全文获取类型
收费全文 | 107671篇 |
免费 | 11729篇 |
国内免费 | 6848篇 |
专业分类
电工技术 | 8310篇 |
技术理论 | 4篇 |
综合类 | 9660篇 |
化学工业 | 15986篇 |
金属工艺 | 6605篇 |
机械仪表 | 7293篇 |
建筑科学 | 8020篇 |
矿业工程 | 3523篇 |
能源动力 | 2978篇 |
轻工业 | 10364篇 |
水利工程 | 2993篇 |
石油天然气 | 4461篇 |
武器工业 | 1172篇 |
无线电 | 12652篇 |
一般工业技术 | 11507篇 |
冶金工业 | 4281篇 |
原子能技术 | 1659篇 |
自动化技术 | 14780篇 |
出版年
2024年 | 548篇 |
2023年 | 1756篇 |
2022年 | 3789篇 |
2021年 | 4901篇 |
2020年 | 3507篇 |
2019年 | 2849篇 |
2018年 | 2986篇 |
2017年 | 3441篇 |
2016年 | 3194篇 |
2015年 | 4674篇 |
2014年 | 5778篇 |
2013年 | 6983篇 |
2012年 | 7872篇 |
2011年 | 8398篇 |
2010年 | 7858篇 |
2009年 | 7290篇 |
2008年 | 7520篇 |
2007年 | 7329篇 |
2006年 | 6481篇 |
2005年 | 5312篇 |
2004年 | 3919篇 |
2003年 | 3202篇 |
2002年 | 3374篇 |
2001年 | 2870篇 |
2000年 | 2387篇 |
1999年 | 1624篇 |
1998年 | 1133篇 |
1997年 | 927篇 |
1996年 | 847篇 |
1995年 | 737篇 |
1994年 | 620篇 |
1993年 | 483篇 |
1992年 | 349篇 |
1991年 | 283篇 |
1990年 | 226篇 |
1989年 | 172篇 |
1988年 | 148篇 |
1987年 | 95篇 |
1986年 | 70篇 |
1985年 | 45篇 |
1984年 | 41篇 |
1983年 | 28篇 |
1982年 | 33篇 |
1981年 | 44篇 |
1980年 | 32篇 |
1979年 | 18篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1959年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
53.
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
54.
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
55.
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
56.
Xi Shen Li-Peng Cao Jian-Fa Zhao Wei-Peng Wang Qing-Qing Liu Yuan Yao Jun-Jie Li Chang-Zhi Gu Ming-Wei Chen Chang-Qing Jin Ri-Cheng Yu 《Journal of the American Ceramic Society》2019,102(11):6469-6474
We propose the question of the modulated structures of copper oxide is caused by the [CuO2] in-plane oxygen vacancy or apical oxygen vacancy. Sr2CuO3+δ single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr2CuO3+δ (δ = 0.4) single-crystal system is found to be constituted by the 5 a modulated structure with the Fmmm space group, which originates from the [CuO2] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO2] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors. 相似文献
57.
Natural Computing - The fiber stretching process plays the key role in the process of fiber production and its effects is measured by the stretching ratio. The stretching ratio is determined by the... 相似文献
58.
二氧化碳制冷技术和提升氨制冷安全体系是绿色制冷的重要支撑,北京冬奥会大量采用绿色制冷技术,不仅推动国内制冷行业可持续发展,而且将对2030年碳达峰和2060年碳中和产生深远影响. 相似文献
59.
氯甲烷在镁修饰的ZSM-5分子筛催化剂上催化转化研究 总被引:1,自引:1,他引:0
在镁修饰的ZSM-5分子筛催化剂上,氯甲烷可以被催化转化为烃类产品。分别采用了离子交换和浸渍的方法来修饰ZSM-5分子筛。离子交换的Mg-ZSM-5催化剂和浸渍的Mg/ZSM-5催化剂都可以提高反应产物中的低碳烯烃的选择性,降低烷烃的选择性,并且保持较高的反应活性,但高的浸渍量对反应活性有一定的影响。NH3-TPD的结果表明,浸渍镁的ZSM-5催化剂的强酸中心数目明显减少。镁的修饰对催化剂酸性的影响导致了产物中低碳烯烃的增加。浸渍Mg的ZSM-5催化剂是潜在氯甲烷转化生成低碳烯烃的催化剂。 相似文献
60.