全文获取类型
收费全文 | 3616篇 |
免费 | 86篇 |
国内免费 | 8篇 |
专业分类
化学 | 2878篇 |
晶体学 | 25篇 |
力学 | 41篇 |
数学 | 170篇 |
物理学 | 596篇 |
出版年
2022年 | 20篇 |
2021年 | 29篇 |
2020年 | 43篇 |
2019年 | 54篇 |
2018年 | 34篇 |
2017年 | 20篇 |
2016年 | 52篇 |
2015年 | 46篇 |
2014年 | 73篇 |
2013年 | 169篇 |
2012年 | 139篇 |
2011年 | 209篇 |
2010年 | 73篇 |
2009年 | 101篇 |
2008年 | 187篇 |
2007年 | 188篇 |
2006年 | 179篇 |
2005年 | 219篇 |
2004年 | 171篇 |
2003年 | 129篇 |
2002年 | 140篇 |
2001年 | 111篇 |
2000年 | 140篇 |
1999年 | 48篇 |
1998年 | 38篇 |
1997年 | 34篇 |
1996年 | 58篇 |
1995年 | 29篇 |
1994年 | 48篇 |
1993年 | 36篇 |
1992年 | 51篇 |
1991年 | 45篇 |
1990年 | 41篇 |
1989年 | 39篇 |
1988年 | 53篇 |
1987年 | 43篇 |
1986年 | 60篇 |
1985年 | 55篇 |
1984年 | 60篇 |
1983年 | 31篇 |
1982年 | 35篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1978年 | 28篇 |
1977年 | 26篇 |
1976年 | 21篇 |
1975年 | 32篇 |
1974年 | 28篇 |
1972年 | 21篇 |
排序方式: 共有3710条查询结果,搜索用时 0 毫秒
991.
Simultaneous determination of ingredients in an ointment by hydrophobic interaction electrokinetic chromatography 总被引:2,自引:0,他引:2
Okamoto H Uetake A Tamaya R Nakajima T Sagara K Ito Y 《Journal of chromatography. A》2001,929(1-2):133-141
Hydrophobic interaction electrokinetic chromatography was used to simultaneously determine seven active ingredients (diphenhydramine hydrochloride, dibucaine hydrochloride, chlorhexidine hydrochloride, phenylephrine hydrochloride, hydrocortisone acetate, allantoin and tocopherol acetate) in an ointment. Not only hydrophobic but also ionic compounds were successfully separated by use of a separation solution composed of acetonitrile-water (80:20, v/v), tetradecylammonium salt and ammonium chloride. The migration behavior of the hydrophobic compound depended on tetradecylammonium concentration, while that of the ionic compounds depended on ammonium chloride concentration. An addition of triethylamine to the separation solution markedly improved the reproducibility of the peak areas of cations with a relative standard deviation (RSD) of less than 1.7% (n=6). The established method was validated and confirmed to be applicable to the determination of the active ingredients in a commercial ointment. Sample preparation was performed by liquid-liquid extraction and no interference from the formulation excipients was observed. Good linearities were obtained, with correlation coefficients above 0.999. Recoveries and precisions ranged from 98.0 to 100.8%, and from 0.4 to 2.9% RSD, respectively. These results suggest that hydrophobic interaction electrokinetic chromatography can be used for the determination of ionic compounds as well as hydrophobic compounds in ointment. 相似文献
992.
Abstract In porphyrin photosensitization, the localization of porphyrin in the cell and the sensitizing activity have been of recent concern. Hydrophobic porphyrins are usually in a highly aggregated state in aqueous systems. This study was designed to see whether the change in the polarity of the environment by adding ethanol could modify the sensitizing effects of porphyrins using a fermentable (alcohol tolerant) yeast ( Saccharomyces cerevisiae ) cells. The results showed that (1) the addition of ethanol (˜15%) to the aqueous suspension remarkably increased inactivation and cell membrane damage both in the hematoporphyrin (HP) and protoporphyrin (PP) photosensitizations, and (2) a sharp induction of genetic changes occurred concomitantly both in HP and PP sensitized cells in the presence of ethanol. In view of the fact that the addition of ethanol modified the absorption spectra and fluorescence intensity of porphyrins in favor of deaggregation, these results may be interpreted to mean that deaggregation of porphyrins promoted by ethanol enhanced their solubility in the lipophilic environment of the cell membrane and even further inside, thereby increasing the sensitizing activities. 相似文献
993.
