全文获取类型
收费全文 | 395篇 |
免费 | 25篇 |
国内免费 | 5篇 |
专业分类
化学 | 265篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 73篇 |
物理学 | 31篇 |
无线电 | 44篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 32篇 |
2013年 | 49篇 |
2012年 | 31篇 |
2011年 | 27篇 |
2010年 | 28篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有425条查询结果,搜索用时 421 毫秒
31.
Vahideh Masoumi Ali Mohammadi Mohsen Amini Mohammad Reza Khoshayand Rasoul Dinarvand 《Journal of Solid State Electrochemistry》2014,18(6):1763-1771
In this work, polyaniline, polypyrrole, and polyaniline/polypyrrole composite fibers were synthesized in the absence and presence of oxidized multiwalled carbon nanotubes using electrochemical cyclic voltammetry with CF3COOH as dopant. Thermal stability of these fibers was studied by differential scanning calorimetry. Then, headspace solid-phase microextraction process coupled with gas chromatography and flame ionization detector was used for comparing extraction capability of benzaldehyde from aqueous solution. Since polyaniline fiber showed better extraction efficiency than the other fibers, its preparation conditions including acid concentration, aniline concentration, scan rate, and amount of multiwalled carbon nanotubes were studied by means of the “one-factor-at-a-time method”. The analytical performance of polyaniline fibers were investigated to determine benzaldehyde from the aqueous solution. The morphology and texture of polyaniline fibers were examined by field emission scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The attained results revealed that the perfect conditions for acid concentration, aniline concentration, scan rate, and multiwalled carbon nanotubes content were 0.5 M, 0.2 M, 25 mV s?1, and 0.02 wt%, respectively. The limit of detection for the proposed polyaniline fiber was 15 ng ml?1. 相似文献
32.
Kaveh Amini Heinz-Bernhard Kraatz 《International journal of environmental analytical chemistry》2016,96(9):836-844
The need for effective and efficient methods for pathogen detection in water is as serious as ever due to the health risk posed to human population by the consumption of pathogen-contaminated water. One of the important research streams which have been focused on by researchers for development of novel techniques for this purpose is biosensor technologies. Using different bio-recognition elements and transduction methodologies, biosensors have the potential to detect their analyte of interest in a fast and highly specific manner. Different pathogenic agents can be recognised by toll-like receptors (TLRs). The innate immune system of higher organisms employs TLRs for triggering intracellular signalling and induction of the expression of immune response genes. In this report, we explore the challenges associated with employing TLRs for pathogen detection in water samples. Although methods using TLR expressing cells also have been discussed, the focus of this review is on using TLR proteins as the bio-recognition elements in biosensors. 相似文献
33.
Magnetic resonance imaging (MRI) is a highly advanced and sophisticated imaging modality for cardiac motion tracking and analysis, capable of providing 3D analysis of global and regional cardiac function with great accuracy and reproducibility. In the past few years, numerous efforts have been devoted to cardiac motion recovery and deformation analysis from MR image sequences. Many approaches have been proposed for tracking cardiac motion and for computing deformation parameters and mechanical properties of the heart from a variety of cardiac MR imaging techniques. In this paper, an updated and critical review of cardiac motion tracking methods including major references and those proposed in the past ten years is provided. The MR imaging and analysis techniques surveyed are based on cine MRI, tagged MRI, phase contrast MRI, DENSE, and SENC. This paper can serve as a tutorial for new researchers entering the field. 相似文献
34.
Mohammadreza Amini Abouzar Samimi Asra Mirzavandi 《International Journal of Electronics》2016,103(4):747-764
Transmission time optimisation is one of the key considerations of cognitive network design. There are many studies in cognitive radio networks (CRNs) focusing on finding the best transmission time for secondary users (SUs) to maximise transmission or energy efficiency. While longer sensing duration leads to a higher sensing accuracy and causes less interference, the SU spends less time for transmission and more energy on sensing spectrum. On the other hand, when the transmission duration becomes longer, although the SU has more opportunities to access the channel, it may encounter higher interference due to primary user (PU) returns and the probability of collision becomes higher. In this article, in a decentralised slotted protocol for CRN, the SU spectrum access is proved as a renewal process, then the interference due to PU return during SU transmission, the missed opportunities due to waiting for the channel to become idle and the energy consumed by the SU in the whole spectrum access process including idling energy, transmission energy and sensing energy consumption are formulated and integrated into newly defined efficiency to obtain the optimum transmission time and waiting time. 相似文献
35.
