全文获取类型
收费全文 | 13422篇 |
免费 | 567篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 139篇 |
综合类 | 23篇 |
化学工业 | 2552篇 |
金属工艺 | 237篇 |
机械仪表 | 237篇 |
建筑科学 | 872篇 |
矿业工程 | 47篇 |
能源动力 | 357篇 |
轻工业 | 1049篇 |
水利工程 | 164篇 |
石油天然气 | 52篇 |
武器工业 | 1篇 |
无线电 | 920篇 |
一般工业技术 | 2398篇 |
冶金工业 | 2680篇 |
原子能技术 | 59篇 |
自动化技术 | 2250篇 |
出版年
2023年 | 70篇 |
2022年 | 141篇 |
2021年 | 234篇 |
2020年 | 170篇 |
2019年 | 186篇 |
2018年 | 266篇 |
2017年 | 221篇 |
2016年 | 330篇 |
2015年 | 257篇 |
2014年 | 404篇 |
2013年 | 850篇 |
2012年 | 670篇 |
2011年 | 912篇 |
2010年 | 700篇 |
2009年 | 645篇 |
2008年 | 763篇 |
2007年 | 754篇 |
2006年 | 621篇 |
2005年 | 587篇 |
2004年 | 509篇 |
2003年 | 402篇 |
2002年 | 478篇 |
2001年 | 292篇 |
2000年 | 281篇 |
1999年 | 246篇 |
1998年 | 279篇 |
1997年 | 234篇 |
1996年 | 194篇 |
1995年 | 238篇 |
1994年 | 192篇 |
1993年 | 202篇 |
1992年 | 167篇 |
1991年 | 79篇 |
1990年 | 138篇 |
1989年 | 124篇 |
1988年 | 115篇 |
1987年 | 116篇 |
1986年 | 86篇 |
1985年 | 141篇 |
1984年 | 131篇 |
1983年 | 86篇 |
1982年 | 71篇 |
1981年 | 69篇 |
1980年 | 48篇 |
1979年 | 54篇 |
1978年 | 45篇 |
1977年 | 31篇 |
1976年 | 41篇 |
1974年 | 27篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
安捷伦HFCT-5942 2.488GB/s LC小封装光纤收发模块是符合SONET和SDH标准,管脚为2×10的短距离单模光纤收发模块。 文中给出了三种不同应用的参考设计。在这些设计中,HFCT.5942光纤收发模块与以下芯片联接 相似文献
83.
The synthesis of new lanthanide allyl complexes of enhanced stability and solubility in saturated hydrocarbons based on silyl-substituted allyl ligands is reported. Thus the potassium salt K(CH2CHCHSiMe3) ( 1 ) reacts with YCl3 in tetrahydrofuran to give the tris-allyl complex Y(CH2CHCHSiMe3)3 ( 2 ), while K(CH2CHCHSiMe2tBu) ( 3 ) affords Y(CH2CHCHSiMe2tBu)3(THF)1.5 ( 4 ). Slow re-crystallization of 4 from light petroleum in the presence of tert-butylcyanide led to multiple insertion to give the sec-amido complex Y{NHC(tBu)(CH)3SiMe2tBu}2{η2-NHC(tBu)CH=CHCH2SiMe2tBu)CH(CHCHSiMe2tBu)CtBuNH}(THF)·(CH3CH(Me)(CH2)2CH3) ( 5 ), which was crystallographically characterized. The reaction of ScCl3(THF)3 with two equivalents of Li{1,3-C3H3(SiMe3)2} in tetrahydrofuran gives the bis-allyl complex {1,3-C3H3(SiMe3)2}2Sc(μ-Cl)2Li(THF)2 ( 6 ), while the analogous reaction of K{1,3-C3H3(SiMe3)2} ( 7 ) with either LaCl3 or YCl3 in tetrahydrofuran affords the bis-allyl complexes MCl{1,3-C3H3(SiMe3)2}2(THF)x (8, M = La, x = 1; 9, M = Y, x = 0). An attempt to prepare the similar neodymium complex gave the mono-allyl complex NdI2{1,3-C3H3(SiMe3)2}(THF)1.25 ( 10 ). The reactions of 8 and 9 with triisobutyl aluminum in benzene-d6 show allyl exchange between lanthanide and aluminum. Complexes 8 , 9 , and 10 have been tested with a variety of activator systems as catalysts for the polymerization of 1,3-butadiene. 相似文献
84.
Mark S. Drew 《Solar Energy》1985,35(3):291-293
85.
