全文获取类型
收费全文 | 321202篇 |
免费 | 5605篇 |
国内免费 | 842篇 |
专业分类
电工技术 | 5264篇 |
综合类 | 183篇 |
化学工业 | 51602篇 |
金属工艺 | 12501篇 |
机械仪表 | 9256篇 |
建筑科学 | 7988篇 |
矿业工程 | 1901篇 |
能源动力 | 7440篇 |
轻工业 | 30431篇 |
水利工程 | 3495篇 |
石油天然气 | 7214篇 |
武器工业 | 20篇 |
无线电 | 33408篇 |
一般工业技术 | 62966篇 |
冶金工业 | 59815篇 |
原子能技术 | 7686篇 |
自动化技术 | 26479篇 |
出版年
2021年 | 2863篇 |
2019年 | 2559篇 |
2018年 | 4984篇 |
2017年 | 4964篇 |
2016年 | 5293篇 |
2015年 | 3450篇 |
2014年 | 5477篇 |
2013年 | 14405篇 |
2012年 | 8903篇 |
2011年 | 11171篇 |
2010年 | 9084篇 |
2009年 | 9971篇 |
2008年 | 10506篇 |
2007年 | 10153篇 |
2006年 | 8840篇 |
2005年 | 8164篇 |
2004年 | 7585篇 |
2003年 | 7269篇 |
2002年 | 7242篇 |
2001年 | 6870篇 |
2000年 | 6547篇 |
1999年 | 6719篇 |
1998年 | 17414篇 |
1997年 | 12628篇 |
1996年 | 9576篇 |
1995年 | 7136篇 |
1994年 | 6461篇 |
1993年 | 6308篇 |
1992年 | 4651篇 |
1991年 | 4619篇 |
1990年 | 4466篇 |
1989年 | 4466篇 |
1988年 | 4401篇 |
1987年 | 3730篇 |
1986年 | 3736篇 |
1985年 | 4321篇 |
1984年 | 4110篇 |
1983年 | 3717篇 |
1982年 | 3550篇 |
1981年 | 3689篇 |
1980年 | 3535篇 |
1979年 | 3460篇 |
1978年 | 3539篇 |
1977年 | 4079篇 |
1976年 | 5370篇 |
1975年 | 3221篇 |
1974年 | 3052篇 |
1973年 | 3091篇 |
1972年 | 2683篇 |
1971年 | 2514篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
171.
172.
James E. Tyrrell Martyn G. Boutelle Alasdair J. Campbell 《Advanced functional materials》2021,31(1):2007086
Biological environments use ions in charge transport for information transmission. The properties of mixed electronic and ionic conductivity in organic materials make them ideal candidates to transduce physiological information into electronically processable signals. A device proven to be highly successful in measuring such information is the organic electrochemical transistor (OECT). Previous electrophysiological measurements performed using OECTs show superior signal-to-noise ratios than electrodes at low frequencies. Subsequent development has significantly improved critical performance parameters such as transconductance and response time. Here, interdigitated-electrode OECTs are fabricated on flexible substrates, with one such state-of-the-art device achieving a peak transconductance of 139 mS with a 138 µs response time. The devices are implemented into an array with interconnects suitable for micro-electrocorticographic application and eight architecture variations are compared. The two best-performing arrays are subject to the full electrophysiological spectrum using prerecorded signals. With frequency filtering, kHz-scale frequencies with 10 µV-scale voltages are resolved. This is supported by a novel quantification of the noise, which compares the gate voltage input and drain current output. These results demonstrate that high-performance OECTs can resolve the full electrophysiological spectrum and suggest that superior signal-to-noise ratios could be achieved in high frequency measurements of multiunit activity. 相似文献
173.
174.
175.
Senthilkumar M. Vasundhara M. G. Kalavathi G. K. 《International Journal of Mechanics and Materials in Design》2019,15(3):611-627
International Journal of Mechanics and Materials in Design - The resonant frequency of electromechanical energy harvester should be tuned to ambient frequency so as to maximize the harvester power.... 相似文献
176.
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,... 相似文献
177.
178.
Ricardo Martínez-Corona Gerardo Vázquez Marrufo Carlos Cortés Penagos Luis Alberto Madrigal-Pérez Juan Carlos González-Hernández 《Yeast (Chichester, England)》2020,37(1):149-162
Lipases are hydrolytic enzymes that break the ester bonds of triglycerides, generating free fatty acids and glycerol. Extracellular lipase activity has been reported for the nonconventional yeast Kluyveromyces marxianus, grown in olive oil as a substrate, and the presence of at least eight putative lipases has been detected in its genome. However, to date, there is no experimental evidence on the physiological role of the putative lipases nor their structural and catalytic properties. In this study, a bioinformatic analysis of the genes of the putative lipases from K. marxianus L-2029 was performed, particularly identifying and characterizing the extracellular expected enzymes, due to their biotechnological relevance. The amino acid sequence of 10 putative lipases, obtained by in silico translation, ranged between 389 and 773 amino acids. Two of the analysed putative proteins showed a signal peptide, 25 and 33 amino acids long for KmYJR107Wp and KmLIP3p, and a molecular weight of 44.53 and 58.23 kDa, respectively. The amino acid alignment of KmLIP3p and KmYJR107Wp with the crystallized lipases from a patatin and the YlLip2 lipase from Yarrowia lipolytica, respectively, revealed the presence of the hydrolase characteristic motifs. From the 3D models of putative extracellular K. marxianus L-2029 lipases, the conserved pentapeptide of each was determined, being GTSMG for KmLIP3p and GHSLG for KmYJR107Wp; besides, the genes of these two enzymes (LIP3 and YJR107W) are apparently regulated by oleate response elements. The phylogenetic analysis of all K. marxianus lipases revealed evolutionary affinities with lipases from abH15.03, abH23.01, and abH23.02 families. 相似文献
179.
The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30?kV, 30?nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30?kV and 30?nA is 700?K for ZrO2. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083?°C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5?kV, 4.8?nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia. 相似文献
180.