全文获取类型
收费全文 | 36680篇 |
免费 | 2565篇 |
国内免费 | 1093篇 |
专业分类
电工技术 | 1724篇 |
技术理论 | 4篇 |
综合类 | 1647篇 |
化学工业 | 6282篇 |
金属工艺 | 1620篇 |
机械仪表 | 1776篇 |
建筑科学 | 1854篇 |
矿业工程 | 814篇 |
能源动力 | 1238篇 |
轻工业 | 2370篇 |
水利工程 | 473篇 |
石油天然气 | 1078篇 |
武器工业 | 179篇 |
无线电 | 5606篇 |
一般工业技术 | 5228篇 |
冶金工业 | 2817篇 |
原子能技术 | 413篇 |
自动化技术 | 5215篇 |
出版年
2024年 | 125篇 |
2023年 | 494篇 |
2022年 | 948篇 |
2021年 | 1332篇 |
2020年 | 1002篇 |
2019年 | 852篇 |
2018年 | 947篇 |
2017年 | 1018篇 |
2016年 | 944篇 |
2015年 | 1166篇 |
2014年 | 1498篇 |
2013年 | 2217篇 |
2012年 | 2112篇 |
2011年 | 2432篇 |
2010年 | 1916篇 |
2009年 | 1925篇 |
2008年 | 2002篇 |
2007年 | 1805篇 |
2006年 | 1627篇 |
2005年 | 1310篇 |
2004年 | 1141篇 |
2003年 | 1223篇 |
2002年 | 1425篇 |
2001年 | 1207篇 |
2000年 | 850篇 |
1999年 | 746篇 |
1998年 | 1017篇 |
1997年 | 715篇 |
1996年 | 600篇 |
1995年 | 502篇 |
1994年 | 412篇 |
1993年 | 359篇 |
1992年 | 256篇 |
1991年 | 228篇 |
1990年 | 230篇 |
1989年 | 204篇 |
1988年 | 180篇 |
1987年 | 158篇 |
1986年 | 130篇 |
1985年 | 130篇 |
1984年 | 112篇 |
1983年 | 76篇 |
1982年 | 71篇 |
1981年 | 60篇 |
1980年 | 83篇 |
1979年 | 49篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
A new modified low-Reynolds-number k-ε turbulence [Chang, Hsieh and Chen (CHC)] model, which possesses the proper near-wall limiting behaviors and is free of the singular defect occurring near the reattachment point when applied to separated flows, is examined for use in wall heat transfer problems in flow with pipe expansion geometry. Another eight low-Reynolds-number k-ε models, found in open literature, are also examined in this study. Attention is specifically focused on the flow region surrounding the reattachment point. Comparative results show that only the CHC model and the model developed by Abe et al. [Abe, Kondoh and Nagano (AKN model)] can yield satisfactory distributions of the Nusselt number along the wall. However, the CHC model adopted the same model constants as conventionally used for the standard k-ε model. Thus, the CHC model is more universal than the AKN model. 相似文献
102.
Haspeslagh D. Moerman E. Chang Z. Haspeslagh J. 《Solid-State Circuits, IEEE Journal of》1994,29(8):914-920
The Digital Phone Interface (DPI) is designed for a new generation of digital telephone terminals for private exchanges, This circuit gives a total solution for all telephone functions, thereby including DSP functions, voice coding/decoding and analog front end, signal generators for DTMF and ringing, a modem for data transfer between terminal and exchange and a multitude of interfaces to communicate to the external world. Besides the normal earpiece micro and speaker, handsfree operation is available by using a selectable input low-noise microphone amplifier and an additional 50 Ω mWLS driver. For the handsfree operation, a digital AGC and anti-oscillation (anti-larsen) function is implemented. The line modem generates a modified RTZ (WAL2) code and is able to cover distances up to 1.5 km. In addition, the component is extensible with external signal processing modules (echo cancelling) and is also able to transfer a 7 kHz speech bandwidth. The device is a mixed analog/digital design produced in a 1.2 μm CMOS technology on 46 mm 2 die area and consumes 200 mW 相似文献
103.
Tahui Wang Chimoon Huang Chou P.C. Chung S.S.-S. Tse-En Chang 《Electron Devices, IEEE Transactions on》1994,41(9):1618-1622
A two-dimensional numerical simulation including a new interface state generation model has been developed to study the performance variation of a LDD MOSFET after a dc voltage stress. The spatial distribution of hot carrier induced interface states is calculated with a breaking silicon-hydrogen bond model. Mobility degradation and reduction of conduction charge due to interface traps are considered. A 0.6 μm LDD MOSFET was fabricated. The drain current degradation and the substrate current variation after a stress were characterized to compare the simulation. A reduction of the substrate current at Vg ≃0.5 Vd in a stressed device was observed from both the measurement and the simulation. Our study reveals that the reduction is attributed to a distance between a maximum channel electric field and generated interface states 相似文献
104.
Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron
spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace
and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the
Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10−6 Ω-cm2 for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed
at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρc increasing to 2.94 × 10−6Ω-cm2 and for an aging at 410°C for 40 h with its ρc increasing to 1.38 × 10−5 Ω-cm2. 相似文献
105.
