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31.
32.
The standard deviation of sample mass was quantitatively related to the number of particles in the sample, individual particle masses and the fractions of the numbers of different types of particles in the mixture. The theory was verified by sampling of cereal grain mixtures with a spinning riffler and Monte Carlo computer simulation. The theory is applicable to random sampling of well-mixed populations containing two or more types of particles. 相似文献
33.
34.
Libor Mat
jka Oksana Dukh Ji
í Brus William J. Simonsick Jr Bohumil Meissner 《Journal of Non》2000,270(1-3):34-47
The sol–gel polymerization of 3-glycidyloxypropyltrimethoxysilane (GTMS) was followed by size exclusion chromatography and 29Si NMR. Extensive non-random cyclization under formation of polyhedral cycles – cubic cages – predominates at the beginning of the reaction. Structure growth of polysilsesquioxanes proceeds by combining the incompletely condensed cage frameworks. The extent of the cage formation increases with dilution and the amount of water and depends appreciably on a catalyst. The cage fraction was isolated from a reaction mixture using preparative size exclusion chromatography and identified by 29Si NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). High content of polyhedral cages prevents gelation of the trifunctional GTMS monomer. Reaction of pendant epoxy groups is much slower; however, at a late reaction stage the epoxy hydrolysis can be significant. Under some conditions, like base catalysis, polysilsesquioxane clusters are crosslinked by intermolecular condensation of SiOH with hydrolyzed epoxy groups and the system gels. The cage with epoxide functionalities may serve as a rigid precursor of crosslinking. 相似文献
35.
Robert Masirek Ewelina Szkudlarek Ewa Piorkowska Miroslav Slouf Jaroslav Kratochvil Josef Baldrian 《Journal of Polymer Science.Polymer Physics》2010,48(4):469-478
Nucleation of isotactic polypropylene (iPP) crystallization by gold (Au) nanoparticles was studied. Regardless of their size, 4.3, 8.8, 28.3, and 84.5 nm, all particles were able to nucleate spherulites when deposited on the iPP surface. However, when added and melt‐mixed with iPP, only the smallest particles affected significantly the iPP bulk crystallization. Au nanoparticles larger than 4.3 nm, at the concentration of 0.001 wt %, did not influence the crystallization of iPP. Contrary to this, 0.001 and 0.005 wt % of Au nanoparticles having the size of 4.3 nm increased crystallization temperature of the iPP by 7–8 °C and decreased markedly the sizes of polycrystalline aggregates. Aggregation of Au nanoparticles in the polymer matrix was evidenced by electron microscopy and contributed to their decreased effectiveness in the nucleation of iPP crystallization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 469–478, 2010 相似文献
36.
Vratislav Langer Bohumil Steiner Miroslav Ko 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(4):o151-o154
In the title compounds, C12H20O6, (I), and C9H16O6, (II), the five‐membered furanose ring adopts a 4T3 conformation and the five‐membered 1,3‐dioxolane ring adopts an E3 conformation. The six‐membered 1,3‐dioxane ring in (I) adopts an almost ideal OC3 conformation. The hydrogen‐bonding patterns for these compounds differ substantially: (I) features just one intramolecular O—H...O hydrogen bond [O...O = 2.933 (3) Å], whereas (II) exhibits, apart from the corresponding intramolecular O—H...O hydrogen bond [O...O = 2.7638 (13) Å], two intermolecular bonds of this type [O...O = 2.7708 (13) and 2.7730 (12) Å]. This study illustrates both the similarity between the conformations of furanose, 1,3‐dioxolane and 1,3‐dioxane rings in analogous isopropylidene‐substituted carbohydrate structures and the only negligible influence of the presence of a 1,3‐dioxane ring on the conformations of furanose and 1,3‐dioxolane rings. In addition, in comparison with reported analogs, replacement of the –CH2OH group at the C1‐furanose position by another group can considerably affect the conformation of the 1,3‐dioxolane ring. 相似文献
37.
