全文获取类型
收费全文 | 2494篇 |
免费 | 79篇 |
国内免费 | 8篇 |
专业分类
化学 | 1525篇 |
晶体学 | 8篇 |
力学 | 112篇 |
数学 | 454篇 |
物理学 | 482篇 |
出版年
2023年 | 27篇 |
2022年 | 51篇 |
2021年 | 79篇 |
2020年 | 44篇 |
2019年 | 59篇 |
2018年 | 41篇 |
2017年 | 40篇 |
2016年 | 81篇 |
2015年 | 65篇 |
2014年 | 69篇 |
2013年 | 128篇 |
2012年 | 162篇 |
2011年 | 154篇 |
2010年 | 112篇 |
2009年 | 111篇 |
2008年 | 135篇 |
2007年 | 146篇 |
2006年 | 150篇 |
2005年 | 133篇 |
2004年 | 111篇 |
2003年 | 71篇 |
2002年 | 66篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 12篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1973年 | 11篇 |
1972年 | 8篇 |
排序方式: 共有2581条查询结果,搜索用时 46 毫秒
951.
Juan C. Espinosa Dr. Sergio Navalón Dr. Ana Primo Dr. Mónica Moral Prof. Javier Fernández Sanz Prof. Mercedes Álvaro Prof. Hermenegildo García 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(34):11966-11971
Reduced graphene oxide exhibits high activity as Fenton catalyst with HO. radical generation efficiency over 82 % and turnover numbers of 4540 and 15023 for phenol degradation and H2O2 consumption, respectively. These values compare favorably with those achieved with transition metals, showing the potential of carbocatalysts for the Fenton reaction. 相似文献
952.
953.
A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core–shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5 × 10−11 M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material. 相似文献
954.
Junhao Zhang Sergio de Juan Antonio Esteban‐Cubillo Julio Santarén De‐Yi Wang 《中国化学》2015,33(2):285-291
The objective of the study was to investigate the effect of the organo‐modified nanosepiolite (ONSep) on improving the fire safety of polypropylene (PP). The composites based on PP, flame retardant master batch (MB‐FR, 25 wt% PP+50 wt% decabromodiphenyl ether (DBDPE)+25% antimony trioxide (ATO)) and ONSep were prepared via melt blending. The results of the limiting oxygen index (LOI) and vertical burning rating (UL‐94) test indicated that PP/40 wt% MB composites had no rating with seriously dripping phenomenon, while the LOI value was only 22.5. However, as 4 wt% ONSep was added in PP/40 wt% MB composites, the composites achieved UL94 V‐0 rating and the LOI value was 24.3. In comparison, PP/50 wt% MB composites could not reach the V‐0 rating either. The TGA results revealed that the addition of ONSep enhanced the thermal stability of the PP/MB‐FR composites. The cone calorimeter results indicated that the heat release rate, average mass loss rate, smoke production rate and smoke temperature of the PP/40 wt% MB‐FR/4 wt% ONSep composites decreased in comparison with those of PP/40 wt% MB‐FR composites. Simultaneously, the Young modulus and impact strength were also much better improved with the increase of ONSep loading. Therefore, the synergistic flame retardancy of ONSep in PP/MB‐FR matrix significantly containing a halogen based flame retardant (DBDPE) significantly improved the fire safety and mechanical properties of the composites, and allowed to decrease the total amount of brominated fire retardants. 相似文献
955.
Theoretical Design and Experimental Realization of Quasi Single Electron Enhancement in Plasmonic Catalysis
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jiale Wang Dr. Tiago V. Alves Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Sergio H. Domingues Prof. Romulo A. Ando Prof. Fernando R. Ornellas Prof. Pedro H. C. Camargo 《Angewandte Chemie (International ed. in English)》2015,54(48):14427-14431
By a combination of theoretical and experimental design, we probed the effect of a quasi‐single electron on the surface plasmon resonance (SPR)‐mediated catalytic activities of Ag nanoparticles. Specifically, we started by theoretically investigating how the E‐field distribution around the surface of a Ag nanosphere was influenced by static electric field induced by one, two, or three extra fixed electrons embedded in graphene oxide (GO) next to the Ag nanosphere. We found that the presence of the extra electron(s) changed the E‐field distributions and led to higher electric field intensities. Then, we experimentally observed that a quasi‐single electron trapped at the interface between GO and Ag NPs in Ag NPs supported on graphene oxide (GO‐Ag NPs) led to higher catalytic activities as compared to Ag and GO‐Ag NPs without electrons trapped at the interface, representing the first observation of catalytic enhancement promoted by a quasi‐single electron. 相似文献
956.
Zahra Hosseinpour Alice Scarpellini Sharif Najafishirtari Dr. Sergio Marras Dr. Massimo Colombo Dr. Abdolali Alemi Dr. Michaël De Volder Dr. Chandramohan George Dr. Vladimir Lesnyak 《Chemphyschem》2015,16(16):3418-3424
Hierarchical superstructures formed by self‐assembled nanoparticles exhibit interesting electrochemical properties that can potentially be exploited in Li‐ion batteries (LIBs) as possible electrode materials. In this work, we tested two different morphologies of CuS superstructures for electrodes, namely, tubular dandelion‐like and ball‐like assemblies, both of which are composed of similar small covellite nanoparticles. These two CuS morphologies are characterized by their markedly different electrochemical performances, suggesting that their complex structures/morphologies influence the electrochemical properties. At 1.12 A g?1, the cells made with CuS tubular structures delivered about 420 mAh g?1, and at 0.56 A g?1, the capacity was as high as about 500 mAh g?1 with good capacity retention. Their ease of preparation and processing, together with good electrochemical performance, make CuS tubular dandelion‐like clusters attractive for developing low‐cost LIBs based on conversion reactions. 相似文献
957.
