全文获取类型
收费全文 | 8572篇 |
免费 | 869篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 122篇 |
综合类 | 19篇 |
化学工业 | 2185篇 |
金属工艺 | 316篇 |
机械仪表 | 558篇 |
建筑科学 | 137篇 |
矿业工程 | 4篇 |
能源动力 | 388篇 |
轻工业 | 799篇 |
水利工程 | 22篇 |
石油天然气 | 3篇 |
无线电 | 1626篇 |
一般工业技术 | 2034篇 |
冶金工业 | 228篇 |
原子能技术 | 172篇 |
自动化技术 | 849篇 |
出版年
2024年 | 15篇 |
2023年 | 128篇 |
2022年 | 176篇 |
2021年 | 323篇 |
2020年 | 249篇 |
2019年 | 276篇 |
2018年 | 354篇 |
2017年 | 332篇 |
2016年 | 428篇 |
2015年 | 355篇 |
2014年 | 476篇 |
2013年 | 611篇 |
2012年 | 612篇 |
2011年 | 780篇 |
2010年 | 566篇 |
2009年 | 624篇 |
2008年 | 493篇 |
2007年 | 349篇 |
2006年 | 333篇 |
2005年 | 259篇 |
2004年 | 261篇 |
2003年 | 242篇 |
2002年 | 209篇 |
2001年 | 143篇 |
2000年 | 134篇 |
1999年 | 142篇 |
1998年 | 128篇 |
1997年 | 84篇 |
1996年 | 81篇 |
1995年 | 67篇 |
1994年 | 41篇 |
1993年 | 26篇 |
1992年 | 29篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有9462条查询结果,搜索用时 15 毫秒
71.
The extinction mechanism of a CH4/N2-air counterflow nonpremixed flame interacting with a single vortex was numerically studied. An augmented reduced mechanism was used to treat the CH4 oxidation reactions. The contribution of each term in the energy and the OH species equations were evaluated to investigate the unsteady extinction mechanism of nonpremixed flame. The flame temperature began to decrease due to the convection heat loss when the flame interacted with a vortex. The investigation of the radical behavior during the flame-vortex interaction process also provided useful information on the unsteady extinction mechanism. The OH radical concentration could be used as a good tracer of the state of the unsteady extinction of nonpremixed flame. The reduction mechanism of OH concentration was confirmed by analyzing the contribution of each term in the OH species equation. At initial stage of flame-vortex interaction, the OH production and consumption rates increased gradually, while the OH concentration was kept nearly constant. Near the extinction limit, the OH production rate decreased rapidly due to the low flame temperature, and the balance between the OH production and OH consumption by diffusion could not be maintained. The unsteady nonpremixed flame interacting with a vortex under the conditions of regime (V) shown in the spectral combustion diagram [Thévenin, D., Renard, P.H., Fiechtner, G.J., Gord, J.R., Rolon, J.C., 2000. Regimes of non-premixed flame-vortex interactions. Proceedings of the Combustion Institute 28, 2101-2108.] was finally extinguished due to low reactivity, which was induced by the low flame temperature. 相似文献
72.
Rubber‐toughened poly(trimethylene terephthalate) (PTT)–organoclay nanocomposite (RTPTTCN) was prepared by a melt mixing technique. The rubber‐toughened PTT (RTPTT) was made by blending it with ethylene propylene diene terpolymer (EPDM) and with a small amount of maleated EPDM as a compatibilizer. XRD and TEM analysis indicated that the RTPTTCN forms a partially exfoliated nanocomposite. It was observed from SEM analysis that the clay nanoparticles induced a reduction of rubber particle size in the PTT matrix. Tensile and dynamic mechanical analysis indicated that the clay nanoparticles enhance the stiffness of the RTPTT without adversely affecting its toughness. Melt rheological studies revealed that the nanocomposites exhibited strong shear thinning behavior, and a percolated network of the clay particles was formed. It was also observed from DSC that the clay nanoparticles caused an increase in the nonisothermal crystallization temperature of the PTT. POLYM. ENG. SCI., 47:863–870, 2007. © 2007 Society of Plastics Engineers 相似文献
73.
Polymethylphenylsilsesquioxane (PMPSQ–OH) and trimethylsilyl end‐blocked PMPSQ (PMPSQ–EC) were prepared. The thermal decomposition behavior of these polymers was studied by thermogravimetric analysis (TGA) and FT‐Raman spectroscopy. Hydroxyl‐functionalized polystyrene (PS–OH) was also prepared by anionic living polymerization. Thin hybrid films of PMPSQ/PS–OH with various blend ratios were obtained by spin‐coating on freshly cleaned glass. The surface morphology of the hybrid films was investigated by atomic force microscopy (AFM). In 80/20 PMPSQ/PS–OH hybrid film, the PS–OH component produced a very uniformly dispersed phase. This hybrid film contained small domains of PS–OH whose size ranged from 60 to 80 nm. As the content of PS–OH was increased, the domain morphology coarsened and phase inversion took place around 50 wt %. In the phase‐inversed system, the PMPSQ‐rich phase was uniformly distributed in the PS–OH‐rich continuous phase. In addition, temperature‐dependent dielectric properties of PMPSQ/PS–OH hybrids were investigated. Relaxation of the hybrids was observed with an increasing content of the PS–OH component due to the amorphous glass transition behavior of PS–OH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2801–2812, 2003 相似文献
74.
