全文获取类型
收费全文 | 9965篇 |
免费 | 1953篇 |
国内免费 | 1003篇 |
专业分类
电工技术 | 235篇 |
综合类 | 665篇 |
化学工业 | 3665篇 |
金属工艺 | 86篇 |
机械仪表 | 175篇 |
建筑科学 | 247篇 |
矿业工程 | 64篇 |
能源动力 | 232篇 |
轻工业 | 4903篇 |
水利工程 | 41篇 |
石油天然气 | 90篇 |
武器工业 | 40篇 |
无线电 | 348篇 |
一般工业技术 | 1465篇 |
冶金工业 | 89篇 |
原子能技术 | 58篇 |
自动化技术 | 518篇 |
出版年
2024年 | 93篇 |
2023年 | 288篇 |
2022年 | 284篇 |
2021年 | 472篇 |
2020年 | 433篇 |
2019年 | 430篇 |
2018年 | 337篇 |
2017年 | 412篇 |
2016年 | 408篇 |
2015年 | 419篇 |
2014年 | 636篇 |
2013年 | 717篇 |
2012年 | 833篇 |
2011年 | 826篇 |
2010年 | 607篇 |
2009年 | 606篇 |
2008年 | 456篇 |
2007年 | 683篇 |
2006年 | 597篇 |
2005年 | 533篇 |
2004年 | 421篇 |
2003年 | 412篇 |
2002年 | 368篇 |
2001年 | 328篇 |
2000年 | 270篇 |
1999年 | 210篇 |
1998年 | 160篇 |
1997年 | 118篇 |
1996年 | 106篇 |
1995年 | 82篇 |
1994年 | 70篇 |
1993年 | 74篇 |
1992年 | 54篇 |
1991年 | 18篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 21篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1968年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Cellulose dissolved in ionic liquid (1‐(carboxymethyl)pyridinium chloride)/water (60/40 w/w) mixture is regenerated in various non‐solvents, namely water, ethanol, methanol and acetone, to gain more insight into the contribution of non‐solvent medium to the morphology of regenerated cellulose. To this end, the initial and regenerated celluloses were characterized with respect to crystallinity, thermal stability, chemical structure and surface morphology using wide‐angle X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. According to the results, regardless of non‐solvent type, all regenerated samples have the same chemical structure and lower crystallinity in comparison to the initial cellulose, making them a promising candidate for efficient biofuel production based on enzymatic hydrolysis of cellulose. The reduction in crystallinity of regenerated samples is explained based on the potential of the non‐solvent to break the hydrogen bonds between cellulose chains and ionic liquid molecules as well as the affinity of water and non‐solvent which can be evaluated based on Hansen solubility parameter. The latter also determines the phase‐separation mechanism during the regeneration process, which in turn affects surface morphology of the regenerated cellulose. The pivotal effect of regenerated cellulose crystallinity on its thermal stability is also demonstrated. Regenerated cellulose with lower crystallinity is more susceptible to molecular rearrangement during heating and hence exhibits enhanced thermal stability. © 2019 Society of Chemical Industry 相似文献
13.
Xiaopeng Yue Yongjian Xu Nina Gou Hongkui Li 《Polymer-Plastics Technology and Engineering》2015,54(6):639-646
A long fatty side chain was introduced into the macromolecule of hydroxyethyl cellulose (HEC) via esterification reaction. The hydrophobicity of hydroxyethyl cellulose lauric acid ester (HECLAE) was enhanced in comparison with HEC. The obtained HECLAE was used as macromolecular coupling agent in poly (butylene succinate)/wood flour composites and exhibited a positive influence on improving the mechanical performance of composites. Besides, HECLAE plays a role as a hydrophobic agent in composites. A significant increase in storage modulus (E’) was observed upon the incorporation of treated wood flour. SEM images showed that the dispersion of treated wood flour in PBS matrix was improved. 相似文献
14.
C. Busuioc C.D. Ghitulica A. Stoica M. Stroescu G. Voicu V. Ionita L. Averous S.I. Jinga 《Ceramics International》2018,44(8):9433-9441
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications. 相似文献
15.
16.
浅谈酶在非接触印刷废纸脱墨中的应用 总被引:3,自引:0,他引:3
简要地介绍了纤维素酶、半纤维素酶和淀粉酶在非接触印刷废纸脱墨中的研究及其应用 相似文献
17.
Masami Ikeda Susumu Fukumoto Hiroshi Takao Shinya Ohtsuka Eiichi Haginomori Masayuki Hikita 《Electrical Engineering in Japan》2002,141(4):16-24
This paper describes the dielectric breakdown characteristics of oil and oil‐impregnated paper for very fast transient (VFT) voltages. Blumlein circuits generate VFT voltages of 60 and 300 ns in a pulse width that simulates disconnecting switching surges in gas‐insulated switch gears. We measured the breakdown voltages of needle‐to‐plane, plane‐to‐plane oil gaps and several pieces of paper between plane electrodes for VFT and lightning impulse voltages. The measured data were formulated in V‐t characteristics and Weibull probability distributions. The inclination n of V‐t characteristics of insulating paper is 150, which is less than n = 13.7 of the plane‐to‐plane oil gap in the VFT time range. The shape parameters of Weibull distribution obtained in this study show that the scattering of breakdown voltages of paper is much less than that of oil. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 16–24, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10043 相似文献
18.
喷墨打印相纸及打印图像质量的分析 总被引:2,自引:1,他引:1
喷墨打印相纸随着数码相机的发展近几年在国内发展迅速。针对目前产品质量没有测量标准的现状,提出喷墨相纸的质量指标主要为4个,即白度、光泽度、油墨吸收性和防水性。给出了相应的测量方法。并指出相纸上油墨点的面积是衡量质量的第一重要指标,其次是点的圆度。另外对图像输出的质量介绍了一种科学的评价方法,即图像的逼真性分析。说明图像的打印墨点直径不应小于方形像素的对角线长,图像才能真实再现。 相似文献
19.
Cellulose can be totally liquefied by heating to 350 °C in the presence of an aqueous phenolic solvent containing a catalyst. The main products are light aromatic hydrocarbons, benzofurans, heavier aromatic hydrocarbons such as substituted indanes and tetralin, and xanthenes. The variation of product distribution with catalyst was examined and it was found that in aqueous phenol, xanthene formation was enhanced by acidity. By substituting guaiacol for phenol, it was determined that most benzofuran formation involved the phenol solvent molecules, although a small proportion did not. This benzofuran may have arises from phenol generated from cellulose, the incorporation of phenol in the products being enhanced through a cage effect. 相似文献
20.
从理论上研究了纸张背衬不同衬底的光反射率,得出下列表达式:Rb=Ro+(R∞-Ro)×(1/R∞-Ro)/(1/B-Ro)(B为衬底的光反射率),该式简单实用且物理意义明确。利用上述公式,可将Tappi标准列出的Tappi不透明度C0.89的换算公式简化,并可从理论上定性地讨论纸张不透明度与印刷透印性的关系。 相似文献