Suk Lee Kyung Chang Lee Man Hyung Lee Harashima F. 《Industrial Electronics, IEEE Transactions on》2002,49(3):693-701
This paper focuses on a method to integrate mobile devices such as a mobile robot, automated guided vehicle, and unmanned container transporter to form an automated material handling system. In this paper, the stationary devices are connected via a Profibus network while the mobile devices are communicating via an IEEE 802.11 wireless LAN. In order to integrate these two networks, a protocol converter is developed on a PC platform that runs two interacting processes with shared internal buffers. The protocol converter performs a role of translator between two different protocols by converting the format of a data frame. In addition to this basic conversion function, the protocol converter has a virtual polling algorithm to reduce the uncertainty involved in accessing the wireless network. Finally, the integrated network. of Profibus and IEEE 802.11 is experimentally evaluated for its data latency and throughput, which shows the feasibility of the Profibus-IEEE 802.11 network for industrial applications involving mobile devices 相似文献
106.
In this paper, a mixed approach for probabilistic structural durability design of mechanical systems is proposed. In this approach, a deterministic design optimization that considers structural crack initiation and crack propagation lives at critical points of the structural component as design constraints is performed first. After an optimal design is obtained, a reliability analysis is performed to ascertain if the deterministic optimal design is reliable. If the probability of the failure of the deterministic optimal design is found to be acceptable, a reliability-based design approach that employs a set of interactive design steps, such as trade-off analysis and what-if study, is used to obtain a near-optimal design that is reliable with an affordable computational cost. A 3-D tracked vehicle roadarm is employed to demonstrate the feasibility of the proposed approach. 相似文献
107.
Hishinuma Earl S.; Else 'Iwalani R. N.; Chang Janice Y.; Goebert Deborah A.; Nishimura Stephanie T.; Choi-Misailidis Soojean; Andrade Naleen N. 《Canadian Metallurgical Quarterly》2006,21(3):286
School psychologists are generally not provided with the knowledge and skills to address both educational and psychosocial issues of Asian American and Pacific Islander students. The present study is the first of its kind in examining 36 independent (i.e., demographic, social, cultural, psychological) variables in association with four school outcomes (i.e., grade point average, absences, suspensions, and school infractions) with a large sample of Caucasian, Filipino, Native Hawaiian, Japanese, mixed/non-Hawaiian, and "other" Hawai'i high school students (N = 2,833). Given the relatively unique sample in question and the sheer number of variables, an exploratory approach was utilized with the goal of determining the most robust independent variables, with the unique inclusion of Hawaiian cultural identification. A cross-validation technique was used, whereby stepwise regressions were performed for each of two cross-validation samples; only common variables were retained in a final stepwise model for each of the four school outcomes. The results indicated that, remarkably, substance use accounted for the most variance (i.e., 8.4% -16.1 %) in the four school measures. Further analyses detailed the relationship, including the finding that smoking cigarettes regularly, accounted for the most variance compared to the other five substance use items. Further research and implications of the findings are discussed, including the need for prevention and intervention programs that incorporate substance use as a component, both within and outside of school environments. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
108.
Chan K.T. Chin A. McAlister S.P. Chang C.Y. Liu J. Chien S.C. Duh D.S. Lin W.J. 《Electron Device Letters, IEEE》2003,24(1):28-30
Very-low-transmission line noise of <0.25 dB at 18 GHz and low power loss /spl les/0.6 dB at 110 GHz have been measured on transmission lines fabricated on proton-implanted Si. In contrast, a standard Si substrate gave much higher noise of 2.5 dB and worse power loss of 5 dB. The good RF integrity of proton-implanted Si results from the high isolation impedance to ground, as analyzed by an equivalent circuit model. The proton implantation is also done after forming the transmission lines at a reduced implantation energy of /spl sim/4 MeV. This enables easier process integration into current VLSI technology. 相似文献
109.
Kuo-Liang Chung Lung-Chun Chang 《IEEE transactions on image processing》2003,12(6):648-652
According to the observation on the distribution of motion differentials among the motion vector of any block and those of its four neighboring blocks from six real video sequences, this paper presents a new predictive search area approach for fast block motion estimation. Employing our proposed simple predictive search area approach into the full search (FS) algorithm, our improved FS algorithm leads to 93.83% average execution-time improvement ratio, but only has a small estimation accuracy degradation. We also investigate the advantages of computation and estimation accuracy of our improved FS algorithm when compared to the edge-based search algorithm of Chan and Siu (see IEEE Trans. Image Processing, vol.10, p.1223-1238, Aug. 2001); experimental results reveal that our improved FS algorithm has 74.33% average execution-time improvement ratio and has a higher estimation accuracy. Finally, we further compare the performance among our improved FS algorithm, the three-step search algorithm, and the block-based gradient descent search algorithm. 相似文献
110.
Sheng-Fuh Chang Jia-Liang Chen Wen-Lin Chen Hann-Ping Hwang 《Microwave and Wireless Components Letters, IEEE》2004,14(6):304-306
A new quadrature broadside coupler is proposed, which employs an array of air-bridges to enhance directivity via its phase-equalization effect on the c-mode and /spl pi/-modes. The realization of air-bridges follows a standard MMIC fabrication process. An experimental chip fabricated on the 75-/spl mu/m GaAs substrate verifies the air-bridge effect and shows wideband characteristics of the coupling of 3.2/spl plusmn/0.4 dB, the insertion loss of 3.9/spl plusmn/0.4 dB, the output phase deviation from quadrature less than 6/spl deg/, and the isolation greater than 18 dB from 20 to 40 GHz. 相似文献