全文获取类型
收费全文 | 63795篇 |
免费 | 6106篇 |
国内免费 | 3854篇 |
专业分类
电工技术 | 2625篇 |
技术理论 | 1篇 |
综合类 | 4961篇 |
化学工业 | 16224篇 |
金属工艺 | 7289篇 |
机械仪表 | 2068篇 |
建筑科学 | 3505篇 |
矿业工程 | 2333篇 |
能源动力 | 3201篇 |
轻工业 | 5762篇 |
水利工程 | 1314篇 |
石油天然气 | 3793篇 |
武器工业 | 665篇 |
无线电 | 4579篇 |
一般工业技术 | 6498篇 |
冶金工业 | 3932篇 |
原子能技术 | 1224篇 |
自动化技术 | 3781篇 |
出版年
2024年 | 129篇 |
2023年 | 996篇 |
2022年 | 1630篇 |
2021年 | 2029篇 |
2020年 | 2200篇 |
2019年 | 1974篇 |
2018年 | 1889篇 |
2017年 | 2325篇 |
2016年 | 2382篇 |
2015年 | 2371篇 |
2014年 | 3660篇 |
2013年 | 4088篇 |
2012年 | 4500篇 |
2011年 | 4874篇 |
2010年 | 3615篇 |
2009年 | 3792篇 |
2008年 | 3356篇 |
2007年 | 4144篇 |
2006年 | 3572篇 |
2005年 | 3080篇 |
2004年 | 2636篇 |
2003年 | 2304篇 |
2002年 | 1943篇 |
2001年 | 1703篇 |
2000年 | 1445篇 |
1999年 | 1074篇 |
1998年 | 961篇 |
1997年 | 788篇 |
1996年 | 775篇 |
1995年 | 617篇 |
1994年 | 500篇 |
1993年 | 422篇 |
1992年 | 386篇 |
1991年 | 319篇 |
1990年 | 276篇 |
1989年 | 175篇 |
1988年 | 123篇 |
1987年 | 97篇 |
1986年 | 92篇 |
1985年 | 83篇 |
1984年 | 78篇 |
1983年 | 38篇 |
1982年 | 58篇 |
1981年 | 49篇 |
1980年 | 47篇 |
1979年 | 22篇 |
1978年 | 29篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
74.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations. 相似文献
75.
??In order to reduce the oxidative burning loss of Fe78Si9B13 amorphous ribbon in the recovery process?? the oxidation behavior of Fe78Si9B13 amorphous ribbon was studied. The results show that the oxidation of Fe78Si9B13 amorphous ribbon at high temperature is related to the heating rate. The oxidation weight gain of Fe78Si9B13 amorphous ribbon at 5 and 10K/min from room temperature to 1223K are 44% and 31% respectively. There is an oxide layer with loose texture and a small amount of microcrack at the interface between the sample and atmosphere by SEM. The oxide layer contains a large amount of Fe2O3 and a little SiO2 by XRD. Oxidation kinetics curve shows that the oxidation weight gain of the samples follows a linear rule within 5hours at 1073 and 1173K?? then a parabolic rule. At 1273K?? however?? it only follows a linear rule?? meanwhile the oxidation speed is very fast?? with the oxidation weight gain reaches 40% in 12min. The oxidation weight gain in the amorphous ribbon recycling process can be reduced through cutting down the furnace gas temperature?? compressing the waste ribbon and unqualified products in the packaging process and blowing argon to reduce the partial pressure of oxygen in the furnace. Thus the slag decreases to 9-10g when 1kg waste ribbon is recovered?? and the Si content of liquid alloy increases to 8. 9%. 相似文献
76.
Marijan Herceg Denis Vranješ Ratko Grbić Josip Job 《International Journal of Electronics》2019,106(1):160-172
Transmitted-reference (TR) ultra-wideband (UWB) communication systems have gained increasing popularity for the usage in the low data rate application, due to its non-coherent receiver structure. In conventional TR system, non-coherency at the receiver is achieved by sending reference pulses prior to the data-bearing pulses. Then, at the receiver side, reference pulses are used as template signals for correlation with data-bearing pulses. Therefore, the orthogonality between reference and data pulses is obtained in time division multiple access (TDMA) fashion. However, the implementation of a wideband delay line is very difficult in the current low power integrated circuits. In this paper, a TR method called Chaos-Based TR (CB-TR) is proposed. In the proposed method, chaotic sequences are used to separate the reference and data pulses. Such approach exploits the benefits of chaotic signals, such as non-periodicity, easy-to-generate, impulse-like autocorrelation value and low cross-correlation value. Furthermore, in order to decrease the influence of some negative properties of conventional chaotic maps, a modified chaotic generator (MCS) is proposed. Simulation results over the IEEE 802.15.4a channel model show comparable bit error rate performance to other TR methods. 相似文献
77.
为解决相控阵雷达事件调度问题中调度成功率、时间偏移率与算法时效性三者之间的矛盾,本文提出一种基于分支定界法的调度算法;该算法首先在现有调度结果上调取所有可执行事件,即获得若干"节点",多步递推后由多"层"节点形成若干条备选"分支",扩大解空间范围,提高算法性能;然后通过"删减"操作删减掉收益较低分支,将解空间控制在一适当范围内,减小搜索盲目性,降低算法计算量.仿真实验表明,与基于综合优先级算法的调度结果相比,利用本文算法调度时调度成功率提升了52%;与基于时间指针算法的调度结果相比,本身算法时间偏移率降低了61%;与基于遗传算法的调度结果相比,本文算法调度耗时仅为前者1~2%. 相似文献
78.
In this paper, the oxidation behaviors of DP980 advanced high strength steel (AHSS) are studied during annealing in a hydrogen atmosphere with different temperatures and heating rates. It is revealed that with the increase in holding time, the different heating rates affecting the surface oxide precipitation on the strip surface will be weakened. Mass transfer of Mn in heating, soaking, and cooling stages has been considered to illustrate the effect of heating rate on the oxide morphology of steel. And then, the Wagner model and aluminothermic reaction kinetics were performed to discuss the transition from external to internal and maximum reduction diameter of MnO oxidation. 相似文献
79.
80.
研究了碳纤维进行氧化处理、铺层形式,以及紫外光照射和不同溶液介质浸泡处理等,对碳纤维/乙烯基酯树脂复合材料拉伸性能的影响。结果表明:碳纤维最佳氧化工艺为浓硝酸氧化1 h,空气氧化温度250℃,空气氧化30 min。碳纤维最佳铺层设计为[0°,0°,45°]2s。随紫外光照射时间增加,复合材料拉伸强度呈先增后降趋势,120 h时达最大值。溶液介质浸泡会降低复合材料的拉伸强度。温度相同溶液介质不同时,复合材料在NaOH溶液中拉伸强度降低程度最大,温度提高会加速复合材料失效老化。 相似文献