全文获取类型
收费全文 | 16976篇 |
免费 | 1394篇 |
国内免费 | 727篇 |
专业分类
电工技术 | 906篇 |
技术理论 | 3篇 |
综合类 | 1148篇 |
化学工业 | 2963篇 |
金属工艺 | 826篇 |
机械仪表 | 932篇 |
建筑科学 | 1373篇 |
矿业工程 | 452篇 |
能源动力 | 497篇 |
轻工业 | 959篇 |
水利工程 | 279篇 |
石油天然气 | 1092篇 |
武器工业 | 110篇 |
无线电 | 2026篇 |
一般工业技术 | 2437篇 |
冶金工业 | 770篇 |
原子能技术 | 181篇 |
自动化技术 | 2143篇 |
出版年
2024年 | 43篇 |
2023年 | 267篇 |
2022年 | 372篇 |
2021年 | 638篇 |
2020年 | 444篇 |
2019年 | 437篇 |
2018年 | 485篇 |
2017年 | 482篇 |
2016年 | 441篇 |
2015年 | 599篇 |
2014年 | 771篇 |
2013年 | 884篇 |
2012年 | 1028篇 |
2011年 | 1129篇 |
2010年 | 1002篇 |
2009年 | 997篇 |
2008年 | 953篇 |
2007年 | 897篇 |
2006年 | 952篇 |
2005年 | 832篇 |
2004年 | 557篇 |
2003年 | 539篇 |
2002年 | 470篇 |
2001年 | 405篇 |
2000年 | 448篇 |
1999年 | 470篇 |
1998年 | 422篇 |
1997年 | 397篇 |
1996年 | 359篇 |
1995年 | 326篇 |
1994年 | 231篇 |
1993年 | 194篇 |
1992年 | 149篇 |
1991年 | 85篇 |
1990年 | 101篇 |
1989年 | 105篇 |
1988年 | 67篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
11.
The polyamide 6-polyurethane copolymer (PA6-b-PU-b-PA6) was synthesized through anionic suspension polymerization and then mixed with polyamide 6/thermoplastic polyurethane (PA6/TPU) and polyamide 6, 6/thermoplastic polyurethane (PA66/TPU) blends using as the compatibilizer. The results show that the PA6-b-PU-b-PA6 copolymers powders several can be obtained through suspension polymerization using dimethicone as disperse medium. The average diameter of PA6-b-PU-b-PA6 copolymer powders decreased with the increasing of PU content. With the addition of PA6-b-PU-b-PA6, the TPU phase dispersed more uniformly in PA6 or PA66 matrix, and the size of TPU dispersed phase decreased obviously. The PA6-b-PU-b-PA6 copolymer with higher PU content shows better compatibilizing effect. Addition of PA6-b-PU-b-PA6 can improve both strength and toughness of the PA/TPU blends. When the amount of PA6-PU25% copolymer was 5 phr, the tensile strength and notched impact strength of PA6/TPU/PA6-PU25% blends increased 29 and 159.4%, respectively, compared to the PA6/TPU blend without compatibilizer. 相似文献
12.
Thien Vuong Nguyen Phi Hung Dao Tuan Anh Nguyen Viet Hung Dang Minh Nguyet Ha Thi Thuy Trang Nguyen Quoc Trung Vu Ngọc Linh Nguyen Tran Chien Dang Phuong Nguyen-Tri Dai Lam Tran Le Trong Lu 《应用聚合物科学杂志》2020,137(37):49116
This work aims to clarify the photocatalytic degradation mechanism and heat reflectance recovery performance of waterborne acrylic polymer/ZnO nanocomposite coating. To fabricate the nanocomposite coating, ZnO nanoparticles (nano-ZnO) were dispersed into acrylic polymer matrix at the various concentrations from 1 to 6% (by total weight of resin solids). The photocatalytic degradation of nanocomposite coating under ultraviolet (UV) light irradiation has been investigated by monitoring its weight loss and chemical/microstructural/morphological changes. As the topcoat layer, its heat reflectance recovery has been evaluated under UV/condensation exposure by using an artificial dirty mixture of 85 wt% nanoclay, 10 wt% silica particles (1–5 μm), 1 wt% carbon black, and 2 wt% engine oil. After 108-cycle UV/condensation exposure, infrared spectra and weight loss analysis indicated that the maximal degradation for nanocomposite coating is observed at 1 wt% nano-ZnO. On the other hand, after 96 hr of UV light exposure, the nanocomposite coating with1 wt% nano-ZnO could restore effectively the reflective index of solar-heat reflectance coating (from 58.45 to 80.78%). Finally, the photodegradation mechanism of this waterborne acrylic polymer coating has been proposed as the UV-induced formation of CC CO conjugated double bonds. As a result, its self-cleaning phenomenon can be achieved as the recovery of heat reflectance. 相似文献
13.
