全文获取类型
收费全文 | 289785篇 |
免费 | 21483篇 |
国内免费 | 11100篇 |
专业分类
电工技术 | 15391篇 |
技术理论 | 31篇 |
综合类 | 17430篇 |
化学工业 | 50186篇 |
金属工艺 | 16873篇 |
机械仪表 | 18427篇 |
建筑科学 | 22865篇 |
矿业工程 | 9523篇 |
能源动力 | 7954篇 |
轻工业 | 16661篇 |
水利工程 | 4778篇 |
石油天然气 | 20256篇 |
武器工业 | 2234篇 |
无线电 | 31460篇 |
一般工业技术 | 34401篇 |
冶金工业 | 15609篇 |
原子能技术 | 2857篇 |
自动化技术 | 35432篇 |
出版年
2024年 | 1217篇 |
2023年 | 4675篇 |
2022年 | 7916篇 |
2021年 | 11465篇 |
2020年 | 8527篇 |
2019年 | 7270篇 |
2018年 | 8167篇 |
2017年 | 9215篇 |
2016年 | 8023篇 |
2015年 | 11168篇 |
2014年 | 13769篇 |
2013年 | 16444篇 |
2012年 | 17749篇 |
2011年 | 19397篇 |
2010年 | 16747篇 |
2009年 | 15901篇 |
2008年 | 15437篇 |
2007年 | 15083篇 |
2006年 | 15972篇 |
2005年 | 14146篇 |
2004年 | 9046篇 |
2003年 | 7904篇 |
2002年 | 7304篇 |
2001年 | 6483篇 |
2000年 | 7098篇 |
1999年 | 8503篇 |
1998年 | 6969篇 |
1997年 | 5901篇 |
1996年 | 5481篇 |
1995年 | 4531篇 |
1994年 | 3778篇 |
1993年 | 2643篇 |
1992年 | 2137篇 |
1991年 | 1604篇 |
1990年 | 1174篇 |
1989年 | 937篇 |
1988年 | 764篇 |
1987年 | 527篇 |
1986年 | 394篇 |
1985年 | 266篇 |
1984年 | 183篇 |
1983年 | 120篇 |
1982年 | 131篇 |
1981年 | 87篇 |
1980年 | 70篇 |
1979年 | 24篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1965年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
van Driel W.D. van Gils M.A.J. Xuejun Fan Zhang G.Q. Ernst L.J. 《Components and Packaging Technologies, IEEE Transactions on》2008,31(2):260-268
Exposed pad packages were introduced in the late 1980s and early 1990s because of their excellent thermal and electrical performance. Despite these advantages, the exposed pad packages experience a lot of thermo-hygro-mechanical related reliability problems during qualification and testing. Examples are die lift, which occurs predominantly after moisture sensitivity level conditions, and die-attach to leadframe delamination leading to downbond stitch breaks during temperature cycling. In this chapter, nonlinear finite element (FE) models using fracture mechanics based J-integral calculations are used to assess the reliability problems of the exposed pad package family. Using the parametric FE models any geometrical and material effects can be explored to their impact on the occurrence diepad delamination, and dielift. For instance the impact of diepad size is found to be of much less importance as the impact of die thickness is. Using the fracture mechanics approach, the starting location for the delamination from thermo-hygro-mechanical point of view is deducted. The results indicate that when diepad delamination is present, cracks are likely to grow beneath the die and dielift will occur. The interaction between dielift and other failure modes, such as lifted ball bonds, are not found to be very significant. The FE models are combined with simulation-based optimization methods to deduct design guidelines for optimal reliability of the exposed pad family. 相似文献
103.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
104.
Dong Zhang 《Korean Journal of Chemical Engineering》2008,25(5):1205-1207
Ceria-zirconia solid particles have been recognized as a key material of the automotive exhaust catalysts since they can release
and uptake oxygen owing to the rapid reversible oxidation states of cerium between Ce3+ and Ce4+. Several methods have recently been described to prepare the CeO2-ZrO2 solid particles used in the catalysts. In this paper, a new coprecipitation method is used to prepare the CeO2-ZrO2 solid particles. The Ce-Zr alcogel is dried and calcined in flowing N2 not in flowing air under atmospheric pressure. The results show that the ceria-zirconia sample calcined at 650 °C has high
surface area over 90 m2g−1, which drops to 40 m2g−1 following treatment at 900°C. 相似文献
105.
Fan Zhang To-yat Cheung 《IEEE transactions on pattern analysis and machine intelligence》2003,29(1):1-14
The fault-state detection approach for blackbox testing consists of two phases. The first is to bring the system under test (SUT) from its initial state to a targeted state t and the second is to check various specified properties of the SUT at t. This paper investigates the first phase for testing systems specified as observable nondeterministic finite-state machines with probabilistic and weighted transitions. This phase involves two steps. The first step transfers the SUT to some state t' and the second step identifies whether t' is indeed the targeted state t or not. State transfer is achieved by moving the SUT along one of the paths of a transfer tree (TT) and state identification is realized by using diagnosis trees (DT). A theoretical foundation for the existence and characterization of TT and DT with minimum weighted height or minimum average weight is presented. Algorithms for their computation are proposed. 相似文献
106.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
107.
绿色易切削无铅黄铜棒的研制 总被引:10,自引:3,他引:7
铅黄铜广泛应用于水暖卫浴领域,但铅易溶出造成污染。我公司开发研制的HB-20易切削无铅黄铜棒,用铋元素替代铅黄铜中的铅元素,既能达到铅黄铜棒的切削性能和机械性能,又能达到水暖卫浴行业的环保要求。 相似文献
108.
本文运用全面质量管理的方法,对设备故障进行分析,提出预防措施,降低设备故障率,进而取消值班制实现减人增效、系统降本。 相似文献
109.
讨论了直流法在线测量钯氢化物电极电阻时的电化学效应,计算了电解液的共导、测量电流与电解电流引起的浓差电池效应以及电极作为集流体引起的电阻贡献。结果表明:当电极具有高的长度与半径比值、粗糙的表面、高的溶液电导以及大的电解电流时容易引起显著的附加电阻。 相似文献
110.