全文获取类型
收费全文 | 251篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 155篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 19篇 |
物理学 | 75篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 18篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 17篇 |
2012年 | 17篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 46 毫秒
61.
Anam Iqbal Syed Ali Raza Naqvi Rashid Rasheed Asim Mansha Matloob Ahmad Ameer Fawad Zahoor 《Applied biochemistry and biotechnology》2018,185(1):127-139
Bacterial infection poses life-threatening challenge to humanity and stimulates to the researchers for developing better diagnostic and therapeutic agents complying with existing theranostic techniques. Nuclear medicine technique helps to visualize hard-to-diagnose deep-seated bacterial infections using radionuclide-labeled tracer agents. Metronidazole is an antiprotozoal antibiotic that serves as a preeminent anaerobic chemotherapeutic agent. The aim of this study was to develop technetium-99m-labeled metronidazole radiotracer for the detection of deep-seated bacterial infections. Radiosynthesis of 99mTc-metronidazole was carried by reacting reduced technetium-99m and metronidazole at neutral pH for 30 min. The stannous chloride dihydrate was used as the reducing agent. At optimum radiolabeling conditions, ~ 94% radiochemical was obtained. Quality control analysis was carried out with a chromatographic paper and instant thin-layer chromatographic analysis. The biodistribution study of radiochemical was performed using Escherichia coli bacterial infection-induced rat model. The scintigraphic study was performed using E. coli bacterial infection-induced rabbit model. The results showed promising accumulation at the site of infection and its rapid clearance from the body. The tracer showed target-to-non-target ratio 5.57 ± 0.04 at 1 h post-injection. The results showed that 99mTc-MNZ has promising potential to accumulate at E. coli bacterial infection that can be used for E. coli infection imaging. 相似文献
62.
Fatimah Saeed Aldughaylibi Muhammad Asam Raza Sumaira Naeem Humera Rafi Mir Waqas Alam Basma Souayeh Mohd Farhan Muhammad Aamir Noushi Zaidi Tanveer Ahmad Mir 《Molecules (Basel, Switzerland)》2022,27(18)
This study was designed to check the potential of secondary metabolites of the selected plants; Citrullus colocynthis, Solanum nigrum, Solanum surattense, Calotropis procera, Agave americana, and Anagallis arvensis for antioxidant, antibacterial, antifungal, and antidiabetic agents. Plant material was soaked in ethanol/methanol to get the crude extract, which was further partitioned via solvent extraction technique. GCMS and FTIR analytical techniques were applied to check the compounds responsible for causing antioxidant, antimicrobial, and antidiabetic activities. It was concluded that about 80% of studied extracts/fractions were active against α-amylase, ranging from 43 to 96%. The highest activity (96.63%) was exhibited by butanol fractions of A. arvensis while the least response (43.65%) was shown by the aqueous fraction of C. colocynthis and the methanol fraction of fruit of S. surattense. The highest antioxidant activity was shown by the ethyl acetate fraction of Anagallis arvensis (78.1%), while aqueous as well as n-hexane fractions are the least active throughout the assay. Results showed that all tested plants can be an excellent source of natural products with potential antimicrobial, antioxidant, and antidiabetic potential. The biological response of these species is depicted as a good therapeutic agent, and, in the future, it can be encapsulated for drug discovery. 相似文献
63.
A new triterpene named as alysinol 3alpha, 22beta-dihydroxyolean-12-ene [structure: see text] along with known compounds usnic acid, methyl 2,4-dihydroxy-3,6-dimethyl benzoate, 3-hydroxy benzoic acid, stigmasterol, poriferasterol and ursolic acid have been isolated from Alysicarpus monolifer. The structure of [structure: see text] has been established through spectroscopic techniques. 相似文献
64.
Nisar Jan Nasir Umar Ali Ghulam Shah Afzal Farooqi Zahoor Hussain Iqbal Munawar Shah Muhammad Raza 《Cellulose (London, England)》2021,28(12):7593-7607
Cellulose - In this work we have attempted to use biomass as energy source which is abundantly available throughout the world. The work is focused on pyrolysis of sugarcane bagasse in a... 相似文献
65.
In this work, we report a novel dinuclear Sn (II) complex, [Sn2(Hpdm)2(H2O)6] 2H2O 2Cl ( 1 ) (H2pdm = pyridine‐2,6‐dimethanol), which has been crystallized out and characterized by elemental analysis, FTIR, 1H and 13C NMR, single crystal X‐ray studies and Density Functional Theory (DFT) analysis. X‐ray structure of 1 has confirmed it to be a dinuclear alkoxo‐bridged Sn (II) species where each metal adopts a seven coordinate distorted pentagonal bipyramidal (pbp) geometry. This is the first hepta‐coordinated Sn (II) complex ever isolated apart from already reported stannylenes. Spin density plots from DFT support the +2 oxidation state of each tin metal. Hirshfeld surface analysis reveals the presence of various H‐bonding interactions in the molecule and molecular docking results along with DFT confirm higher binding affinity of the present complex towards DNA. Moreover, the complex exhibits promising anticancer activities against HeLa and A549 cancer cell lines. 相似文献
66.