36.
Mohammad Mahdi Najafpour Mojtaba Amini Mojtaba Bagherzadeh Davar M. Boghaei Vickie McKee 《Transition Metal Chemistry》2010,35(3):297-303
A manganese(II) complex of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) has been synthesized and characterized by single-crystal
X-ray diffraction, elemental analyses, IR, and UV–Vis spectroscopic techniques. Oxidation of alcohols to their corresponding
aldehydes and ketones was conducted by this catalyst using oxone (2KHSO5·KHSO4·K2SO4) as an oxidant under biphasic reaction conditions (CH2Cl2/H2O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature. Easy preparation, mild reaction conditions,
high yields of the products, short reaction times, no further oxidation to the corresponding carboxylic acids, high selectivity
and inexpensive reagents make this catalytic system a useful oxidation method for aliphatic and benzylic alcohols. 相似文献
37.
A. A. Karimi Zarchi N. Mokhtari M. Arfan T. Rehman M. Ali M. Amini R. Faridi Majidi A. R. Shahverdi 《Applied Physics A: Materials Science & Processing》2011,103(2):349-353
In this study a sunlight-induced method for rapid synthesis of silver nanoparticles using an ethanol extract of Andrachnea chordifolia is described. The silver nitrate solutions (1 mM) containing the ethanol extract of Andrachnea chordifolia were irradiated by both sunlight radiation and by sunlight radiation passed through different colored filters (red, yellow
or green). The smallest size of silver nanoparticles was obtained when a silver ion solution was irradiated for 5 minutes
by direct sunlight radiation. Further examination of the shape and size and of the surface chemistry of these biogenic silver
nanoparticles, which were prepared under sunlight radiation, was carried out using transmission electron microscopy and infrared
spectroscopy, respectively. Transmission electron microscopy images show spherical particles with an average size of 3.4 nm.
Hydroxyl residues were also detected on the surface of these biogenic silver nanoparticles fabricated using plant extract
of Andrachnea chordifolia under sunlight radiation. Our study on the reduction of silver ions by this plant extract in darkness shows that the synthesis
process can take place under dark conditions at much longer incubations (48 hours). Larger silver polydispersed nanoparticles
ranging in size from 3 to 30 nm were obtained when the silver ions were treated with the ethanol extract of Andrachnea chordifolia under dark conditions for 48 hours. 相似文献
38.
Hashemzadeh Alireza Amini Mostafa M. Najafi Ezzatollah Khavasi Hamid Reza 《Research on Chemical Intermediates》2017,43(10):5741-5753
Research on Chemical Intermediates - To systematically examine the effects of the length and number of aromatic rings in carboxylic acid ligands on the structure and properties of lead(II)... 相似文献
39.
Condensation of aldehydes, isonitriles and 2‐aminopyridines in the presence of H3PMo12O40 affords different derivatives of 3‐aminoimidazo[1,2‐a]pyridine in good to excellent yields. 相似文献
40.
A simple flow injection spectrophotometric method for the determination of nitrite is described. Nitrite injected into the flow system reacts with thiourea in acidic medium and the generated thiocyanate ion reacts with Fe(III) in the reagent solution to produce a highly colored product. The influences of chemical and physical parameters including reagent concentrations, sample volume injected, flow rates of the carrier and reagent solutions, reaction coil length and reaction temperature, were studied and optimum values of these parameters were established. Under the optimum conditions, the calibration curve for nitrite was linear over the concentration range 0.36 - 90 microg ml(-1) without preconcentration and over the range 3.8 - 500 ng ml(-1) with a simple online preconcentration step using an anion exchange column. The corresponding detection limits were 0.36 micro ml(-1) and 3.8 ng ml(-1), respectively. Up to 25 samples can be analyzed per hour, with an average relative standard deviation of < or = 1.2%. Interferences by various foreign ions were studied and the method was applied to the determination of nitrite in water and spiked water samples. 相似文献