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排序方式: 共有101条查询结果,搜索用时 15 毫秒
21.
Ashengroph M Nahvi I Zarkesh-Esfahani H Momenbeik F 《Applied biochemistry and biotechnology》2012,166(1):1-12
To screen strains of halotolerant or halophile bacteria which are able to convert isoeugenol to vanillin, 36 different strains
of bacteria isolated from the salty environments in Iran were investigated. During growth on isoeugenol, a moderately halotolerant
Gram-negative coccobacil showed capability of converting isoeugenol to vanillin. Based on morphological, physiological, and
phylogenetic studies, strain CSW4 was classified as a bacterium belonging to the genus Psychrobacter. The bioconversion products were confirmed by thin-layer chromatography, high-performance liquid chromatography, and spectral
data obtained from UV/Vis spectroscopy, FTIR, and mass-spectroscopy. Using growing cells, vanillin reached its maximum level
of 88.18 mg L−1 after 24 h of reaction time in the presence of 1 g L−1 isoeugenol, resulting in a molar yield of 10.2%. The use of resting cells led to the optimal yield of vanillin (16.4%) which
was obtained after 18-h reaction using 1 g L−1 isoeugenol and 3.1 g of dry weight of cells per liter harvested at the end of the exponential growth phase. To improve vanillin
yield, the effect of substrate concentration on vanillin production under resting cells conditions was also investigated.
Using 10 g L−1 isoeugenol, the maximal vanillin concentration (1.28 g L−1) was achieved after a 48-h reaction, without further optimization. The present study brings the first evidence for biotransformation
of isoeugenol to vanillin in the genus Psychrobacter. 相似文献
22.
23.
Separation of B6 vitamers with micellar liquid chromatography using UV and electrochemical detection
Separation of six vitamers of vitamin B6 was performed by RP-HPLC using micellar mobile phase, UV and electrochemical detection. Effect of temperature, type and amount of organic modifier in mobile phase on efficiency and asymmetry factor showed that, the appropriate conditions were temperature of 35 degrees C and 3.0-5.0% (v/v) 1-butanol in mobile phase. Variations of selectivity factor versus 1-butanol concentration, pH of mobile phase, and SDS concentration was investigated and the following optimized conditions were selected for the separation: 3.0% (v/v) 1-butanol, pH=5.5 and 65 mM SDS in mobile phase. Electrochemical behavior of vitamers in optimized mobile phase was investigated using cyclic voltammetry, and potential of +1.2 V versus Ag/AgCl(Sat.) was chose as working potential. Finally, separation of B6 vitamers using UV detection at 254 nm and electrochemical detection at +1.2 V was compared. 相似文献
24.
Kragulj Isakovski Marijana Molnar Jazić Jelena Maletić Snežana Tubić Aleksandra Agbaba Jasmina Tričković Jelena Dalmacija Božo 《Accreditation and quality assurance》2018,23(4):243-250
Accreditation and Quality Assurance - This study investigates measurement procedure validation for the determination of hexachlorobenzene, pentachlorobenzene and trifluralin as priority hazardous... 相似文献
25.
Mehdi Moayed Mohseni Fariborz Rashidi 《ournal of non Newtonian Fluid Mechanics》2010,165(21-22):1550-1553
An analytical solution is derived for the steady state, laminar, axial, fully developed flow of a viscoelastic fluid obeying the Giesekus model without any retardation time in a concentric annulus.An approximation is used for the estimation of radial normal stress. The influence of Deborah number (De) and the mobility factor (α) on the velocity profile, axial pressure gradient are investigated and results show strong effects of mobility factor and Deborah number on above parameters. 相似文献
26.
In this paper, flexible job shop scheduling problem with a new approach, overlapping in operations, is discussed. In many flexible job shops, a customer demand can be released more than one for each job, where demand determines the quantity of each finished job ordered by a customer. In these models each job has a demand more than one. This assumption is an important and practical issue for many flexible job shops such as petrochemical industries. To consider this assumption, we use a new approach, named overlapping in operations. In this approach, embedded operations of each job can be performed due to overlap considerations in which each operation may be overlapped with the others because of its nature. The overlapping is limited by structural constraints, such as the dimensions of the box to be packed or the capacity of the container used to move the pieces from one machine to the next. Since this problem is well known as NP-Hard class, a hierarchical approach used simulated annealing algorithm is developed to solve large problem instances. Moreover, a mixed integer linear programming (MILP) method is presented. To evaluate the validity of the proposed SA algorithm, the results are compared with the optimal solution obtained with the traditional optimization technique (The Branch and Bound method). The computational results validate the efficiency and effectiveness of the proposed algorithm. Also the computational results show that the overlapping considering can improve the makespan and machines utilization measures. So the proposed algorithm can be applied easily in real factory conditions and for the large size problems and it should thus be useful to both practitioners and researchers. 相似文献
27.
In this study the possibility of derivatizing sugars using microwave irradiation was investigated. The amount of reagent,
irradiation intensity, and derivatization time were optimized. In the derivatization of sugars with p-nitroaniline the reaction is complete within 5 min at 600 W when the p-nitroaniline-to-sugar and NaBH3CN-to-sugar mole ratios were above 1.4 and 3.1, respectively. A Doehlert design was used to optimize the mobile phase for
separation of p-nitroaniline-labeled sugars; and the best separation was obtained by use of 0.01 mol L−1 acetate buffer at pH 4.40 containing 11.0% acetonitrile. Analysis using this method was highly sensitive and analysis time
was short. Finally, a food sample was analyzed using the proposed method. 相似文献
28.
Glued-diaphragm fibre optic pressure sensors that utilize standard telecommunications components which are based on Fabry–Perot
interferometry are appealing in a number of respects. Principally, they have high spatial and temporal resolution and are
low in cost. These features potentially make them well suited to operation in extreme environments produced in short-duration
high-enthalpy wind tunnel facilities where spatial and temporal resolution are essential, but attrition rates for sensors
are typically very high. The sensors we consider utilize a zirconia ferrule substrate and a thin copper foil which are bonded
together using an adhesive. The sensors show a fast response and can measure fluctuations with a frequency up to 250 kHz.
The sensors also have a high spatial resolution on the order of 0.1 mm. However, with the interrogation and calibration processes
adopted in this work, apparent errors of up to 30% of the maximum pressure have been observed. Such errors are primarily caused
by mechanical hysteresis and adhesive viscoelasticity. If a dynamic calibration is adopted, the maximum measurement error
can be limited to about 10% of the maximum pressure. However, a better approach is to eliminate the adhesive from the construction
process or design the diaphragm and substrate in a way that does not require the adhesive to carry a significant fraction
of the mechanical loading.
相似文献
29.
Seyed Behrouz Khodadadi Fariborz Jolai 《Central European Journal of Operations Research》2012,20(2):281-297
In this paper we deal with a single server retrial queue with vacations. The server serves the customers until the system
becomes empty, then it takes a vacation. The system consists of two types of costs. The blocking cost is considered whenever
a customer is blocked either because of the server is busy or off. There is also a cost each time the server is turned on.
The problem is to find an effective policy for turning on the dormant server. We propose a Fuzzy Based Threshold Policy (FBTP)
to control the server, substitute for conventional threshold policies. The FBTP is based on four input parameters, an inference
stage and it is tuned up using a stochastic List Based Threshold Accepting (LBTA) algorithm. Simulation models are developed
to validate the fuzzy controller. Numerical experiments are provided to show that the proposed method is superior to crisp
threshold policies. 相似文献
30.