全文获取类型
收费全文 | 3066篇 |
免费 | 285篇 |
国内免费 | 116篇 |
专业分类
电工技术 | 176篇 |
综合类 | 189篇 |
化学工业 | 539篇 |
金属工艺 | 177篇 |
机械仪表 | 137篇 |
建筑科学 | 225篇 |
矿业工程 | 81篇 |
能源动力 | 64篇 |
轻工业 | 163篇 |
水利工程 | 63篇 |
石油天然气 | 201篇 |
武器工业 | 12篇 |
无线电 | 445篇 |
一般工业技术 | 407篇 |
冶金工业 | 180篇 |
原子能技术 | 41篇 |
自动化技术 | 367篇 |
出版年
2024年 | 13篇 |
2023年 | 47篇 |
2022年 | 91篇 |
2021年 | 118篇 |
2020年 | 87篇 |
2019年 | 68篇 |
2018年 | 96篇 |
2017年 | 106篇 |
2016年 | 103篇 |
2015年 | 125篇 |
2014年 | 127篇 |
2013年 | 189篇 |
2012年 | 193篇 |
2011年 | 210篇 |
2010年 | 153篇 |
2009年 | 147篇 |
2008年 | 173篇 |
2007年 | 143篇 |
2006年 | 153篇 |
2005年 | 149篇 |
2004年 | 108篇 |
2003年 | 90篇 |
2002年 | 69篇 |
2001年 | 83篇 |
2000年 | 75篇 |
1999年 | 89篇 |
1998年 | 76篇 |
1997年 | 53篇 |
1996年 | 74篇 |
1995年 | 42篇 |
1994年 | 34篇 |
1993年 | 36篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3467条查询结果,搜索用时 15 毫秒
61.
苯与羰基钼相互作用的密度泛函研究 总被引:1,自引:1,他引:0
用密度泛函理论在B3LYP/LANL2DZ基组水平上自由优化(η~x-C_6H_6)Mo(CO)_n(x=1-6;n=1-5)复合物体系的可能构型及计算相互作用能,探索不同羰基数对复合物稳定性、苯和羰基钼相互作用的影响,并分析苯和羰基钼相互作用的NBO。结论(1)苯以η~6与Mo(CO)_n(n=1-3)配位形成的复合物比较稳定,但η~6配位复合物CO的个数越多,则越不稳定;(2)复合物1、2、3和10中,Mo(CO)_n与苯的相互作用拉动电荷由苯的π键电子向Mo(CO)_n的σ_(Mo-CO)~*键转移,而在复合物7中,苯的π键电子向Mo(CO)_n中Mo的孤对电子轨道d转移。 相似文献
62.
This study proposes a technique based upon Fuzzy C-Means (FCM) classification theory and related fuzzy theories for choosing an appropriate value of the Variable Precision Rough Set (VPRS) threshold parameter (β) when applied to the classification of continuous information systems. The VPRS model is then combined with a moving Average Autoregressive Exogenous (ARX) prediction model and Grey Systems theory to create an automatic stock market forecasting and portfolio selection mechanism. In the proposed mechanism, financial data are collected automatically every quarter and are input to an ARX prediction model to forecast the future trends of the collected data over the next quarter or half-year period. The forecast data are then reduced using a GM(1, N) model, classified using a FCM clustering algorithm, and then supplied to a VPRS classification module which selects appropriate investment stocks in accordance with a pre-determined set of decision-making rules. Finally, a grey relational analysis technique is employed to weight the selected stocks in such a way as to maximize the rate of return of the stock portfolio. The validity of the proposed approach is demonstrated using electronic stock data extracted from the financial database maintained by the Taiwan Economic Journal (TEJ). The portfolio results obtained using the proposed hybrid model are compared with those obtained using a Rough Set (RS) selection model. The effects of the number of attributes of the RS lower approximation set and VPRS β-lower approximation set on the classification are systematically examined and compared. Overall, the results show that the proposed stock forecasting and stock selection mechanism not only yields a greater number of selected stocks in the β-lower approximation set than in the RS approximation set, but also yields a greater rate of return. 相似文献
63.
64.
匡晓雪 《计算机工程与应用》2001,37(1):104-105,118
该文阐述了分布式打印环境的概念和特点,并对Internet打印的思想和技术进行了分析和描述,就IPP的设计和实现提供了基本方法。 相似文献
65.
Wei Kuang Lai 《Parallel and Distributed Systems, IEEE Transactions on》2000,11(8):829-837
In this paper, we present an algorithm for performing permutations of messages on multistage interconnection networks. Permutations of messages are needed in many parallel algorithms. The proposed algorithm is feasible for any networks that can connect each input to each output using a set of N nonblocking connections, where N is the number of ports on the network. Messages are segmented into N submessages that are sent independently in each time step. For any permutation, the settings of switches are changed with fixed patterns. Partitioning of the network into independent subnetworks is also supported, each capable of simultaneously routing a different permutation 相似文献
66.
A. Norman J. Berman K. Brehm M. Drake A. Dyer J. Frisby C. Govil C. Hinchey L. Heuer J. Ke S. Kejriwal K. Kuang S. Keyburn S. Ler K. Powers A. Robertson J. Sanghai C. Schulze J. Schieck J. Sussman L. Tan A. Tello R. Wang K. Yan T. Zeinullayev 《Computational Economics》2012,39(3):243-257
Consumers check few sites in online purchases. Previous research and experiments we perform demonstrate that consumers can not calculate the optimal strategy for price search. They use heuristics whose performance is better than random and less than optimal. To investigate online price search performance we survey student online textbook purchases. Students achieve good performance because they start with a good strategy and online market organization of marketplace and meta-search sites. An important factor is that algorithms at sites searched perform calculations that reduce the computational complexity of the search. 相似文献
67.
人类对太湖湿地利用存在多种形式,但是在特定经济发展阶段的主导地位不同,存在太湖湿地利用阶段的演变,这个演变过程是在人类需求和湖泊湿地资源比较优势的共同作用下实现的,是实现丰富的自然资源对相对稀缺的自然资源的替代,是人造资本对自然资本和自然生产力进行替代的过程,是人类对太湖湿地依附性利用向和谐性利用转变的过程。 相似文献
68.
成钢 《武汉理工大学学报(材料科学英文版)》2013,28(4):840-843
The effects of Dy on the microstructure and magnetic properties of Dy x Co50?x Pt50 alloys were investigated. The XRD results indicate that all the alloys homogenized at 1000 °C contain only a single A1 (fcc) phase, while the alloys annealed at 675 °C consist of a hard-magnetic face-centered-tetragonal (fct) phase and a magnetically soft face-centered-cube (fcc) phase. Maximum values for the coercivity H c and remanence ratio m r were achieved in Dy0.4Co49.6Pt50 alloys annealed at 675 °C for 80 min. For the series of Dy x Co50?x Pt50 alloys annealed at 675 °C for 60 min, H c decreases monotonically with increasing Dy concentration, but m r is first enhanced and then weakened. 相似文献
69.
Obituaries
Grigorii Valentinovich Samsonov 相似文献70.