全文获取类型
收费全文 | 3084篇 |
免费 | 85篇 |
国内免费 | 240篇 |
专业分类
化学 | 2770篇 |
晶体学 | 9篇 |
力学 | 51篇 |
综合类 | 5篇 |
数学 | 30篇 |
物理学 | 544篇 |
出版年
2024年 | 5篇 |
2023年 | 70篇 |
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 85篇 |
2019年 | 107篇 |
2018年 | 77篇 |
2017年 | 146篇 |
2016年 | 120篇 |
2015年 | 103篇 |
2014年 | 163篇 |
2013年 | 153篇 |
2012年 | 248篇 |
2011年 | 255篇 |
2010年 | 167篇 |
2009年 | 238篇 |
2008年 | 224篇 |
2007年 | 228篇 |
2006年 | 205篇 |
2005年 | 116篇 |
2004年 | 106篇 |
2003年 | 86篇 |
2002年 | 46篇 |
2001年 | 68篇 |
2000年 | 44篇 |
1999年 | 31篇 |
1998年 | 37篇 |
1997年 | 30篇 |
1996年 | 19篇 |
1995年 | 11篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有3409条查询结果,搜索用时 15 毫秒
71.
Gold nanotubule membranes were prepared by using electroless deposition of gold within the pores and surfaces of polycarbonate track-etched membranes.And the gold nanotubule membrane was used as an electrode for determination of uric acid in urine samples for the first time.In Britton-Robinson buffer of pH 4.56,uric acid exhibited well-defined differential pulse voltammograms.And the interference between coexistent ascorbic acid and uric acid was overcome owing to the attractive ability of the gold nanotubule electrode to yield a large anodic peak difference ca.0.404 V(vs.SCE).The proposed method was then applied to the determination of uric acid in urine without any pretreatment. 相似文献
72.
Synthesis, Crystal Structure and Spectroscopic Characterization of [Au12(PPh)2(P2Ph2)2(dppm)4Cl2]Cl2 The reaction of [(AuCl)2dppm] (dppm = Ph2PCH2PPh2) with P(Ph)(SiMe3)2 in CHCl3 results in the formation of [Au12(PPh)2(P2Ph2)2(dppm)4Cl2]Cl2 ( 1 ), the crystal structure of which was determined by single crystal X‐ray analysis (space group P21/c, a = 1425.3(3) pm, b = 2803.7(6) pm, c = 2255.0(5) pm, β = 95.00(3)°, V = 8977(3)·106 pm3, Z = 2). The dication in 1 consists of two Au6P3 units built by highly distorted Au3P and Au2P2 heterotetrahedra, connected via four bidentate phosphine ligands. Additionally, the compound was characterized by IR‐, UV‐ and NMR spectroscopy. The 31P{1H} NMR spectrum is discussed in detail. 相似文献
73.
《Journal of organometallic chemistry》2004,689(10):1788-1795
Gold(III) and gold(I) anionic salts mediate the 1,3-dipolar cycloaddition of N-benzyl-C(2-pyridyl)nitrone (2-PyBN) (1) and methyl acrylate (2) (gold 5-10 mol% with respect to the nitrone) decreasing the reaction time and favouring the formation of the exo (cis) isomer. The best catalyst found was Na[AuCl4] (7) able to perform the addition reaction in 56 h (instead of the 96 h required for the control experiment) and giving an endo/exo relation between isomers of 44/56 (as opposed to 73/27, blank reaction). The catalytic activity of several organometallic gold complexes with the radicals pentafluorophenyl (C6F5) or mesityl (2,4,6-(CH3)3C6H2) has been also investigated. In some cases the activity is very similar to that obtained with inorganic salts. With the aim of identifying possible metallic intermediates in the cycloaddition reaction, novel gold(III) and gold(I) nitrone derivatives such as [Au(C6F5)Cl2(2-PyBN)] (21), [Au(C6F5)2Cl(2-PyBN)] (22) and [Au(C6F5)(2-PyBN)] (23) have been prepared and characterized. The reaction between [AuCl3(tht)] and 2-PyBN unexpectedly affords the ionic compound [2-PyBN-H][AuCl4] (5) which also displays catalytic activity and moderate regioselectivity and whose crystal structure has been confirmed by X-ray studies. 相似文献
74.
