全文获取类型
收费全文 | 580篇 |
免费 | 29篇 |
国内免费 | 5篇 |
专业分类
化学 | 446篇 |
力学 | 11篇 |
数学 | 71篇 |
物理学 | 86篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 26篇 |
2012年 | 40篇 |
2011年 | 50篇 |
2010年 | 33篇 |
2009年 | 18篇 |
2008年 | 38篇 |
2007年 | 36篇 |
2006年 | 38篇 |
2005年 | 29篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 22篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 1篇 |
1968年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有614条查询结果,搜索用时 15 毫秒
111.
Ben Rejeb S Abbott M Davies D Querry J Cléroux C Streng C Delahaut P Yeung JM 《Journal of AOAC International》2003,86(3):557-563
A competitive enzyme-linked immunosorbent assay (ELISA) was developed to detect hazelnut by using polyclonal antibodies generated against a protein extract of roasted hazelnut. No cross-reactivity was observed in tests against 39 commodities, including many common allergens, tree nuts, and legumes. Hazelnut protein standard solutions at 0.45 ng/mL [inhibition concentration (IC80) of the competitive test] were clearly identified by the ELISA. An extraction and quantification method was developed and optimized for chocolate, cookies, breakfast cereals, and ice cream, major food commodities likely to be cross-contaminated with undeclared hazelnut during food processing. No sample cleanup was required when extracts were diluted 10-fold. Recovery results were generated with blank matrixes spiked at 4 levels from 1 to 10 microg/g hazelnut protein. With the developed extraction and sample handling procedure, hazelnut proteins were recovered at 64-83% from chocolate and at 78-97% from other matrixes. A confirmatory technique was developed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western transfer. The developed methods were applied to a small market survey of chocolate products and allowed the identification of undeclared hazelnut in these products. 相似文献
112.
An HPLC method with a fluorescence detector (HPLC-FLD) was described for the quantitative determination of closantel and rafoxanide in bovine and ovine muscles. A structural analog closely related to rafoxanide, viz., N-[4-(4-chlorophenoxy)phenyl]-2-hydroxy-3,5-diiodobenzamide, was synthesized as an internal standard. Bovine and ovine muscles were extracted with acetonitrile-acetone (60 + 40, v/v) followed by cleanup on mixed mode anionic exchange SPE cartridges. After evaporation and reconstitution with the mobile phase, the sample was analyzed by HPLC-FLD using internal standard calibration. The method was validated by using fortified bovine and ovine muscles at 15, 30, and 60 microg/kg. The accuracy and RSD were 70-110% and < or =10%, respectively. 相似文献
113.
R. Zeleny S. Voorspoels M. Ricci R. Becker C. Jung W. Bremser M. Sittidech N. Panyawathanakit W. F. Wong S. M. Choi K. C. Lo W. Y. Yeung D. H. Kim J. Han J. Ryu S. Mingwu W. Chao M. M. Schantz K. A. Lippa S. Matsuyama 《Analytical and bioanalytical chemistry》2010,396(4):1501-1511
An international intercomparison involving eight national metrology institutes (NMIs) was conducted to establish their current measurement capabilities for determining five selected congeners from the brominated flame retardant classes polybrominated diphenyl ethers and polybrominated biphenyls. A candidate reference material consisting of polypropylene fortified with technical mixtures of penta-, octa- and decabromo diphenyl ether and decabromo biphenyl, which was thoroughly assessed for material homogeneity and stability, was used as study material. The analytical procedures applied by the participants differed with regard to sample pre-treatment, extraction, clean-up, employed calibrants and type of calibration procedure as well as regarding analytical methods used for separation, identification and quantification of the flame retardant congeners (gas chromatography coupled to an electron capture detector (GC-ECD), gas chromatography-mass spectrometry in the electron ionisation mode (GC-EI-MS), gas chromatography-mass spectrometry in the electron capture negative ionisation mode (GC-ECNI-MS), and liquid chromatography-inductive coupled plasma-mass spectrometry (LC-ICP-MS)). The laboratory means agreed well with relative standard deviations of the mean of means of 1.9%, 4.8%, 5.5% and 5.4% for brominated diphenyl ether (BDE) 47, 183 and 209 and for the brominated biphenyl (BB) congener 209, respectively. For BDE 206, a relative standard deviation of 28.5% was obtained. For all five congeners, within-laboratory relative standard deviations of six measurements obtained under intermediate precision conditions were between 1% and 10%, and reported expanded measurements uncertainties typically ranged from 4% to 10% (8% to 14% for BDE 206). Furthermore, the results are in good agreement with those obtained in the characterization exercise for determining certified values for the flame retardant congeners in the same material. The results demonstrate the state-of-the-art measurement capabilities of NMIs for quantifying representative BDE congeners and BB 209 in a polymer. The outcome of this intercomparison (pilot study) in conjunction with possible improvements for employing exclusively calibrants with thoroughly assessed purity suggests that a key comparison aiming at underpinning calibration and measurement capability (CMC) claims of NMIs can be conducted. Figure
Mass fraction of deca-brominated diphenyl ether (BDE 209) in the polypropylene study material analysed in the international intercomparison CCQM-P114 相似文献
114.
115.
