全文获取类型
收费全文 | 171篇 |
免费 | 11篇 |
国内免费 | 5篇 |
专业分类
化学 | 157篇 |
力学 | 6篇 |
数学 | 7篇 |
物理学 | 17篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 17篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 5篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1995年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 78 毫秒
131.
Nonlinear excitable systems far from equilibrium can exhibit pattern formation such as spirals, target patterns, etc. One such system is the heterogeneous catalytic reaction of CO with oxygen on platinum single crystals. It has been established that the resonant periodic forcing of spirals in such excitable systems can cause a spiral drift. Here, we investigate the effects of a linear thermal gradient on the spiral dynamics during CO oxidation on platinum (110) for the first time, both in simulations and with experiments. Our results suggest that a spatial thermal gradient established across the surface can act as an internal forcing drive and cause the spiral patterns to drift. This drift has components both parallel and perpendicular to the external gradient. 相似文献
132.
Khorshidi Parisa Shirazi Reza Haji Seyed Mohammad Miralinaghi Mahsasadat Moniri Elham Saadi Sommayeh 《Research on Chemical Intermediates》2020,46(7):3607-3627
Research on Chemical Intermediates - The aim of the present study was to develop a novel adsorbent through decorating the surface of graphene oxide (GO) nanosheets with nickel ferrite (NiFe2O4)... 相似文献
133.
Mehdi Bakavoli Mohammad Rahimizadeh Esmaeel Rezaei-Seresht Majid Mokaber Esfahani Parisa Ziaee 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2152-2158
The synthesis of some novel crown and thiacrown ethers via the reaction of 2,3-bis(4-hydroxyphenyl) or 2,3-bis(4-mercaptophenyl)quinoxalines and pyridopyridazine with diethylene and triethylene glycol ditosylate is described. The complexing ability of compounds 5b and 5h, as the representatives of both groups of compounds, with alkali and alkali earth metal cations were measured by the solvent extraction method. The results showed that crown ether 5b comparatively had more affinity towards the Mg2+ cation, while thiacrown ether 5h had greater affinity towards the Ca2+ cation. 相似文献
134.
Hamid Ravaghi Nazanin Abolhassani Parisa Dahim Nasrin Shaarbafchizadeh Soghra Anjarani Nooshafarin Safadel 《Accreditation and quality assurance》2014,19(4):301-305
To establish a national accreditation system for medical laboratories, Iran has set national standards based on the international standard ISO 15189. Central to the accreditation process are the technical assessors. Their attitude in this regard and their experiences should be identified. This study aims to explore assessors’ attitudes toward national laboratory accreditation and their experiences of assessment process in order to identify current gaps and suggest required interventions to solve them. A qualitative study using an open-ended questionnaire was employed. A total of 150 assessors working in the General Directorate of Laboratory Affairs participated in the study. While almost all Iranian laboratory accreditation assessors were generally supportive about the necessity of laboratory accreditation and cited benefits of this process, they pointed to improvement areas including developing assessor selection and appraisal criteria, continuous training, taking into consideration the heterogeneity of laboratories throughout the country, participation of professional associations and adopting measures to increase laboratories’ involvement. 相似文献
135.
136.
The formation constants of the species formed in the systems H+ + thallium(I) + AMP and H+ + AMP have been determined in aqueous solutions of methanol at 25 degrees C and constant ionic strength 0.1 mol dm(-3) sodium perchlorate, using spectrophotometric and potentiometric techniques. Thallium(I) forms two mononuclear 1:1 complexes with AMP of the type TlHL and TlL- in the pH range of study (1-11), where L2- represents the fully dissociated ligand. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, beta111, and beta101, versus alpha (hydrogen-bond donor acidity), beta (hydrogen-bond accepter basicity), and for pi* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlation represents significant improvement with regard to the single-parameter models. Finally, the results are discussed in terms of the effect of the solvent on complexation. 相似文献
137.
Tahereh Ahmadi Ghodsi Mohammadi Ziarani Parisa Gholamzadeh Hoda Mollabagher 《Tetrahedron: Asymmetry》2017,28(5):708-724
Asymmetric multicomponent reactions (AMCRs) include the reaction of three or more reactants simultaneously to produce chiral products that they have some advantages containing simple procedures, saving time and energy, and being environmentally friendly processes. AMCRs have seen much development and their potent synthetic approaches are discussed in this review. 相似文献
138.
