全文获取类型
收费全文 | 134531篇 |
免费 | 14663篇 |
国内免费 | 9461篇 |
专业分类
电工技术 | 11057篇 |
技术理论 | 5篇 |
综合类 | 12681篇 |
化学工业 | 18186篇 |
金属工艺 | 8775篇 |
机械仪表 | 9357篇 |
建筑科学 | 11064篇 |
矿业工程 | 5093篇 |
能源动力 | 3762篇 |
轻工业 | 12433篇 |
水利工程 | 3504篇 |
石油天然气 | 5783篇 |
武器工业 | 1838篇 |
无线电 | 15182篇 |
一般工业技术 | 13258篇 |
冶金工业 | 5705篇 |
原子能技术 | 1946篇 |
自动化技术 | 19026篇 |
出版年
2024年 | 818篇 |
2023年 | 2427篇 |
2022年 | 4919篇 |
2021年 | 6691篇 |
2020年 | 4694篇 |
2019年 | 3376篇 |
2018年 | 3723篇 |
2017年 | 4360篇 |
2016年 | 3844篇 |
2015年 | 5816篇 |
2014年 | 7120篇 |
2013年 | 8506篇 |
2012年 | 10204篇 |
2011年 | 10611篇 |
2010年 | 9880篇 |
2009年 | 9282篇 |
2008年 | 9600篇 |
2007年 | 9296篇 |
2006年 | 8438篇 |
2005年 | 6903篇 |
2004年 | 4925篇 |
2003年 | 3740篇 |
2002年 | 3724篇 |
2001年 | 3324篇 |
2000年 | 2859篇 |
1999年 | 2067篇 |
1998年 | 1272篇 |
1997年 | 1111篇 |
1996年 | 1069篇 |
1995年 | 858篇 |
1994年 | 704篇 |
1993年 | 537篇 |
1992年 | 473篇 |
1991年 | 349篇 |
1990年 | 247篇 |
1989年 | 220篇 |
1988年 | 173篇 |
1987年 | 114篇 |
1986年 | 75篇 |
1985年 | 67篇 |
1984年 | 47篇 |
1983年 | 31篇 |
1982年 | 39篇 |
1981年 | 28篇 |
1980年 | 39篇 |
1979年 | 21篇 |
1978年 | 2篇 |
1959年 | 13篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
61.
62.
63.
紫砂壶以造型为基本的载体,通过形神兼备的造型表现出深厚的文化情感,它将自然万物融汇其中,将各种不同的生命、思想和个性呈现其上,使人观壶如同与人交流,产生深刻的情感、精神共鸣,感受到内心的平静,这十分有益于舒缓当代人的精神心理压力,让人们通过泡茶品茗这种生活方式来获得暂时的悠闲,并通过对紫砂壶的把玩来感悟其中的文化内蕴,从而获得自由淡泊的心态,更好地面对生活。本文以紫砂壶“知竹”为例,浅谈其文化意境。 相似文献
64.
Zhimei Zheng Taixiu Liu Qibin Liu Jing Lei Juan Fang 《International Journal of Hydrogen Energy》2021,46(38):19846-19860
Solar thermochemical hydrogen production with energy level upgraded from solar thermal to chemical energy shows great potential. By integrating mid-and-low temperature solar thermochemistry and solid oxide fuel cells, in this paper, a new distributed energy system combining power, cooling, and heating is proposed and analyzed from thermodynamic, energy and exergy viewpoints. Different from the high temperature solar thermochemistry (above 1073.15 K), the mid-and-low temperature solar thermochemistry utilizes concentrated solar thermal (473.15–573.15 K) to drive methanol decomposition reaction, reducing irreversible heat collection loss. The produced hydrogen-rich fuel is converted into power through solid oxide fuel cells and micro gas turbines successively, realizing the cascaded utilization of fuel and solar energy. Numerical simulation is conducted to investigate the system thermodynamic performances under design and off-design conditions. Promising results reveal that solar-to-hydrogen and net solar-to-electricity efficiencies reach 66.26% and 40.93%, respectively. With the solar thermochemical conversion and hydrogen-rich fuel cascade utilization, the system exergy and overall energy efficiencies reach 59.76% and 80.74%, respectively. This research may provide a pathway for efficient hydrogen-rich fuel production and power generation. 相似文献
65.
Hechun Cao Hui Zheng Lining Fan Zifeng Cheng Jianwei Zhou Qiong Wu Peng Zheng Liang Zheng Yang Zhang 《International Journal of Applied Ceramic Technology》2020,17(2):813-822
In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). 相似文献
66.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
67.
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
68.
Yang Yang Yibei Zhou Juan Ren Qiaoji Zheng Kwok Ho Lam Dunmin Lin 《Journal of the European Ceramic Society》2018,38(2):557-566
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response. 相似文献
69.
70.