全文获取类型
收费全文 | 494篇 |
免费 | 34篇 |
国内免费 | 8篇 |
专业分类
化学 | 247篇 |
晶体学 | 3篇 |
力学 | 28篇 |
数学 | 50篇 |
物理学 | 102篇 |
无线电 | 106篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 20篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 28篇 |
2016年 | 41篇 |
2015年 | 26篇 |
2014年 | 29篇 |
2013年 | 63篇 |
2012年 | 57篇 |
2011年 | 38篇 |
2010年 | 18篇 |
2009年 | 18篇 |
2008年 | 16篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有536条查询结果,搜索用时 18 毫秒
31.
Polypyrrole–montmorillonite nanocomposite as sorbent for solid‐phase microextraction of phenolic compounds in water
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)
Mir Mahdi Abolghasemi Sheyda Parastari Vahid Yousefi 《Journal of separation science》2014,37(23):3526-3532
A fiber‐coated polypyrrole–montmorillonite nanocomposite was prepared for solid‐phase microextraction. The fiber coating can be prepared easily; it is mechanically stable and exhibits relatively high thermal stability. The prepared fiber was evaluated for the extraction of some phenolic compounds from aqueous sample solutions by gas chromatography–mass spectrometry. The effects of the extraction and desorption parameters including extraction time, extraction temperature, stirring rate, ionic strength, pH and desorption temperature and time have been studied. At optimum conditions, the repeatability for one fiber (n = 5), expressed as % relative standard deviation was between 6.5 and 7.8% for the phenolic compounds. The detection limits for the studied phenolic compounds were between 0.05–1.3 ng/mL. The developed method offers the advantage of being simple to use, with shorter analysis time, lower cost, thermal stability of the fibers, and high relative recovery in comparison to conventional methods of analysis. 相似文献
32.
Salek Farhad Babaie Meisam Ghodsi Ali Hosseini Seyed Vahid Zare Ali 《Journal of Thermal Analysis and Calorimetry》2021,145(3):817-828
Journal of Thermal Analysis and Calorimetry - Number of hybrid vehicles has increased around the world significantly. Automotive industry is utilizing the hybridization of the powertrain system to... 相似文献
33.
Gerhardt I Wrigge G Bushev P Zumofen G Agio M Pfab R Sandoghdar V 《Physical review letters》2007,98(3):033601
We present an experiment where a single molecule strongly affects the amplitude and phase of a laser field emerging from a subwavelength aperture. We achieve a visibility of -6% in direct and +10% in cross-polarized detection schemes. Our analysis shows that a close to full extinction should be possible using near-field excitation. 相似文献
34.
Vahid Beigi-Somar Seyed Saied Homami Majid Ghazanfarpour-Darjani Amirhossein Monzavi 《Journal of heterocyclic chemistry》2020,57(1):140-150
In situ generated copper acetylides react with isocyanates and oxiranes to form a decent range of morpholine derivatives. The reactions proceeded with acceptable yields and excellent regioselectivity. The presence of oxygen and moisture completely inhibited the reaction. The scope of the reaction is wide and the reactions involve consecutive C–C, C–N, and C–O bond formations. 相似文献
35.
We studied sensor application of a graphene oxide and hematite (α‐Fe2O3/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe2O3/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10?5 cm2 s?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe2O3/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10?4 cm2 s?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum. 相似文献
36.
Two new complexes of [Mn(2-MPyzCI)2Cl2].H2O (1) and [Mn(2-MPyzCI)2(H2O)2](NO3)2 (2) were synthesized from the reaction of MnX2.4H2O (X=Cl? and NO3?) with 2-cyanopyrazine in methanolic solution. The chelating methyl pyrazine-2-carboximidate (2-MPyzCI) ligand is formed via the methanolysis of 2-cyanopyrazine. Although coordination environment around manganes(II) ions is similar, but these complexes are different in geometrical position of 2-MPyzCI ligands. As both compounds are synthesized under the same reaction conditions, the only difference between these two complexes are counter ions and changing of geometrical position of ligands can be considered as a result of influence of the counter-anions on the molecular structures. 相似文献
37.
38.
High resolution capillary electrophoresis of carbon nanotubes 总被引:2,自引:0,他引:2
Doorn SK Fields RE Hu H Hamon MA Haddon RC Selegue JP Majidi V 《Journal of the American Chemical Society》2002,124(12):3169-3174
Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field. 相似文献
39.
We show theoretically that photonic crystal membranes cause large variations in the spontaneous emission rate of dipole emitters, not only inside but also in the near field above the membranes. Our three-dimensional finite-difference time-domain calculations reveal an inhibition of more than five times and an enhancement of more than ten times for the spontaneous emission rate of emitters with select dipole orientations and frequencies. Furthermore, we demonstrate theoretically the potential of a nanoscopic emitter attached to the end of a glass fiber tip as a local probe for mapping the large spatial variations of the photonic crystal local radiative density of states. This arrangement is promising for on-command modification of the coupling between an emitter and the photonic crystal in quantum optical experiments. 相似文献
40.