Nga-Chun Ng Mian HR Mahmood Chi-K.Chang Hai-Yang Liu Fei Yam Lam-Lung Yeung Chi-K.Chang 《中国化学快报》2014,25(4):571-574
A series of N-base appended corroles and their manganese complexes were synthesized and their binding constants with three different nitrogenous ligands, triethylamine, N-methylimidazole and pyridine, were evaluated by spectroscopy. Kinetic studies indicated that the presence of appended N- donor ligands may cause a significant enhancement of the rate of oxygen atom transfers (OAT) from (oxo)manganese(V) corrole to alkene, and the stronger axial ligand binding has impact on the rate of the oxidation reaction. Turnover frequency (TOF) for the catalytic oxidation of alkenes by appended manganese corroles varies with the following ligand order: acetamido 〈 pyridyl 〈 imidazolyl. The influence of the external axial ligands on the catalytic epoxidation was investigated by using appended acetamido manganese corrole as catalyst, with the results revealing that N-methylimidazole gave the best enhancement on the yields of total oxidation products among the investigated nitrogenous ligands. 相似文献
116.
Atomic force microscopy (AFM) was used for in-situ observation of nanoscale morphological transformations during the ageing
step in sol-gel synthesis. Silica, alumina and silica-alumina samples with different Si/Al ratios were prepared from inorganic
salt precursors and geled at low pH. Silica and silica-alumina samples formed branch-like gel network made of nanometer-sized clusters. During ageing at room temperature, the overall structure of the gel network
remained unchanged but the clusters underwent phase transformation, coaslesence, coarsening, fragmentation, as well as dissolution
resulting in the internal restructuring of the gel material. Morphological transformation associated with crystallization
of pseudo-boehmite phase was observed for the alumina samples. These nanometer-scale processes are expected to play a key
role in dictating the material properties of the final sol-gel product. 相似文献
117.
Two MCM-41 derived adsorbents have been tailor-made for the separation of silver and copper ions using the hard-soft, acid-base (HSAB) principle as the design guideline. NH2-MCM-41 containing "hard" Lewis base adsorption sites (i.e., RNH2) was prepared for the adsorption of the "hard" Lewis acid, Cu2+, and SH-MCM-41 with a grafted "soft" thiolpropyl base was prepared for the selective removal of Ag+, a "soft" Lewis acid. Single- and binary-component adsorption studies were conducted at different metal concentrations, solution compositions, and pH values. The experimental results showed that SH-MCM-41 has excellent affinity and capacity for silver adsorption and adsorbed only the silver ions with copper remaining in the solution. The selectivity was not affected by the metal concentration and composition, anion, and pH. Under similar experimental conditions, NH2-MCM-41 selectively adsorbed copper from the binary solution. The selectivity of NH2-MCM-41 remained for the copper at different pH values, although the adsorption capacity diminished at lower pH values. The type of anions used affected copper adsorption on NH2-MCM-41 with an increased copper uptake in the presence of the sulfate ions. A simple Freundlich adsorption model was sufficient to describe metal adsorption on SH-MCM-41 and NH2-MCM-41, and the LeVan and Vermeulen model was successfully used to predict the adsorption capacity and selectivity for binary-component adsorptions. 相似文献
118.
Molecular sensors able to detect ions are of interest due to their potential application in areas such as pollutant sequestration. Alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety have been synthesized and characterized. Their anion binding properties based on host–guest interactions have been examined with the use of UV-vis absorption and emission spectral titration studies. Spectral changes were observed for both complexes upon the addition of spherical and nonspherical anions. Their titration profiles were shown to be in good agreement with theoretical results predicting a 1:1 binding model, and the binding constants were determined from the experimental data. Drastic color changes from yellow to orange–red were observed for one of the complexes upon titration with fluoride (F−) ion in acetone. These changes were ascribed to the deprotonation of the amide functionalities induced by F− ion, and this was confirmed by the restoration of spectral changes upon addition of trifluoroacetic acid to the F− ion–complex mixture as well as by electrospray ionization mass spectrometry (ESI-MS) data. 相似文献
119.
Krishnan Kumar Elias Saion M. K. Halimah Yap CK Muhd Suhaimi Hamzah 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):667-676
A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 1012 cm?2 s?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75). 相似文献
120.
A‐D‐A Type Small Molecules Based on Boron Dipyrromethene for Solution‐Processed Organic Solar Cells 下载免费PDF全文
Liangang Xiao Dr. Hongda Wang Ke Gao Dr. Lisheng Li Chang Liu Prof. Dr. Xiaobin Peng Prof. Dr. Wai‐Yeung Wong Prof. Dr. Wai‐Kwok Wong Dr. Xunjin Zhu 《化学:亚洲杂志》2015,10(7):1513-1518
The unique properties of boron dipyrromethene (BODIPY) dyes including facile synthesis, high absorption coefficients, and delocalized molecular orbitals as well as excellent photochemical and thermal stability, make them promising as materials for organic solar cells. Accordingly, in this study three A‐D ‐A structural small molecules of BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY have been synthesized, in which two BODIPY acceptor units are symmetrically conjugated to 4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)benzo[1,2‐b:4,5‐b]dithiophene (BDTT), 9,9‐dioctyl‐9H‐fluorene (FL), and thieno[3,2‐b]thiophene (TT) donor cores, respectively. The manipulation of the structural parameters significantly improves the performances of the BHJ OSCs, which show power conversion efficiencies of 4.75 %, 1.51 %, and 1.67 % based on [6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) as the acceptor material and BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY as the donor materials, respectively. 相似文献