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   8752篇
  免费   540篇
  国内免费   308篇
电工技术   839篇
技术理论   1篇
综合类   1119篇
化学工业   411篇
金属工艺   244篇
机械仪表   488篇
建筑科学   794篇
矿业工程   331篇
能源动力   252篇
轻工业   221篇
水利工程   262篇
石油天然气   502篇
武器工业   36篇
无线电   458篇
一般工业技术   353篇
冶金工业   2346篇
原子能技术   51篇
自动化技术   892篇
  2024年   19篇
  2023年   59篇
  2022年   129篇
  2021年   145篇
  2020年   201篇
  2019年   139篇
  2018年   131篇
  2017年   150篇
  2016年   183篇
  2015年   234篇
  2014年   420篇
  2013年   362篇
  2012年   569篇
  2011年   685篇
  2010年   557篇
  2009年   513篇
  2008年   458篇
  2007年   598篇
  2006年   592篇
  2005年   538篇
  2004年   469篇
  2003年   475篇
  2002年   371篇
  2001年   302篇
  2000年   176篇
  1999年   127篇
  1998年   97篇
  1997年   79篇
  1996年   71篇
  1995年   57篇
  1994年   49篇
  1993年   32篇
  1992年   23篇
  1990年   25篇
  1989年   23篇
  1988年   21篇
  1987年   19篇
  1966年   17篇
  1965年   56篇
  1964年   32篇
  1963年   16篇
  1962年   27篇
  1961年   23篇
  1960年   20篇
  1959年   32篇
  1958年   22篇
  1957年   26篇
  1956年   21篇
  1955年   31篇
  1954年   23篇
排序方式: 共有9600条查询结果,搜索用时 31 毫秒
1.
Adult neurogenesis is a highly regulated process during which new neurons are generated from neural stem cells in two discrete regions of the adult brain: the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. Defects of adult hippocampal neurogenesis have been linked to cognitive decline and dysfunction during natural aging and in neurodegenerative diseases, as well as psychological stress-induced mood disorders. Understanding the mechanisms and pathways that regulate adult neurogenesis is crucial to improving preventative measures and therapies for these conditions. Accumulating evidence shows that mitochondria directly regulate various steps and phases of adult neurogenesis. This review summarizes recent findings on how mitochondrial metabolism, dynamics, and reactive oxygen species control several aspects of adult neural stem cell function and their differentiation to newborn neurons. It also discusses the importance of autophagy for adult neurogenesis, and how mitochondrial and autophagic dysfunction may contribute to cognitive defects and stress-induced mood disorders by compromising adult neurogenesis. Finally, I suggest possible ways to target mitochondrial function as a strategy for stem cell-based interventions and treatments for cognitive and mood disorders.  相似文献   
2.
Data fitting with B-splines is a challenging problem in reverse engineering for CAD/CAM, virtual reality, data visualization, and many other fields. It is well-known that the fitting improves greatly if knots are considered as free variables. This leads, however, to a very difficult multimodal and multivariate continuous nonlinear optimization problem, the so-called knot adjustment problem. In this context, the present paper introduces an adapted elitist clonal selection algorithm for automatic knot adjustment of B-spline curves. Given a set of noisy data points, our method determines the number and location of knots automatically in order to obtain an extremely accurate fitting of data. In addition, our method minimizes the number of parameters required for this task. Our approach performs very well and in a fully automatic way even for the cases of underlying functions requiring identical multiple knots, such as functions with discontinuities and cusps. To evaluate its performance, it has been applied to three challenging test functions, and results have been compared with those from other alternative methods based on AIS and genetic algorithms. Our experimental results show that our proposal outperforms previous approaches in terms of accuracy and flexibility. Some other issues such as the parameter tuning, the complexity of the algorithm, and the CPU runtime are also discussed.  相似文献   
3.
Although previous research has investigated widespread use of social media, especially Facebook, by youth attending college, the conditions under which these media foster adjustment to college remain unclear. This study tested a model illuminating pathways linking social competence to college adjustment via students’ perceptions about the usefulness of Facebook and ways in which they used the medium. Self-report survey data from 321 college students (M age = 20.09; 58% female; 84% Caucasian) attending a major Midwestern university supported the proposed model, indicating that higher social competence could foster or impede college adjustment, depending upon how it was related to beliefs about the usefulness of different Facebook functions and how these perceptions, in turn, were associated with patterns of Facebook use. Findings underscore the importance of considering connections among personal attributes, perception of media effectiveness, and media behaviors in assessing the implications of social media for users’ psychosocial well-being.  相似文献   
4.
M1080B无心外圆磨床砂轮及导轮宽度较窄,磨削轴承套圈外圆时,磨削效率低,托板架调整较为繁琐、皮带打滑、磨损较为严重。针对上述问题,提出了相应的解决办法,提高了磨削效率。  相似文献   
5.
心理测试的根本目的是为了让人们在测试过程中,产生某些特定行为,即个体对测试题目的反应,并根据这些行为反应来推论其相应的心理特性。在一定程度上帮助我们了解人类的心理活动,并从中得到帮助。因此,本文对基于学生群体心理测试系统的设计进行深入研究。  相似文献   
6.
运用过程中各类相关因子的变化,会使得机车柴油机配气相位出现一定程度变化,采取某种措施调整或是处理可以解决动力不足的问题。  相似文献   
7.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking.  相似文献   
8.
The polymer electrolyte based solid-state lithium metal batteries are the promising candidate for the high-energy electrochemical energy storage with high safety and stability. Moreover, the intrinsic properties of polymer electrolytes and interface contact between electrolyte and electrodes have played critical roles for determining the comprehensive performances of solid-state lithium metal batteries. In this review, the development of polymer electrolytes with the design strategies by functional units adjustments are firstly discussed. Then the interfaces between polymer electrolyte and cathode/anode, including the interface issues, remedy strategies for stabilizing the interface contact and reducing resistances, and the in-situ polymerization method for enhancing the compatibilities and assembling the batteries with favorable performances, have been introduced. Lastly, the perspectives on developing polymer electrolytes by functional units adjustment, and improving interface contact and stability by effective strategies for solid-state lithium metal batteries have been provided.  相似文献   
9.
论激励教育     
分析了高职学生的心理、惩罚教育的弊端,并从理论、心理、现实论述的基础上提出应大力提倡激励教育.  相似文献   
10.
分层注水井智能测试调配技术试验评价   总被引:3,自引:0,他引:3  
注水井智能测试调配技术在不改变原注水管柱的基础上,利用井下可调式堵塞器,通过地面电脑控制,实现了测试调配同步进行。通过7口井的现场试验及分析评价,表明该工艺具有测调精度高、测调时间短、测试资料准确等特点。  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