全文获取类型
收费全文 | 280060篇 |
免费 | 31961篇 |
国内免费 | 20894篇 |
专业分类
电工技术 | 23740篇 |
技术理论 | 8篇 |
综合类 | 29716篇 |
化学工业 | 36325篇 |
金属工艺 | 18680篇 |
机械仪表 | 19192篇 |
建筑科学 | 21885篇 |
矿业工程 | 10943篇 |
能源动力 | 7147篇 |
轻工业 | 31548篇 |
水利工程 | 8811篇 |
石油天然气 | 10459篇 |
武器工业 | 3939篇 |
无线电 | 29787篇 |
一般工业技术 | 24276篇 |
冶金工业 | 10511篇 |
原子能技术 | 4224篇 |
自动化技术 | 41724篇 |
出版年
2024年 | 1440篇 |
2023年 | 4545篇 |
2022年 | 10760篇 |
2021年 | 14008篇 |
2020年 | 10309篇 |
2019年 | 7203篇 |
2018年 | 7793篇 |
2017年 | 8976篇 |
2016年 | 7876篇 |
2015年 | 12754篇 |
2014年 | 16148篇 |
2013年 | 18856篇 |
2012年 | 22966篇 |
2011年 | 24204篇 |
2010年 | 22848篇 |
2009年 | 21656篇 |
2008年 | 21914篇 |
2007年 | 20998篇 |
2006年 | 18136篇 |
2005年 | 14527篇 |
2004年 | 10688篇 |
2003年 | 7824篇 |
2002年 | 7712篇 |
2001年 | 6724篇 |
2000年 | 4892篇 |
1999年 | 2264篇 |
1998年 | 942篇 |
1997年 | 757篇 |
1996年 | 640篇 |
1995年 | 458篇 |
1994年 | 369篇 |
1993年 | 309篇 |
1992年 | 257篇 |
1991年 | 188篇 |
1990年 | 169篇 |
1989年 | 138篇 |
1988年 | 93篇 |
1987年 | 84篇 |
1986年 | 66篇 |
1985年 | 32篇 |
1984年 | 35篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 40篇 |
1980年 | 75篇 |
1979年 | 47篇 |
1977年 | 4篇 |
1959年 | 46篇 |
1958年 | 2篇 |
1951年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
23.
比喻是一种利用事物之间的相似点建立关系的修辞方式。明喻是比喻中最常见的形式,具有明显的喻词,例如"像",用于关联本体和喻体。近年来高考语文散文类鉴赏题中多有考查明喻句的试题,为了解答此类鉴赏题,需要识别比喻句中的本体和喻体要素。该文提出了基于词性特征的明喻识别及要素抽取方法。首先将句子中词向量化表示与词性特征向量化表示进行融合,将融合后的向量输入到BiLSTM中进行训练,然后利用CRF解码出全局最优标注序列;最后得到明喻识别和要素抽取的结果。公开数据集上的实验结果表明,该方法优于已有的单任务方法;同时也将该文方法应用于北京高考语文鉴赏题中比喻句的识别与要素抽取,验证了方法的可行性。 相似文献
24.
26.
Jieyun Tu Xinghui Shi Yuanrong Jing Huimin Zou Jakub Kadlcak Zhanfu Yong Susu Liu Guangyong Liu 《Polymer Engineering and Science》2021,61(8):2213-2221
Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide-cured rubbers. 相似文献
27.
28.
Sheng Mingming Yang Rongkun Gong Hongyu Zhang Yujun Lin Xiao Jing Jie 《Journal of Materials Science》2022,57(10):5805-5824
Journal of Materials Science - With the extensive use of high-power electronic appliances, polymer-based thermal insulation composites with excellent thermal properties are utilized in the field of... 相似文献
29.
Jinshuang Wang Luyao Chen Mengdi Chen Yuyang Wu Yinghui Wang Yongsheng Yu Junbin Sun Bing Liu Qiangshan Jing 《Ceramics International》2021,47(16):22965-22975
In this study, the destabilization resistance of Sc2O3 and CeO2 co-stabilized ZrO2 (SCZ) ceramics was tested in Na2SO4 + V2O5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V2O5 to produce m-ZrO2 and CeVO4, and little ScVO4 was detected in the Sc2O3-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO2 and m-ZrO2 due to the mineralization effect. The Sc2O3-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. 相似文献
30.
Hongli Liu Peng Wang Bo Zhang Hongyan Li Jing Li Yajing Li Zhong Chen 《Ceramics International》2021,47(5):6487-6495
A novel carbon/m-HNTs composite aerogel was synthesized by introducing the modified halloysite nanotubes (m-HNTs) into phenolic (PR) aerogels through chemical grafting, followed with carbonization treatment. In order to explore the best proportion of HNTs to phenolic, the micromorphology of PR/m-HNTs were investigated by SEM before carbonization, confirming 10 wt% of m-HNTs is most beneficial to the porous network of aerogels. The interaction between PR and HNTs was studied by FTIR spectra, and microstructure evolution of the target product-carbon/m-HNTs composite aerogel were illustrated by SEM and TEM techniques. SEM patterns indicated that the carbon/m-HNTs aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), while a ~20 nm carbon layer was formed around m-HNTs generating an integral unit through TEM analysis. Specific surface area and pore size distribution of composite aerogels were analyzed based on mercury intrusion porosimetry and N2 adsorption–desorption method, the obtained results stayed around 500 m2g?1 and 1.00 cm3g?1 (pore volume) without significant discrepancy, compared with pure aerogel, showing the uniformity of pore size. The weight loss rate (26.76%) decreased greatly compared with pure aerogel, at the same time, the best volumetric shrinkage rate was only 30.83%, contributed by the existence of HNTs supporting the neighbor structure to avoid over-shrinking. The highest compressive strength reached to 4.43 MPa, while the data of pure aerogel was only 1.52 MPa, demonstrating the excellent mechanical property of carbon/m-HNTs aerogels. 相似文献