全文获取类型
收费全文 | 275篇 |
免费 | 17篇 |
国内免费 | 7篇 |
专业分类
化学 | 212篇 |
力学 | 14篇 |
数学 | 12篇 |
物理学 | 61篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 21篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1983年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 15 毫秒
91.
Muhammad Mohsin Iqbal Muhammad Imran Tousif Hussain Muhammad Asif Naeem Abdullah A. Al-Kahtani Ghulam Mustafa Shah Sajjad Ahmad Amjad Farooq Muhammad Rizwan Abdul Majeed Abdul Rehman Khan Shafaqat Ali 《Journal of Saudi Chemical Society》2021,25(2):101176
Widespread application of dyes and disposal of their untreated effluents into water bodies adversely affect the ecosystem due to their complex aromatic structures and persistent nature. The present study aims to utilize the cotton stalks biochar (CSB) and its composite with zinc oxide nanoparticles (CSB/ZnONPs) to evaluate for the decontamination their batch scale potential of Congo red dye from wastewater. The characterization of CSB and CSB/ZnONPs was performed with Fourier-transform infra-red (FTIR) spectroscopy, scanning electron microscopy, energy-dispersive X-ray (EDX) and point of zero charge (PZC) to get insight of their potential for the decontamination of CR. The effects of initial CR concentration (25–500 mg/L), dosage of CSB and CSB/ZnONPs (0.5–2 g/L), solution pH (2–10) and contact time (0–180 min) were evaluated on CR removal at temperature (25 ± 1.5 °C). The results disclosed that CSB/ZnONPs showed excellent adsorption potential (556.6 mg/g) in comparison with CSB (250 mg/g) and most of the other adsorbents previously studies in the literature. The equilibrium experimental data were equally explained with Freundlich and Langmuir isotherm models (R2 > 0.98) while kinetic data demonstrated the best fit with pseudo second order model. The CSB/ZnONPs composite exhibited excellent reusability (89.65%) after five adsorption/desorption cycles for the sequestration of CR from contaminated systems. The present study demonstrated that metallic nanocomposite of CSB (CSB/ZnONPs) is an excellent candidate for the cost effective and environment friendly decontamination of CR from industrial wastewater and is suggested to be considered for the decontamination of other pollutants from the wastewater. 相似文献
92.
Pengcheng Wang Ruirui Yu Sajjad Ali Zhengshen Wang Zhigang Liu Jinming Gao Huaiji Zheng 《Molecules (Basel, Switzerland)》2021,26(10)
As an important moiety in natural products, N,O-acetal has attracted wide attention in the past few years. An efficient method to construct N,O-acetal has been developed. Using silver catalyst, cyclobutenediones were smoothly converted to the corresponding γ-aminobutenolides in the presence of formamides, in which cyclobutenediones likely proceed with a key decarbonylative [3 + 2] cycloaddition process. In this way, a series of products with varied substituents were isolated in moderate yield and fully characterized. 相似文献
93.
Sajjad Salahia Malek Taher Maghsoodloua Nourallah Hazeria Mojtaba Lashkaria Santiago Garcia-Granda Laura Torre-Fernandez 《催化学报》2015,(7):1023-1028
The one-pot eight-component reaction between Meldrum's acid, an aromatic aldehyde, and an aryl amine was achieved in the presence of citric acid catalyst. The corresponding dispirohydroquino-lines were obtained in good yields with excellent diastereoselectivity. This method is a combination of the Knoevenagel and Michael reactions. 相似文献
94.
This article reports the efficiency response curve of the high-purity germanium detector over the wide energy range, covering from 120 to 8500 keV. The efficiencies were measured for different counting geometries by using point radionuclide standards (mono-energetic as well as multi-gamma emitters) supplied by IAEA and the capture gamma-ray facility installed at PINSTECH nuclear reactor PARR-1. The measured efficiencies were required to fit with a suitable fitting function for interpolation within the energy range of interest. Several fitting functions were proposed in the literature covering different energy ranges. The functions giving the best fit to experimental data are presented. The work has successfully extended the response curve beyond 1500–8500 keV, which is the region where the standard calibration radionuclides are not available. The thermal neutron capture gamma-ray facility provided the collimated neutron beam, extracted from the core of the reactor and made to react with ammonium chloride target to produce the capture gamma rays for determining the efficiencies in the extended region. It was found that the capture gamma-ray provides a satisfactory solution to extend the absolute efficiency calibration in the MeV range. It was also found that the fitting function that is linear in its parameter was highly satisfactory up to 1500 keV but proved insufficient upto 8500 keV. The exponential function giving the good fit over the range has been presented. Good agreement has been found between the experimentally measured absolute efficiencies and the predicted result. 相似文献
95.