基于伴刀豆球蛋白固定过氧化物酶无介体新型生物传感器的研制 总被引:2,自引:0,他引:2
以纳米金吸附辣根过氧化物酶,用活化的伴刀豆球蛋白(Con A)将其固定在裸金电极表面,研制成一种新型的无介体辣根过氧化物酶生物传感器。探讨了纳米金的尺寸、组装膜层数、工作电位和pH等实验条件对传感器性能的影响。在pH7.0,外加电压-150mV(vs.SCE)条件下,传感器对H2O2在5.0×10-6~1.2×10-2mol/L范围内呈线性关系;检出限为2.9×10-6mol/L。将传感器用于实际样品的测定,结果良好。 相似文献
75.
Shu-ning Li Xin-lin Yang Wen-qiang Huang 《高分子科学》2007,(6):555-563
Narrow disperse poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine)(poly(EGDMA-co-4-VPy))microspheres were prepared by distillation-precipitation copolymerization of ethyleneglycol dimethacrylate(EGDMA)and 4-vinylpyridine (4-VPy)with 2,2'-azobisisobutyronitrile(AIBN)as initiator in neat acetonitrile.The polymer microspheres containing pyridyl group were then utilized as stabilizer for gold metallic colloids with the diameter around 7 nm,which were prepared by the in situ reduction of gold chloride trihydrate with sodium borohydride through the coordination of the pyridyl group on the gel layer and surface of the microsphere with the gold metallic nano-particles.The catalytic properties of the pyridyl- functionalized microsphere-stabilized gold metallic colloids and the behavior of the stabilized-catalyst for the recycling were investigated with reduction of 4-nitrophenol to 4-aminophenol as a model reaction. 相似文献
76.
Self-assembled monolayer gold electrode for surfactant analysis 总被引:2,自引:0,他引:2
Marc Gerlache Zühre Senturk Guy Quarin Jean-Michel Kauffmann 《Journal of Solid State Electrochemistry》1997,1(2):155-160
A gold electrode coated with a self-assembled monolayer of octane-thiol (SAM/Au) has been used as an amperometric detector
for the determination of surfactants. This detector operated in the presence of a high percentage of organic solvent and was
adapted to an HPLC System. At the SAM/Au, the electrochemical response of an electroactive tracer (potassium ferricyanide)
was completely inhibited, but, in the presence of a cationic surfactant, the electrochemical reduction was progressively restored.
In flow injection analysis, using the SAM/Au in an amperometric flow-through detector polarised at 0.0 V vs Ag/AgCl, a linear
response (i=f{[surfactant]}) was observed for cationic surfactants e.g. cetylpyridinium chloride in the concentration range 2 × 10−6–1 × 10−3 M. The electrochemical data along with the determination of the ion pair stoichiometry between the redox tracer and the surfactant
suggest an electrochemical response related to ion pair formation and governed by electron transfer by tunneling effect.
Received: 28 January 1997 / Accepted: 7 March 1997 相似文献
77.
The behaviour of gold and elements impeding its x-ray fluorescence spectrometric (XRF) determination, namely zinc, lead and arsenic, was studied during their extraction from hydrochloric acid, nitric acid, and aqua regia solutions using tributyl phosphate as a solid extractant [SE(TBP)]. Extraction of gold from pulps after aqua regia leaching was found to be the most favourable approach for the quantitative and selective recovery of gold. The gold distribution ratio, DAu, is ca. 104 ml g?1. For extraction from hydrochloric acid solutions the DAu value also exceeds 104 in the whole range of gold concentrations studied (10?8?10?4 M), but it decreases substantially with increasing extraction temperature, from 5 × 105 ml g?1 at 20°C to 9 × 103 ml g?1 at 70°C. An anomalously high distribution ratio of lead, DPb ≈ 103 ml g?1, was observed during extraction from hydrochloric solutions in the presence of chlorine. This could be explained by the formation of the chloro complexes of lead(IV). An XRF method for the determination of gold in natural samples was developed, which includes back-extraction of gold from SE(TBP) using a hot 0.025 M thiourea solution, providing a thin sample layer for secondary XRF. For 25 g of sample material the limit of determination is 10 ng g?1 (10?6%). The accuracy of the technique was checked using different reference materials. The results agreed within 10%. 相似文献
78.
