全文获取类型
收费全文 | 125篇 |
免费 | 1篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 75篇 |
建筑科学 | 1篇 |
轻工业 | 1篇 |
无线电 | 12篇 |
一般工业技术 | 30篇 |
冶金工业 | 5篇 |
自动化技术 | 1篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2010年 | 1篇 |
2007年 | 1篇 |
2006年 | 3篇 |
2004年 | 1篇 |
1999年 | 1篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有126条查询结果,搜索用时 31 毫秒
1.
During the formation of ultrahigh modulus fibers by the “surface-growth process,” the takeup stress is the main limiting factor lowering the attainable takeup speeds. This paper presents an investigation into the relative importance of the various factors contributing to takeup force and stress. Equations for force and stress have been derived which appear to agree with measurements. It has been concluded that the major part of the stress stems from the friction with the rotor surface and a smaller contribution arises from the coil deformation due to the flow. The equation for the stress has been employed to compute the maximum takeup speed. 相似文献
2.
3.
This paper describes a study on the solidification of the pseudo binary eutectic system, consisting of unfractionated linear polyethylene and the faceted growing diluent 1, 2, 4, 5-tetrachlorobenzene. Crystallization under eutectic conditions resulted in very fine-grained structures, which were found to depend on the growth rate. This rate of solidification was varied by pulling the polymer solutions through a fixed temperature gradient of 3° C mm–1 at different speeds ranging from 1 to 216 mm h–1. Fibrillar polymer crystals with lateral dimensions of about 0.5 m remained after removal of the solid diluent. At rates of solidification in the region of 2 to 20 mm h–1, the fibrils appeared to be aggregated in domains of well oriented structures, closely resembling the complex regular structures of the eutectic Sn-Bi system. At higher speeds the fibrillar crystals formed an irregular three-dimensional network. The polymeric structures grown from more dilute mixtures were characterized by rectangular holes originating from the growth of faceted primary diluent crystals. Despite the complexity of the crystallization of the highly entangled polymer solutions there appears to be quite some similarities between the eutectic polymeric system investigated and faceted/non-faceted atomic or small molecular eutectics. 相似文献
4.
A. J. Pennings R. J. van der Hooft A. R. Postema W. Hoogsteen G. ten Brinke 《Polymer Bulletin》1986,16(2-3):167-174
Summary This communication is concerned with the gel-spinning of ultrahigh molecular weight polyethylene (UHMWPE) at speeds up to 1500 m/min. It was found that 5 wt% solutions of UHMWPE in paraffin oil could be extruded through a conical die at a rate of 100 m/min. without the appearance of filament irregularities due to elastic solution fracture. These elastic turbulences occur at extrusion speeds of about 5 m/min. Without the addition of 1 wt% of Aluminium-stearate the spinline could be stretched at most to 60 m/min at 170°C but at 210°C it did not break at a speed of 1500 m/min.These high-speed gel-spinning experiments at temperatures around 200°C yielded polyethylene fibers with a tensile strength of 3.5 GPa. It was observed that drying of the as-spun fiber containing n-hexane at constant length led to excessive crazing. 相似文献
5.
Design, synthesis and properties of a degradable polyurethane scaffold for meniscus regeneration 总被引:5,自引:0,他引:5
Heijkants RG van Calck RV De Groot JH Pennings AJ Schouten AJ van Tienen TG Ramrattan N Buma P Veth RP 《Journal of materials science. Materials in medicine》2004,15(4):423-427
Longitudinal lesions in menisci are among the most frequent orthopedic problems of the knee. Repair by simple techniques is only limited to the vascular part of the meniscus. For repair of the avascular part of the meniscus a scaffold, which will assist the body in the formation of new meniscus cell tissue, might be applicable. In this study a biomedical segmented polyurethane with poly(epsilon-caprolactone) as soft segment and 1,4-butanediisocyanate and 1,4-butanediol as uniform hard segments has been synthesised. The material has a micro phase separated morphology and excellent mechanical properties. A porous scaffold was prepared via a combination of liquid-liquid phase separation and salt leaching. The foams prepared combined a very high interconnectivity and porosity with the desired compression modulus. After six months of implantation in the knees of beagles full ingrowth with cells was obtained and it was found that meniscus like tissue had been formed in the scaffold. Moreover, compression behaviour appeared to be comparable to native meniscus tissue. 相似文献
6.
