全文获取类型
收费全文 | 5949篇 |
免费 | 117篇 |
国内免费 | 387篇 |
专业分类
化学 | 5448篇 |
晶体学 | 73篇 |
力学 | 15篇 |
综合类 | 6篇 |
数学 | 9篇 |
物理学 | 902篇 |
出版年
2024年 | 4篇 |
2023年 | 124篇 |
2022年 | 71篇 |
2021年 | 66篇 |
2020年 | 101篇 |
2019年 | 105篇 |
2018年 | 143篇 |
2017年 | 158篇 |
2016年 | 115篇 |
2015年 | 116篇 |
2014年 | 214篇 |
2013年 | 271篇 |
2012年 | 703篇 |
2011年 | 331篇 |
2010年 | 293篇 |
2009年 | 312篇 |
2008年 | 334篇 |
2007年 | 425篇 |
2006年 | 340篇 |
2005年 | 317篇 |
2004年 | 286篇 |
2003年 | 213篇 |
2002年 | 164篇 |
2001年 | 142篇 |
2000年 | 137篇 |
1999年 | 139篇 |
1998年 | 137篇 |
1997年 | 102篇 |
1996年 | 114篇 |
1995年 | 90篇 |
1994年 | 63篇 |
1993年 | 59篇 |
1992年 | 85篇 |
1991年 | 57篇 |
1990年 | 42篇 |
1989年 | 29篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有6453条查询结果,搜索用时 10 毫秒
41.
《Arabian Journal of Chemistry》2020,13(2):3934-3945
A hierarchical nanostructure consisting of uniform copper oxide nanowires vertically grown on three-dimensional copper framework (CuO NWs/3D-Cu foam) was prepared by a two-step synthetic process. The uniform CuO NWs anchored onto the 3D foam exhibited outstanding electrocatalytic activity towards hydrogen peroxide reduction due to the unique one‐dimensional direction with its excellent catalytic activity and large surface area of 3D substrate, which enhanced electroactive sites and charge conductivity. As a result, a wide linear detection range of 1 µM–1 mM, good sensitivity of 8.87 µA/(mM ⋅ cm2), low detection limit of 0.98 µM, and rapid response time of 5 s to hydrogen peroxide were achieved under a working potential of −0.4 V in phosphate buffer solution (pH of 7.4). In addition, the CuO NWs/3D-Cu foam material showed excellent selectivity to hydrogen peroxide and good resistance against poisonous interferents, including ascorbic acid, dopamine, urea, uric acid, and potassium chloride. Furthermore, the CuO NWs/3D-Cu foam presented good reproducibility, stability, and accurate detection for hydrogen peroxide in real sample; therefore, it may be considered to be a potential free-standing hydrogen peroxide sensor in practical analysis applications. 相似文献
42.
We optimized photocatalytic hydrogen production over TiO2-based photocatalyst by varying the dopant (nickel and copper oxide), thin film active area, nature and concentration of sacrificial agents, and light intensity in a photoelectrochemical (PEC) cell/dye-sensitized solar cell (DSSC). Various characterization techniques have been used to investigate the structural, morphological, optical, and PEC behavior of single and codoped TiO2. The TiO2 decorated with both Cu and Ni oxides with active area of 1 cm2 in a mixture of 5 vol % glycerol and 1 M KOH under light intensity of 100 mWcm?2 produced the maximum hydrogen of 338.4 μmol cm?2 for 2 h. The superior photocatalyst performance of this photocatalyst is attributed to its small crystallite size and large pore size, as confirmed by X-ray diffractometer, Transmission electron microscopy (TEM), and surface area of Brunauer-Emmet-Teller (SBET). The absorption edges of this photocatalyst had the highest red shift compared with single doped and pure TiO2 because of more indirect transitions of the photoexcited electrons, greater charge carrier separation, and lower recombination rate. The photoanode active area of 1 cm2 with better photocatalytic performance correlated with the number of defects and grain boundaries. Glycerol shifted the conduction band of the photocatalyst to more negative flat potential compared with others. Increasing the concentration of glycerol further than 5 vol% saturated the photocatalyst active sites, increased photooxidation intermediates of glycerol, and reduced the hydrogen production. The light intensity had the maximum impact on the hydrogen production and could strongly control the number of charge carriers in both the PEC cell and the DSSC. 相似文献
43.
