全文获取类型
收费全文 | 11507篇 |
免费 | 947篇 |
国内免费 | 429篇 |
专业分类
电工技术 | 518篇 |
综合类 | 524篇 |
化学工业 | 1954篇 |
金属工艺 | 718篇 |
机械仪表 | 713篇 |
建筑科学 | 650篇 |
矿业工程 | 232篇 |
能源动力 | 380篇 |
轻工业 | 560篇 |
水利工程 | 194篇 |
石油天然气 | 408篇 |
武器工业 | 55篇 |
无线电 | 1589篇 |
一般工业技术 | 1781篇 |
冶金工业 | 1030篇 |
原子能技术 | 106篇 |
自动化技术 | 1471篇 |
出版年
2024年 | 64篇 |
2023年 | 177篇 |
2022年 | 359篇 |
2021年 | 451篇 |
2020年 | 342篇 |
2019年 | 344篇 |
2018年 | 340篇 |
2017年 | 346篇 |
2016年 | 331篇 |
2015年 | 449篇 |
2014年 | 520篇 |
2013年 | 719篇 |
2012年 | 705篇 |
2011年 | 731篇 |
2010年 | 609篇 |
2009年 | 643篇 |
2008年 | 580篇 |
2007年 | 535篇 |
2006年 | 502篇 |
2005年 | 461篇 |
2004年 | 348篇 |
2003年 | 320篇 |
2002年 | 280篇 |
2001年 | 281篇 |
2000年 | 245篇 |
1999年 | 290篇 |
1998年 | 291篇 |
1997年 | 233篇 |
1996年 | 194篇 |
1995年 | 168篇 |
1994年 | 145篇 |
1993年 | 114篇 |
1992年 | 99篇 |
1991年 | 82篇 |
1990年 | 63篇 |
1989年 | 68篇 |
1988年 | 59篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Zhiqiang Wu Qiang Guo Yang Liu Huihui Zhou Hua Zheng Xingfeng Lei Lei Gong Yanhui Chen Zhenguo Liu Qiuyu Zhang 《大分子材料与工程》2021,306(11):2100456
In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm−3 under the field of 426 kV mm−1, the high tensile strength (90 MPa) and the excellent thermal stability (Td5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density. 相似文献
62.
采用全三维有限元方法对大锭型开坯过程进行变形.传热耦合分析,定量计算了铸锭在整个工艺过程中热力参数(应变、应变速率和温度)的分布及演化情况;分析了铸锭的锻透性;获得了开坯后坯料内部应变和温度的分布规律,并与实际生产中的金相检测结果进行了对比。结果表明,模拟结果与试验结果一致,可为科学地制定大规格GH4169合金铸锭的开坯工艺提供理论依据。 相似文献
63.
PRESSUREDISTRIBUTIONINTHEAIR-SPARGEDHYDROCYCLONE¥Chu,Liangyin;LuoQian(MineralEngineeringDepartment,NortheasternUniversity,She... 相似文献
64.
FLOWFIELDINAIR-SPARGEDHYDROCYCLONEChu,Liangyin;Luo,Qian(MineralEngineeringDepartment,P.O.Box139NortheasternUniversity,Shenyan... 相似文献
65.
Ti-24Al-11Nb腐蚀疲劳断口形貌的研究张跃,褚武扬,王燕斌,肖纪美(北京科技大学北京100083)1引言对Ti-24AI-11Nb合金的断裂特征和断口形貌已进行了较多的研究[“].在300oC的氢气中该合金能发生氢致开裂,其断口形貌与过载断口... 相似文献
66.
VAc/AA改性的VAE乳液高速接嘴卷烟胶的研制 总被引:4,自引:0,他引:4
介绍了VAc/AA改性的VAE乳液高速接嘴卷烟胶的制备方法。研究了各种因素对胶粘剂性能的影响。结果表明 :VAc/AA用量增加 ,VAE乳液的粘接性能增强。选择与VAE乳液相适应的乳化剂和控制适宜的pH值 ,可以增加VAE乳液的稳定性。采用滴加引发剂和混合单体的方法 ,可以避免过速反应产生及大粒径胶粒生成 相似文献
67.
