全文获取类型
收费全文 | 101821篇 |
免费 | 11795篇 |
国内免费 | 7822篇 |
专业分类
电工技术 | 8620篇 |
技术理论 | 2篇 |
综合类 | 10474篇 |
化学工业 | 13540篇 |
金属工艺 | 6844篇 |
机械仪表 | 7599篇 |
建筑科学 | 7826篇 |
矿业工程 | 4160篇 |
能源动力 | 2944篇 |
轻工业 | 10591篇 |
水利工程 | 3033篇 |
石油天然气 | 4023篇 |
武器工业 | 1531篇 |
无线电 | 11016篇 |
一般工业技术 | 9258篇 |
冶金工业 | 4000篇 |
原子能技术 | 1533篇 |
自动化技术 | 14444篇 |
出版年
2024年 | 470篇 |
2023年 | 1793篇 |
2022年 | 3927篇 |
2021年 | 5240篇 |
2020年 | 3643篇 |
2019年 | 2649篇 |
2018年 | 2892篇 |
2017年 | 3203篇 |
2016年 | 2999篇 |
2015年 | 4543篇 |
2014年 | 5612篇 |
2013年 | 6576篇 |
2012年 | 8184篇 |
2011年 | 8565篇 |
2010年 | 7940篇 |
2009年 | 7499篇 |
2008年 | 7652篇 |
2007年 | 7485篇 |
2006年 | 6531篇 |
2005年 | 5312篇 |
2004年 | 3839篇 |
2003年 | 2908篇 |
2002年 | 2971篇 |
2001年 | 2666篇 |
2000年 | 2094篇 |
1999年 | 1134篇 |
1998年 | 528篇 |
1997年 | 477篇 |
1996年 | 436篇 |
1995年 | 351篇 |
1994年 | 233篇 |
1993年 | 206篇 |
1992年 | 181篇 |
1991年 | 124篇 |
1990年 | 102篇 |
1989年 | 96篇 |
1988年 | 68篇 |
1987年 | 53篇 |
1986年 | 43篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 18篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1959年 | 13篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm2 for Mg alloy to 13 μA/cm2 for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications. 相似文献
52.
Although Mg alloy possesses high specific strength, low density, and good biocompatibility, poor corrosion resistance hinders its further applications. In the present study, an innovative protective layer against corrosion was prepared on the AZ31 Mg alloy via alkali pretreatment followed by vanillic acid treatment. The alkali pretreatment supplied –OH for the AZ31 Mg alloy surface to react with vanillic acid. The vanillic acid treatment played a crucial role in enhancing the corrosion resistance due to the excellent ability to act as a barrier and retard aqueous solution penetration, which effectively isolated the underlying Mg alloy from the corrosive environment. The corrosion current density of alkali and vanillic acid-treated Mg alloy (AZ31V) almost showed two orders of magnitude lower values in comparison with that of the AZ31 Mg alloy, and the corrosion potential of AZ31V Mg alloy increased from −1.41 to −1.25 V. The immersion tests proved that there was no occurrence of severe corrosion. Hence, the alkali pretreatment and vanillic acid treatment may represent a promising method to improve the corrosion resistance of Mg alloy. 相似文献
53.
54.
在制导炸弹半实物仿真试验中经常发现,同一发制导炸弹多次仿真的俯仰角差别较大,同一批次制导炸弹投弹试验的遥测俯仰角与仿真俯仰角差别也较大,但是俯仰角的收敛趋势均一致,实测脱靶量与仿真脱靶量都合格,且具有一致性。为了分析出现上述现象的原因,基于协方差分析描述函数法(CADFT),建立了制导炸弹半实物仿真系统的误差传播理论,计算了仿真姿态角和姿态角速度的误差。分析了仿真姿态角和姿态角速度的误差对仿真结果的影响。结果表明,在仿真系统各种误差中,气动力和气动力矩误差是主要误差,是引起仿真俯仰角差别的重要原因; 姿态角的动态验模方法不适用于制导炸弹仿真模型,而脱靶量的静态验模方法适用于制导炸弹仿真模型。 相似文献
55.
WENXI GAO QIANQIAN MA CHENYU TANG YUELI ZHAN YINONG DUAN HUIHUA NI YUNZHAO XU 《Biocell》2020,44(4):597-605
Cervical cancer (CESC) is one of the most common cancers and affects the female genital tract. Consistent HPV
infection status has been determined to be a vital cause of tumorigenesis. HPV infection may induce changes to the
immune system and limit the host’s immune response. Immunotherapy is therefore essential to improving the overall
survival of both locally advanced and recurrent CESC patients. Using 304 relevant samples from TCGA, we assessed
immune cell function in CESC patients to better understand the status of both tumor micro-environment cells and
immune cells in CESC. Functional enrichment analysis, pathway enrichment analysis, and PPI network construction
were performed to explore the differentially expressed genes (DEGs). The analysis identified 425 DEGs, which
included 295 up-regulated genes and 130 down-regulated genes. We established that upregulation of CCL5 was
correlated with significantly better survival, meaning that CCL5 expression could serve as a novel prognostic
biomarker for CESC patients. We further focused on CCL5 as a hub gene in CESC, as it had significant correlations
with increased numbers of several types of immune cells. Cell-type fractions of M1 macrophages were significantly
higher in the high-immune-scores group, which was associated with better overall survival. Finally, we concluded that
CCL5 is a promising prognostic biomarker for CESC, as well as a novel chemotherapeutic target. 相似文献
56.
介绍了基于SMIC 0.18 μm 3.3 V工艺设计研究的第一款小像元红外探测器读出电路,间距10 μm,规模1024×1024。文章详细介绍了像素输入级以及列级、输出级运放的设计,为提高线性摆伏,设计选用了低阈值NMOS管nmvt 33,仿真分析证明低阈值管nmvt 33的噪声性能优于普通管n 33;版图设计对关键信号线和敏感点采取隔离处理措施,对像元间串扰进行了仿真分析,有效控制了信号串扰。电路经测试使用各项功能正常,最大电荷处理能力达到4.3 Me-,动态范围≥65 dB,读出速率达到10 MHz,性能指标满足设计要求。 相似文献
57.
58.
系统地论述了氧气底吹熔炼氧枪的结构、工作原理、设计计算方法、材质及蚀损机理.指出了延长氧枪使用寿命的措施。 相似文献
59.
60.