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941.
A hydrophilic fluorescent derivatization reagent for fatty acids, 4-N-(4-N-aminoethyl)piperazino-7-nitro-2,1,3-benzoxadiazole (NBD-PZ-NH(2)), was designed and synthesized. NBD-PZ-NH(2) possesses not only a fluorophore and a reacting group but also a positive charge group and, thus, was hydrophilic and suitable for application to capillary electrophoresis. NBD-PZ-NH(2) reacted with fatty acids in the presence of triphenylphosphine (TPP) and 2,2'-dipyridyl disulfide (DPDS) at room temperature within 10 min. The derivatives were strongly fluoresced and were positively charged at pH below 3. The derivatives of C4-C20 fatty acids were separated within 10 min in 50% acetonitrile in water containing 30 mM ammonium acetate and 1.0 M acetic acid by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection. The detection limits attained were 6.5 nM (signal-to-noise ratio of 3). It is proposed that NBD-PZ-NH(2) is a prominent derivatization reagent for fatty acids which is suitable for CE-LIF application. 相似文献
942.
A simple and rapid technique for the simultaneous isolation and analysis of fifteen kinds of bile acid was developed using reversed-phase high-performance liquid chromatography with an automatic dual-precolumn switching system. The serum samples were directly injected onto a first precolumn (hydroxyapatite), which was flushed with 1 mM phosphate buffer. Serum proteins were strongly retained on the hydroxyapatite column, but bile acids were unretained. The bile acids were absorbed on a second precolumn (Serumout-25) and eluted onto the analytical column with solvent B (acetonitrile-methanol-30 mM ammonium acetate, 20:20:60, v/v/v). For the separation of each bile acid, the gradient elution technique was used (solvent A was acetonitrile-methanol-30 mM ammonium acetate, 30:30:40). After separation of the bile acids, NADH was produced by use of immobilized 3 alpha-hydroxysteroid dehydrogenase column and then determined fluorimetrically (gamma em = 460 nm, gamma ex = 350 nm). The recoveries of bile acids in serum generally approached 100%. 相似文献
943.
Trace amount of uranium in sea water was preconcentrated on Chelex 100 chelating resin. The resin was directly applied as
a support for irradiation.239U was selectively and quantitatively recovered from the irradiated resin by elution, using 1.0M sodium carbonate solution
as eluant. γ-Ray spectrum was measured with a Ge(Li) detector. 相似文献
944.
Mechanistic studies of a palladium-mediated decarboxylative olefination of arene carboxylic acids are presented, providing spectroscopic and, in two instances, crystallographic evidence for intermediates in a proposed stepwise process. Sequentially, the proposed pathway involves carboxyl exchange between palladium(II) bis(trifluoroacetate) and an arene carboxylic acid substrate, rate-determining decarboxylation to form an arylpalladium(II) trifluoroacetate intermediate (containing two trans-disposed S-bound dimethyl sulfoxide ligands in a crystallographically characterized form), then olefin insertion and beta-hydride elimination. Because of the unique mode of generation of the arylpalladium(II) trifluoroacetate intermediate, a species believed to be substantially electron-deficient relative to phosphine-containing arylpalladium(II) complexes previously studied, it has been possible to gain new insights into those steps that are common to the Heck reaction, namely, olefin insertion and beta-hydride elimination. The present results show that there are notable differences in reactivity between arylpalladium(II) intermediates generated by decarboxylative palladation and those produced in conventional Heck reactions. Specifically, we have found that more electron-rich alkenes react preferentially with an arylpalladium(II) trifluoroacetate intermediate formed by decarboxylative palladation, whereas an opposite trend is found in conventional Heck reactions. In addition, we have found that the aralkylpalladium(II) trifluoroacetate intermediates that are formed upon olefin insertion in the present study are stabilized with respect to beta-hydride elimination as compared to the corresponding phosphine-ligated aralkylpalladium(II) complexes. We have also crystallographically characterized an aralkylpalladium(II) trifluoroacetate intermediate derived from arylpalladium(II) insertion into norbornene, and this structure, too, contains an S-bound dimethyl sulfoxide ligand; the ipso-carbon of the transferred aryl group and trifluoroacetate function as the third and fourth ligands in the observed distorted square-planar palladium(II) complex. 相似文献
945.