14.
浙江省废弃矿井占据了大量的土地资源,未经治理的废弃矿井区域普遍存在地面建筑物破旧,地下采空区安全隐患,地下、地表水体及土壤污染,环境景观恶劣等现象,局部存在引发地质灾害的危险。通过对全省范围内的废弃矿井展开系统全面调查,查明各类废弃矿井2 806处,主要集中于浙西低山丘陵区的衢州市1 442个、浙南西部山地丘陵区的丽水市509个、浙中丘陵盆地的金华市445个,占全省废弃矿井总数的85.39%,并对各类废弃矿井进行影响分析,归纳总结废弃矿井影响现状,为开展系统、全面、有针对性的治理工作提供依据。 相似文献
15.
Yu Zhang Xiaofei Dai Haonan Jin Chaoxin Man Yujun Jiang 《Journal of dairy science》2021,104(4):4023-4032
This study aimed to predict the optimal carbon source for higher production of exopolysaccharides (EPS) by Lactobacillus paracasei TD 062, and to evaluate the effect of this carbon source on the production and monosaccharide composition of EPS. We evaluated the EPS production capacity of 20 strains of L. paracasei under the same conditions. We further investigated L. paracasei TD 062, which showed the highest EPS-producing activity (0.609 g/L), by examining the associated biosynthesis pathways for EPS. Genomics revealed that fructose, mannose, trehalose, glucose, galactose, and lactose were carbon sources that L. paracasei TD 062 could use to produce EPS. We identified an EPS synthesis gene cluster that could participate in transport, export, and sugar chain synthesis, and generate 6 sugar nucleotides. Experimental results showed that the sugar content of the EPS produced using fermentation with the optimized carbon source (fructose, mannose, trehalose, glucose, galactose, and lactose) increased by 115%. Furthermore, use of the optimized carbon source changed the monosaccharide content of the associated EPS. The results of enzyme activity measurements showed significant increases in the activity of 2 key enzymes involved in the glycoside synthesis pathway. Our study revealed that optimizing the carbon source provided for fermentation not only increased the production of EPS, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways, suggesting an important role for carbon source in the production of EPS by L. paracasei TD 062. 相似文献
16.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
17.
18.
论述了我国建筑沥青标准的变化历程及现状,对我国建筑沥青的生产、产品质量情况及现行国家标准GB/T 494-1998《建筑石油沥青》的不足之处进行了分析。提出了今后应生产的建筑沥青品种及应参照美国材料与试验协会标准ASTM D312《屋顶用沥青的标准规格》、我国石化行业标准SH/T0002-1990(1998)《防水防潮石油沥青》,修订GB/T494- 1998的建议。以进一步达到增加建筑沥青牌号,提高建筑沥青质量和使用性能的目的,满足建筑工业的发展对沥青多牌号、高质量、使用性能好的要求。 相似文献
19.
20.
W. Wang J. Dai J. Tang D.-T. Jiang Y. Chen J. Fang J. He W. Zhou L. Spinu 《Journal of Superconductivity》2003,16(1):155-157
Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO2). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO2 films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed. 相似文献