首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   75519篇
  免费   6938篇
  国内免费   3563篇
电工技术   4521篇
技术理论   12篇
综合类   4978篇
化学工业   13218篇
金属工艺   4169篇
机械仪表   4412篇
建筑科学   5495篇
矿业工程   2053篇
能源动力   2262篇
轻工业   4732篇
水利工程   1425篇
石油天然气   4125篇
武器工业   764篇
无线电   9200篇
一般工业技术   9330篇
冶金工业   3882篇
原子能技术   902篇
自动化技术   10540篇
  2024年   342篇
  2023年   1265篇
  2022年   2327篇
  2021年   3209篇
  2020年   2418篇
  2019年   2046篇
  2018年   2250篇
  2017年   2446篇
  2016年   2141篇
  2015年   2999篇
  2014年   3589篇
  2013年   4560篇
  2012年   4789篇
  2011年   5073篇
  2010年   4506篇
  2009年   4442篇
  2008年   4211篇
  2007年   4028篇
  2006年   4039篇
  2005年   3451篇
  2004年   2516篇
  2003年   2263篇
  2002年   2348篇
  2001年   2073篇
  2000年   1829篇
  1999年   1948篇
  1998年   1646篇
  1997年   1398篇
  1996年   1174篇
  1995年   1007篇
  1994年   785篇
  1993年   625篇
  1992年   486篇
  1991年   390篇
  1990年   260篇
  1989年   276篇
  1988年   197篇
  1987年   115篇
  1986年   107篇
  1985年   91篇
  1984年   46篇
  1983年   32篇
  1982年   43篇
  1981年   42篇
  1980年   27篇
  1979年   22篇
  1977年   16篇
  1976年   19篇
  1974年   13篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies.  相似文献   
22.
Orthorhombic molybdenum trioxide (MoO3) is one of the most promising anode materials for sodium‐ion batteries because of its rich chemistry associated with multiple valence states and intriguing layered structure. However, MoO3 still suffers from the low rate capability and poor cycle induced by pulverization during de/sodiation. An ingenious two‐step synthesis strategy to fine tune the layer structure of MoO3 targeting stable and fast sodium ionic diffusion channels is reported here. By integrating partially reduction and organic molecule intercalation methodologies, the interlayer spacing of MoO3 is remarkably enlarged to 10.40 Å and the layer structural integration are reinforced by dimercapto groups of bismuththiol molecules. Comprehensive characterizations and density functional theory calculations prove that the intercalated bismuththiol (DMcT) molecules substantially enhanced electronic conductivity and effectively shield the electrostatic interaction between Na+ and the MoO3 host by conjugated double bond, resulting in improved Na+ insertion/extraction kinetics. Benefiting from these features, the newly devised layered MoO3 electrode achieves excellent long‐term cycling stability and outstanding rate performance. These achievements are of vital significance for the preparation of sodium‐ion battery anode materials with high‐rate capability and long cycling life using intercalation chemistry.  相似文献   
23.
24.
曾雄伟  程红莉  王桂彩 《玻璃》2015,42(6):14-17
简述了压力管道用安全阀的分类及选择,通过实例介绍如何选用安全阀。  相似文献   
25.
Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co2+ was oxidized to Co3+ after oxidation reaction.  相似文献   
26.
In this article, the silver-plated polyamide fabrics (SPPAFs) with high electroconductibility and shielding effectiveness were fabricated by using in situ reduction of polydopamine and chemical silvering. The effects of SPPAFs dopamine (C8H11O2N) and silver nitrate (AgNO3) concentration on surface resistivity and electromagnetic interference shielding effectiveness were studied. The results showed that the surface resistivity of SPPAFs can reach a minimum value of 0.06 ± 0.014 Ω cm−1, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 120 g L−1. The shielding effectiveness of SPPAFs in the wide frequency range of 10–3000 MHz increases with the increase in the concentration of AgNO3, and increases first and stabilizes afterward with increasing C8H11O2N concentration. When the concentration of C8H11O2N and AgNO3 is 3 and 120 g L−1, respectively, mean shielding effectiveness values in the low-, medium-, and high-frequency bands are 71.3, 73.8, and 76.1 dB, respectively. Moreover, the mean shielding effectiveness values is 83.79 dB in the frequency range of 1.2–2.3 GHz. The dominant shielding mechanism of SPPAFs is the reflected electromagnetic waves and the absorption shielding effectiveness is less than 2 dB. The average electromagnetic shielding values of SPPAFs are above 67 dB after 16 weeks of storage, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 80 and 100 g L−1. The prepared SPPAFs show promising applications in military textiles and smart wearable clothing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48227.  相似文献   
27.
A series of hyperbranched poly(citric polyethylene glycol) (PCPEG) materials with varied polyethylene glycol (PEG) chain lengths as plasticizers were mixed with maize starch (MS) via cooking and film‐forming. The structure, pasting property, plasticization, aging property, moisture absorption and compatibility of plasticized starches were studied by means of Fourier transform infrared spectroscopy, X‐ray diffraction, rapid viscosity analysis, tension testing, moisture absorption measurements and scanning electron microscopy. Compared with PEG and citric acid, PCPEG was more effective in promoting starch chain movement and inhibiting the retrogradation of starch film. Also, PCPEG/MS had smaller moisture content. The longer the plasticizer chain, the better were the aging resistance and moisture resistance of starch. But with an increase of PEG chain length, mechanical properties of PCPEG/MS deteriorated and the compatibility between PCPEG and MS decreased. The hyperbranched derivative of PEG with longer chain exhibited improved plasticization and compatibility with starch. © 2019 Society of Chemical Industry  相似文献   
28.
29.
30.
【摘要】   目的 研究和探讨125I粒子条联合胆道支架植入治疗恶性梗阻性黄疸的临床疗效。方法 2011年6月—2013年9月收治恶性梗阻性黄疸患者40例。行胆道支架植入术治疗患者18例,为对照组;采用125I粒子条联合胆道支架植入患者22例,为观察组。两组均采用经皮肝穿刺胆道引流(PTCD)并胆道支架植入。结果 观察组与对照组的平均胆道开通时间分别为(8.7 ± 0.7)和(6.2 ± 0.4)个月,两组比较差异有统计学意义(P < 0.05)。观察组与对照组术后平均生存时间分别为(11.4 ± 0.8)和(8.7 ± 0.5)个月,生存时间的差异有统计学意义(P < 0.05)。术后近期疗效及并发症两组之间的比较无明显差异(P > 0.05),但是远期疗效有显著差异(P < 0.05)。结论 与对照组相比,观察组的术后生存时间及胆道开通时间明显延长,对于125I粒子条联合支架治疗恶性梗阻性黄疸值得进一步临床研究。
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号