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91.
Kinetics of copolymerization of acrylonitrile(AN) with N-vinylpyrrolidone(NVP) initiated by azodi-isobutyronitrile(AIBN) was investigated in H2O/dimethyl sulphoxide(DMSO) mixture between 50℃ and 70℃ under N2 atmosphere. The rate of copolymerization and particle size were measured respectively. The kinetic equation of copolymerization system is obtained as Rpat 60℃. The overall activation energy for copolymerization system was computed as 87.3kJ.mol-1. Effect of additives of hydroquinone and dioxane on copolymerization was discussed. The polymerization is retarded by hydroquinone and accelerated by dioxane, which confirms the free radical copolymerization of AN with NVP. 相似文献
92.
Summary Tensile fracture morphologies of three kinds of polyacrylonitrile-based carbon fibers were investigated by scanning electron
microscope and high resolution transmission electron microscope. Homogeneous and granular texture could be observed in cross
sections of all these three carbon fibers. There is a void up to 1 μm in diameter in fracture surface of T1, which limits
its compactness and tensile strength. Apart from homogeneous texture, linear and fan-shaped morphology are found on surface
of T300 and T700, respectively. No core-sheath structure was found in these specimens. Misoriented crystallites are also found
from HRTEM images in the transverse sections of T1, T300 and T700, which initiate fiber tensile failure. The tensile fracture
mechanism and the implication of the fiber structure under tensile force were also elucidated. T700 has the smallest interplanar
spacing, the highest degree of graphitization and the highest crystallinity among three carbon fibers. 相似文献
93.
Chengguo Hu 《Electrochimica acta》2006,51(15):3013-3021
MWNTs can be conveniently dispersed in Nafion solution on the basis of the special interactions between the sidewall of MWNTs and the hydrophobic domains of Nafion. Casting of the resulting mixture on electrode surfaces produced uniform composite films having wide electroanalytical applications. In this work, the electrochemical properties of the MWNTs-Nafion composite film on a glassy carbon electrode were systematically investigated by various electrochemical methods using incorporated europium(III) ions (Eu3+) as the probe. The voltammetric studies showed that the increase of MWNTs concentration in the composite film could effectively improve the redox currents of Eu3+ and reduce the peak separation, whereas the increase of Nafion concentration generally increased both the redox currents and the peak separation. These results suggested the different roles of MWNTs and Nafion in the composite films. The electrochemical impedance spectroscopic (EIS) investigations showed that MWNTs mainly contributed to the charge transfer and mass transfer processes of the composite film through the increases of the electrode/electrolyte interfacial area and the film porosity while Nafion generally dominated the mass transport from the solution into the film via ion exchange. The potential application of the sensitive response of Eu3+ at the MWNTs-Nafion composite film in electroanalytical chemistry was evaluated. In the range of 0.04-100 μM, the concentration of Eu3+ showed excellent linear relationships with the differential pulse voltammetric response with a low detection limit of 10 nM (S/N = 3) for 60 s accumulation at −0.1 V. 相似文献
94.
Monomer reactivity ratios of acrylonitrile/ammonium itaconate during aqueous‐deposited copolymerization initiated by ammonium persulfate were investigated. Kelen–Tudos method was used to examine the reactivity ratios. It was shown that the reactivity ratios were influenced by the conversions and temperatures of copolymerization. The reactivity ratios in aqueous‐deposited copolymerization system were similar to those in the solution polymerization system at polymerization conversions of less than 5% [reactivity ratio of acrylonitrile (r1) 0.842 ± 0.02, reactivity ratio of ammonium itaconate (r2) = 3.624 ± 0.02]. The reactivity ratio of AN rises and that of (NH4)2IA decreases, when the polymerization conversion increases till 13%. Aqueous‐deposited copolymerization initiated by AIBN was also studied. It was found that some polymers were formed in water phase and the monomers had different reactivity ratios by comparison with those initiated by ammonium persulfate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4645–4648, 2006 相似文献
95.
A single‐pot atom transfer radical polymerization was used for the first time to successfully synthesize polyacrylonitrile with a molecular weight higher than 80,000 and a narrow polydispersity as low as 1.18. This was achieved with CuBr/isophthalic acid as the catalyst, 2‐bromopropionitrile as the initiator, and N,N‐dimethylformamide as the solvent. The effects of the solvent on the polymerization of acrylonitrile were also investigated. The induction period was shorter in N,N‐dimethylformamide than in propylene carbonate and toluene, and the rate of the polymerization in N,N‐dimethylformamide was fastest. The molecular weight of polyacrylonitrile agreed reasonably well with the theoretical molecular weight in N,N‐dimethylformamide. When chlorine was used in either the initiator or the catalyst, the rate of polymerization showed a trend of decreasing, and the molecular weight deviated from the theoretical predication significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3372–3376, 2006 相似文献
96.
