全文获取类型
收费全文 | 3240篇 |
免费 | 393篇 |
国内免费 | 236篇 |
专业分类
化学 | 2587篇 |
晶体学 | 11篇 |
力学 | 320篇 |
综合类 | 51篇 |
数学 | 96篇 |
物理学 | 804篇 |
出版年
2024年 | 11篇 |
2023年 | 48篇 |
2022年 | 63篇 |
2021年 | 116篇 |
2020年 | 118篇 |
2019年 | 111篇 |
2018年 | 70篇 |
2017年 | 121篇 |
2016年 | 136篇 |
2015年 | 151篇 |
2014年 | 134篇 |
2013年 | 265篇 |
2012年 | 234篇 |
2011年 | 149篇 |
2010年 | 149篇 |
2009年 | 178篇 |
2008年 | 150篇 |
2007年 | 214篇 |
2006年 | 195篇 |
2005年 | 164篇 |
2004年 | 159篇 |
2003年 | 115篇 |
2002年 | 89篇 |
2001年 | 93篇 |
2000年 | 81篇 |
1999年 | 68篇 |
1998年 | 81篇 |
1997年 | 60篇 |
1996年 | 46篇 |
1995年 | 63篇 |
1994年 | 43篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 50篇 |
1990年 | 42篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有3869条查询结果,搜索用时 15 毫秒
991.
《Electroanalysis》2005,17(4):319-326
Thallium hexacyanoferrate films have been prepared from various aqueous electrolyte solutions using consecutive cyclic voltammetry. The cyclic voltammograms recorded the direct deposition of thallium hexacyanoferrate films from the mixing of Tl3+ and [Fe(CN)6]3? ions from solutions of seven cations: Li+, Na+, K+, Rb+, Cs+, H+, and Tl+. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the thallium hexacyanoferrate films. The thallium hexacyanoferrate film shows a single redox couple with a formal potential between +0.6 V and +1.2 V, and shows a cation effect (H+, Li+, Na+, K+, Rb+, Cs+, and Tl+). A mixed film and a two‐layered modified electrodes composed of a thallium hexacyanoferrate film with cobalt(II) hexacyanoferrate film were prepared. 相似文献
992.
Michael Schindler Frank C. Hawthorne Rory A. Kutluoglu Petre Mandaliev Roger H. Mitchell 《Journal of solid state chemistry》2006,179(8):2616-2628
The potential insertion-electrode compounds Na1.2[V3O8] (NaV) and Na0.7Li0.7[V3O8] (NaLiV) were synthesized from mixtures of Na2CO3, Li2CO3 and V2O5, which were melted at 750° and subsequently cooled to room temperature. The structures of NaV and LiV contain sheets of polymerized (VOn) polyhedra, which are topologically identical to the sheet of polymerized polyhedra in Li1.2[V3O8] (LiV). Vanadium occurs in three different coordination environments: [2+3] V(1), [2+2+2] V(2) and [1+4+1] V(3). Calculated bond-valence sums indicate that V4+ occurs preferentially at the V(3) site, which agrees with the general observation that [6]-coordinated V4+ prefers [1+4+1]-rather than [2+2+2]-coordination. The M-cations Na and Li occur at three distinct sites, M(1), M(2) and M(3) between the vanadate sheets. The M(1)-site is fully occupied and has octahedral coordination. The M(2) sites are partly occupied in NaV and NaLiV, in which they occur in [4]- and [6]-coordination, respectively. Li partly occupies the M(3) site in NaLiV, in which it occurs in [3]-coordination. The M(2) and M(3) sites in NaLiV occur closer to the vanadate sheets than the M(2) sites in NaV and LiV. The shift in these cation positions is a result of the larger distance between the vanadate sheets in NaLiV than in LiV, which forces interstitial Li to move toward one of the vanadate sheets to satisfy its coordination requirements. Bond-valence maps for the interstitial cations Na and Li are presented for NaV, NaLiV and LiV. These maps are used to determine other potential cation positions in the interlayer and to map the regions of the structure where the Na and Li have their bond-valence requirements satisfied. These regions are potential pathways for Na and Li diffusion in these structures, and are used to explain chemical diffusion properties of Na and Li in the Na-Li-[V3O8] compounds. 相似文献
993.
Mei-Chun Lu 《Analytica chimica acta》2004,522(1):25-33
The electrochemical and electrogenerated chemiluminescence (ECL) properties of indium tin oxide (ITO) electrodes modified with poly(4-vinylpyridine) (PVP)-bound Ru(bpy)2Cl+ (where bpy = 2,2′-bipyridine) have been studied. In a sodium oxalate solution, two irreversible oxidation waves as well as two ECL emission waves were observed during the potential scan in the range 0.4-1.4 V (versus Ag/AgCl/saturated KCl reference). The first ECL wave appeared at ca. 0.8 V, which was caused by the excited-state Ru2+* generated through a bimolecular redox reaction between electrogenerated Ru3+ and the strong reducing agent, C−O2. The latter was formed via a Ru3+-mediated oxidation of oxalate. Direct oxidation of oxalate was not involved in the first ECL process. The second ECL wave started at ca. 1.1 V, which was also from the excited-state Ru2+* generated via the redox reaction between Ru3+ and C−O2. However, both direct and Ru3+-mediated oxidation of oxalate contributed to the formation of C−O2. The important role of the direct oxidation of oxalate in the ECL mechanism of PVP-bound Ru(bpy)2Cl+/oxalate system was demonstrated. The relative contribution of direct oxidation of oxalate to the observed ECL depended upon the surface concentration of PVP-bound Ru2+, the concentration of oxalate and the electrode potential applied. 相似文献
994.
