全文获取类型
收费全文 | 40470篇 |
免费 | 3407篇 |
国内免费 | 1742篇 |
专业分类
电工技术 | 2206篇 |
技术理论 | 2篇 |
综合类 | 2787篇 |
化学工业 | 7105篇 |
金属工艺 | 2325篇 |
机械仪表 | 2324篇 |
建筑科学 | 3086篇 |
矿业工程 | 1251篇 |
能源动力 | 1063篇 |
轻工业 | 2474篇 |
水利工程 | 643篇 |
石油天然气 | 2822篇 |
武器工业 | 268篇 |
无线电 | 4708篇 |
一般工业技术 | 4828篇 |
冶金工业 | 1878篇 |
原子能技术 | 546篇 |
自动化技术 | 5303篇 |
出版年
2024年 | 178篇 |
2023年 | 648篇 |
2022年 | 1145篇 |
2021年 | 1618篇 |
2020年 | 1240篇 |
2019年 | 1069篇 |
2018年 | 1214篇 |
2017年 | 1347篇 |
2016年 | 1130篇 |
2015年 | 1531篇 |
2014年 | 1897篇 |
2013年 | 2368篇 |
2012年 | 2468篇 |
2011年 | 2729篇 |
2010年 | 2370篇 |
2009年 | 2106篇 |
2008年 | 2086篇 |
2007年 | 1974篇 |
2006年 | 2075篇 |
2005年 | 1839篇 |
2004年 | 1350篇 |
2003年 | 1315篇 |
2002年 | 1375篇 |
2001年 | 1218篇 |
2000年 | 1058篇 |
1999年 | 1146篇 |
1998年 | 890篇 |
1997年 | 776篇 |
1996年 | 731篇 |
1995年 | 606篇 |
1994年 | 485篇 |
1993年 | 383篇 |
1992年 | 287篇 |
1991年 | 203篇 |
1990年 | 176篇 |
1989年 | 149篇 |
1988年 | 115篇 |
1987年 | 77篇 |
1986年 | 59篇 |
1985年 | 30篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 35篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
On the basis of the compensation of errors it is postulated that the most accurate correction may not always give the most accurate result for calorific value, and experimental evidence for this is presented. A new criterion is therefore suggested for judging the best (not necessarily the most accurate) cooling correction. Using this principle the cooling correction formula previously proposed is improved which results in higher accuracy whilst retaining the original simplicity. 相似文献
72.
H. Luo 《Microsystem Technologies》2006,12(4):324-329
This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic
view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic
image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed
and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre
and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro
world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel
level, respectively. 相似文献
73.
Luo J. Ulukus S. Ephremides A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(8):2760-2769
The optimal signature sequences that maximize the sum capacity of a direct sequence code-division multiple-access (CDMA) system are characterized in the general case of symbol delay profile and user power constraints. It is shown that the optimal sum capacity of the symbol asynchronous system equals that of the symbol synchronous system with the same user power constraints. With the optimal signature sequence set, the maximum sum capacity is achieved with white Gaussian input signals. The existence of the optimal signature sequence set is proved by the proposal of an explicit construction method for arbitrary user delay profiles and power constraints. 相似文献
74.
75.
CoNiFe-based amorphous films were magnetron-sputtered to investigate their structural and magnetic properties, including annealing-induced effects and interfacial influence from additional layers of Ta and Cu. The amorphous structure was confirmed by diffraction experiments. The magnetic measurements showed a well-defined uniaxial anisotropy in plane, arising possibly from atom oblique incidence effects competing with the stray field of the magnetron. The anisotropy could be influenced by using a Ta buffer layer, though the interfacial reaction gives rise to a dead layer. A coercive force H
c of 1–2 Oe and a magnetization of 680 emu/cm3 were measured at room temperature; properties which show promise for application in magnetotunneling junction devices. Thermal analyses showed a two-stage crystallization behavior, which started at 400°C and ended at about 600°C. The Curie temperature of the amorphous phase was estimated to be about 440°C. 相似文献
76.
