全文获取类型
收费全文 | 566篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
化学 | 337篇 |
晶体学 | 7篇 |
力学 | 31篇 |
数学 | 131篇 |
物理学 | 80篇 |
出版年
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 12篇 |
2018年 | 22篇 |
2017年 | 8篇 |
2016年 | 23篇 |
2015年 | 10篇 |
2014年 | 24篇 |
2013年 | 71篇 |
2012年 | 34篇 |
2011年 | 37篇 |
2010年 | 32篇 |
2009年 | 23篇 |
2008年 | 26篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 20篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1965年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有586条查询结果,搜索用时 31 毫秒
561.
562.
Antoine Bechalany Nabil El Tayar Pierre-Alain Carrupt Bernard Testa Jean-Bernard Falconnet Yahia Cherrah Youssef Benchekroun Jean-Louis Brazier 《Helvetica chimica acta》1989,72(3):472-476
In the present study, it is confirmed that the deuteration of C? H groups is accompanied by a small but genuine decrease in lipophilicity. The lipophilicity of deuterated isotopomers of caffeine was measured by reversed-phase HPLC. Overall, lipophilicity was shown to decrease when going from unlabelled caffeine to the three isomeric trideuterated caffeines, then to the three isomeric hexadeuterated caffeines, and finally to nonadeuterated caffeine. In addition, position-specific effects were also proven. E.g. (7-methyl-2H3)caffeine experienced a smaller isotope effect than its two positional isomers. Both a cavity factor (decreased volume of deuterated isotopomers) and intramolecular electronic effects are postulated to operate. 相似文献
563.
Mahmoud O. Abd El-Magied Ali M. A. Hassan Hamdi M. H. Gad Tarek F. Mohammaden Mohamed A. M. Youssef 《Journal of Dispersion Science and Technology》2018,39(6):862-873
Removal nickel from the aquatic environment is a serious environmental problem in view of public health. The present article studies the applicability of activated carbon, obtained from graphite, as a source of adsorbents to remove nickel from the aqueous polluted water. Activated carbon was obtained by steam activation of graphite and then was oxidized by nitric acid followed by modification with Tetraethylenepentamine (TEPA). The applicability of graphite activated carbon (GAC), and modified activated carbon by Tetraethylenepentamine (GACA) to remove nickel ions Ni(II) from aqueous media was studied. The effect of pH, initial concentration, contact time, and the temperature was evaluated during Ni(II) removal operating in a batch process. Experimental results show that the studied activated carbon have a good adsorption capacity for Ni(II) ions and could reduce the concentrations of it in the groundwater. A maximum removal efficient of Ni(II) was observed at 55°C. The experimental data showed an endothermic and spontaneous process, which was fitted to Langmuir isotherm. Based on our results, we can conclude that it is possible to use GAC and GACA for removing Ni(II) effectively from groundwater. 相似文献
564.
Ahmed S. A. Youssef Magdy M. Hemdan Mohammad E. Azab Samir A. Emara Galal A. Elsayed Rabaa M. Kamel 《Journal of heterocyclic chemistry》2020,57(3):1133-1142
Syringaldehyde was utilized in synthesis of different heterocyclic systems. Some of the synthesized compounds 2 , 7 , 8 , 10 , 11 , and 13 were tested for antioxidant activity where they showed ability to inhibit oxidation in kidney and rat brain homogenates using 2, 2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Also, the activity against cancer was examined using the standard MTT method for two human tumor cell lines namely; mammary gland breast cancer MCF-7 and hepatocellular carcinoma HepG2. The highest activity as antioxidant and antitumor agents was exhibited by compounds 8 and 11 . However, moderate activities were shown by compounds 10 and 13 . While, compounds 2 , 7 showed weak activities. 相似文献
565.
AbstractIn this study, a new series of quinazoline and their annulated derivatives have been synthesized. A number of quiazolinone derivatives substituted at position-3 were prepared from 3, 1-benzoxazinone by the treatment of 3,1-benzoxazinone with different nitrogen nucleophiles such as, hydrazine hydrate, phenylhydrazine, ethanolamine, and cyano acetohydrazide afforded the quinazolinone derivatives 7–11. The reaction of hydrazide derivative 5 with aromatic aldehydes gave the Schiff’s bases derivative 16a–c. Some of the synthesized compounds were tested against the breast cancer cell line (MCF-7). The structures of all the newly synthesized compounds were established based on IR, 1H, 13C NMR, mass spectral data, and elemental analyses. 相似文献
566.
