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921.
922.
Watabe Y Hosoya K Tanaka N Kondo T Morita M Kubo T 《Analytical and bioanalytical chemistry》2005,381(6):1193-1198
A new analytical method for the determination of bisphenol A (BPA) by LC/MS was developed and applied to environmental water samples. Quantitative MS detection of BPA was carried out in the negative mode. In order to preconcentrate the target compound yet prevent serious contamination of the water samples from the experimental environment, we employed column switching HPLC coupled with a pretreatment column of surface-modified molecularly-imprinted polymers. The recovery of BPA from a spiked environmental water sample was 102% and the repeatability of actual determinations of water samples containing 20 ng/L of BPA was 5.4% RSD. By modifying the surfaces of the molecularly-imprinted polymer particles packed in the pretreatment column, interference from the water samples was effectively removed, resulting in a significant increase in sensitivity and more reliable results. This method was successfully applied to the trace determination of BPA in environmental water samples using LC/MS. 相似文献
923.
Fukuzumi S Yoshida Y Okamoto K Imahori H Araki Y Ito O 《Journal of the American Chemical Society》2002,124(24):6794-6795
A newly designed ferrocene-quinone dyad with an amide space (Fc-Q) is employed to examine formation of the hydrogen bonding in the one-electron reduced form (Q*-) and the dynamics in the photoinduced electron-transfer reaction from the ferrocene to the quinone moiety. Photoexcitation of the Q moiety in Fc-Q in deaerated PhCN with 388 nm results in intramolecular electron transfer from Fc to the singlet excited state of Q to produce Fc+-Q*- without changing the conformation (<1 ps), followed by hydrogen bond formation with the amide proton of the spacer (tau = approximately 5 ps). The resulting radical ion pair decays via a back electron transfer to the ground state at a longer time scale with a rate constant of 2.6 x 108 s-1. 相似文献
924.
Compounds of the type π-C5H5NiPBu3SC(S)X (X = R, OR and NRH) are obtained from reactions between [π-C5H5Ni(PBu3)2]+Cl? and SC(S)X? in aqueous solution. Compounds such as π-C5H5NiPBu3SC(S)NRH are also obtained by reactions of π-C5H5NiPBu3SH with RNCS.Reactions of C6H5NCS with π-C5H5NiPBu3SEt or [π-C5H5NiPBu3S(CH2)n]2 (n = 1, 2 and 3) give π-C5H5NiPBu3[SC(NC6H5)SC2H5] or [π-C5H5NiPBu3 {SC(NC6H5)S(CH2)n}]2 respectively.Similar reactions of π-C5H5NiPBu3SH and RNCO given π-C5H5NiPBu3SC(O)NRH.Treatment of π-C5H5NiPBu3SC(S)R with HCl gives π-C5H5NiSC(S)R. 相似文献
925.
Ken Fujimori Tomoko Komiyama Hideo Tabata Takayuki Nojima Katsuya Ishiguro Yasuhiko Sa-waki Hidetaka Tatsuzawa Minoru Nakano 《Photochemistry and photobiology》1998,68(2):143-149
The chemiluminescence of the Cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroirnidazo[1,2-a]pyrazin-3-one (MCLA), with O2 (1Δg) generated by the retro-Diels-Alder reaction of 3-(4′-methyI-l'-naphthyl)-propionic acid endoperoxide was studied in an aqueous solution with pH 7.12 at 37°C. The retro-Diels-Alder reaction occurs with a first-order rate constant of (4.16 ± 0.13) × 10?4/s to quantitatively yield O2 (1Δg) and 3-(4′-methyl-l'-naphthyl (-propionic acid. MCLA consumed equimolar amounts of O2 (1Δg) with a second-order rate constant (6.96 ± 0.27) × 108/M/s to emit light in an aqueous solution with pH 7.12 at 37°C. The chemiluminescence spectrum was identified as the fluorescence spectrum of 2-acetylamino-5-(p-methoxyphenyl)pyrazine (OMCLA), a major chemiluminescence reaction. Chemiluminescence spectra and product yields for MCLA reactions with O21Δg, with O2 (3Σ?g) and with superoxide anion radicals are identical, suggesting that all of these reactions occur via a common MCLA-2-hydrope-roxide intermediate formed by a combination of MCLA radicals and superoxide anion radicals. We have established practical use of NEPO as an O2 (1Δg) source and MCLA as a biological probe for detecting O2 (1Δg). 相似文献
926.
