全文获取类型
收费全文 | 3713篇 |
免费 | 196篇 |
国内免费 | 78篇 |
专业分类
电工技术 | 21篇 |
综合类 | 180篇 |
化学工业 | 2320篇 |
金属工艺 | 59篇 |
机械仪表 | 57篇 |
建筑科学 | 52篇 |
矿业工程 | 16篇 |
能源动力 | 125篇 |
轻工业 | 198篇 |
石油天然气 | 361篇 |
武器工业 | 10篇 |
无线电 | 60篇 |
一般工业技术 | 466篇 |
冶金工业 | 41篇 |
原子能技术 | 7篇 |
自动化技术 | 14篇 |
出版年
2024年 | 10篇 |
2023年 | 42篇 |
2022年 | 50篇 |
2021年 | 79篇 |
2020年 | 89篇 |
2019年 | 80篇 |
2018年 | 78篇 |
2017年 | 114篇 |
2016年 | 90篇 |
2015年 | 114篇 |
2014年 | 178篇 |
2013年 | 220篇 |
2012年 | 278篇 |
2011年 | 295篇 |
2010年 | 193篇 |
2009年 | 242篇 |
2008年 | 185篇 |
2007年 | 271篇 |
2006年 | 224篇 |
2005年 | 191篇 |
2004年 | 161篇 |
2003年 | 127篇 |
2002年 | 112篇 |
2001年 | 109篇 |
2000年 | 89篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 48篇 |
1996年 | 43篇 |
1995年 | 37篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有3987条查询结果,搜索用时 46 毫秒
61.
Hydrogenolysis of biomass-derived glycerol is an alternative route to sustainable production of propylene glycol. Cu–ZnO catalysts
were prepared by coprecipitation with a range of Cu/Zn atomic ratio (0.6–2.0) and examined in glycerol hydrogenolysis to propylene
glycol at 453–513 K and 4.2 MPa H2. These catalysts possess acid and hydrogenation sites required for bifunctional glycerol reaction pathways, most likely involving
glycerol dehydration to acetol and glycidol intermediates on acidic ZnO surfaces, and their subsequent hydrogenation on Cu
surfaces. Glycerol hydrogenolysis conversions and selectivities depend on Cu and ZnO particle sizes. Smaller ZnO and Cu domains
led to higher conversions and propylene glycol selectivities, respectively. A high propylene glycol selectivity (83.6%), with
a 94.3% combined selectivity to propylene glycol and ethylene glycol (also a valuable product) was achieved at 22.5% glycerol
conversion at 473 K on Cu–ZnO (Cu/Zn = 1.0) with relatively small Cu particles. Reaction temperature effects showed that optimal
temperatures (e.g. 493 K) are required for high propylene glycol selectivities, probably as a result of optimized adsorption
and transformation of the reaction intermediates on the catalyst surfaces. These preliminary results provide guidance for
the synthesis of more efficient Cu–ZnO catalysts and for the optimization of reaction parameters for selective glycerol hydrogenolysis
to produce propylene glycol. 相似文献
62.
含多羟基功能基树脂的合成及其与硼酸螯合性能的研究 总被引:1,自引:0,他引:1
合成了数种含有多羟基醇单醚功能基的树脂,研究了反应条件及树脂的吸附性能。 相似文献
63.
64.
The solubility of CO2 in triethylene glycol monomethyl ether (TEGMME) has been measured at 40, 70 and 100°C at pressures up to 8.8 MPa. The results were correlated with the Peng-Robinson (1976) equation of state. The interaction parameters and Henry's constants were derived. 相似文献
65.
用共沉淀法制备Fe3O4磁流体,总结出用十二烷基磺酸钠与聚乙二醇作为表面活性剂制备水基磁流体的合适条件:(1)反应温度为室温或不高于35℃;(2)表面活性剂十二烷基磺酸钠的最佳用量为0.0030~0.0040 g/80 mL;(3)第一次包裹的最佳pH为9~10;(4)聚乙二醇作为第二次包裹的表面活剂时,体系最佳温度为40℃左右;(5)表面活性剂聚乙二醇的最佳用量为0.0050~0.0060 g/80 mL。通过实验制得了能稳定存在180 d的水基磁流体。并用透射电镜、红外光谱、分光光度计、古埃磁天平等进行了初步表征。 相似文献
66.
乙二醇二甲醚的合成及应用 总被引:4,自引:0,他引:4
综述了乙二醇二甲醚的各种合成方法,指出相转移催化法是目前理想的工艺路线,并详细介绍了乙二醇二甲醚在各领域的应用。 相似文献
67.
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
68.
A series of nanocomposite hydrogels for mucoadhesive were prepared from acrylic acid, poly(ethylene glycol) methyl ether acrylate, and intercalated bentonite clay by photopolymerization. The microstructures were identified by X‐ray diffraction (XRD). Results showed that the swelling ratio for the present nanocomposite hydrogels decreased with an increase of bentonite, whereas the gel strength and Young's modulus of the present gels increased with an increase of bentonite. However, the adhesive force of the present gels did not decrease with an increase of bentonite. XRD results indicated that the exfoliation of bentonite was achieved in the xerogels and swollen gels. Finally, the drug‐release behaviors for these gels were also assessed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2934–2941, 2004 相似文献
69.
Three types of layered silicates, namely octosilicate, magadiite and kenyaite, were synthesized using poly(ethylene glycol) (PEG). The influence of reaction parameters, including alkali source, silica source, PEG molecular weight, reaction time and temperature, on the formation of these three phases was investigated. The results indicate that magadiite is preferred when (i) using NaOH as the alkali source and at a lower temperature (150°C), with fumed silica, tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), Ludox-AS 40 or colloidal sol acting as the silica source in the presence of PEG 200; (ii) using fumed silica as the silica source and PEG 300 as the template at 150°C; (iii) at a higher temperature (180°C), using PEG 200 as template and TEOS as the silica source; and (iv) at 180°C with a combination of PEG 300 and fumed silica. Compared to magadiite, kenyaite was favored at a higher temperature (180°C) with PEG 200 and NaOH, KOH or RbOH, while using fumed silica, silica gel, or colloidal sol as silica source; or at the lower temperature (150°C) using NaOH as alkali source, PEG 200 as template, and silica gel or silicic acid as the silica source. Octosilicate was obtained at 90°C with the combination of NaOH, PEG 200 and fumed silica. 相似文献
70.
Three types of pegylated amphiphilic copolymers of poly(δ‐valerolactone) (PVL) were copolymerized with methoxy poly(ethylene glycol) (MePEG) and poly(ethylene glycol) (PEG4000 and PEG10,000), respectively. Pegylation of PVL allowed copolymers possessing amphiphilic property and efficiently self‐assembled to form micelles with a low critical micelle concentration (CMC) in the range of 10?7–10?8M. The average molecular weight of copolymers was in the range of 10,000–20,000 Da, and the polydispersity of copolymers was about 1.7–1.8. Higher mobility of low molecular weight PEG (i.e., MePEG and PEG4000) than high molecular weight PEG10,000 allowed valerolactone ring opening more efficient in terms of PVL/MePEG and PVL/PEG4000 copolymers possessing longer chain length in hydrophobic domain. Pegylated PVL with low CMC and triblock structure was preferred to encapsulate drug during micelle formation. Although all of these amphiphilic copolymers exhibited controlled release character, the micelles formed by triblock copolymer possessed a more stable core‐shell conformation than that by diblock copolymer, and resulted in the release of drug from triblock micelles slower than that from diblock micelles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1836–1841, 2006 相似文献