全文获取类型
收费全文 | 362631篇 |
免费 | 5807篇 |
国内免费 | 1665篇 |
专业分类
电工技术 | 6710篇 |
综合类 | 296篇 |
化学工业 | 55920篇 |
金属工艺 | 14372篇 |
机械仪表 | 12901篇 |
建筑科学 | 8539篇 |
矿业工程 | 1350篇 |
能源动力 | 10866篇 |
轻工业 | 30043篇 |
水利工程 | 3161篇 |
石油天然气 | 5281篇 |
武器工业 | 58篇 |
无线电 | 47205篇 |
一般工业技术 | 73616篇 |
冶金工业 | 62588篇 |
原子能技术 | 7890篇 |
自动化技术 | 29307篇 |
出版年
2022年 | 2785篇 |
2021年 | 4395篇 |
2020年 | 3198篇 |
2019年 | 3732篇 |
2018年 | 5972篇 |
2017年 | 6007篇 |
2016年 | 6610篇 |
2015年 | 4267篇 |
2014年 | 7277篇 |
2013年 | 17487篇 |
2012年 | 11380篇 |
2011年 | 14682篇 |
2010年 | 11587篇 |
2009年 | 12908篇 |
2008年 | 13210篇 |
2007年 | 12422篇 |
2006年 | 11038篇 |
2005年 | 9643篇 |
2004年 | 9235篇 |
2003年 | 9410篇 |
2002年 | 8670篇 |
2001年 | 8915篇 |
2000年 | 8274篇 |
1999年 | 8527篇 |
1998年 | 20885篇 |
1997年 | 14469篇 |
1996年 | 11121篇 |
1995年 | 8369篇 |
1994年 | 7393篇 |
1993年 | 7329篇 |
1992年 | 5205篇 |
1991年 | 5142篇 |
1990年 | 5001篇 |
1989年 | 4764篇 |
1988年 | 4550篇 |
1987年 | 3914篇 |
1986年 | 3809篇 |
1985年 | 4120篇 |
1984年 | 3686篇 |
1983年 | 3544篇 |
1982年 | 3247篇 |
1981年 | 3176篇 |
1980年 | 3055篇 |
1979年 | 2896篇 |
1978年 | 2681篇 |
1977年 | 3325篇 |
1976年 | 4439篇 |
1975年 | 2293篇 |
1974年 | 2228篇 |
1973年 | 2156篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
981.
982.
Kerber A. Cartier E. Pantisano L. Degraeve R. Kauerauf T. Kim Y. Hou A. Groeseneken G. Maes H.E. Schwalke U. 《Electron Device Letters, IEEE》2003,24(2):87-89
The magnitude of the V/sub T/ instability in conventional MOSFETs and MOS capacitors with SiO/sub 2//HfO/sub 2/ dual-layer gate dielectrics is shown to depend strongly on the details of the measurement sequence used. By applying time-resolved measurements (capacitance-time traces and charge-pumping measurements), it is demonstrated that this behavior is caused by the fast charging and discharging of preexisting defects near the SiO/sub 2//HfO/sub 2/ interface and in the bulk of the HfO/sub 2/ layer. Based on these results, a simple defect model is proposed that can explain the complex behavior of the V/sub T/ instability in terms of structural defects as follows. 1) A defect band in the HfO/sub 2/ layer is located in energy above the Si conduction band edge. 2) The defect band shifts rapidly in energy with respect to the Fermi level in the Si substrate as the gate bias is varied. 3) The rapid energy shifts allows for efficient charging and discharging of the defects near the SiO/sub 2//HfO/sub 2/ interface by tunneling. 相似文献
983.
Birnessites containing Na, K or Li in the interlayer have been prepared by oxidation of Mn(II) cations with H2O2 in a basic medium with different alkaline cation/Mn molar ratios. The solids prepared have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analyses (differential thermal analysis and thermogravimetric analysis), FT-IR spectroscopy and surface texture assessment by adsorption of N2 at –196°C. Crystalline birnessites are obtained for A/Mn ratios (A = K, Li) larger than 3.4, but MnO(OH) has been also identificed when such a ratio is smaller than 3.4. Ion exchange is topotactic, but is not complete for exchanging Na, K, or Mg for pre-existing Li. The solids are stable up to 400°C, and formation of spinels and solids with tunnel structures is observed at this temperature. Li-containing birnessites are transformed to LiMn2O4 spinel at 400°C, and co-crystallization of bixbyte (Mn2O3) is observed at higher temperatures. Bixbyte and cryptomelane are formed at 500°C for the K-containing birnessites. 相似文献
984.
Randall Billi; Moss Helen E.; Rodd Jennifer M.; Greer Mike; Tyler Lorraine K. 《Canadian Metallurgical Quarterly》2004,30(2):393
Patients with category-specific deficits have motivated a range of hypotheses about the structure of the conceptual system. One class of models claims that apparent category dissociations emerge from the internal structure of concepts rather than fractionation of the system into separate substores. This account claims that distinctive properties of concepts in the living domain are vulnerable because of their weak correlation with other features. Given the assumption that mutual activation among correlated properties produces faster activation in the normal system, the authors predicted a disadvantage for the distinctive features of living things for unimpaired adults. Results of a speeded feature verification study supported this prediction, as did a computational simulation in which networks mapped from orthography to semantics. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
985.
986.
The excavation of soil for the construction of basements or cut-and-cover tunnels results in ground movements. One particular concern is that the excavation-induced lateral soil movements may adversely affect any nearby pile foundation. The lateral loads imposed by the soil movements induce bending moments and deflections in the pile, which may lead to structural distress and failure. This paper presents the results of an actual full-scale instrumented study that was carried to examine the behavior of an existing pile due to nearby excavation activities resulting from the construction of a 16 m deep cut-and-cover tunnel. The pile was located 3 m behind a 0.8 m thick diaphragm wall. Excavation to the formation level that was 16 m below the ground surface resulted in a maximum lateral pile movement of 28 mm. A simplified numerical procedure based on the finite-element method was used to analyze the pile response. Generally, the theoretical predictions were in reasonable agreement with the measured results. 相似文献
987.
988.
989.
Suwanprateeb K. E. Tanner S. Turner W. Bonfield 《Journal of materials science. Materials in medicine》1995,6(12):804-807
Isochronous stress-strain relationships and long term creep performance for unfilled and hydroxyapatite filled polyethylene composites have been studied. The tests were carried out in a buffered (pH=7.5) Ringer's solution at 37°C. It was observed that the inclusion of hydroxyapatite does not remove the non-linear viscoelasticity of polyethylene. The creep resistance is found to increase with increase in volume fraction of hydroxyapatite. The creep failure of composites at long times can occur due to debonding of the interface. 相似文献
990.
Streit D.C. Hafizi M.E. Umemoto D.K. Velebir J.R. Tran L.T. Oki A.K. Kim M.E. Wang S.K. Kim C.W. Sadwick L.P. Hwu R.J. 《Electron Device Letters, IEEE》1991,12(5):194-196
The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×1019 cm-3 at the emitter edge to 5×1018 cm-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×1019 cm-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40% 相似文献