全文获取类型
收费全文 | 106159篇 |
免费 | 1682篇 |
国内免费 | 1227篇 |
专业分类
电工技术 | 1951篇 |
综合类 | 140篇 |
化学工业 | 11309篇 |
金属工艺 | 5543篇 |
机械仪表 | 3287篇 |
建筑科学 | 2170篇 |
矿业工程 | 168篇 |
能源动力 | 3213篇 |
轻工业 | 6577篇 |
水利工程 | 728篇 |
石油天然气 | 687篇 |
武器工业 | 15篇 |
无线电 | 16113篇 |
一般工业技术 | 22309篇 |
冶金工业 | 25558篇 |
原子能技术 | 1445篇 |
自动化技术 | 7855篇 |
出版年
2022年 | 497篇 |
2021年 | 853篇 |
2020年 | 632篇 |
2019年 | 773篇 |
2018年 | 1310篇 |
2017年 | 1258篇 |
2016年 | 1364篇 |
2015年 | 1035篇 |
2014年 | 1645篇 |
2013年 | 5100篇 |
2012年 | 2764篇 |
2011年 | 4055篇 |
2010年 | 3311篇 |
2009年 | 3906篇 |
2008年 | 4056篇 |
2007年 | 4242篇 |
2006年 | 3779篇 |
2005年 | 3384篇 |
2004年 | 3230篇 |
2003年 | 3067篇 |
2002年 | 2705篇 |
2001年 | 2998篇 |
2000年 | 2740篇 |
1999年 | 3109篇 |
1998年 | 9552篇 |
1997年 | 6206篇 |
1996年 | 4814篇 |
1995年 | 3191篇 |
1994年 | 2803篇 |
1993年 | 2734篇 |
1992年 | 1639篇 |
1991年 | 1600篇 |
1990年 | 1524篇 |
1989年 | 1333篇 |
1988年 | 1182篇 |
1987年 | 865篇 |
1986年 | 893篇 |
1985年 | 922篇 |
1984年 | 806篇 |
1983年 | 702篇 |
1982年 | 708篇 |
1981年 | 687篇 |
1980年 | 577篇 |
1979年 | 485篇 |
1978年 | 416篇 |
1977年 | 542篇 |
1976年 | 983篇 |
1975年 | 303篇 |
1974年 | 278篇 |
1973年 | 258篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
Takauchi H. Tamura H. Matsubara S. Kibune M. Doi Y. Chiba T. Anbutsu H. Yamaguchi H. Mori T. Takatsu M. Gotoh K. Sakai T. Yamamura T. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2094-2100
We describe a CMOS multichannel transceiver that transmits and receives 10 Gb/s per channel over balanced copper media. The transceiver consists of two identical 10-Gb/s modules. Each module operates off a single 1.2-V supply and has a single 5-GHz phase-locked loop to supply a reference clock to two transmitter (Tx) channels and two receiver (Rx) channels. To track the input-signal phase, the Rx channel has a clock recovery unit (CRU), which uses a phase-interpolator-based timing generator and digital loop filter. The CRU can adjust the recovered clock phase with a resolution of 1.56 ps. Two sets of two-channel transceiver units were fabricated in 0.11-/spl mu/m CMOS on a single test chip. The transceiver unit size was 1.6 mm /spl times/ 2.6 mm. The Rx sensitivity was 120-mVp-p differential with a 70-ps phase margin for a common-mode voltage ranging from 0.6 to 1.0 V. The evaluated jitter tolerance curve met the OC-192 specification. 相似文献
103.
P. G. Muzykov Y. I. Khlebnikov S. V. Regula Y. Gao T. S. Sudarshan 《Journal of Electronic Materials》2003,32(6):505-510
To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement
techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable
graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique,
and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values
of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable
graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe
method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer
was also obtained and reported in this work. 相似文献
104.
Nanocrystalline Gd2O3:A (A=Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd2O3 phosphor films due to an efficient energy transfer from Gd2O3 host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd3+ in Gd2O3 films, respectively. 相似文献
105.
In order to ascertain the metastable phase relation in the Cr2O3-Fe2O3 system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr2O3-rich (CC) and Fe2O3-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders. 相似文献
106.
Nayve R. Fujii M. Fukugawa A. Takeuchi T. Murata M. Yamada Y. Koyanagi M. 《Journal of microelectromechanical systems》2004,13(5):814-821
This paper describes the fabrication and characterization of a thermal ink jet (TIJ) printhead suitable for high speed and high-quality printing. The printhead has been fabricated by dicing the bonded wafer, which consists of a bubble generating heater plate and a Si channel plate. The Si channel plate consists of an ink chamber and an ink inlet formed by KOH etching, and a nozzle formed by inductively couple plasma reactive ion etching (ICP RIE). The nozzle formed by RIE has squeezed structures, which contribute to high-energy efficiency of drop ejector and, therefore, successful ejection of small ink drop. The nozzle also has a dome-like structure called channel pit, which contributes to high jetting frequency and high-energy efficiency. These two wafers are directly bonded using electrostatic bonding of full-cured polyimide to Si. The adhesive-less bonding provided an ideal shaped small nozzle orifice. Use of the same material (Si substrate) in heater plate and channel plate enables the fabrication of high precision long printhead because no displacement and delamination occur, which are caused by the difference in thermal expansion coefficient between the plates. With these technologies, we have fabricated a 1" long printhead with 832 nozzles having 800 dots per inch (dpi) resolution and a 4 pl. ink drop volume. 相似文献
107.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
108.
A multipath structure of a ring resonator is proposed to expand the free spectral range. Simulation work indicates that the multipath ring resonator has 25 GHz-adjacent-channel crosstalk of -41 dB, maximum interchannel crosstalk of -18 dB, and -1 dB bandwidth of 4 GHz for a typical expansion factor of 10. The results show the advantages of characteristics compared with a double-cavity ring resonator and a triple-coupler ring resonator. 相似文献
109.
A novel super-multi-fibre planar lightwave circuit (PLC) connector, designed to connect tens of optical fibres and a PLC for super-multichannel PLC-based optical modules with a receptacle interface, is proposed. This connector employs an angled connection instead of a PC connection. A 0.127 mm pitch 32-fibre connector is also demonstrated, which exhibits low connection and high return losses. 相似文献
110.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献