全文获取类型
收费全文 | 320篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
化学 | 252篇 |
力学 | 13篇 |
数学 | 43篇 |
物理学 | 42篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 28篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2017年 | 15篇 |
2016年 | 27篇 |
2015年 | 19篇 |
2014年 | 11篇 |
2013年 | 42篇 |
2012年 | 25篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 11篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
排序方式: 共有350条查询结果,搜索用时 171 毫秒
341.
Maged Abdeltawab El-Kemary Ibrahim Mahmoud El-mehasseb Shaymaa Elsayed El-Shafey Ola Ibrahim El-Shafey Hind Abdullah Aljohani 《Journal of Dispersion Science and Technology》2018,39(6):911-921
Calcined eggshell (CES) food residue was modified by depositing sol-gel titanium dioxide (TiO2) nanoparticles with narrow size distribution onto it through in situ precipitation and a novel hybrid nano biosorbent, namely TiO2-CES, was obtained. The deposition was characterized and the TiO2-CES nano network was used for efficient adsorption of single azo class anionic dye acid red nylon 57 (AN57) from aqueous solutions and the adsorption was pH dependent. Lower pH favored the sorption at the tested different pHs of 1.0–8.0. The calcination temperature had a cogent influence on the adsorption process. The sorption process reached equilibrium within 40?min, and the mathematical models were positively verified and could be described by a pseudo-second-order pattern, while equilibrium was described with Langmuir-type equation. In addition, the reusability study has proven that 0.5?M HNO3 was efficient enough to desorb AN57 from the hybrid nano sorbent. All results validated that TiO2-CES is Eco-Friendly adsorbent material practical treatment of dyes contaminated water. 相似文献
342.
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
343.
Sherifa M. Abu-Bakr Maha D. Khidre Mohamed A. Omar Samira A. Swelam Hanem M. Awad 《Journal of heterocyclic chemistry》2020,57(2):731-743
A series of furo[3,2-g]chromone derivatives were synthesized via the reaction of furochromone carbaldehyde 1 with amines 3a - d and thioglycolic acid to give thiazolidinones 4a - d . The later react with benzaldehyde/thiourea or hydroxylamine and DMF-DMA in glacial acetic acid to give thiazolopyrimidines 5a - d or thiazoloisoxazoles 6a - d , respectively. Also, the synthesis of α-aminophosphonates via the one-pot reaction of 1 and amines 3a , b were trapped by dialkylphosphites 7a - c afforded the corresponding α-aminophosphonates 8a - f . Applying hexaalkyltriamidophosphites 9a , b to 1 gives alkylidenephosphorane ylides 11a , b in an open structure form. In the present investigation, the in vitro inhibition capacity of compounds ( 4a , 4c , 5b , 5c , 6b - d , 8a - f , and 11a ) was screened in three human cancer cell lines HCT-116, MCF-7, and HepG2. The anticancer activity results revealed that 8b and 8e had more potent cytotoxic inhibition activity against HCT-116 cell line; however, all the tested compounds had obviously less cytotoxic activity against MCF-7 cell line, while 5b , 5c , and 6d were potent against HepG2 cell line compared with that of doxorubicin. 相似文献
344.
345.
346.
Synchronous spectrofluorimetric methods could be successfully adopted for simultaneous determination of Octinoxate (OMC), Avobenzone (AVO), Octyltriazone (OT), and Phenyl benzimidazole sulfonic acid (PBSA) in moisturizing sunscreen lotion, utilizing β-CD as fluorescence enhancer, and determination of Avobenzone (AVO), Homosalate, Tinosorb M and Phenyl benzimidazole sulfonic acid (PBSA) in presence of Octocrylene (OCR) in whitening sunscreen cream, using micellar medium of Sodium Dodecyl Sulfate (SDS) to enhance fluorescence intensity. For first product, zero order synchronous spectrofluorimetric method was used for determination of OMC and AVO, and derivative synchronous spectrofluorimetric technique was utilized for OT and PBSA in quaternary mixture. Linear calibration curves were obtained in a concentration range of 0.5–8 μg mL??1 for OMC and AVO, and in range of 0.05–3 μg mL??1 for OT and 0.001–5 μg mL??1 for PBSA, by measuring the fluorescence at 370, 405, 333.2 and 340.6 nm, respectively. For second product, first derivative synchronous fluorescence method was used for each UV-filter. A linear calibration curves were obtained in a concentration range of 0.5–8 μg mL??1 for AVO, in range of 0.1–8 μg mL??1 for Homosalate, 2–10 μg mL??1 for Tinosorb M and 0.001–5 μg mL??1 for PBSA, by measuring the fluorescence at 409.8, 373, 307.2 and 316.8 nm, respectively. The detection limits are well below the maximum admissible concentration. The proposed methods were validated according to ICH guidelines and successfully applied to determine sunscreens in pure form and in Cosmeceutical formulations. All the results obtained were compared with those of published methods, where no significant difference was observed. 相似文献
347.
