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   22282篇
  免费   582篇
  国内免费   21篇
电工技术   273篇
综合类   26篇
化学工业   3004篇
金属工艺   278篇
机械仪表   385篇
建筑科学   990篇
矿业工程   47篇
能源动力   504篇
轻工业   2242篇
水利工程   286篇
石油天然气   29篇
无线电   1867篇
一般工业技术   2757篇
冶金工业   7144篇
原子能技术   159篇
自动化技术   2894篇
  2023年   73篇
  2022年   134篇
  2021年   301篇
  2020年   158篇
  2019年   232篇
  2018年   299篇
  2017年   280篇
  2016年   324篇
  2015年   288篇
  2014年   453篇
  2013年   746篇
  2012年   771篇
  2011年   1039篇
  2010年   725篇
  2009年   762篇
  2008年   788篇
  2007年   782篇
  2006年   633篇
  2005年   618篇
  2004年   566篇
  2003年   533篇
  2002年   479篇
  2001年   385篇
  2000年   351篇
  1999年   516篇
  1998年   2455篇
  1997年   1467篇
  1996年   999篇
  1995年   600篇
  1994年   581篇
  1993年   571篇
  1992年   247篇
  1991年   232篇
  1990年   238篇
  1989年   237篇
  1988年   247篇
  1987年   158篇
  1986年   165篇
  1985年   223篇
  1984年   160篇
  1983年   113篇
  1982年   129篇
  1981年   142篇
  1980年   111篇
  1979年   113篇
  1978年   95篇
  1977年   189篇
  1976年   275篇
  1975年   95篇
  1974年   78篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
181.
Shifts, duration of work and accident risk of bus drivers   总被引:2,自引:0,他引:2  
  相似文献   
182.
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   
183.
Summary Linear discriminant analysis of GLC-aromagram data is used to separate several classes of wine distillates, namely cognac, armagnac and brandy. In this paper we demonstrate how this method was used to detect adulteration. The adulteration was confirmed by the presence of ethyl heptanoate and limonene, which are well-known flavour compounds. They were analysed by means of a Purge and Trap headspace technique. Mass spectrometry was used to identify these flavours.
Ein Beispiel für die Verfälschung von Cognac
Zusammenfassung Die Linear-Discriminanz-Analyse von GLC-Aromagramm-Daten wird zur Klassifizierung von Weindestillaten wie Cognac, Armagnac und Brandy verwendet. In dieser Arbeit werden mit dieser Methode Verfälschungen nachgewiesen, die durch die Gegenwart der Ethylester der Heptansäure und des Limonen belegt werden konnten. Diese Substanzen wurden mit der Purge- und Trap-Methode erfaßt und massenspektrometrisch identifiziert.
  相似文献   
184.
For a case-study of a wafer scanner from the semiconductor industry it is shown how model checking techniques can be used to compute (1) a simple yet optimal deadlock avoidance policy, and (2) an infinite schedule that optimizes throughput. in the absence of errors. Deadlock avoidance is studied based on a simple finite state model using Smv, and for throughput analysis a more detailed timed automaton model has been constructed and analyzed using the Uppaal tool. The Smv and Uppaal models are formally related through the notion of a stuttering bisimulation. The results were obtained within 2 weeks, which confirms once more that model checking techniques may help to improve the design process of realistic, industrial systems. Methodologically, the case study is interesting since two models were used to obtain results that could not have been obtained using only a single model. Supported by the European Community Project IST-2001-35304 (Ametist), http://ametist.cs.utwente.nl/.  相似文献   
185.
Multi-field packet classification using ternary CAM   总被引:10,自引:0,他引:10  
A new method for multi-field packet classification using a ternary CAM (TCAM) is presented. It is based on a preprocessing step that encodes classification rule information in the form of prefixes within an intermediate search key. The scheme enables TCAMs to handle larger rule sets more efficiently  相似文献   
186.
187.
