全文获取类型
收费全文 | 580篇 |
免费 | 14篇 |
国内免费 | 112篇 |
专业分类
化学 | 622篇 |
晶体学 | 1篇 |
力学 | 4篇 |
物理学 | 79篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 12篇 |
2014年 | 30篇 |
2013年 | 24篇 |
2012年 | 38篇 |
2011年 | 41篇 |
2010年 | 27篇 |
2009年 | 41篇 |
2008年 | 33篇 |
2007年 | 53篇 |
2006年 | 44篇 |
2005年 | 49篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2002年 | 31篇 |
2001年 | 10篇 |
2000年 | 28篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有706条查询结果,搜索用时 15 毫秒
1.
Two new compounds have been isolated from the whole plant of Monochoria vaginalis and characterized as: (10Z)‐1‐(2,6‐dihydroxyphenyl)octadec‐10‐en‐1‐one ( 1 ) (20R, 24R)‐campest‐5‐ene‐3β, 4β‐diol ( 2 ) together with nine known ones. The structures of these compounds were elucidated on the basis of spectral data and chemical evidence. 相似文献
2.
Halina Y. Neujahr 《Applied biochemistry and biotechnology》1982,7(1-2):107-111
The enzyme phenol 2-hydroxylase was immobilized on Sepharose and used in conjunction with an O2 electrode for quantitating phenol. Similarly, catechol 1,2-oxygenase was used for quantitating catechol. A third probe was
prepared by immobilization ofTrichosporon cutaneum cells rather than purified phenol 2-hydroxylase for phenol quantitation. The whole cell system gave results comparable to
the immobilized enzyme system. 相似文献
3.
This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and
desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally
activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics,
thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better
adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter
case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed
in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated
the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption.
The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was
desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed
to higher energies of 2-CP adsorption. 相似文献
4.
Jadranka Vuković Shiro Matsuoka Kazuhisa Yoshimura Vladimir Grdinić Renata Jurišić Grubešić 《Mikrochimica acta》2007,159(3-4):277-285
A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol
with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements
of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The
sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological
characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation
of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations
(−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable
working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations
as well as other matrices. 相似文献
5.
水中酚的膜萃取分离流动注射技术测定的研究 总被引:6,自引:1,他引:6
本文提出了硅橡胶膜在线萃取分离流动注射技术测定水样中苯酚的方法。由于水样中的苯酚透过硅橡胶进入萃取液的萃取量随时间的增加和温度的升高而增大,故采用停流技术及升高温度以降低酚的检出限。 相似文献
6.
Gregory D. Cuny 《Tetrahedron letters》2004,45(26):5167-5170
A synthesis of the alkaloid (±)-aporphine is reported. The initial key step of the synthesis involves a Pictet-Spengler cyclization of N-tosyl tyramine with 2-bromophenylacetaldehyde in trifluoroacetic acid. This step was followed by the second strategic transformation a palladium-mediated intramolecular phenol ortho-arylation reaction utilizing tricyclohexylphosphine as co-catalysts in the presence of cesium carbonate. Finally, de-oxygenation of the phenol, removal of the tosyl group and methylation gave the desired alkaloid. 相似文献
7.
《Electroanalysis》2003,15(17):1403-1409
The effect of F? on the modified films of lead dioxide in morphology and structure was studied. The results obtained by cyclic voltammetry (CV), X‐diffractometer (XRD) and scanning electron microscope (SEM) techniques indicated that F? could change the magnitude of lead dioxide crystal grain and the preferred crystallizing orientation on the substrate surface, even though it didn't change the basic structure of PbO2. When the modified electrode was applied as an analytical sensor to determine phenolic compounds, the linearity was in the range of 2×10?5 – 1×10?3 mol/L and the detection limit was 2.5×10?6 mol/L. It was all found that the stability and reproducibility of the oxide‐modified electrodes were improved by additional F?. 相似文献
8.
A sequence of two known reactions, palladium catalyzed arylboronation of arybromide and subsequent oxidation of arylboronate with oxone, has been carried out to prepare functionalized phenols and pyridin-2(1H)-one which were later loaded on to resin for solid-phase synthesis. Using these resin-bound templates, a number of solid-phase methods were developed to generate libraries of substituted phenols and pyridin-2(1H)-one. 相似文献
9.
Lingping Wang Aiguo Kong Bo Chen Hanming Ding Yongkui Shan Mingyuan He 《Journal of molecular catalysis. A, Chemical》2005,230(1-2):143-150
Transition metal copper substituted mesoporous silica (Cu-SBA-15) was synthesized using triblock copolymers surfactant as template agent under acidic condition. The result Cu-SBA-15 was characterized with XRD, ICP-AES, FT-IR and N2 adsorption–desorption measurements, which prove that Cu(II) was mainly incorporated into the framework of Cu-SBA-15. Its catalytic activity was studied for phenol hydroxylation using H2O2 (30%). The substituting element (Cu2+) is incorporated into the framework position forming a new type of active site which raises the phenol conversion to 62.4% and the diphenol (the mixture of catechol (CAT) and hydroquinone (HQ)) selectivity to 97%. The Cu-SBA-15 has very high selectivity for catechol (about 71% selectivity), which is completely different from that of the microporous titanium silicalite zeolites (47.1% phenol conversion and about 50% selectivity to CAT under same reaction conditions). The results obtained indicate that the selective oxidation of phenol with H2O2 by a radical substitution mechanism. 相似文献
10.