全文获取类型
收费全文 | 511篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
化学 | 385篇 |
晶体学 | 5篇 |
力学 | 19篇 |
数学 | 42篇 |
物理学 | 95篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 27篇 |
2021年 | 46篇 |
2020年 | 33篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 21篇 |
2016年 | 34篇 |
2015年 | 17篇 |
2014年 | 23篇 |
2013年 | 46篇 |
2012年 | 42篇 |
2011年 | 43篇 |
2010年 | 35篇 |
2009年 | 21篇 |
2008年 | 10篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有546条查询结果,搜索用时 31 毫秒
131.
132.
Azhar Iqbal Yousaf Iqbal Abdul Majeed Khan Safeer Ahmed 《Journal of Saudi Chemical Society》2018,22(4):449-458
This report describes the detailed structural and electrochemical characterization of a series of low content (0.01 to 0.05) Cu-Cr bi-metal doped LiMn2O4 cathode material synthesized by sol–gel method. The structural and morphological features were described using XRD, SEM, TEM, EDAX and FTIR techniques. The electron transfer and its feasibility were discussed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge–discharge studies were performed to evaluate the capacity fading and rate capability. It was found that the electrochemical performance is very much dependent on the amount of Cu-Cr bi-metal doping and interestingly decreased the capacity fading with high cycleability. The sample with the least amount of dopants (i.e., LiCu0.01Cr0.01Mn1.98O4) demonstrated much improved capacity, cycleability and high rate capability. The LiCu0.01Cr0.01Mn1.98O4 cathode exhibited a discharge capacity of 112 mA h g?1 at very first cycle and retained 93 mA h g?1 after 100 cycles at a C rate of 0.3. Further, the same material at very high current density (5 C) retained 83% of the initial discharge capacity. The Cu-Cr doping stabilized the spinel structure by suppressing the Jahn-Teller distortion effect and Mn dissolution and the resultant material showed the workability of the cathodes for devices which work at substantially high C-rate of 5C. 相似文献
133.
Task-specific ionic liquid dispersive liquid–liquid microextraction (TSIL-DLLME) is a simple and rapid preconcentration approach for the measurement of cadmium in serum and blood samples of human subjects. In this method a novel task-specific ionic liquid, trioctylmethyl ammonium thiosalicylate (TOMATS), which has dual characteristics as a chelating agent and extractive solvent, was investigated. TOMATS complexes with Cd due to the chelating effect of the ortho-positioned carboxylate relative to the thiol functionality. The assessment of the optimum values of variables including the pH, amount of reagents (TOMATS, diluents, Triton X114, and back extracting acid solution), temperature, and incubation time, which affect the recoveries of analyte by TSIL-DLLME method were studied. After enrichment experiments, acidic solution was used to back extract the metal ions from the ionic liquid rich phase and with determination by electrothermal atomic absorption spectrometry. Using the optimal experimental conditions, the limit of detection (3?s), precision (relative standard deviation), preconcentration, and enhancement factors of developed method for Cd were found to be 0.05?µg/L, greater than 5%, 62.5, and 52.8, respectively. To check the accuracy of the developed method, certified reference material of serum and blood were analyzed by the developed method, and the measured values of Cd were in good agreement with the certified values. The developed method was applied successfully to determine Cd in blood and serum samples of lymphatic cancer patients relative to healthy controls. 相似文献
134.
