全文获取类型
收费全文 | 13155篇 |
免费 | 852篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 130篇 |
综合类 | 8篇 |
化学工业 | 2687篇 |
金属工艺 | 431篇 |
机械仪表 | 567篇 |
建筑科学 | 273篇 |
矿业工程 | 11篇 |
能源动力 | 391篇 |
轻工业 | 1162篇 |
水利工程 | 37篇 |
石油天然气 | 21篇 |
无线电 | 1593篇 |
一般工业技术 | 2348篇 |
冶金工业 | 3166篇 |
原子能技术 | 130篇 |
自动化技术 | 1073篇 |
出版年
2023年 | 96篇 |
2022年 | 169篇 |
2021年 | 280篇 |
2020年 | 206篇 |
2019年 | 262篇 |
2018年 | 298篇 |
2017年 | 343篇 |
2016年 | 402篇 |
2015年 | 352篇 |
2014年 | 498篇 |
2013年 | 775篇 |
2012年 | 661篇 |
2011年 | 826篇 |
2010年 | 594篇 |
2009年 | 562篇 |
2008年 | 561篇 |
2007年 | 434篇 |
2006年 | 351篇 |
2005年 | 327篇 |
2004年 | 319篇 |
2003年 | 309篇 |
2002年 | 262篇 |
2001年 | 213篇 |
2000年 | 196篇 |
1999年 | 285篇 |
1998年 | 1063篇 |
1997年 | 631篇 |
1996年 | 413篇 |
1995年 | 277篇 |
1994年 | 271篇 |
1993年 | 271篇 |
1992年 | 116篇 |
1991年 | 111篇 |
1990年 | 116篇 |
1989年 | 100篇 |
1988年 | 81篇 |
1987年 | 60篇 |
1986年 | 67篇 |
1985年 | 82篇 |
1984年 | 68篇 |
1983年 | 46篇 |
1982年 | 51篇 |
1981年 | 52篇 |
1980年 | 49篇 |
1979年 | 39篇 |
1978年 | 37篇 |
1977年 | 91篇 |
1976年 | 157篇 |
1975年 | 43篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Tai Won Um Jun Kyun Choi Young Ae Kim Hyeong Ho Lee Hae Won Jung Sang Gug Jong 《ETRI Journal》2002,24(2):69-80
This paper reviews the existing research activities on signaling and control procedures for IP over optical networks. We focus on the IP‐centric signaling and control architecture based on the generalized multi‐protocol label switching (GMPLS) protocol and analyze various scenarios and technical issues for deploying the IP over an optical network. We analyze the signaling and operations and administration and maintenance requirements for integrating an IP network and an optical network in order to cope with the high bandwidth and poor resource granularity of the optical network, including the optical cross‐connect system. On the basis of network architecture and a reference configuration model, we investigate the GMPLS‐based control architecture and interconnection model appropriate for controlling IP bandwidth and optical lambda resources. The signaling and control procedure based on GMPLS on optical user‐network interface and network‐network interface are comparatively investigated to provide the optical lightpath. We also study protection and restoration procedures to protect link failure when it applies to GMPLS signaling. 相似文献
72.
Se Young Yang Ilho Kim Soon-Bok Lee 《Components and Packaging Technologies, IEEE Transactions on》2008,31(1):3-12
Failure mechanisms exposed by environmental accelerating testing methods such as thermal cycling or thermal shock test, may differ from those at service operating conditions. While the device is heated up or cooled down evenly on its external surface during environmental testing, real operating powered devices experience temperature gradients caused by internal local heating, components' different heat dissipation capability, and ambient temperature variation, etc. In this study, a power cycling technique is introduced to better approximate the field operating conditions so as to activate the field failure modes. Power cycling thermal fatigue test is performed with different ball grid array solder joints, that is, lead contained [Sn/37 Pb (SP)] and lead free [Sn/4.0Ag/0.5 Cu (SAC)], and the result is compared. In order to account for the thermal fatigue life behavior discrepancy for different solder joint composition, real time Moire interferometry is applied to measure the global/local thermo-mechanical behavior during power cycling excursion. Effective damage parameter, the total average shear strain, is extracted from the experiment and applied to account for the difference in fatigue life result of two different solders. In addition, amount of experimentally measured total average shear strain is mutually verified with finite element method analysis. It is clear that total average shear strain of a solder joint can be an effective damage parameter to predict thermo-mechanical fatigue life. A physical mechanism in terms of thermal material property of solder joints' is proposed to offer some thoughts to abnormal shear strain behavior that leads to discrepancies in fatigue life of two solders. An importance of power cycling testing method is emphasized for certain package designs. 相似文献
73.