Byung-Han Ko Sang-Geuk Jeong Young-Ghyu Ahn Kyoung-Su Park No-Cheol Park Young-Pil Park 《Microsystem Technologies》2014,20(8-9):1671-1677
Acoustic noise generated by a multi-layer ceramic capacitor (MLCC) makes users uncomfortable, so the problem must be analyzed to reduce the noise. There is a correlation between the acoustic noise and the vibration of MLCCs and the circuit board. Therefore, the acoustic noise problem must be investigated from a vibration perspective. In this study, the acoustic noise-generating mechanism was investigated, and the relationship between the characteristics of the noise and the dynamic characteristics of the circuit board with MLCC was analyzed. And a correlation criterion was proposed to predict the acoustic noise using the vibration response of the circuit board. 相似文献
75.
Kyoung Duck Seo Jang Min Park Hyeonsoo Jeong Dong Sung Kim 《Microsystem Technologies》2014,20(2):243-250
We develop a miniaturized batch-type screw mixer (BSM) for uniform mixing of polymer resin and nanoparticles, based on the stretching of material elements. This stretching is induced by the combination of recirculating cross-sectional flows in deep channels of the screw and high shear stress developed at flight regions. The BSM is used to produce a polymer nano-composite composed of multi-walled carbon nanotubes and polydimethylsiloxane resin. The mixing performance of the BSM is characterized quantitatively by estimating two different types of mixing efficiencies (i.e., dispersive mixing and distributive mixing) via transmitted light microscope images. The developed BSM highly improves the mixing performance rather than that of a conventional ultrasonic mixing device. 相似文献
76.
Hyun Ju Lim Sung Jun Lee Han Gon Choi Jung Ae Kim Chul Soon Yong Sung Soo Han Seok Kyun Noh Jinho Jang Won Seok Lyoo 《应用聚合物科学杂志》2007,106(5):3268-3272
High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
77.
Seon Jeong Kim Seoung Gil Yoon Young Moo Lee Kay Hyeok An Sun I. Kim 《应用聚合物科学杂志》2003,90(5):1389-1392
Temperature‐responsive interpenetrating polymer network (IPN) hydrogels constructed with poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) using the sequential IPN method were studied. The characteristics of IPN hydrogels were investigated using the dynamic vapor sorption system. IPN hydrogels exhibited a relatively high sorption ratio, 180–360% at room temperature. The sorption ratio of hydrogels depended on temperature. Diffusion coefficients were calculated according to the Fickian Law at several temperatures. The apparent activation energy was 5.43 kJ mol?1, which corresponds to typical diffusion processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1389–1392, 2003 相似文献
78.
An interpenetrating polymer network (IPN) hydrogel composed of chitosan and polyallylamine exhibited electric‐sensitive behavior. The chitosan/polyallylamine IPN hydrogel was synthesized by radical polymerization using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The swelling behavior of the IPN was studied by immersion of the gel samples in aqueous NaCl solutions at various concentrations and pHs. The swelling ratio decreased with increasing concentration and pH of electrolyte solution. The stimuli response of the IPN hydrogel in electric fields was also investigated. When a swollen the IPN was placed between a pair of electrodes, the IPN exhibited bending behavior in response to the applied electric field. The IPN also showed stepwise bending behavior depending on the electric stimulus. In addition, thermal properties of the IPN were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2290–2295, 2002 相似文献
79.
Richard Kotek Dong‐Wook Jung Joon Ho Kim Brent Smith Patricia Guzman Benjamin Schmidt 《应用聚合物科学杂志》2004,92(3):1724-1730
The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004 相似文献
80.
The synergistic effects of boron nitride (BN) powder and die on the rheology and processability of metallocene‐catalyzed low density polyethylene (mLDPE) were investigated. The processability in the extrusion process is closely related to the interfacial properties between the polymer melts and the die wall. BN powder was added to mLDPE to reduce the friction coefficient and surface energy. Adding 0.5 wt% BN powder to mLDPE was very effective in improving the processability and the extrudate appearance. To study the effect of die surface property, three different dies were applied in capillary extrusion. One was conventional tungsten carbide (TC) die, and the others were hot‐pressed BN (hpBN) die and hot‐pressed BN composite (hpBNC) die. The applications of these BN dies were quite effective in delaying surface melt fracture (sharkskin) and postponing gross melt fracture to higher shear rate compared to the TC die. These improvements result from the fact that BN dies reduce the wall shear stress significantly and promote slip. The synergistic effect of processability could be obtained when both BN powder and hpBN die were used together. 相似文献