A DFT Study of the Reactivity of Anatase TiO2 and Tetragonal ZrO2 Stepped Surfaces Compared to the Regular (101) Terraces
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Sergio Tosoni Dr. Hsin‐Yi Tiffany Chen Prof. Gianfranco Pacchioni 《Chemphyschem》2015,16(17):3642-3651
It is generally assumed that low‐coordinated sites at extended defects of oxide surfaces like steps or edges are more reactive than the regular, fully coordinated sites at the flat terraces. In this work we have considered the properties of stepped surfaces of anatase TiO2 and tetragonal ZrO2 by means of periodic DFT+U calculations. For both oxides, the stability of oxygen vacancies located near the step edges is compared to that of the same defects at the regular terraces. The capability of the steps to induce nucleation of metal nanoparticles on the surface has been evaluated by simulating the adsorption of a single ruthenium adatom. We conclude that, for anatase, step edges have no particular role in favouring the reduction of the oxide by reducing the cost for oxygen abstraction; in the same way, there is no special role of the stepped anatase surface in stabilizing adsorbed Ru atoms. On the contrary, step edges on zirconia display some capability to stabilise oxygen vacancies and ruthenium adatoms. 相似文献
958.
Molecularly imprinted solid‐phase extraction coupled with ultra high performance liquid chromatography and fluorescence detection for the determination of estrogens and their metabolites in wastewater
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rayco Guedes‐Alonso Sergio Santana‐Viera Zoraida Sosa‐Ferrera José Juan Santana‐Rodríguez 《Journal of separation science》2015,38(22):3961-3968
Estrogens are an important class of endocrine‐disrupting compounds, and their contamination of environmental waters through the effluents of wastewater treatment plants could have an important impact on aquatic biota, even at low concentrations. For this reason, the development of selective and sensitive extraction methodologies, which permit the identification and quantification of these compounds at trace level concentrations, is very important. In this study, a quantitative method based on molecularly imprinted solid phase extraction coupled to ultra high performance liquid chromatography with fluorescence detection has been developed. It has been used for the simultaneous determination of three estrogens and two of their metabolites in water samples from wastewater treatment plants. The method developed presents satisfactory limits of detection (between 0.18 and 0.45 ng·mL?1), good recoveries (higher than 60%) and low relative standard deviations (under 10%). The method was used to analyze wastewater from a veterinary hospital as well as influent and effluent samples of a wastewater treatment plant of Gran Canaria (Spain) The concentrations of the detected hormones ranged from 1.35 to 2.57 ng·mL?1. 相似文献
959.
In previous papers, the type-I intermittent phenomenon with continuous reinjection probability density (RPD) has been extensively studied. However, in this paper type-I intermittency considering discontinuous RPD function in one-dimensional maps is analyzed. To carry out the present study the analytic approximation presented by del Río and Elaskar (Int. J. Bifurc. Chaos 20:1185–1191, 2010) and Elaskar et al. (Physica A. 390:2759–2768, 2011) is extended to consider discontinuous RPD functions. The results of this analysis show that the characteristic relation only depends on the position of the lower bound of reinjection (LBR), therefore for the LBR below the tangent point the relation \(\left\langle l \right\rangle \propto \varepsilon ^{-1/2}\) , where \(\varepsilon \) is the control parameter, remains robust regardless the form of the RPD, although the average of the laminar phases \(\left\langle l \right\rangle \) can change. Finally, the study of discontinuous RPD for type-I intermittency which occurs in a three-wave truncation model for the derivative nonlinear Schrodinger equation is presented. In all tests the theoretical results properly verify the numerical data. 相似文献
960.
Sergio Rojas-Buzo Benjamin Bohigues Christian W. Lopes Dbora M. Meira Mercedes Boronat Manuel Moliner Avelino Corma 《Chemical science》2021,12(29):10106
The Lewis/Brønsted catalytic properties of the Metal–Organic Framework (MOF) nodes can be tuned by simply controlling the solvent employed in the synthetic procedure. In this work, we demonstrate that Hf-MOF-808 can be prepared from a material with a higher amount of Brønsted acid sites, via modulated hydrothermal synthesis, to a material with a higher proportion of unsaturated Hf Lewis acid sites, via modulated solvothermal synthesis. The Lewis/Brønsted acid properties of the resultant metallic clusters have been studied by different characterization techniques, including XAS, FTIR and NMR spectroscopies, combined with a DFT study. The different nature of the Hf-MOF-808 materials allows their application as selective catalysts in different target reactions requiring Lewis, Brønsted or Lewis–Brønsted acid pairs.The Brønsted/Lewis acid properties of Hf-MOF-808 can be tuned by simply controlling the solvent employed in its synthesis, with direct catalytic implications on the activity and selectivity of organic reactions sensitive to the active site nature. 相似文献