全文获取类型
收费全文 | 1323篇 |
免费 | 58篇 |
国内免费 | 15篇 |
专业分类
化学 | 969篇 |
晶体学 | 8篇 |
力学 | 68篇 |
数学 | 165篇 |
物理学 | 186篇 |
出版年
2023年 | 10篇 |
2022年 | 55篇 |
2021年 | 69篇 |
2020年 | 44篇 |
2019年 | 65篇 |
2018年 | 70篇 |
2017年 | 41篇 |
2016年 | 61篇 |
2015年 | 52篇 |
2014年 | 82篇 |
2013年 | 136篇 |
2012年 | 96篇 |
2011年 | 93篇 |
2010年 | 71篇 |
2009年 | 53篇 |
2008年 | 54篇 |
2007年 | 58篇 |
2006年 | 51篇 |
2005年 | 45篇 |
2004年 | 22篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1965年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1396条查询结果,搜索用时 31 毫秒
921.
Habib Firouzabadi Hassan Hassani Mostafa Gholizadeh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1417-1422
Zinc dichromate trihydrate (ZnCr2O7·3H2O) is an efficient reagent for the immediate deprotection of aromatic and aliphatic silyl and pyranyl ethers into their corresponding carbonyl compounds in high yields at room temperature under solvent-free conditions. 相似文献
922.
Mostafa Fazly Yannick Sire 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2019,36(2):523-543
We pursue the study of one-dimensional symmetry of solutions to nonlinear equations involving nonlocal operators. We consider a vast class of nonlinear operators and in a particular case it covers the fractional p-Laplacian operator. Just like the classical De Giorgi's conjecture, we establish a Poincaré inequality and a linear Liouville theorem to provide two different proofs of the one-dimensional symmetry results in two dimensions. Both approaches are of independent interests. In addition, we provide certain energy estimates for layer solutions and Liouville theorems for stable solutions. Most of the methods and ideas applied in the current article are applicable to nonlocal operators with general kernels where the famous extension problem, given by Caffarelli and Silvestre, is not necessarily known. 相似文献
923.
Mostafa Abdelrahman Nur Aeni Ariyanti Yuji Sawada Fumitada Tsuji Sho Hirata Tran Thi Minh Hang Mami Okamoto Yutaka Yamada Hiroshi Tsugawa Masami Yokota Hirai Masayoshi Shigyo 《Molecules (Basel, Switzerland)》2020,25(22)
Shallot landraces and varieties are considered an important genetic resource for Allium breeding due to their high contents of several functional metabolites. Aiming to provide new genetic materials for the development of a novel bulb onion cultivar derived from intraspecific hybrids with useful agronomic traits from shallots, the metabolic profiles in the bulbs of 8 Indonesian shallot landraces and 7 short-day and 3 long-day bulb onion cultivars were established using LC–Q-TOF-MS/MS. Principal component analysis, partial least squares discriminant analysis, and dendrogram clustering analysis showed two major groups; group I contained all shallot landraces and group II contained all bulb onion cultivars, indicating that shallots exhibited a distinct metabolic profile in comparison with bulb onions. Variable importance in the projection and Spearman’s rank correlation indicated that free and conjugated amino acids, flavonoids (especially metabolites having flavonol aglycone), and anthocyanins, as well as organic acids, were among the top metabolite variables that were highly associated with shallot landraces. The absolute quantification of 21 amino acids using conventional HPLC analysis showed high contents in shallots rather than in bulb onions. The present study indicated that shallots reprogrammed their metabolism toward a high accumulation of amino acids and flavonoids as an adaptive mechanism in extremely hot tropical environments. 相似文献
924.
The reaction of ethyl benzoylacetate with malononitrile in an oil bath at 120°C gave the condensation product 3. The latter compound underwent a series of heterocyclization to give thiophene, thiazole, pyridine, and pyran derivatives. The structures of the synthesized products were established on the basis of analytical and spectral data. The antitumor evaluation of the newly synthesized products against the six cancer cell lines namely human gastric cancer (NUGC and HR), human colon cancer (DLD1), human liver cancer (HA22T and HEPG2), human breast cancer (MCF), nasopharyngeal carcinoma (HONE1), and normal fibroblast cells (WI38) indicated that many compounds expressed high inhibition against the six cancer cell lines. Compounds 3, 8a, 8c, 14b, 16b, 16c, 16d, 19a, 19b, 20a, 22a, 27b, and 28a were the most cytotoxic compounds among the tested compounds. 相似文献
925.