Large bone flaps for free transfer can be successfully and safely harvested based on the deep branch of the superior gluteal artery. The anatomy is consistent, the vessels are large, and the complications of this technique are minimal.  相似文献   
188.
High-resolution two-dimensional (2-D) polyacrylamide gel electrophoresis allows the separation of complex biological mixtures (i.e., several hundred proteins from a bacterial cell lysate) in a single experiment. In this report proteins from Haemophilus influenzae were separated by 2-D gels and analyzed by peptide mass fingerprinting and/or amino acid analysis. By comparing the peptide mass profiles and the amino acid composition with the Haemophilus influenzae database, 119 protein spots were identified. The combination of amino acid analysis and peptide mass fingerprinting is a powerful tool for a rapid and economical identification of a large number of proteins resolved by 2-D gels. Studies on gene regulation and changes of protein expression upon drug treatment require quick and serial analysis techniques to efficiently identify potential new drug targets.  相似文献   
189.
Annuloaortic ectasia due to Shprintzen-Goldberg syndrome (SGS) is reported. A 10-year-old boy was admitted to our hospital for evaluation of chest pain. On admission, he was diagnosed as SGS on the basis of his various anomalies. Two-dimensional echocardiography showed a bicuspid aortic valve and marked annular dilatation, Doppler flow studies revealed severe aortic regurgitation, and retrograde aortography showed severe aortic regurgitation with annular dilatation. Successful aortic root replacement was performed; subsequent histologic examination of the ascending aorta demonstrated cystic medial necrosis. In conclusion, SGS is a generalized connective tissue dysplasia, with clinical manifestations of cardiovascular lesions similar to those in Marfan syndrome. Aortic root replacement was successfully performed; however, recurrence of aortic aneurysms outside of the ascending aorta should be carefully observed. Surgical treatment for cardiovascular disorders may be necessary to save the life of patients with SGS.  相似文献   
190.
The TaqIB cholesteryl ester transfer protein (CETP) gene polymorphism (B1B2) is a determinant of HDL cholesterol in nondiabetic populations. Remarkably, this gene effect appears to be modified by environmental factors. We evaluated the effect of this polymorphism on HDL cholesterol levels and on the lipoprotein response to a linoleic acid-enriched, low-cholesterol diet in patients with type 1 diabetes. In 44 consecutive type 1 diabetic patients (35 men), CETP polymorphism, apolipoprotein (apo) E genotype, serum lipoproteins, serum CETP activity (measured with an exogenous substrate assay, n = 30), clinical variables, and a diet history were documented. The 1-year response to diet was assessed in 14 type 1 diabetic patients, including 6 B1B1 and 6 B1B2 individuals. HDL cholesterol was higher in 10 B2B2 than in 14 B1B1 homozygotes (1.63 +/- 0.38 vs. 1.24 +/- 0.23 mmol/l, P < 0.01). HDL cholesterol, adjusted for triglycerides and smoking, was 0.19 mmol/l higher for each B2 allele present. CETP activity levels were not significantly different between CETP genotypes. Multiple regression analysis showed that VLDL + LDL cholesterol was associated with dietary polyunsaturated:saturated fatty acids ratio (P < 0.02) and total fat intake (P < 0.05) in the B1B1 homozygotes only and tended to be related to the presence of the apo E4 allele (P < 0.10). In response to diet, VLDL + LDL cholesterol fell (P < 0.05) and HDL cholesterol remained unchanged in 6 B1B1 homozygotes. In contrast, VLDL + LDL cholesterol was unaltered and HDL cholesterol decreased (P < 0.05) in 6 B1B2 heterozygotes (P < 0.05 for difference in change in VLDL + LDL/HDL cholesterol ratio). This difference in response was unrelated to the apo E genotype. Thus, the TaqIB CETP gene polymorphism is a strong determinant of HDL cholesterol in type 1 diabetes. This gene effect is unlikely to be explained by a major influence on the serum level of CETP activity, as an indirect measure of CETP mass. Our preliminary data suggest that this polymorphism may be a marker of the lipoprotein response to dietary intervention.  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