The effect of β-CD and α-CD on the electrochemical behaviour of H2A and HA− on platinum is studied. The adsorption of β-CD on this electrode is demonstrated and proved to be dependent on the base electrolyte composition. The maximum adsorption coverage was reached in phosphate solution at pH 6.95. The homogeneous H2A---β-CD complex formation produced a decrease in the oxidation current and a positive shift in the oxidation peak potential. These effects are predominant in acid solutions. In neutral solutions the opposite behaviour is observed, i.e. an increase in the oxidation current at lower oxidation potentials. The presence of a parallel oxidation route for the vitamin involving strongly adsorbed CO residues is considered, and evidence for a decrease in COad in the presence of β-CD was given by variations in hydrogen adsorption charges. This fact, more important in neutral solutions, must be responsible for the catalytic effect observed. α-CD was not adsorbed, neither did it modify the electro-oxidation behaviour of H2A and HA−. 相似文献
995.
996.
Adina Arvinte Federica Valentini Antonio Radoi Fabiana Arduini E. Tamburri Lucian Rotariu Giuseppe Palleschi Camelia Bala 《Electroanalysis》2007,19(14):1455-1459
In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10?5 to 2.1×10?3 mol L?1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm2), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors. 相似文献
997.
《Electroanalysis》2006,18(18):1833-1837
Proof‐of‐concept is shown for the indirect electrochemical detection of model amphetamines, D ‐amphetamine sulfate and pseudoephedrine, based on the labeling of the amphetamine models with sodium 1,2‐naphthoquinone‐4‐sulfonate (NQS). The presence of the amphetamine models is monitored via either the reduction in the magnitude of the voltammetric peak corresponding to the electrochemical reduction of the quinone functionality of the sodium 1,2‐naphthoquinone‐4‐sulfonate or via growth of a new voltammetric peak related to reaction between the amphetamine model and NQS, both of which are well resolved from one another. The protocol is shown to be successful in artificial saliva and authentic human oral (saliva) fluid. Such a protocol may be particularly attractive for roadside testing of amphetamines in drug drivers. 相似文献
998.
A. Sánchez A. Zapardiel F.López de Prado E. Bermejo M. Moreno J. A. Pérez‐López M. Chicharro 《Electroanalysis》2007,19(16):1683-1688
A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10?7 to 1.0×10?4 mol L?1). A detection limit of 1.4×10?8 mol L?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples. 相似文献
999.
Antonella Curulli Stella Nunziante Cesaro Adriana Coppe Claudia Silvestri Giuseppe Palleschi 《Mikrochimica acta》2006,152(3-4):225-232
Single-Walled Carbon Nanotubes (SWCNTs) possess a wealth of exceptional structural, mechanical and electronic properties.
These have made them potentially useful for applications in nanotube-reinforced materials, nanoelectronic devices, field emitters,
probe tips for SPM, as well as for sensors, biosensors, and actuators.
However, manipulation and processing of SWCNTs has been limited by their insolubility in most common solvents, although some
dissolution has recently been obtained. Their chemical modification might pave the way to many useful applications, including
the preparation of composite materials or the immobilization of biological molecules as enzymes (i.e., for biosensors and
electrochemical sensors). Attachment of oxygen-containing functional groups (i.e., carboxy groups, carbonyl groups, hydroxy
groups, etc.) on the surface of the carbon nanotubes could be achieved using different pretreatments of the nanostructured
material. These involved (a) chemical and physical procedures; and (b) electrochemical functionalization. Different attempts
at sidewall modification have been hampered by the presence of significant contaminants as graphitic and amorphous carbon
or have required solubilization via chemical reactions on the ends of cut nanotubes. A more accommodating and direct approach
to functionalize nanotubes is therefore required.
We report here the sidewall functionalization of purified SWCNTs, obtained by different approaches and finally, we can discuss
possible applications of functionalized SWCNTs in the sensing area. 相似文献
1000.
《Electroanalysis》2005,17(1):7-14
This review addresses recent advances in carbon‐nanotubes (CNT) based electrochemical biosensors. The unique chemical and physical properties of CNT have paved the way to new and improved sensing devices, in general, and electrochemical biosensors, in particular. CNT‐based electrochemical transducers offer substantial improvements in the performance of amperometric enzyme electrodes, immunosensors and nucleic‐acid sensing devices. The greatly enhanced electrochemical reactivity of hydrogen peroxide and NADH at CNT‐modified electrodes makes these nanomaterials extremely attractive for numerous oxidase‐ and dehydrogenase‐based amperometric biosensors. Aligned CNT “forests” can act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centers of enzymes. Bioaffinity devices utilizing enzyme tags can greatly benefit from the enhanced response of the biocatalytic‐reaction product at the CNT transducer and from CNT amplification platforms carrying multiple tags. Common designs of CNT‐based biosensors are discussed, along with practical examples of such devices. The successful realization of CNT‐based biosensors requires proper control of their chemical and physical properties, as well as their functionalization and surface immobilization. 相似文献