全文获取类型
收费全文 | 591篇 |
免费 | 34篇 |
国内免费 | 15篇 |
专业分类
化学 | 365篇 |
力学 | 56篇 |
数学 | 92篇 |
物理学 | 127篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 31篇 |
2020年 | 26篇 |
2019年 | 30篇 |
2018年 | 31篇 |
2017年 | 36篇 |
2016年 | 41篇 |
2015年 | 24篇 |
2014年 | 46篇 |
2013年 | 77篇 |
2012年 | 66篇 |
2011年 | 56篇 |
2010年 | 42篇 |
2009年 | 26篇 |
2008年 | 16篇 |
2007年 | 21篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有640条查询结果,搜索用时 31 毫秒
191.
Yu S Ahmadi S Zuleta M Tian H Schulte K Pietzsch A Hennies F Weissenrieder J Yang X Göthelid M 《The Journal of chemical physics》2010,133(22):224704
The fast development of new organic sensitizers leads to the need for a better understanding of the complexity and significance of their adsorption processes on TiO(2) surfaces. We have investigated a prototype of the triphenylamine-cyanoacrylic acid (donor-acceptor) on rutile TiO(2) (110) surface with special attention on the monolayer region. This molecule belongs to the type of dye, some of which so far has delivered the record efficiency of 10%-10.3% for pure organic sensitizers [W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, and P. Wang, Chem. Mater. 22, 1915 (2010)]. The molecular configuration of this dye on the TiO(2) surface was found to vary with coverage and adopt gradually an upright geometry, as determined from near edge x-ray absorption fine structure spectroscopy. Due to the molecular interaction within the increasingly dense packed layer, the molecular electronic structure changes systematically: all energy levels shift to higher binding energies, as shown by photoelectron spectroscopy. Furthermore, the investigation of charge delocalization within the molecule was carried out by means of resonant photoelectron spectroscopy. A fast delocalization (~1.8 fs) occurs at the donor part while a competing process between delocalization and localization takes place at the acceptor part. This depicts the "push-pull" concept in donor-acceptor molecular system in time scale. 相似文献
192.
Laura Osete-Cortina María Teresa Doménech-Carbó Antonio Doménech Dolores Julia Yusá-Marco Hossein Ahmadi 《Analytical and bioanalytical chemistry》2010,397(1):319-329
The present work describes an analytical study performed on several pieces of Iranian Ilkhanate glazed ceramics from the Takht-e
Soleyman palace (Iran, thirteenth century). Several advanced instrumental techniques, including pyrolysis–gas chromatography–mass
spectrometry, Fourier transform IR spectroscopy, light microscopy, X-ray diffraction, scanning electron microscopy–X-ray microanalysis
and voltammetry of microparticles, were used. The results obtained led to identification of the chemical and mineralogical
composition of the pastes and glazes and the colouring agents. Corrosion processes associated with the extreme burial conditions
in which the pieces remained for centuries were characterized in some areas of the glazes. A drying oil was identified as
the main component of the organic material that was used as the adhesive for the decorative gold sheets applied on the glazes.
This finding is in good agreement with traditional recipes. Interestingly, this drying oil exhibits an unusual composition
as the gold sheet preserved it from external ageing agents (light, atmosphere, etc.). 相似文献
193.
S. Masoud Hosseini E. Ghasemi H. Ahmadi Moghaddam 《Journal of magnetism and magnetic materials》2010,322(23):3792-3796
A stable γ-Fe2O3 paraffin-based ferrofluid was prepared via high energy milling. The magnetic particles were characterized using X-ray diffraction, dynamic light scattering and vibrating sample magnetometer techniques. The rheological properties of the ferrofluid were studied using a standard rotating rheometer. The magnetoviscous effect and thixotropy in the ferrofluid were studied. The formation and destruction of magnetically induced structures and the interactions of nanoparticles and aggregates are discussed. 相似文献
194.
