全文获取类型
收费全文 | 134篇 |
免费 | 7篇 |
国内免费 | 4篇 |
专业分类
化学 | 77篇 |
晶体学 | 6篇 |
力学 | 2篇 |
数学 | 43篇 |
物理学 | 17篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2014年 | 4篇 |
2013年 | 17篇 |
2012年 | 19篇 |
2011年 | 16篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 5篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 171 毫秒
81.
82.
Rasheed Ahmad Khera Asad Ali Hummera Rafique Munawar HussainJovana Tatar Aamer SaeedAlexander Villinger Peter Langer 《Tetrahedron》2011,67(29):5244-5253
Suzuki-Miyaura reactions of N-protected tribromopyrazoles were studied. The reactions proceed with excellent site-selectivity. The first attack occurs at position 5, while the second and third attack occur at positions 3 and 4, respectively. A variety of 3,4,5-triaryl-pyrazoles, 3,5-diaryl-4-bromopyrazoles, and 5-aryl-3,4-dibromopyrazoles were efficiently prepared. The products are not readily available by other methods. 相似文献
83.
84.
Enver Tatar Türkan Berrin Kağizmanli 《International Journal of Mathematical Education in Science & Technology》2013,44(7):980-995
This study was carried out to examine the effects of computer-assisted instruction (CAI) using dynamic software on the achievement of students in mathematics in the topic of reflection symmetry. The study also aimed to ascertain the pre-service mathematics teachers’ opinions on the use of CAI in mathematics lessons. In the study, a mixed research method was used. The study group of this research consists of 30 pre-service mathematics teachers. The data collection tools used include a reflection knowledge test, a survey and observations. Based on the analysis of the data obtained from the study, the use of CAI had a positive effect on achievement in the topic of reflection symmetry of the pre-service mathematics teachers. The pre-service mathematics teachers were found to largely consider that a mathematics education which is carried out utilizing CAI will be more beneficial in terms of ‘visualization’, ‘saving of time’ and ‘increasing interest/attention in the lesson’. In addition, it was found that the vast majority of them considered using computers in their teaching on the condition that the learning environment in which they would be operating has the appropriate technological equipment. 相似文献
85.
D. Takači D. Pešić J. Tatar 《International Journal of Mathematical Education in Science & Technology》2013,44(7):783-791
In this paper, results of a questionnaire about continuity of functions are analysed. The tested students attend Novi Sad grammar school. The aim of this test was to check the student's theoretical and visual knowledge of continuous functions at the end of their high school education. The questions were given with and without the graphs of functions. The main conclusion is that the graph of a function has a significant influence on the students opinion about continuity. Looking at the graphs of functions mostly led to correct answers, but sometimes it causes problems, if it has a break. The idea came from a 1981 paper by Tall and Vinner, where the “concept image” of a continuous functions was examined. 相似文献
86.
A new high-performance liquid chromatographic method is described for the determination of bisoprolol in human plasma. The proposed method was based on the derivatization of bisoprolol with 4-chloro-7-nitro-2,1,3-benzoxadiazole in borate buffer at pH 9.5 to yield a fluorescent product. Chromatographic separation of bisoprolol was achieved by using isocratic elution at a flow rate of 1.2 mL/min on a C18 reversed-phase column (Inertsil, 4 μm, 150 4.6 mm) at 40°C. The mobile phase used for the analysis was methanol-water (70:30, % v/v). Fluorescence detector was used at the excitation and emission wavelengths of 458 and 525 nm, respectively. The method was validated for linearity, limit of detection, limit of quantification, precision, accuracy, recovery and system suitability. The assay was linear over the concentration range of 10-2000 ng/mL. This method was applied in pharmacokinetic studies of bisoprolol preparations in healthy volunteers. 相似文献
87.
Sulfonic acid functionalized poly(ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole), poly(EGDMA-VTAZ-SO(3)H), is evaluated in the esterification of lactic acid with methanol. From nitrogen physisorption data, high surface area (220 m(2)/g) and type IV isotherm are obtained. Conversion measurements indicate a stronger interaction of poly(EGDMA-VTAZ-20%SO(3)H) with water molecules than that occurring in poly(EGDMA-VTAZ-10%SO(3)H). Hence, the higher catalytic activity of poly(EGDMA-VTAZ-10%SO(3)H) is related to the more hydrophobic microenvironment of -SO(3)H sites, which reduces the acid site deactivation associated with adsorption of water generated during the reaction. Moreover, apparent activation energy is found to be 48.02 kJ mol(-1), which can be comparable with the literature values. 相似文献
88.
A simple, precise and sensitive spectrofluorimetric method was developed and validated for the determination of ranitidine in pharmaceutical preparations. The method is based on derivatization of ranitidine with 4-fluoro-7-nitrobenzofurazan (NBD-F). The method was successfully validated in accordance to ICH guidelines. The validation characteristics included linearity, limit of detection, limit of quantification, accuracy, precision, specificity and robustness. The method is linear over the range of 40?C1200 ng/mL. The recoveries were ranged from 98.97 to 99.43%. The proposed method was applied for the determination of ranitidine in commercially available tablets. The results were compared with those obtained by reference method using t and F-tests. 相似文献
89.
90.
Beyhan SM Götz AW Ariese F Visscher L Gooijer C 《The journal of physical chemistry. A》2011,115(9):1493-1499
Isoflavones are known to show fluorescence with intensities that depend strongly on the solvent properties and exhibit Stokes' shifts as large as 1.4 eV. While some of this behavior can be explained by (excited state) deprotonation, this mechanism does not apply for all isoflavones. The aim of this study is to computationally and experimentally investigate the reasons for this anomalous behavior of neutral isoflavones, taking the daidzein molecule as a model compound. We find that the absence in fluorescence in aprotic solvents and the weak fluorescence in protic solvents can be explained by a change of order of the lowest singlet states in which a fluorescent charge-transfer state lies below the nonfluorescent locally excited state in water but not in acetonitrile. The large Stokes' shift is partly due to a significant rotation among the chromone-phenyl bond in the excited state. 相似文献