Liou K.-Y. Koren U. Burrows E.C. Oron M. Miller B.I. Young M. Raybon G. Burrus C.A. 《Photonics Technology Letters, IEEE》1990,2(12):878-880
Monolithic integration of a monitoring detector with an optical amplifier simplifies the use of an amplifier in lightwave systems. The structure and performance are described of a monolithically integrated semiconductor optical amplifier with low-loss Y -branching waveguides and a monitoring p-i-n detector. The photocurrent of the integrated detector can be used as a single control parameter for amplifier output leveling, gain optimization, and in situ monitoring of facet antireflective coatings 相似文献
74.
Hui Yang Yongli Zhao Jie Zhang Lei Cheng Yuefeng Ji Jialin Wu Jianrui Han Yi Lin Young Lee 《Photonic Network Communications》2014,28(1):58-70
IP over elastic optical network is a very promising networking architecture to interconnect data centers. It can enable efficient resource utilization and support heterogeneous bandwidth demands in cost-effective, highly available, and energy-effective manner. In case of aggregation elastic optical network node failure, to ensure a high-level quality of service for user request after the failure becomes a research focus. In this paper, we present a novel multi-stratum resources resilience (MSRR) architecture for the data center services in software defined data center interconnection based on IP over elastic optical networks. The MSRR can enable joint optimization of IP network, elastic optical network, and application stratum resources, and enhance the service resilience and the data center responsiveness to the dynamic end-to-end service demands. Additionally, a service-aware resource collaborative resilience strategy for MSRR is introduced based on the proposed architecture, which can provide the restoration using the multiple stratums resources in case of failure. The overall feasibility and efficiency of the proposed architecture are experimentally verified on our testbed. Moreover, the network performances are quantitatively evaluated through the simulation under heavy traffic load scenario in terms of path blocking probability, resource occupation rate, and path resilience latency. 相似文献
75.
Joon Ho Jeon Seung Ji Cha Young Min Jeon Ji-Hoon Lee Min Chul Suh 《Organic Electronics》2014,15(11):2802-2809
Laser Induced Thermal Imaging (LITI) is a laser addressed thermal patterning technology with unique advantages such as an excellent uniformity of transfer film thickness, a capability of multilayer stack transfer and a possibility to fabricate high resolution as well as large-area display. Nevertheless, it has been an obstacle to use such a laser imaging process as a commercial technology so far because of serious deterioration of the device performances plausibly due to a re-orientation of the molecular stacking especially in the emitting layer during thermal transfer process. To improve device performances, we devised a new concept to suppress the thermal degradation during such kind of thermal imaging process by using a high molecular weight small molecular species with large steric hindrance as well as high thermostability as a thermal buffer layer to realize highly efficient LITI devices. As a result, we obtained very high relative efficiency (by EQE) up to 91.5% at 1000 cd/m2 from the LITI devices when we utilize 10-(naphthalene-2-yl)-3-(phenanthren-9-yl)spiro[benzo[ij]tetraphene-7,9′-fluorene] as a thermal buffer material. 相似文献
76.
In this work, the coplanar waveguide is fabricated on a PES (poly[ether sulfone]) substrate for application to a flexible monolithic microwave integrated circuit, and its RF characteristics were thoroughly investigated. The quality factor of the coplanar waveguide on PES is 40.3 at a resonance frequency of 46.7 GHz. A fishbone‐type transmission line (FTTL) structure is also fabricated on the PES substrate, and its RF characteristics are investigated. The wavelength of the FTTL on PES is 5.11 mm at 20 GHz, which is 55% of the conventional coplanar waveguide on PES. Using the FTTL, an impedance transformer is fabricated on PES. The size of the impedance transformer is 0.318 mm × 0.318 mm, which is 69.2% of the size of the transformer fabricated by the conventional coplanar waveguide on PES. The impedance transformer showed return loss values better than –12.9 dB from 5 GHz to 50 GHz and an insertion loss better than –1.13 dB in the same frequency range. 相似文献
77.
