全文获取类型
收费全文 | 429099篇 |
免费 | 33494篇 |
国内免费 | 17893篇 |
专业分类
电工技术 | 23933篇 |
技术理论 | 37篇 |
综合类 | 29241篇 |
化学工业 | 71607篇 |
金属工艺 | 25030篇 |
机械仪表 | 28211篇 |
建筑科学 | 34055篇 |
矿业工程 | 13742篇 |
能源动力 | 11929篇 |
轻工业 | 27254篇 |
水利工程 | 7534篇 |
石油天然气 | 28128篇 |
武器工业 | 3414篇 |
无线电 | 47088篇 |
一般工业技术 | 48817篇 |
冶金工业 | 21409篇 |
原子能技术 | 4528篇 |
自动化技术 | 54529篇 |
出版年
2024年 | 1368篇 |
2023年 | 6064篇 |
2022年 | 10473篇 |
2021年 | 15866篇 |
2020年 | 12048篇 |
2019年 | 10062篇 |
2018年 | 11329篇 |
2017年 | 12915篇 |
2016年 | 11639篇 |
2015年 | 16291篇 |
2014年 | 20497篇 |
2013年 | 24639篇 |
2012年 | 27106篇 |
2011年 | 29468篇 |
2010年 | 25934篇 |
2009年 | 24841篇 |
2008年 | 24302篇 |
2007年 | 23605篇 |
2006年 | 24651篇 |
2005年 | 21637篇 |
2004年 | 14486篇 |
2003年 | 12961篇 |
2002年 | 12816篇 |
2001年 | 11431篇 |
2000年 | 11014篇 |
1999年 | 12020篇 |
1998年 | 9379篇 |
1997年 | 7942篇 |
1996年 | 7498篇 |
1995年 | 6208篇 |
1994年 | 5122篇 |
1993年 | 3537篇 |
1992年 | 2904篇 |
1991年 | 2135篇 |
1990年 | 1587篇 |
1989年 | 1265篇 |
1988年 | 1027篇 |
1987年 | 672篇 |
1986年 | 482篇 |
1985年 | 338篇 |
1984年 | 234篇 |
1983年 | 167篇 |
1982年 | 169篇 |
1981年 | 123篇 |
1980年 | 99篇 |
1979年 | 51篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Fang Wu Yaojiang Zhang Zaw Zaw Oo Erping Li 《Antennas and Propagation Magazine, IEEE》2005,47(4):110-118
The Multilevel Fast Multipole Method (FMM) is a well-established method and can be applied to solve electromagnetic (EM) scattering problems. Compared with other traditional methods, it requires less computational time and memory. However, constrained by a single processor's speed and memory limitations, the problem size that can be solved by serial implementation is still relatively small. For a million-unknown target, the computational time on a single processor is intolerable, and memory could be easily exhausted. Parallel-computing technology, which can utilize multiprocessors, provides an efficient way to solve electrically large-scale EM problems. This paper will focus on discussing the parallel methodologies applied to a multilevel FMM code, as well as demonstrating the computational efficiency of the parallel approach. 相似文献
992.
Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds. 相似文献
993.
对称非线性系统的无交互控制 总被引:1,自引:0,他引:1
本文讨论了具有对称性的非线性系统的无交互控制问题。通过定义对称系统的导出分布族的新概念,我们得出了问题可解的条件。我们取得的结果较不具对称性的情况要简单一些。从而说明,对称性不仅使得系统具有较好的结构,而且使得它的其它一些问题的研究得到简化。 相似文献
994.
In this paper we verified the submodeling technique applied in the thermomechanical reliability assessment of a flip-chip BGA under accelerated thermal cycling test conditions. Since the steady-state creep model was implemented for the solder bump to better represent its realistic mechanical behavior, submodeling procedures developed specifically for path-dependent thermomechanical problems were considered. A detailed global model for the flip-chip BGA was built up to verify submodeling solutions. This model also served as a benchmark to examine solution discrepancies caused by different simplifications of the global model. 相似文献
995.
996.
本文对广钢创建学习型企业和搞好职工培训工作的问题进行了探讨,提出了在创建学习型企业过程中,加强和改进职工培训工作的思路和办法。 相似文献
997.
聚乙烯丙纶复合防水卷材的特点及其应用 总被引:2,自引:0,他引:2
介绍了聚乙烯丙纶复合防水卷材的产品结构特点和性能特点、防水系统结构特点和配套材料、应用拼接技术以及产品应用范围。 相似文献
998.
999.
How to select a generator of Zp* is an important problem in cryptographic applications, where p is an odd prime. In this paper, we mainly consider the especial case that p is a safe prime, and give an algorithm for selecting a generator of Zp*,and find all generators of Zp* , where p is a safe prime. Our algorithm is more faster than the algorithm in [1]. Based on the proposed algorithm, one could find all generators of Zp* as well, where p is a perfect prime. 相似文献
1000.
We present a multiple-channel video transmission scheme in wireless CDMA networks over multipath fading channels. We map an embedded video bitstream, which is encoded into multiple independently decodable layers by 3D-ESCOT video coding technique, to multiple CDMA channels. One video source layer is transmitted over one CDMA channel. Each video source layer is protected by a product channel code structure. A product channel code is obtained by the combination of a row code based on rate compatible punctured convolutional code (RCPC) with cyclic redundancy check (CRC) error detection and a source-channel column code, i.e., systematic rate-compatible Reed-Solomon (RS) style erasure code. For a given budget on the available bandwidth and total transmit power, the transmitter determines the optimal power allocations and the optimal transmission rates among multiple CDMA channels, as well as the optimal product channel code rate allocation, i.e., the optimal unequal Reed-Solomon code source/parity rate allocations and the optimal RCPC rate protection for each channel. In formulating such an optimization problem, we make use of results on the large-system CDMA performance for various multiuser receivers in multipath fading channels. The channel is modeled as the concatenation of wireless BER channel and a wireline packet erasure channel with a fixed packet loss probability. By solving the optimization problem, we obtain the optimal power level allocation and the optimal transmission rate allocation over multiple CDMA channels. For each CDMA channel, we also employ a fast joint source-channel coding algorithm to obtain the optimal product channel code structure. Simulation results show that the proposed framework allows the video quality to degrade gracefully as the fading worsens or the bandwidth decreases, and it offers improved video quality at the receiver. 相似文献