Raza A 《Chemical & pharmaceutical bulletin》2006,54(4):432-434
Study was carried out to develop two simple, fast, accurate and sensitive spectrophotometric methods (A and B) for the determination of citalopram hydrobromide in commercial tablet formulations. In method A, UV spectrophotometer determined the contents of citalopram hydrobromide in tablets at 240 nm in methanol solvent. The linear range was 5-40 microg ml-1 with molar absorptivity 1.4x10(4) l mol-1 cm-1. While the method B based on the reaction of citalopram base as n-electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as pi-acceptors to give highly colored complex species that absorb maximally at 590 nm. Beer's law was obeyed in the concentration limit of 10-250 microg ml-1 with molar absorptivity 3.3x10(3) l mol-1 cm-1 for citalopram hydrobromide. The limits of detection and limit of quantification was calculated and found to be 5.2 microg ml-1 and 17.4 microg ml-1 respectively. The proposed methods were found to be rapid, accurate, precise and sensitive for the determination of citalopram hydrobromide in commercial tablet formulations with out interferences from common additives encountered. 相似文献
67.
Synthesis and surface engineering of magnetic nanoparticles for environmental cleanup and pesticide residue analysis: A review 下载免费PDF全文
Ranjeet Kaur Abshar Hasan Nusrat Iqbal Samsul Alam Mahesh Kr Saini Syed Kalbe Raza 《Journal of separation science》2014,37(14):1805-1825
In recent years, water pollution and pesticide accumulation in the food chain have become a serious environmental and health hazard problem. Direct determination of these contaminants is a difficult task due to their low concentration level and the matrix interferences. Therefore, an efficient separation and preconcentration procedure is often required prior to the analysis. With the advancement in nanotechnology, various types of magnetic core–shell nanoparticles have successfully been synthesized and received considerable attention as sorbents for decontamination of diverse matrices. Magnetic core–shell nanoparticles with surface modifications have the advantages of large surface‐area‐to‐volume ratio, high number of surface active sites, no secondary pollutant, and high magnetic properties. Due to their physicochemical properties, surface‐modified magnetic core–shell nanoparticles exhibit high adsorption efficiency, high rate of removal of contaminants, and easy as well as rapid separation of adsorbent from solution via external magnetic field. Such facile separation is essential to improve the operation efficiency. In addition, reuse of nanoparticles would substantially reduce the treatment cost. In this review article, we have attempted to summarize recent studies that address the preconcentration methods of pesticide residue analysis and removal of toxic contaminants from aquatic systems using magnetic core–shell nanoparticles as adsorbents. 相似文献
68.
This critical review covers synthetic ion channels and pores created between January 2004 and December 2005 comprehensively. The discussion of a rich collection of structural motifs may particularly appeal to organic, biological, supramolecular and polymer chemists. Functions addressed include ion selectivity and molecular recognition, as well as responsiveness to light, heat, voltage and membrane composition. The practical applications involved concern certain topics in medicinal chemistry (antibiotics, drug delivery), catalysis and sensing. An introduction to principles and methods is provided for the non-specialist; some new sources of inspiration from fields beyond chemistry are highlighted. 相似文献
69.
Muhammad Asad Anam Zulfiqar Rizwan Raza Minghui Yang Akhtar Hayat Naeem Akhtar 《Electroanalysis》2020,32(1):11-18
A novel electrode based on orange peel derived C‐dots decorated CuO nanorods (CR@C‐dot) modified lead pencil (LP) electrode has been fabricated for highly sensitive and selective monitoring of dopamine (DA). Prior to the functionalization with C‐dot, electrochemical efficacy of CR was evaluated and compared with CuO nano‐needles (CN) and nano‐spheres (CS). The morphology, surface area and composition of synthesized nanoparticles was confirmed through field emission scanning electron microscopy (FE‐SEM), N2‐adsorption‐desorption isotherm, X‐ray diffraction (XRD), Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS). Our results indicated that CR has high electrocatalytic activity compared to CN and CS by expositing greater fraction of catalytic active sites, large surface area and short diffusion pathways. The electrochemical efficacy of CR is further enhanced by decorating with orange peel derived C‐dots, which surprisingly lead to the integrations of surface‐active sites with current collectors with minimum resistance by acting as an electron transport mediator and providing more surface defects. The developed CR@C‐dot sensor enables highly sensitive and selective recognition of DA detection (0.0007 μM), over good linear range (5–2250 μM) with rapid response time. the developed CR@C‐dot sensor was successfully used to monitor the DA from deboned chicken, thus suggesting reliability of the developed electrode. 相似文献
70.
Syed Abdul Wadood Guo Boli Zhang Xiaowen Ali Raza Wei Yimin 《Journal of mass spectrometry : JMS》2020,55(1)
This study aimed to develop a potential analytical method to discriminate the Chinese winter wheat according to geographical origin and cultivars. A total of 90 wheat samples of 10 different wheat cultivars among three regions were examined by headspace solid phase microextraction coupled with gas chromatography‐mass spectrometry (GC‐MS). The peak areas of 32 main volatile compounds were selected and subjected to statistical analysis, which revealed significant differences among different regions and cultivars. Multivariate analysis of variance showed a significant influence of regions, wheat genotypes, and their interaction on the volatile composition of wheat. Principal component analysis of the aromatic profile showed better visualization for wheat geographical origins. Finally, a classification model based on the linear discriminant analysis was successfully constructed for the discrimination of regions and cultivars with the correct classification percentages of 90 and 100%, respectively. 相似文献