全文获取类型
收费全文 | 6240篇 |
免费 | 368篇 |
国内免费 | 46篇 |
专业分类
化学 | 4293篇 |
晶体学 | 71篇 |
力学 | 265篇 |
数学 | 938篇 |
物理学 | 1087篇 |
出版年
2023年 | 48篇 |
2022年 | 93篇 |
2021年 | 212篇 |
2020年 | 150篇 |
2019年 | 262篇 |
2018年 | 222篇 |
2017年 | 161篇 |
2016年 | 327篇 |
2015年 | 206篇 |
2014年 | 329篇 |
2013年 | 626篇 |
2012年 | 390篇 |
2011年 | 395篇 |
2010年 | 279篇 |
2009年 | 270篇 |
2008年 | 286篇 |
2007年 | 258篇 |
2006年 | 248篇 |
2005年 | 202篇 |
2004年 | 178篇 |
2003年 | 155篇 |
2002年 | 197篇 |
2001年 | 82篇 |
2000年 | 123篇 |
1999年 | 70篇 |
1998年 | 57篇 |
1997年 | 58篇 |
1996年 | 43篇 |
1995年 | 41篇 |
1994年 | 48篇 |
1993年 | 44篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 26篇 |
1989年 | 40篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 22篇 |
1985年 | 39篇 |
1984年 | 35篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1973年 | 10篇 |
排序方式: 共有6654条查询结果,搜索用时 875 毫秒
971.
M. Dolores Garrido Carolina García-Llacer Jamal El Haskouri María D. Marcos Juan F. Sánchez-Royo Aurelio Beltrán 《Journal of Coordination Chemistry》2018,71(6):776-785
AbstractThe use of atrane complexes as hydrolytic precursors enables the homogeneous incorporation of manganese (25 ≤ Si/Mn ≤ 48) throughout the porous walls of the nanoparticles of a surfactant-templated bimodal mesoporous silica (UVM-7). The subsequent leaching of the manganese nanodomains allows adding controlled microporosity to the host silica framework. The resulting final silica material presents three pore systems structured at different length scales: interparticle textural-type macroporosity (ca. 43.2 nm), ordered intraparticle mesoporosity (ca. 2.63 nm; after template removal), and well-dispersed microporosity (< 2 nm; as consequence of the lixiviation of the Mn-rich domains). The good dispersion of the guest element (Mn) in the silica intermediate provided by the atrane route is responsible for the disordered but regular microporosity achieved. 相似文献
972.
Mahmoud F. Ismail 《合成通讯》2018,48(8):892-905
Dodecanoyl isothiocyanate 1 was utilized for the construction of thioureido, 2-thioxo-2,3-dihydroquinazolin-4(1H)-one, benzo[d]-1,3-thiazin-4(H)-one and 3-amino quinazolin-4(3H)-one derivatives 2, 3, 4, and 5 respectively. However, N′-(2-cyanoacetyl) dodecanehydrazide 6 was also used as a key starting material for the construction of a variety of new pyrazolone, pyrazole, thiadiazole, pyridazine, chromeno[2,3-c]pyrazole, and dithiolane derivatives 7, 9, 12, 15, 18, and 20, respectively. The newly synthesized compounds were characterized by elemental analyses and spectral data (IR, 1H NMR, and mass spectra). Some of the newly synthesized compounds bearing heterocyclic moieties were tested for antioxidant activity as reflected in their ability to inhibit oxidation in rat brain and kidney homogenates using 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) inhibition. Also, in vitro anticancer activity was examined using the standard (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) (MTT) method against a panel of two human tumor cell lines namely; hepatocellular carcinoma HepG2 and mammary gland breast cancer MCF-7. Compounds 12 and 16b exhibited the highest activities as antioxidant and antitumor agents. Meanwhile, compounds 7 and 20 showed moderate activities and the rest of the tested compounds showed weak activities. 相似文献
973.
