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   5959篇
  免费   713篇
  国内免费   276篇
电工技术   77篇
综合类   459篇
化学工业   1007篇
金属工艺   56篇
机械仪表   76篇
建筑科学   442篇
矿业工程   45篇
能源动力   153篇
轻工业   1494篇
水利工程   367篇
石油天然气   93篇
武器工业   16篇
无线电   1106篇
一般工业技术   321篇
冶金工业   283篇
原子能技术   99篇
自动化技术   854篇
  2024年   18篇
  2023年   194篇
  2022年   208篇
  2021年   436篇
  2020年   300篇
  2019年   281篇
  2018年   238篇
  2017年   268篇
  2016年   253篇
  2015年   247篇
  2014年   334篇
  2013年   392篇
  2012年   397篇
  2011年   444篇
  2010年   369篇
  2009年   372篇
  2008年   349篇
  2007年   366篇
  2006年   267篇
  2005年   212篇
  2004年   163篇
  2003年   155篇
  2002年   159篇
  2001年   100篇
  2000年   60篇
  1999年   62篇
  1998年   33篇
  1997年   35篇
  1996年   37篇
  1995年   28篇
  1994年   25篇
  1993年   19篇
  1992年   25篇
  1991年   19篇
  1990年   15篇
  1989年   6篇
  1988年   11篇
  1987年   11篇
  1986年   9篇
  1985年   5篇
  1984年   4篇
  1980年   7篇
  1975年   2篇
  1972年   1篇
  1970年   1篇
  1963年   1篇
  1960年   2篇
  1959年   1篇
  1954年   1篇
  1951年   1篇
排序方式: 共有6948条查询结果,搜索用时 15 毫秒
41.
42.
Organizational structures are complex and vary according to sector, field, and type of business or service. In order to be effective, an organization needs to tailor its activities to the environment in which is it located. Based on contingency perspectives, this study is focused on investigating effective ways to design team diversity and maximize team creativity according to task difficulty levels. Considering the organizational team member as an agent, the study employed a multi-agent simulation method to understand the progress of creative manifestation, by observing the exploration and exploitation activity of team members over certain periods of time. The results first reveal that the level of team diversity influences the amount of creativity manifested by team members’ activities, such as exploration and exploitation. Second, managers have to properly facilitate either exploration or exploitation depending on task difficulty by striking a balance between them.  相似文献   
43.
Given a collection of n locations and a symmetric measure of distance (difference) between each pair of locations, we seek to identify (select) a subset of p locations so as to achieve two distinct objectives. The first objective is to use the selected locations as centers (medians) of p groups that would partition the entire collection and minimize the total distance between the locations and their respective group medians. The second objective is to maximize the minimum distance (diversity) among the selected locations themselves. We study this problem as a multi-objective optimization problem and propose an iterative algorithm to obtain its non-dominated frontier. At each iteration we construct and solve a 0–1 integer programming problem. Through a computational experiment we show that this algorithm is computationally effective for small to medium size instances of the problem. We also propose a Lagrangian heuristic algorithm for solving larger instances of this problem.  相似文献   
44.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel.  相似文献   
45.
Functional mesoporous Mo–SiO2 materials were synthesized by a one‐pot and facile room‐temperature procedure, and characterized by X‐ray diffraction, TEM, Raman spectroscopy, FT‐IR, diffuse reflectance spectra, and BET analysis. The experimental results demonstrated that the mesoporous materials presented a high dispersion of molybdenum species and excellent catalytic activity for the removal of dibenzothiophene (DBT) without organic solvents as extractants. The catalytic performance on different sulfur‐containing compounds was also investigated in detail. After recycling for eight times, the removal of the oxidation desulfurization system could still reach high values. GC‐MS analysis detected the oxidation product of DBT. A mechanism was proposed for the absorptive oxidation process of sulfur compounds.  相似文献   
46.
为了评估北盘江鱼类增殖放流效果,2017~2018年期间采用体外荧光、剪鳍、"T"型标三种标志方法对目标鱼类进行标志放流,通过集中捕捞方式进行回捕调查,集中捕捞时间为2017年7月、2018年8月,捕捞水域为董菁-马马崖-光照-善泥坡库区。结果表明,白甲鱼回捕率较高,为0.82%,其他鱼类均在0.5%左右,其中主要为低龄鱼类,高龄鱼类较少;董菁打邦河及各库尾水域物种丰富度较高,善泥坡高家渡码头和马马崖库区试验库尾物种多样性指数相对较低。建议在以后的增殖放流活动中,加大每年的监测频次。  相似文献   
47.
The microbiological and physicochemical changes of industrially fermented Halkidiki and Conservolea green table olives were determined. Samples were analysed to monitor the population of lactic acid bacteria (LAB), yeasts and Enterobacteriaceae, together with changes in pH, acidity, salinity, colour, lactic acid, acetic acid and ethanol. LAB and yeast species diversity was evaluated at the beginning (1 day), middle (75 days) and final (135 days) stages of fermentation by RAPD-PCR genomic fingerprinting. Results revealed vigorous lactic acid processes as indicated by the dominance of LAB over yeasts. No Enterobacteriaceae could be detected after 30 days. Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) dominated in the beginning of fermentation in both varieties. In the end, Lactiplantibacillus pentosus (formerly Lactobacillus pentosus) and Pediococcus ethanolidurans prevailed in Halkidiki and Conservolea varieties, respectively. As for yeasts, Kluyveromyces lactis/marxianus and Pichia manshurica prevailed at the onset of fermentation in Halkidiki and Conservolea varieties, whereas in the end Pichia membranifaciens dominated in both varieties.  相似文献   
48.
49.
The sociodemographic diversity of residential customers can affect the level of financial risk that an electricity provider experiences in the retail market. To demonstrate the relationship between sociodemographic diversity and financial risk, electricity consumption data drawn from the United Kingdom Power Networks ‘Low Carbon London’ project was analyzed to explore the relationship between sociodemographic diversity and financial risk experienced by electricity retailers. The results show that when increasing the sociodemographic diversity amongst a group of residential customers the effect on financial risk depends on the electricity consumption patterns of individual customers and the relationship of consumption patterns between residential customers. Increasing sociodemographic diversity amongst residential customers with very distinct energy consumption patterns can decrease the overall financial risk associated with the aggregated revenue received from these customers. However, the results showed that adding customers to a customer base without consideration for their sociodemographic background can cause the overall financial risk associated with the aggregated revenue received to change erratically. Whilst previous studies have considered customer diversity and its influence on peak electricity demand, this research advances the state-of-the-art by showing the importance of customer diversity to the financial quantity risk experienced by electricity retailers. This finding has serious implications for electricity providers seeking to mitigate financial risk in the retail electricity market.  相似文献   
50.
淋巴瘤是常见的血液系统恶性肿瘤,对人类健康造成极大的威胁。目前淋巴瘤的治疗方法包括化疗、分子靶向治疗、造血干细胞移植等,但耐药和复发难治仍是待解决的问题。铁死亡是新发现的一种细胞死亡模式,与铁依赖性的脂质过氧化损伤相关。靶向铁死亡为抑制淋巴瘤进展提供了新思路。本文从铁死亡的起始信号、中间事件、效应阶段、防御机制来阐述铁死亡的机制并回顾了铁死亡在淋巴瘤中的研究进展,为铁死亡在淋巴瘤治疗方法的应用方面提供新的思路。  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