In this Letter, we create an optical nanoantenna array composed of parasitic plasmonic loops that can enhance radiation characteristics and direct the optical energy successfully. Three metallic loops inspired by the concept of the Yagi-Uda antenna are optimized around the region where they feature high scattering performance to control the radiation beam. The loop geometry, when compared to the dipole configuration, has the benefit of using the available aperture in an effective way to provide higher directivity. The angular emission of the nanoloop array antenna is highly directive, and a directivity of 8.2 dB for upward radiation is established. 相似文献
195.
Kourosh Tabar-Heydar Golriz Khanalizadeh Mohammad Mostaghim Seyyed Hamid Ahmadi 《Chromatographia》2009,69(11-12):1341-1346
In this study, a new sample vial has been designed for the extraction and determination of methyl tert-butyl ether (MTBE) in water samples by headspace solid-phase microextraction method. The special feature of this new vial is cooling the HS above the aqueous sample by cold water stream for maximum analyte absorption on SPME fiber coating. The analysis was by a gas chromatograph equipped with flame ionization detector and a capillary column (CP-sil 13 CB). Some significant variables affecting the extraction procedure were optimized. By use of divinylbenzene/carboxen/polydimethylsiloxane fiber, a sample volume of 10 mL, stirring rate of 1,000 rpm, salt concentration of 24%, extraction time of 15 min and extraction temperature of 83 °C, detection limit of 0.022 μg L?1 and a good linearity (R 2 = 0.998) in a calibration range of 0.1–400 μg L?1 were achieved. The relative standard deviation for triplicate runs ranged between 6 and 8%. The method could be applied to the analysis of trace levels of MTBE in various water samples. 相似文献
196.
197.
H. Faghihian M. Kabiri-Tadi S. J. Ahmadi 《Journal of Radioanalytical and Nuclear Chemistry》2010,285(3):499-504
The aim of this research is adsorption of ruthenium by natural zeolite, clinoptilolite. The experimental conditions were optimized in order to obtain higher adsorption capacity and the study was done under optimum conditions. Maximal adsorption capacity was obtained using 103Ru as a tracer at 25 °C, pH 2.0 and contact time of 10 h and found to be 0.074 meq g?1. Ruthenium measurments were done using inductively coupled plasma-optical emission spectrometry (ICP-OES) and gamma spectrometer methods. Break points were calculated from breakthrough curve at the 1%, 5% and 50%. The obtained results are respectively 2.8, 4.5 and 19.5 mL, which are equal to 2.5 × 10?3, 1.35 × 10?2 and 5.85 × 10?2 meq g?1. Desorption behavior of column packed zeolite using some eluents was also investigated. The highest recovery of 97.4 ± 0.2% was obtained using 2 mol L?1 HCl solution as an eluent. The results of this study can be used for separation and preconcentration of ruthenium. 相似文献
198.
Ahmadi Syed Javad Sepehrian Hamid Waqifhusain Syed Faghihian Hossein Alighanbari Hadi 《中国化学》2010,28(11):2193-2198
Hexagonal mesoporous titanosilicates (Ti‐MCM‐41) have been prepared using cetyltrimethylammonium bromide (CTAB) as the structure directing agent under the mild alkaline conditions. Powder X‐ray diffraction, nitrogen gas sorption, FTIR spectroscopy and thermogravimetry analysis of samples have confirmed that well ordered MCM‐41 type mesoporous materials were prepared. The potential of removing toxic metal ions from waste waters using mesoporous titanosilicates was evaluated. Separation of CoII‐UVI, CsI‐UVI and SmIII‐UVI has been developed on columns of this adsorbent. 相似文献
199.
In this study of water hammer with fluid–structure interaction (FSI) the main aim was the investigation of junction coupling effects. Junction coupling effects were studied in various types of discrete points, such as pumps, valves and branches. The emphasis was placed on an unrestrained pump and branch in the system, and the associated relations were derived for modelling them. Proposed relations were considered as boundary conditions for the numerical modelling which was implemented using the finite element method for the structural equations and the method of characteristics for the hydraulic equations. The results can be used by engineers in finding where junction coupling is significant. 相似文献
200.