全文获取类型
收费全文 | 5620篇 |
免费 | 51篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 30篇 |
综合类 | 1篇 |
化学工业 | 602篇 |
金属工艺 | 208篇 |
机械仪表 | 84篇 |
建筑科学 | 94篇 |
矿业工程 | 10篇 |
能源动力 | 51篇 |
轻工业 | 294篇 |
水利工程 | 31篇 |
石油天然气 | 5篇 |
无线电 | 433篇 |
一般工业技术 | 637篇 |
冶金工业 | 2812篇 |
原子能技术 | 51篇 |
自动化技术 | 340篇 |
出版年
2021年 | 35篇 |
2019年 | 40篇 |
2018年 | 37篇 |
2017年 | 27篇 |
2016年 | 52篇 |
2015年 | 29篇 |
2014年 | 45篇 |
2013年 | 152篇 |
2012年 | 93篇 |
2011年 | 131篇 |
2010年 | 88篇 |
2009年 | 117篇 |
2008年 | 135篇 |
2007年 | 120篇 |
2006年 | 117篇 |
2005年 | 107篇 |
2004年 | 105篇 |
2003年 | 105篇 |
2002年 | 90篇 |
2001年 | 80篇 |
2000年 | 94篇 |
1999年 | 143篇 |
1998年 | 686篇 |
1997年 | 464篇 |
1996年 | 352篇 |
1995年 | 204篇 |
1994年 | 161篇 |
1993年 | 231篇 |
1992年 | 97篇 |
1991年 | 84篇 |
1990年 | 90篇 |
1989年 | 84篇 |
1988年 | 93篇 |
1987年 | 112篇 |
1986年 | 73篇 |
1985年 | 75篇 |
1984年 | 39篇 |
1983年 | 48篇 |
1982年 | 47篇 |
1981年 | 49篇 |
1980年 | 57篇 |
1979年 | 30篇 |
1978年 | 51篇 |
1977年 | 91篇 |
1976年 | 148篇 |
1975年 | 45篇 |
1974年 | 33篇 |
1973年 | 33篇 |
1972年 | 31篇 |
1970年 | 33篇 |
排序方式: 共有5683条查询结果,搜索用时 0 毫秒
1.
B. Ma P.I. Djurovich S. Garon B. Alleyne M.E. Thompson 《Advanced functional materials》2006,16(18):2438-2446
Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula C∧NPt(μ‐pz)2PtC∧N (where C∧N = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (~ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (~ 5 %) and brightness (~ 600 Cd m–2 at 10 V). 相似文献
2.
3.
Dyspnea may be easily appreciated during exercise with dyspneic scales, but methodological standardisation still needs to be specified. Authors review the basic physiological mechanism relating dyspnea to indices obtained during a stress test. They propose to use the dyspnea/VE relationship. With the concept of dyspneic threshold (close to the ventilatory threshold) and the ramp that both could be modified (for instance by rehabilitation programmes including exercise training). Interpretation of dyspnea during an exercise test obviously needs to be integrated with other parameters studied during exercise. 相似文献
4.
5.
6.
7.
8.
W. S. Walston I. M. Bernstein A. W. Thompson 《Metallurgical and Materials Transactions A》1991,22(6):1443-1451
The microstructure of a single-crystal nickel-base superalloy, PWA 1480, has been varied by heat treatment and hot isostatic
pressing in order to study the role of the γ/yγ′ eutectic and porosity on subsequent tensile behavior. The level of porosity
was found not to affect any of the tensile properties, while the γ/γ′ eutectic strongly influenced ductility. Eliminating
the γ/γ′ eutectic increased ductility which was attributed to the cleavage fracture of this constituent. It is proposed that
such cleavage of the γ/γ′ eutectic is initiated by the stress created from impinging slip bands, promoting shear localization,
and final fracture along {111} slip planes. The precise nature of this fracture process is discussed with emphasis on the
role of the γ/′ micro-structure. The deformation structure of PWA 1480 was also studied, and while different in some respects
from many other single-crystal superalloys, its fracture process appears to be similar.
Formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University. 相似文献
9.
Bismuth is a semimetal that has a relatively low lattice thermal conductivity. A positive energy gap can be created by alloying with antimony, leading to useful alloys for thermoelectric energy conversion. This paper gives an insight into the basic properties of BiSb alloys for thermoelectric applications. 相似文献
10.
Enhancing echo cancellation via estimation of delay 总被引:2,自引:0,他引:2
Youhong Lu Fowler R. Tian W. Thompson L. 《Signal Processing, IEEE Transactions on》2005,53(11):4159-4168
The advent of packetized audio transmission, such as voice over IP (VoIP), has resulted in challenging requirements for echo cancellation technology. One key aspect of this technology is the need to characterize, quickly and accurately, the echo paths in the transmission media. Echo paths consist of a constant time delay with no echo signal and active regions in which the echo signal is present. When an adaptive filter echo cancellation algorithm is used, its performance can be greatly increased, and its complexity can be reduced if it is only applied to the active regions. This requires an algorithm to estimate the constant delay and locate the active regions. Traditionally, delay estimation has been based on direct application of cross-correlation. This method has poor performance because the input signals are highly correlated and has a high implementation cost because many cross-correlation lags have to be computed for longer time delays. The delay estimation addressed in this paper has two major advantages over the traditional methods. The first is that it has improved performance because the input signals are processed to have less correlation. The second is that the implementation cost is significantly reduced because fewer cross-correlation lags are computed, and an efficient method to estimate lags is created. 相似文献