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排序方式: 共有239条查询结果,搜索用时 343 毫秒
91.
P. Hübner Edgar Studer Daniel Häfliger Markus Stadler Christian Wolf Martin Looser 《Accreditation and quality assurance》1999,4(7):292-298
The detection of genetically modified organisms (GMOs) by the polymerase chain reaction (PCR) is a complex multiparameter
problem. Therefore, a number of critical issues in respect to quality control need to be considered. For practical purposes,
the PCR process itself can be divided into three subprocesses: template isolation and reaction setup (pre-PCR), PCR reaction
and detection of amplification products, and data evaluation (post-PCR). Crucial factors for the pre-PCR process are the following:
homogeneity of the sample to be analysed, performance of template isolation and purification in terms of yield and purity,
standardized process for the estimation of concentrations of genomic DNA and all reagents used in the reaction. For the PCR
itself, crucial factors to be controlled are: setup of reactions, batch to batch variations of reagents, temperature-time
programs used for the PCR amplification, and the performance of different types of hardware (e.g. different brands of thermocyclers).
The crucial factor for the post-PCR process is the detection of the amplification products of the PCR. The tremendous sensitivity
of PCR methods requires a careful and consequent separation of the three processes in terms of hardware, laboratory space
and sample handling. The avoidance of contamination is one of the most critical factors. The goal of quality assurance measures
must be to ensure appropriate results at maximum sensitivity. The complexity of any PCR system used for the detection of GMOs
leads to the requirement of a careful validation process for any laboratory using such methods. For qualitative analyses crucial
validation parameters are: specificity, selectivity, repeatability, intermediate precision, reproducibility, limit of detection
and robustness.
Received: 5 October 1998 / Accepted: 22 February 1999 相似文献
92.
To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, 13C-2H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from Ginkgo biloba L. by feeding D-glucose-[6-2H2], coniferin-[α-13C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of 13C and 2H confirmed that D-glucose-[6-2H2] and coniferin-[α-13C] were involved in the normal metabolism of ginkgo cambial cells that had been effectively labelled with dual isotopes. In the ginkgo CW-DHP, ketal and ether linkages were formed between the C-α of lignin side chains and carbohydrates, as revealed by solid state CP/MAS 13C-NMR differential spectroscopy. Furthermore, the DMSO/TBAH ionic liquids system was used to fractionate the ball-milled CW-DHP into three lignin-carbohydrate complex (LCC) fractions: glucan–lignin complex (GL), glucomannan–lignin complex (GML), and xylan–lignin complex (XL). The XRD determination indicated that the cellulose type I of the GL was converted into cellulose type II during the separation process. The molecular weight was in the order of Ac-GL > Ac-GML > XL. The 13C-NMR and 1H-NMR differential spectroscopy of 13C-2H-enriched GL fraction indicated that lignin was linked with cellulose C-6 by benzyl ether linkages. It was also found that there were benzyl ether linkages between the lignin side chain C-α and glucomannan C-6 in the 13C-2H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the 13C-2H-enriched XL fraction. 相似文献
93.
Cover Picture: Transport of Nucleoside Triphosphates into Cells by Artificial Molecular Transporters (Angew. Chem. Int. Ed. 31/2018) 下载免费PDF全文
94.
YUANJINJIANG ZHOUSANMING 《高校应用数学学报(英文版)》1995,10(3):337-344
This paper shows that, for every unit interval graph, there is a labelling which is simultaneously optimal for the following seven graph labelling problems: bandwidth, cyclic bandwidth, profile, fill-in, cutwidth, modified cutwidth, and bandwidth sum(linear arrangement). 相似文献
95.
96.
《Surface and interface analysis : SIA》2004,36(12):1542-1549
The photodegradation of poly(ether sulphone) (PES) was investigated systematically by time‐of‐flight SIMS (ToF‐SIMS) and x‐ray photoelectron spectroscopy (XPS). The effect of varying the irradiation dose, wavelength and the atmosphere was studied along with mechanistic photooxidation studies using 18O2. Photoinduced ? SO3H group formation was observed at 199, 260 and 315 nm for an oxygen‐containing atmosphere only. Photoinduced ? OH group formation is observed at all investigated wavelengths and atmospheres. Photoinduced cross‐linking was an important process in a vacuum. The oxygen reacts quickly with the PES surface during photoirradiation and chain scission was found to be the dominant process, and oxygen incorporation was found to be non‐specific but pronounced for ? SO3H group formation. It was found that for conditions where processes are affected by photoirradiation the extent is observed to follow the UV absorption and showed little dependence on the wavelength. The wavelength only affects the extent of the process in question, which is ascribed to a fast equilibrium of the absorbed energy. The photoinduced processes are very sensitive towards the presence of the smallest amounts of oxygen in the atmosphere. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
97.
98.
A number of primary and secondary amines have been rapidly methylated under microwave-enhanced conditions using formic acid-formaldehyde mixtures, providing a route to 2H(D)-containing compounds and the potential for 3H(T), 11C, 13C and 14C labelling. 相似文献
99.
Fluorescent labelling of α-amino acids at their N or C terminals in the main and lateral chains at short and long wavelengths was carried out in different ways. The N-[3-(naphthalen-1-ylamino)propanoyl]amino acid methyl esters synthesised showed strong fluorescence in the visible region (∼415 nm) of the electromagnetic spectrum. Condensation of these compounds with 5-diethylamino-2-nitrosophenol or 5-ethylamino-4-methyl-2-nitrosophenol produced the benzo[a]phenoxazine derivatives, with maximum emission wavelengths shifted to values higher than 644 nm. The synthesis of novel functionalised 5,9-diaminobenzo[a]phenoxazinium salts, by reaction of 5-ethylamino-4-methyl-2-nitrosophenol and N-substituted 1-naphthylamine and their use in the covalent labelling of the N or C terminals of valine, produced derivatives with long-wavelength emissions (644-653 nm). Photophysical studies using the synthesised compounds both in different solvents and in controlled pH were undertaken. Preliminary evaluation of photostability of the cationic polycyclic heterocycles in ethanol and water at physiological pH was also performed. 相似文献
100.
Dr. Yury Gorbanev Dr. Deborah O'Connell Dr. Victor Chechik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3496-3505
Non‐thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma‐treated aqueous solutions was investigated by using spin‐trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and 1H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ?OOH, ?OH and ?H are proposed to originate from the region between the plasma nozzle and the liquid sample. 相似文献