全文获取类型
收费全文 | 74550篇 |
免费 | 8618篇 |
国内免费 | 4492篇 |
专业分类
电工技术 | 6363篇 |
技术理论 | 5篇 |
综合类 | 5635篇 |
化学工业 | 11241篇 |
金属工艺 | 4465篇 |
机械仪表 | 5001篇 |
建筑科学 | 6002篇 |
矿业工程 | 2470篇 |
能源动力 | 2199篇 |
轻工业 | 5534篇 |
水利工程 | 1797篇 |
石油天然气 | 4171篇 |
武器工业 | 856篇 |
无线电 | 8996篇 |
一般工业技术 | 8347篇 |
冶金工业 | 2915篇 |
原子能技术 | 765篇 |
自动化技术 | 10898篇 |
出版年
2024年 | 396篇 |
2023年 | 1772篇 |
2022年 | 3306篇 |
2021年 | 4686篇 |
2020年 | 3377篇 |
2019年 | 2533篇 |
2018年 | 2638篇 |
2017年 | 2888篇 |
2016年 | 2537篇 |
2015年 | 3580篇 |
2014年 | 4226篇 |
2013年 | 4846篇 |
2012年 | 5453篇 |
2011年 | 5697篇 |
2010年 | 4900篇 |
2009年 | 4567篇 |
2008年 | 4534篇 |
2007年 | 4137篇 |
2006年 | 3844篇 |
2005年 | 3366篇 |
2004年 | 2135篇 |
2003年 | 1783篇 |
2002年 | 1762篇 |
2001年 | 1519篇 |
2000年 | 1321篇 |
1999年 | 1287篇 |
1998年 | 890篇 |
1997年 | 743篇 |
1996年 | 668篇 |
1995年 | 556篇 |
1994年 | 455篇 |
1993年 | 292篇 |
1992年 | 240篇 |
1991年 | 165篇 |
1990年 | 136篇 |
1989年 | 100篇 |
1988年 | 73篇 |
1987年 | 60篇 |
1986年 | 55篇 |
1985年 | 28篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 2篇 |
1959年 | 8篇 |
1953年 | 1篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Tian Xiao Qing Huo Liu 《Antennas and Propagation, IEEE Transactions on》2008,56(3):765-773
In this paper, we present an enlarged cell technique (ECT) to avoid the time step reduction encountered in the conformal finite-difference time-domain (CFDTD) method due to small irregular cells truncated by metallic boundaries. We focus our efforts on the discussion of the accuracy and stability of the ECT and its comparison with other conformal methods, especially the one called the uniformly stable conformal (USC) method. We also provide a simplified ECT, which is much easier to implement. In the ECT, a stability criterion is first constructed to identify instable irregular cells, i.e., those having so small an area to cause instability. Those instable cells are then enlarged into their adjacent cells to obtain a large, stable area. Careful treatment is performed on the communication between the intruding and intruded cells in terms of electromotive force by keeping the total electromotive force conservative. This technique is verified by several 3-D numerical experiments. Results show that the ECT is second-order accurate and numerically stable at the regular Courant time step limit. 相似文献
143.
数控车床的回转刀架故障发生频繁,影响零部件的加工.通过对电动回转刀架的电气控制原理分析,结合实际的维修经验,提出相应的维修方法及措施. 相似文献
144.
MIP-CGP工艺专用催化剂CGP-1的开发与应用 总被引:11,自引:3,他引:8
阐述了生产汽油组分满足欧Ⅲ排放标准并多产丙烯的催化裂化工艺(简称MIP-CGP)专用催化剂(简称CGP-1)的研究开发与工业应用结果。CGP-1催化剂的基质具有良好的容炭性能,使活性组元受到良好保护,其优势作用在第二反应区得以充分发挥,具有更高的氢转移活性和强的汽油小分子烯烃裂化活性。中国石化九江分公司和镇海炼化公司的MIP-CGP工业试验标定结果表明,与常规FCC相比,采用CGP-1催化剂的MIP-CGP技术在生产烯烃体积分数小于18%的汽油组分的同时,丙烯产率达到8%以上。此外,汽油诱导期大幅提高,抗爆指数增加;总液体收率有所提高,干气产率下降,焦炭选择性良好。 相似文献
145.
镍氢电池负极用低成本储氢合金的研究 总被引:1,自引:0,他引:1
研究了ABS型储氢合金在低Co含量条件下,随B组元替代元素Co,Al,Si等含量的变化对合金电化学性能的影响规律,同时研究了A组元中不同La/Ce比对合金电化学性能的影响情况。结果表明,随合金中Co含量的降低,合金的活化性能和放电容量得以改善,但合金的循环寿命下降也比较明显;在试验范围内,随Al元素的加入,合金的循环寿命得以改善,但材料的放电容量和活化性能均有所下降;随合金La/Ce比的降低,合金的放电容量略有下降,但其循环寿命和放电电压平台有较大提高。 相似文献
146.
Y. L. Hao R. Yang M. Niinomi D. Kuroda Y. L. Zhou K. Fukunaga A. Suzuki 《Metallurgical and Materials Transactions A》2003,34(4):1007-1012
Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible
with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures,
and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is
found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility.
The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For
an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties. 相似文献
147.
Bingyong Yan Zuohua Tian Songjiao Shi 《International Journal of Electrical Power & Energy Systems》2008,30(5):343-360
In this paper, we propose a novel distributed robust fault detection and identification (RFDI) scheme for a class of nonlinear systems. Firstly, a detection and identification estimator—robust fault tracking approximator (RFTA) is designed for online health monitoring. A novel feature of the RFTA is that it can simultaneously detect and accurately identify the shape and magnitude of the fault and disturbance. Moreover, it takes less online training time compared with the traditional neural network based fault diagnosis schemes. For some distributed systems, a network of distributed estimators is constructed where the RFTA is embedded into each estimator. Then we use consensus filter to filter the outputs of each estimator. One of the most important merits of the consensus filter is that its outputs can dramatically improve the accuracy of fault detection and identification. Next, the stability of the distributed RFDI scheme is rigorously investigated. Finally, two numerical examples are given to illustrate the feasibility and effectiveness of the proposed approach. 相似文献
148.
149.
150.
Yanqing Ji Hao Ying John Yen Shizhuo Zhu Daniel C. Barth‐Jones Richard E. Miller R. Michael Massanari 《国际智能系统杂志》2007,22(8):827-845
Discovering unknown adverse drug reactions (ADRs) in postmarketing surveillance as early as possible is highly desirable. Nevertheless, current postmarketing surveillance methods largely rely on spontaneous reports that suffer from serious underreporting, latency, and inconsistent reporting. Thus these methods are not ideal for rapidly identifying rare ADRs. The multiagent systems paradigm is an emerging and effective approach to tackling distributed problems, especially when data sources and knowledge are geographically located in different places and coordination and collaboration are necessary for decision making. In this article, we propose an active, multiagent framework for early detection of ADRs by utilizing electronic patient data distributed across many different sources and locations. In this framework, intelligent agents assist a team of experts based on the well‐known human decision‐making model called Recognition‐Primed Decision (RPD). We generalize the RPD model to a fuzzy RPD model and utilize fuzzy logic technology to not only represent, interpret, and compute imprecise and subjective cues that are commonly encountered in the ADR problem but also to retrieve prior experiences by evaluating the extent of matching between the current situation and a past experience. We describe our preliminary multiagent system design and illustrate its potential benefits for assisting expert teams in early detection of previously unknown ADRs. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 827–845, 2007. 相似文献