全文获取类型
收费全文 | 128960篇 |
免费 | 13113篇 |
国内免费 | 8546篇 |
专业分类
电工技术 | 10099篇 |
技术理论 | 4篇 |
综合类 | 10562篇 |
化学工业 | 18222篇 |
金属工艺 | 8079篇 |
机械仪表 | 8899篇 |
建筑科学 | 10718篇 |
矿业工程 | 4112篇 |
能源动力 | 3909篇 |
轻工业 | 9165篇 |
水利工程 | 3222篇 |
石油天然气 | 6114篇 |
武器工业 | 1617篇 |
无线电 | 15819篇 |
一般工业技术 | 13637篇 |
冶金工业 | 5107篇 |
原子能技术 | 1923篇 |
自动化技术 | 19411篇 |
出版年
2024年 | 614篇 |
2023年 | 1854篇 |
2022年 | 3726篇 |
2021年 | 5385篇 |
2020年 | 3988篇 |
2019年 | 3312篇 |
2018年 | 3612篇 |
2017年 | 4090篇 |
2016年 | 3756篇 |
2015年 | 5503篇 |
2014年 | 7035篇 |
2013年 | 8058篇 |
2012年 | 9539篇 |
2011年 | 10411篇 |
2010年 | 9797篇 |
2009年 | 9239篇 |
2008年 | 9250篇 |
2007年 | 8917篇 |
2006年 | 8276篇 |
2005年 | 6642篇 |
2004年 | 4915篇 |
2003年 | 4202篇 |
2002年 | 4216篇 |
2001年 | 3605篇 |
2000年 | 2754篇 |
1999年 | 2006篇 |
1998年 | 1223篇 |
1997年 | 1012篇 |
1996年 | 822篇 |
1995年 | 681篇 |
1994年 | 513篇 |
1993年 | 418篇 |
1992年 | 284篇 |
1991年 | 197篇 |
1990年 | 158篇 |
1989年 | 150篇 |
1988年 | 99篇 |
1987年 | 73篇 |
1986年 | 63篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 34篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1959年 | 23篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
易逝品联合采购订货决策分析 总被引:1,自引:0,他引:1
采购联盟成员间的信息不完全,彼此均以对方的期望需求作为对方实际需求的估计.针对易逝品的特点,提出了调剂价格的特殊约束条件并建立了联盟期望利润模型,最后进行了数值仿真.研究表明:联合采购使联盟总体利润得到改善,但不能使联盟成员的利润都得到改善. 相似文献
92.
本文介绍了南钢中板厂将系统工程最优化技术中的随机服务系统理论和可靠性设计方法引入到电气设备的维护和管理工作中,并结合现场实际情况摸索出一套电气设备可靠性保障方法。 相似文献
93.
Strategies to increase CdTe solar-cell voltage 总被引:1,自引:0,他引:1
There is a significant difference in performance between today's highest efficiency of CdTe solar cells and single-crystal cells of comparable band gap. The largest contribution to this difference is the voltage, where the values for the best CdTe cells are about 230 mV below the best GaAs cells when an appropriate adjustment is made for band gap. CdTe voltage and fill-factor are currently compromised by low recombination lifetime (near 1 ns), low hole density (near 1014 cm− 3), and in some cases an excessive back-contact barrier. Numerical simulation is used to evaluate how combinations of lifetime, carrier density, back electron reflection, and interfacial properties affect voltage and cell performance. Two different strategies for improving voltage and performance are explored. 相似文献
94.
基于高抗热震性能的陶瓷刀具材料的微观结构设计 总被引:1,自引:0,他引:1
本文以现有的抗热震断裂和抗热震损伤的评价理论为基础,通过对材料中微裂纹的长度进行预测,从而实现了对陶瓷刀具材料的抗热震性能的微观结构设计。根据此理论对现有材料的抗热震性能的进行预测,预测结果与实际的测量结果相符,验证了该理论的正确性。 相似文献
95.
96.
Chongjin Xie Xiang Liu 《Photonics Technology Letters, IEEE》2003,15(8):1070-1072
We propose a novel polarization-mode dispersion (PMD) compensation scheme for wavelength-division-multiplexing (WDM) systems, in which many WDM channels share one or a few PMD compensators at receiver site. It is shown, both analytically and numerically, that this scheme can achieve virtually the same performance as that using per-channel-based PMD compensation. 相似文献
97.
Xiaofeng Liao Xueming Li Jun Pen Guanrong Chen 《International Journal of Communication Systems》2004,17(5):437-445
In this paper, a simple image secure communication scheme based on the chaotic Chebyshev map and chaos synchronization is proposed. The scheme relies on the excellent correlation property of chaotic sequences, which is very desirable for secure image communication. The results obtained by computer simulation indicate that the transmitted source image can be correctly and reliably recovered using the proposed scheme, even through a noisy channel. Notably, the scheme possesses relatively high security and can be easily implemented. Moreover, the quality of the recovered image is satisfactory, quantified by such common criteria as the bit‐error rate performance. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
98.
99.
Victor Chabanenko Roman Puźniak Adam Nabiałek Sergei Vasiliev Vladimir Rusakov Loh Huanqian Ritta Szymczak Henryk Szymczak Jan Jun Janusz Karpiński Vitaly Finkel 《Journal of Low Temperature Physics》2003,130(3-4):175-191
We present a study of magneto-thermal instabilities in polycrystalline MgB2 superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated. 相似文献
100.
Due to the salient characteristics such as the time-varying and error-prone wireless links, the dynamic and limited bandwidth, the time-varying traffic pattern and user locations, and the energy constraints, it is a challenging task to efficiently support heterogeneous traffic with different quality of service (CoS) requirements in multihop mobile ad hoc networks. In the last few years, many channel-dependent mechanisms are proposed to address this issue based on the cross-layer design philosophy. However, a lot of problems remain before more efficient solutions are found. One of the problems is how to alleviate the conflict between throughput and fairness for different prioritized traffic, especially how to avoid the bandwidth starvation problem for low-priority traffic when the high-priority traffic load is very high. In this paper, we propose a novel scheme named Courtesy Piggybacking to address this problem. With the recognition of interlayer coupling, our Courtesy Piggybacking scheme exploits the channel dynamics and stochastic traffic features to alleviate the conflict. The basic idea is to let the high-priority traffic help the low-priority traffic by sharing unused residual bandwidth with courtesy. Another noteworthy feature of the proposed scheme is its implementation simplicity: The scheme is easy to implement and is applicable in networks using either reservation-based or contention-based MAC protocols. 相似文献