A true direct solid sampling electrothermal atomic absorption spectrometry method with Zeeman-effect background correction (Analytik Jena ZEEnit 60 AAS) was developed for the determination of As, Cd, Hg, Pb, Sb and Zn in powdered titanium dioxide of pharmaceutical, food and cosmetics grade. The interaction of the titanium matrix and graphite surface of the sample carrier boat in a transversely heated graphite tube atomizer was investigated. Conversion of titanium dioxide to interfering TiO2–TiC-liquid phase, running out the sampling boat, was observed at temperatures above 2000 °C. The temperature program was optimized accordingly for these volatile analytes in atomization and cleaning steps in order to prevent this interference and to prolong significantly the analytical lifetime of the boat to more than one thousand runs. For all elements, calibration by aqueous standard addition method, by wet-chemically analyzed samples with different content of analytes and/or by dosing one sample in different amounts, were proved as adequate quantification procedures. Linear dynamic calibration working ranges can be considerably expanded up to two orders of magnitude within one measurement run by applying three-field dynamic mode of the Zeeman background correction system. The results obtained by true direct solid sampling technique are compared with those of other independent, mostly wet-chemical methods. Very low limits of detection (3σ criterion) of true solid sampling technique of 21, 0.27, 24, 3.9, 6.3 and 0.9 ng g− 1 were achieved for As, Cd, Hg, Pb, Sb and Zn, respectively. 相似文献
38.
Holub J Grüner B Perekalin DS Golovanov DG Lyssenko KA Petrovskii PV Kudinov AR Stíbr B 《Inorganic chemistry》2005,44(6):1655-1659
A room-temperature reaction between the [7-tBuNH-nido-7,8,9-C3B8H10]- anion (1a) and [Cp*RuCl]4 leads to the ruthenatricarbollide [1-Cp*-12-tBuNH-1,2,4,12-RuC3B8H10] (2) (yield 85%). Analogously, the room-temperature photochemical reaction of 1a with [CpFe(C6H6)]PF6 gives the previously reported iron complex [1-Cp-12-tBuNH-1,2,4,12-FeC3B8H10] (3) (yield 82%). Both reactions are associated with extensive polyhedral rearrangement, which occurs under very mild conditions and brings the carbon atoms to positions of maximum separation within the framework. Compounds 2 and 3 were also surprisingly obtained via complexation of the isomeric [8-tBuNH-nido-7,8,9-C3B8H10]- (1b) anion. Complex 2 rearranges further to [1-Cp*-10-tBuNH-1,2,4,10-RuC3B8H10] (4) upon refluxing in xylene (145 degrees C). Density functional theory calculations at the B3LYP/SDD level were used to estimate relative stabilities of these metallacarborane isomers. Compounds 2 and 4, along with the 11-vertex closo compounds [1-Cp*-1,2,3,10-RuC3B7H10] (5) and [1-Cp*-10-tBuNH-1,2,3,10-RuC3B7H9] (6), were also isolated from the reaction between [Cp*RuCl2]2 and 1a in boiling xylene. The structure of 2 was established by an X-ray diffraction study, and the constitution of all compounds was determined unambiguously by multinuclear NMR spectroscopy, mass spectrometry, and elemental analyses. 相似文献
39.
The polarography of B(12) coenzyme (5,6-dimethylbenzimidazolylcobamide, DBC coenzyme) has been investigated at the dropping mercury electrode. Exposure of solutions of the coenzyme to light and then to oxygen give polarograms comparable to those of B(12r) and hydroxocobalamin (B(12a)) respectively. At pH 11.6 the coenzyme gives two reduction waves, at -1.43 and -1.62 V vs. the S.C.E.; in less basic solutions the two waves merge to give one multielectron wave. 相似文献
40.
Pervinder K. Dosangh Jonathan Bould Michael G. S. Londesborough Tom
Jelínek Mark Thornton-Pett Bohumil
tíbr John D. Kennedy 《Journal of organometallic chemistry》2003,680(1-2):312-322
Thermolysis of [arachno-4-SB8H12] (1) in boiling cyclohexane gives two isomers 2 and 3 of 18-vertex [S2B16H16], together with known 12-vertex [closo-1-SB11H11] (4) and known 11-vertex [nido-7-SB10H12] (5). Compounds 2 and 3 are characterised by single-crystal X-ray diffraction analyses and single- and double-resonance 11B- and 1H-NMR spectroscopy. The [n-S2B16H16] isomer 2 takes the form of nido ten-vertex: nido ten-vertex [anti-B18H22] with the 9 and 9′ positions occupied by S vertices, whereas the [iso-S2B16H16] isomer 3 takes the form of a nido 11-vertex {SB10} subcluster fused via a common two-boron edge to a nido-type {B8} subcluster that is additionally linked exo to the {SB10} subcluster by a bridging S atom that is held endo to the {B8} unit. Isomer 2 is readily deprotonated and its monoanion 6 is characterised by NMR spectroscopy and by a single-crystal X-ray diffraction analysis of its [tmndH]+[n-S2B16H15] salt 6b; deprotonation has occurred from an open-face B---H---B bridging site. 相似文献