Naohiko Mikami Atsunari Hiraya Ichiro Fujiwara Mitsuo Ito 《Chemical physics letters》1980,74(3):531-535
The fluorescence excitation spectrum of the first singlet transition of aniline in a supersonic free jet has been measured. Vibronic transitions involving the inversion vibration of the NH2 group in the excited state have been observed. The double minimum potential function in the excited state has been determined from the observed vibrational levels. 相似文献
994.
K. Ito K. Abe H. L. Li Y. Ujihira N. Ishikawa S. Hayashi 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(1):53-60
Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a microscopic point of view. The relationship between free volume contents and the formation of hydrogen bonds significantly suggests that the shape memory occurs due to the configurational recovery of the microscopic regulation around urethane bundles of hard segment and consequent restoration of soft-segment in polyurethane. 相似文献
995.
Takeo Ito Hideki Shirakawa Sakuji Ikeda 《Journal of polymer science. Part A, Polymer chemistry》1975,13(8):1943-1950
Thermal cis-trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC4H9)4–Al(C2H5)3 (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis-polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis-trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis-trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content. 相似文献
996.
Makoto Minato Susumu Hiratsuka Takashi Ito 《Journal of organometallic chemistry》2004,689(6):1025-1028
The reaction of Cp2MoH2 (Cp=η5-C5H5) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η3-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η3-crotyl complex. 相似文献
997.
Palladium(II) enolate complexes have been prepared by the reaction of Pd(II)Cl2-(PhCN)2 with trimethylsilyl enol ethers and reacted with CO and ethylene. 相似文献
998.
A trial transdermal dosage form designed to sustain a suitable plasma concentration of clonazepam (CZP) was produced using a porous membrane (Hipore 2100 or 4050) and applied to rabbits and rats for pharmacokinetic and pharmacodynamic evaluations. The release rate constants for the drug through the porous membranes were significantly smaller than that without any membrane. The transdermal system (Hipore 4050 system, ointment 0.25 g, 2.25 cm2) provided a well sustained plasma concentration of CZP and the therapeutic plasma concentration range was maintained for about 26 h. When the Hipore 4050 system with an increased amount of ointment and enlarged absorption area (0.5 g, 4.0 cm2) was applied, the therapeutic range was sustained for about 40 h, and slightly higher plasma levels over the whole application period and much higher bioavailability (37%) were obtained compared with those after the 2.25 cm2-Hipore 4050 system. The transdermal system exerted an excellent anticonvulsant activity in rats, with the best (3+ or 4+) protective score. The plasma concentrations of CZP when the activity was estimated were in the therapeutic range. Thus, the transdermal system has the potential to be an efficient drug delivery system. 相似文献
999.
Ito H Imae T Nakamura T Sugiura M Oshibe Y 《Journal of colloid and interface science》2004,276(2):290-298
The self-association of the fluorinated diblock copolymer, poly(methacrylic acid)-block-poly(perfluorooctylethyl methacrylate) (PMAA-b-PFMA), in water has been investigated by light scattering, potentiometry, atomic force microscopy, and transmission electron microscopy. The size of the polymer micelles increases, as the degree of dissociation of the PMAA blocks increases. Since the charged PMAA block takes the stretched structure, PMAA-b-PFMA can easily form large micelles due to the low steric hindrance of PMAA blocks. Addition of NaCl shielded electrostatic repulsion in the PMAA chain and induced the formation of smaller micelles than water without NaCl did because of the bulky structure of the PMAA chain in the shell of the micelles. The micelle of PMAA-b-PFMA in ethanol is larger than that of poly(t-butyl methacrylate)-block-poly(perfluorooctylethyl methacrylate) (PtBMA-b-PFMA) in ethanol as a result of the higher steric hindrance of the PtBMA block. The dimensions of the core and shell of the micelles were estimated. The micelle of PMAA-b-PFMA in water possesses a rather thick shell and a large volume per molecule, consistent with the extended PMAA chain. On the other hand, the shell of the micelle in an ethanol solution of PtBMA-b-PFMA is thin but has a large surface area. Facts are consistent with the shrunk structure of the PtBMA block in poor solvent. 相似文献
1000.
Y. Sawada K. Omika Y. Ito F. Muta M. Momota 《Journal of Thermal Analysis and Calorimetry》1993,40(3):1145-1150
The formation process of a ceramic (indium oxide) thin film (thickness: approximately 20 nm to several microns) was investigated by thermal analyses. Thermal changes of an organic precursor, indium(III) 2-ethylhexanoate, dip-coated on a glass substrate was successfully detected by DSC in air. Exothermic phenomena were observed at marked lower temperatures for the thin films than for the bulk material; thinner films had slightly lower peak temperatures. The reaction mechanism is discussed with reference to mass spectra of the evolved gases. 相似文献