全文获取类型
收费全文 | 709722篇 |
免费 | 11283篇 |
国内免费 | 2396篇 |
专业分类
电工技术 | 13260篇 |
综合类 | 912篇 |
化学工业 | 106785篇 |
金属工艺 | 28297篇 |
机械仪表 | 20391篇 |
建筑科学 | 17937篇 |
矿业工程 | 2768篇 |
能源动力 | 19113篇 |
轻工业 | 65761篇 |
水利工程 | 6611篇 |
石油天然气 | 10363篇 |
武器工业 | 50篇 |
无线电 | 81752篇 |
一般工业技术 | 134839篇 |
冶金工业 | 141291篇 |
原子能技术 | 13158篇 |
自动化技术 | 60113篇 |
出版年
2021年 | 6272篇 |
2020年 | 4591篇 |
2019年 | 5803篇 |
2018年 | 9824篇 |
2017年 | 9505篇 |
2016年 | 10093篇 |
2015年 | 7343篇 |
2014年 | 11803篇 |
2013年 | 32849篇 |
2012年 | 18845篇 |
2011年 | 25899篇 |
2010年 | 20579篇 |
2009年 | 22927篇 |
2008年 | 23867篇 |
2007年 | 23545篇 |
2006年 | 20791篇 |
2005年 | 19020篇 |
2004年 | 18099篇 |
2003年 | 17870篇 |
2002年 | 17232篇 |
2001年 | 17195篇 |
2000年 | 15937篇 |
1999年 | 17108篇 |
1998年 | 44268篇 |
1997年 | 31056篇 |
1996年 | 23921篇 |
1995年 | 17850篇 |
1994年 | 15523篇 |
1993年 | 15177篇 |
1992年 | 10884篇 |
1991年 | 10424篇 |
1990年 | 9904篇 |
1989年 | 9638篇 |
1988年 | 9137篇 |
1987年 | 7963篇 |
1986年 | 7890篇 |
1985年 | 8986篇 |
1984年 | 8393篇 |
1983年 | 7406篇 |
1982年 | 6960篇 |
1981年 | 7099篇 |
1980年 | 6720篇 |
1979年 | 6449篇 |
1978年 | 6214篇 |
1977年 | 7692篇 |
1976年 | 10583篇 |
1975年 | 5407篇 |
1974年 | 5072篇 |
1973年 | 5195篇 |
1972年 | 4250篇 |
排序方式: 共有10000条查询结果,搜索用时 788 毫秒
931.
T. Herrmannsdörfer J. Friebel F. Pobell J. Mrachkov M. Kirov E. Leyarovski 《Journal of Low Temperature Physics》1997,107(1-2):209-224
We have measured the 16 Hz susceptibility of the diluted Van Vleck paramagnets Pr1−x
Y
x
Ni5 withx=0.00, 0.05, 0.10. 0.20 at temperatures 1.5 K≤T≤50 K and magnetic fields up to 15T. Their Van Vleck type magnetic susceptibility χ(T, B, x) strongly depends on the field atB≥6 T. The temperatureT
max(B, x) of the maximum of χ(T, B, x) decreases at increasing the field from zero to 15 T by approximately one order of magnitude for all Pr1−x
Y
x
Ni5 compounds. Changing the dilutionx from zero to 0.20, the field whereT
max(B, x) strongly drops is increased from 9 T to 11 T. Our data agree qualitatively with the predictions of a point charge model
which considers the Zeeman term in addition to the electronic exchange and the dominating crystal field contributions. 相似文献
932.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies 相似文献
933.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
934.
935.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel 相似文献
936.
Sugawara F. Aoki K. Yamaguchi H. Sasaki K. Sasaki T. Fujisaki H. 《Electron Device Letters, IEEE》1997,18(10):483-485
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor 相似文献
937.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices 相似文献
938.
The European Telecommunications Standards Institute (ETSI) has recently defined a European standard for a high performance radio LAN (known as HIPERLAN). To operate as wired LAN replacements, these systems will operate at 5.2 GHz and support instantaneous bit rates of just under 24 Mb/s. To counteract the time dispersive nature of the indoor radio channel, the use of adaptive equalisation is suggested. In this paper a number of possible modulation and equalisation techniques are presented and, in particular, the Bit Error Rate (BER) performance of quasi-coherent GMSK combined with Decision Feedback Equalisation is explored through computer simulation. The trade off between symbol spaced and fractionally spaced equalisation is considered together with the importance of feedfoward and feedback synchronisation to the channel's power delay profile. The paper also includes a comparison of the RLS and LMS based training algorithms and compares the modem developed under the ESPRIT III LAURA project with that specified in HIPERLAN.The application of dual antenna diversity is investigated and its impact on the number of received error free data packets obtained as a function of signal leval and rms delay spread. The use of such diversity is shown to greatly improve the BER performance of a HIPERLAN modem. The problem of frequency offset is considered and modifications are proposed to the HIPERLAN frame structure to improve the receiver's tolerance to such errors. Important practical issues such as frame and symbol synchronisation, frequency offset correction and hardware implementation are discussed from both the LAURA and HIPERLAN viewpoint. 相似文献
939.
A simple phenomenological model for giant magnetoresistance (GMR) is employed for current and field parallel (CIP) to the magnetic multilayer planes in ordinary and discontinuous multilayer films. To our knowledge, it is the first model to include hysteresis in the field (H) dependence of the GMR. The computed GMR versus H curves qualitatively reproduce the GMR hysteresis seen experimentally. In particular, two GMR peaks are found to be symmetrically placed about H=0, and the GMR hysteresis curve itself is found to have an inverted butterfly shape. Also seen in the computed results is the general increase in GMR magnitude found for annealed discontinuous multilayer films. Various parameter variations are examined in the computed results. While the model reproduces GMR hysteresis quite well and the general increase in GMR for discontinuous multilayer films, it does not, in its present form, account for the oscillations seen in the GMR when the nonmagnetic layer thicknesses are varied, which is expected as a strictly quantum mechanical result 相似文献
940.
Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×1015cm-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×1015cm-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen
at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation
led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when
aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can
be attributed to their different roles in modifying the structure and properties of the oxide formed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献