Performance analysis of HomePlug 1.0 MAC with CSMA/CA 总被引:1,自引:0,他引:1
Min Young Chung Myoung-Hee Jung Tae-Jin Lee Yutae Lee 《Selected Areas in Communications, IEEE Journal on》2006,24(7):1411-1420
As demands for data communications among home/personal devices in home environments increase, various types of home-networking technologies have appeared. Among them, power line communication is one of the most promising wired home-networking technologies, because the existing power line facilities can be utilized for data transmission without deploying any new physical links. HomePlug 1.0 is the most popular power line communication technology, which has been standardized by the HomePlug power line alliance, and attempts to mitigate the effect of time- and frequency-varying channels by enhanced modulation and channel coding. Although HomePlug 1.0 has undergone field trials and simulations, its analytic model and performance was only conducted for throughput under saturation conditions. We propose a new analytic model to evaluate MAC throughput and delay of HomePlug 1.0 both under saturation and under normal traffic conditions. We verify our proposed model via simulations and evaluate the performance of HomePlug 1.0. 相似文献
78.
This paper presents a learning approach for wafer temperature control in a rapid thermal processing system (RTP). RTP is very important for semiconductor processing system and requires an accurate trajectory following. Numerous studies have addressed this problem and most research on this problem requires exact knowledge of the system dynamics. The various approaches do not guarantee the desired performance in practical applications when there exist some modeling errors between the model and the actual system. In this paper, iterative learning control scheme is applied to RTP without exact information on the dynamics. The learning gain of the iterative learning law is estimated by neural networks instead of a mathematical model. In addition, the control information obtained by the iterative learning controller (ILC) is accumulated in the feedforward neuro controller (FNC) for generalization to various reference profiles. Through numerical simulations, it is demonstrated that the proposed method can achieve an accurate output tracking even without an exact RTP model. The output errors decrease rapidly through iterations when using the learning gain estimated and the FNC yields a reduced initial error, and so requires small iterations 相似文献
79.
Fiona M. Blighe Karen Young Juan J. Vilatela Alan H. Windle Ian A. Kinloch Libo Deng Robert J. Young Jonathan N. Coleman 《Advanced functional materials》2011,21(2):364-371
We have measured the mechanical properties of coagulation‐spun polymer–nanotube composite fibers. Both the fiber modulus, Y, and strength, σB, scale linearly with volume fraction, Vf, up to Vf ~10%, after which these properties remain constant. We measured dY/dVf = 254 GPa and dσB/dVf = 2.8 GPa in the linear region. By drawing fibers with Vf < 10% to a draw ratio of ~60%, we can increase these values to dY/dVf = 600 GPa and dσB/dVf = 7 GPa. Raman measurements show the Herman's orientation parameter, S, to increase with drawing, indicating that significant nanotube alignment occurs. Raman spectroscopy also shows that the nanotube effective modulus, YEff, also increases with drawing. We have calculated an empirical relationship between the nanotube orientation efficiency factor, ηo, and S. This allows us to fit the data for YEff versus ηo, showing that the fiber modulus scales linearly with ηo, as predicted theoretically by Krenchel. From the fit, we estimate the nanotube modulus to be; YNT = 480 GPa. Finally, we show that the fiber strength also scales linearly with ηo, giving an effective interfacial stress transfer of τ = 40 MPa and a nanotube critical length of lc=1250 nm. This work demonstrates the validity of the Cox‐Krenchel rule of mixtures and shows that continuum theory still applies at the near‐molecular level. 相似文献
80.
A 9‐bit 80‐MS/s CMOS pipelined folding analog‐to‐digital converter employing offset‐canceled preamplifiers and a subranging scheme is proposed to extend the resolution of a folding architecture. A fully differential dc‐decoupled structure achieves high linearity in circuit design. The measured differential nonlinearity and integral nonlinearity of the prototype are ×0.6 LSB and ×1.6 LSB, respectively. 相似文献