An electrochemical nanoaptasensor is described that is based on the use of a glassy carbon electrode (GCE) modified with electrodeposited silver nanoparticles (AgNPs). An aptamer (Apt) against trinitrotoluene (TNT) was then immobilized on the AgNPs. The addition of TNT to the modified GCE leads to decrease in peak current (typically measured at a potential of ?0.45 V vs. Ag/AgCl) of riboflavin which acts as an electrochemical probe. Even small changes in the surface (as induced by binding of Apt to TNT) alter the interfacial properties. As a result, the LOD is lowered to 33 aM, and the dynamic range extends from 0.1 fM to 10 μM without sacrificing specificity. 相似文献
974.
The authors describe a method for functionalization of gold nanoparticles (AuNPs) with the supramolecular host molecule, curcubit[7]uril (CB[7]) which can bind rhodamine B (RhB). The fluorescence of RhB is quenched by the AuNPs via surface energy transfer. On addition of ATP, a dimeric RhB-ATP complex is formed and RhB is pushed out of CB[7]. Hence, fluorescence increases by a factor of 8. This fluorescence recovery effect has been utilized to develop a new detection scheme for ATP. The assay, measured at fluorescence excitation and emission wavelengths of 500 nm and 574 nm respectively, works in the 0.5–10 μM concentration range and has a 100 nM detection limit. The method is not interfered by UTP, GTP, CTP, TTP, ascorbic acid and glutathione. 相似文献
975.
Hassan Shahraki Mahmoud Tabrizchi Hossein Farrokhpour 《Journal of the Iranian Chemical Society》2018,15(4):863-870
In this work, a new long-life alkali ion source is proposed that is based on alkali halide salts doped in nano-γ-alumina (Al2O3). Depending on the polarity, the ion source produces both alkali and halide ions. The source was characterized using different techniques such as scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR), and ion mobility spectrometry (IMS). SEM images confirm a strong interaction between the alkali halide (MX) and nano-γ-alumina. The average particle size of the doped nanoparticles was calculated to be 44 nm by TEM. Formation of new phases (KAlCl2O and K3AlF6) was confirmed by XRD and that of Al–O–K group in the synthesized particles by FT-IR. Alkali and halide ion peaks were observed by IMS in the positive and negative modes, respectively. The lifetime of the ion source for different alkali halides was measured to range from 216 to 960 h. The total ion current emitted from the source was about 2 µA, while it was 12 nA at the collector plate of the IMS. Finally, application of the new source in ion mobility spectrometry was demonstrated by observing ion mobility spectra of compounds ionized via cation and anion attachment reaction. 相似文献
976.
Rabab Boyaala Rafika El Ati Mohamed Khoutoul Mohamed El Kodadi Rachid Touzani Belkheir Hammouti 《Journal of the Iranian Chemical Society》2018,15(1):85-92
In the present work, catecholase activity is presented. The complexes were prepared by condensation of the organic ligand pyrazolyl L 1 –L 4 and copper(II) ion in situ. The pyrazolyl compounds L 1 –L 4 used in this study are: L 1 is (3,5-dimethyl-pyrazol-1-ylmethyl)-(4-methyl-pyridin-2-yl)-pyrazol-1-ylmethyl-amine; L 2 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-pyrazol-1-ylmethyl-amino]-phenyl}-ethanone; L 3 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-phenyl}-ethanone, and L 4 is 2-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-6-methyl-pyrimidin-4-ol, and copper ions salts Cu(II) are (Cu(CH3COO)2, CuCl2, Cu(NO3)2 and CuSO4). In order to determine factors influencing the catecholase activity of these complexes, the effect of ligand nature, ligand concentration, nature of solvent and nature of counter anion has been studied. The best activity of catechol oxidation is given by the combination formed by one equivalent of ligand L 2 and one equivalent of Cu(CH3COO)2 in methanol solvent which is equal to 9.09 µmol L?1 min?1. The Michaelis–Menten model is applied for the best combination, to obtain the kinetic parameters, and we proposed the mechanism for oxidation reaction of catecholase. 相似文献
977.
