全文获取类型
收费全文 | 39746篇 |
免费 | 4249篇 |
国内免费 | 2705篇 |
专业分类
电工技术 | 2370篇 |
技术理论 | 1篇 |
综合类 | 3805篇 |
化学工业 | 6088篇 |
金属工艺 | 3081篇 |
机械仪表 | 1752篇 |
建筑科学 | 2800篇 |
矿业工程 | 1859篇 |
能源动力 | 1759篇 |
轻工业 | 3102篇 |
水利工程 | 1183篇 |
石油天然气 | 2457篇 |
武器工业 | 574篇 |
无线电 | 4048篇 |
一般工业技术 | 4284篇 |
冶金工业 | 2827篇 |
原子能技术 | 1014篇 |
自动化技术 | 3696篇 |
出版年
2024年 | 68篇 |
2023年 | 502篇 |
2022年 | 1038篇 |
2021年 | 1256篇 |
2020年 | 1404篇 |
2019年 | 1190篇 |
2018年 | 1176篇 |
2017年 | 1544篇 |
2016年 | 1676篇 |
2015年 | 1699篇 |
2014年 | 2571篇 |
2013年 | 2804篇 |
2012年 | 3146篇 |
2011年 | 3195篇 |
2010年 | 2370篇 |
2009年 | 2303篇 |
2008年 | 2083篇 |
2007年 | 2577篇 |
2006年 | 2155篇 |
2005年 | 1872篇 |
2004年 | 1609篇 |
2003年 | 1384篇 |
2002年 | 1171篇 |
2001年 | 1006篇 |
2000年 | 829篇 |
1999年 | 676篇 |
1998年 | 582篇 |
1997年 | 489篇 |
1996年 | 461篇 |
1995年 | 400篇 |
1994年 | 298篇 |
1993年 | 230篇 |
1992年 | 212篇 |
1991年 | 163篇 |
1990年 | 137篇 |
1989年 | 99篇 |
1988年 | 66篇 |
1987年 | 43篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 9篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 853 毫秒
31.
32.
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
33.
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
34.
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
35.
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
36.
《能源学会志》2020,93(4):1624-1633
Depletion of fossil fuels and stringent emission norms focus attention to discover an evitable source of alternative fuel in order to attribute a significant compensation on conventional fuels. Besides, waste management policies encourage the valorization of different wastes for the production of alternative fuels in order to reduce the challenges of waste management. In this context, pyrolysis has become an emerging trend to convert different wastes into alternate fuel and suitable to be used as a substitute fuel for CI engines. The current investigation provides a sustainable and feasible solution for waste plastic management by widening the gap between global plastic production and plastic waste generation. It investigates the performance and emission of a single cylinder DI four stroke diesel engine using waste plastic oil (WPO) derived from pyrolysis of waste plastics using Zeolite-A as catalyst. Engine load tests have been conducted taking waste plastic oil and subsequently a blend of waste plastic oil by 10%, 20%, and 30% in volume proportions with diesel as fuel. The performance of the test engine in terms of brake thermal efficiency is found marginally higher and brake specific fuel consumption comparatively lowest for 20% WPO-diesel blend than pure diesel. The NOx and HC emission is found lower under low load condition and became higher by increasing the load as compared to diesel. Fuel exergy was significantly increasing after blending of WPO with pure diesel, but exergetic efficiency of the blended fuels followed the reverse trend. However, increase in load of the engine improved the exergetic efficiency. The 20% WPO–diesel blended fuel is found suitable to be used as an alternative fuel for diesel engine. 相似文献
37.
A Takagi-Sugeno adaptive neuro-fuzzy inference system (TSFIS) model is developed and applied to a dataset of wellhead flow-test data for the Resalat oil field located offshore southern Iran, the objective is to assist in the prediction and control of multi-phase flow rates of oil and gas through the wellhead chokes. For this purpose, 182 test data points (Appendix 1) related to the Resalat field are evaluated. In order to predict production flow rate (QL) expressed as stock-tank barrels per day (STB/D), this dataset includes four selected input variables: upstream pressure (Pwh); wellhead choke sizes (D64); gas to liquid ratio (GLR); and, base solids and water including some water-soluble oil emulsion (BS&W). The test data points evaluated include a wide range of oil flow rate conditions and values for the four input variables recorded. The TSFIS algorithm applied involves five data processing steps: a) pre-processing, b) fuzzification, c) rules base and adaptive neuro-fuzzy inference engine, d) defuzzification, and e) post-processing of the fuzzy model. The developed TSFIS model for the Resalat oil field database predicted oil flow rate to a high degree of accuracy (root mean square error = 247 STB/D, correlation coefficient = 0.9987), which improves substantially on the commonly used empirical algorithms used for such predictions. TSFIS can potentially be applied in wellhead choke fuzzy controllers to stabilize flow in specific wells based on real-time input data records. 相似文献
38.
本文以神达朝凯煤矿正在开采的台阶为工程背景,针对该矿在台阶爆破过程中存在着大块率高、根底多的现象,通过改变装药结构的方式对爆破参数进行优化。实践证明,优化后大块率和根底问题的治理效果明显。 相似文献
39.
基于大黑河流域6个气象站1966~2013年气温、降水量、蒸发皿蒸发量、相对湿度和日照时数长期数据系列,采用气候倾向率和滑动t检验法分析了近50年大黑河流域气象要素的变化趋势及变异年份。结果表明,大黑河流域整体呈现暖干气候倾向,气温呈显著增高趋势,变化率为0.43~0.57℃/10a,气温增温变点大致出现了两次,分别在1986、1997年;降水量和蒸发量多呈不显著减少趋势,降水量先减(1981年)后增(1990年),蒸发皿蒸发量先减(1986年)后增(1996年);相对湿度、日照时数多呈显著减小趋势。 相似文献
40.
在流程工业生产中,移动物料计量信息的传输普遍采用电台和无线模块。接收电台周围环境严重影响计量信息的传输效果,尤其是钢结构厂房、电磁干扰区内,数据传输过程中的丢包率、误码率相当严重。本文提出一种多节点分布式传输方法,根据各个生产作业区环境条件设置相应的WIFI节点数,实现对作业区的无线信号覆盖。网络覆盖区内无线模块、PDA终端(PDA)、终端查询设备通过节点工作频段和阵列天线自适应调节,实现数据传输最佳化。铜熔炼生产现场测试表明,此种传输方法可以有效消除周围环境的电磁干扰,数据丢包率低于0.1%。 相似文献