全文获取类型
收费全文 | 57347篇 |
免费 | 4584篇 |
国内免费 | 1987篇 |
专业分类
电工技术 | 2825篇 |
技术理论 | 5篇 |
综合类 | 2987篇 |
化学工业 | 10402篇 |
金属工艺 | 3349篇 |
机械仪表 | 3332篇 |
建筑科学 | 3854篇 |
矿业工程 | 1752篇 |
能源动力 | 1809篇 |
轻工业 | 4404篇 |
水利工程 | 883篇 |
石油天然气 | 3720篇 |
武器工业 | 396篇 |
无线电 | 5977篇 |
一般工业技术 | 7449篇 |
冶金工业 | 3015篇 |
原子能技术 | 687篇 |
自动化技术 | 7072篇 |
出版年
2024年 | 207篇 |
2023年 | 909篇 |
2022年 | 1629篇 |
2021年 | 2411篇 |
2020年 | 1774篇 |
2019年 | 1547篇 |
2018年 | 1856篇 |
2017年 | 1986篇 |
2016年 | 1823篇 |
2015年 | 2266篇 |
2014年 | 2913篇 |
2013年 | 3601篇 |
2012年 | 3554篇 |
2011年 | 3876篇 |
2010年 | 3446篇 |
2009年 | 3091篇 |
2008年 | 2952篇 |
2007年 | 2830篇 |
2006年 | 2956篇 |
2005年 | 2500篇 |
2004年 | 1591篇 |
2003年 | 1395篇 |
2002年 | 1320篇 |
2001年 | 1040篇 |
2000年 | 1240篇 |
1999年 | 1508篇 |
1998年 | 1193篇 |
1997年 | 1036篇 |
1996年 | 1039篇 |
1995年 | 904篇 |
1994年 | 738篇 |
1993年 | 485篇 |
1992年 | 394篇 |
1991年 | 315篇 |
1990年 | 250篇 |
1989年 | 211篇 |
1988年 | 187篇 |
1987年 | 123篇 |
1986年 | 106篇 |
1985年 | 90篇 |
1984年 | 88篇 |
1983年 | 68篇 |
1982年 | 63篇 |
1981年 | 55篇 |
1980年 | 39篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 46篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The present study was conducted to develop subcritical water extraction (SWE) of Echinacea purpurea flowers. The influence of temperature and extraction time on quality of extracts considering total phenols content, total flavonoids content, antioxidant capacity and extraction yield, was determined. Optimized extraction parameters for maximised investigated responses were as follows: 147.56 °C and 8.43 min. The experimental values agreed with the values predicted, thus indicating the adequacy of central composite experimental design for modelling the SWE of bioactive compounds from E. purpurea. Results of the study also highlighted the potential application of E. purpurea subcritical water extracts as a source of valuable bioactive compounds. 相似文献
32.
Ting Liu Huimin Zhang Panfei Ma Aimin Chang Hui Jiang 《Journal of the American Ceramic Society》2019,102(8):4393-4398
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics. 相似文献
34.
This paper presents an analytical solution to the non-uniform pressure on thick-walled cylinder. The formulation is based on the linear elasticity theory (plain strain) and stress function method. As an example, the proposed solution is used to model the stress distribution due to non-uniform steel reinforcement corrosion in concrete. The model is formulated considering different scenarios of corrosion pressure distribution. It is validated against the finite element model for different cases of non-uniform pressure distributions. The results show that the corrosion-induced cracks are likely to start just beyond the anodic zone. This is confirmed by the experimental tests on concrete cylinder exposed to non-uniform accelerated corrosion of steel reinforcement. The model can be effectively used to calculate the distribution of corrosion-induced stresses in concrete. 相似文献
35.
36.
37.
Anxiang Su Gaoxing Ma Minhao Xie Yang Ji Xiangfei Li Liyan Zhao Qiuhui Hu 《International Journal of Food Science & Technology》2019,54(6):2277-2287
In this study, in vitro digestion and fermentation of Flammulina velutipes -derived polysaccharides (FVP) were investigated. It was found that FVP mainly consisted of 48.45% glucose, 15.40% mannose, 14.60% xylose, 11.80% fucose and 9.90% galactose. The -human saliva, simulated gastric and small intestinal juices conditions did not break down the FVP. Based on in vitro fermentation tests, FVP modulated the composition of gut microbiota by elevating the amounts of Bifidobacteriaceae and Bacteroidaceae and reducing the numbers of genera Lachnospiraceae and Enterococcaceae. Meanwhile, FVP affected the synthesis of short-chain fatty acids derived from gut microbiota. 相似文献
38.
39.
40.
Process object is the instance of process. Vertexes and edges are in the graph of process object. There are different types of the object itself and the associations between object. For the large-scale data, there are many changes reflected. Recently, how to find appropriate real-time data for process object becomes a hot research topic. Data sampling is a kind of finding c hanges o f p rocess o bjects. There i s r equirements f or s ampling to be adaptive to underlying distribution of data stream. In this paper, we have proposed a adaptive data sampling mechanism to find a ppropriate d ata t o m odeling. F irst o f all, we use concept drift to make the partition of the life cycle of process object. Then, entity community detection is proposed to find changes. Finally, we propose stream-based real-time optimization of data sampling. Contributions of this paper are concept drift, community detection, and stream-based real-time computing. Experiments show the effectiveness and feasibility of our proposed adaptive data sampling mechanism for process object. 相似文献