全文获取类型
收费全文 | 5959篇 |
免费 | 713篇 |
国内免费 | 276篇 |
专业分类
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 |
出版年
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.
Enhanced Oxidative Desulfurization of Dibenzothiophene by Functional Mo‐Containing Mesoporous Silica 下载免费PDF全文
Ming Zhang Wenshuai Zhu Suhang Xun Jun Xiong Wenjing Ding Meng Li Qian Wang Huaming Li 《化学工程与技术》2015,38(1):117-124
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.
Aikaterini P. Tzamourani Elisa Di Napoli Spiros Paramithiotis Georgios Economou-Petrovits Stavros Panagiotidis Efstathios Z. Panagou 《International Journal of Food Science & Technology》2021,56(8):3845-3857
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.