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排序方式: 共有182条查询结果,搜索用时 125 毫秒
31.
I.A. Alnour H. Wagiran N. Ibrahim Z. Laili M. Omar S. Hamzah Bello.Y. Idi 《Radiation Physics and Chemistry》2012,81(12):1842-1847
This study was conducted to determine the concentration of natural radionuclides in the granite rocks of selected quarry sites in Johor state, Malaysia and their possible radiological effects. The activity concentrations of 238U, 232Th and 40K in the areas of study indicated varying values of 238U, 232Th and 40K. The highest values of 238U and 232Th concentrations (67±1 and 85±2 Bq kg?1, respectively) were observed at Kamad Quarry (IJM), whereas the highest value of 40K concentration (722±18 Bq kg?1) was detected in Kim Seng Quarry, while the values of activity concentration are lower in Hanson Quarry Products (Kulai) (25±0.5 for 238U, 24±0.5 for 232Th and 429±11 for 40K). Overall, 40K has the highest concentration in the granite rocks of the quarry sites, followed by 232Th and the least for 238U. The radium equivalent activity concentration was found in the range between 94 and 239 Bq kg?1, the absorbed dose rate was found to be in the range between 47 and 112 nGy h?1, and effective dose ranged from 58 to 137 μSv h?1. Moreover, the internal and external hazard index values were given in results lower than unity. 相似文献
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33.
Hisham Ben Hamidane Aleksey Vorobyev Maud Larregola Aneta Lukaszuk Dirk Tourwé Dr. Solange Lavielle Philippe Karoyan Dr. Yury O. Tsybin Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4612-4622
We report on the characteristics of the radical‐ion‐driven dissociation of a diverse array of β‐amino acids incorporated into α‐peptides, as probed by tandem electron‐capture and electron‐transfer dissociation (ECD/ETD) mass spectrometry. The reported results demonstrate a stronger ECD/ETD dependence on the nature of the amino acid side chain for β‐amino acids than for their α‐form counterparts. In particular, only aromatic (e.g., β‐Phe), and to a substantially lower extent, carbonyl‐containing (e.g., β‐Glu and β‐Gln) amino acid side chains, lead to N? Cβ bond cleavage in the corresponding β‐amino acids. We conclude that radical stabilization must be provided by the side chain to enable the radical‐driven fragmentation from the nearby backbone carbonyl carbon to proceed. In contrast with the cleavage of backbones derived from α‐amino acids, ECD of peptides composed mainly of β‐amino acids reveals a shift in cleavage priority from the N? Cβ to the Cα? C bond. The incorporation of CH2 groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical‐driven β‐amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research. 相似文献
34.
Najim N Bathich Y Zain MM Hamzah AS Shaameri Z 《Molecules (Basel, Switzerland)》2010,15(12):9340-9353
The aim of this study was to investigate the in vitro cellular activity of novel spiroisoxazoline type compounds against normal and cancer cell lines from lung tissue (Hs888Lu), neuron-phenotypic cells (SH-SY5Y), neuroblastoma (SH-SY5Y), human histiocytic lymphoma (U937), lung cancer (A549), and leukaemia (HL-60). Our bioassay program revealed that the spiroisoxazoline type compounds show cytotoxicity only in lymphoma cell lines, which is in contrast with the pyrrolidine precursor of these spiroisoxazoline compounds, where significant cytotoxicity is seen in all normal and cancer cell lines. These data suggest a tumour-specific mechanism of action. In addition these data also show that spiroisoxazoline compounds are non-toxic in the human neuronphenotypic neuroblastoma SH-SY5Y cell line, and furthermore that they might protect cells from neurodegenerative disease. 相似文献
35.