Copper(I) catalyzed radical benzylation and cyclization reaction of tertiary enamides was investigated and 3,3-disubstituted N-Alkyl isoindolin-1-ones were obtained in moderate to good yields. In this reaction, two new C–C bonds were formed in one step with high atom economy. Possible reaction pathway for the formation of the products was also discussed in this paper. 相似文献
44.
A.A. Saranin A.V. Zotov O.A. Utas V.G. Kotlyar C.M. Wei Y.L. Wang 《Surface science》2009,603(18):2874-2878
Basing on the results of the scanning tunneling microscopy (STM) observations and density functional theory (DFT) calculations, the structural model for the Cu magic clusters formed on Si(1 1 1)7 × 7 surface has been proposed. Using STM, composition of the Cu magic clusters has been evaluated from the quantitative analysis of the Cu and Si mass transport occurring during magic cluster converting into the Si(1 1 1)‘5.5 × 5.5’-Cu reconstruction upon annealing. Evaluation yields that Cu magic cluster accommodates 20 Cu atoms with 20 Si atoms being expelled from the corresponding 7 × 7 half unit cell (HUC). In order to fit these values, it has been suggested that the Cu magic clusters resemble fragments of the Cu2Si-silicide monolayer incorporated into the rest-atom layer of the Si(1 1 1)7 × 7 HUCs. Using DFT calculations, stability of the nineteen models has been tested of which five models appeared to have formation energies lower than that of the original Si(1 1 1)7 × 7 surface. The three of five models having the lowest formation energies have been concluded to be the most plausible ones. They resemble well the evaluated composition and their counterparts are found in the experimental STM images. 相似文献
45.
《Journal of Saudi Chemical Society》2022,26(4):101486
Nanotechnology deals with the materials at nanoscale to synthesize nanoparticles. The current study introduced a new green approach for the synthesis of Copper and Nickel hybrid nanoparticles by using Zingiber officinale rhizome extract as a capping and reducing agent. The nanoparticles were physico-chemically characterized by UV–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, Energy-dispersive X-ray spectroscopy, and Scanning electron microscopy. It was revealed by scanning electron micrograph that the Cu-Ni hybrid nanoparticles have spherical geometries with average grain size of 25.12 ± 1.2 nm. Furthermore, biocatalytic and photocatalytic applications of the biosynthesized nanoparticles were assessed. The results of antibacterial assay revealed that Cu-Ni hybrid nanoparticles had an inhibition zones of 28 ± 1.0, 25 ± 0.8, and 25 ± 1.5 mm against P. aeruginosa, E. coli and Proteus vulgaris. Commercially available antibiotics were purchased and coated with Cu-Ni hybrid nanoparticles, it was found that their antimicrobial efficacy was increased twice. To evaluate the antioxidant potential, nanoparticles having a concentration of 200 µg/mL were applied against 2,2-diphenyl-1-picrylhydrazyl free radicals and NPs showed 42.1 ± 0.71 % inhibition. Cu-Ni nanoparticles have shown a dose-dependent cytotoxicity against amastigote and promastigote in anti-leishmanial assay. The synthesized nanoparticles were found biocompatible and safe in nature to be used in vivo, as they showed no significant hemolysis of human red blood cells at their highest concentration. In antidiabetic assay, NPs inhibited alpha-amylase enzyme up to 38.07 ± 0.65 %. An organic crystal violet dye was successfully degraded by the synthesized nanoparticles in photocatalytic assay. Hence, it is concluded that Cu-Ni hybrid nanoparticles can be used both in vitro and in vivo for drug delivery in biomedical research. These nanoparticles can also be used in the remediation of organic dyes as a catalyst. 相似文献
46.
Shubhamoy Chowdhury Arnab Bhattacharya Pinki Saha Smita Majumder E. Suresh 《Journal of Coordination Chemistry》2016,69(24):3664-3676
Employing 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole (bpb) as a monodentate ligand, a new greenish-blue copper(II) complex, [Cu(bpb)2(NO3)2] (1a), has been synthesized. 1a has been characterized analytically and spectroscopically. The X-ray crystal structure of 1a reveals that it adopts a cis disposition with respect to the ligands. The solid state structure of 1a is stabilized by intramolecular offset face-to-face π–π stacking. Non-covalent supramolecular edge-to-face C–H?π interactions with neighboring molecules give 1-D supramolecular chains that further lead to the formation of an assembled 3-D supramolecular metal-organic framework via hydrogen bonding interactions. 1a shows blue fluorescence most likely due to intramolecular offset face-to-face π–π stacking. At room temperature, 1a is one-electron paramagnetic. It shows a rhombic EPR spectrum with g1 = 2.12, g2 = 2.42, and g3 = 2.52 in the solid state at liquid nitrogen temperature. In cyclic voltammetry, 1a displays a one-electron oxidative Cu(II)/Cu(III) couple. Our DFT calculations, corroborate the observed experimental results of 1a. 相似文献
47.
