全文获取类型
收费全文 | 454篇 |
免费 | 24篇 |
国内免费 | 4篇 |
专业分类
化学 | 298篇 |
晶体学 | 8篇 |
力学 | 2篇 |
数学 | 16篇 |
物理学 | 158篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 33篇 |
2012年 | 19篇 |
2011年 | 31篇 |
2010年 | 22篇 |
2009年 | 12篇 |
2008年 | 25篇 |
2007年 | 32篇 |
2006年 | 25篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 12篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 6篇 |
1968年 | 4篇 |
1966年 | 1篇 |
排序方式: 共有482条查询结果,搜索用时 843 毫秒
11.
A microanalytical method for the measurement of selenium in waters and biological materials by a flameless atomic-absorption technique has been developed. The ammonium pyrrolidinedithiocarbamate-methyl isobutyl ketone extraction system is used for separation from interfering materials such as large amounts of alkali and alkaline earth metal salts and mineral acids. The atomic-absorption sensitivity for selenium is found to be enhanced to a large extent by co-extraction of some transition metal ions. Copper(II) has been used successfully as such an additive to diminish the volatility of selenium in the graphite furnace during the ashing step of the atomization cycle. When the aqueous phase/organic solvent volume ratio is 5 and the volume injected into the graphite furnace is 20 mul, the sensitivity for selenium is 0.3 ng/ml for 1% absorption. The relative standard deviation is ca. 2%. Interference by other metal ions is prevented by masking with EDTA. The method has been applied satisfactorily for the determination of minute amounts of selenium in waters and various biological materials. 相似文献
12.
Shouhong Xu Yuan Song Shizuko Sato Isamu Miyata Junpei Yamanaka Masakatsu Yonese 《Colloid and polymer science》2005,283(4):383-392
Two-dimensional structures and characteristics of the complexes between sodium hyaluronate (NaHA) and bovine serum albumin (BSA) were studied by using a quartz crystal microbalance method and an atomic force microscope (AFM). NaHA did not adsorb on poly(-methyl-l-glutamate) (PMLG) film. On the other hand, the complexes adsorbed on it and the adsorption behaviors were found to be Langmuir types. With increasing weight ratio of BSA to NaHA, W
BSA, the adsorption constants K decreased and the saturated adsorption masses increased. The adsorbed complexes were spherical particles and at saturated adsorption states they covered compactly on the PMLG film. The mean diameters d
AFM estimated from the topographic images decreased from 70 to 54 nm with increasing W
BSA. The adhesion force F
ad and the frictional force F
f between the complex layers and the AFM tip were obtained by using the contact mode of the AFM. With increasing W
BSA, the values of F
ad decreased and the values of F
f increased. Compared with the frictional coefficient of the NaHA adsorption layer on the BSA monolayer, the values for the NaHA–BSA complex layer were found to be much higher. 相似文献
13.
14.
The extraction behaviour of selenium(IV) and selenium(VI) with sodium diethyldithiocarbamate, ammonium pyrrolidinedithiocarbamate and dithizone in organic solvents has been investigated by means of flameless atomic-absorption spectrophotometry with a carbon-tube atomizer. The selective extraction of selenium(IV) and differential determination of selenium(IV) and selenium(VI) have been developed. With sodium diethyldithiocarbamate and carbon tetrachloride, when the aqueous phase/organic solvent volume ratio is 5 and the injection volume in the carbon tube is 20 microl, the sensitivity for selenium is 0.4 ng/ml for 1% absorption. The relative standard deviations are ca. 3%. Interference by many metal ions can he prevented by masking with EDTA. The proposed methods have been applied satisfactorily to determination of Se(IV) and Se(VI) in various types of water. 相似文献
15.
Yoichiro Iwase Koichi Kondo Kenji Kamada Koji Ohta 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3534-3541
1,4‐Bis(4‐benzylpyridinium)butadiyne triflate was aggregated in dimethylformamide and spontaneously converted into the 1,4‐addition type of polydiacetylene. The polymerization took place in a dipolar aprotic solvent with a large dielectric constant that could enhance the aggregation of the ionic diacetylene salt through the electrostatic interaction. The molecular weight of the diacetylene was leveled off after 30 h at 80 °C to reach 1.5 × 104 (number‐average molecular weight) that consisted of the 1,4‐addition type of polydiacetylene similar to polydiacetylenes obtained in the conventional solid‐state polymerization. Electron spin resonance spectra revealed that diradicals were generated at the earlier state aggregation to give rise to a solution polymerization. The UV spectra also suggested the presence of the activated aggregation associated with the polymerization as well as the eximer emission spectra. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3534–3541, 2002 相似文献
16.
