全文获取类型
收费全文 | 5481篇 |
免费 | 137篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 53篇 |
综合类 | 4篇 |
化学工业 | 1156篇 |
金属工艺 | 89篇 |
机械仪表 | 92篇 |
建筑科学 | 190篇 |
矿业工程 | 18篇 |
能源动力 | 133篇 |
轻工业 | 381篇 |
水利工程 | 68篇 |
石油天然气 | 22篇 |
无线电 | 333篇 |
一般工业技术 | 846篇 |
冶金工业 | 1583篇 |
原子能技术 | 32篇 |
自动化技术 | 621篇 |
出版年
2021年 | 69篇 |
2020年 | 45篇 |
2019年 | 56篇 |
2018年 | 68篇 |
2017年 | 77篇 |
2016年 | 78篇 |
2015年 | 65篇 |
2014年 | 106篇 |
2013年 | 288篇 |
2012年 | 149篇 |
2011年 | 229篇 |
2010年 | 207篇 |
2009年 | 192篇 |
2008年 | 211篇 |
2007年 | 202篇 |
2006年 | 214篇 |
2005年 | 183篇 |
2004年 | 161篇 |
2003年 | 168篇 |
2002年 | 125篇 |
2001年 | 104篇 |
2000年 | 107篇 |
1999年 | 111篇 |
1998年 | 246篇 |
1997年 | 183篇 |
1996年 | 140篇 |
1995年 | 130篇 |
1994年 | 134篇 |
1993年 | 110篇 |
1992年 | 104篇 |
1991年 | 55篇 |
1990年 | 87篇 |
1989年 | 72篇 |
1988年 | 73篇 |
1987年 | 65篇 |
1986年 | 60篇 |
1985年 | 86篇 |
1984年 | 85篇 |
1983年 | 75篇 |
1982年 | 60篇 |
1981年 | 53篇 |
1980年 | 46篇 |
1979年 | 57篇 |
1978年 | 59篇 |
1977年 | 56篇 |
1976年 | 69篇 |
1975年 | 35篇 |
1974年 | 40篇 |
1973年 | 30篇 |
1972年 | 33篇 |
排序方式: 共有5621条查询结果,搜索用时 15 毫秒
951.
Data from compartment tests of polyurethane foam seating assemblies are reported. Results show that the behavior of such assemblies during fires is strongly dependent on the type and position of interliners and upholstery fabrics. An incidental comparison of peak rate of heat release obtained in a compartment test with a predictive model equation is made and selected data from the tests are presented. 相似文献
952.
钢管混凝土组合柱的研究进展 总被引:7,自引:0,他引:7
本文对钢管混凝土组合柱的研究现状进行了概述,并就其发展前景进行了展望. 相似文献
953.
Li Z Pickett MD Stewart D Ohlberg DA Li X Wu W Robinett W Williams RS 《Nanotechnology》2008,19(16):165203
Ultradense memory and logic circuits fabricated at local densities exceeding 100 × 10(9) cross-points per cm(2) have recently been demonstrated with nanowire crossbar arrays. Practical implementation of such nanocrossbar circuitry, however, requires effective demultiplexing to solve the problem of electrically addressing individual nanowires within an array. Importantly, such a demultiplexer (demux) must also be tolerant of the potentially high defect rates inherent to nanoscale circuit fabrication. We have built a 50?nm half-pitch nanocrossbar circuit using imprint lithography and configured it for a demux application. Utilizing a class of Hamming codes in the hardware design, we experimentally demonstrate defect-tolerant demux operations on a 12 × 8 nanocrossbar array with up to two stuck-open defects per addressed line. 相似文献
954.
Lee S Fursina A Mayo JT Yavuz CT Colvin VL Sofin RG Shvets IV Natelson D 《Nature materials》2008,7(2):130-133
Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV approximately 120 K from a high-temperature 'bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound. 相似文献
955.
The two-photon absorption coefficients (beta) and the third-order nonlinear susceptibilities (chi(3)) of several semiconductor nanoparticles (CdS, Cd(x)Ag(1-x)S, and core-shell CdS/Ag2S) that are confined and stabilized by random and block ionomers have been measured by nonlinear transmission and degenerate four-wave mixing techniques using 21 picosecond laser pulses at near-infrared spectral region. The imaginary part of the third-order nonlinear susceptibility that is related to the two-photon absorption coefficient was then calculated. The absorptive nonlinearity of the nanoparticles (2 approximately 9 nm) was found to be dependent on the particle size, composition and wavelength, i.e., larger CdS particles exhibit higher two-photon absorption coefficients and the presence of Ag improves two-photon absorption of CdS nanoparticles. The obtained two-photon absorption coefficients of nanoparticles corrected for their volume fraction in solution are significantly greater that those of corresponding bulk semiconductors. 相似文献
956.