金纳米微粒与盐酸氯丙嗪相互作用的共振Rayleigh散射光谱研究及其分析应用 总被引:2,自引:3,他引:2
在pH 1.8~3.3的酸性介质中,金纳米微粒本身有一定的共振瑞利散射(RRS)强度,但盐酸氯丙嗪本身的RRS强度十分微弱,当二者共存时,溶液的RRS强度显著增强并出现新的RRS光谱,在280~368 nm之间产生强烈的散射带,其最大散射波长位于368 nm,并在284、440、498 nm处有明显的散射峰。在一定条件下,盐酸氯丙嗪在0~0.08 mg/L范围内与ΔIRRS强度成正比,方法具有较高的灵敏度,对盐酸氯丙嗪的检出限(3σ)达到1.75μg/L。本文考察了反应体系的RRS光谱特征,研究了适宜的反应条件、影响因素及分析化学性质,研究了共存物质的影响,表明方法具有较好的选择性,据此发展了一种用金纳米微粒作RRS探针测定盐酸氯丙嗪的新方法。 相似文献
79.
《Electroanalysis》2003,15(22):1756-1761
Mercaptoundecanoic acid (MUA) and glutathione (GSH) self‐assembled monolayers were prepared on gold‐ wire microelectrode. Cyclic voltammetry was used to investigate the influence of temperature on electrochemical behaviors of Fe(CN)63?/4? and Ru(NH3)63+/2+ at these SAMs modified electrodes in aqueous solution. It is found that temperature shows great influence on electron transfer (ET) and mass transport (MT) for the two SAMs modified electrodes and the influence of temperature depends on the charge properties of the redox couples and terminal groups of SAMs and the structure of the monolayer on gold surface. The temperature can greatly increase MT rate of Fe(CN)63?/4? at both MUA and GSH modified electrodes. However, the increased MT rate doesn't have any effect on the CV's for Fe(CN)63?/4? /MUA system. For Ru(NH3)63+/2+ , temperature can greatly improve the electrochemical reaction in both MUA and GSH modified electrodes, which is ascribed to temperature‐induced diffusion and convection and the electrostatic interaction between Ru(NH3)63+/2+ and negatively charged carboxyl groups on the electrode surface. 相似文献
80.
Elena E. Ferapontova John Castillo Dmitri Hushpulian Vladimir Tishkov Tatiana Chubar Irina Gazaryan Lo Gorton 《Electrochemistry communications》2005,7(12):1291-1297
Direct electron transfer (DET) reactions of recombinant tobacco peroxidase (rTOP), namely direct electroreduction of Compound I/Compound II and heme Fe3+/2+ conversion, were studied on gold electrodes. rTOP of wild type, non-glycosylated, was produced using an Escherichia coli expression system. At pH 5.0, the redox potential for direct electrochemical transformation of the Fe3+/2+ of the peroxidase heme was −143 mV vs. AgAgCl, and 0.26 ± 0.07 pmol of the adsorbed rTOP were in DET contact with the gold electrode. The total amount of the adsorbed rTOP estimated from QCM data was 53 ± 5 pmol/cm2 or 1.67 pmol when referred to the surface area of the electrodes used for electrochemical measurements. Of 1.67 pmol of adsorbed rTOP, only 0.76 pmol were catalytically active. DET between Au and the enzyme was also studied in the reaction of the bioelectrocatalytic reduction of H2O2 by cyclic voltammetry and amperometric detection of H2O2 at +50 mV with rTOP-modified Au electrodes placed in a wall-jet flow-through electrochemical cell. Maximal bioelectrocatalytic current response of the rTOP-modified gold electrodes to H2O2 was observed at pH 5.0 and stemmed from its bioelectrocatalytic reduction based on DET between Au and the active site of rTOP. Kinetic analysis of the DET reactions gave 52% of the adsorbed rTOP molecules active in DET reactions (0.4 pmol of adsorbed catalytically active rTOP, correspondingly), which correlated well with the non-catalytic-voltammetry data. DET was characterised by a heterogeneous ET rate constant of 13.2 s−1, if one takes into account the QCM data, and 19.6 s−1, if the amount of rTOP estimated from the data on DET transformation of Fe3+/2+ couple of rTOP is considered. The sensitivity for H2O2 obtained for the rTOP-modified Au electrodes was 0.7 ± 0.1 A M−1 cm−2. These are the first ever-reported data on DET reactions of anionic plant peroxidases on bare gold electrodes. 相似文献