首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5421篇
  免费   363篇
  国内免费   5篇
电工技术   66篇
综合类   7篇
化学工业   1642篇
金属工艺   60篇
机械仪表   106篇
建筑科学   212篇
矿业工程   10篇
能源动力   203篇
轻工业   700篇
水利工程   45篇
石油天然气   7篇
无线电   358篇
一般工业技术   1012篇
冶金工业   390篇
原子能技术   29篇
自动化技术   942篇
  2024年   16篇
  2023年   98篇
  2022年   327篇
  2021年   401篇
  2020年   185篇
  2019年   188篇
  2018年   219篇
  2017年   192篇
  2016年   265篇
  2015年   194篇
  2014年   283篇
  2013年   361篇
  2012年   356篇
  2011年   457篇
  2010年   293篇
  2009年   253篇
  2008年   303篇
  2007年   245篇
  2006年   168篇
  2005年   153篇
  2004年   130篇
  2003年   119篇
  2002年   84篇
  2001年   61篇
  2000年   46篇
  1999年   53篇
  1998年   43篇
  1997年   37篇
  1996年   42篇
  1995年   28篇
  1994年   23篇
  1993年   25篇
  1992年   25篇
  1991年   15篇
  1990年   8篇
  1989年   11篇
  1988年   9篇
  1987年   9篇
  1986年   5篇
  1985年   6篇
  1984年   10篇
  1983年   10篇
  1982年   11篇
  1981年   6篇
  1980年   2篇
  1979年   8篇
  1972年   1篇
  1971年   1篇
  1967年   2篇
  1948年   1篇
排序方式: 共有5789条查询结果,搜索用时 0 毫秒
51.
The first evidence of out‐of‐plane resonances in hybrid metallo‐dielectric quasi‐crystal (QC) nanostructures composed of metal‐backed aperiodically patterned low‐contrast dielectric layers is reported. Via experimental measurements and full‐wave numerical simulations, these resonant phenomena are characterized with specific reference to the Ammann‐Beenker (quasi‐ periodic, octagonal) tiling lattice geometry and the underlying physics is investigated. In particular, it is shown that, by comparison with standard periodic structures, a moderately richer spectrum of resonant modes may be excited, due to the easier achievement of phase‐matching conditions endowed by its denser Bragg spectrum. Such modes are characterized by a distinctive plasmonic or photonic behavior, discriminated by their field distribution and dependence on the metal film thickness. Moreover, the response is accurately predicted via computationally affordable periodic‐approximant‐based numerical modeling. The enhanced capability of QCs to control number, spectral position, and mode distribution of hybrid resonances may be exploited in a variety of possible applications. To assess this aspect, label‐free biosensing is studied via characterization of the surface sensitivity of the proposed structures with respect to local refractive index changes. Moreover, it is also shown that the resonance‐engineering capabilities of QC nanostructures may be effectively exploited in order to enhance the absorption efficiency of thin‐film solar cells.  相似文献   
52.
53.
Novel hafnium oxide (HfO2)‐based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite‐based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake‐up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake‐up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake‐up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.  相似文献   
54.
55.
This paper presents a front-end circuit for optical rotary encoders. The light pulses modulated by the encoder disc are transduced into current signals, which are pre-processed and converted into digital waveforms related to the disc angular position information. The proposed front-end circuit is compensated against temperature drifts. Digitally programmable calibration is provided to account for spreads in impinging light pulse power. Measurement results on integrated prototypes are shown, demonstrating correct operation of the front-end with an optical input power from 0.5 W to 3 W up to a signal frequency of 500 kHz in a temperature range from 0 °C to 80 °C.  相似文献   
56.
Vestibular Deiters' neurons have been isolated from bovine brain by the Hydén's freehand dissection technique and challenged with monoclonal antibodies directed toward the alpha 1 and beta 2/3 subunits of the GABAA receptors. Subsequent challenge with fluorescent secondary antibodies and confocal microscopy allowed the study of the cellular distribution of such subunits. In Deiters' neurons the beta 2/3 subunit displayed a clear presence all along the cell body profile and the initial parts of the dendrites. The alpha 1 subunit was found highly present all over the cell interior except the nuclear profiles. The strong presence inside the cells possibly masked its presence on the plasma membrane. However, in part of the cells studied a distinct presence on the plasma membrane was evident. This subunit was visualized also all along the long dendrites of these neurons. The approach we describe here, involving freehand isolated mature neurons from adult animals, may allow a better characterization of the tridimensional distribution of different types of neuronal GABAA receptors in the respect of the approach with brain slices.  相似文献   
57.
Label-free DNA detection plays a crucial role in developing point-of-care biochips. Capacitance detection is a promising technology for label-free detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To address these problems, mercapto-hexanol or similar alkanethiols are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, florescence microscopy, and capacitance measurements are used to investigate new lipoate and ethylene-glycol molecules. The new surfaces offer further improvements in terms of diminished detection errors. Film structures are investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.  相似文献   
58.
In this paper we present a comparative study of two e-Beam Lithography (EBL) processes for Nanoimprinting Lithography (NIL) master mold, i.e. the standard PMMA based EBL Si patterning process and the HSQ process. 20 nm features with minimal sidewall roughness and high uniformity are demonstrated on large surface by using HSQ process. Moreover, to validate this ultra-high resolution HSQ EBL process and to check NIL resolution performances, soft UV-NIL replications were performed using soft hard-PDMS/PDMS bi-layer stamps casted on the HSQ master mold. We demonstrate the replication of sub-20 nm nanodots of high density (pitch 60 nm) with a good uniformity on the whole field area.  相似文献   
59.
This paper investigates the influence of the position of the antennas in a dual-radio mesh router by characterizing the router components from an electromagnetic point of view. Since the behavior of a wireless router equipped with multiple devices and antennas can be affected by mutual coupling among several close conducting bodies, numerical and experimental tests are carried out to provide some suggestions for an accurate positioning of the antennas. A reference configuration is implemented in an electromagnetic Computer-Aided Design (CAD) simulator. The most significant numerical results are validated by performing a campaign of measurements in anechoic chamber and deploying a testbed for the derivation of the experimental values of throughput, return loss, power density, and directivity.  相似文献   
60.
The integration of satellite and terrestrial networks is a promising solution for extending broadband coverage to areas not connected to a terrestrial infrastructure, as also demonstrated by recent commercial and standardisation endeavours. However, the large delays and Doppler shifts over the satellite channel pose severe technical challenges to traditional terrestrial systems, as long‐term evolution (LTE) or 5G. In this paper, 2 architectures are proposed for a low Earth orbit mega‐constellation realising a satellite‐enabled LTE system, in which the on‐ground LTE entity is either an eNB (Sat‐eNB) or a relay node (Sat‐RN). The impact of satellite channel impairments as large delays and Doppler shifts on LTE PHY/MAC procedures is discussed and assessed. The proposed analysis shows that, while carrier spacings, random access and RN attach procedures do not pose specific issues and hybrid automatic repeat request requires substantial modifications. Moreover, advanced handover procedures will be also required due to the satellites' movement.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号