Novel PVC membrane electrodes for the determination of betaine ion based on the formation of betaine-tetraphenylborate (Be-TPB) and betaine-phosphotungstate (Be-PT) ion-exchangers as electroactive materials are described. The sensors show a fast, stable, near Nernstian response for 6.92 x 10(-6) to 7.94 x 10(-3) M and 1.0 x 10(-4) to 1.0 x 10(-2) M betaine hydrochloride (Be.Cl) in case of Be-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 2.95 x 10(-5) to 2.26 x 10(-3) M and 3.16 x 10(-5) to 1.0 x 10(-2) M in case of Be-PT electrode for batch and FIA electrodes, respectively, at 25 degrees C over the pH range of 3.5-10 with a cationic slope of 60.2 and 59.1 mV decade(-1) and a fast potential response of < or =15 s. The lower detection limits are 7.94 x 10(-6) and 3.18 x 10(-5) M Be.Cl for Be-TPB and Be-PT electrodes, respectively. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components other than betaine, of the mixed drug investigated show negligible interference. The electrodes have been applied to the direct potentiometric determination of betaine hydrochloride in water and in a pharmaceutical preparation under batch and FIA conditions. Potentiometric titrations of Be.Cl with NaTPB and PTA as titrants were monitored with the developed betaine electrodes as an end point indicator electrode. The determination of Be.Cl shows an average recovery of 100.8% with mean relative standard deviation of 0.61%. The effect of temperature on the electrodes was also studied. 相似文献
567.
Zeroual Y Kim BS Yang MW Blaghen M Lee KM 《Applied biochemistry and biotechnology》2007,142(3):307-316
Geotrichum sp. strain, which is able to decolorize azo dyes enzymatically, was used in this study for decolorization of synthetics solutions
contaminated by toxic azo dyes orange G, trypan blue, azorubine, and methyl red. The biomass of Geotrichum sp. was immobilized in calcium alginate and polyacrylamide gels and used for the decolorization of tested azo dyes in fluidized
bed bioreactor. The highest specific decolorization rate was obtained when the fungal biomass was entrapped in calcium alginate
beads. Immobilized biomass in calcium alginate continuously decolorized azo dyes after eight repeated batch decolorization
experiments without significant loss of activity whereas polyacrylamide immobilized biomass retained only 10% of its activity
after 4 days of incubation. The effects of some physicochemical parameters such as temperature, pH, and dyes concentration
on decolorization performance of isolated fungal strain were also investigated. 相似文献
568.
We construct a global solution with $\mathcal {C}^{k}$‐estimates for the $\bar{\partial }$‐equation on q‐convex intersections. 相似文献
569.
Garcia P Harrak Y Diab L Cordier P Ollivier C Gandon V Malacria M Fensterbank L Aubert C 《Organic letters》2011,13(11):2952-2955
A variety of allenynamides can undergo cycloisomerization reactions in the presence of silver triflate thus leading to the formation of N-containing heterocycles incorporating cross-conjugated trienes. Access to new dienic 4-piperidinone and azepane motifs was achieved. An extension to one-pot tandem sequences involving silver-catalyzed cycloisomerization/Diels-Alder reaction was also examined. 相似文献
570.
Chemical composition and antibacterial activity of the essential oil of Moroccan Juniperus phoenicea
Fouad B Abderrahmane R Youssef A Rajae H El Fels MA 《Natural product communications》2011,6(10):1515-1518
The antibacterial activity of the essential oil from leaves of Juniperus phoenicea (Cupressaceae) and its chemical constituents were investigated in this study. The essential oil was obtained by hydro-distillation and analyzed by gas chromatography equipped with a flame ionisation detector (GC-FID), and gas chromatography coupled to a mass spectrometer (GC-MS). Sixty-three volatile compounds were identified representing 52 to 92% of the total oil compositions. The main monoterpenes were a-pinene (26.7-78.7%) and 6-3carene (7.6-15.4%). The antibacterial activity of J. phoenicea essential oil, when tested against both Gram-positive and Gram-negative bacteria, showed high activity against all bacteria tested, except Pseudomonas. 相似文献