全文获取类型
收费全文 | 167371篇 |
免费 | 13522篇 |
国内免费 | 7037篇 |
专业分类
电工技术 | 9592篇 |
技术理论 | 15篇 |
综合类 | 10777篇 |
化学工业 | 28165篇 |
金属工艺 | 9013篇 |
机械仪表 | 10443篇 |
建筑科学 | 12886篇 |
矿业工程 | 4282篇 |
能源动力 | 4726篇 |
轻工业 | 10718篇 |
水利工程 | 2866篇 |
石油天然气 | 8596篇 |
武器工业 | 1166篇 |
无线电 | 20989篇 |
一般工业技术 | 21349篇 |
冶金工业 | 7951篇 |
原子能技术 | 1958篇 |
自动化技术 | 22438篇 |
出版年
2024年 | 541篇 |
2023年 | 2420篇 |
2022年 | 4354篇 |
2021年 | 6093篇 |
2020年 | 4528篇 |
2019年 | 3917篇 |
2018年 | 4401篇 |
2017年 | 4991篇 |
2016年 | 4591篇 |
2015年 | 6143篇 |
2014年 | 7685篇 |
2013年 | 9661篇 |
2012年 | 10274篇 |
2011年 | 11311篇 |
2010年 | 9999篇 |
2009年 | 9574篇 |
2008年 | 9577篇 |
2007年 | 8927篇 |
2006年 | 9187篇 |
2005年 | 8112篇 |
2004年 | 5722篇 |
2003年 | 5135篇 |
2002年 | 5058篇 |
2001年 | 4602篇 |
2000年 | 4332篇 |
1999年 | 4618篇 |
1998年 | 3886篇 |
1997年 | 3354篇 |
1996年 | 3027篇 |
1995年 | 2560篇 |
1994年 | 2079篇 |
1993年 | 1628篇 |
1992年 | 1265篇 |
1991年 | 979篇 |
1990年 | 771篇 |
1989年 | 634篇 |
1988年 | 502篇 |
1987年 | 352篇 |
1986年 | 248篇 |
1985年 | 205篇 |
1984年 | 122篇 |
1983年 | 90篇 |
1982年 | 106篇 |
1981年 | 74篇 |
1980年 | 60篇 |
1979年 | 40篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 48篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Yu Zhang Xiaofei Dai Haonan Jin Chaoxin Man Yujun Jiang 《Journal of dairy science》2021,104(4):4023-4032
This study aimed to predict the optimal carbon source for higher production of exopolysaccharides (EPS) by Lactobacillus paracasei TD 062, and to evaluate the effect of this carbon source on the production and monosaccharide composition of EPS. We evaluated the EPS production capacity of 20 strains of L. paracasei under the same conditions. We further investigated L. paracasei TD 062, which showed the highest EPS-producing activity (0.609 g/L), by examining the associated biosynthesis pathways for EPS. Genomics revealed that fructose, mannose, trehalose, glucose, galactose, and lactose were carbon sources that L. paracasei TD 062 could use to produce EPS. We identified an EPS synthesis gene cluster that could participate in transport, export, and sugar chain synthesis, and generate 6 sugar nucleotides. Experimental results showed that the sugar content of the EPS produced using fermentation with the optimized carbon source (fructose, mannose, trehalose, glucose, galactose, and lactose) increased by 115%. Furthermore, use of the optimized carbon source changed the monosaccharide content of the associated EPS. The results of enzyme activity measurements showed significant increases in the activity of 2 key enzymes involved in the glycoside synthesis pathway. Our study revealed that optimizing the carbon source provided for fermentation not only increased the production of EPS, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways, suggesting an important role for carbon source in the production of EPS by L. paracasei TD 062. 相似文献
132.
133.
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
134.
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
135.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献
136.
137.
基于四候煤矿3108回风顺槽过F3断层期间,顶板出现严重破碎、下沉现象,提出了俯斜台阶法施工工艺,并对断层破碎带顶板采取MF-2型化学材料注浆加固以及"钢筋锚索网+U29梯形棚"联合支护措施。支护效果检验结果表明,联合支护有效控制了断层破碎区顶板下沉、破碎现象,保证了巷道顶板稳定性。 相似文献
138.
139.
Linlin Zhu Liyuan Zhang Xi Li Xiaoqi Jin Tiejun Shi 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(7):551-560
AbstractGraphene oxide (GO) was functionalized by polyether amine (PEA) via two methods which were one-pot modification in acetone (GON) and two steps with the intermediate product of GOCO-Cl generated (GONS). There were more PEA successfully grafted onto GO for GONS than GON. The onset polymerization temperatures of the benzoxazine (Bz) composites decreased by the inclusion of 1?wt% of GO, GON or GONS. Thermal stability of the polybenzoxazine (PBz) composites was significantly improved indicated from the increase of weight loss temperature. T10, T20 and T50 values of the composites with GONS were higher than that of the others. Toughness of PBzs may be enhanced by the incorporation of nanofillers, and GONS had stronger interfacial interaction with PBz matrix than GON. 相似文献
140.