Fukuzumi S Yuasa J Satoh N Suenobu T 《Journal of the American Chemical Society》2004,126(24):7585-7594
Photoinduced electron transfer from a variety of electron donors including alkylbenzenes to the singlet excited state of acridine and pyrene is accelerated significantly by the presence of scandium triflate [Sc(OTf)(3)] in acetonitrile, whereas no photoinduced electron transfer from alkylbenzenes to the singlet excited state of acridine or pyrene takes place in the absence of Sc(OTf)(3). The rate constants of the Sc(OTf)(3)-promoted photoinduced electron-transfer reactions (k(et)) of acridine to afford the complex between acridine radical anion and Sc(OTf)(3) remain constant under the conditions such that all the acridine molecules form the complex with Sc(OTf)(3). In contrast to the case of acridine, the k(et) value of the Sc(OTf)(3)-promoted photoinduced electron transfer of pyrene increases with an increase in concentration of Sc(OTf)(3) to exhibit first-order dependence on [Sc(OTf)(3)] at low concentrations, changing to second-order dependence at high concentrations. The first-order and second-order dependence of k(et) on [Sc(OTf)(3)] is ascribed to the 1:1 and 1:2 complexes formation between pyrene radical anion and Sc(OTf)(3). The positive shifts of the one-electron redox potentials for the couple between the singlet excited state and the ground-state radical anion of acridine and pyrene in the presence of Sc(OTf)(3) as compared to those in the absence of Sc(OTf)(3) have been determined by adapting the free energy relationship for the photoinduced electron-transfer reactions. The Sc(OTf)(3)-promoted photoinduced electron transfer from hexamethylbenzene to the singlet excited state of acridine or pyrene leads to efficient oxygenation of hexamethylbenzene to produce pentamethylbenzyl alcohol which is further oxygenated under prolonged photoirradiation of an O(2)-saturated acetonitrile solution of hexamethylbenzene in the presence of acridine or pyrene which acts as a photocatalyst together with Sc(OTf)(3). The photocatalytic oxygenation mechanism has been proposed based on the studies on the quantum yields, the fluorescence quenching, and direct detection of the reaction intermediates by ESR and laser flash photolysis. 相似文献
17.
Proteome analysis of Oncorhynchus species during embryogenesis 总被引:3,自引:0,他引:3
Kanaya S Ujiie Y Hasegawa K Sato T Imada H Kinouchi M Kudo Y Ogata T Ohya H Kamada H Itamoto K Katsura K 《Electrophoresis》2000,21(9):1907-1913
To understand the molecular mechanisms underlying normal and abnormal development of two salmonids, masu salmon (Oncorhynchus masou) and rainbow trout (O. mykiss), we used two-dimensional (2-D) electrophoresis to construct a series of 2-D maps during the embryonic period. We identified all visible protein spots on the 2-D map by assigning numbers for masu salmon and rainbow trout, and we determined N-terminal sequences of proteins for one hundred of the spots, that appear at very high concentrations in the whole embryos of masu salmon and rainbow trout. We also characterized embryonic stages according to the periods of appearance of spots. Most of the N-terminal sequences were identical or at least highly similar to partial sequences reported for vitellogenin (Vtg) of O. mykiss. A potential proteolytic processing of Vtg for rainbow trout is discussed in relation to the time of appearance and relative position of Vtg fragments within the complete protein sequence. 相似文献
18.
19.
Junpei Naito Yoko Yamamoto Megumi Akagi Satoshi Sekiguchi Masataka Watanabe Nobuyuki Harada 《Monatshefte für Chemie / Chemical Monthly》2005,60(1):411-445
The CD exciton chirality method was applied to various phenylacetylene alcohols to determine their absolute configurations; the long axis polarized –* transition (max=252nm) of the 4-methoxyphenylacetylene chromophore couples with the transition (max=257nm) of the 4-methoxybenzoate group to generate intense exciton split CD Cotton effects, from the signs of which the absolute configurations of phenylacetylene alcohols were unambiguously determined. As an extension of the results, a new methodology for determining the absolute configurations of acetylene alcohols having the HCCCH(OH)-moiety by combination of the Sonogashira reaction and the CD exciton chirality method has been developed and applied. Since the –* transition of acetylene triple bond is located below 180nm, it is difficult to observe ideal bisignate CD Cotton effects due to the exciton coupling between acetylene and benzoate chromophores. To observe the ideal exciton split Cotton effects necessary for the unambiguous determination of absolute configuration, the terminal acetylene group was converted, by the Sonogashira reaction, to the 4-methoxyphenylacetylene moiety, which exhibits an intense –* absorption band polarized along the long axis of the chromophore at 252nm. As a partner of exciton coupling, 4-methoxybenzoate showing a –* band at 257nm was introduced into the alcohol moiety, and the benzoates formed showed intense bisignate CD Cotton effects, from the signs of which the absolute configurations of original acetylene alcohols could be determined in an unambiguous manner. 相似文献
20.
Metallic Na formation in/on NaCl crystals with irradiation by electron or vacuum ultraviolet photons
Shigehiro Owaki Shigeko Koyama Masao Takahashi Masao Kamada Ryouichi Suzuki 《Radiation Physics and Chemistry》1997,49(6):609-615
Metallic Na was formed in/on NaCl single crystals by irradiating them with a variety of radiation sources, namely, 21 MeV electron pulses, an electron beam of 30 keV and photon fluxes in the VUV region. The physical states were analysed using several methods, optical absorption, lifetime measurement of positron annihilation, Auger electron spectroscopy and UV photoelectron spectroscopy. Metallic Na was obtained in different physical states; clusters were formed in bulk, thin layers (islands) and thick layers on the surface. 相似文献