全文获取类型
收费全文 | 530505篇 |
免费 | 62249篇 |
国内免费 | 40321篇 |
专业分类
电工技术 | 47813篇 |
技术理论 | 2篇 |
综合类 | 55134篇 |
化学工业 | 66665篇 |
金属工艺 | 36850篇 |
机械仪表 | 36750篇 |
建筑科学 | 40436篇 |
矿业工程 | 21751篇 |
能源动力 | 14011篇 |
轻工业 | 56432篇 |
水利工程 | 18034篇 |
石油天然气 | 19502篇 |
武器工业 | 7688篇 |
无线电 | 56926篇 |
一般工业技术 | 46700篇 |
冶金工业 | 22500篇 |
原子能技术 | 8246篇 |
自动化技术 | 77635篇 |
出版年
2024年 | 1501篇 |
2023年 | 8319篇 |
2022年 | 19761篇 |
2021年 | 25679篇 |
2020年 | 18476篇 |
2019年 | 13089篇 |
2018年 | 13867篇 |
2017年 | 15853篇 |
2016年 | 14346篇 |
2015年 | 23211篇 |
2014年 | 29634篇 |
2013年 | 35382篇 |
2012年 | 43792篇 |
2011年 | 46237篇 |
2010年 | 43487篇 |
2009年 | 41670篇 |
2008年 | 42865篇 |
2007年 | 41645篇 |
2006年 | 35945篇 |
2005年 | 29012篇 |
2004年 | 20734篇 |
2003年 | 13971篇 |
2002年 | 13157篇 |
2001年 | 11806篇 |
2000年 | 9746篇 |
1999年 | 4704篇 |
1998年 | 2556篇 |
1997年 | 2136篇 |
1996年 | 1806篇 |
1995年 | 1558篇 |
1994年 | 1197篇 |
1993年 | 1031篇 |
1992年 | 804篇 |
1991年 | 652篇 |
1990年 | 568篇 |
1989年 | 471篇 |
1988年 | 350篇 |
1987年 | 267篇 |
1986年 | 246篇 |
1985年 | 194篇 |
1984年 | 139篇 |
1983年 | 120篇 |
1982年 | 103篇 |
1981年 | 149篇 |
1980年 | 177篇 |
1979年 | 104篇 |
1977年 | 72篇 |
1976年 | 129篇 |
1959年 | 87篇 |
1951年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Li-Xiang Wu Lin-Lin Zhu Yang You Rui-Lin Lin Qing-Qing Liu Wei-Ming Guo Hua-Tay Lin Kevin Paul Plucknett 《Ceramics International》2021,47(1):935-942
Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3–MgO–Y2O3 sintering additive. The addition of Eu2O3–MgO–Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3–MgO–Y2O3 were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m?1 K?1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods. 相似文献
2.
3.
汽车同步器是自动变速器的重要组成部分.对同步器的模拟优化能为同步器的设计生产提供重要的参考.为了获得一个较好的优化效果,提出了一种改进的遗传算法.通过对遗传算法选择过程的标准进行了改进,结合适应度函数与染色体之间差异,形成一种新的适应度函数.该函数同时考虑了选择压力和物种多样性.通过对函数中两个常量的调整,可以使算法在不同情况下可以有不同的偏重.引入两种典型测试函数的分别从高纬度变量和低纬度变量进行试验,分析改进算法中两个影响因子的作用.并与几类遗传算法进行比较,结果表明该改进的遗传算法能更快更稳定的找到较优的解.最后将改进选择策略结合自适应遗传算法对同步器进行优化,证明了该选择策略具有良好的鲁棒性和实效性. 相似文献
4.
5.
药物相互作用改变了剂量效应关系,可能会降低疗效或增加毒性,是临床应用中合并用药治疗时重要的考虑因素。预测具有临床意义的药物相互作用是药物研发过程中获益风险评估的重要环节。本文概述了药物研发过程中药物相互作用研究的目的和意义,体内和体外研究的主要内容;梳理分析了2020年国家药品监督管理局(National Medical Products Administration, NMPA)和美国食品药品监督管理局(Food and Drug Administration, FDA)批准上市的新药药物相互作用研究情况,旨在为我国药物研发过程中药物相互作用研究及其监管审评提供参考。 相似文献
6.
中国钢铁工业“十二五”发展规划明确提出全面推广使用400、500 MPa高强度螺纹钢筋,促进建筑钢材升级换代和减量应用。本文通过化学成分设计确定了钢筋混凝土用HRB500E螺纹钢的化学成分,通过控制装入制度、供氧制度、造渣制度、温度及终点控制制度、出钢及脱氧合金化制度和吹氩处理等工艺,成功冶炼出了符合国标化学成分要求的钢液。生产试验结果表明,钢液具有较低的氧含量,并且生产试验过程中的钢铁料消耗、合金消耗和冶炼周期均在合理范围内,后续可以批量生产。 相似文献
7.
8.
Mingming Yang Siwei Long Yunzhong Zhu Haozhe Ma Shaopeng Lin Jiliang Quan Biao Wang 《Ceramics International》2021,47(2):1970-1975
LiNbO3 crystals activated by Sm3+ and co-doped with Zr4+ (Sm:Zr:LN) or Hf4+ (Sm:Hf:LN) were prepared by the Czochralski method. Detailed investigation on spectroscopic properties was conducted on the frame of Judd-Ofelt (J-O) theory. The J-O intensity parameters Ωi (i = 2, 4, 6), fluorescence branching ratios and radiative lifetime of excited level 4G5/2 were determined. Furthermore, the thermal stability of the strong orange-red emissions obtained under near-UV excitation in both crystals was evaluated. As high as 100% and 97% of integrated intensities at room temperature in Sm:Zr:LN and Sm:Hf:LN respectively were retained at 423 K, demonstrating the suppressed thermal attenuation. The temperature sensing performance based on fluorescence intensity ratio strategy was degraded at higher temperatures with relatively low sensitivities, while the shift of CIE chromaticity coordinates of Sm:Zr:LN and Sm:Hf:LN in the orange-red region was insignificant, demonstrating the color constancy with increasing temperature. With the efficient and thermally stable orange-red luminescence, Sm:Zr:LN and Sm:Hf:LN could serve as promising candidate materials for near-UV excited white light-emitting diodes. 相似文献
9.
Carlo Dal Lin Claudia Maria Radu Giuseppe Vitiello Paola Romano Albino Polcari Sabino Iliceto Paolo Simioni Francesco Tona 《International journal of molecular sciences》2021,22(1)
Mechanical vibrations seem to affect the behaviour of different cell types and the functions of different organs. Pressure waves, including acoustic waves (sounds), could affect cytoskeletal molecules via coherent changes in their spatial organization and mechano-transduction signalling. We analyzed the sounds spectra and their fractal features. Cardiac muscle HL1 cells were exposed to different sounds, were stained for cytoskeletal markers (phalloidin, beta-actin, alpha-tubulin, alpha-actinin-1), and studied with multifractal analysis (using FracLac for ImageJ). A single cell was live-imaged and its dynamic contractility changes in response to each different sound were analysed (using Musclemotion for ImageJ). Different sound stimuli seem to influence the contractility and the spatial organization of HL1 cells, resulting in a different localization and fluorescence emission of cytoskeletal proteins. Since the cellular behaviour seems to correlate with the fractal structure of the sound used, we speculate that it can influence the cells by virtue of the different sound waves’ geometric properties that we have photographed and filmed. A theoretical physical model is proposed to explain our results, based on the coherent molecular dynamics. We stress the role of the systemic view in the understanding of the biological activity. 相似文献
10.