全文获取类型
收费全文 | 513987篇 |
免费 | 6192篇 |
国内免费 | 1985篇 |
专业分类
电工技术 | 8913篇 |
综合类 | 671篇 |
化学工业 | 78073篇 |
金属工艺 | 20787篇 |
机械仪表 | 15363篇 |
建筑科学 | 12274篇 |
矿业工程 | 3100篇 |
能源动力 | 12546篇 |
轻工业 | 43900篇 |
水利工程 | 5673篇 |
石油天然气 | 11466篇 |
武器工业 | 56篇 |
无线电 | 58562篇 |
一般工业技术 | 102480篇 |
冶金工业 | 93801篇 |
原子能技术 | 13003篇 |
自动化技术 | 41496篇 |
出版年
2021年 | 3892篇 |
2019年 | 3679篇 |
2018年 | 6546篇 |
2017年 | 6564篇 |
2016年 | 7065篇 |
2015年 | 4563篇 |
2014年 | 7743篇 |
2013年 | 21964篇 |
2012年 | 12563篇 |
2011年 | 17227篇 |
2010年 | 13771篇 |
2009年 | 15826篇 |
2008年 | 16325篇 |
2007年 | 16190篇 |
2006年 | 14185篇 |
2005年 | 13255篇 |
2004年 | 12766篇 |
2003年 | 12279篇 |
2002年 | 12202篇 |
2001年 | 12074篇 |
2000年 | 11473篇 |
1999年 | 11809篇 |
1998年 | 28244篇 |
1997年 | 20591篇 |
1996年 | 15950篇 |
1995年 | 12187篇 |
1994年 | 10856篇 |
1993年 | 10756篇 |
1992年 | 8060篇 |
1991年 | 7922篇 |
1990年 | 7627篇 |
1989年 | 7582篇 |
1988年 | 7264篇 |
1987年 | 6380篇 |
1986年 | 6353篇 |
1985年 | 7222篇 |
1984年 | 6767篇 |
1983年 | 6242篇 |
1982年 | 5865篇 |
1981年 | 5977篇 |
1980年 | 5862篇 |
1979年 | 5644篇 |
1978年 | 5671篇 |
1977年 | 6432篇 |
1976年 | 8426篇 |
1975年 | 5079篇 |
1974年 | 4873篇 |
1973年 | 4880篇 |
1972年 | 4203篇 |
1971年 | 3834篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
Tkachenko Yurii G. Britun Yurchenko Djema Z. Ochkas Larisa F. Bovkun Galina A. 《Powder Metallurgy and Metal Ceramics》2004,43(1-2):99-104
The influence which the composition of powder mixtures, the treatment conditions which the mixtures are subjected to, and the conditions under which the hot-pressed composite materials B4C – (5-10 mass%) calcium-silicon are fabricated exert on the structure, nature of failure, and mechanical properties of these materials is investigated. Optimum properties are possessed by material containing 10 mass% of addition. It is shown that the structure, morphology, and dispersivity, as well as the nature of the distribution of the components that are added to the composite material (secondary phase) vary as the temperature of hot pressing changes. Maximal mechanical characteristics of the composite material (σbend = 560 MPa, K 1c = 4.7 MPa·m1/2, HV = 37 GPa) are attained at hot-pressing temperatures in the range 2000-2100°C. 相似文献
962.
Combined time and wavelength multiplexing technique of optical fiber grating sensor arrays using commercial OTDR equipment 总被引:1,自引:0,他引:1
Valente L.C.G. Braga A.M.B. Ribeiro A.S. Regazzi R.D. Ecke W. Chojetzki C. Willsch R. 《IEEE sensors journal》2003,3(1):31-35
The use of a commercial optical time domain reflectometry device for simultaneous wavelength and time domain multiplexing of fiber-optic Bragg grating sensors is proposed and demonstrated. The realization of such systems provides an inexpensive way of interrogating several hundreds of sensors in a single fiber. Strain resolution of 30 /spl mu/m/m over a strain measuring range of 0.5% was obtained. 相似文献
963.
964.
A method of measuring static and pulsed pressures using electrically conducting rubber sensors is proposed. The method is
based on a change in the volume resistivity of a filled rubber under the action of external pressure. The pressure-induced
change in resistance of the rubber sensor is proportional to the applied pressure and can be measured by a bridge circuit.
Using this method, it is possible to evaluate the degree of homogeneity of the pressure distribution over a solid surface.
This is achieved by distributing rubber sensors over the given surface. 相似文献
965.
