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   1467篇
  免费   85篇
  国内免费   139篇
  2023年   18篇
  2022年   29篇
  2021年   27篇
  2020年   30篇
  2019年   42篇
  2018年   48篇
  2017年   42篇
  2016年   45篇
  2015年   37篇
  2014年   42篇
  2013年   167篇
  2012年   64篇
  2011年   72篇
  2010年   40篇
  2009年   42篇
  2008年   46篇
  2007年   76篇
  2006年   54篇
  2005年   48篇
  2004年   34篇
  2003年   38篇
  2002年   35篇
  2001年   57篇
  2000年   49篇
  1999年   49篇
  1998年   21篇
  1997年   12篇
  1995年   12篇
  1993年   12篇
  1992年   14篇
  1991年   24篇
  1990年   28篇
  1989年   17篇
  1988年   13篇
  1987年   16篇
  1986年   19篇
  1985年   19篇
  1983年   11篇
  1982年   12篇
  1980年   9篇
  1979年   10篇
  1978年   14篇
  1976年   12篇
  1975年   13篇
  1973年   15篇
  1972年   11篇
  1970年   13篇
  1969年   11篇
  1968年   14篇
  1967年   10篇
排序方式: 共有1691条查询结果,搜索用时 15 毫秒
161.
本研究以200名大学生为被试,以访谈及问卷的方式对大学生心理健康必备能力的认知进行了调查研究,并建立了大学生心理健康必备能力认知结构模型,结果表明:大学生所认知的自己心理健康必备能力由自我调控、社会应对、学习和人际交往这四个方面的能力组成,它们彼此独立,但又相互关联。  相似文献   
162.
163.
Magnesium oxide (MgO) films and particles have been collected by pressurised filtration of a Mg-8.6wt%Al-0.67wt%Zn (AZ91D) alloy melt. The morphology of the oxides and their interfaces with the α-Mg phase were investigated by high-resolution transmission electron microscopy. It was found that the oxide films consisted of large numbers of sub-micrometre-sized MgO particles, and that melt shearing can effectively break up the oxide films and disperse the oxide particles. For the first time, orientation relationships (ORs) of OR I: [1?1?1]MgO~2° from (0?0?0?1)α-Mg and (0?1?1)MgO?//[2?1?1?0)α-Mg; and OR II: (1?1?1)MgO//(1?1?0?1)α-Mg and [0?1?1]MgO//[1?2?1?1]α-Mg, were observed between the MgO particles and the α-Mg matrix. The calculated Bramfitt planar disregistries were 5.5% and 2.5% for the two ORs, respectively, indicating good lattice matching between MgO and α-Mg at the interface. With the evidence of grain refinement effect observed in the sheared AZ91D magnesium alloy, the possibility of MgO particles to act as potent nucleants for heterogeneous nucleation of α-Mg grains is discussed in terms of the crystallographic criterion.  相似文献   
164.
Ti–Al–Zr alloy has been oxidized at 360°C in alkaline steam at a pressure of 10.3?±?0.7?MPa. Cross-sectional transmission electron microscopy (TEM) observations indicated that the oxide scale of Ti–Al–Zr alloy was composed of outer and inner subscales, in which the outer layer consists of anatase-TiO2 and the inner layer a mixture of TiO and Ti2O. The thickness of the Ti2O, TiO and anatase-TiO2 were approximately 50, 100 and 400?nm, respectively. These results were confirmed by X-ray energy dispersive spectrometry (EDS) measurements. The enhanced corrosion of titanium alloys in LiOH solution is attributed to a high hexagonal Ti2O to tetragonal TiO2 phase transformation rate induced by the substitution of Li+ for Ti4+ in the oxide layer.  相似文献   
165.
The compressive deformation and fracture features of Zr59Cu20Al10Ni8Ti3 bulk metallic glassy samples with aspect ratios in the range of 0.67–2.00 have been investigated. The compressive plastic strain of the glass monotonically increases with decreasing aspect ratio, but the maximum strength almost maintains a constant value of 1.77–1.88?GPa. All the compressive shear-band angles are equal to?~40° if modified by the rotation of the primary shear bands.  相似文献   
166.
167.
The grain size variation in a gradient surface produced by a punching and recovery process on a Cu-30Ni alloy has been observed by atomic force microscopy. The friction characteristics of the gradient surface in a 3.5 wt% NaCl solution were investigated using a micro-indenter probe, a pin-on-disc type tribometer, a strain sensor and an optical microscope. The results showed that the hardness and grain size can be well represented by the Hall–Petch relationship when the gain size is more than 30?nm. The wear rate, friction coefficient and adhesive force all increase depth below the surface. These variations are attributed to a gradual increasing grain size with depth. The morphologies of the worn track were also studied to understand further the corrosive wear behaviour of gradient surfaces.  相似文献   
168.
In the current literature, empirical and conceptual distinctions have been drawn between a more or less passive short-term memory (STM) system and a more dynamic working memory (WM) system. Distinct tasks have been developed to measure their capacity and research has generally shown that, for adults, WM, and not STM, is a reliable predictor of general cognitive ability. However, the locus of the differences between the tasks has received little attention. We present data from children concerning measures of matrices reasoning ability, reading, and numerical skill along with forward and backward order serial recall of WM, STM, and STM with articulatory suppression tasks. As indices of children's cognitive skills, STM and WM are shown to be rather similar in terms of memory per se. Neither the opportunity for rehearsal nor task complexity provides satisfactory explanations for differences between memory tests.  相似文献   
169.
Functional magnetic resonance imaging (fMRI) was used to compare directly episodic encoding and retrieval. During encoding, subjects studied visually presented words and reported via keypress whether each word represented a pleasant or unpleasant concept (intentional, deep encoding). During the retrieval phase, subjects indicated (via keypress) whether visually presented words had previously been studied. No reliable differences were found during the recognition phase for words that had been previously studied and those that had not been studied. Areas preferentially active during encoding (relative to retrieval) included left superior frontal cortex, medial frontal cortex, left superior temporal cortex, posterior cingulate, left parahippocampal gyrus, and left inferior frontal gyrus. Regions more active in retrieval than encoding included bilateral inferior parietal cortex, bilateral precuneus, right frontal polar cortex, right dorsolateral prefrontal cortex, and right inferior frontal/insular cortex.  相似文献   
170.
近年来我国部分重点医学院校陆续推出精英教育培养模式,以八年制医学生的培养为代表.临床医学八年制的培养更需要基础医学与临床医学之间相互整合,是完善“八年一贯,本博融通”培养模式的关键.转化医学的出现,为消除基础与临床的屏障,提高八年制医学生基础医学研究水平,加强临床思维培养提供了新的平台和途径.  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