A bismuth oxychloride (BiOCl) nanostructure is prepared by a new low temperature route using sodium dodecyl sulfate as template and urea as hydrolytic agent. A novel heterojunction is developed between BiOCl and tungsten oxide (WO(3)) to make it an efficient visible light photocatalyst. The catalysts were characterized by X-ray diffraction analysis, Raman spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and N(2) sorption isotherms. The WO(3)/BiOCl heterojunction system extends the absorption edge to the visible region efficiently. BiOCl works as a main photocatalyst while WO(3) acts as the photosensitizer absorbing visible light in the WO(3)/BiOCl composite. The individual BiOCl and WO(3) show very low photocatalytic efficiency under visible light irradiation but their heterojunction provides unexpectedly high efficiency in decomposing rhodamine B as compared to Degussa P25, pure BiOCl, and WO(3). 相似文献
96.
A three component catalyst system entailing an amino acid (O(t)Bu-L-threonine), a hydrogen bond donor (sulfamide), and an amine base (DMAP) allows α-branched aldehyde addition to nitroalkenes in good to high yield and excellent ee. Importantly, the lowest reported catalyst loading (5.0 mol%) and aldehyde stoichiometry (1.2-2.0 equiv) is demonstrated and in most instances the best current product profile is observed. 相似文献
97.
The catalytic epoxidation of styrene using urea-hydrogen peroxide and heterotrinuclear Cu(II) complexes with general formula
(ML
n
)2Cu(acac)2, where n = 1–3 and M = VO2+ or Mn2+ is reported. Schiff base complexes ML
n
involving a 3,4-diaminopyridine bridge with free coordination site were used as the ligand, where (Ln)2− is [(5-x-Sal)2Py]2 and x = H, Br or NO2. The complexes were characterized by physico-chemical and spectroscopic methods. The electrochemical properties of M were
modified upon trinuclear complex formation. The trinuclear complexes show high catalytic activity, with up to 86% conversion
and 93% selectivity, while no catalytic properties were observed for the monomeric complexes. The catalyst could be reused
with some loss of activity. 相似文献
98.
Collective behavior of cortico-thalamic circuits: Logic gates as the thalamus and a dynamical neuronal network as the cortex
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alireza Bahramian Sajjad Shaukat Jamal Fatemeh Parastesh Kartikeyan Rajagopal and Sajad Jafari 《中国物理 B》2022,31(2):28901-028901
This paper introduces a two-layer network to investigate the effects of cortico-thalamic circuits on the cortex's collective behavior. In the brain, different parts of the cortex collaborate to process information. One of the main parts, which is the path of different cortex contacts, is the thalamus whose circuit is referred to as the "vertical" cortico-thalamic connectivity. Thalamus subnuclei can participate in the processing of the information that passes through them. It has been shown that they play the functional role of logic gates (AND, OR and XOR). To study how these thalamus circuits affect the cortical neuron behavior, a two-layer network is proposed wherein the cortex layer is composed of Hindmarsh-Rose models and the thalamus layer is constructed with logic gates. Results show that considering these logic gates can lead the network towards different synchronization, asynchronization, chimera and solitary patterns. It is revealed that for AND-gate and OR-gate, increasing the number of gates or their outputs can increase and decrease the network's coherency in excitatory and inhibitory cases, respectively. However, considering XOR-gates always results in the chimera state. 相似文献
99.
Sajjad Ahmadi Zinatossadat Hossaini Daryoush Zareyee Somayeh Soleimani Amiri Sattar Arshadi 《Journal of heterocyclic chemistry》2024,61(1):110-117
In this research, the synthesis of novel derivatives of spiroisatins in high yields was investigated. These new compounds were synthesized using a multicomponent reaction (MCR) of isatin, malononitrile, acetophenone derivatives, diethyl oxalate, primary amines, and Et3N in aqueous media. Under similar conditions, spiropyrroloisatins were prepared using MCRs of synthesized spiroistins. The antioxidant activity of newly synthesized spiroisatins is due to having an NH group which was evaluated by two procedures. Also, the antimicrobial activity of newly generated spiroisatins was evaluated by a disk distribution process utilizing two kinds of Gram-negative bacteria and Gram-positive bacteria and bacterial growth was stopped using these compounds. The advantages of this method are short reaction times, high yields of products, and the easy separation of catalyst and product using simple procedures. 相似文献
100.
Ahmad Shaabani Sajjad Keshipour Morteza Aghaei M. Hassan Khodabandeh Mansour Zahedi 《中国化学》2012,30(8):1893-1900
The zwitterionic intermediate generated from the reaction of triphenylphosphine with electron deficient acetylenic compounds was trapped by various NH acids. The synthesis resulted in a new class of highly functionalized heterocyclic compounds. Some of the reactions produced E and Z isomers. And the stability and transformation of them were studied by dynamic 1H NMR and density functional theory (DFT) calculations. 相似文献