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   26365篇
  免费   2548篇
  国内免费   24篇
电工技术   1456篇
综合类   407篇
化学工业   10309篇
金属工艺   392篇
机械仪表   566篇
建筑科学   1256篇
矿业工程   188篇
能源动力   408篇
轻工业   2545篇
水利工程   224篇
石油天然气   96篇
无线电   1036篇
一般工业技术   4768篇
冶金工业   1460篇
原子能技术   60篇
自动化技术   3766篇
  2023年   678篇
  2022年   435篇
  2021年   851篇
  2020年   812篇
  2019年   758篇
  2018年   764篇
  2017年   597篇
  2016年   842篇
  2015年   989篇
  2014年   1124篇
  2013年   2023篇
  2012年   1066篇
  2011年   1175篇
  2010年   1250篇
  2009年   1358篇
  2008年   985篇
  2007年   885篇
  2006年   703篇
  2005年   650篇
  2004年   544篇
  2003年   507篇
  2002年   383篇
  2001年   262篇
  2000年   223篇
  1999年   234篇
  1998年   330篇
  1997年   286篇
  1996年   333篇
  1995年   300篇
  1994年   251篇
  1993年   307篇
  1992年   234篇
  1991年   183篇
  1990年   229篇
  1989年   238篇
  1988年   179篇
  1987年   223篇
  1986年   236篇
  1985年   226篇
  1984年   221篇
  1983年   243篇
  1982年   207篇
  1981年   245篇
  1980年   202篇
  1979年   210篇
  1976年   176篇
  1975年   224篇
  1974年   202篇
  1973年   378篇
  1972年   221篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Evaluated the validity of self-efficacy expectations as predictors of mortality for 119 patients with chronic obstructive pulmonary disease. Ss completed 4 physiological measures that represent common clinical indicators of disease severity: forced expiratory volume in 1 s(FEV1.0), arterial blood gas measurement of resting partial pressure of oxygen (PaO?), single-breath diffusing capacity (DLCO), and maximum oxygen uptake (V02max) during exercise. In addition, self-reported self-efficacy expectation for walking on a treadmill was measured. Self-efficacy was a significant univariate predictor of 5-yr survival. However, when controlling for FEV1.0 in multivariate survival analysis, self-efficacy had only a marginal effect. Simple self-report scales may provide significant information about health status. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
Investigators have concluded that excessive numbers of errors in test administration and scoring are routinely committed by both graduate students and practicing psychologists. Developing new methods for teaching assessment is viewed as a major means of improving competency. Unlike previous studies, this investigation examined the impact of both lecture and laboratory interventions designed to improve graduate student performance in assessment. Interventions consisted of weekly lecture quizzes and a variety of laboratory interventions. The results suggest that the interventions used can significantly improve students' lecture and laboratory performance when compared with controls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
93.
QUEUE     
Ohne Zusammenfassung  相似文献   
94.
An articulated geometry which overcomes the problem of loss of traction in differentially steered skid tractor automatic guided vehicles is described.  相似文献   
95.
96.
Contents Surface charge accumulation and its decay at a GIS spacer are studied at atmospheric conditions employing a two step-calibration method. The results show that the accumulation saturates within 30 minutes; the dominant mechanism of surface charge accumulation is the drift of charged particles via air, while that of the decay is surface conduction. The characteristics are similar at both polarities.
Sättigungskonzentration und Abklingverhalten der Oberflächenladung an einem mit Gleichspannung beanspruchten Abstandshalter unter atmosphärischen Bedingungen
Übersicht Die Konzentration und das Abklingen von Oberflächenladungen an einem GIS Abstandshalter wurden unter atmosphärischen Bedingungen mit Hilfe eines zweistufigen Kalibrierungsverfahrens untersucht. Die Ergebnisse zeigen eine Sättigung der Ladungskonzentration innerhalb von 30 Minuten. Als Hauptursache der Ladungskonzentration ist die Drift geladener Teilchen in Luft anzusehen, während das Abklingen auf die Oberflächenleitung zurückzuführen ist. Ähnliche Charakteristiken ergeben sich mit beiden Polaritäten.
  相似文献   
97.
Three-dimensional, turbulent fluid flow analysis with computational methods has emerged as a viable tool in the design process of engine components for passenger cars. If applied in the early stages of the component development such analysis can help reduce the product development time drastically, and may support the design engineer to evaluate several competing design aspects before product completion. However the grid generation for complex geometries still poses a difficult and time consuming taks which strongly influences the accuracy of the numerical solution. The present paper studies the numerical solution of the flow in an inlet-manifold of a five-cylinder engine with two intake-ports for each cylinder. A fast and reliable grid generation technique is discussed in detail. The finite volume based Navier-Stokes solver with schemes of first and second order accuracy for the convective terms is used. Numerical results at several mass flow rates and different boundary conditions at the intake ports are compared with measurements. Finally, the computational results are discussed with respect to their applicability to support the design process of an inlet-manifold.  相似文献   
98.
Examined pre- and posttreatment changes in life stressors and social resources and their association with treatment outcomes in a 12-mo follow-up of 424 Ss (aged 18–83 yrs) with unipolar depression. Assessment measures included the Family Environment Scale, Work Environment Scale, and Health and Daily Living Form. As expected, Ss reported significant, multidimensional improvements in their functioning at follow-up. There were modest increases in Ss' social resources but, suprisingly, no overall decrease in stressors. Life stress and resource factors were significantly related to Ss' functioning at follow-up, even after considering the severity of their dysfunction at treatment intake and their length of treatment. Implications for developing a general body of knowledge about the process of recovery and relapse in behavioral disorders are discussed. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
99.
A method is presented for the fully automatic conversion of a general finite element mesh containing triangular elements into a mesh composed of exclusively quadrilateral elements. The initial mesh may be constructed of entirely triangular elements or may consist of a mixture of triangular and quadrilateral elements. The technique used employs heuristic procedures and criteria to selectively combine adjacent triangular elements into quadrilaterals based on preestablished criteria for element quality. Additional procedures are included to eliminate isolated triangles. The methods operates completely without user intervention once the nodal co-ordinates and element connectivity of the original mesh are supplied.  相似文献   
100.
IT/Business alignment   总被引:3,自引:2,他引:1  
Ohne Zusammenfassung
IT/Business alignment
  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