全文获取类型
收费全文 | 1986篇 |
免费 | 28篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 116篇 |
金属工艺 | 13篇 |
机械仪表 | 3篇 |
建筑科学 | 25篇 |
能源动力 | 18篇 |
轻工业 | 60篇 |
水利工程 | 6篇 |
石油天然气 | 1篇 |
无线电 | 42篇 |
一般工业技术 | 62篇 |
冶金工业 | 1597篇 |
原子能技术 | 1篇 |
自动化技术 | 64篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2017年 | 21篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 8篇 |
2013年 | 35篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 28篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 41篇 |
1998年 | 481篇 |
1997年 | 273篇 |
1996年 | 202篇 |
1995年 | 154篇 |
1994年 | 89篇 |
1993年 | 92篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1978年 | 7篇 |
1977年 | 57篇 |
1976年 | 105篇 |
1975年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2014条查询结果,搜索用时 15 毫秒
1.
A new dual-quantisation sigma-delta modulator is proposed, which introduces an additional feedback path in the input of the second integrator. In this way, unlike other dual-quantisation architectures, larger signal-to-noise ratios can be obtained by means of aggressive noise-shaping, like in a conventional multibit modulator. The proposed modulator is also shown to be more robust against non-idealities than other dual-quantisation architectures. 相似文献
2.
M Vives ME Garcia P Saenz MA Mora L Mata H Sabharwal C Svanborg 《Canadian Metallurgical Quarterly》1997,16(9):852-858
BACKGROUND: The establishment of the nasopharyngeal flora was followed in Costa Rican children from birth to 1 year of age. METHODS: Nasopharyngeal cultures were obtained at 1 (n = 413), 3 (n = 393), 6 (n = 376) and 12 months (n = 356) of age from children representative of the population in the Puriscal district. Weekly cultures were obtained from a subcohort of these children (n = 101). Mother-infant diads (n = 95) and preschool children (n = 208) attending day-care centers were also studied. RESULTS: The estimated proportion of colonized children in the population differed markedly depending on the frequency of culture. Quarterly cultures showed a slow increase in carrier rates from 3.9% for Haemophilus influenzae, 3.1% for Streptococcus pneumoniae and 6.5% for Moraxella catarrhalis at 1 month of age to 10.1% carrying H. influenzae and 19.4% carrying S. pneumoniae by the end of the first year. By quarterly culture the proportion of children colonized at least once was 36% for S. pneumoniae, 26% for H. influenzae and 28% for M. catarrhalis. In contrast weekly sampling showed that 95 to 100% of the children were colonized at least once during the first year of life with H. influenzae, S. pneumoniae or M. catarrhalis. Nasopharyngeal carriage of H. influenzae, S. pneumoniae and M. catarrhalis was low in the mothers, and very few mother-infant pairs carried identical bacteria at the same time. In contrast carrier rates were high in the siblings attending day care (H. influenzae 27.9%, S. pneumoniae 39.4%, both organisms 26.6%). Infants with siblings had significantly higher bacterial carriage at all ages than infants without siblings. CONCLUSIONS: Quarterly nasopharyngeal cultures showed that Costa Rican infants acquire their nasopharyngeal flora at a rate comparable with that for infants in developed countries and that siblings are an important source of the bacteria. Weekly samplings showed that virtually all children were colonized at least once during the first year of life. 相似文献
3.
4.
M. Delgado-Pinar J. Mora A. Diez J.L. Cruz M.V. Andres 《Photonics Technology Letters, IEEE》2005,17(3):552-554
We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating. 相似文献
5.
6.
IuP Spizhenko AV Biliaiev AM Zaremba IV Nahorny? AP Tkachenko 《Canadian Metallurgical Quarterly》1997,43(5-6):42-48
Investigated all links of oxygen homeostasis of patients in early period afterwards surgical stoppage gastro-intestinal bleeding and urgent intravascular volume replacement. Macrodelivery of oxygen (DO2) was reduced in two and more time in comparison with norm predominant in connection with anemia. In spite of the infringement of transport of oxygen through alveolar-capillary membrane (especially in patients with complications and death in early postoperative period), little affected of degree of hemoglobin saturation by oxygen. Despite decrease of erythrocyte zeta-potential, largely expressed in cases of lethal outcome, considerable infringement of passage through microcirculation vessels is fixed was not. The increase of degree of morbidity and anaerobic metabolism in early postoperative period was accompanied of hyperdynamic hemodynamic reaction. The increase of degree of morbidity was accompanied of increase oxygen deficit owing to infringement of oxidoreduction in fabries also. 相似文献
7.
DI Timokhin AV Istomin TS Shushkova TG Voronel' IG Mikha?lov 《Canadian Metallurgical Quarterly》1997,(2):19-21
Based on generalization and analysis of instructions and guidelines for therapeutical and prophylactic diets of workers, ways of its optimization were proposed, by using bifide-containing acid dairy products as a preventive agent against possible occupational diseases caused by occupational factors. 相似文献
8.
9.
Linares-Barranco B. Serrano-Gotarredona T. Ramos-Martos J. Ceballos-Caceres J. Mora J.M. Linares-Barranco A. 《IEEE transactions on circuits and systems. I, Regular papers》2004,51(4):649-663
We present a very-large-scale integration continuous-time sinusoidal operational transconductance amplifiers quadrature oscillator fabricated in a standard double-poly 0.8-/spl mu/m CMOS process. The oscillator is tunable in the frequency range from 50 to 130 MHz. The two phases produced by the oscillator show a low-quadrature phase error. A novel current-mode amplitude control scheme is developed that allows for very small amplitudes. Stability of the amplitude control loop is studied as well as design considerations for its optimization. Experimental results are provided. 相似文献
10.