全文获取类型
收费全文 | 239027篇 |
免费 | 18396篇 |
国内免费 | 9689篇 |
专业分类
电工技术 | 13177篇 |
技术理论 | 25篇 |
综合类 | 14931篇 |
化学工业 | 40273篇 |
金属工艺 | 13720篇 |
机械仪表 | 15158篇 |
建筑科学 | 18330篇 |
矿业工程 | 7805篇 |
能源动力 | 6753篇 |
轻工业 | 14348篇 |
水利工程 | 3808篇 |
石油天然气 | 17011篇 |
武器工业 | 1767篇 |
无线电 | 26372篇 |
一般工业技术 | 28491篇 |
冶金工业 | 13365篇 |
原子能技术 | 2318篇 |
自动化技术 | 29460篇 |
出版年
2024年 | 1044篇 |
2023年 | 3959篇 |
2022年 | 6839篇 |
2021年 | 9556篇 |
2020年 | 7412篇 |
2019年 | 6274篇 |
2018年 | 7018篇 |
2017年 | 7912篇 |
2016年 | 7109篇 |
2015年 | 9279篇 |
2014年 | 11795篇 |
2013年 | 13868篇 |
2012年 | 14933篇 |
2011年 | 16141篇 |
2010年 | 14089篇 |
2009年 | 13352篇 |
2008年 | 12944篇 |
2007年 | 12419篇 |
2006年 | 12832篇 |
2005年 | 11158篇 |
2004年 | 7617篇 |
2003年 | 6550篇 |
2002年 | 5890篇 |
2001年 | 5264篇 |
2000年 | 5682篇 |
1999年 | 6630篇 |
1998年 | 5563篇 |
1997年 | 4545篇 |
1996年 | 4290篇 |
1995年 | 3582篇 |
1994年 | 2889篇 |
1993年 | 2011篇 |
1992年 | 1559篇 |
1991年 | 1250篇 |
1990年 | 952篇 |
1989年 | 758篇 |
1988年 | 549篇 |
1987年 | 345篇 |
1986年 | 287篇 |
1985年 | 202篇 |
1984年 | 144篇 |
1983年 | 114篇 |
1982年 | 127篇 |
1981年 | 100篇 |
1980年 | 74篇 |
1979年 | 37篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 36篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
93.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection. 相似文献
94.
Joel P. Martin J. Edward Swan II Robert J. Moorhead II Zhanping Liu Shangshu Cai 《Computer Graphics Forum》2008,27(3):991-998
We present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter‐clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter‐clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields. 相似文献
95.
Xin Sun Qiang Lu Moroz V. Takeuchi H. Gebara G. Wetzel J. Shuji Ikeda Changhwan Shin Tsu-Jae King Liu 《Electron Device Letters, IEEE》2008,29(5):491-493
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control). 相似文献
96.
Stable social foraging swarms in a noisy environment 总被引:2,自引:0,他引:2
Bacteria, bees, and birds often work together in groups to find food. A group of robots can be designed to coordinate their activities to search for and collect objects. Networked cooperative uninhabited autonomous vehicles are being developed for commercial and military applications. Suppose that we refer to all such groups of entities as "social foraging swarms". In order for such multiagent systems to succeed it is often critical that they can both maintain cohesive behaviors and appropriately respond to environmental stimuli (e.g., by optimizing the acquisition of nutrients in foraging for food). In this paper, we characterize swarm cohesiveness as a stability property and use a Lyapunov approach to develop conditions under which local agent actions will lead to cohesive foraging even in the presence of "noise" characterized by uncertainty on sensing other agent's position and velocity, and in sensing nutrients that each agent is foraging for. The results quantify earlier claims that social foraging is in a certain sense superior to individual foraging when noise is present, and provide clear connections between local agent-agent interactions and emergent group behavior. Moreover, the simulations show that very complicated but orderly group behaviors, reminiscent of those seen in biology, emerge in the presence of noise. 相似文献
97.
98.
相对于传统的数字滤波器实现方法,符号的2次幂和(SPT)滤波器用移位寄存器替代乘法器,因而资源消耗少、速度快,更加适于专用集成电路(ASIC)设计.介绍了一种适用于宽带码分多址(WCDMA)前向信道中给定基带成形滤波器单位脉冲响应后设计SPT滤波器的方法.相对于传统的理想SPT系数优化方法,此方法更适于给定单位脉冲响应后SPT滤波器的设计,计算复杂度低;仿真结果显示,相对于更加简单的四舍五入方法,此算法在性能上又有可观的增益. 相似文献
99.
高可用度的冗余UPS 总被引:1,自引:0,他引:1
简述通信行业标准《通信局(站)电源系统总技术要求》(YD/T1051)对UPS可用度的要求,介绍适用于电信系统的高可用度冗余UPS。 相似文献
100.