全文获取类型
收费全文 | 172篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 120篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 28篇 |
物理学 | 24篇 |
出版年
2023年 | 1篇 |
2022年 | 13篇 |
2021年 | 12篇 |
2020年 | 23篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 18篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2001年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有179条查询结果,搜索用时 401 毫秒
81.
Mahreen Akram Shazia Bashir Muhammad Shahid Rafique Asma Hayat Khaliq Mahmood 《Plasma Chemistry and Plasma Processing》2017,37(1):287-304
Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm2 under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. Laser Induced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 × 1018 to 0.72 × 1018 cm?3 respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm2 followed by a decrease from 19 to 25 GW/cm2 and then a saturation from 25 to 50 GW/cm2. The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters. 相似文献
82.
He Jian Khedher Asma Spreij Peter 《Statistical Inference for Stochastic Processes》2021,24(2):353-403
Statistical Inference for Stochastic Processes - In this paper we address the problem of estimating the posterior distribution of the static parameters of a continuous-time state space model with... 相似文献
83.
Belhadj Asma Bessrour Jamel Bouhafs Mahmoud Barrallier Laurent 《Journal of Thermal Analysis and Calorimetry》2009,97(3):911-915
In this paper we are concerned with the t-dependent cooling velocity during laser welding sequences. The temperature profile
has been yielded by using keyhole approximation for the melted zone and solving the heat transfer equation. A polynomial expansion
has been adopted as a guide to determining the cooling velocity during welding cut-off stage. A thorough comparison with experimental
results and recently published profiles has been carried out. 相似文献
84.
Sayed Mehdi Ghoreishi Mohsen Behpour Mona Delshad Asma Khoobi 《Central European Journal of Chemistry》2012,10(6):1824-1829
Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10?7?1×10?4 M and 3×10?7?2×10?4 M. Their detection limits were 1×10?7 and 5.1×10?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10?7 to 6.9×10?8 M. The electrode was successfully used to quantitate Tyr and UA in serum. 相似文献
85.
Abdul Wajid Khan Saleem Jan Shaista Parveen Rahmat Ali Khan Asma Saeed Abdul Jabbar Tanveer Anwar Ali Shad 《Chemistry Central journal》2012,6(1):1-6
Background
Nickel ferrite, a kind of soft magnetic materials is one of the most attracting class of materials due to its interesting and important properties and has many technical applications, such as in catalysis, sensors and so on. In this paper the synthesis of NiFe2O4 nanoparticles by the hydrothermal method is reported and the inhibition of surfactant (Glycerol or Sodium dodecyl sulfate) on the particles growth is investigated.Methods
For investigation of the inhibition effect of surfactant on NiFe2O4 particles growth, the samples were prepared in presence of Glycerol and Sodium dodecyl sulfate. The X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM) and inductively coupled plasma atomic emission spectrometer (ICP-AES) techniques were used to characterize the samples.Results
The results of XRD and ICP-AES show that the products were pure NiFe2O4 and also nanoparticles grow with increasing the temperature, while surfactant prevents the particle growth under the same condition. The average particle size was determined from the Scherrer's equation and TEM micrographs and found to be in the range of 50-60 nm that decreased up to 10-15 nm in presence of surfactant. The FT-IR results show two absorption bands near to 603 and 490 cm-1 for the tetrahedral and octahedral sites respectively. Furthermore, the saturated magnetization and coercivity of NiFe2O4 nanoparticles were in the range of 39.60 emu/g and 15.67 Qe that decreased for samples prepared in presence of surfactant. As well as, the nanoparticles exhibited a superparamagnetic behavior at room temperature.Conclusions
Nanosized nickel ferrite particles were synthesized with and without surfactant assisted hydrothermal methods. The results show that with increasing of temperature, the crystallinity of nanoparticles is increased. In the presence of surfactants, the crystallinity of NiFe2O4 nanoparticles decreased in comparison with surfactant- free prepared samples. All of the nickel ferrite nanoparticles were superparamagnetic at room temperature.Graphical abstract
相似文献86.
Tougerti A Llorens I D'Acapito F Fonda E Hazemann JL Joly Y Thiaudière D Che M Carrier X 《Angewandte Chemie (International ed. in English)》2012,51(31):7697-7701
Surface-dependent precipitation: The adsorption of Ni(II) complexes in aqueous solution on (0001) and (1102) α-Al(2)O(3) single-crystal surfaces has been studied (see the X-ray absorption spectra obtained for parallel and perpendicular polarization directions). The use of planar model systems emphasizes the crucial role of the Al(2)O(3) orientation for Ni dispersion with practical implications in catalyst preparation procedures. 相似文献
87.
Wansi JD Wandji J Mbaze Meva'a L Kamdem Waffo AF Ranjit R Khan SN Asma A Iqbal CM Lallemand MC Tillequin F Fomum Tanee Z 《Chemical & pharmaceutical bulletin》2006,54(3):292-296
The CH2Cl2/MeOH extract of the stem bark of Oriciopsis glaberrima ENGL. afforded four new acridone alkaloids namely oriciacridone C, D, E and F along with six known compounds: atalaphyllidine, oleanolic acid, butulinic acid, beta-sitosterol, stigmasterol, glucoside of stigmasterol and one synthetically known acridone: 1,3,5-trihydroxy-4-prenylacridone. The structures were established on the basis of MS, 1D and 2D NMR experiments. The acridones 1, 4 and 5 showed potent activity against alpha-glucosidase, while the acridones 1-5 showed moderate free radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH). 相似文献
88.
A new approach to decoupling of bacterial adhesion energies measured by AFM into specific and nonspecific components 总被引:1,自引:0,他引:1
A new method to decoupling of bacterial interactions measured by atomic force microscopy (AFM) into specific and nonspecific components is proposed. The new method is based on computing the areas under the approach and retraction curves. To test the efficacy of the new method, AFM was used to probe the repulsion and adhesion energies present between Listeria monocytogenes cells cultured at five pH values (5, 6, 7, 8, and 9) and silicon nitride (Si3N4). Overall adhesion energy was then decoupled into its specific and nonspecific components using the new method as well as using Poisson statistical approach. Poisson statistical method represents the most commonly used approach to decouple bacterial interactions into their components. For all pH conditions investigated, specific energies dominated the adhesion, and a transition in adhesion and repulsion energies for cells cultured at pH 7 was observed. When compared, the differences in the specific and nonspecific energies obtained using Poisson analysis and the new method were on average 2.2 % and 6.7 %, respectively. The relatively close energies obtained using the two approaches demonstrate the efficacy of the new method as an alternative way to decouple adhesion energies into their specific and nonspecific components. 相似文献
89.
JPC – Journal of Planar Chromatography – Modern TLC - A thin-layer chromatographic system comprising of silica gel as stationary phase and 1.0% aqueous urea solution as mobile phase (pH... 相似文献
90.
Let ? be a prime ring, 𝒞 the extended centroid of ?, ? a Lie ideal of ?, F be a nonzero generalized skew derivation of ? with associated automorphism α, and n ≥ 1 be a fixed integer. If (F(xy) ? yx) n = 0 for all x, y ∈ ?, then ? is commutative and one of the following statements holds: (1) Either ? is central; (2) Or ? ? M 2(𝒞), the 2 × 2 matrix ring over 𝒞, with char(𝒞) = 2. 相似文献