The reverse atom transfer radical polymerization (RATRP) technique using FeCl3/iminodiacetic acid (IMA) complex as a catalyst was applied to the living radical polymerization of acrylonitrile (AN). A hexa-substituted ethane thermal initiator, diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS), was firstly used as the initiator in this iron-based RATRP system. The polymerization in N,N-dimethylformamide not only shows the best control of molecular weight and its distribution but also provides rather rapid reaction rate with the ratio of [AN]:[DCDPS]:[FeCl3]:[IMA] at 500:1:2:4. The rate of polymerization increases with increasing the polymerization temperature and the apparent activation energy was calculated to be 49.9 kJ mol−1. The polymers obtained were end-functionalized by chlorine atom, and they were used as macroinitiators to proceed the chain extension polymerization in the presence of FeCl2/IMA catalyst system via a conventional ATRP process. The resultant polyacrylonitrile fibers were obtained with the fineness at 1.16 dtex and the tenacity at 6.01cN dtex−1. 相似文献
97.
Juan Chen Chengguo Wang Heyi Ge Yujun Bai Yanxiang Wang 《Journal of Polymer Research》2007,14(3):223-228
A dimethyl sulfoxide (DMSO)-water system was used as the coagulation bath in the wet-spun process for poly(acrylonitrile-itaconic
acid) fibers. The coagulation bath concentration of DMSO was kept constant at 65%, and the jet stretch ratio was 1. The coagulation
bath temperature was varied from 40 to 70 °C. The properties of the fibers so obtained were investigated. The diffusion coefficient
of solvent was calculated and the concentration profiles of solvent in a moving filament were computed by using a MOL (method
of lines) method. The nascent fibers coagulated at 50 °C obtained a circular symmetrical cross section with high density and
strength. The diffusion coefficients of solvent (DMSO) increase with the bath temperature increase. Simulation results show
that the noncircular cross section form was the response of the rapid diffusion rate and the loose structure in the core of
nascent fibers was caused by the overmuch remained solvent. 相似文献
98.
Determination of the degradation apparent activation energy of acrylonitrile/acrylic acid copolymers
Acrylonitrile/acrylic acid copolymers were prepared by H2O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry was used to investigate the degradation of acrylonitrile/acrylic acid copolymers in air. The apparent activation energy of degradation of the copolymer was calculated with the Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. It has been found that increasing the dimethyl formamide concentration in the solvent mixture led to a gradual increase (97.3–149.4 kJ mol?1) in the apparent activation energy of degradation of the acrylonitrile/acrylic acid copolymers. The apparent activation energy decreases with increase in acrylic acid concentration, and this change became less prominent as the acrylic acid/acrylonitrile weight ratio is more than 5/95. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4668–4671, 2006 相似文献
99.
针对视频中运动行人遮挡问题,提出了一种基于区域特征的顶视运动行人检测算法.首先结合三帧差分和背景减除算法检测出所有可能的行人运动区域,然后找出运动区域的轮廓以及区域的外接矩形,并计算运动区域的面积,最后根据外接矩形的长宽比以及运动区域面积进行区域筛选,找出有效的运动区域,从而检测出行人.实验结果表明,该方法能够快速准确地检测出视频中的行人. 相似文献
100.
Xie Zexiao Zhang Chengguo Zhang Qiumei Zhang Guoxiong 《The International Journal of Advanced Manufacturing Technology》2005,26(4):391-398
Today several new kinds of laser beam sensors appear with high resolution and accuracy and find their applications in reverse engineering and quality control. Due to the incapability of changing their orientations continuously in response to the surface fluctuation of a part to be measured, they are not competent for measuring parts with complicated structures. In this paper a five-axis laser scanning system integrated with a CMM, a laser beam sensor and a PH10 rotary head is proposed, which can measure complicated parts by frequently indexing the laser sensor approximately consistent with the normal direction of the surface. As the laser value is a 1-D data and the measured data must be given in 3-D expression in the world coordinate system, a system model for coordinate transformation is established. An “equivalent probe” approach is presented for system verification, and an iterative verifying process is adopted to eliminate the verification error caused by the inclination error of the laser sensor. Experiment study shows that the system can measure a part from any direction with an accuracy of 30 μm. 相似文献