全文获取类型
收费全文 | 2066篇 |
免费 | 67篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 51篇 |
综合类 | 2篇 |
化学工业 | 789篇 |
金属工艺 | 32篇 |
机械仪表 | 36篇 |
建筑科学 | 166篇 |
矿业工程 | 4篇 |
能源动力 | 70篇 |
轻工业 | 150篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 107篇 |
一般工业技术 | 223篇 |
冶金工业 | 185篇 |
原子能技术 | 11篇 |
自动化技术 | 304篇 |
出版年
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 17篇 |
2016年 | 49篇 |
2015年 | 53篇 |
2014年 | 72篇 |
2013年 | 76篇 |
2012年 | 91篇 |
2011年 | 104篇 |
2010年 | 69篇 |
2009年 | 87篇 |
2008年 | 93篇 |
2007年 | 81篇 |
2006年 | 91篇 |
2005年 | 79篇 |
2004年 | 81篇 |
2003年 | 57篇 |
2002年 | 51篇 |
2001年 | 41篇 |
2000年 | 50篇 |
1999年 | 50篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 44篇 |
1993年 | 39篇 |
1992年 | 37篇 |
1991年 | 31篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 21篇 |
1973年 | 14篇 |
1972年 | 13篇 |
排序方式: 共有2135条查询结果,搜索用时 0 毫秒
11.
The syntheses of polyenynes as model compounds for poly(diacetylene)s (PDAs) are described. Variation of properties (UV–VIS, Raman, NMR and bond geometries) as a function of the chain length was investigated. After extrapolation to infinite chain length these data were compared to those for PDAs. From UV–VIS spectra a value of λ = 551 nm (2.25 eV) was calculated corresponding to the electronic transition of a single polyenyne chain. This energy is located at the low energy end of a yellow PDA solution spectrum. From Raman scattering v(C?C) = 2108–2128 cm?1 and v(C?C) = 1505–1532 cm?1 were calculated after extrapolation. Similarly sp-C13C NMR data yielded a shift of δ = 100 ppm. These data are almost identical to data known for yellow PDA solutions. Bond geometries are almost identical to those of poly(diacetylene)s and theoretical data. 相似文献
12.
13.
The conditions for ferrite and pearlite banding in strip and plate made of structural steels were investigated. Factors found to influence the formation of banded structures were the cooling rate during the γ/α-transformation, the former austenite grain size, and the work-hardened condition of the former austenite. Analyses with the aid of an electron beam microprobe made it possible to demonstrate that the carbon-rich bands correspond locally with banded manganese enrichments, yet that they do not form before the course of the γ/α-transformation as a result of secondary segregation. It was possible to explain the mechanism of action of the influencing factors on the basis of this model. 相似文献
14.
15.
16.
van der Ploeg Eleonore; Dorresteijn Sasja M.; Kleber Rolf J. 《Canadian Metallurgical Quarterly》2003,8(2):157
Workers in medium- or high-risk professions are often confronted with critical incidents at the workplace. The impact of these acute stressors may be serious and enduring. Many workers also experience chronic job stressors, such as work overload or role conflicts. This study examined the frequently neglected relationship of acute and chronic stressors with self-reported health symptoms, such as posttraumatic responses, fatigue, and burnout. This association was investigated in a sample of forensic doctors in the Netherlands (N = 84). It was found that the more traumatic events the respondents experienced, the more problems they reported in coping with the traumatic events. Chronic job stressors were associated with posttraumatic responses (intrusions and avoidances) and with burnout and fatigue. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
18.
Rinkenauer Gerhard; Osman Allen; Ulrich Rolf; Müller-Gethmann Hiltraut; Mattes Stefan 《Canadian Metallurgical Quarterly》2004,133(2):261
Lateralized readiness potentials (LRPs) were used to determine the stage(s) of reaction time (RT) responsible for speed-accuracy trade-offs (SATs). Speeded decisions based on several types of information were examined in 3 experiments, involving, respectively, a line discrimination task, lexical decisions, and an Erikson flanker task. Three levels of SAT were obtained in each experiment by adjusting response deadlines with an adaptive tracking algorithm. Speed stress affected the duration of RT stages both before and after the start of the LRP in all experiments. The latter effect cannot be explained by guessing strategies, by variations in response force, or as an indirect consequence of the pre-LRP effect. Contrary to most models, it suggests that SAT can occur at a late postdecisional stage. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
20.
Palmitoyl-CoA hydrolase [EC 3.1.2.2.] activity in rat liver was found to be enhanced by high fat diets. Partially hydrogenated
marine oil and high-erucic acid rapeseed oil diets produced a greater increase than a diet containing soybean oil.
With diets containing from 5 to 30% (w/w) of partially hydrogenated marine oil the increase in palmitoyl-CoA hydrolase activity
was similar to the increase observed in peroxisomal β-oxidation activity (correlation coefficient r=0.94). A positive correlation
(r=0.86) also was observed between the activity of palmitoyl-CoA hydrolase and previously determined levels of long-chain
acyl-CoA.
The results presented may suggest a common “induction” mechanism for palmitoyl-CoA hydrolase and peroxisomal β-oxidation enzymes,
possibly exerted through an increased cellular level of long-chain acyl-CoA. 相似文献