Alexander Gerianne M.; Packard Mark G.; Hines Melissa 《Canadian Metallurgical Quarterly》1994,108(2):424
Evidence from mammalian species, including humans, suggests that testosterone (TST) enhances motivational aspects of sexual behavior, although the mechanism by which TST exerts this effect is unknown. The hypothesis that increases in plasma TST have rewarding affective properties was examined. Acute elevations of plasma TST were induced in intact male rats by systemic administration of a recently developed testosterone-hydroxypropyl-β-cyclodextrin inclusion complex that mimics pulsatile release of the hormone. In a conditioned-place-preference paradigm, rats displayed a preference for an environment previously paired with TST administration (800 μg/kg and 1,200 μg/kg) as opposed to an environment paired with saline administration, indicating that TST has rewarding affective properties. The findings suggest that TST may enhance motivational aspects of mammalian sexual behavior by facilitating acquisition or expression of learned associations between environmental stimuli and sexual activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
86.
Although multidisciplinary pain programs have been demonstrated to be effective, the processes of improvement have yet to be clarified. Cognitive-behavioral models posit that improvement is due, in part, to changes in patient pain beliefs and coping strategies. To test the relationships between treatment outcome and changes in beliefs and coping strategies, 94 chronic pain patients (aged 21–64 yrs) completed measures of physical and psychological functioning, health care utilization, pain beliefs, and use of pain coping strategies at admission and 3 to 6 mo after inpatient pain treatment. Improved functioning and decreased health care use were associated with changes in both beliefs and cognitive coping strategies. However, changes in some coping strategies, such as exercise and use of rest, were not associated with improvement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
Reinitz Mark Tippens; Morrissey Joseph; Demb Jonathan 《Canadian Metallurgical Quarterly》1994,20(1):161
Ss studied faces in a full- or a divided-attention condition and then received a recognition test that included old faces, new faces constructed by combining facial features from previously studied faces ("conjunction faces"), and partly or completely new faces. Full- but not divided attention Ss responded "old" more often to old than to conjunction faces; all Ss responded "old" to these faces more often than to partially or completely new faces. Thus it is less attentionally demanding to encode facial features than it is to encode their interrelations. Dividing attention had identical effects on an incidental and an intentional learning group. Exp 3 demonstrated that dividing attention primarily affected explicit recollection rather than stimulus familiarity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
Recent, as well as past, studies of reactor trip frequencies and other types of operating experience have shown that relatively high frequencies are likely in new plants with little accumulated operating time. In order to better understand all the factors which contribute to high frequencies in new plants, the authors have made a comparison of reactor trip frequencies between plants which went into operation in the 1960's and the early 1970's and those which have gone into operation more recently. Trip frequency versus accumulated operating time for two plant groups are compared to see the extent to which design differences (e.g., capacity, thermal margin) affect trip frequency.This paper also presents a review of some recent events in which plant age has played a major role. The events which are reviewed have been identified through the normal systematic event analysis program conducted by the NRC. Information regarding these events was obtained through followup by reviews conducted by NRC Resident Inspectors as well as event reports submitted by licensees. 相似文献
89.
Performance of a system design for digital video broadcasting is examined with emphasis on mobile reception. Orthogonal frequency division multiplexing (OFDM) is used to achieve good bandwidth efficiency and to mitigate the intersymbol interference resulting from the channel delay spread. The resulting equivalent channel including OFDM can be modeled as a flat Rayleigh fading channel plus an interchannel interference (ICI) term due to the channel Doppler spread. This ICI term is analyzed and shown to result in an error floor. Performance improvements due to antenna diversity and trellis-coded modulation (TCM) are given. Finally, multiresolution modulation is discussed as a means of achieving graceful degradation and giving degrees of freedom for further performance improvement.This research was supported by the Multimedia Systems R & D Laboratory, Hitachi, Ltd. 相似文献
90.
G. Mark Tanner 《Engineering Failure Analysis》1994,1(4):289-306
A waste-heat boiler at a chemical plant suffered an unusual tube failure. The boiler is part of the partial oxidation (POx) syngas production for a 2-ethyl hexanol unit. The syngas primarily consists of H2, CO and CO2 with trace amounts of CH4. Steam is also reportedly injected into the process. The syngas enters the boiler at approximately 1800°F (980°C) on the internal side of the tube and is cooled, while generating approximately 640 psi (4.41 MPa) steam at 490°F (255°C) on the outside of the tube. The internal surface of the tube contained a region of metal loss that was approximately 1
inches long by
inch wide (44.5 mm by 19 mm). The metal loss was very localized with little evidence of attack elsewhere on the tube's surface. Molten salt attack, sulfidation and metal dusting were considered as possible mechanisms for the metal loss. It was determined that metal dusting, also called catastrophic carburization, was the cause of the metal loss. The cause of the metal dusting was localized overheating of the tube, which developed because of water/steam flow disruption due to contact of the tube baffle with the tube. Approximately one year after this tube failure, the boiler suffered two more tube failures, which were also attributed to metal dusting. 相似文献