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11.
Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10?2M and 10?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium. 相似文献
12.
The preconcentration and separation of palladium and iridium from base metals is studied with cellulose (Cellex T) and styrene-divinylbenzene (Varion AT 400) anion exchangers. In spite of lower capacity of Cellex T to chloride complexes of Pd and Ir, it allowed to get a higher preconcentration factor. Yields of 92–99% are achieved for Pd and 96–97% for Ir from the solutions containing great excess of base and heavy metals. Graphite furnace atomic absorption spectrometry is used for the final measurements. The procedure has been applied to the determination of palladium in natural samples. 相似文献
13.
Krystyna Cieśla H. Rahier Grażyna Zakrzewska-Trznadel 《Journal of Thermal Analysis and Calorimetry》2004,77(1):279-293
One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated
cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment
and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation
processes. A large amount of non-freezable strongly bounded water was also detected.
Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction
occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module
at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected
during the first, the second and the third heating.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Andrzej Olczak Marek L. Gwka Jolanta Goka Magorzata Szczesio Joanna Bojarska Krystyna Kozowska Henryk Foks Czesawa Orlewska 《Journal of Molecular Structure》2007,830(1-3):171-175
Crystal structures of two title compounds and several their relatives known earlier reveal conservative and characteristic features, which may be related to their tuberculostatic activity. The molecules are predominantly planar due to conjugation through five successive bonds in the zwitterionic fragment S−–C(sp2)–N–NH+–C(sp2)–NH2 and intramolecular hydrogen bonds, which prevent rotation of the adjacent pyrazine (or pyridine) ring. It has been suggested that in spatial sense such planar molecules resemble acridines intercalating with nucleic acids and that similar process may be responsible for tuberculostatic activity of the title pyrazine-2-carboxamide-N′-carbonothioyl-hydrazones. 相似文献
15.
An HPLC procedure for determination of phenoxyalkanoic acid herbicides in water samples is proposed. The analytical column Phenomenex C18(2) Luna 5 µm and UV detection at 225 nm were applied. Baseline resolution was achieved in isocratic mode with a mobile phase consisting of acetonitrile/acetic acid (40/60, v/v), adjusted to pH 2.5. SPE sorbents – C18 BondElut, phenyl-silica, LiChrolut SAX and polymeric sorbents – were compared for isolation and preconcentration of 6 phenoxyalkanoic acid herbicides. Higher (above 95%) and more reproducible recoveries were obtained with polymeric and phenyl-silica sorbents using pure methanol for elution. The method was tested for river water samples with the limit of detection in the range of 2–3 µg L−1 (for 50 mL sample) and a reproducibility of 5% RSD. 相似文献
16.
Gustav Zigeuner W.-Bernd Lintschinger Alfred Fuchsgruber Krystyna Kollmann 《Monatshefte für Chemie / Chemical Monthly》1976,107(1):171-181
2- and 3-aminoalcohols, o-aminobenzylalcohol, o-hydroxybenzylamine and o-amino(thio)-phenol react with 4-isothiocyanato-4-methyl-2-pentanone (1) to yield derivatives of condensed heterocycles (oxazolopyrimidines7, pyrimidooxazine8, pyrimidobenzoxazines9, 10, pyrimidobenzoxazole11 a and pyrimidobenzothiazole11 c respectively). Ethylenediamine or 1,3-diaminopropane react with1 to yield either imidazo-pyrimidine13 and pyrimidopyrimidine14 respectively or the 1,2-ethylene- and trimethylenebisdihydro-2(1H)-pyrimidinethione15 a, b respectively, according to the molar ratio of the reactants. o-Phenylenediamine gives pyrimidobenzimidazole11 d. 11a undergoes ring cleavage in boiling dimethylformamide followed by methylpyrimidine-pyridine rearrangement to dihydrohydroxyphenylamino-2(1H)-pyridinethione12, while15 a is converted into the bis-4-(ethanediimino)-pyridinthione16. 相似文献
17.
Carbon nanotubes and graphitized carbon are investigated as adsorbents for solid phase extraction of dicamba and 2,4,5-T,
two phenoxyalkanoic acid herbicides. These adsorbents have much greater adsorption capability than that of C18 bonded silica, which was also tested for comparison studies. The adsorption capacity increases remarkably at lower pH of
the sample solution. Freundlich isotherms were applied to analyze the data. Our studies suggest that carbon nanotubes have
great potential applications in environmental analysis. 相似文献
18.
Krystyna Bogdanowicz-Szwed Regina Gil 《Monatshefte für Chemie / Chemical Monthly》2004,35(12):1415-1425
A convenient method is described for the synthesis of functionalized spiro[cycloalkanono-2,3-thiophenes] by treatment of cyclic 3-oxoacid thioanilides with -nitrostyrenes. Reaction of the obtained products with acetic anhydride yielded the corresponding oxime acetates. 相似文献
19.
Krystyna B. Lesiak Bogdan Uznanski Paul F. Torrence 《Applied biochemistry and biotechnology》1997,67(1-2):33-44
To increase the accessibility of 8-bromo-2′,5′-oligoadenylates, we developed a synthesis of 2′-5′-linked oligoriboadenylates containing varying numbers of 8-bromoadenosine residues based on the use of a CPG-LCA solid support and the phosphoramidite approach. Although N6benzoyl protection was satisfactory for incorporation of nonmodified adenine residues into 2′,5′-oligonucleotides, the effective incorporation of 8-bromoadenine into such 2′,5′-linked oligomers required use of a non acyl protecting group. Amidine protection of the purine exocyclic amino function proved compatible with all aspects of the phophoramidite approach and with the hydroxyl protection groups employed. 相似文献
20.
James P. Kutney Peter Grice Krystyna Piotrowska Steven J. Rettig Jerzy Szykula James Trotter Loc Van Chu 《Helvetica chimica acta》1983,66(6):1820-1826
The thujone-derived enone 1 , upon base-catalyzed reaction with 2-methyl-6-vinylpyridine is converted to the pyridine analogue 5 (Scheme 1). Catalytic reduction of the latter to 6 generates two new centers of chirality which eventually become C(8) and C(14) in the ultimate synthetic steroid analogue 12 . An X-ray analysis of 6 establishes the structure and absolute configuration so as to determine its suitability in subsequent synthetic studies. The acetal derivative 7 , via Birch reduction, hydrolysis, and internal aldol cyclization, is converted into the cyclohexenone analogue 10 (Scheme 2). This ‘one-pot’ process affords an efficient conversion of the pyridine ring into a cyclohexenone system required for A-ring construction of the steroid skeleton. Finally, conversion of 10 , via the unsaturated diketone 11 , provides the chiral steroid analogue 12 . 相似文献