全文获取类型
收费全文 | 284篇 |
免费 | 13篇 |
专业分类
化学 | 239篇 |
力学 | 2篇 |
数学 | 27篇 |
物理学 | 29篇 |
出版年
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 15篇 |
2012年 | 20篇 |
2011年 | 26篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1943年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 15 毫秒
61.
Klaudia Stando Ewa Korzeniewska Ewa Felis Monika Harnisz Sylwia Bajkacz 《Molecules (Basel, Switzerland)》2022,27(14)
Manure is a major source of soil and plant contamination with veterinary drugs residues. The aim of this study was to evaluate the uptake of 14 veterinary pharmaceuticals by parsley from soil fertilized with manure. Pharmaceutical content was determined in roots and leaves. Liquid chromatography coupled with tandem mass spectrometry was used for targeted analysis. Screening analysis was performed to identify transformation products in the parsley tissues. A solid-liquid extraction procedure was developed combined with solid-phase extraction, providing recoveries of 61.9–97.1% for leaves and 51.7–95.6% for roots. Four analytes were detected in parsley: enrofloxacin, tylosin, sulfamethoxazole, and doxycycline. Enrofloxacin was detected at the highest concentrations (13.4–26.3 ng g−1). Doxycycline accumulated mainly in the roots, tylosin in the leaves, and sulfamethoxazole was found in both tissues. 14 transformation products were identified and their distribution were determined. This study provides important data on the uptake and transformation of pharmaceuticals in plant tissues. 相似文献
62.
63.
E. Klemt P. Bopp L. Hornig J. Last S. J. Freedman D. Dubbers O. Schärpf 《Zeitschrift fur Physik C Particles and Fields》1988,37(2):179-189
The beta-decay asymmetry of the free neutron is measured with polarized neutrons and a long solenoidal beta-spectrometer with 4π electron-detection solid angle. The asymmetry parameter corrected for recoil and weak magnetism isA 0=?0.1146±0.0019, implyingg A /g v =1.262±0.005 for the ratio of the axial-vector to the vector weak coupling constants. 相似文献
64.
We report a spatially resolved kinetic finite element model of parahydrogen-induced polarisation (PHIP) in a microfluidic chip that was calibrated using on-chip and off-chip NMR data. NMR spectroscopy has great potential as a read-out technique for lab-on-a-chip (LoC) devices, but is often limited by sensitivity. By integrating PHIP with a LoC device, a continuous stream of hyperpolarised material can be produced, and mass sensitivities of have been achieved. However, the yield and polarisation levels have so far been quite low, and can still be optimised. To facilitate this, a kinetic model of the reaction has been developed, and its rate constants have been calibrated using macroscopic kinetic measurements. The kinetic model was then coupled with a finite element model of the microfluidic chip. The model predicts the concentration of species involved in the reaction as a function of flow rate and position in the device. The results are in quantitative agreement with published experimental data. 相似文献
65.
66.
Amanda Grylewicz Kacper Szymaski Dominika Darowna Sylwia Mozia 《Molecules (Basel, Switzerland)》2021,26(9)
Ultrafiltration polyethersulfone (PES) membranes were prepared by wet phase inversion. Commercial halloysite nanotubes (HNTs) in the quantities of 0.5 wt% vs. PES (15 wt%) were introduced into the casting solution containing the polymer and different solvents: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), or 1-methyl-2-pyrrolidinone (NMP). The type of solvent influenced the membranes’ morphology and topography, as well as permeability, separation characteristics, and antifouling and antibacterial properties. The membranes prepared using DMA exhibited the loosest cross-section structure with the thinnest skin and the roughest surface, while the densest and smoothest were the DMF-based membranes. The advanced contact angles were visibly lower in the case of the membranes prepared using DMF compared to the other solvents. The highest water permeability was observed for the DMA-based membranes, however, the most significant effect of the modification with HNTs was found for the NMP-based series. Regardless of the solvent, the introduction of HNTs resulted in an improvement of the separation properties of membranes. A noticeable enhancement of antifouling performance upon application of HNTs was found only in the case of DMF-based membranes. The study of the antibacterial properties showed that the increase in surface roughness had a positive effect on the inhibition of E. coli growth. 相似文献
67.
Renata Kasprzyk Beata J. Starek Sylwia Ciechanowicz Dorota Kubacka Joanna Kowalska Jacek Jemielity 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6728-6740
The m7G cap is a unique nucleotide structure at the 5′-end of all eukaryotic mRNAs. The cap specifically interacts with numerous cellular proteins and participates in biological processes that are essential for cell growth and function. To provide small molecular probes to study important cap-recognizing proteins, we synthesized m7G nucleotides labeled with fluorescent tags via the terminal phosph(on)ate group and studied how their emission properties changed upon protein binding or enzymatic cleavage. Only the pyrene-labeled compounds behaved as sensitive turn-on probes. A pyrene-labeled m7GTP analogue showed up to eightfold enhanced fluorescence emission upon binding to eukaryotic translation initiation factor 4E (eIF4E) and over 30-fold enhancement upon cleavage by decapping scavenger (DcpS) enzyme. These observations served as the basis for developing binding- and hydrolytic-activity assays. The assay utility was validated with previously characterized libraries of eIF4E ligands and DcpS inhibitors. The DcpS assay was also applied to study hydrolytic activity and inhibition of endogenous enzyme in cytoplasmic extracts from HeLa and HEK cells. 相似文献
68.
Miriam M. Schwab Daniel Himmel Sylwia Kacprzak Daniel Kratzert Valentin Radtke Philippe Weis Kallol Ray Ernst‐Wilhelm Scheidt Wolfgang Scherer Bas deBruin Stefan Weber Ingo Krossing 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(49):14919-14922
The straightforward synthesis of the cationic, purely organometallic NiI salt [Ni(cod)2]+[Al(ORF)4]− was realized through a reaction between [Ni(cod)2] and Ag[Al(ORF)4] (cod=1,5‐cyclooctadiene). Crystal‐structure analysis and EPR, XANES, and cyclic voltammetry studies confirmed the presence of a homoleptic NiI olefin complex. Weak interactions between the metal center, the ligands, and the anion provide a good starting material for further cationic NiI complexes. 相似文献
69.
The synthesis of S-alkylated cysteine derivatives was carried out successfully in the presence of 1,1,3,3-tetramethylguanidine. Alkylation proceeded in high yields on unprotected amino acids and peptides containing a sulfhydryl group. 相似文献
70.
Igor Perevyazko Antje Vollrath Stephanie Hornig Georges M. Pavlov Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2010,48(18):3924-3931
Nanoprecipitation represents an effective method for the production of polymeric nanoparticles. This technique was used to prepare nanoparticles from solutions of poly(methyl methacrylate) and its copolymers. Since the regulation of main parameters like particle size, particle size distribution, and molar particle mass is very important for future applications, the stable nanoparticle dispersions were examined by scanning electron microscopy, velocity sedimentation, and dynamic light scattering, whereby advantages and disadvantages of each characterization techniques are discussed. Polydispersities of particle size distributions are determined by the ratio of dw/dn, where dw and dn are weight‐ and number‐average diameters, respectively. The particle characteristics strongly depend on the chemical structure of the polymers and the way of preparation and, therefore, vary in the studied cases in the range of 6 < dw < 680 nm, whereas the polydispersity index dw/dn changes in the range of 1.02 to 1.40. It is shown that nanoparticles in a desirable size range can be prepared by solvent–nonsolvent methods (dialysis technique or dropping technique). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3924–3931, 2010 相似文献