真空制盐蒸发结晶器的设计与实践 总被引:2,自引:0,他引:2
真空蒸发制盐外热式强制逆循环轴向出料蒸发结晶器,经多个厂家生产应用实践证明是成功的,具有生命力的。这种新型结构,作为一项新技术新设备应加强研究,总结提高,推广应用。不断完善。文章从流体力学、结晶机理角度要求,到具体工程设计参数和材质选用。论述了该罐的特点。 相似文献
77.
Optimal diagonal precoder for multiantenna communication systems 总被引:3,自引:0,他引:3
In this paper, we examine a multiantenna single-user wireless communication system fitted with a QR-based successive cancellation receiver (QR receiver). Initially, our consideration is confined to uncoded binary phase shift keying (BPSK) signals transmitted through independent and identically distributed (IID) Rayleigh fading channels and to the design of an optimum precoder for the transmitter. For minimum feeding back of the channel state information (CSI) to the transmitter from the receiver, we stipulate the precoder to be in the form of a power loading square diagonal matrix. We proceed to develop the theory for the design of this diagonal matrix based on the minimization of the lower bound of the average bit error rate (BER) of transmission. The design obtained provides substantially lower error rates than most of other existing schemes under the same environment. The corresponding gain in signal-to-noise ratio (SNR) can be several decibels. To further improve the performance, we extend the design to include an optimal detection order of the received bits using an iterative approach. This iterative process proves to have fast convergence and results in a design providing significant SNR gain. We also propose a subchannel dropping scheme for cases in which SNR is low, and when the minimum BER precoder is equipped with this scheme, its average performance can be substantially superior to the Vertical Bell Laboratories Layered Space-Time (V-BLAST) detection. We extend our design of the optimum precoder to quadrature amplitude modulation (QAM) modulation scheme and similar performance gain has been observed. 相似文献
78.
The Jian kiln, located in present-day Jianyang county of Fujian province, mainly produced black-glazed tea bowls. Jian tea bowl was used as a utensil for tea tasting and was greatly appreciated by emperor Huizong of the Northern Song dynasty. The black glaze of Jian bowl was sometimes marked with streaks or spots, usually called “hare's fur” or “oil spot”, which are the crystalline markings of iron oxide precipitated during firing in the dragon kiln. In this study, black-glazed Jian bowl sherds excavated from the late Northern Song strata of Luhuaping and Daluhoumen Jian kiln sites were adopted as test samples. Based on the physico-chemical foundation for the formation of glaze microstructure, the correlation among composition, microstructure, and visual appearance has been investigated by means of energy-dispersive X-ray fluorescence, X-ray diffraction, and field emission electron microscopy. For the first time, the study provides realizing proofs for two kinds of microstructural forming mechanics. 相似文献
79.
Alan A. Luo Robert C. Kubic John M. Tartaglia 《Metallurgical and Materials Transactions A》2003,34(11):2549-2557
This study investigated the microstructure and fatigue properties of hydroformed sections of the 5754 and 6063 aluminum alloys.
The second-phase particles in 6063-T7 are identified as a mixture of Al12Fe3Si and Al9Fe2Si2, with a slightly higher fraction of the former. The constituent particles in the 5754 alloy are Al4Mn-type hexagonal compounds, where Mn is partially substituted by various other elements, resulting in Al4(Fe,Mn,Si,Cr). The results show that despite its lower yield strength, the hydroformed 5754 alloy has higher ultimate tensile
strength, ductility, and, more importantly, higher fatigue resistance than the 6063 material. Both crystallographic stage
I and noncrystallographic stage II cracking are found in the 6063-T7 samples, but only stage II cracking is observed in the
5754 alloy. This implies that the low fatigue strength of 6063-T7 is related to its relatively large grain size, resulting
in rapid stage I crack propagation. The higher fatigue lives of the 5754 alloy compared to the 6063 alloy in both the low-
and high-cycle life regimes are due to the increased fatigue-crack-initiation and propagation resistance of the 5754 alloy
and its probable cyclic strain-hardening behavior. 相似文献
80.
IRIS/AP型电感耦合等离子体光谱仪激发光源常见故障分析 总被引:1,自引:0,他引:1
本文介绍IRIS/AP型ICP的激发光源(炬管),并较为全面地阐述和分析其不能正常激发点燃的常见故障及其原因。 相似文献