全文获取类型
收费全文 | 1145篇 |
免费 | 87篇 |
国内免费 | 26篇 |
学科分类
数理化 | 1258篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 29篇 |
2021年 | 48篇 |
2020年 | 78篇 |
2019年 | 75篇 |
2018年 | 108篇 |
2017年 | 77篇 |
2016年 | 84篇 |
2015年 | 59篇 |
2014年 | 91篇 |
2013年 | 122篇 |
2012年 | 101篇 |
2011年 | 83篇 |
2010年 | 55篇 |
2009年 | 47篇 |
2008年 | 58篇 |
2007年 | 43篇 |
2006年 | 21篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1258条查询结果,搜索用时 312 毫秒
991.
In this paper, we present a new generalized modular version of the Meir–Keeler fixed point theorem endowed with an orthogonal relation. Our results improve the results of (Eshaghi Gordji et al., On orthogonal sets and Banach fixed point theorem, Fixed Point Theory, 2017). Finally, this result is applied to the existence and uniqueness of solutions to perturbed integral equations in modular function spaces. 相似文献
992.
Nafiseh Moazzen Mohammadreza Khanmohammadi Amir Bagheri Garmarudi Maryam Kazemipour Mehdi Ansari Dogaheh 《Journal of the Iranian Chemical Society》2017,14(3):671-680
Fourier transform infrared spectroscopy coupled with chemometrics was employed to detect packaging polylactic acid-based biocomposite samples adulterated with polypropylene (PP) 30–45% and linear low-density polyethylene 2–10%. Principal component analysis, soft independent modeling of class analogy (SIMCA) and partial least square discriminate analysis (PLS-DA) chemometric techniques were utilized to classify samples in different classes. Totally, 362 samples were modeled in three different classes (two adulterated and one non-adulterated). The obtained results revealed that PLS-DA is the most suitable chemometric approach for prediction of probable adulteration in biocomposite samples with reliable specificity and selectivity. It could provide 99% correct class prediction rate between non-adulterated biocomposite samples and adulterated ones, while SIMCA methods provided 73.33% prediction accuracy in classification. 相似文献
993.
994.
Maryam Bordbar Somaye Jafari Ali Yeganeh-Faal Bahar Khodadadi 《Journal of the Iranian Chemical Society》2017,14(4):897-906
Mn-doped ZnO single-crystal micronuts were synthesized via hydrothermal method in an hexamethylenetetramine aqueous solution. These micronuts are of wurtzite crystal structure. The effects of Mn doping amount and precursor concentration on the structural, optical properties and photocatalytic activity have been investigated. The synthesized Mn-doped ZnO was characterized by X-ray powder diffraction, field emission scanning electron microscopy (FESEM), UV–Vis absorption and photoluminescence spectroscopy. The structural analyses based on X-ray diffraction revealed the absence of Mn-related secondary phases. According to FESEM results, the length of ZnO micronuts was in the range of 5–8 μm. The band gap energy increased on increasing Mn doping concentration. The photocatalytic activity was studied by degradation of methyl orange aqueous solution, which showed that the Mn-doped ZnO micronuts prepared in precursor concentration of 0.1 M and 4% Mn doping had the highest photocatalytic activity. The effects of crystal defect and band gap energy on photocatalytic activity of Mn-doped ZnO samples were studied in different precursors and Mn doping amounts. 相似文献
995.
Abolfazl Bezaatpour Sahar Khatami Kamellia Nejati 《Journal of the Iranian Chemical Society》2017,14(10):2105-2115
In this work, paramagnetic Fe3O4/SiO2 nanoparticles were synthesized, characterized and functionalized with dioxo-Mo(VI) tetradentate Schiff base complex and characterized using IR spectroscopy, X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, diffuse reflectance spectroscopy and atomic absorption spectroscopy. Catalyst was used for the selective epoxidation of cyclooctene, cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilbene using tert-butyl hydroperoxide as oxidant in 1,2-dichloroethane. This catalyst is efficient for oxidation of cyclooctene with a 100% selectivity for epoxidation with 100% conversion in 1 h. After the reaction, the magnetic nanocatalyst was easily separated by simply applying an external magnetic field and was used at least five successive times without significant decrease in conversion.
相似文献
996.
Aslak S. Hellestø Maryam Ghaffari Alex C. Hoffmann 《Journal of Dispersion Science and Technology》2017,38(5):611-620
In this study, we investigate numerically the shear-induced agglomeration of cohesive inertial particles in a simple shear flow. We conduct a series of numerical simulations by implementing a soft-sphere collision model. Post-processing tools are developed in-house to analyze the results of the simulations in terms of transient and terminal numbers of primary particles and agglomerates, magnitudes and distributions of agglomerate size, and fractal dimension as functions of the salient physical parameters. The obtained numerical results compared with existing transient models suggest that, as the system transitions from formation of duplets to larger agglomerates, in most cases the number of agglomerates in the system reveals clear maxima. The results also show evidence of agglomerate densification, as weaker agglomerates with lower fractal dimensions are broken up and stronger ones with higher fractal dimensions are formed. Furthermore, we found that a simple theoretical model proposed by, among others, Chimmili et al. is able to predict the temporal development of the agglomerate size properly. 相似文献
997.
