全文获取类型
收费全文 | 179844篇 |
免费 | 15733篇 |
国内免费 | 8455篇 |
专业分类
电工技术 | 11410篇 |
技术理论 | 13篇 |
综合类 | 11700篇 |
化学工业 | 29385篇 |
金属工艺 | 9954篇 |
机械仪表 | 11316篇 |
建筑科学 | 13742篇 |
矿业工程 | 5461篇 |
能源动力 | 5302篇 |
轻工业 | 12523篇 |
水利工程 | 3288篇 |
石油天然气 | 10784篇 |
武器工业 | 1408篇 |
无线电 | 21575篇 |
一般工业技术 | 21559篇 |
冶金工业 | 8785篇 |
原子能技术 | 1932篇 |
自动化技术 | 23895篇 |
出版年
2024年 | 905篇 |
2023年 | 3427篇 |
2022年 | 6368篇 |
2021年 | 8529篇 |
2020年 | 6425篇 |
2019年 | 5082篇 |
2018年 | 5734篇 |
2017年 | 6413篇 |
2016年 | 5720篇 |
2015年 | 7606篇 |
2014年 | 9419篇 |
2013年 | 11292篇 |
2012年 | 12273篇 |
2011年 | 12908篇 |
2010年 | 11017篇 |
2009年 | 10411篇 |
2008年 | 9932篇 |
2007年 | 9158篇 |
2006年 | 9353篇 |
2005年 | 7990篇 |
2004年 | 5325篇 |
2003年 | 4476篇 |
2002年 | 4017篇 |
2001年 | 3617篇 |
2000年 | 3546篇 |
1999年 | 4173篇 |
1998年 | 3467篇 |
1997年 | 2949篇 |
1996年 | 2759篇 |
1995年 | 2223篇 |
1994年 | 1801篇 |
1993年 | 1300篇 |
1992年 | 1052篇 |
1991年 | 789篇 |
1990年 | 569篇 |
1989年 | 466篇 |
1988年 | 369篇 |
1987年 | 252篇 |
1986年 | 210篇 |
1985年 | 129篇 |
1984年 | 116篇 |
1983年 | 87篇 |
1982年 | 86篇 |
1981年 | 68篇 |
1980年 | 62篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
21.
22.
简要介绍了鞍钢现有人造富矿生产能力,分析了鞍钢生产1600万t/a生铁所需要的炉料数量、品种和质量,并提出了解决炉料缺口的方法和措施。 相似文献
23.
Kollipara R.T. Arodzero A. Bashindzhagyan G. Brau J.E. Frey R. Gao D. Mason D. Sinev N. Strom D. Yang X. 《IEEE transactions on nuclear science》1995,42(2):92-101
The SSC GEM silicon Central Tracker design incorporated 18-cm long single-sided AC-coupled silicon microstrip ladders. Compared to the 12-cm long ladders considered in the preliminary stages of the tracker design, the 18-cm long ladders have the advantage of reduced cost, channel count and overall power consumption, and led to a simplified tracker assembly. However, such long ships also present the challenge of maintaining satisfactory performance. The increased capacitance and series resistance contribute to lower signal-to-noise ratios, longer time walk, higher power consumption per channel and increased probability of crosstalk to neighboring channels. In this paper, an accurate method to calculate the geometric capacitance of the AC-coupled microstrips is presented and the calculated results are compared with measurements, SPICE simulations are performed to predict the noise, the extent of interstrip capacitive coupling and the dispersion of the detector signal due to the finite series resistance of the metal strips and the long length of the detector. The influence of the preamplifier current and the shaping time on the signal and noise levels is also presented. The study concludes that the 18-cm long ladders can successfully satisfy the performance goals of the GEM silicon Central Tracker 相似文献
24.
Ku T.K. Chen S.H. Yang C.D. She N.J. Wang C.C. Chen C.F. Hsieh I.J. Cheng H.C. 《Electron Device Letters, IEEE》1996,17(5):208-210
Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities 相似文献
25.
In this paper, we investigate the problem of determining the optimal bandwidth allocation for a Dynamic Bandwidth Allocation Scheme (DBAS). The objective is to minimize the total amount of bandwidth required to satisfy the Quality of Service (QoS) requirements of all traffic streams. It is shown that when the performance functions satisfy a certain number of conditions, there exists a unique optimal bandwidth allocation such that, for each traffic stream, either its QoS is just satisfied or its QoS is over-satisfied and it is allocated zero bandwidth. Such an allocation is said to be efficient. It is also shown that there exists a unique efficient allocation in the entire feasible region. An iterative algorithm is developed to compute the efficient allocation employing its special properties. Numerical examples are presented to demonstrate how the algorithm works. Future extensions of this work are also discussed.Partially supported by NSERC of Canada through grants OGP14020 and STRIN-200. 相似文献
26.
Z. -G. Fan Y. -X. Zhuang G. Yang R. Shao G. -F. Zhang 《Journal of Alloys and Compounds》1993,200(1-2):33-36
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt
The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed. 相似文献
27.
A technique for SiO2 formation by liquid-phase deposition (LPD) at nearly room temperature for low-temperature processed (LTP) polysilicon thin-film transistor (poly-Si TFT) was developed. LPD SiO2 film with a lower P-etch rate shows a dense structure. LPD SiO2 also exhibits good electrical characteristics. LTP poly-Si thin-film transistors (TFTs) with LPD SiO 2 as the gate insulator have been fabricated and investigated. Their characteristics indicate performance adequate for their use as pixel transistors in liquid crystal displays (LCDs) 相似文献
28.
29.
The use of the analytically decoupled near-tip displacement solutions as an alternative approach, is presented in this paper for the efficient finite element evaluation of the decoupled weight functions for an orthotropic 2-D crack. This alternative approach has been validated by directly comparing the prior weight function results with a symmetric mesh approach in the crack-tip neighborhood, and indirectly by comparing the calculated stress intensity factors (KI(II)) values using the computed weight functions with available KI(II) solutions of the 2-D mixed mode orthotropic cracks. In addition, this approach with analytically decoupled near-tip displacement solutions for calculating weight functions at all locations, can facilitate further extension of weight function evaluations to a more general 2-D anisotropic crack. 相似文献
30.
Motoharu Fujigaki In Hong Yang Yoshiharu Morimoto Eung Kyo Han 《NDT & E International》1996,29(4):197-203
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown. 相似文献