The \(\phi ^{6}\)-model expansion method combined with the conformable time-fractional derivative is applied in this paper for finding many new exact solutions including Jacobi elliptic function solutions, solitary wave solutions, trigonometric function solutions and other solutions to the nonlinear conformable time-fractional Schrödinger equation with fourth-order dispersion and parabolic law nonlinearity. This method presents a wider applicability for handling the nonlinear partial differential equations. Comparing our results with the well-known results are given. 相似文献
348.
Non‐isothermal studies by means of thermogravimetric (TG) measurements were carried out using a derivatograph to obtain the number of water molecules per repeat unit of yeast ribonucleic acid (RNA) before and after exposure to γ‐doses of 3 to 600 Gray. IR spectroscopy was utilized to determine which molecular subgroups of RNA adsorb water molecules and to investigate the conformational changes produced in RNA after γ‐irradiation. γ‐Irradiation was found to lead to ring opening or bond cleavage per unit nucleotide, which results in the formation of crosslinked regions (increase in molecular size). Such cleavage becomes more pronounced at doses >300 Gy leading to an increase in the number of water molecules per repeat unit and a decrease in molecular weight (degradation effect). A γ‐dose of 300 Gy may be considered as a critical damaging dose for yeast RNA molecules. 相似文献
349.
Han-Bin Xu Dr. Hua-Ying Chen Dr. Jian Lv Dr. Bin-Bin Chen Ze-Rui Zhou Shuai Chang Ya-Ting Gao Wen-Fei Huang Ming-Jie Ye Zi-Jian Cheng Dr. Mahmoud Elsayed Hafez Prof. Ruo-Can Qian Prof. Da-Wei Li 《Angewandte Chemie (International ed. in English)》2023,62(44):e202311002
Artificially performing chemical reactions in living biosystems to attain various physiological aims remains an intriguing but very challenging task. In this study, the Schiff base reaction was conducted in cells using Sc(OTf)3 as a catalyst, enabling the in situ synthesis of a hollow covalent organic polymer (HCOP) without external stimuli. The reversible Schiff base reaction mediated intracellular Oswald ripening endows the HCOP with a spherical, hollow porous structure and a large specific surface area. The intracellularly generated HCOP reduced cellular motility by restraining actin polymerization, which consequently induced mitochondrial deactivation, apoptosis, and necroptosis. The presented intracellular synthesis system inspired by the Schiff base reaction has strong potential to regulate cell fate and biological functions, opening up a new strategic possibility for intervening in cellular behavior. 相似文献
350.
Dr. Kévin Renault Romain Horion Xavier Maes Maha Rzeigui Dr. Yoann Joyard Dr. Nicolas Maindron Dr. Vincent Tadino Prof. Stéphane Vincent 《European journal of organic chemistry》2023,26(26):e202300307
2-Nitroimidazole based PET tracers are widely used for non-invasive hypoxic tumor diagnosis. In this context, we report here a general method based on a central Mitsunobu reaction to easily access 2-nitroimidazole precursors. Optimization of fluorination conditions is described and successfully applied to the radiofluorination of the 2-nitroimidazole precursors. Moreover, the radiosynthesis of a new potential hypoxia PET tracer is also described. Finally, this article presents a SFC analytical method allowing both an easy monitoring of the fluorination reactions and the measurement of partition coefficients (logP). 相似文献