Boon-Seang Chu Sosaku Ichikawa Sumiyo Kanafusa Mitsutoshi Nakajima 《Journal of the American Oil Chemists' Society》2007,84(11):1053-1062
This work was initiated to prepare protein-stabilized β-carotene nanodispersions using emulsification–evaporation. A pre-mix
of the aqueous phase composed of a protein and hexane containing β-carotene was subjected to high-pressure homogenization
using a microfluidizer. Hexane in the resulting emulsion was evaporated under reduced pressures, causing crystallization and
precipitation of β-carotene inside the droplets and formation of β-carotene nanoparticles. Sodium caseinate (SC) was the most
effective emulsifier among selected proteins in preparing the nanodispersion, with a monomodal β-carotene particle-size distribution
and a 17-nm mean particle size. The results were confirmed by transmission-electron microscopy analysis. SC-stabilized nanodispersion
also had considerably high ζ-potential (−27 mV at pH 7), suggesting that the nanodispersion was stable against particle aggregation.
Increasing the SC concentration decreased the mean particle size and improved the polydispersity of the nanodispersions. Nanodispersions
prepared with higher β-carotene concentrations and higher organic-phase ratios resulted in larger β-carotene particles. Although
increased microfluidization pressure did not decrease particle size, it did improve the polydispersity of the nanodispersions.
Repeating the microfluidization process at 140 MPa caused the nanodispersions to become polydisperse, indicating the loss
of emulsifying capacity of SC due to protein denaturation. 相似文献
68.
The objective of this study was to examine how and to what extent a new degradable polymeric fiber, poly(p-dioxanone), used as a surgical suture material, degrades in the presence of enzymes and after γ-irradiation. The degradation of the fiber was studied mechanically using an Instron and morphologically by SEM. Both esterase and trypsin enzymes and their corresponding buffer controls were used. The fibers were γ-irradiated at the dosages ranging from 0 to 20 Mrad, immersed in the solution for up to 70 days, and then removed for tensile strength and morphological examinations. It was found that γ-irradiation alone lowered the tensile strength of PDS fibers and made them more susceptible to hydrolysis. Esterase and trypsin did not accelerate the hydrolytic degradtion of this fiber to any significant level. Both γ-irradiation and enzymes influenced the gross morphological characteristic of PDS fibers when they were subjected to hydrolysis. The most important morphological observations were the formation of surface cracks and chips on the fibers and the subsequent peeling of the chips. Enzyme-treated PDS fibers exhibited similar morphological findings but the size of the chips was smaller. The morphological observations of PDS fibers were consistent with the tensile strength data. 相似文献
69.
The mechanism of color reversion in soybean salad oil 总被引:5,自引:0,他引:5
Ming-Tain Lai Woan-Meei Lin Yan-Hwa Chu Shih-Ling Y. Chen Kwan-Shean Kong Chieh-Wu Chen 《Journal of the American Oil Chemists' Society》1989,66(4):565-571
An enzymatic reaction might be the major cause of color reversion in soybean oil. During the soybean flaking process, enzymatic
reactions take place to convertγ-tocopherol to 5-(tocopheryloxy)-γ-tocopherol (γ-TED), and then further convertγ-TED to the precursors which are the cause of color reversion. The variations ofγ-tocopherol andγ-TED contents in soybean oil are accompanied by an inverse change in the precursors’ concentration. Therefore, the contents
ofγ-tocopherol orγ-TED in crude soybean oil could be used as an index for predicting the color quality (color reversion) of soybean salad oil.
Almost all the precursors (such as tocored) were converted to color-reverted substances under catalysis after bleaching treatment,
and they were converted back to the precursors during deodorization. Those precursors might be gradually reconverted into
the color reverted substances during storage to cause the color reversion in soybean salad oil. 相似文献
70.
C. C. Chu 《应用聚合物科学杂志》1981,26(5):1727-1734
The hydrolytic degradation of polyglycolic acid (PGA) was studied by examining the changes of tensile strength and the level of crystallinity of the suture material. It was found that the breaking stress decreased from 6.369 × 10?1 at 0 day to 3.97 × 10?3 Newton/Tex at 49 days. The sigmodial shape of the stress–strain curves gradually disappeared with increase in the duration of in vitra degradation. The endpoint titration method used to assess the degree of degradation beyond the period of measurable tensile strength showed that the percent of PGA degraded were 42, 56, and 70% at 49, 60, and 90 days, respectively. The level of crystallinity of PGA at various durations of degradation exhibited an initial increase in the degree of crystallinity from 40% at 0 day to an upper limit of 52% at 21 days, then gradual decrease to 23% at 90 days. This observation is essentially parallel to hydrolysis of cellulose and polyethylene terephthalate. The concept of microfibrillar structure of fibers provides the basis for the proposed degradation mechanism of PGA in vitro. It is believed that degradation proceeds through two main stages which are different in rate of degradation. 相似文献