全文获取类型
收费全文 | 266077篇 |
免费 | 26903篇 |
国内免费 | 15843篇 |
专业分类
电工技术 | 21037篇 |
技术理论 | 13篇 |
综合类 | 23114篇 |
化学工业 | 38580篇 |
金属工艺 | 16034篇 |
机械仪表 | 17869篇 |
建筑科学 | 21958篇 |
矿业工程 | 8210篇 |
能源动力 | 7776篇 |
轻工业 | 22476篇 |
水利工程 | 6256篇 |
石油天然气 | 13109篇 |
武器工业 | 2979篇 |
无线电 | 30817篇 |
一般工业技术 | 26775篇 |
冶金工业 | 10106篇 |
原子能技术 | 2987篇 |
自动化技术 | 38727篇 |
出版年
2024年 | 1103篇 |
2023年 | 4115篇 |
2022年 | 8430篇 |
2021年 | 11671篇 |
2020年 | 8704篇 |
2019年 | 6745篇 |
2018年 | 7486篇 |
2017年 | 8743篇 |
2016年 | 7649篇 |
2015年 | 11558篇 |
2014年 | 14798篇 |
2013年 | 17383篇 |
2012年 | 20444篇 |
2011年 | 21706篇 |
2010年 | 19963篇 |
2009年 | 18785篇 |
2008年 | 18646篇 |
2007年 | 17586篇 |
2006年 | 16246篇 |
2005年 | 12785篇 |
2004年 | 8969篇 |
2003年 | 7586篇 |
2002年 | 7419篇 |
2001年 | 6437篇 |
2000年 | 5233篇 |
1999年 | 4286篇 |
1998年 | 2884篇 |
1997年 | 2296篇 |
1996年 | 2094篇 |
1995年 | 1694篇 |
1994年 | 1376篇 |
1993年 | 899篇 |
1992年 | 745篇 |
1991年 | 542篇 |
1990年 | 400篇 |
1989年 | 351篇 |
1988年 | 229篇 |
1987年 | 165篇 |
1986年 | 141篇 |
1985年 | 60篇 |
1984年 | 52篇 |
1983年 | 44篇 |
1982年 | 52篇 |
1981年 | 62篇 |
1980年 | 72篇 |
1979年 | 32篇 |
1978年 | 11篇 |
1976年 | 12篇 |
1959年 | 18篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
172.
The molecular design of short peptides to achieve a tailor-made functional architecture has attracted attention during the past decade but remains challenging as a result of insufficient understanding of the relationship between peptide sequence and assembled supramolecular structures. We report a hybrid-resolution model to computationally explore the sequence–structure relationship of self-assembly for tripeptides containing only phenylalanine and isoleucine. We found that all these tripeptides have a tendency to assemble into nanofibers composed of laterally associated filaments. Molecular arrangements within the assemblies are diverse and vary depending on the sequences. This structural diversity originates from (1) distinct conformations of peptide building blocks that lead to different surface geometries of the filaments and (2) unique sidechain arrangements at the filament interfaces for each sequence. Many conformations are available for tripeptides in solution, but only an extended β-strand and another resembling a right-handed turn are observed in assemblies. It was found that the sequence dependence of these conformations and the packing of resulting filaments are determined by multiple competing noncovalent forces, with hydrophobic interactions involving Phe being particularly important. The sequence pattern for each type of assembly conformation and packing has been identified. These results highlight the importance of the interplay between conformation, molecular packing, and sequences for determining detailed nanostructures of peptides and provide a detailed insight to support a more precise design of peptide-based nanomaterials. 相似文献
173.
Jialong Tian M. Babar Shahzad Wei Wang Lichang Yin Zhouhua Jiang Ke Yang 《材料科学技术学报》2018,34(9):1671-1675
The effect of Co addition on the formation of Ni-Ti clusters in maraging stainless steel was studied by three dimensional atom probe (3DAP) and first-principles calculation. The cluster analysis based on the maximum separation approach showed an increase in size but a decrease in density of Ni-Ti clusters with increasing the Co content. The first-principles calculation indicated weaker Co-Ni (Co-Ti) interactions than Co-Ti (Fe-Ti) interactions, which should be the essential reason for the change of distribution characteristics of Ni-Ti clusters in bcc Fe caused by Co addition. 相似文献
174.
Xueliang Wang Huiqin Yin Wenguan Liu Guojun Yu Jian He Zhongfeng Tang Long Yan 《工业材料与腐蚀》2020,71(6):931-937
Understanding the corrosion of molten ZnCl2 on metal surfaces is significant for the corrosion protection of metals, sustainable use of molten salts, preparation of ZnO coatings, and so on. In this paper, surfaces of pure Ni, Cr, and Fe corroded by molten ZnCl2 were investigated. The results show that Ni suffered very slight corrosion, while Cr experienced more serious corrosion than Ni, but lighter corrosion than Fe. The morphology of the corrosion of Cr and Fe, respectively, presented pitting and intergranular corrosion characteristics. Furthermore, nanostructured ZnO coatings were obtained on the surfaces of Ni and Fe, but not on the surface of Cr. The ZnO coating on the Ni surface was doped with a small amount of Zn5(OH)8Cl2, and the ZnO coating on the Fe surface was doped with ZnFe2O4 and Zn2OCl2. The coatings on the Ni and Fe surfaces had an average thickness of 1.5 and 50 μm, respectively. 相似文献
175.
Yejun Wu Bowen Yan Juan Zhou Huizhang Lian Xiaojun Yu Jianxin Zhao Hao Zhang Wei Chen Daming Fan 《Journal of food science》2020,85(10):3282-3292
176.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
177.
178.
主要分析国产电牵引采煤机控制系统中PLC电源故障,介绍输入回路、输出回路故障的分析、判断及排除方法。 相似文献
179.
Li Wei Ren Yinghui Li Chenfang Li Zhipeng Li Maojun 《The International Journal of Advanced Manufacturing Technology》2020,106(3):921-935
The International Journal of Advanced Manufacturing Technology - The wear of micro-grinding tools less than 1 mm in diameter is crucial for achieving acceptable surface quality and accurate... 相似文献
180.