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141.
A sequence-ordered, periodic copolymer of ethylene, ethylene, and acrylic acid, poly (ethylene-per-ethylene-per-acrylic acid) (PEEA), with M
w=1.44×105 has been synthesized by alternating copolymerization of 1,3-butadiene and methyl acrylate, followed by hydrogenation and
hydrolysis. Aqueous solution and dissociation properties of the alkali-soluble PEEA were explored by potentiometric titration
and intrinsic viscosity at 25 °C. The pH values of PEEA were almost constant (pH = 6.48 ∼ 6.55) with an increasing degree
of dissociation (α) from 0.3 to 0.8 at C
s=50 mN NaCl. Correspondingly, the plots of negative logarithm of apparent dissociation constant (pK
a) against α showed a reversed S-shape curve over the whole α, indicating an extensive precipitation and subsequent tran-sition
from compact to coiled conformation. The intrinsic viscosity steeply increased with α above 0.4 up to 9.97 dl/g at α = 1.0.
Good agreement between the observed electrostatic potential and that calculated from the rod model with a smeared charge density
was observed in the region of α higher than 0.9. The dissociation and dissolution processes of PEEA with neutralization in
water were described.
Received: 14 April 1998 Accepted: 3 June 1998 相似文献
142.
143.
The separation of rare earth metals has been studied with a micro-column of 0.5 mm i.d.×75 mm length, packed with TSK LS-212
high-performance cation exchange resin 16 rare earth metals were separated within 38 min, using only 304 μl of 0.4M α-hydroxyisobutyric
acid solution adjusted to pH 3.1–6.0 with ammonia solution as gradient carrier solution. The gradient elution was successfully
performed by applying a new technique developed for microscale liquid chromatography.
Studies on micro-high-performance liquid chromatography, VII. 相似文献
144.
Kazuo Kamaike Kumi Hirose Yoshihiro Kayama Etsuko Kawashima 《Tetrahedron letters》2004,45(30):5803-5806
The phosphorodithioate octamer [(TpS2)7T] was efficiently synthesized using bis(2,6-dimethylphenyl) phosphorochloridate as a coupling agent by application of the H-phosphonothioate method, where oxidation was facilitated using elemental sulfur following completion of oligonucleoside H-phosphonothioates assembly, as with the standard H-phosphonate method. 相似文献
145.
p-Nitrobenzenediazonium tetrafluoroborate dissolved in dimethylsulfoxide (DMSO) at 50° forms p-nitrophenol in 88–90% yield. The phenolic oxygen atom originates exclusively from the oxygen atom of DMSO as demonstrated by the use of 18O-labelled DMSO. The first-order rate of dediazoniation is the same under N2 as it is in the presence of air. The rate is little influenced by the addition of benzene or iodobenzene. However, the products formed in the presence of these additives are significantly different. UV. spectra and the reactivity of diazonium salt solutions in DMSO when mixed with reagents in aqueous solution demonstrate that a relatively stable charge-transfer complex is formed between the diazonium ion and DMSO. The product analyses and the kinetic and spectral results of dediazoniation in DMSO with and without additives are consistent with a mechanism in which the rate-limiting step is the formation of a p-nitrophenyl radical from the charge-transfer complex. p-Nitrophenol and the products with benzene and iodobenzene are formed in subsequent fast competition steps. In the presence of small amounts of pyridine the dediazoniation is much faster and follows a different kinetic law. Pyridine effectively competes with DMSO in the reaction with diazonium ions. 相似文献
146.
The neutron activation determination of rare earth elements and heavy metals in river water has been studied with Chelex 100 resin as a preconcentration agent. The resin is applied directly as a support for irradiation and for radiochemical separation. The radioactive rare earth elements are recovered selectively and quantitatively from the irradiated resin by elution with hot 1 M sodium carbonate solution; radioactive heavy metals are recovered with 2 M nitric acid. Activities from each eluate are counted with a Ge(Li) detector connected to a multichannel analyzer; La, Sm, Eu, Dy, Mn, Cu and Zn can be determined. The recoveries were almost quantitative and the measurement of chemical yield was unnecessary. 相似文献
147.
Molar excess enthalpies for aqueous solutions of 3-methoxy-1-butanol (3-MB) and 1-methoxy-2-butanol (M-2B) have been measured at 298.15 K over the whole concentration range with a flow microcalorimeter. From the experimental data, we evaluated the enthalpic interaction parameter hxx and obtained the following order:h
xx
(3 MB) hxx(M-2B)This large difference in hxx. provided us some new factors which might have the influence on hydrophobic interaction: fundamental frame, hydroxyl group, and ether oxygen atom.
Zusammenfassung Mittels eines Fluß-Mikrokalorimeters wurden bei 298.15 K im gesamten Konzentrationsintervall die molaren Überschußenthalpien für wäßrige Lösungen aus 3-Methoxy-1-Butanol (3-MB) und 1-Methoxy-2-Butanol (M-2B) gemessen. Anhand der experimentellen Daten erstellten wir den Enthalpiepaar-Wechselwirkungsparameter hxx und erhielten folgende Reihenfolge: hxx(3-MB) hxx(M-2B)Diese große Abweichung bei hxx legte uns einige neue Faktoren nahe, die einen Einfluß auf die hydrophobe Wechselwirkung haben können: Grundgerüst, Hydroxylgruppen als auch Sauerstoffatome.相似文献
148.
Uranium shows relatively conservative behaviour in seawater because of the formation of stable carbonato complexes, whereas particulate uranium, involved in suspended particles with the particle size of more than 0.45 m, is a minor constituent. It was found that particulate uranium, with a range from 0.24 to 39 Bq·1–1, varies spatially and temporally. Its highest concentration occurs in the tropical region of the western North Pacific during the winter of 1983, corresponding to the 1983 El Nifio event. A leaching experiment revealed that major species of particulate uranium are labile organic complexes. Mass balance considerations suggest that particulate uranium in open ocean waters correlates with the presence of particulate organic matter (POM). A high peak of particulate uranium in 1983 may indicate that POM, i.e., primary productivity, increased in the western tropical Pacific during the El Niño event. 相似文献
149.
The intermediates in the reactions of 2,4-dinitro-(2) or 2,4,5-trinitro-1-naphthyl ethyl ether (11) with secondary amines have been studied. In the reaction of 2 with piperidine, the NMR spectrum of the reaction system indicated the coexistence of the three species-starting material, Meisenheimer complex, and substituted product. In the reaction of 11 with piperidine or N-methyl-n-butylamine, the the NMR spectra of the reaction system indicated the presence of a Meisenheimer complex, but did not indicate the formation of a substituted product. In addition, the spiro Meisenheimer complex (9) was prepared from 1-[N-methyl-(2′-hydroxy)ethylamino]-2,4,5-trinitronaphthalene (8) and sodium methoxide. 相似文献