Khalid Mahmoud Hassan 《Journal of the Iranian Chemical Society》2018,15(5):1007-1014
A highly sensitive sensor based on Ni nanoparticles/poly (1,2-diaminoanthraquinone) modified electrode was fabricated at glassy carbon (GC) electrode (Ni/PDAAQ@GC ME) using cyclic voltammetry technique. The incorporation of nickel (II) ions nanoparticles (Ni NPs) followed by anodic polarization process was achieved. Surface morphologies of both PDAAQ@GC ME and Ni/PDAAQ@GC MEs were studied by scanning electron microscope. Ni/PDAAQ@GC ME was tested for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) by square wave voltammetry technique. The ME showed excellent electrocatalytic activity toward electrooxidation of these biomolecules in their single, binary and ternary systems in alkaline 0.1 M NaOH solutions. Experiment revealed that the low detection limits (LOD) for AA, DA and UA were 0.11, 0.072 and 1.2 µM in single system, respectively, and 0.069, 0.29 and 0.12 µM in ternary system, respectively. 相似文献
978.
Subir Goswami Prof. Dr. Kenichi Harada Prof. Dr. Mohamed F. El‐Mansy Dr. Rajinikanth Lingampally Prof. Dr. Rich G. Carter 《Angewandte Chemie (International ed. in English)》2018,57(29):9117-9121
The efficient, 12–14 step (LLS) total synthesis of (?)‐halenaquinone has been achieved. Key steps in the synthetic sequence include: (a) proline sulfonamide‐catalyzed, Yamada–Otani reaction to establish the C6 all‐carbon quaternary stereocenter, (b) multiple, novel palladium‐mediated oxidative cyclizations to introduce the furan moiety, and (c) oxidative Bergman cyclization to form the final quinone ring. 相似文献
979.
Faten I. Abou El Fadl Nabila A Maziad Sabrnal H El-Hamouly H. R. Hassan 《高分子科学杂志,A辑:纯化学与应用化学》2018,55(2):107-115
Using polymer hydrogels and nanocomposites hydrogels still promising materials for many applications. Polyvinyl pyrrolidone (PVP) has been used with various polymers synthetic and natural for different applications. In this study PVP and hydroxyl ethyl methacrylate (HEMA) copolymer hydrogels were prepared by the aid of gamma radiation and the PVP/HEMA nanocomposite hydrogels were obtained by in situ adsorption and reduction method of iron salts and silver nitrates (AgNO3) to form PVP/HEMA-Fe3O4 and PVP/HEMA-Ag nanocomposites. The prepared hydrogels and the formed nanoparticles were studied by various techniques; FTIR, TEM, SEM and also the gel content and swelling behavior were evaluated. The prepared hydrogels and nanocomposites hydrogels were examined as drug delivery systems for Ciprofloxacin HCl as model drug. The PVP/HEMA-Fe3O4 nanocomposite gave the suitable load and release behavior towards Ciprofloxacin HCl. 相似文献
980.
Dr. Alexandre Barrozo Prof. Mohamed Y. El‐Naggar Prof. Anna I. Krylov 《Angewandte Chemie (International ed. in English)》2018,57(23):6805-6809
Shewanella oneidensis MR‐1 gains energy by extracellular electron transfer to solid surfaces. They employ c‐type cytochromes in two Mtr transmembrane complexes, forming a multiheme wire for electron transport across the cellular outer membrane. We investigated electron‐ and hole‐transfer mechanisms in the external terminal of the two complexes, MtrC and MtrF. Comparison of computed redox potentials with previous voltammetry experiments in distinct environments (isolated and electrode‐bound conditions of PFV or in vivo) suggests that these systems function in different regimes depending on the environment. Analysis of redox potential shifts in different regimes indicates strong coupling between the hemes via an interplay between direct Coulomb and indirect interactions through local structural reorganization. The latter results in the screening of Coulomb interactions and explains poor correlation of the strength of the heme‐to‐heme interactions with the distance between the hemes. 相似文献