全文获取类型
收费全文 | 220285篇 |
免费 | 3163篇 |
国内免费 | 891篇 |
专业分类
电工技术 | 3858篇 |
综合类 | 735篇 |
化学工业 | 32978篇 |
金属工艺 | 8472篇 |
机械仪表 | 6037篇 |
建筑科学 | 5392篇 |
矿业工程 | 1275篇 |
能源动力 | 5137篇 |
轻工业 | 18812篇 |
水利工程 | 2274篇 |
石油天然气 | 3183篇 |
武器工业 | 6篇 |
无线电 | 21856篇 |
一般工业技术 | 37216篇 |
冶金工业 | 52844篇 |
原子能技术 | 4490篇 |
自动化技术 | 19774篇 |
出版年
2021年 | 1471篇 |
2019年 | 1324篇 |
2018年 | 2624篇 |
2017年 | 2841篇 |
2016年 | 3311篇 |
2015年 | 2419篇 |
2014年 | 3245篇 |
2013年 | 8373篇 |
2012年 | 6722篇 |
2011年 | 8877篇 |
2010年 | 5836篇 |
2009年 | 6758篇 |
2008年 | 6598篇 |
2007年 | 6554篇 |
2006年 | 5665篇 |
2005年 | 8037篇 |
2004年 | 7045篇 |
2003年 | 6228篇 |
2002年 | 5022篇 |
2001年 | 4910篇 |
2000年 | 4265篇 |
1999年 | 4652篇 |
1998年 | 15936篇 |
1997年 | 10877篇 |
1996年 | 7981篇 |
1995年 | 5647篇 |
1994年 | 4609篇 |
1993年 | 4617篇 |
1992年 | 2857篇 |
1991年 | 2833篇 |
1990年 | 2726篇 |
1989年 | 2708篇 |
1988年 | 2654篇 |
1987年 | 2351篇 |
1986年 | 2263篇 |
1985年 | 2542篇 |
1984年 | 2271篇 |
1983年 | 2109篇 |
1982年 | 2025篇 |
1981年 | 2138篇 |
1980年 | 1992篇 |
1979年 | 1894篇 |
1978年 | 1886篇 |
1977年 | 2689篇 |
1976年 | 3959篇 |
1975年 | 1682篇 |
1974年 | 1619篇 |
1973年 | 1668篇 |
1972年 | 1406篇 |
1971年 | 1329篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
Demiguel S. Giraudet L. Joulaud L. Decobert J. Blache F. Coupe V. Jorge F. Pagnod-Rossiaux P. Boucherez E. Achouche M. Devaux F. 《Lightwave Technology, Journal of》2002,20(12):2004-2014
The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes. 相似文献
53.
Martinez-Munoz D. Rosa-Zurera M. Cruz-Roldan F. Lopez-Ferreras F. Ruiz-Reyes N. 《Electronics letters》2002,38(16):932-933
The problem of computing, in a subband audio coder, the maximum quantisation noise power that can be injected in each band to ensure transparent coding when low selectivity filter banks are used, is addressed. A low complexity strategy, taking into account the frequency responses of the synthesis filter bank, is proposed for achieving an overall distortion due to quantisation noise always below the masking threshold (provided by a psycho-acoustic model) for any length prototype filters. 相似文献
54.
Mine K. Kubota N. Morimoto F. Sanada M. Zhang Qi 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(3):253-255
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance 相似文献
55.
1/f noise sources 总被引:2,自引:0,他引:2
This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an α value with a magnitude in the order of 10-4. Damaging the crystal has a strong influence on α, α may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The α values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices 相似文献
56.
A. A. Kovalev A. F. Kotyuk B. N. Levinskii A. A. Liberman 《Measurement Techniques》1994,37(2):151-158
The authors survey published results on the application of metal diffraction gratings as laser power or energy dividers when the laser beam is split into two approximately equal pans. The normal incidence of laser radiation on metal diffraction gratings of various profiles in the case of three propagating diffraction orders n=0, ±1 is discussed, along with the case of oblique incidence with only two propagating diffraction orders n=0 and n =–1.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 22–26, February, 1994. 相似文献
57.
ABSTRACT: The objective of this work was to observe the microstructure of feta cheese using confocal scanning laser microscopy. Low fat cheese and cheese containing capsule-producing cultures were made. The protein network was observed using the reflectance mode of the confocal microscope. Fat was stained by Nile red dye diluted with whey. More even distribution of fat with a larger number of smaller globules was observed in cheese made with noncapsule-forming culture compared to that made with the capsule-forming culture. Nonfat cheese had compact structure when made with noncapsule-forming culture which contrasted with the open structure observed in cheese made with the capsule-forming culture 相似文献
58.
59.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification. 相似文献
60.