M. Shamsipur F. Nasri A. Taherpour 《Journal of inclusion phenomena and macrocyclic chemistry》2014,78(1-4):429-436
The complex formation between Zn2+, Cd2+ and Pb2+ ions with macrocyclic ligand, tetrathia12-crown-4 (12S4) was studied in dimethylsulfoxide (DMSO)–nitrobenzene binary mixtures at different temperatures using conductometric and 1H NMR methods. In all cases, 12S4 found to form 1:1 complexes with these cations. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the resulting molar conductance- and chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The stability of the resulting M2+-12S4 complexes found to decrease in the order Pb2+ > Cd2+ > Zn2+. The values of ?H°, ?S° and ?G° for complexation reactions were evaluated from the temperature dependence of formation constants via van’t Hoff method. The obtained results revealed that, in all cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ?H° and ?S° are strongly depend on the nature of medium. There is also a linear relationship between all ΔH° and TΔS° values indicating the existence of entropy–enthalpy compensation in complexation of the three cations and ligand in the solvent systems studied. 相似文献
926.
One‐pot Solvent Free Synthesis of Some Tert‐indolylmethane Amine Derivatives by Fe(HSO4)3 as a Recyclable Catalyst 下载免费PDF全文
Mohammad Rahimizadeh Hossein Eshghi Majid Mokaber‐Esfahani Mostafa Gholizadeh 《中国化学会会志》2014,61(11):1265-1269
Solvent‐free synthesis of 3‐substituted indole derivatives by a one‐pot three‐component coupling reaction between aldehyde, N‐alkyl aniline and indole by Fe(HSO4)3 catalyzed is described. The noticeable features of this protocol are the simplicity of the procedure, easy synthesized, recyclable and inexpensive catalyst, no organic solvent and high yields in relatively short reaction times. 相似文献
927.
Mostafa M. H. Khalil Sayed S. Abd El Rehim H. Abd El Monem 《Journal of Dispersion Science and Technology》2014,35(12):1691-1698
The adsorption of Fe(III) onto glycine-modified chitosan (G@Chs) resin has been investigated. The parameters studied include the effects of pH, contact time, and initial metal ion concentrations by batch method. The optimal pH for the adsorption of Fe(III) was found to be 2.5. The results obtained from equilibrium adsorption studies are fitted in various adsorption models such as Langmuir and Freundlich, and each model parameter were evaluated. Kinetics and thermodynamic parameters of the adsorption process were also investigated. The maximum uptake was found to be 0.9 mmol g?1 at 25°C. 相似文献
928.
Nakisa Zarrabi Ahrabi Mostafa Erfani Kazem Parivar Davood Beiki Amir Reza Jalilian 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):461-469
Neurotensin receptors are overexpressed in several human tumors and can be targets for tumors diagnosis and therapy. In this study, a new neurotensin analogue was labeled with 99mTc via HYNIC and tricine/EDDA as coligands and investigated further. [HYNIC0, Gly7, Lys9, d-Tyr11]-Neurotensin (7–13) was synthesized using a standard Fmoc strategy. Labeling with 99mTc was performed at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of humane serum at 37 °C up to 24 h. The receptor bound internalization and externalization rates were studied in neurotensin receptor expressing HT-29 cells. Biodistribution of radiopeptide was studied in nude mice bearing HT-29 tumor. Labeling yield of 98.6 ± 0.54 % (n = 3) was obtained corresponding to a specific activity of 81 MBq/nmol. Peptide conjugate showed good stability in the presence of human serum. The radioligand showed specific internalization into HT-29 cells (12.43 ± 0.52 % at 4 h). In biodistribution studies, a receptor-specific uptake was observed in neurotensin receptor positive organs so that after 1 h the uptakes in mouse intestine and tumor were 0.87 ± 0.16 and 0.63 ± 0.12 % ID/g respectively. 相似文献
929.
Mohammad Behbahani Mostafa Najafi Mostafa M. Amini Omid Sadeghi Akbar Bagheri Mani Salarian 《Mikrochimica acta》2013,180(9-10):911-920
We are introducing nanoporous fructose (np-F) modified with dithizone as a new solid-phase for extraction of heavy metals ions including cadmium(II), copper(II), nickel(II) and lead(II). Effects of pH value, flow rates, type, concentration and volume of the eluent, breakthrough volume, and of other ions were studied. Under optimized conditions, the extraction efficiency is >97 %, and the limits of detection are 0.025, 0.15, 0.5 and 1.2 ng mL?1 for the ions of cadmium, copper, nickel, and lead, respectively, and the adsorption capacities for these ions are 101, 81, 74 and 178 mg g?1. The modified np-F sorbent was characterized by thermogravimetric analysis, differential thermal analysis, transmission electron microscopy, Fourier transform infrared spectrometry, X-ray diffraction, and nitrogen adsorption surface area (BET) measurements. Figure
We are introducing nanoporous fructose (np-F) modified with dithizone as a new solid-phase for extraction of heavy metals ions including cadmium(II), copper(II), nickel(II) and lead(II). This SPE technique was successfully applied for separation, determination, and preconcentration of cadmium, copper, nickel and lead in biological, food and environmental water samples 相似文献
930.
A wide range of mono‐ and disubstituted dihydroquinazolinones were synthesised via condensation of isatoic anhydride, primary amines, or ammonium salts with aromatic aldehydes in the presence of montmorillonite K‐10. The catalyst is reusable and could be recycled for several runs without any decrease in its efficiency. 相似文献