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81.
The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding. 相似文献
82.
Nita H. Shah Hardik N. Soni Jyoti Gupta 《International journal of systems science》2014,45(8):1723-1727
In a recent paper, Begum et al. (2012, International Journal of Systems Science, 43, 903–910) established pricing and replenishment policy for an inventory system with price-sensitive demand rate, time-proportional deterioration rate which follows three parameters, Weibull distribution and no shortages. In their model formulation, it is observed that the retailer's stock level reaches zero before the deterioration occurs. Consequently, the model resulted in traditional inventory model with price sensitive demand rate and no shortages. Hence, the main purpose of this note is to modify and present complete model formulation for Begum et al. (2012). The proposed model is validated by a numerical example and the sensitivity analysis of parameters is carried out. 相似文献
83.
Optical properties of nano-silicon 总被引:2,自引:0,他引:2
We investigated the optical properties of silicon clusters and Si nanocrystallites using photolumine-scence (PL) and Raman
scattering technique. Broad luminescence band in the red region was observed from Si-doped SiO2 thin films deposited by co-sputtering of Si and SiO2 onp-type Si (100) substrates, annealed in Ar and O2 atmosphere. Nanocrystalline Si particles fabricated by pulsed plasma processing technique showed infrared luminescence from
as grown film at room temperature. Raman spectra from these films consisted of broad band superimposed on a sharp line near
516 cm−1 whose intensity, frequency, and width depend on the particle sizes arising from the phonon confinement in the nanocrystalline
silicon. We also performed PL, Raman and resonantly excited PL measurements on porous silicon film to compare the optical
properties of Si nanostructures grown by different techniques. An extensive computer simulation using empirical pseudo-potential
method was carried out for 5–18 atoms Si clusters and the calculated gap energies were close to our PL data.
Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore. 相似文献
84.
Microsystem Technologies - In clarification of wireless sensor network (WSN) clustering process at household and overseas, an energy efficient cluster head formation technique for WSN are set forth... 相似文献
85.
86.
Ritu Khullar V. K. Varshney Sanjay Naithani Thomas Heinze P. L. Soni 《应用聚合物科学杂志》2005,96(4):1477-1482
Carboxymethylation of cellulosic material (average degree of polymerization 2600) containing 76.5% cellulose and 23.6% xylose isolated from cotton (Gossypium) linters was studied under varying reaction conditions with respect to maximum degree of substitution (DS). The influence of reaction conditions on the apparent viscosity of the prepared derivatives was also studied. The conditions optimized were sodium hydroxide concentration 3.75M, monochloroacetic acid concentration 2.05 mol/AGU, carboxymethylation time 3.5 h, and temperature 55°C, to yield carboxymethyl cellulose of DS 0.77. Rheological studies of 1 and 2% solutions of the optimized product revealed their non‐Newtonian pseudoplastic behavior. Repeating units of the optimized product were also determined by HPLC after complete depolymerization of the polymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1477–1482, 2005 相似文献
87.
88.
Conventional dummy based testing procedures suffer from known limitations. This report addresses issues in finite element
human body models in evaluating pedestrian and occupant crash safety measures. A review of material properties of soft tissues
and characterization methods show a scarcity of material properties for characterizing soft tissues in dynamic loading. Experiments
imparting impacts to tissues and subsequent inverse finite element mapping to extract material properties are described. The
effect of muscle activation due to voluntary and non-voluntary reflexes on injuries has been investigated through finite element
modelling. 相似文献
89.
The effect of catalyst on the degradation of poly (ethylene terephthalate) (PET) waste by ammonolysis was investigated at
ambient temperature and atmospheric pressure. The products obtained by ammonolysis in the presence and absence of catalyst
were separated and characterized by spectroscopic techniques namely FTIR and Mass Spectrometry (MS) together with Scanning
Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The end products were characterized as 1, 4-benzene dicarboxamide
in both the cases and were found to be same throughout the course of reaction. The absence of peak for PET and appearance
of peak for 1, 4-benzene dicarboxamide in the FTIR spectra of end product along with MS, SEM and thermal analysis confirms
the completion of the reaction. The results show that the catalyst cut shorts the time of completion of reaction from 45 to
15 days only. 相似文献
90.
The crystals of In
x
Bi2−x
Te3 (x=0·1 to 0·5) have been grown by zone-melting method. In order to study anisotropy exhibited by the (0001) plane of the crystals,
the directional hardness was determined by producing indentations at various azimuthal orientations of the indentor with respect
to the surface over a range 0–180°. The crystal was rotated about the indentor axis in steps of 15° while keeping applied
load and loading time constant at 50 g and 20 sec, respectively. For annealing study, the sample was kept at a temperature
of 375°C. It was observed that softening of crystal takes place and the hardness decreases to a considerable extent. 相似文献