全文获取类型
收费全文 | 10147篇 |
免费 | 943篇 |
国内免费 | 1655篇 |
专业分类
化学 | 10428篇 |
晶体学 | 105篇 |
力学 | 392篇 |
综合类 | 129篇 |
数学 | 525篇 |
物理学 | 1166篇 |
出版年
2024年 | 12篇 |
2023年 | 177篇 |
2022年 | 343篇 |
2021年 | 393篇 |
2020年 | 483篇 |
2019年 | 429篇 |
2018年 | 407篇 |
2017年 | 580篇 |
2016年 | 655篇 |
2015年 | 531篇 |
2014年 | 576篇 |
2013年 | 707篇 |
2012年 | 783篇 |
2011年 | 671篇 |
2010年 | 587篇 |
2009年 | 623篇 |
2008年 | 512篇 |
2007年 | 619篇 |
2006年 | 547篇 |
2005年 | 464篇 |
2004年 | 390篇 |
2003年 | 321篇 |
2002年 | 308篇 |
2001年 | 215篇 |
2000年 | 207篇 |
1999年 | 198篇 |
1998年 | 167篇 |
1997年 | 164篇 |
1996年 | 140篇 |
1995年 | 128篇 |
1994年 | 110篇 |
1993年 | 49篇 |
1992年 | 39篇 |
1991年 | 25篇 |
1990年 | 36篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 3篇 |
1971年 | 1篇 |
1959年 | 4篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
The tribological performance of fullerene‐like hydrogenated carbon films under ionic liquid lubrication 下载免费PDF全文
Kunyao Wu Li Qiang Zhenbin Gong Gengrui Zhao Kaixiong Gao Bin Zhang Junyan Zhang 《Surface and interface analysis : SIA》2015,47(9):903-910
Fullerene‐like hydrogenated carbon films were deposited on Si substrate by plasma‐enhanced chemical vapor deposition. The microstructures of films were characterized by high‐resolution transmission electron microscopy and Raman spectrum. The tribological performance of films was tested by reciprocating ball‐on‐disc tester under 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid. The surface morphology and chemical composition of wear tracks and wear rates were investigated by optical microscope, X‐ray photoelectron spectroscopy, and 3D surface profiler. The results indicated that the film with a typical fullerene‐like structure embedded into the amorphous sp2 and sp3 carbon networks could be prepared successfully, and the film shows a higher hardness (26.7 GPa) and elastic recovery (89.9%) compared with the amorphous carbon film. Furthermore, the film shows a lower friction coefficient at low contact load and friction frequency, and excellent wear‐resistance performance at high load and frequency under ionic liquid lubrication. Meanwhile, the wear life of fullerene‐like hydrogenated carbon films could be improved significantly using ionic liquid as a lubrication material. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
102.
Effects of anodic oxidation on corrosion properties of Al coating by arc spraying in seawater 下载免费PDF全文
A layer of Al coatings was prepared on the S355 steel by arc spraying, which was conducted by anodic oxidation treatment; the morphologies, chemical element compositions and phases of Al coating, and anodic oxide layer were analyzed with field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and X‐ray diffraction (XRD), respectively. The corrosion protections of Al coating before and after anodic oxidation were discussed with a seawater immersion test; the corrosion resistance mechanisms of Al coating and anodic oxide layer in the seawater were also investigated. The results show that the thickness of Al coating is about 300 µm by arc spraying, the sample surfaces become loose after seawater immersion corrosion and Cl? and O2? penetrate into the substrate from the cracks, destroying the binding properties of coating–substrate, and the coating fails. After anodic oxidation, the oxide layer is formed in the surface of Al coating with the thickness of about 30 µm; the corrosion products are mainly composed of Al(OH)3, which barraged the holes caused by seawater corrosion. The corrosion cracks are formed during the corrosion, while the number and depth of cracks decrease obviously after anodic oxidation treatment. The corrosion of Al coating becomes the local corrosion after anodic oxidation treatment, and the grains are smaller, which are easily nucleated to form a new corrosion resistance layer. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
103.
Electro‐oxidation and reduction of H2 on platinum studied by scanning electrochemical microscopy for the purpose of local detection of H2 evolution 下载免费PDF全文
Sina S. Jamali Simon E. Moulton Dennis E. Tallman Jan Weber Gordon G. Wallace 《Surface and interface analysis : SIA》2015,47(13):1187-1191
Electrochemical detection of H2 using scanning electrochemical microscopy (SECM) has shown to hold great promise as a sensitive characterization method with high spatial resolution for active surfaces generating H2. Herein, the factors contributing to the current that is measured by SECM in generation/collection mode for H2 detection are studied. In particular, the concentration gradient of H2 at the substrate, the H2/H+ recycling between the SECM tip and substrate and hemispherical profile of H2 diffusion has been discussed. It was postulated that H2/H+ recycling plays a dominant role in the oxidative current measured in generation/collection mode of SECM when the microelectrode is positioned in close vicinity of substrate. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
104.
