全文获取类型
收费全文 | 163656篇 |
免费 | 13432篇 |
国内免费 | 6719篇 |
专业分类
电工技术 | 9185篇 |
技术理论 | 19篇 |
综合类 | 10093篇 |
化学工业 | 27705篇 |
金属工艺 | 8581篇 |
机械仪表 | 9772篇 |
建筑科学 | 12453篇 |
矿业工程 | 4521篇 |
能源动力 | 4745篇 |
轻工业 | 9938篇 |
水利工程 | 2774篇 |
石油天然气 | 8898篇 |
武器工业 | 1319篇 |
无线电 | 20430篇 |
一般工业技术 | 20459篇 |
冶金工业 | 8653篇 |
原子能技术 | 1904篇 |
自动化技术 | 22358篇 |
出版年
2024年 | 661篇 |
2023年 | 2568篇 |
2022年 | 4533篇 |
2021年 | 6232篇 |
2020年 | 4747篇 |
2019年 | 3969篇 |
2018年 | 4542篇 |
2017年 | 5025篇 |
2016年 | 4438篇 |
2015年 | 5992篇 |
2014年 | 7425篇 |
2013年 | 9478篇 |
2012年 | 9936篇 |
2011年 | 10777篇 |
2010年 | 9405篇 |
2009年 | 9222篇 |
2008年 | 9118篇 |
2007年 | 8584篇 |
2006年 | 8883篇 |
2005年 | 7767篇 |
2004年 | 5457篇 |
2003年 | 4734篇 |
2002年 | 4463篇 |
2001年 | 4233篇 |
2000年 | 4138篇 |
1999年 | 4648篇 |
1998年 | 4022篇 |
1997年 | 3484篇 |
1996年 | 3045篇 |
1995年 | 2566篇 |
1994年 | 2026篇 |
1993年 | 1629篇 |
1992年 | 1283篇 |
1991年 | 997篇 |
1990年 | 775篇 |
1989年 | 673篇 |
1988年 | 526篇 |
1987年 | 379篇 |
1986年 | 288篇 |
1985年 | 250篇 |
1984年 | 140篇 |
1983年 | 105篇 |
1982年 | 122篇 |
1981年 | 90篇 |
1980年 | 69篇 |
1979年 | 53篇 |
1978年 | 35篇 |
1977年 | 40篇 |
1976年 | 56篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
Kang Zhang Rong‐rong Wang Kai‐rui Zhang Fei Cheng Yu Tian Yi Lin Mi Zhou Pu‐xin Zhu 《Polymer International》2020,69(3):274-279
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
63.
Wai-Ching Liu Huey-Yuan Wang Lung-Chien Chen Shih-Wei Huang Chengtie Wu Ren-Jei Chung 《Ceramics International》2019,45(5):5668-5679
Tricalcium silicate (C3S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C3S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C3S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C3S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C3S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C3S. Lastly, HAp/C3S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C3S biocompatibility with this new composites HAp/C3S. C-75 (75% C3S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers. 相似文献
64.
65.
66.
67.
电网的安全水平主要取决于其使用产品的质量是否过关。如果产品的质量较好,则能建造出优质的电网,电网的安全水平便会随之提高。因此,应加强对产品质量的监督管理,从而提高电网的安全水平。我们可建立质量监督管理系统,及时抽检出质量不过关的产品,从而消除电网运行过程中潜在的安全隐患。 相似文献
68.
【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
相似文献
69.
70.
Multimedia Tools and Applications - We present three stages of a novel backgrounds subtraction method in this paper: a new pixel-block based randomized arrangement is utilized to preprocess all the... 相似文献