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911.
A new C-8 prenylated 5,7-dimethoxycoumarin named omphamurrayin was isolated from the leaves of Murraya paniculata var. omphalocarpa, and its structure was established as 5,7-dimethoxy-8-(1-oxo-2-senecioyl-3-methyl-3-butenyl)-2H-1-benzopyran-2-one on the basis of the spectroscopic evidence. The taxonomic status of M. paniculata var. omphalocarpa is briefly discussed, along with its synonymity to M. paniculata from the chemosystematic viewpoint. 相似文献
912.
The modification of hexagonal BaFeO2.85 with a = 5.700 Å and C = 28.03 Å has been synthesized at high oxygen pressure. The ratio of 4.917 indicates that it has 12-layer sequence according to the general equation . From Mossbauer spectra at 300 K, it is revealed that there are two different valance states of iron, the isomer shifts are 0.03 mm/sec for Fe4+ and 0.37 mm/sec for Fe4+, respectively. 相似文献
913.
The retention behaviour of twenty cardiac steroids and four fluorescent derivatives was examined by the addition of cyclodextrin to the mobile phase in reversed-phase high-performance liquid chromatography. The addition of a suitable cyclodextrin improved the separation of isomeric cardiac steroids. The steroid A/B ring junction is the most important factor in the choice of the optimum cyclodextrin to be added; the C/D ring junction is less important. The hydroxyl group at the 3- or 12-position of the steroid enhanced the changes in retention times of these compounds. The effect of an unsaturated lactone ring at the 17 beta-position on the retention in the presence of cyclodextrin was also determined with cardenolide (five-membered ring) and bufadienolide (six-membered ring) but little difference was observed. Isomeric cardiac steroids, whose separation has not been done by the conventional method, were clearly separated by this method. The fluorescence intensity of 3-(1-anthroyl)-cardiac steroid was enhanced by the addition of cyclodextrin to the mobile phase. 相似文献
914.
The effects of the acid catalysts HF, H2S04, BF3, CF3S03H, FSO3H, and SbF5.FS03H on the reactions of CsSO4F with toluene, nitrobenzene and naphthalene in CH3CN have been studied. The catalys general accelerate reaction and enhance yields of ring-fluorinated products. Efficacity roughly parallels H0 of the acids, though H2S04 is more effective than stronger acids for the fluorination of naphthalene. Combined room temperature yields of fluorine-substituted products are as much as 45-50% for toluene and naphthalene and up to 30% for nitrobenzene. The predominant products are o-fluorotoluene, 1- fluoronaphthalene, and m-fluoronitrobenzene. With naphthalene the isomer selectivity is considerably less than in the absence of catalyst. Low yields (10%) of monomeric oxygenated products are obtained, along with considerable oxygen- and fluorine-containing dimers and higher polymers. The results are interpreted in terms of acid-catalyzed electrophilic fluorination or oxygenation, followed by further fluorination and/or free-radical-induced oxidative coupling of the oxygenated products. 相似文献
915.
Tatsuya Higashi Natsuko Takido Akinori Yamauchi Kazutake Shimada 《Analytical sciences》2002,18(12):1301-1307
Derivatization of neutral steroids for increasing sensitivity in liquid chromatography/negative atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) has been examined. Under APCI conditions, gas-phase electrons are provided by the corona discharge and captured by electron-affinitive compounds. In negative APCI-MS, therefore, ultrahigh sensitivity can be obtained by tagging neutral steroids, whose ionization efficiencies are low in the conventional APCI-MS, with electron-capturing moieties, such as a nitro group. We synthesized various boronic acid and hydrazine derivatives having electron-capturing moieties as derivatization reagents for 1,2-diol compounds and oxosteroids, respectively. Among reagents examined, those having the 2-nitro-4-trifluoromethylphenyl moiety were most effective in increasing sensitivity. That is, the detection responses of the derivatives with these reagents were increased by several to more than 200-fold over intact steroids, where limits of detection were some picograms. The developed derivatization procedures were applied to analyses of small amounts of steroids in human plasma and gave satisfactory results. 相似文献
916.
Sadakatsu Shimada 《Journal of heterocyclic chemistry》1987,24(5):1237-1241
Reaction of 5-aminooxazoles with N-phenylmaleimide gave 7-hydroxy-2-phenylpyrrolo[3,4-c]pyridine-1,3-diones and 7-amino-2-phenylpyrrolo[3,4-c]pyridine-1,3-diones via tricyclic adducts. The ratio of the 7-hydroxy compound and 7-amino compound depended on the basicity of the leaving group of the adducts. The reaction of 5-acetaminooxazole with dienophiles is described. 相似文献
917.
