全文获取类型
收费全文 | 9191篇 |
免费 | 872篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 150篇 |
综合类 | 31篇 |
化学工业 | 2270篇 |
金属工艺 | 364篇 |
机械仪表 | 634篇 |
建筑科学 | 127篇 |
矿业工程 | 8篇 |
能源动力 | 371篇 |
轻工业 | 621篇 |
水利工程 | 40篇 |
石油天然气 | 6篇 |
武器工业 | 1篇 |
无线电 | 1749篇 |
一般工业技术 | 2326篇 |
冶金工业 | 409篇 |
原子能技术 | 133篇 |
自动化技术 | 854篇 |
出版年
2024年 | 5篇 |
2023年 | 115篇 |
2022年 | 147篇 |
2021年 | 310篇 |
2020年 | 225篇 |
2019年 | 279篇 |
2018年 | 281篇 |
2017年 | 351篇 |
2016年 | 417篇 |
2015年 | 332篇 |
2014年 | 487篇 |
2013年 | 654篇 |
2012年 | 689篇 |
2011年 | 795篇 |
2010年 | 538篇 |
2009年 | 576篇 |
2008年 | 515篇 |
2007年 | 391篇 |
2006年 | 353篇 |
2005年 | 299篇 |
2004年 | 256篇 |
2003年 | 269篇 |
2002年 | 246篇 |
2001年 | 185篇 |
2000年 | 175篇 |
1999年 | 155篇 |
1998年 | 195篇 |
1997年 | 141篇 |
1996年 | 121篇 |
1995年 | 83篇 |
1994年 | 70篇 |
1993年 | 69篇 |
1992年 | 60篇 |
1991年 | 53篇 |
1990年 | 43篇 |
1989年 | 33篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 33篇 |
1984年 | 14篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
141.
Summary Isothermal cure kinetics ofEPON HPT 1071/DDS system have been performed by means of differential scanning calorimetry. The maximum cure rate and the extent of conversion at various DDS concentrations were studied as a function of cure temperature. Maximum cure rate increases with increasing cure temperature and DDS concentration. At various DDS concentrations, the maximum cure rate occured between 19–22% conversion. In order to evaluate the kinetic parameters, numerical calculations by means of a Newton-Raphson technique and experimental results obtained from the peak of reaction rate curve were undertaken. 相似文献
142.
The removal of hydrogen sulfide (H2S) from simulated gas was carried out in a batch type fluidized-bed reactor using natural manganese ore (NMO), which consists
of several metal oxides (MnOx: 51.85%, FeOy: 3.86%, CaO: 0.11%). The H2S breakthrough curves were obtained by changing temperature, gas velocity, initial H2S concentration, and aspect ratio. Moreover, the effects of the particle size and the particle-mixing fraction on H2S removal were investigated in a binary system of different particle size. From this study, H2S removal efficiency increased with increasing temperature but decreased with increasing excess gas velocity. The breakthrough
time for H2S decreased as the gas velocity increased, which leads to reducing gas-solid contacting due to gas bypassing in a fluidized
bed reactor. Improvement of H2S removal efficiency in continuous process can be expected from the results of the binary particle system with different size
in a batch experiment. The NMO could be considered as a potential sorbent in H2S removal. 相似文献
143.
The interfaces between metal organic chemical vapor deposited PbTiO3 thin films and various diffusion barrier layers deposited on Si substrates were investigated by transmission electron microscopy. Several diffusion barrier thin films such as polycrystalline TiO2 , amorphous TiO2 , ZrO2 , and TiN were deposited between the PbTiO3 thin film and Si substrate, because the deposition of PbTiO3 thin films on bare Si substrates produced Pb silicate layers at the interface irrespective of the deposition conditions. The TiO2 films were converted to PbTiO3 by their reaction with diffused Pb and O ions during PbTiO3 deposition at a gubstrate temperature of 410°C. Further diffusion of Pb and O induces formation of a Pb silicate layer at the interface. ZrO2 did not seem to react with Pb and O during PbTiO3 deposition at the same temperature, but the Pb and O ions that diffused through the ZrO2 layer formed a Pb silicate layer between the ZrO2 and Si substrate. The TiN films did not seem to react with Pb and O ions during the deposition of PbTiO3 at 410°C, but reacted with PbTiO3 to form a lead-deficient pyrochlore during postdeposition rapid thermal annealing at 700°C. However, TiN could effectively block the diffusion of Pb and O ions into the Si substrate and the formation of Pb silicate at the interface. 相似文献
144.
The key to the success of flip‐chip technology lies in the availability of sucessful underfill materials. However, the reliability of flip‐chip technology using current underfill materials is generally found to be lower than that of conventional wire‐bond connection packaging materials such as epoxy molding compound (EMC) because of the high coefficients of thermal expansion (CTE) and moisture absorption of cured underfill material. In this study desbimide (DBMI), which has a low melting point (about 80°C), was used in the underfill materials as a cohardener. As a result, DBMI‐added underfill can show excellent thermal reliability, which is due to the superior properties of the CTE, the elastic modulus, and water resistance. When the properties of a 2 wt % DBMI‐added underfill were compared with those of a typical underfill (epoxy/anhydride), the CTE value was reduced to less than one‐half at the solder reflow temperature (about 200°C), the elastic modulus was reduced to less than one‐half in the temperature region below the glass‐transition temperature, and the water resistance was improved twofold. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2617–2624, 2002 相似文献
145.