将氧化石墨凝胶超声不同时间制备氧化石墨烯(GO)溶胶,再以GO溶胶为前驱体采用一步水热法制备了三维还原氧化石墨烯(3DRGO),采用X射线衍射(XRD)、拉曼光谱、原子力显微镜(AFM)、扫描电子显微镜(SEM)和电化学测试等研究了不同超声时间对3DRGO的形貌、结构及超级电容性能的影响.结果表明,当超声时间不超过120 min时,经水热反应后还原氧化石墨烯均能形成稳定的三维结构,但随着超声时间的延长,三维结构尺寸不断减小,强度增加,样品的内部结构也由片状逐渐向多孔网状转化;当超声时间超过120 min时,还原氧化石墨烯虽具有网状结构,但在宏观上不利于形成稳定的三维结构.电化学测试结果表明,经不同超声时间所制备的还原氧化石墨烯均表现出较好的超级电容性能,其中超声时间为120 min时制备的3DRGO具有更均匀的多孔网状结构,表现出了最佳的超级电容性能,在1 A/g电流密度下其比电容可达328 F/g,即使在20 A/g的大电流密度条件下,其比电容仍可高达240 F/g. 相似文献
105.
Electrodes/Electrolyte Interfaces in the Presence of a Surface‐Modified Photopolymer Electrolyte: Application in Dye‐Sensitized Solar Cells 下载免费PDF全文
Dr. Adriano Sacco Federico Bella Stefano De La Pierre Dr. Micaela Castellino Dr. Stefano Bianco Prof. Roberta Bongiovanni Prof. Candido Fabrizio Pirri 《Chemphyschem》2015,16(5):960-969
Since hundreds of studies on photoanodes and cathodes show that the electrode/electrolyte interfaces represent a key aspect at the base of dye‐sensitized solar cell (DSSC) performances, it is reported here that these interfaces can be managed by a smart design of the spatial composition of quasi‐solid electrolytes. By means of a cheap, rapid, and green process of photoinduced polymerization, composition‐tailored polymer electrolyte membranes (PEMs) with siloxane‐enriched surfaces are prepared, and their properties are thoroughly described. When assembled in DSSCs, the interfacial action promoted by the composition‐tailored PEMs enhances the photocurrent and fill factor values, thus increasing the global photovoltaic conversion efficiency with respect to the non‐modified PEMs. Moreover, the presence of the siloxane‐chain‐enriched surface increases the hydrophobicity and reduces the water vapor permeation into the device, thus enhancing the cell′s durability. 相似文献
106.
Kamonwad Ngamchuea Dr. Kristina Tschulik Shaltiel Eloul Prof. Dr. Richard G. Compton 《Chemphyschem》2015,16(11):2338-2347
Partially blocked electrodes (PBEs) are important; many applications use non‐conductive nanoparticles (NPs) to introduce new electrode functionalities. As aggregation is a problem in NP immobilization, developing an in situ method to detect aggregation is vital to characterise such modified electrodes. We present chronoamperometry as a method for detection of NP surface aggregation and semi‐quantitative sizing of the formed aggregates, based on the diffusion limited current measured at PBEs as compared with the values calculated numerically for different blocking feature sizes. In contrast to voltammetry, no approximations on electrode kinetics are needed, making chronoamperometry a more general and reliable method. Sizing is shown for two modification methods. Upon drop casting, significant aggregation is observed, while it is minimized in electrophoretic NP deposition. The aggregate sizes determined are in semi‐quantitative agreement with ex situ microscopic analysis of the PBEs. 相似文献
107.
Non‐destructive Patterning of Carbon Electrodes by Using the Direct Mode of Scanning Electrochemical Microscopy 下载免费PDF全文
Prof. Wolfgang Schuhmann 《Chemphyschem》2015,16(16):3477-3482
Patterning of glassy carbon surfaces grafted with a layer of nitrophenyl moieties was achieved by using the direct mode of scanning electrochemical microscopy (SECM) to locally reduce the nitro groups to hydroxylamine and amino functionalities. SECM and atomic force microscopy (AFM) revealed that potentiostatic pulses applied to the working electrode lead to local destruction of the glassy carbon surface, most likely caused by etchants generated at the positioned SECM tip used as the counter electrode. By applying galvanostatic pulses, and thus, limiting the current during structuring, corrosion of the carbon surface was substantially suppressed. After galvanostatic patterning, unambiguous proof of the formation of the anticipated amino moieties was possible by modulation of the pH value during the feedback mode of SECM imaging. This patterning strategy is suitable for the further bio‐modification of microstructured surfaces. Alkaline phosphatase, as a model enzyme, was locally bound to the modified areas, thus showing that the technique can be used for the development of protein microarrays. 相似文献
108.