Studies on thermal, thermal ageing and morphological characteristics of EPDM-g-VTES/LLDPE 总被引:1,自引:0,他引:1
A novel graft copolymer of vinyltriethoxysilane onto ethylene propylene diene terpolymer has been developed by grafting varying contents of VTES using dicumyl peroxide as an initiator in a twin-screw extruder. Grafting of VTES and EPDM has been ascertained using FTIR. The EPDM-g-VTES developed has been blended with different weight percentage of linear low density polyethylene [LLDPE] by melt mixing. Thermal, thermal ageing and morphological behaviour of the blends are studied with respect to the effect of blend composition, static vulcanization and dynamic vulcanization with varying quantities of VTES and LLDPE. The incorporation of silane moiety onto EPDM raises the inception and final decomposition temperature. The stability EPDM-g-VTES/LLDPE blend increases with increase in concentration of EPDM-g-VTES due to thermally stable Si-O-Si linkage. It was ascertain from SEM micrograph that EPDM-g-VTES/LLDPE blends lead to formation of interpenetrating crosslinked network during hot water treatment and by treatment with DCP, respectively. The linear, statically vulcanized, dynamically vulcanized and filled blends of EPDM-g-VTES/LLDPE have been characterized to assess the suitability of the blends for high performance applications. In addition, it is also observed that the incorporation of fillers improves thermal stability of the blends. 相似文献
135.
Khan I Cunningham D Graham D McComb DW Smith WE 《The journal of physical chemistry. B》2005,109(8):3454-3459
The surface-enhanced resonance Raman scattering (SERRS) activity of a statistically significant number of silver nanoparticles has been studied using a correlated SERRS mapping and transmission electron microscopy (TEM) method. TEM allowed the nature of each entity to be directly identified, and the SERRS activity was obtained from the corresponding SERRS map. Particles in various states of aggregation were analyzed to establish relative activities. It was established that SERRS activity is dependent on the specific batch of colloid tested. By averaging different colloid batches, it was shown that increasing SERRS activity is observed with increasing numbers of particles in the aggregates. By reducing the surface coverage of the particles to the extent that single moieties could be examined optically, the ratio of the relative activities of single particles, dimers, trimers, and larger aggregates was estimated. High-resolution TEM images of a number of active and inactive particles are reported. However, no clear correlation between microstructure and SERRS activity was observed. 相似文献
136.
Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
137.
The simple, reliable and reproducible HPLC and extraction methods were developed for the analysis of tadalafil in pharmaceutical preparation. The column used was monolithic silica column, Chromolith Performance RP-18e (100 mm × 4.6 mm, i.d.). The mobile phase used was phosphate buffer (100 mM, pH 3.0)-acetonitrile (80:20, v/v) at the flow rate of 5 mL min−1 with UV detection at 230 nm at ambient temperature. Extraction of tadalafil from tablet was carried out using methanol. Linearity was observed in the concentration range from 100 to 5000 ng mL−1 for tadalafil with a correlation coefficient (R2) 0.9999 and 100 ng mL−1 as the limit of detection. The values of linearity range, correlation coefficient (R2) and limit of detection were 50-5000 ng mL−1, 0.9999-50 ng mL−1, respectively for sildenafil. Parameters of validation prove the precision of the method and its applicability for the determination of tadalafil in pharmaceutical tablet formulation. The method is suitable for high throughput analysis of the drug. 相似文献
138.
Spectrophotometric Determination of Prochlorperazine Maleate in Pure and Pharmaceutical Preparations
Tehseen Aman Zeeshan Majeed Asrar Ahmad Kazi Islam Ullah Khan 《Mikrochimica acta》2002,138(1-2):13-17
Prochlorperazine maleate reacts with 1-naphthylamine and sodium nitrite, after heating for 110 s at 80 °C to give an orange
red colour having maximum absorbance at 460 nm. The reaction is selective for prochlorperazine maleate with 0.01 mg/mL as
visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s
law from 0.01 mg/10 mL to 0.33 mg/10 mL of prochlorperazine maleate and the relative standard deviation is 0.68%. The quantitative
assessment of tolerable amounts of other drugs is also studied.
Received September 22, 2000. Revision June 19, 2001 相似文献
139.
JPC – Journal of Planar Chromatography – Modern TLC - An inexpensive, simple, and reproducible SPE-TLC method has been developed and validated for analysis of haloperidol and its three... 相似文献