Those generalized geometries satisfying the conditions that (a) parallel transfer with respect to the connection is path independent and (b) the geodesics of the metricg have the same trajectories as the autoparallels of the connection , are determined. Some uniqueness theorems of the metric in terms of the curvature are shown for such generalized geometries. Geometries of this type may be useful for constructing geometrized theories of gravitation more general than Einstein's theory. 相似文献
927.
Sasaki K Nakagawa H Zhang X Sakurai S Kano K Kuroda Y 《Chemical communications (Cambridge, England)》2004,(4):408-409
A new host porphyrin bearing four permethyl-beta-cyclodextrin moieties for multi-porphyrin assembly forms a unique 2 : 2 assembly with the tetra-anion of tetrakis(p-sulfonylphenyl)porphyrin (TPPS) in aqueous solution. 相似文献
928.
Let A be an n×n integral matrix with determinant D>0, and let P(A) be the n-parallelepiped determined by the columns {Ai}ni=1 of A, Let L be the set of integral vectors in P(A), and let G(A) be the subset of L consisting of vectors whose coefficients xi satisfy 0?xi<1. We show that G(A), equipped with addition modulo 1 on the coefficients xi, is an Abelian group of order D, whose invariant factors are the invariant factors of the integral matrix A. We give a formula for |L|, and show that |L| is not a similarity invariant. 相似文献
929.
Asymmetric Synthesis of Protected Cyclohexenylamines and Cyclohexenols by Rhodium‐Catalyzed [2+2+2] Cycloaddition
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Koji Masutomi Haruki Sugiyama Hidehiro Uekusa Yu Shibata Ken Tanaka 《Angewandte Chemie (International ed. in English)》2016,55(49):15373-15376
It has been established that cationic rhodium(I)/axially chiral biaryl bis(phosphine) complexes catalyze the asymmetric [2+2+2] cycloaddition of 1,6‐enynes with electron‐rich functionalized alkenes, enamides, and vinyl carboxylates, to produce the corresponding protected cyclohexenylamines and cyclohexenols. Interestingly, regioselectivity depends on structures of substrates. The present cycloaddition was successfully applied to the enantioselective total synthesis of (?)‐porosadienone by using the amide moiety as a leaving group. 相似文献
930.
Ken Kusakari Tadao Fukuhara Nobuhiko Ochiai Takashi Watanabe Yukihiro Sugimoto 《Natural product research》2016,30(8):954-959
Three known iridoid glucosides (gentiournoside A, gentiournoside E and depressoside) were isolated from the flowers of Gentiana urnula Harry Sm. through activity-guided fractionations with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. All three compounds exhibited excellent DPPH radical scavenging activities (IC50: 10–20 μmol L?1) comparable to that of ascorbic acid and Trolox. However, examination of the NMR data revealed that the reported chemical structure of depressoside, previously isolated from the leaves of G. depressa, needed correcting due to incorrect elucidation around C-7 of the iridane skeleton, and was corrected to 6-β-(2,3-dihydroxyphenyl)-d-glucosyl 7-O-(2,3-dihydroxybenzoyl)-loganate. Depressoside exhibited a much higher scavenging activity against superoxide radicals (IC50: 45.5 μmol L?1) than the other two extracted compounds (IC50: more than 900 μmol L?1) due to the crucial presence of a pyrogallyl unit. 相似文献