全文获取类型
收费全文 | 66468篇 |
免费 | 6849篇 |
国内免费 | 4242篇 |
专业分类
电工技术 | 5228篇 |
技术理论 | 4篇 |
综合类 | 5674篇 |
化学工业 | 9654篇 |
金属工艺 | 4107篇 |
机械仪表 | 4330篇 |
建筑科学 | 5198篇 |
矿业工程 | 1969篇 |
能源动力 | 1793篇 |
轻工业 | 7296篇 |
水利工程 | 1655篇 |
石油天然气 | 3070篇 |
武器工业 | 796篇 |
无线电 | 7440篇 |
一般工业技术 | 6516篇 |
冶金工业 | 2523篇 |
原子能技术 | 754篇 |
自动化技术 | 9552篇 |
出版年
2024年 | 283篇 |
2023年 | 1055篇 |
2022年 | 2179篇 |
2021年 | 2888篇 |
2020年 | 2221篇 |
2019年 | 1725篇 |
2018年 | 1979篇 |
2017年 | 2161篇 |
2016年 | 2015篇 |
2015年 | 3044篇 |
2014年 | 3706篇 |
2013年 | 4404篇 |
2012年 | 5276篇 |
2011年 | 5662篇 |
2010年 | 5167篇 |
2009年 | 4852篇 |
2008年 | 4945篇 |
2007年 | 4564篇 |
2006年 | 4050篇 |
2005年 | 3240篇 |
2004年 | 2336篇 |
2003年 | 1934篇 |
2002年 | 1854篇 |
2001年 | 1578篇 |
2000年 | 1129篇 |
1999年 | 831篇 |
1998年 | 528篇 |
1997年 | 439篇 |
1996年 | 348篇 |
1995年 | 286篇 |
1994年 | 206篇 |
1993年 | 154篇 |
1992年 | 105篇 |
1991年 | 110篇 |
1990年 | 95篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1979年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1959年 | 9篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
22.
Ting Liu Huimin Zhang Panfei Ma Aimin Chang Hui Jiang 《Journal of the American Ceramic Society》2019,102(8):4393-4398
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics. 相似文献
23.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
24.
In this article, two novel kinds of focusing elements as reflectors are analyzed and compared. One is the grooved Fresnel zone plate reflector with continuous phase‐correcting. The other called subzone paraboloid reflector, has the profile that consists of a series of paraboloids. Their diffraction efficiencies and bandwidths are described. The two elements still preserve the advantages of Fresnel zone plates, namely, low profile, high efficiency, and simple fabrication. Two dual‐reflector antennas using the proposed focusing elements as the main reflectors are simulated and the results show that these antennas have good radiation performances. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:101–108, 2015. 相似文献
25.
在高压耐压实验中,由于施加耐压较大(可达额定电压的3倍),因此常遇到实验线路对设备或对地距离不够导致实验中发生放电或实验数据测试异常的情况.为了保证实验线路对设备或对地有足够的距离,常用绝缘操作杆将高压实验线路挑起或用绝缘带拉紧高压实验线使其悬空,既费时费力又不安全,尤其在刮风天气极易造成绝缘杆滑落、塑料带摆动等,导致实验数据不准确,影响判断.这种情况下,就必须进行多次实验,降低了工作效率.为此研制一款功能完善、能有效解决现场实验困难的实验线支撑工具,以达到提高工作效率和安全性的目的. 相似文献
26.
Zhang Xi Wang Xianhai Zhao Hongke Ordóñez de Pablos Patricia Sun Yongqiang Xiong Hui 《Scientometrics》2019,119(3):1311-1344
Scientometrics - Altmetrics indices are increasingly applied to measure scholarly influence in recent years because they can reflect the influence of research outputs more timely comparing with... 相似文献
27.
性能效率是APP软件的重要质量属性,但目前缺乏APP软件性能效率的通用模型。分析了APP软件的性能特征,基于ISO/IEC 25010标准提出了APP软件的性能效率模型,定义了APP软件性能效率的子特性和度量指标。基于提出的APP软件性能效率模型,通过实验对APP软件的性能效率进行了度量及相关分析。 相似文献
28.
Junling Guo Huayu Pei Ying Dou Siyuan Zhao Guosheng Shao Jinping Liu 《Advanced functional materials》2021,31(18):2010499
Lithium-sulfur batteries (LSBs) are considered a promising next-generation energy storage device owing to their high theoretical energy density. However, their overall performance is limited by several critical issues such as lithium polysulfide (PS) shuttles, low sulfur utilization, and unstable Li metal anodes. Despite recent huge progress, the electrolyte/sulfur ratio (E/S) used is usually very high (≥20 µL mg−1), which greatly reduces the practical energy density of devices. To push forward LSBs from the lab to the industry, considerable attention is devoted to reducing E/S while ensuring the electrochemical performance. To date, however, few reviews have comprehensively elucidated the possible strategies to achieve that purpose. In this review, recent advances in low E/S cathodes and anodes based on the issues resulting from low E/S and the corresponding solutions are summarized. These will be beneficial for a systematic understanding of the rational design ideas and research trends of low E/S LSBs. In particular, three strategies are proposed for cathodes: preventing PS formation/aggregation to avoid inadequate dissolution, designing multifunctional macroporous networks to address incomplete infiltration, and utilizing an imprison strategy to relieve the adsorption dependence on specific surface area. Finally, the challenges and future prospects for low E/S LSBs are discussed. 相似文献
29.
30.
Xueli Chen Ke Liu Qianwan Qin Zhenlu Yu Meiqing Li Xingyu Qu Yu Zhou Aichun Dou Mingru Su Yunjian Liu 《Ceramics International》2021,47(11):15400-15407
With excellent specific capacity, superior cycle stability, safety and strong practical, Nb2O5 has been considered as one of the prospective anode materials for lithium-ion batteries (LIBs). However, current study suggests that Nb2O5 electrode materials for LIBs still face the vital issues of low electrical conductivity and poor rate performance. Therefore, carbon-coated TT-Nb2O5 materials are designed and synthesized through solid state method in this work, which present high specific capacity (228 mA h g?1 at 0.2C), satisfactory rate properties (107 mA h g?1 at 20 C). The outstanding electrochemical property can not only give the credit to the pseudocapacitance effect of TT-Nb2O5, but also attribute to introduction of carbon. The homogeneous carbon-coated materials enhance the electrical conductivity, increase the electron transmission speed and alleviate particle crushing. This research not only offers a new method for preparing excellent electrode materials, but also provides a kind of excellent anode material with prospective application for LIBs. 相似文献