全文获取类型
收费全文 | 273篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 169篇 |
晶体学 | 2篇 |
力学 | 23篇 |
数学 | 38篇 |
物理学 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 20篇 |
2019年 | 15篇 |
2018年 | 24篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 8篇 |
2014年 | 22篇 |
2013年 | 25篇 |
2012年 | 30篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 4篇 |
2007年 | 12篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有286条查询结果,搜索用时 15 毫秒
71.
F.?Ghasemi J.?Peinke M.?Sahimi M. R.?Rahimi TabarEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(3):411-415
We propose a novel inverse method that utilizes a set of data to
construct a simple equation that governs the stochastic process
for which the data have been measured, hence enabling us to
reconstruct the stochastic process. As an example, we analyze the
stochasticity in the beat-to-beat fluctuations in the heart rates
of healthy subjects as well as those with congestive heart
failure. The inverse method provides a novel technique for
distinguishing the two classes of subjects in terms of a drift and
a diffusion coefficients which behave completely differently for
the two classes of subjects, hence potentially providing a novel
diagnostic tool for distinguishing healthy subjects from those
with congestive heart failure, even at the early stages of the
disease development. 相似文献
72.
The electrochemical oxidation of iodide ion in the presence of 4-hydroxycoumarin (1) was studied using cyclic voltammetry and controlled-potential coulometry. The result indicates that the resulting iodine takes part in a halogenation reaction and reacts with 4-hydroxycoumarin (1). According to the obtained results, a new and simple coulometric titration method with potentiometric end-point detection for the determination of 4-hydroxycoumarin (1) is presented. In the presented method, 2-200 micromol of 4-hydroxycoumarin (1) was successfully determined. 相似文献
73.
Link JM Reyes M Yager PM Anjos JC Bediaga I Göbel C Magnin J Massafferi A de Miranda JM Pepe IM dos Reis AC Simão FR Carrillo S Casimiro E Sánchez-Hernández A Uribe C Vazquez F Cinquini L Cumalat JP O'Reilly B Ramirez JE Vaandering EW Butler JN Cheung HW Gaines I Garbincius PH Garren LA Gottschalk E Kasper PH Kreymer AE Kutschke R Bianco S Fabbri FL Sarwar S Zallo A Cawlfield C Kim DY Rahimi A Wiss J Gardner R Chung YS Kang JS Ko BR Kwak JW Lee KB Park H Alimonti G Boschini M Caccianiga B 《Physical review letters》2001,86(14):2955-2958
Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay D0-->K+pi- with a signal yield of 149+/-31 events compared to a similarly cut sample consisting of 36 760+/-195 D0-->K-pi+ events. We use the observed ratio of D0-->K+pi- to D0-->K-pi+ (0.404+/-0.085+/-0.025)% to obtain a relationship between the D0 mixing and doubly Cabibbo suppressed decay parameters. 相似文献
74.
Nawroth F Isachenko V Dessole S Rahimi G Farina M Vargiu N Mallmann P Dattena M Capobianco G Peters D Orth I Isachenko E 《Cryo letters》2002,23(2):93-102
The aim of our study was to investigate the effects of vitrification (cooling rate approximately 10000(C/min) without cryoprotectants on swim-up prepared human spermatozoa in comparison to standard conventional freezing with cryoprotectants. Motility, morphology, rate of viability and acrosome reaction of spermatozoa were evaluated. The described method of cryopreservation of human spermatozoa by direct plunging into liquid nitrogen slush without cryoprotectants was effective and could be recommended for routine IVF. 相似文献
75.
A series of new symmetrical tetrazole-based carbazole derivatives starting from the initially generated 3,6-diformyl-N-alkylcarbazoles were successfully synthesized through a one-pot Ugi-azide reaction in moderate to high yields. Simplicity, easily accessible chemicals, mild reaction conditions, and fast separation of the products with the formation of bistetrazole-based carbazole derivatives in one step are some advantages of this method. The structure of the products was characterized and confirmed by using spectroscopic techniques such as 1H NMR, 13C NMR, FT-IR, and MS spectroscopy. 相似文献
76.
