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   22941篇
  免费   795篇
  国内免费   84篇
电工技术   293篇
综合类   44篇
化学工业   5146篇
金属工艺   478篇
机械仪表   461篇
建筑科学   1720篇
矿业工程   160篇
能源动力   686篇
轻工业   2135篇
水利工程   182篇
石油天然气   56篇
武器工业   1篇
无线电   1483篇
一般工业技术   4226篇
冶金工业   2771篇
原子能技术   137篇
自动化技术   3841篇
  2023年   152篇
  2022年   308篇
  2021年   534篇
  2020年   312篇
  2019年   327篇
  2018年   493篇
  2017年   426篇
  2016年   533篇
  2015年   481篇
  2014年   691篇
  2013年   1508篇
  2012年   1086篇
  2011年   1522篇
  2010年   1095篇
  2009年   1045篇
  2008年   1270篇
  2007年   1101篇
  2006年   939篇
  2005年   869篇
  2004年   778篇
  2003年   694篇
  2002年   663篇
  2001年   395篇
  2000年   378篇
  1999年   414篇
  1998年   411篇
  1997年   372篇
  1996年   344篇
  1995年   298篇
  1994年   302篇
  1993年   300篇
  1992年   251篇
  1991年   214篇
  1990年   202篇
  1989年   230篇
  1988年   187篇
  1987年   178篇
  1986年   175篇
  1985年   239篇
  1984年   214篇
  1983年   184篇
  1982年   168篇
  1981年   195篇
  1980年   130篇
  1979年   147篇
  1978年   143篇
  1977年   127篇
  1976年   138篇
  1975年   120篇
  1974年   105篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Evaluated the impact of pretreatment depression severity and functional impairment on the response of 2 samples of older depressed adolescents (115 Ss total divided into low-severity groups and high-severity groups) to 2 group cognitive-behavioral treatments. Differences between the 2 active treatments and between active treatment and a waiting-list control condition were expected to be greater in the more severely depressed-impaired group. Improvement for the 2 active treatments in comparison to the control condition was greater in the more severely depressed group in one of the samples but not the other. The prediction that the relative effectiveness of the 2 treatments would be accentuated in the more severely depressed adolescents received no support in either sample. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
84.
In a prospective study of adolescent depression, adolescents (N?=?1,508) were assessed at Time 1 and after 1 yr (Time 2) on psychosocial variables hypothesized to be associated with depression. Most psychosocial variables were associated with current (n?=?45) depression. Formerly depressed adolescents (n?=?217) continued to differ from never depressed controls on many of the psychosocial variables. Many of the depression-related measures also acted as risk factors for future depression (n?=?112), especially past depression, current other mental disorders, past suicide attempt, internalizing behavior problems, and physical symptoms. Young women were more likely to be, to become, and to have been depressed. Controlling for the psychosocial variables eliminated the gender difference for current and future but not for past depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
85.
Reviews the research concerning the possible functional roles of the prosodic aspects of infant-directed speech ("baby-talk"), and shows that this style of speaking could have both attentional and affective functions (in addition to linguistic ones). Studies of other speech registers could profit from taking similar approaches and even using similar techniques to those used in infant-directed speech research to tease apart the linguistic, attentional, and affective components of these other speaking styles. Nursing-home register is used to exemplify the importance of examining the social, emotional, and linguistic ramifications of a communication style separately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
86.
Electrochemical impedance spectroscopy was used to determine the effective charge transfer resistances of porous dye-sensitized solar cell counter electrodes prepared by low-temperature spray deposition and compression of conductive carbon and platinized Sb-doped SnO2 powders on indium tin oxide-coated plastic substrates. The charge transfer resistances were 0.5–2 and 8–13 Ω cm2, respectively, when using 3-methoxypropionitrile as the electrolyte solvent. The manufacturing method used lends itself to produce mechanically stable and even-quality electrodes in an easy and fast manner.  相似文献   
87.
88.
Encompassing such versatile analytical techniques as scanning tunneling microscopy and atomic (or scanning) force microscopy, scanning probe microscopes produce high-resolution three-dimensional images. Because of their power as quantitative tools for three-dimensional surface measurement and analysis, the techniques are being used in materials science and engineering for the study of a variety of advanced materials and for investigations into numerous phenomena, including reaction chemistry, crystallinity, kinetics, equilibrium processes, tribology, and conductivity.  相似文献   
89.
The Revised Memory and Behavior Problems Checklist (RMBPC), a 24-item, caregiver-report measure of observable behavioral problems in dementia patients, provides 1 total score and 3 subscale scores for S problems (memory-related, depression, and disruptive behaviors) and parallel scores for caregiver reaction. Data were obtained from 201 geriatric Ss and their caregivers. Factor analysis confirmed 3 1st-order factors, consistent with subscales just named, and 1 general factor of behavioral disturbance. Overall scale reliability was good, with alphas of .84 for S behavior and .90 for caregiver reaction. Subscale alphas ranged from .67 to .89. Validity was confirmed through comparison of RMBPC scores with well-established indexes of depression, cognitive impairment, and caregiver burden. The RMBPC is recommended as a reliable and valid tool for the clinical and empirical assessment of behavior problems in dementia Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
90.
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   
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