The present study explores the relation among 4 personality traits associated with impulsive behavior and alcohol abuse. Personality traits were measured using the 4 subscales of the UPPS Impulsive Behavior Scale (UPPS: S. P. Whiteside & D. R. Lynam. 2001). The UPPS and measures of psychopathology were administered to clinical samples of alcohol abusers high in antisocial personality traits (AAPD), alcohol abusers low in antisocial personality traits (AA), and a control group (total N = 60). Separate analyses of variance indicated that AAPDs had significant elevations on all 4 UPPS scales, whereas the AAs and controls differed only on the Urgency subscale. However, when controlling for psychopathology, group differences on the UPPS scales disappeared. The results suggest that personality traits related to impulsive behavior are not directly related to alcohol abuse but rather are associated with the elevated levels of psychopathology found in a subtype of alcohol abusers. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
966.
967.
V. Iakovlev G. Suruceanu A. Caliman A. Mereuta A. Mircea C.-A. Berseth A. Syrbu A. Rudra E. Kapon 《Photonics Technology Letters, IEEE》2005,17(5):947-949
High-performance vertical-cavity surface-emitting lasers (VCSELs) emitting in the 1310-nm waveband are fabricated by bonding AlGaAs-GaAs distributed Bragg reflectors on both sides of a InP-based cavity. A 2-in wafer bonding process is optimized to produce very good on-wafer device parameter uniformity. Carrier injection is implemented via double intracavity contact layers and a tunnel junction. A 1.2-mW single-mode output power is obtained in the temperature range of 20/spl deg/C-80/spl deg/C. Modulation capability at 3.2 Gb/s is demonstrated up to 70/spl deg/C. Overall VCSEL performance complies with the requirements of the 10 GBASE-LX4 IEEE.802.3ae standard, which opens the way for novel applications of VCSELs emitting in the 1310-nm band. 相似文献
968.
van der Wielen P.C.J.M. Steennis E.F. Wouters P.A.A.F. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2003,10(4):678-688
On-line partial discharge (PD) detection of three-phase belted medium voltage cable connections results in a number of interpretation differences as compared to off-line measurements where only one phase is energized. The induced currents and charges in the phase conductors and earth screen upon a PD not only depend on the discharge site, but also become phase angle dependent. Furthermore, simulations show that the PD distribution itself varies with the amount of eccentricity of the rotating electric field and may differ from the off-line distributions obtained with a linear field. Finally, the PD propagation in a multi-conductor cable also alters the signals measured at the cable terminals. In this paper, induced charges and PD distributions are studied by means of computer simulation. The cable propagation characteristics are verified by measurements. 相似文献
969.
Perturbation analysis and control of two-class stochastic fluid models for communication networks 总被引:2,自引:0,他引:2
Cassandras C.G. Gang Sun Panayiotou C.G. Wardi Y. 《Automatic Control, IEEE Transactions on》2003,48(5):770-782
This paper uses stochastic fluid models (SFMs) for the control and optimization (rather than performance analysis) of communication network nodes processing two classes of traffic: one is uncontrolled and the other is subject to threshold-based buffer control. We derive gradient estimators for packet loss and workload related performance metrics with respect to threshold parameters. These estimators are shown to be unbiased and directly observable from a sample path without any knowledge of underlying stochastic characteristics of the traffic processes. This renders them computable in online environments and easily implementable for network management and control. We further demonstrate their use in buffer control problems where our SFM-based estimators are evaluated based on data from an actual system. 相似文献
970.
Wilcox Sara; Evenson Kelly R.; Aragaki Aaron; Wassertheil-Smoller Sylvia; Mouton Charles P.; Loevinger Barbara Lee 《Canadian Metallurgical Quarterly》2003,22(5):513
This study examined whether widowhood was associated with physical and mental health, health behaviors, and health outcomes using a cross-sectional (N=72,247) and prospective (N=55,724) design in women aged 50-79 years participating in the Women's Health Initiative observational study (85.4% White). At baseline, married women reported better physical and mental health and generally better health behaviors than widowed women. Whereas women who remained married over the 3-year period showed stability in mental health, recent widows experienced marked impairments and longer term widows showed stability or slight improvements. Both groups of widows reported more unintentional weight loss over the 3-year period. Changes in physical health and health behaviors were inconsistent, with generally small effect sizes. Findings underscore the resilience of older women and their capacity to reestablish connections, but point to the need for services that strengthen social support among women who have difficulty during this transition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献