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   532793篇
  免费   7513篇
  国内免费   1547篇
电工技术   9719篇
综合类   614篇
化学工业   80055篇
金属工艺   20148篇
机械仪表   15440篇
建筑科学   12971篇
矿业工程   2282篇
能源动力   14779篇
轻工业   47457篇
水利工程   5252篇
石油天然气   9378篇
武器工业   39篇
无线电   61313篇
一般工业技术   103103篇
冶金工业   104548篇
原子能技术   10630篇
自动化技术   44125篇
  2022年   3283篇
  2021年   5073篇
  2020年   3615篇
  2019年   4676篇
  2018年   7987篇
  2017年   7791篇
  2016年   8113篇
  2015年   5737篇
  2014年   9509篇
  2013年   24542篇
  2012年   15020篇
  2011年   20570篇
  2010年   16136篇
  2009年   18086篇
  2008年   18475篇
  2007年   18116篇
  2006年   15809篇
  2005年   14467篇
  2004年   13842篇
  2003年   13637篇
  2002年   12840篇
  2001年   13005篇
  2000年   12024篇
  1999年   12756篇
  1998年   33204篇
  1997年   23163篇
  1996年   17623篇
  1995年   13154篇
  1994年   11386篇
  1993年   11085篇
  1992年   7973篇
  1991年   7486篇
  1990年   7319篇
  1989年   7053篇
  1988年   6510篇
  1987年   5813篇
  1986年   5707篇
  1985年   6290篇
  1984年   5924篇
  1983年   5187篇
  1982年   4907篇
  1981年   4999篇
  1980年   4722篇
  1979年   4627篇
  1978年   4430篇
  1977年   5368篇
  1976年   7007篇
  1975年   3806篇
  1974年   3559篇
  1973年   3671篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances.  相似文献   
2.
3.
4.
Programming and Computer Software - Image segmentation using a hierarchical sequence of piecewise constant approximations that minimally differ from the original image in terms of the total squared...  相似文献   
5.
6.
7.
8.
9.
10.
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance.  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