High‐performance liquid chromatographic column packings with different particle sizes: Chromatographic behavior for the quality analysis of HuanglianShangqing pill 下载免费PDF全文
Dongzhi Yang Ying Li Fangxiu Yang Yan Du Yinjie Li Xiaoxiao Zheng Daoquan Tang 《Journal of separation science》2015,38(3):381-389
The chromatographic separation of traditional Chinese medicines is still a highly challenging task in analytical science with respect to its hundreds and thousands of chemical compounds, while increase of separation efficiency can greatly improve the separation power of chromatographic column for traditional Chinese medicine. In this study, 13 bioactive components in HuanglianShangqing pill were selected as an index to optimize the separation conditions and evaluate the system suitability of three commercially available columns packed with 1.8, 3.5, and 5.0 μm particles. The chromatographic separations were obtained by the most appropriate Eclipse Plus C18 column (100 × 2.1 mm, 3.5 μm) within 45 min using gradient elution with aqueous‐ammonium acetate (10 mmol/L, pH 5.0) and acetonitrile, at a flow rate of 0.3 mL/min and an operating temperature of 30°C. The quality of HuanglianShangqing pill was assessed through combining simultaneous quantification of 13 compounds with fingerprint analysis. For the qualitative analysis, mass spectrometry was used to confirm the 13 compounds. All the validation data conformed to the acceptable requirements. For the fingerprint analysis, 32 peaks were selected as the common peaks at 254 nm to evaluate the similarities among HuanglianShangqing pills obtained from ten manufacturers. 相似文献
109.
Analysis of a new drug of abuse: Cathinone derivative 1‐(3,4‐dimethoxyphenyl)‐2‐(ethylamino)pentan‐1‐one 下载免费PDF全文
Jennifer A. Weiß Magdalena Taschwer Olaf Kunert Martin G. Schmid 《Journal of separation science》2015,38(5):825-828
Recently, novel psychoactive drugs for human abuse such as amphetamines, phenethylamines, benzofuries, and tryptamines, cathinones have gained high popularity. These designer drugs are mainly sold via online stores as “bath salts” and are labeled “not for human consumption.” Due to the novelty of the compounds, only a little information about pharmacology, toxicology, and the long‐term damage they may cause is available. Moreover, there are only few analytical methods for their identification and analysis. Among new cathinone derivatives, 1‐(3,4‐dimethoxyphenyl)‐2‐(ethylamino)pentan‐1‐one (DL‐4662), became available via an internet shop. A sample of this compound was purchased and investigated. The first aim of our study was an identity check by NMR spectroscopy and gas chromatography with mass spectrometry. As many of the recreational drugs are chiral and are mainly sold as racemates, a further goal of our research was enantioseparation by gas chromatography with mass spectrometry and high‐performance liquid chromatography with UV detection, to prove whether DL‐4662 was traded enantiomerically pure or as racemic mixture. Both chiral separation methods showed the presence of a racemate. 相似文献
110.
Determination of diflubenzuron and chlorbenzuron in fruits by combining acetonitrile‐based extraction with dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography 下载免费PDF全文
In this study, a simple and low‐organic‐solvent‐consuming method combining an acetonitrile‐partitioning extraction procedure followed by “quick, easy, cheap, effective, rugged and safe” cleanup with ionic‐liquid‐based dispersive liquid–liquid microextraction and high‐performance liquid chromatography with diode array detection was developed for the determination of diflubenzuron and chlorbenzuron in grapes and pears. Ionic‐liquid‐based dispersive liquid–liquid microextraction was performed using the ionic liquid 1‐hexyl‐3‐methylimidazolium hexafluorophosphate as the extractive solvent and acetonitrile extract as the dispersive solvent. The main factors influencing the efficiency of the dispersive liquid–liquid microextraction were evaluated, including the extractive solvent type and volume and the dispersive solvent volume. The validation parameters indicated the suitability of the method for routine analyses of benzoylurea insecticides in a large number of samples. The relative recoveries at three spiked levels ranged between 98.6 and 109.3% with relative standard deviations of less than 5.2%. The limit of detection was 0.005 mg/kg for the two insecticides. The proposed method was successfully used for the rapid determination of diflubenzuron and chlorbenzuron residues in real fruit samples. 相似文献