全文获取类型
收费全文 | 246913篇 |
免费 | 20185篇 |
国内免费 | 10695篇 |
专业分类
电工技术 | 14559篇 |
技术理论 | 10篇 |
综合类 | 14979篇 |
化学工业 | 39364篇 |
金属工艺 | 14996篇 |
机械仪表 | 15668篇 |
建筑科学 | 16490篇 |
矿业工程 | 6767篇 |
能源动力 | 5769篇 |
轻工业 | 14568篇 |
水利工程 | 4898篇 |
石油天然气 | 13735篇 |
武器工业 | 1891篇 |
无线电 | 27124篇 |
一般工业技术 | 35306篇 |
冶金工业 | 14534篇 |
原子能技术 | 5754篇 |
自动化技术 | 31381篇 |
出版年
2024年 | 1059篇 |
2023年 | 3395篇 |
2022年 | 6997篇 |
2021年 | 9435篇 |
2020年 | 7118篇 |
2019年 | 5950篇 |
2018年 | 7299篇 |
2017年 | 8064篇 |
2016年 | 7442篇 |
2015年 | 9186篇 |
2014年 | 11572篇 |
2013年 | 13988篇 |
2012年 | 15344篇 |
2011年 | 16459篇 |
2010年 | 14512篇 |
2009年 | 14312篇 |
2008年 | 13944篇 |
2007年 | 13291篇 |
2006年 | 12208篇 |
2005年 | 10435篇 |
2004年 | 7603篇 |
2003年 | 7033篇 |
2002年 | 6922篇 |
2001年 | 6232篇 |
2000年 | 5363篇 |
1999年 | 4876篇 |
1998年 | 3662篇 |
1997年 | 3136篇 |
1996年 | 2780篇 |
1995年 | 2401篇 |
1994年 | 2006篇 |
1993年 | 1637篇 |
1992年 | 1522篇 |
1991年 | 1316篇 |
1990年 | 1291篇 |
1989年 | 1179篇 |
1988年 | 1027篇 |
1987年 | 920篇 |
1986年 | 836篇 |
1985年 | 749篇 |
1984年 | 734篇 |
1982年 | 688篇 |
1979年 | 743篇 |
1978年 | 785篇 |
1977年 | 744篇 |
1976年 | 762篇 |
1975年 | 716篇 |
1974年 | 724篇 |
1973年 | 725篇 |
1972年 | 707篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent performance in magneto-optical devices, magnetic resonance imaging, ferrofluids and magnetic separation. The purpose of this study is to fabricate P-type one dimensional CuAlO2-based diluted magnetic semiconductor nanofibers. First, we fabricated Cu Al0.95Co0.05O2 nanofibers with an average diameter of 1 μm with the electrospinning method. The annealed nanofibers were thermally treated at a temperature of 1 100 ℃ and then shrunk to a diameter of about 650 nm. We used X-ray diffraction measurements and Raman spectra to confirm that the Cu Al0.95Co0.05O2 nanofibers had a single impurity free delafossite phase. The X-ray photoelectron spectroscopy analysis indicates that Co was present in the +2 oxidation state, resulting in an room temperature ferromagnetism in the Cu Al0.95Co0.05O2 fiber. This contrasts with nonmagnetism in pristine CuAlO2 fiber. The coercivity(Hc) value of 65.26 Oe and approximate saturation magnetization(Ms) of 0.012 emu/g demonstrate good evidence of ferromagnetism at room temperature for Cu Al0.95Co0.05O2 nanofibers. 相似文献
92.
Bochkareva N. I. Ivanov A. M. Klochkov A. V. Kogotkov V. S. Rebane Yu. T. Virko M. V. Shreter Y. G. 《Semiconductors》2015,49(6):827-835
Semiconductors - It is shown that the emission efficiency and the 1/f noise level in light-emitting diodes with InGaN/GaN quantum wells correlate with how the differential resistance of a diode... 相似文献
93.
94.
95.
96.
陕南山地烟田不同植烟年限土壤养分的变化 总被引:1,自引:0,他引:1
为给陕南山地烟草生产布局及有针对性的施肥措施提供依据,分析了陕南山地烟田不同植烟年限(0~15年)与土壤养分含量的关系。结果表明:随着植烟年限延长,有机质线性下降,全氮和速效钾显著上升,有效磷先上升后下降;氯、有效铁、有效锰、有效硼和有效铜无显著变化或变化很小,有效锌则在第1年急剧下降,之后保持稳定,10年后再次显著下降。认为陕南山地烟区烟叶生产中应适当增加有机肥的施用而合理控制氮肥、磷肥和钾肥的施用,并要注意锌肥的补充。 相似文献
97.
Combination of heat treatment and chitosan coating to improve postharvest quality of wolfberry (Lycium barbarum) 下载免费PDF全文
Zhaojun Ban Wenwen Wei Xiangzheng Yang Jianhua Feng Junfeng Guan Li Li 《International Journal of Food Science & Technology》2015,50(4):1019-1025
The synergistic application of hot water dip at 42 °C for 30 min and 1% chitosan coating on differentiation in postharvest quality traits, microstructure as well as microbiological evolution of wolfberry fruits was investigated. Fresh wolfberry fruits were stored at 2 ± 0.5 °C and 90% relative humidity (RH) for 28 days. Results indicated the combination of prestorage heat treatment and chitosan coating maintained higher levels of ascorbic acid, total phenolic contents and antioxidant capacity as well as lower decay, compared with untreated wolfberry fruits. The possible mechanism was that the heat treatment almost sealed open stomata to limit the sites of pathogen penetration into fruits independently, followed by the biofilm formed by chitosan which controlled secondary infections as well as slowed changes in fruit respiration and metabolic activity in wolfberries. The synergistically treated fruit also exhibited a higher acceptability obtained by sensory analysis after cold storage. In this sense, the integrated application of heat treatment and chitosan coating could be regarded as an effective strategy to extend storage life and maintain the postharvest quality of wolfberry fruits. 相似文献
98.
Zehu Xie Na Peng Tingting Liu Xing Cheng Wuquan Ye Runtian Zheng Jundong Zhang Haoxiang Yu Jie Shu 《Ceramics International》2019,45(9):11812-11818
Here, LiY(WO4)2 nanotubes are prepared via a feasible electrospinning technique. This new anode material shows excellent electrochemical properties. The capacity loss of LiY(WO4)2 nanotubes is as low as 6.9% after 156 cycles, while bulk LiY(WO4)2 presents the capacity loss higher than 55.0%. Even after 600 long-life cycles, the capacity loss of the nanotubes is only 9%. It can be seen that the hollow structure with a rough surface and a porous morphology contributes to the improvement of electrochemical performance. Furthermore, online X-ray diffraction (XRD) method is firstly applied to understand the lithium ions insertion/extraction mechanism of LiY(WO4)2 nanotubes. It can be concluded that it is an asymmetrical two-phase reaction. A phase transformation from LiY(WO4)2 to Li3Y(WO4)2 can be obviously seen from the in situ XRD during discharge process. While Li2Y(WO4)2 appears as an intermediate phase with a reverse charge reaction. In addition, in situ XRD also demonstrates that LiY(WO4)2 nanotubes have surprised electrochemical reversibility. All the above results indicate that LiY(WO4)2 nanotubes can be expected to be anode candidate for rechargeable lithium ion batteries (LIBs). 相似文献
99.
100.
Metallurgist - We consider domestic and foreign standards for rolled metals used in bridge building. Domestic standards contain elevated requirements to the reliability of rolled metals in terms of... 相似文献