Kamyar Mollazadeh Moghaddam Mohammad Arfan Jamal Rafique Sassan Rezaee Parisa Jafari Fesharaki Ahmad Reza Gohari Ahmad Reza Shahverdi 《Applied biochemistry and biotechnology》2010,162(1):127-133
Microbial resistance is a major drawback in chemotherapy of microbial or fungal infection disease. In this study, the antifungal
activity of ethanol extract of a selected plant (Sarcococca saligna) has been investigated against clinical isolates of Aspergillus niger, Aspergillus treus, Aspergillus flavus, and Aspergillus fumigatus. Also, the enhancement of the antifungal activity of fluconazole by this extract was further evaluated against mentioned
test strains. Conventional disk diffusion method was used to assay the antifungal activity of S. saligna ethanol extract in the absence and presence of fluconazole. The highest antifungal activity was observed against A. treus. The ethanol extract of S. saligna enhanced the antifungal activity of fluconazole against A. niger and A. treus and A. flavus. At the highest tested contents (4 mg/disk), 1.15-, 0.64-, and 2.47-fold increases in inhibition zone surface area were observed
for A. niger, A. treus, and A. flavus, respectively. However, no enhancing effect was observed for this plant extract against Aspergillus fumigates at tested contents (0.5, 1, 2, 3, and 4 mg/disk). In a separate experiment, the general cytotoxicity of the ethanol extract
of S. saligna was examined with brine shrimp assay. This plant extract showed low cytotoxicity against Artemia salina (LC50 = 186 μg/ml). 相似文献
139.
Nooshafarin Safadel Soghra Anjarani Marjan Rahnamaye Farzami Rana Amini Siamak Mirab Samiee Parisa Dahim 《Accreditation and quality assurance》2014,19(6):473-476
To strengthen clinical laboratories’ capabilities, the Reference Health Laboratory (RHL) of the Ministry of Health decided to compile a national professional laboratory standard to be followed by all medical laboratories in the country. Providing a national laboratory standard, as approved criteria for competency assessment, is also essential for establishment of a national accreditation system for medical laboratories. ISO 15189 addresses different processes and activities in a medical laboratory, but considering the local situation and limitations in the country it was not feasible to implement all the requirements of ISO 15189 at once in laboratories in different sectors and in different provinces of the country. For this reason, the RHL decided to define and publish the national standard, as minimum quality requirements that could be mandatory for all clinical laboratories throughout the country. After conducting a countrywide situation analysis, a national standard was composed by RHL expert committees and officially announced in September 2007. The main reference of this standard was ISO 15189:2007, although some important technical details were added to it from other credible references, such as WHO documents and CLSI guidelines. In this study, the Iranian national standard is compared to ISO 15189:2007 in terms of format and content in order to show how an international standard was localized for compiling a national standard. 相似文献
140.
Quantification and transformation of organic compounds are pivotal in understanding atmospheric processes, because such compounds
contribute to the oxidative capacity of the atmosphere and drive climate change. It has recently been recognized that chemical
reactions in snow play a role in the production or destruction of photolabile volatile organic compounds (VOC). We present
an environmentally friendly method for determination of VOC and semi-VOC in snow collected at three sites—remote, urban, and
(sub-)arctic. A solid-phase micro-extraction (SPME) procedure was developed and (semi-)VOC were identified by gas chromatography
with mass spectrometric detection (GC–MS). A broad spectrum of (semi-)VOC was found in snow samples, including aldehydes,
and aromatic and halogenated compounds. Quantification was performed for 12 aromatic and/or oxygenated compounds frequently
observed in snow by use of neat standard solutions. The concentrations detected were between 0.12 (styrene and ethylbenzene)
and 316 μg L−1 (toluene) and limits of detection varied between 0.11 (styrene) and 1.93 μg L−1 (benzaldehyde). These results indicate that the SPME technique presented is a broad but selective, versatile, solvent-free,
ecological, economical, and facile method of analysis for (semi-)VOC in natural snow samples. 相似文献