首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22467篇
  免费   588篇
  国内免费   24篇
电工技术   282篇
综合类   23篇
化学工业   3089篇
金属工艺   296篇
机械仪表   410篇
建筑科学   1177篇
矿业工程   56篇
能源动力   583篇
轻工业   2296篇
水利工程   306篇
石油天然气   43篇
无线电   1992篇
一般工业技术   3024篇
冶金工业   5771篇
原子能技术   162篇
自动化技术   3569篇
  2023年   87篇
  2022年   181篇
  2021年   330篇
  2020年   188篇
  2019年   267篇
  2018年   365篇
  2017年   367篇
  2016年   377篇
  2015年   347篇
  2014年   500篇
  2013年   939篇
  2012年   899篇
  2011年   1198篇
  2010年   851篇
  2009年   854篇
  2008年   955篇
  2007年   887篇
  2006年   774篇
  2005年   706篇
  2004年   616篇
  2003年   580篇
  2002年   549篇
  2001年   418篇
  2000年   395篇
  1999年   502篇
  1998年   1985篇
  1997年   1228篇
  1996年   840篇
  1995年   526篇
  1994年   495篇
  1993年   478篇
  1992年   230篇
  1991年   218篇
  1990年   207篇
  1989年   209篇
  1988年   209篇
  1987年   145篇
  1986年   141篇
  1985年   197篇
  1984年   159篇
  1983年   105篇
  1982年   116篇
  1981年   119篇
  1980年   90篇
  1979年   105篇
  1978年   87篇
  1977年   135篇
  1976年   152篇
  1975年   80篇
  1974年   73篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
Distilled fractions of a coal-derived liquid from the H-Coal process were upgraded to diesel fuel by catalytic hydrotreatment. The total hydrotreated products were distilled into naphtha (<180°C) and diesel fuel fractions (>180°C) and the diesel fractions were analysed for hydrocarbon-type composition, hydrogen content and some diesel fuel properties. GC—MS-analyses were carried out on the hydrocarbon-type fractions to identify individual chemical compounds. To investigate the effect of different distillation cut points on diesel fuel yield and properties, cut points for one hydrotreated product were varied. The diesel fuel cetane numbers were correlated with percentage hydrogen, total aromatics and saturates. Cetane numbers above 40 were obtained for diesel fuels containing (i) more than 75% saturates, (ii) less than 15% total aromatics and (iii) a hydrogen content above 12.8%. Compounds identified by GC—MS-analyses (in the diesel fractions) were typical aromatic and cycloparaffin compounds. Normal-and iso-paraffin compounds were not detected. By varying the distillation cut point from 135 to 180°C, the cetane number of the residual diesel fraction improved from 37 to 44. This increase is ascribed to the removal of aromatic compounds in the 135–180°C boiling point range.  相似文献   
22.
23.
24.
26 previously treated patients with progressive recurrent small cell lung cancer (SCLC) were given vinorelbine (Navelbine), 30 mg/m2 weekly. All patients had responded to first-line chemotherapy and were off therapy for at least 3 months. Partial response was observed in 4 out of 25 eligible patients (16%; 95% confidence interval 4-36%), stable disease in 7 patients and progression in 12 patients. The limiting toxicity was a non-cumulative leucopenia (80%, 32% WHO grade 3-4). Reaction at the site of injection was observed in 5 patients, causing treatment discontinuation in 2 cases. Other non-haematological toxicities were moderate. These results suggest acceptable toxicity and some antitumour activity of vinorelbine in pretreated SCLC patients.  相似文献   
25.
26.
In a previous study a solvent mixture of heptane containing 40 mass % heptanol was selected as an alternative in the industrial extraction of caprolactam to replace benzene, toluene, or chlorinated hydrocarbons. This work reports the equilibrium distribution ratio of caprolactam and four model impurities of organic nature, namely, cyclohexanone, aniline, n‐methylcaprolactam, and cyclohexane‐carboxamide, comparing the mixed solvents with toluene as a reference. The resulting phase equilibria were interpreted using the equilibrium stage model. Based on these calculations it was found that, compared to toluene, the co‐extracted fraction of cyclohexanone and aniline was higher, that of n‐methylcaprolactam was comparable, and that of cyclohexane‐carboxamide was lower using the mixed solvent. Overall, the mixed solvent reduced the fraction of co‐extracted impurities by almost 10 %.  相似文献   
27.
28.
The mycotoxin contamination of feed components used by the Dutch cooperative feed industry was surveyed to estimate the risk for animal production losses. Of 89 randomly and 6 selectively taken samples of raw materials harvested in 1988 and 1989 27% were contaminated with ochratoxin A (OCHRA), 31% with zearalenone (ZEA) and 20% with deoxynivalenol (DON). The mean content (microgram/kg) of all positive randomly taken samples was 18 (OCHRA), 62 (ZEA) and 630 (DON). The highest level (microgram/kg) for all samples was 120 (OCHRA) in barley, 3100 (ZEA) in corn cob mix and 1900 (DON) in maizegluten feed. The results of this survey show that feed components are often contaminated with mycotoxins. However, the contamination level could only sporadically cause production losses in animal husbandry.  相似文献   
29.
Simulations with regional climate models (RCMs), carried out for the Rhine basin, have been analyzed in the context of implications of the possible future discharge of the Rhine river. In a first analysis, the runoff generated by the RCMs is compared to observations, in order to detect the way the RCMs treat anomalies in precipitation in their land surface component. A second analysis is devoted to the frequency distribution of area averaged precipitation, and the impact of selection of various driving global climate models.  相似文献   
30.
Often companies in the (petro‐) chemical industry claim that all possible countermeasures against potential accidents have been taken and therefore accidents are unforeseeable. In this paper we question this statement by analysing the pre‐warning signals (precursors) preceding a number of industrial accidents. 17 accidents that occurred in the (petro‐) chemical industry have been investigated by exploring FACTS, an accident database containing information about industrial accidents worldwide. This paper will demonstrate that the existence of precursor information could have been used to foresee and even prevent these accidents if a proper control action had been initiated. The accidents are analysed further, according to a control model, which was adapted from that of C. Argyris. It demonstrates the ineffectiveness of several elements of business process control loops and that the so‐called ‘double‐loop learning’ cycle is more important than the ‘single‐loop learning’ cycle if one considers safety improvement. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号