Synthesis and Characterization of Copper(II)–Phosphonate Coordination Chain Array of Metallocages 下载免费PDF全文
Reaction of CuCl2 ·2H2O and 2,4,6‐tris(phosphorylmethyl)mesitylene (H6tpmm) in H2O?DMF solution at room temperature afforded green crystals of [Cu6(H2tpmm)3(H2O)9]·3H2O ( 1 ), which were characterized by Fourier transform infrared (FT‐IR), thermogravimetric (TG) analysis, and powder X‐ray diffraction (PXRD). The solid‐state structure of 1 reveals a one‐dimensional chain array of M4L2 ‐metallocages constituted by the connection of two kinds of metallocage units, namely MC‐A (phosphonate/water‐bridged) and MC‐B (phosphonate‐bridged only), via μ2‐O(phosphonate)? Cu bonds in ABAABA order. The tris‐phosphonate ligand H6tpmm is partially deprotonated to form H2tpmm4?, which displays a cis,cis,cis conformation to bridge six Cu(II) centers via two monodentate phosphonate groups in a η 0:η 0:η 1‐bonding mode and one tridentate phosphonate group in a μ4, η 1:η 1:η 2‐bondingng mode. 相似文献
48.
《中国化学会会志》2017,64(6):607-611
Copper nanoparticles (Cu NPs ) coated with polystyrene (PS ) (Cu NPs @PS ) were prepared by precipitation polymerization. First, Cu NPs were prepared by chemical reduction using cupric acetate as precursor, sodium polyacrylate (PAANa ) as stabilizer, and hydrazine hydrate as reducing agent. Then Cu NPs were coated by precipitation polymerization using styrene as monomer, 3‐(trimethoxysilyl) propyl acrylate as co‐monomer, and 2, 2‐azobisisobutyronitrile (AIBN ) as initiator. Ultraviolet–visible (UV –vis) spectroscopy and transmission electron microscopy (TEM ) results showed that stable composite particles could be synthesized by precipitation polymerization. The amount of PAANa had a significant effect on the size of Cu NPs . The addition of more PAANa resulted in smaller Cu NPs . The spherical Cu NPs became nanowires when increasing the stirring rate from 350 to 700 rpm during precipitation polymerization. Ag NPs @PS with core–shell structure were also prepared by this method, which appears to be universal. 相似文献
49.
Pacheco WF Miguel EM Ramos GV Cardoso CE Farias PA Aucélio RQ 《Analytica chimica acta》2008,625(1):22-27
In this work, a new approach is presented to allow interference-free determination of Cu (II) by stripping voltammetry using the bismuth-film electrode. The addition of hydrogen peroxide to the electroanalytical cell has promoted complete resolution between re-dissolution peaks of Bi (III) and Cu (II). The absence of interference could be evaluated by the correlation coefficient (r > 0.99) between Cu (II) concentration and its shifted current peak (at +212 mV) while achieving a slightly fluctuation of the bismuth current peak at −180 mV. Studies were performed aiming towards the optimum conditions for trace determination of Cu (II) using hydrogen peroxide. The methodology was applied to a real sample (sugarcane spirits) and the results were compared to those from graphite furnace atomic absorption spectrometry. The analytical parameters of merit and the results of the analysis indicated that the analytical methodology could be readily used for trace determination of Cu (II). 相似文献
50.
Clément Lansalot-Matras 《Journal of organometallic chemistry》2008,693(3):393-398
A library of N-tripodal ligands, based on a central nitrogen atom connected to three different functionalized arms, was investigated via a parallel approach for the polymerization of methyl-methacrylate (MMA) in presence of late transition metal salts. Copper salts CuCl2 and Cu(OAc)2 in combination with N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N- (phenylmethyl)amine were detected as efficient catalysts for the syndiotactic polymerization of MMA ([rr] up to 78%). Kinetic studies and X-ray structures of the best catalysts were reported. 相似文献