Chang‐Gyu Kim Sung‐Hoon Joo Cheol Hong Cheon Mi‐Yun Jeong Soon‐Wook Cha Byung‐Hee Sohn Jung‐Il Jin 《应用聚合物科学杂志》2006,100(1):307-317
Three new soluble polyconjugated polymers, all of which emitted blue light in photoluminescence and electroluminescence, were synthesized, and their luminescence properties were studied. The polymers were poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene}, poly((9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)vinylene‐1,4‐phenylene]}) [P(DOF‐PVP)], and poly([N‐(2‐ethyl) hexylcarbazole‐3,6‐diyl]‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)]vinylene‐1,4‐phenylene}). The last two polymers had alternating sequences of the two structural units. Among the three polymers, P(DOF‐PVP) performed best in the light‐emitting diode devices of indium–tin oxide/poly(ethylenedioxythiophene) doped with poly(styrene sulfonate) (30 nm)/polymer (150 nm)/Li:Al (100 nm). This might have been correlated with the balance in and magnitude of the mobility of the charge carriers, that is, positive holes and electrons, and also the electronic structure, that is, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, of the polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 307–317, 2006 相似文献
146.
Changyong Choi Su Young Chae Tai‐Hyoung Kim Jung Keon Kweon Chong Su Cho Mi‐Kyeong Jang Jae‐Woon Nah 《应用聚合物科学杂志》2006,99(6):3520-3527
Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using 1H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (Kv) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006 相似文献
147.
Seokkyu Lee Wonbong Jang Seunghyuk Choi Kannan Tharanikkarasu Yonggun Shul Haksoo Han 《应用聚合物科学杂志》2007,104(5):2965-2972
Semi‐interpenetrating polymer network (semi‐IPN) membranes based on novel sulfonated polyimide (SPI) and poly (ethylene glycol) diacrylate (PEGDA) have been prepared for the fuel cell applications. SPI was synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, and 2‐bis [4‐(4‐aminophenoxy) phenyl] hexafluoropropane. PEGDA was polymerized in the presence of SPI to synthesize semi‐IPN membranes of different ionic contents. These membranes were characterized by determining, ion exchange capacity, water uptake, water stability, proton conductivity, and thermal stability. The proton conductivity of the membranes increased with increasing PEGDA content in the order of 10?1 S cm?1 at 90°C. These interpenetrating network membranes showed higher water stability than the pure acid polyimide membrane. This study shows that semi‐IPN SPI membranes based on PEGDA which gives hydrophilic group and structural stability can be available candidates comparable to Nafion® 117 over 70°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
148.
Ji Hoon Yang Min Hyung Yum Eun Jung Kim Myeung Hoi Kwon Cheol Woong Yang Ha-Jin Song Yong-Wan Jin 《Carbon》2006,44(11):2219-2223
Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C2H2, NH3, and N2 gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules. 相似文献
149.
Byeongdu Lee Jin Won Lee Seung Woo Lee Jinhwan Yoon Moonhor Ree 《Polymer Engineering and Science》2004,44(9):1682-1691
A series of poly(ethylene phthalate‐co‐terephthalate)s were synthesized by melt polycondensation of ethylene glycol (EG) with dimethyl phthalate (DMP) and dimethyl terephthalate (DMT) in various proportions. The DMT‐rich polymers were obtained with reasonably high molecular weights, whereas the DMP‐rich polymers were synthesized with relatively low molecular weights due to steric effects associated with the highly kinked DMP monomer. The compositions and thermal properties of the polymers were determined. The copolymers containing DMP in amounts of ≤ 21 mol% were crystallizable, whereas the other polymers were not. All the polymers exhibited a single glass transition temperature. Analysis of the measured glass transition temperatures and crystal melting temperatures confirmed that the DMT‐rich copolymers are random copolymers. The non‐isothermal crystallization behaviors of the DMT‐rich copolymers were investigated by calorimetry and modified Avrami analysis. The Avrami exponents n were found to range from 2.7 to 3.8, suggesting that the copolymers crystallize via a heterogeneous nucleation and spherulitic growth mechanism; that is, the incorporation of DMP units as the minor component does not change the growth mechanism of the copolymers. In addition, the activation energies of the crystallizations of the copolymers were determined; the copolymers were found to have higher activation energies than the PET homopolymer. Polym. Eng. Sci. 44:1682–1691, 2004. © 2004 Society of Plastics Engineers. 相似文献
150.
Sang Hern Kim Won Keun Son Yong Joo Kim Eu‐Gene Kang Dong‐Won Kim Chang Woo Park Whan‐Gi Kim Hyung‐Joong Kim 《应用聚合物科学杂志》2003,88(3):595-601
A polystyrene (PS)/poly(butyl acrylate) (PBA) composite emulsion was produced by seeded emulsion polymerization of butyl acrylate (BA) with PS seed particles which were prepared by emulsifier‐free polymerization of styrene with potassium persulfate (KPS) under a nitrogen atmosphere at 70°C for 24 h with stirring at 60 rpm and swelled with the BA monomer in an ethanol/water medium. The structure of the PS/PBA composite particles was confirmed by the presence of the characteristic absorption band attributed to PS and PBA from FTIR spectra. The particles for pure PS and PS/PBA with a low content of the BA monomer were almost spherical and regular. As the BA monomer content was increased, the particle size of the PS/PBA composite particles became larger, and more golf ball‐like particles were produced. The surface morphology of the PS/PBA composite particles was investigated by AFM and SEM. The Tg's attributed to PS and PBA in the PS/PBA composite particles were found at 110 and ?49°C, respectively. The thermal degradation of the pure PS and PS/PBA composite particles occurred in one and two steps, respectively. With an increasing amount of PBA, the initial thermal decomposition temperature increased. On the contrary the residual weight at 450°C decreased with an increasing amount of PBA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 595–601, 2003 相似文献