H(20)], in 36% yield from anti-B(18)H(22), sodium naphthalene and (ter)BuNC, constitutes the first example of a clean cluster carbon-addition Aufbau to form a macropolyhedral carbaborane. 相似文献