The nature of the deformation process involved in hot drawing of porous high-molecular-weight polyethylene was examined by apparent elongational viscosity measurements at drawing temperatures between 100°C and 150°C and deformation rates in the range of 10?6–10?3 m/s. The temperature dependence of the apparent elongational viscosity revealed three distinguishable intervals with different activation energies. In the range of 100–133°C, the activation energy amounted to 50 kJ/mol, indicating that hot-drawing in this region proceeds by a sliding motion of separate fibrillar units. The interval between 133°C and 143°C was characterized by an activation energy of about 150 kJ/mol. Moreover, the porous character of the polyethylene fibers was found to decrease in the drawing process above 133°C. These observations were ascribed to an aggregation of the elementary fibrils upon hot-drawing due to partial melting at the surface of the fibrils. At temperatures above 143°C the activation energy was strongly affected by the initial morphology and the draw ratio of the fibers and amounted to values in the range of 200–600 kJ/mol. Molecular orientation in this region is accomplished by a slippage of individual chains, with entanglements acting as semipermanent crosslinks. Decreasing of the rate of elongation in the drawing process resulted in premature fiber breakage, indicating that the crosslinking action of the entanglements is limited by the time scale of the process. 相似文献
7.
In this paper the influence of the ambient temperature of the spinline during dry spinning of PLLA solutions has been discussed. Variation of this ambient temperature induced variation of the extrudate swell of the spinline, affected by the rate of solidification of the PLLA. By way of phase separation, porous filaments were achieved in which the morphology depended on the applied ambient temperature. Hot drawing of these filaments led to tensile strengths varying between 1.1 and 2.2 GPa. An optimal tensile strength of 2.2 GPa was achieved by hot drawing of a filament which was spun into a surrounding of 25°C. 相似文献
8.
Summary
New biomedical polyurethanes and a polyurethane urea based on Ε-caprolactone and 1,4-butanediisocyanate have been developed.
On degradation, only non-toxic products are produced. The polyurethane urea with poly(Ε-caprolactone) soft segments and butanediisocyanate/butanediamine
hard segments shows a high tensile strength, a high modulus and a high resistance to tearing but as a result of the strong
interactions between the solvent and the polymer processing is difficult. When butanediamine is replaced by butanediol in
the chain extension step, a processible polyurethane is obtained but the polymer lacks the desired mechanical properties for
biomedical applications. By chain extending with a longer urethane diol block, a processible polymer was obtained with mechanical
properties comparable to the polyurethane urea. This polyurethane has been made porous and can be used as a meniscal prosthesis.
Received: 12 March 1998/Accepted: 27 March 1998 相似文献
9.
van Brug H. Groen F.H. Oei Y.S. Pedersen J.W. Pennings E.C.M. Doeksen D.K. van der Tol J.J.G.M. 《Electronics letters》1989,25(20):1330-1332
Loss measurements on ridge waveguides in LPE-grown GaInAsP at a wavelength of 1.3 mu m are presented. An attenuation of 4.5 dB/cm has been obtained for straight waveguides, and for curved waveguides an excess loss at low as 0.7 dB was found for a 20.8 degrees S-bend with a radius of 300 mu m ( approximately=1.5 dB/90 degrees ).<> 相似文献
10.
P Vermeij JL Pennings SM Maassen JT Keltjens GD Vogels 《Canadian Metallurgical Quarterly》1997,179(21):6640-6648
Methanobacterium thermoautotrophicum deltaH was grown in a fed-batch fermentor and in a chemostat under a variety of 80% hydrogen-20% CO2 gassing regimes. During growth or after the establishment of steady-state conditions, the cells were analyzed for the content of adenylylated coenzyme F420 (factor F390-A) and other methanogenic cofactors. In addition, cells collected from the chemostat were measured for methyl coenzyme M reductase isoenzyme (MCR I and MCR II) content as well as for specific activities of coenzyme F420-dependent and H2-dependent methylenetetrahydromethanopterin dehydrogenase (F420-MDH and H2-MDH, respectively), total (viologen-reducing) and coenzyme F420-reducing hydrogenase (FRH), factor F390 synthetase, and factor F390 hydrolase. The experiments were performed to investigate how the intracellular F390 concentrations changed with the growth conditions used and how the variations were related to changes in levels of enzymes that are known to be differentially expressed. The levels of factor F390 varied in a way that is consistently understood from the biochemical mechanisms underlying its synthesis and degradation. Moreover, a remarkable correlation was observed between expression levels of MCR I and II, F420-MDH, and H2-MDH and the cellular contents of the factor. These results suggest that factor F390 is a reporter compound for hydrogen limitation and may act as a response regulator of methanogenic metabolism. 相似文献