全文获取类型
收费全文 | 515090篇 |
免费 | 36261篇 |
国内免费 | 19491篇 |
专业分类
电工技术 | 28030篇 |
技术理论 | 65篇 |
综合类 | 30883篇 |
化学工业 | 84782篇 |
金属工艺 | 29589篇 |
机械仪表 | 32593篇 |
建筑科学 | 37121篇 |
矿业工程 | 15495篇 |
能源动力 | 13778篇 |
轻工业 | 29711篇 |
水利工程 | 9050篇 |
石油天然气 | 32737篇 |
武器工业 | 3955篇 |
无线电 | 54779篇 |
一般工业技术 | 66231篇 |
冶金工业 | 29962篇 |
原子能技术 | 8206篇 |
自动化技术 | 63875篇 |
出版年
2024年 | 1902篇 |
2023年 | 7108篇 |
2022年 | 13331篇 |
2021年 | 18515篇 |
2020年 | 14342篇 |
2019年 | 11812篇 |
2018年 | 14124篇 |
2017年 | 15827篇 |
2016年 | 14446篇 |
2015年 | 18262篇 |
2014年 | 23732篇 |
2013年 | 28948篇 |
2012年 | 30855篇 |
2011年 | 34132篇 |
2010年 | 29624篇 |
2009年 | 28574篇 |
2008年 | 27993篇 |
2007年 | 26931篇 |
2006年 | 27165篇 |
2005年 | 23678篇 |
2004年 | 16191篇 |
2003年 | 14517篇 |
2002年 | 13653篇 |
2001年 | 12572篇 |
2000年 | 12113篇 |
1999年 | 13139篇 |
1998年 | 10828篇 |
1997年 | 9059篇 |
1996年 | 8364篇 |
1995年 | 7083篇 |
1994年 | 5885篇 |
1993年 | 4370篇 |
1992年 | 3700篇 |
1991年 | 3059篇 |
1990年 | 2600篇 |
1989年 | 2252篇 |
1988年 | 1917篇 |
1987年 | 1521篇 |
1986年 | 1299篇 |
1985年 | 1062篇 |
1984年 | 950篇 |
1983年 | 861篇 |
1982年 | 862篇 |
1981年 | 802篇 |
1980年 | 771篇 |
1979年 | 802篇 |
1978年 | 810篇 |
1977年 | 777篇 |
1976年 | 812篇 |
1973年 | 734篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth. 相似文献
12.
Zenan Yu Julian Moore Jean Calderon Lei Zhai Jayan Thomas 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(39):5289-5295
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. 相似文献
13.
Effects of different carbon sources and C/N values on nonvolatile taste components of Pleurotus eryngii 下载免费PDF全文
Wen Li Xiaobei Li Yan Yang Feng Zhou Yanfang Liu Shuai Zhou Hailong Yu 《International Journal of Food Science & Technology》2015,50(11):2360-2366
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels. 相似文献
14.
15.
核桃雄花中总多酚提取工艺的研究 总被引:2,自引:0,他引:2
采用单因素和正交试验研究核桃雄花中多酚类物质的最佳提取工艺条件。通过对4种不同溶剂(无水乙醇、甲醇、丙酮和乙酸乙酯)在相同试验条件下的浸提效果比较发现,甲醇是核桃雄花中总酚类物质的最佳提取试剂。然后分别采用常规水浴浸提法和超声波辅助浸提法对甲醇体分数、浸提温度、浸提时间和料液比等因素进行研究,在确定最佳单因素水平的基础上,再利用正交试验优化以甲醇为浸提剂的提取工艺条件,试验得出超声波辅助浸提法具有用时短、总多酚提取量高的优点,其最佳工艺条件为:料液比1∶30(g/m L)、甲醇溶液体积分数30%、温度70℃、浸提时间10 min。在此条件下,核桃雄花中的总多酚含量可达6.56%,明显高于其他条件下的。 相似文献
16.
17.
Yuanyuan Zhang Haiyan Lu Bing Wang Zhuo Zhang Xiaorong Lin Zhongzheng Chen Bin Li 《International Journal of Food Science & Technology》2015,50(6):1397-1404
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions. 相似文献
18.
19.
20.