全文获取类型
收费全文 | 4148篇 |
免费 | 67篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 428篇 |
金属工艺 | 45篇 |
机械仪表 | 36篇 |
建筑科学 | 94篇 |
矿业工程 | 21篇 |
能源动力 | 114篇 |
轻工业 | 301篇 |
水利工程 | 18篇 |
石油天然气 | 8篇 |
无线电 | 246篇 |
一般工业技术 | 349篇 |
冶金工业 | 2227篇 |
原子能技术 | 22篇 |
自动化技术 | 283篇 |
出版年
2022年 | 15篇 |
2021年 | 35篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 40篇 |
2017年 | 28篇 |
2016年 | 38篇 |
2015年 | 41篇 |
2014年 | 66篇 |
2013年 | 114篇 |
2012年 | 92篇 |
2011年 | 114篇 |
2010年 | 79篇 |
2009年 | 86篇 |
2008年 | 121篇 |
2007年 | 107篇 |
2006年 | 85篇 |
2005年 | 84篇 |
2004年 | 64篇 |
2003年 | 70篇 |
2002年 | 52篇 |
2001年 | 69篇 |
2000年 | 42篇 |
1999年 | 105篇 |
1998年 | 732篇 |
1997年 | 402篇 |
1996年 | 262篇 |
1995年 | 157篇 |
1994年 | 124篇 |
1993年 | 172篇 |
1992年 | 55篇 |
1991年 | 51篇 |
1990年 | 46篇 |
1989年 | 45篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 22篇 |
1983年 | 28篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1978年 | 17篇 |
1977年 | 56篇 |
1976年 | 108篇 |
1975年 | 15篇 |
1973年 | 17篇 |
1972年 | 12篇 |
1969年 | 12篇 |
排序方式: 共有4218条查询结果,搜索用时 125 毫秒
11.
A voltage-controlled oscillator (VCO) with sine wave output has been built using a tunable inductor along with a tunable capacitor to operate at frequencies ranging from 100 kHz to over 20 MHz. The method of tuning the inductor by changing the permeability of its ferrite core and the ability to extend the frequency response of the core are discussed. Dynamic characteristics of the VCO are explained with examples of a parallel and series tank implementation 相似文献
12.
Responds to the comments by L. T. Hoshmand (see record 2003-08988-012) and J. Aros (see record 2003-08988-013) on the article by J. Arnett (see record 2002-18352-003) regarding the psychology of globalization. In this response, Arnett discusses the moral implications of globalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
13.
Yuanjing Zheng Anker Degn Jensen Jan Erik Johnsson 《Applied catalysis. B, Environmental》2005,60(3-4):253-264
The deactivation of a commercial type V2O5-WO3-TiO2 monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH3 and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH3 on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H2SO4 the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion. 相似文献
14.
15.
C Wang ME Nicol MK Chakrabarti A Holdcroft JG Whitwam 《Canadian Metallurgical Quarterly》1993,16(6):354-357
We compared high frequency ventilation (HFV) to conventional mechanical ventilation (CMV) under normoxic and normocapnic condition in surfactant depleted rabbits with bilateral pneumothoraces. We hypothesized that lower airway pressures would be required with HFV under these conditions. We applied CMV and HFV in 8 anaesthetized rabbits with a prototype ventilator at frequencies of 30, 100, 200, and 300 cycles/min. A positive end-expiratory pressure (PEEP) just below the pressure sufficient to open the air leak from the pneumothoraces was applied at all frequencies. Airway pressures, gas exchange, heart rate, and mean arterial pressure were recorded. Peak airway pressure decreased significantly from 2.50 to 2.10 kPa when the frequency of ventilation was increased from 30 to 300 cycles/min. There were no significant changes in mean airway pressure, PaO2, arterial pH, heart rate, and mean arterial pressure when HFV was compared to CMV. In conclusion, during HFV peak airway pressures measured at the mouth were decreased. Our ability to maintain adequate gas exchange in the face of ongoing pulmonary air leaks may reflect lower alveolar pressures. 相似文献
16.
17.
MK Potts 《Canadian Metallurgical Quarterly》1997,42(4):348-362
Using socioemotional selectivity theory as a framework, the study described in this article examined the extent to which social support from friends both within and outside of a retirement community was associated with depression. Although levels of social support from friends within the retirement community were quantitatively high, they failed to have a significant effect on depression. In contrast, social support from friends living elsewhere consistently predicted low levels of depression. Practice implications include the importance of maintaining friendship ties with people living elsewhere and of strengthening friendship ties within the retirement community. 相似文献
18.
19.
Discrimination of simple visual attributes can improve significantly with practice. We have trained human observers to perform peripherally presented tasks involving the localization of short line segments and examined the specificity of the learning for the visual location, orientation, and geometric arrangement of the trained stimulus. Several weeks of training resulted in dramatic threshold reductions. The learning was specific for the orientation and location of the trained stimulus, indicating the involvement of the earliest cortical stages in the visual pathway where the orientation and location of stimuli are mapped with highest resolution. Furthermore, improvement was also specific for both the configuration of the trained stimulus and the attribute of the stimulus that was under scrutiny during training. This degree of specificity suggests that the learning cannot be achieved by cortical recruitment alone, as proposed in current models, but is likely to involve a refinement of lateral interactions within the cortex and possibly a gating of lower level changes by attentional mechanisms. 相似文献
20.
VN Bhattathiri L Bindu P Remani B Chandralekha CA Davis MK Nair 《Canadian Metallurgical Quarterly》1996,41(2):139-142
The role of the propeptide sequence and a disulfide bridge between sites 1 and 122 in chymotrypsin has been examined by comparing enzyme activities of wild-type and mutant enzymes. The kinetic constants of mutants devoid of the Cys1-Cys122 disulfide-linked propeptide show that this linkage is not important either for activity or substrate specificity. However this linkage appears to be the major factor in keeping the zymogen stable against non-specific activation. A comparison of zymogen stabilities showed that the trypsinogen propeptide is ten times more effective than the chymotrypsinogen propeptide in preventing non-specific zymogen activation during heterologous expression and secretion from yeast. This feature can also be transferred in trans to chymotrypsinogen; i.e. the chymotrypsin trypsin propeptide chimera forms a stable zymogen. 相似文献