Nishida H Miyazaki Y Mukaihira T Shimada H Suzuki K Saitoh F Mizuno M Matsusue T Okamoto A Hosaka Y Matsumoto M Ohnishi S Mochizuki H 《Chemical & pharmaceutical bulletin》2004,52(4):459-462
Compounds containing an ethylenediamine structure in place of the piperazine ring of M55113 (1) and M55551 (2) were synthesized to investigate the effects of a piperazine moiety and evaluated for activity as factor Xa (FXa) inhibitors. Most such compounds, however, exhibited lower activity (1/10-1/100) than that of M55113 and M55551 as FXa inhibitors. 相似文献
918.
Seventeen aliphatic, hydroxyl, sulfur-containing, aromatic, imino, and heterocyclic DL-amino acids were resolved without derivatization using a native-cellulose column. Chirality was assigned by either CD spectra or co-chromatography. Under these conditions, it is known that the hydrophobic interaction of amino acids with the hydroxyl groups on the cellulose played an important role in the separations. The cellulose column chromatographic system for resolution of amino acid enantiomers was combined with an amino acid analyzer. Thus, the DL-amino acids separated by the latter system were successively resolved by the former. 相似文献
919.
The formation process of LiNbO3 in the system Li2CO3Nb2O5 was discussed from the results of non-isothermal or isothermal TG experiments and X-ray analysis. The mixture Li2CO3 and Nb2O5 in mole ratios of 1:3, 1:1 or 3:1 was heated at a rate of 5°C min?1 or at various temperatures fixed in the range 475 to 677°C. If the system has a composition of Li2CO3 + 3Nb2O5 or 3Li2CO3 + Nb2O5, the reaction between Li2CO3 and Nb2O5 proceeds with CO2 evolution to form LiNbO3 at ca. 300–600°C, but Nb2O5 or Li2CO3 remains unreacted. A composition of Li2CO3 + Nb2O5 gives LiNbO3 at 300–700°C. The diffusion of Li2O through the layer of LiNbO3 is rate-controlling with an activation energy of 51 kcal mol?1. The reaction between LiNbO3 and Nb2O5 gives LiNb3O8 at 600–700°C. At 700–800°C, a slight formation of Li3NbO4 occurs by the reaction between LiNbO3 and Li2O at the outer surface of LiNbO3 and the Li2O component of Li3NbO4 diffuses toward the boundary of the LiNb3O8 layer through the LiNbO3 layer. The single phase of LiNbO3 is formed above 850°C. 相似文献
920.
Heimei Yuki Yoshio Okamoto Yoshiki Shimada Koji Ohta Koichi Hatada 《Journal of polymer science. Part A, Polymer chemistry》1979,17(4):1215-1225
Monomer reactivity ratios r1 and r2 were determined in the copolymerizations of methyl methacrylate (MMA, M1) with 1, 1-diphenylethyl (DPEMA), α,α-dimethylbenzyl (DMBMA), tert-butyl (t-BuMA), diphenylmethyl (DPMMA), phenyl (PhMA), and 1-naphthyl (NpMA) methacrylates (M2) in tetrahydrofuran (THF) by azobisisobutyronitrile (AIBN) at 60°C and butyllithium (n-BuLi) at ?78°C. The reactivities of the monomers were explained in terms of the polar effect of the ester groups in both copolymerizations. All the copolymers isolated in low yields were converted to PMMA either directly or by copoly(MMA—methacrylic acid) to determine the triad tacticities of the copolymers. Coisotactic parameters σ12 and σ21 were determined by assuming the terminal model statistics. The σ21 values always accorded to the σ21 values within experimental error, and in radical copolymerizations they were between isotactic parameters σ11 and σ22 of the homopolymerizations of MMA and M2 monomers. In anionic copolymerizations, however, the σ12 = σ21 values varied, depending on the M2 monomers. In copolymerization with DPEMA the values were less than both σ11 and σ22 with DMBMA they were between σ11 and σ22, with DPMMA, nearly equal to σ11, and with PhMA and NpMA, greater than both σ11 and σ22. The application of these parameters to copolymerizations performed at high conversion was also investigated. 相似文献