957.
Whisman Mark A.; Beach Steven R. H.; Snyder Douglas K. 《Canadian Metallurgical Quarterly》2008,76(5):745
Addressing potential weaknesses in an earlier investigation, the authors examined the latent structure of marital discord using 4 product indicators from the Marital Satisfaction Inventory-Revised (Snyder, 1997) in a representative sample of community couples (N = 1,020). Results from 3 taxometric procedures suggested that marital discord is taxonic, with an estimated base rate of .31. Cut scores for classifying members of this marital discord taxon were identified. Additional analyses with several data sets of community and clinic couples provided evidence that the marital discord taxon classification demonstrated good (a) 6-week test-retest reliability, (b) criterion validity (i.e., differences in taxon prevalence in community vs. clinic couples), and (c) construct validity (i.e., correlations with therapist ratings of relationship quality). These results suggest that discordant couples differ qualitatively and not just quantitatively from nondiscordant couples and that user friendly methods, suitable for a range of research and clinical applications, can be used to identify marital discord. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
958.
Hamilton Joanne M.; Salmon David P.; Galasko Douglas; Raman Rema; Emond Jenn; Hansen Lawrence A.; Masliah Eliezer; Thal Leon J. 《Canadian Metallurgical Quarterly》2008,22(6):729
Dementia with Lewy bodies (DLB) is often characterized by pronounced impairment in visuospatial skills, attention, and executive functions. However, the strength of the phenotypic expression of DLB varies and may be weaker in patients with extensive concomitant Alzheimer's disease (AD). To determine whether strength of the DLB clinical phenotype impacts cognitive decline, visuospatial and language tests were retrospectively used to predict 2-year rate of global cognitive decline in 22 autopsy-confirmed DLB patients (21 with concomitant AD) and 44 autopsy-confirmed "pure" AD patients. Generalized estimating equations (GEE) revealed a significant interaction such that poor baseline performances on tests of visuospatial skills were strongly associated with a rapid rate of cognitive decline in DLB but not AD (p 相似文献
959.
Mitchell Alexandra E.; Castellani Angela M.; Herrington Rachael L.; Joseph Jana I.; Doss Brian D.; Snyder Douglas K. 《Canadian Metallurgical Quarterly》2008,22(1):21
The interpersonal process model of intimacy (H. T. Reis & P. Shaver, 1988) proposes that self-disclosure and empathic responding form the basis of intimate interactions. This study examined this model in 102 community couples who completed intimacy measures following videotaped discussions about relationship injuries occurring both within and outside the relationship. Observational assessments of self-disclosure and empathic responding, as well as their respective components, were related to self-reported ratings of post-interaction intimacy. Men's own disclosure and empathic responding predicted their feelings of intimacy, whereas women's intimacy was predicted by their partner's disclosure and empathic responding. Self-disclosure and empathic responding appear to be important behavioral determinants of intimate feelings, but the manner in which they influence intimacy differs according to gender. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
960.
El-Sheikh Mona; Buckhalt Joseph A.; Keller Peggy S.; Granger Douglas A. 《Canadian Metallurgical Quarterly》2008,27(1):26
Objective: The purpose of this study was to determine possible relations between the quality and amount of children's sleep and cortisol in healthy children. Design: Children's sleep was monitored with actigraphs for 7 nights. Children came to the laboratory to provide saliva samples, which were used to assess cortisol. Children reported on their sleepiness and sleep/wake problems. Sixty-four healthy children participated (M = 8.75 years; SD = .55). Main Outcome Measures: Self-reported sleepiness and sleep/wake problems, actigraphy-measured total sleep minutes, sleep efficiency, minutes awake after sleep onset, and sleep activity, and afternoon cortisol levels. Results: After controlling for demographic variables and child characteristics, higher levels of cortisol were related to increased subjective sleep problems and objective measures of shorter sleep duration and poorer sleep quality. Conclusion: These findings are of importance for understanding critical facets of children's health and well-being, and are noteworthy given the high prevalence of sleep disruptions in otherwise normally developing children in the United States. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献