全文获取类型
收费全文 | 536342篇 |
免费 | 7601篇 |
国内免费 | 1480篇 |
专业分类
电工技术 | 9737篇 |
综合类 | 558篇 |
化学工业 | 80610篇 |
金属工艺 | 20159篇 |
机械仪表 | 15399篇 |
建筑科学 | 13207篇 |
矿业工程 | 2314篇 |
能源动力 | 14694篇 |
轻工业 | 48365篇 |
水利工程 | 5296篇 |
石油天然气 | 9350篇 |
武器工业 | 37篇 |
无线电 | 60780篇 |
一般工业技术 | 104137篇 |
冶金工业 | 105309篇 |
原子能技术 | 10634篇 |
自动化技术 | 44837篇 |
出版年
2022年 | 3257篇 |
2021年 | 5084篇 |
2020年 | 3633篇 |
2019年 | 4708篇 |
2018年 | 8106篇 |
2017年 | 7886篇 |
2016年 | 8274篇 |
2015年 | 5813篇 |
2014年 | 9586篇 |
2013年 | 24709篇 |
2012年 | 15080篇 |
2011年 | 20698篇 |
2010年 | 16248篇 |
2009年 | 18155篇 |
2008年 | 18591篇 |
2007年 | 18266篇 |
2006年 | 15871篇 |
2005年 | 14535篇 |
2004年 | 13867篇 |
2003年 | 13664篇 |
2002年 | 12868篇 |
2001年 | 12995篇 |
2000年 | 12014篇 |
1999年 | 12772篇 |
1998年 | 33404篇 |
1997年 | 23307篇 |
1996年 | 17752篇 |
1995年 | 13223篇 |
1994年 | 11465篇 |
1993年 | 11138篇 |
1992年 | 8003篇 |
1991年 | 7504篇 |
1990年 | 7335篇 |
1989年 | 7095篇 |
1988年 | 6563篇 |
1987年 | 5835篇 |
1986年 | 5738篇 |
1985年 | 6406篇 |
1984年 | 5988篇 |
1983年 | 5230篇 |
1982年 | 4968篇 |
1981年 | 5035篇 |
1980年 | 4776篇 |
1979年 | 4671篇 |
1978年 | 4465篇 |
1977年 | 5393篇 |
1976年 | 7058篇 |
1975年 | 3832篇 |
1974年 | 3590篇 |
1973年 | 3708篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
Self-induced effects in a passive polarization-independent vertical-cavity semiconductor gate are investigated numerically and experimentally. We demonstrate all-optical seed-pulse extraction for synchronization of differential phase-shift keying and ON-OFF keying packets at 10 Gb/s. Our results provide evidence that vertical-cavity gates, exploiting saturable absorption in semiconductor quantum-wells, exhibit attractive performances in terms of efficiency, power consumption, and polarization independency. 相似文献
52.
This paper provides an overview of the main aspects of modern fluorescence microscopy. It covers the principles of fluorescence and highlights the key discoveries in the history of fluorescence microscopy. The paper also discusses the optics of fluorescence microscopes and examines the various types of detectors. It also discusses the signal and image processing challenges in fluorescence microscopy and highlights some of the present developments and future trends in the field. 相似文献
53.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
54.
Separation tests using hollow-fibre modules were performed for the difficult selective extraction of trivalent actinides over fission lanthanides from acidic media. This article shows that with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant, up to 94% americium could be extracted from 1.0 kmol/m3 HNO3, with minimal lanthanide co-extraction. Using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tri-n-octyl phosphine oxide, tests were performed on extraction, lanthanide scrubbing and stripping. In the extraction test, up to 99.99% americium could be extracted from 0.5 kmol/m3 HNO3, with approximately one third of the lanthanides being co-extracted. Mass transfer calculations using a consistent set of input data showed good agreement with the experiments. 相似文献
55.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase. 相似文献
56.
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
57.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
58.
59.
This paper proposes a method to reduce the vibration of the three-phase HB-type stepping motor with cogging torque by the feedforward compensation control. The compensation signal to suppress the vibration of the motor frame is obtained by the repetitive controller installing an online Fourier transformer and utilizing an acceleration sensor attached to the motor frame or an acoustic sensor such as a microphone placed close to the frame. The sensor is used only for the acquisition of the feedforward compensation data. The feedforward compensation signal at an arbitrary operating point is derived from the amplitude and phase data of the frequency components and the operating point data. Compensation data obtained by the repetitive controller is applied to the operating point changed by reference frequency and load condition in steady state. The compensation signal for the new operating point will be generated from compensation data utilizing polynomial equation approximation and linear interpolation method. The effectiveness of this proposed method is confirmed by the experimental results. 相似文献
60.
Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal 相似文献