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   2476篇
  免费   19篇
  国内免费   1篇
电工技术   30篇
综合类   1篇
化学工业   228篇
金属工艺   16篇
机械仪表   30篇
建筑科学   52篇
矿业工程   2篇
能源动力   33篇
轻工业   76篇
水利工程   10篇
石油天然气   2篇
无线电   150篇
一般工业技术   197篇
冶金工业   1524篇
原子能技术   8篇
自动化技术   137篇
  2021年   9篇
  2020年   9篇
  2019年   8篇
  2018年   11篇
  2017年   15篇
  2015年   12篇
  2014年   12篇
  2013年   44篇
  2012年   21篇
  2011年   29篇
  2010年   24篇
  2009年   47篇
  2008年   47篇
  2007年   47篇
  2006年   40篇
  2005年   35篇
  2004年   27篇
  2003年   25篇
  2002年   33篇
  2001年   27篇
  2000年   19篇
  1999年   61篇
  1998年   467篇
  1997年   273篇
  1996年   156篇
  1995年   119篇
  1994年   90篇
  1993年   93篇
  1992年   23篇
  1991年   32篇
  1990年   33篇
  1989年   27篇
  1988年   40篇
  1987年   37篇
  1986年   37篇
  1985年   19篇
  1984年   12篇
  1983年   18篇
  1982年   13篇
  1981年   14篇
  1980年   19篇
  1979年   11篇
  1978年   22篇
  1977年   50篇
  1976年   96篇
  1975年   11篇
  1974年   13篇
  1971年   9篇
  1966年   7篇
  1954年   7篇
排序方式: 共有2496条查询结果,搜索用时 14 毫秒
21.
Air combat scenarios present unique problems where the solution is not obvious. An advanced networked simulation environment can be used to train high-level cognitive air combat skills such as problem solving. A problem in the development of principled and construct oriented assessment is related to determining the level of specificity of the assessment. We present a detailed discussion of the definition of critical competencies associated with combat mission problem solving performance, and we describe our approach to develop and implement an embedded performance assessment system that maps outcomes to these competencies. Finally, we discuss the implications for our approach for comprehensive assessment and discuss our goals for an evaluation of the competency-based approach to assessment.  相似文献   
22.
23.
A monolithic grating surface-emitting, GaAs/AlGaAs, separate-confinement-heterostructure, single-quantum-well diode laser has been fabricated on a Si substrate using a single-step metalorganic chemical vapour deposition process. An output power of 30 mW has been obtained under pulsed operation with a peak emission wavelength of 885 nm.<>  相似文献   
24.
25.
The pyrolytic behavior of inulin, a (2-->1)-linked fructofuranan, is described. Parallel investigations of the pyrolysis of glucose and of fructose were conducted to supplement the inulin results and to aid comparison with previous results from glucans. Effects of neutral and basic additives are emphasized. As with glucans, the addition of such additives (especially basic) increases the yields of the one-, two-, and three-carbon products (as well as of hexosaccharinolactones), while generally decreasing the yields of anhydro sugar and furan derivatives. The former products include glycolaldehyde, acetol, dihydroxy-acetone, acetic acid, formic acid, and lactic acid. Mechanistic speculations are made regarding the origins of these compounds, as well as of furan derivatives and saccharinic acid lactones. Parallels with alkaline degradation are considered.  相似文献   
26.
Reports an error in the original article by P. M. Lewinsohn et al ( Journal of Abnormal Psychology, 1993[Feb], Vol 102[1], 133–244). On page 140, in the Total Incidence columns in Table 4, the data for the Attention Deficit row should be switched with that for the Conduct row. (The following abstract of this article originally appeared in record 1993-25780-001.) Data were collected on the point and lifetime prevalences, 1-yr incidence, and comorbidity of depression with other Diagnostic and Statistical Manual of Mental Disorders-III-Revised (DSM-III-R) disorders in a randomly selected sample (n?=?1,710) of high school students at point of entry and at 1-yr follow-up (n?=?1,508). The Schedule for Affective Disorders and Schizophrenia for School-Age Children was used to collect diagnostic information; 9.6% met criteria for a current disorder, more than 33% had experienced a disorder over their lifetimes, and 31.7% of the latter had experienced a 2nd disorder. High relapse rates were found for all disorders, especially for unipolar depression (18.4%) and substance use (15.0%). Female Ss had significantly higher rates at all age levels for unipolar depression, anxiety disorders, eating disorders, and adjustment disorders; male Ss had higher rates of disruptive behavior disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
27.
28.
29.
30.
Two machine learning techniques were evaluated for automatic design of a rule-based control of functional electrical stimulation (FES) for locomotion of spinal cord injured humans. The task was to learn the invariant characteristics of the relationship between sensory information and the FES-control signal by using off-line supervised training. Sensory signals were recorded using pressure sensors installed in the insoles of a subject's shoes and goniometers attached across the joints of the affected leg. The FES-control consisted of pulses corresponding to time intervals when the subject pressed on the manual push-button to deliver the stimulation during FES-assisted ambulation. The machine learning techniques used were the adaptive logic network (ALN) and the inductive learning algorithm (IL). Results to date suggest that, given the same training data, the IL learned faster than the ALN while both performed the test rapidly. The generalization was estimated by measuring the test errors and it was better with an ALN, especially if past points were used to reflect the time dimension. Both techniques were able to predict future stimulation events. An advantage of the ALN over the IL was that ALN's can be retrained with new data without losing previously collected knowledge. The advantages of the IL over the ALN were that the IL produces small, explicit, comprehensible trees and that the relative importance of each sensory contribution can be quantified  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