Daisuke Uemura Katsuhiro Ueda Yoshimasa Hirata Hideo Naoki Takashi Iwashita 《Tetrahedron letters》1981,22(20):1909-1912
The structures of two degradation products of N-(p-bromobenzoyl) palytoxin were elucidated, and then the sequences of those fragments were determined. 相似文献
946.
Drying dissipative structural patterns of aqueous solutions of biological polyelectrolytes, sodium poly (α, L-glutamate; NaPGA) and poly (-L-lysine hydrobromide; PLL.HBr), were studied on a cover glass. Below the critical polymer concentration, m* (ca. 0.003 and ca. 0.01 monoM for NaPGA and PLL.HBr, respectively), the dried patterns shrank only around the center of
the initial solution area wetted on a cover glass. Above the m* values, on the other hand, the drying pattern extended throughout the initial solution area. The m* values agreed excellently with the critical polymer concentrations, where the surface tensions started to decrease sharply
as the polymer concentrations increased. The broad rings were always observed in the drying patterns of any solutions examined.
The spoke-like cracks appeared at the polymer concentrations above the m* values and only in the area of the broad rings. Microscopic structures such as cross-like, rod-like, and block-like patterns
formed irrespective of polymer concentrations. Especially, the city-road-like microscopic pattern was observed for PLL.HBr
solutions, which strongly supports the formation of crystal structures of PLL.HBr that remain in the whole processes of dryness.
These patterns were correlated deeply with the crystal-like orientation of the biological polyelectrolytes at the air–solution
interfaces. 相似文献
947.
Xanthene dyes such as eosin and tetraiodofluorescein form 1:2 ion associates with quaternary ammonium ions at pH 7-9; however, the development of color in the organic solvent is poor. When a quaternary ammonium salt is added in the extractable 1:2 associate formed between a xanthene dye and a cinchona-alkaloid in the neutral media, a mixed ternary ion associate (xanthene dye:cinchona-alkaloid:quaternary ammonium ion=1:1:1) is formed. Its extractability is enhanced due to the more bulky associate formation. The ion association caused by addition of cinchona-alkaloids is unique. Of the cinchona-alkaloids, quinidine and cinchonidine with tetraiodofluorescein show excellent effects on sensitivity and extractability. Eosin and tetraiodofluorescein are useful as ion association reagents in the ion associate formation. The apparent molar absorptivities are about 1×105 l mol−1 cm−1 and the calibration range for quaternary ammonium salt is from 2.5×10−7 to 1.5×10−6 M. The proposed method is applicable to the selective and sensitive determination of cetylpyridinium chloride, berberine chloride and benzethonium chloride in pharmaceuticals. 相似文献
948.
[structure: see text] A highly convergent, fourth-generation total synthesis of (+)-discodermolide (1), with a longest linear sequence of 17 steps and an overall yield of 9.0%, has been achieved. Highlighting the strategy is the efficient construction and sequential, bidirectional union of a linchpin comprising the C(9)-C(14) Wittig salt-vinyl iodide (-)-18. Importantly, Wittig salt generation proceeded in excellent yield under ambient pressure. 相似文献
949.
950.
Summary The hydrophobic retention characteristics of stationary ligands for reversed-phase high-performance liquid chromatography have been evaluated from the slope (r-value) of the plots relating the capacity factors (log k) of selected aliphatic and aromatic compounds with the reciprocal of methanol concentration (log (1/[MeOH])) in aqueous mobile phase. Octadecylsilyl (ODS), trimethylsilyl (TMS) and phenyldimethylsilyl (phenyl) groups were selected as the stationary ligands bonded to silica support.On ODS or TMS silicas, unlike on phenyl silica, aliphatic compounds gave slightly larger r-values than aromatic compounds, indicating that the shape of the ligand recognizes the hydrophobic surfaces of aliphatic and aromatic solute molecules. On TMS and phenyl silicas, the degree of solute hydrophobicity contributing to its retention is about 90% and 85% of that on ODS silica, respectively. On the other hand, on TMS and phenyl silicas, the polar functional group on the solute molecule brought about a smaller decrease in retention than on ODS silica. 相似文献