Hisham Ben Hamidane Huan He Oleg Yu. Tsybin Mark R. Emmett Christopher L. Hendrickson Alan G. Marshall Yury O. Tsybin 《Journal of the American Society for Mass Spectrometry》2009,20(6):1182-1192
The rules for product ion formation in electron capture dissociation (ECD) mass spectrometry of peptides and proteins remain
unclear. Random backbone cleavage probability and the nonspecific nature of ECD toward amino acid sequence have been reported,
contrary to preferential channels of fragmentation in slow heating-based tandem mass spectrometry. Here we demonstrate that
for amphipathic peptides and proteins, modulation of ECD product ion abundance (PIA) along the sequence is pronounced. Moreover,
because of the specific primary (and presumably secondary) structure of amphipathic peptides, PIA in ECD demonstrates a clear
and reproducible periodic sequence distribution. On the one hand, the period of ECD PIA corresponds to periodic distribution
of spatially separated hydrophobic and hydrophilic domains within the peptide primary sequence. On the other hand, the same
period correlates with secondary structure units, such as α-helical turns, known for solution-phase structure. Based on a number of examples, we formulate a set of characteristic features
for ECD of amphipathic peptides and proteins: (1) periodic distribution of PIA is observed and is reproducible in a wide range
of ECD parameters and on different experimental platforms; (2) local maxima of PIA are not necessarily located near the charged
site; (3) ion activation before ECD not only extends product ion sequence coverage but also preserves ion yield modulation;
(4) the most efficient cleavage (e.g. global maximum of ECD PIA distribution) can be remote from the charged site; (5) the
number and location of PIA maxima correlate with amino acid hydrophobicity maxima generally to within a single amino acid
displacement; and (6) preferential cleavage sites follow a selected hydrogen spine in an α-helical peptide segment. Presently proposed novel insights into ECD behavior are important for advancing understanding of
the ECD mechanism, particularly the role of peptide sequence on PIA. An improved ECD model could facilitate protein sequencing
and improve identification of unknown proteins in proteomics technologies. In structural biology, the periodic/preferential
product ion yield in ECD of α-helical structures potentially opens the way toward de novo site-specific secondary structure determination of peptides and
proteins in the gas phase and its correlation with solution-phase structure. 相似文献
36.
Mohamed H Russo AP Szarowski DH McDonnell E Lepak LA Spencer MG Martin DL Caggana M Turner JN 《Journal of chromatography. A》2006,1111(2):214-219
In lab-on-a-chip applications, filtration is currently performed prior to sample loading or through pre-cast membranes adhered to the substrate. These membranes cannot be patterned to micrometer resolution, and their adhesion may be incompatible with the fabrication process or may introduce contaminants. We have developed an on-chip separation process using a biocompatible polymer that can be patterned and has controllable molecular rejection properties. We spun cast cellulose acetate (CA) membranes directly onto silicon wafers. Characterization of the molecular flux across the membrane showed that molecular weight and charge are major factors contributing to the membranes' rejection characteristics. Altering casting conditions such as polymer concentration in the casting solution and the quenching-bath composition and/or temperature allowed control of the molecular weight cut-off (MWCO). Three MWCOs; 300, 350, and 700 Da have been achieved for non-linear molecules. Molecular shape is also very important as much higher molecular weight single-stranded DNA was electrophoresed across the membranes while heme with a similar negative charge density was rejected. This was due to DNA's small molecular cross section. This is an important result because heme inhibits polymerase chain reactions (PCR) reducing the detection and characterization of DNA from blood samples. 相似文献
37.
The chromatographic behaviour of a new HPLC-stationary phase (Chromolith RP-18e) is described for separation of beta-blockers. The effects of the different chromatographic conditions (buffer system, pH value, content of organic modifier, injection volume and flow rate) on the separation behaviour were studied. At higher flow rates the peaks seemed to be more symmetrical than at lower flow rates. The use of buffer or salt in the mobile phase for this separation is found to be very essential and the counter-anion type of this buffer or salt significantly affected the retention behaviour of beta-blockers while the cation type did not play the same important role. 相似文献
38.
Endothelial cell dysfunction is considered to be one of the major causes of vascular complications in diabetes. Polyphenols are known as potent antioxidants that can contribute to the prevention of diabetes. Corn silk has been reported to contain polyphenols and has been used in folk medicine in China for the treatment of diabetes. The present study aims to investigate the potential protective role of the phenolic-rich fraction of corn silk (PRF) against injuries to vascular endothelial cells under high glucose conditions in vitro and in vivo. The protective effect of PRF from high glucose toxicity was investigated using human umbilical vein endothelial cells (HUVECs). The protective effect of PRF was subsequently evaluated by using in vivo methods in streptozotocin (STZ)-induced diabetic rats. Results showed that the PRF significantly reduced the cytotoxicity of glucose by restoring cell viability in a dose-dependent manner. PRF was also able to prevent the histological changes in the aorta of STZ-induced diabetic rats. Results suggested that PRF might have a beneficial effect on diabetic patients and may help to prevent the development and progression of diabetic complications such as diabetic nephropathy and atherosclerosis. 相似文献
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40.
In this paper we analyze composite non-adaptive algorithms for optimization of one-dimensional Brownian motion. We show that a composite deterministic algorithm has a better average performance than the best random one. 相似文献