In this paper, we theoretically study the propagation of electromagnetic waves in one-dimensional double-period quasi-regular structures consisting of negative-permittivity and negative-permeability metamaterials. A Drude-type dispersive response for both permittivity and permeability of single-negative metamaterials is considered. From the numerical results performed by transfer matrix method and effective medium theory, it is found that double-period photonic crystals can exhibit an omnidirectional gap at given microwave frequency. Such an omnidirectional gap is insensitive to incident angle and polarization, and is invariant upon the change of scale length. It is also found that this gap exists in all double-period sequences, and it is independent of structure sequence. Moreover, electromagnetic field distributions in this structures show that the fields are localized at each interface of two media. These results can lead to further applications of quasi-regular structures. 相似文献
77.
78.
79.
Saeid Rahimi‐Razin Vahid Haddadi‐Asl Mehdi Salami‐Kalajahi Farid Behboodi‐Sadabad Hossein Roghani‐Mamaqani 《国际化学动力学杂志》2012,44(8):555-569
A new approach was developed to functionalize multiwalled carbon nanotubes (MWCNTs) with a polymerizable methyl methacrylate (MMA) groups, and the structure of functionalized MWCNTs were characterized by FTIR, Raman, XPS, and TEM. Using the strategy of “grafting through,” poly(methyl methacrylate) (PMMA) chains were grafted onto the surface of MWCNTs during the in situ synthesis of MWCNT/PMMA nanocomposites over reversible addition‐fragmentation chain transfer (RAFT) polymerization. Kinetics of RAFT‐mediated polymerization of MMA in the presence of MMA‐grafted MWCNTs was studied by using gas chromatography and gel permeation chromatography. To further study, attached polymers were detached and their molecular characteristics were compared to freely formed chains. Results of kinetic studies showed that the utilized commercial chain transfer agent strictly reduced the rate of polymerization as well as relatively controlled molecular weights and narrow molecular weight distributions of free chains. MWCNTs showed a radical activity, retarding the polymerization and reducing the rate of reaction. The effect of MWCNTs concentrations on molecular weights and polydispersity indexes (PDI) was different at the surface and in the bulk. The molecular weights of free chains increased, and the PDI was decreased with increasing MWCNTs. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 555–569, 2012 相似文献
80.
Chemically functionalized silica nanoparticles‐based solid‐phase extraction for effective pre‐concentration of highly toxic metal ions from food and water samples
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this research study, an efficient solid‐phase extraction procedure based on a new organometallic, effective, eco‐friendly and bio‐degradable nanoadsorbent was firstly introduced for influential pre‐concentration of Cu(II), Zn(II), Pb(II), Cd(II) and Mn(II) ions from food and water samples followed by flame atomic absorption spectrophotometric determination. This safe adsorbent consisted of silica nanoparticles chemically functionalized with di‐ethylen tri‐amine (SiO2@NH2NPs); easily prepared via an effective and simple approach. Characterization of SiO2@NH2NPs was subsequently implemented via SEM, FT‐IR and XRD; certifying high quality of the modified nanoadsorbent in terms of size, shape and surface functional groups. The effects of the main factors on the extraction efficiency were then optimized. Efficient extraction of the analytes of interest at neutral media accompanied with the aid of a bio‐compatible organometallic nanoadsorbent can be considered as valuable advantages of the proposed approach. In the optimum conditions, calibration graphs were linear in the range of 4–700 μg l?1, with higher correlation coefficients than 0.997 and limits of detection of 1.45–4.10 ng ml?1. The enrichment factor values were found to be in the span of 120–400. The resultant extraction recovery values were satisfactory; possessing the proper relative standard deviation (%, n = 5) values of 2.05–4.28%. 相似文献