全文获取类型
收费全文 | 2627篇 |
免费 | 82篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 33篇 |
综合类 | 5篇 |
化学工业 | 573篇 |
金属工艺 | 75篇 |
机械仪表 | 40篇 |
建筑科学 | 134篇 |
矿业工程 | 29篇 |
能源动力 | 63篇 |
轻工业 | 233篇 |
水利工程 | 17篇 |
石油天然气 | 17篇 |
无线电 | 224篇 |
一般工业技术 | 405篇 |
冶金工业 | 489篇 |
原子能技术 | 25篇 |
自动化技术 | 350篇 |
出版年
2023年 | 11篇 |
2021年 | 41篇 |
2020年 | 29篇 |
2019年 | 35篇 |
2018年 | 47篇 |
2017年 | 44篇 |
2016年 | 55篇 |
2015年 | 43篇 |
2014年 | 69篇 |
2013年 | 165篇 |
2012年 | 112篇 |
2011年 | 128篇 |
2010年 | 118篇 |
2009年 | 103篇 |
2008年 | 106篇 |
2007年 | 88篇 |
2006年 | 88篇 |
2005年 | 79篇 |
2004年 | 54篇 |
2003年 | 70篇 |
2002年 | 66篇 |
2001年 | 42篇 |
2000年 | 33篇 |
1999年 | 44篇 |
1998年 | 104篇 |
1997年 | 67篇 |
1996年 | 67篇 |
1995年 | 56篇 |
1994年 | 44篇 |
1993年 | 60篇 |
1992年 | 36篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 39篇 |
1980年 | 35篇 |
1979年 | 24篇 |
1978年 | 25篇 |
1977年 | 29篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1973年 | 16篇 |
1972年 | 14篇 |
排序方式: 共有2712条查询结果,搜索用时 46 毫秒
11.
Withdrawal from an escalating-dose, bingelike regimen of cocaine administration in rats produced significantly depressed levels of locomotor activity during the nocturnal portion of the day-night cycle. This effect was observed during the first 48 hrs of testing. Extracellular single-unit recordings of ventral tegmental area (VTA) dopamine (DA) neurons revealed no differences between saline- and cocaine-treated rats with respect to basal firing rates. However, significantly fewer spontaneously active VTA DA neurons were encountered in rats withdrawn from binge cocaine. As with the nocturnal hypoactivity, this effect was observed only during the first 48 hrs of withdrawal. These findings suggest that short-term DA neuron dysfunction during cocaine withdrawal temporally corresponds to behavioral disruptions that are similar to those described in human addicts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
12.
Investigated relationships between the performance levels of incumbents on job skills and the importance attributed to those job skills. Supervisors and job incumbents rated both the performance of skill dimensions and the importance of those skills for respective incumbents' positions. Results indicate that the ratings of performance and importance on matched skill areas correlated positively, although relationships were somewhat stronger for incumbent data as compared with data provided by supervisors. Supervisors and incumbents agreed moderately on which skill areas were important for various positions, but the interrater agreement was much lower for performance ratings of the skill areas. For some skill areas, incumbent-rated importance and supervisor-rated performance, as well as incumbent-rated performance and supervisor-rated importance, were significantly correlated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
13.
Studied the social reputations of elementary school children. Ss were 76 2nd-grade (mean age 7.5 yrs), 71 3rd-grade (mean age 8.5 yrs), and 83 4th-grade students (mean age 9.7 yrs). Using the peer nomination technique, Ss were assessed collectively on 8 dimensions requiring both social and academic judgments. A cluster analysis was performed to identify groups with different sociometric profiles. Correlations between peer evaluations and teacher evaluations of Ss' social reputations were determined. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
15.
Viswanathan Mahalakshmi Vaidyanathan Subramanian Francis R. Bidinger Ramamurthi Jambunathan 《Journal of the science of food and agriculture》1985,36(12):1237-1242
Seventy-two pearl millet genotypes were water stressed at panicle development and grain filling stages. Neither grain yields, yield components, protein percent nor total protein per unit area were affected by water deficit during panicle development but protein content per grain was increased. When plants were water stressed during grain filling, grain yield, grains per unit area and 1000 grain weight were reduced, but grain protein percentage increased. Total protein per unit area was reduced primarily due to lower grain yield. The protein content per grain was unaffected by stress, suggesting that the apparent increase in protein percentage is due to reduced carbohydrate accumulation under stress. 相似文献
16.
17.
18.
Characterization of C-S-H from Highly Reactive β-Dicalcium Silicate Prepared from Hillebrandite 总被引:1,自引:1,他引:0
Yoshihiko Okada Hideki Ishida Kaori Sasaki J. Francis Young Takeshi Mitsuda 《Journal of the American Ceramic Society》1994,77(5):1313-1318
β-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca2 (SiO3 )(OH)2 ) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29 Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form β-C2 S. The temperature at which βC2 S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes higher. The high activity of β-C2 S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed. 相似文献
19.
Bench-scale tests were conducted with raw and beneficiated shales in an advanced multi-purpose research reactor. Raw Alabama shale and raw and beneficiated Indiana shales were retorted at 515 °C using hydrogen pressures of 4 and 7 MPa. Shale feed rates were 15 to 34 kg h−1. High oil yields and carbon conversions were achieved in all tests. Oil yield from Alabama shale hydroretorted at 7 MPa was 200% of Fischer assay. Raw and beneficiated Indiana shales hydroretorted at 7 MPa produced oil yields of 170 and 195% of Fischer assay respectively. Total carbon conversions were >70% for all tests conducted at 7 MPa. 相似文献
20.
Over the last decade there have emerged many electronic applications of HTS technology which have important military as well as commercial implications. Examples of these include space communications, terrestrial wireless communications, radar, surveillance, countermeasures, medical applications and cryo-electronics. I will review many of the efforts in in this area that have been supported by the DoD which has invested over $350M on this technology. In addition I will discuss the efforts to develop cryocoolers to support the HTS technology. 相似文献