Zeinab Moradi-Shoeili Maryam Zare Serdar Akbayrak Saim Özkar 《Transition Metal Chemistry》2017,42(4):357-363
A molybdenum(VI) oxido-diperoxido complex of salicylidene 2-picoloyl hydrazine (sal-phz) was synthesized and successfully grafted onto chloro-functionalised Fe3O4 nanoparticles. The resulting heterogeneous and magnetically recoverable nanoscale catalyst MoO3(sal-phz)/Fe3O4 was characterized by physicochemical and spectroscopic techniques. The activity of this heterogeneous catalyst for the oxidation of olefins to corresponding epoxides was efficiently increased by increasing the reaction temperature up to 95 °C. The nanocatalyst proved to be efficient for the selective epoxidation of a variety of alkenes using t-BuOOH with high conversion and selectivity. Leaching and recycling tests showed that the nanocatalyst can be reused at least six times without significant decrease in efficiency. 相似文献
998.
Maryam Heydari Mahboube Eslami Moghadam AliAkbar Tarlani Hossein Farhangian 《Applied biochemistry and biotechnology》2017,182(1):110-127
Imidazole ring is a known structure in many natural or synthetic drug molecules and its metal complexes can interact with DNA and do the cleavage. Hence, to study the influence of the structure and size of the ligand on biological behavior of metal complexes, two water-soluble Pd(II) complexes of phen and FIP ligands (where phen is 1,10-phenanthroline and FIP is 2-(Furan-2-yl)-1H–Imidazo[4,5-f][1, 10]phenanthroline) with the formula of [Pd(phen)(FIP)](NO3)2 and [Pd(FIP)2]Cl2, that were activated against chronic myelogenous leukemia cell line, K562, were selected. Also, the interaction of these anticancer Pd(II) complexes with highly polymerized calf thymus DNA was extensively studied by means of electronic absorption, fluorescence, and circular dichroism in Tris-buffer. The results showed that the binding was positive cooperation and [Pd(phen)(FIP)](NO3)2 (K f = 127 M-1 G = 1.2) exhibited higher binding constant and number of binding sites than [Pd(FIP)2]Cl2 (K f = 13 M-1 G = 1.03) upon binding to DNA. The fluorescence data indicates that quenching effect for [Pd(phen)(FIP)](NO3)2 (K SV = 58 mM?1) was higher than [Pd(FIP)2]Cl2 (K SV = 12 mM?1). Also, [Pd(FIP)2]Cl2 interacts with ethidium bromide-DNA, as non-competitive inhibition, and can bind to DNA via groove binding and [Pd(phen)(FIP)](NO3)2 can intercalate in DNA. These results were confirmed by circular dichroism spectra. Docking data revealed that longer complexes have higher interaction energy and bind to DNA via groove binding. 相似文献
999.
Mohamed Atia Dóra Bogdán Maryam Brügger Norbert Haider Péter Mátyus 《Tetrahedron》2017,73(23):3231-3239
Ethyl 4-oxo-3,4-dihydroquinazoline-2-carboxylate reacts selectively with trimethylaluminium-activated 2-amino- or 4-aminobenzoic acid ethyl esters to give the corresponding anilides without self-condensation of the aminobenzoate building blocks. After propargylation, the quinazolinones were treated with Hendrickson's reagent, but only the para-substituted ester was found to undergo the expected [4 + 2] cycloaddition reaction, affording a new Luotonin A derivative. A different regioselectivity was observed with the ortho-substituted ester which affords a benzoxazinone under identical conditions. When the ester group in the ortho-substituted intermediate is replaced with a nitrile function, the outcome of the reaction with Hendrickson's reagent depends on the absence or presence of a base (DBU), yielding either a triphenylphosphonium-substituted iminobenzoxazine or a 4-cyano-substituted Luotonin A derivative. 相似文献
1000.
Sayed Zia Mohammadi Hadi Beitollahi Maryam Mousavi 《Russian Journal of Electrochemistry》2017,53(4):374-379
A carbon paste electrode that was chemically modified with 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid (3,4-AA) was used as a selective electrochemical sensor for the detection of hydroxylamine. Cyclic voltammetry (CV), choronoamperometry (CHA) and square wave voltammetry (SWV) were used to investigate oxidation of hydroxylamine in aqueous solution. Under optimized concentration the electrocatalytic oxidation current peak for hydroxylamine increased linearly with concentration in the range of 0.025–10.0 μM. The detection limits for hydroxylamine was 0.012 μM. Finally, the modified electrode was applied to detection hydroxylamine in water samples. 相似文献