全文获取类型
收费全文 | 176638篇 |
免费 | 16542篇 |
国内免费 | 9264篇 |
专业分类
电工技术 | 12030篇 |
技术理论 | 11篇 |
综合类 | 13139篇 |
化学工业 | 27609篇 |
金属工艺 | 10360篇 |
机械仪表 | 11601篇 |
建筑科学 | 14164篇 |
矿业工程 | 5196篇 |
能源动力 | 5444篇 |
轻工业 | 11168篇 |
水利工程 | 3758篇 |
石油天然气 | 10752篇 |
武器工业 | 1784篇 |
无线电 | 20351篇 |
一般工业技术 | 20204篇 |
冶金工业 | 8298篇 |
原子能技术 | 2132篇 |
自动化技术 | 24443篇 |
出版年
2024年 | 663篇 |
2023年 | 2471篇 |
2022年 | 4612篇 |
2021年 | 6601篇 |
2020年 | 5034篇 |
2019年 | 4214篇 |
2018年 | 4702篇 |
2017年 | 5519篇 |
2016年 | 5102篇 |
2015年 | 6716篇 |
2014年 | 8902篇 |
2013年 | 10297篇 |
2012年 | 11976篇 |
2011年 | 12877篇 |
2010年 | 11708篇 |
2009年 | 11202篇 |
2008年 | 11074篇 |
2007年 | 10573篇 |
2006年 | 10357篇 |
2005年 | 8716篇 |
2004年 | 6366篇 |
2003年 | 6127篇 |
2002年 | 6305篇 |
2001年 | 5667篇 |
2000年 | 4413篇 |
1999年 | 4184篇 |
1998年 | 2927篇 |
1997年 | 2517篇 |
1996年 | 2311篇 |
1995年 | 1910篇 |
1994年 | 1571篇 |
1993年 | 1145篇 |
1992年 | 850篇 |
1991年 | 650篇 |
1990年 | 560篇 |
1989年 | 437篇 |
1988年 | 362篇 |
1987年 | 228篇 |
1986年 | 184篇 |
1985年 | 104篇 |
1984年 | 76篇 |
1983年 | 55篇 |
1982年 | 64篇 |
1981年 | 45篇 |
1980年 | 30篇 |
1979年 | 18篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1959年 | 6篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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
112.
113.
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
114.
115.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献
116.
117.
Amun Amri Ahmad Fadli Zhong-Tao Jiang Chun-Yang Yin M. Mahbubur Rahman Hantarto Widjaja Syamsu Herman Silvia Reni Yenti M. Miftahul Munir Gadang Priyotomo M. Iqbal Neni Frimayanti 《Ceramics International》2018,44(13):15274-15280
The copper and cobalt oxides composites coatings on aluminum substrates have been successfully synthesized via sol-gel method using nitrate-based sol precursors. The composites were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and UV–Vis–NIR spectrophotometry. The sol-gel reactions were discussed and Molecular Dynamics (MD) simulation was integrated into the study to predict molecules assembly properties. The XRD analyses revealed that the CuO and the Co3O4 composites were formed after the annealing process with the average difference of the calculated lattice parameters compared to ICDDs was 1.17%. The surface electronic structure was mainly consisted of tetrahedral Cu(I), octahedral Cu(II), tetrahedral Co(II), octahedral Co(III) as well as surface, sub-surface and lattice oxygen O?. The XRD, XPS and MD simulation results showed that there was minimal (or possibly non-existing) indication of copper-cobalt mixed phase oxides formations. FESEM and AFM surveys revealed that the coating had a porous surface composed of interlinked nanoparticles in the range of ~?10 to ~?40?nm. UV–Vis–NIR reflectance spectra showed that the sol precursors concentration and the dip-drying cycle significantly influenced the absorptance value with optimum absorptance (α) of 88.7% exhibited by coating synthesized using sol concentration of 0.1?M and 10 dip-drying cycles. High absorptance value and simplicity in the synthesis process render the coatings to be very promising candidates for solar selective absorber (SSA) applications. 相似文献
118.
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
119.
120.
Xu Zhi-Zheng Jiang Feng Zhong Chong-Quan Gou Yong-Jie Teng Hong-Fei 《Structural and Multidisciplinary Optimization》2020,61(1):207-223
Structural and Multidisciplinary Optimization - The overall layout optimization design of an orbital propellant depot involves the optimization of shape, size, and positions of propellant tanks in... 相似文献