全文获取类型
收费全文 | 794篇 |
免费 | 23篇 |
国内免费 | 4篇 |
专业分类
化学 | 622篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 28篇 |
物理学 | 168篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 33篇 |
2012年 | 36篇 |
2011年 | 46篇 |
2010年 | 21篇 |
2009年 | 19篇 |
2008年 | 50篇 |
2007年 | 30篇 |
2006年 | 41篇 |
2005年 | 57篇 |
2004年 | 44篇 |
2003年 | 34篇 |
2002年 | 43篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 27篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有821条查询结果,搜索用时 15 毫秒
21.
Hashizaki K Taguchi H Itoh C Sakai H Abe M Saito Y Ogawa N 《Chemical & pharmaceutical bulletin》2005,53(1):27-31
Poly(ethylene glycol)-grafted liposomes (PEG-liposomes) were prepared from dipalmitoylphosphatidylcholine (DPPC) with various amounts of distearoyl-N-monomethoxy poly(ethylene glycol)-succinyl-phosphatidylethanolamines (DSPE-PEG) with PEG molecular weights of 1000, 2000, 3000 and 5000. The effects of DSPE-PEG concentration on the permeability of PEG-liposomes were investigated using carboxyfluorescein (CF). In the gel state, the CF leakage from PEG-liposomes was decreased with increasing mole fractions of DSPE-PEG for all PEG molecular weights. In the liquid-crystalline state, the CF leakage from PEG-liposomes containing DSPE-PEG1000 gradually increased with increasing mole fractions of DSPE-PEG, while that of PEG-liposomes whose molecular weight in PEG units was above 2000 rapidly decreased by the addition of DSPE-PEG. Furthermore, no effect of PEG molecular weight on CF leakage was observed. The relationship between the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) (or 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH)) and the mole fraction of DSPE-PEG for PEG-liposomes was also investigated. No significant changes in fluorescence polarization of DPH for liposomal bilayer membranes was observed in the gel and liquid-crystalline states due to the addition of DSPE-PEG, while that of TMA-DPH was decreased compared with that of liposomes without DSPE-PEG in both states. 相似文献
22.
23.
Ken-ichi Fujita Shigeru HashimotoAkihiro Oishi Yoichi Taguchi 《Tetrahedron letters》2003,44(19):3793-3795
After immobilizing arylselenenyl bromide on polymer resin, the oxyselenenylation reaction of olefin was carried out in water. An amphiphilic polymer-supported arylselenenyl bromide was employed, and various intramolecular oxyselenenylation and deselenenylation reactions proceeded smoothly in water in fair chemical yields (up to an 83% yield). 相似文献
24.
The three-component aminoallylation reaction of the activated olefins 2 with the phthalimide 1a and allyl chloride proceeded very smoothly in the presence of Pd(2)dba(3).CHCl(3) (5 mol %)/P(4-FC(6)H(4))(3) (40 mol %) and Cs(2)CO(3) (3 equiv against 2) in dichloromethane at room temperature to give the corresponding aminoallylated products, N-pent-4-enylphthalimides 3, in 58-99% yields. The reaction of oxazolidinone 1b also proceeded very smoothly to give N-(2,2-dicyano-1-phenylpent-4-enyl)oxazolidinone in a quantitative yield; however, the Tsuji-Trost-type allylation products 4 were obtained in the case of dibenzylamine, N-tosylaniline, and pyrrolidin-2-one. Further, 2 underwent cycloaddition with N-tosylvinylaziridine 9a in the presence of Pd(2)dba(3).CHCl(3) (5 mol %)/P(4-FC(6)H(4))(3) (40 mol %) in THF at room temperature, giving the corresponding pyrrolidines 11 in 69-99% yields. 相似文献
25.
S. Kulprecha T. Nihira C. Shimomura K. Yamada N. Nilubol T. Yoshida H. Taguchi 《Tetrahedron》1984,40(15):2843-2846
The microbiological transformation of lithocholic acid (3α-hydroxy-5β-cholanic acid) into 3α, 15β-dihydroxy-5β-cholanic acid by Cunninghamella sp. is Investigated. The structure has been determined on the basis of two-dimensional 1H-NMR. 相似文献
26.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
27.
Silaned glass beads are applied to the preconcentration and spectrophotometric determination of phosphorus as the phosphomolybdenum blue complex. Traces of phosphorus in water are collected as a phosphomolybdenum blue complex on a column of the beads. The phosphomolybdenum blue is eluted with N,N-dimethylformamide and the absorbance of the eluate continuously monitored at 700 nm. The height of the very sharp peak obtained is proportional to the amount of phosphorus present and 0.1-0.5 mug of phosphorus in a 10-ml sample can be determined reproducibly. Interference from arsenate is eliminated by addition of a reducing agent. High concentrations of silica cause a small positive error. This method is applicable to the analysis of river water and sea-water samples. 相似文献
28.
The effects of the phenyl substituent on the dimerization of copper(II) carboxylate in the solvent extraction of copper(II) with phenylacetic acid using benzene and 1-octanol as a solvent were investigated, at 25 degrees and at the aqueous ionic strength of 0.1M (NaClO(4)). The dimerization of copper(II) phenylacetate has been found to be written as: 2CuA(2)Cu(2)A(4) in 1-octanol, and 2CuA(2)(HA)(2)Cu(2)A(4)(HA)(2) + (HA)(2) in benzene, with the dimerization constants, log K = 2.24 and log K = 4.19, respectively. It was proved that the phenyl group inhibits the formation of the dimeric copper(II) phenylacetate, and its effect is partially shielded by a methylene substituent. 相似文献
29.
Yoshihiko Taguchi Yasuyuki Ishida Hajime Ohtani Hiroyuki Bekku Masaya Sera 《Analytical sciences》2004,20(3):495-499
A polymeric hindered amine light stabilizer (HALS), Tinuvin 622 (MW [symbol: see text] 4000), in PP materials formulated with a magnesium hydroxide flame retardant was determined by reactive thermal desorption (RTD) gas chromatography (GC). Two kinds of the HALS components that were formed through the RTD in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH] were clearly observed in the chromatograms of the PP samples, with negligible interference from the other additives and the PP substrate. Here, the coexisting flame retardant was proved to affect significantly the RTD process of the occluded HALS. As a result, the recovery of the HALS components in the RTD-GC chromatograms of the PP samples increased with increase in the content of the flame retardant. This enhancement of the HALS recovery is attributed mainly to the preferential exposure of the HALS on the surface of the ground PP sample through the interaction between the polymeric HALS and the flame retardant in the molten PP during kneading. In spite of such a considerable action of the flame retardant, the observed intensities of the characteristic peaks of HALS by RTD-GC showed a good linear relationship with the HALS content in the PP samples with constant content of the flame retardant (50 phr); this relationship could be used as the calibration line for the determination of the polymeric HALS in the PP materials containing the flame retardant. 相似文献
30.
Ishii Y Iwahama T Sakaguchi S Nakayama K Nishiyama Y 《The Journal of organic chemistry》1996,61(14):4520-4526
A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8. 相似文献