全文获取类型
收费全文 | 27661篇 |
免费 | 3452篇 |
国内免费 | 2025篇 |
专业分类
电工技术 | 2522篇 |
综合类 | 2810篇 |
化学工业 | 3591篇 |
金属工艺 | 1745篇 |
机械仪表 | 1966篇 |
建筑科学 | 2066篇 |
矿业工程 | 1116篇 |
能源动力 | 825篇 |
轻工业 | 2752篇 |
水利工程 | 975篇 |
石油天然气 | 990篇 |
武器工业 | 480篇 |
无线电 | 3010篇 |
一般工业技术 | 2355篇 |
冶金工业 | 1732篇 |
原子能技术 | 370篇 |
自动化技术 | 3833篇 |
出版年
2024年 | 172篇 |
2023年 | 523篇 |
2022年 | 1356篇 |
2021年 | 1727篇 |
2020年 | 1199篇 |
2019年 | 851篇 |
2018年 | 910篇 |
2017年 | 961篇 |
2016年 | 851篇 |
2015年 | 1309篇 |
2014年 | 1592篇 |
2013年 | 1855篇 |
2012年 | 2243篇 |
2011年 | 2251篇 |
2010年 | 2218篇 |
2009年 | 1936篇 |
2008年 | 1968篇 |
2007年 | 1901篇 |
2006年 | 1641篇 |
2005年 | 1305篇 |
2004年 | 910篇 |
2003年 | 618篇 |
2002年 | 522篇 |
2001年 | 586篇 |
2000年 | 405篇 |
1999年 | 188篇 |
1998年 | 318篇 |
1997年 | 201篇 |
1996年 | 143篇 |
1995年 | 74篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 27篇 |
1991年 | 30篇 |
1990年 | 20篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1977年 | 18篇 |
1976年 | 38篇 |
1959年 | 12篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
2.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
3.
4.
5.
相似用户挖掘是提高社交网络服务质量的重要途径,在面向大数据的社交网络时代,准确的相似用户挖掘对于用户和互联网企业等都有重要的意义,而根据用户自己的兴趣话题挖掘的相似用户更符合相似用户的要求。提出了一种基于用户兴趣话题进行相似用户挖掘的方法。该方法首先使用TextRank话题提取方法对用户进行兴趣话题提取,再对用户发表内容进行训练,计算出所有词之间的相似度。提出CP(Corresponding Position similarity)、CPW(Corresponding Position Weighted similarity)、AP(All Position similarity)、APW(All Position Weighted similarity)四种用户兴趣话题词相似度计算方法,通过用户和相似用户间关注、粉丝重合率验证相似用户挖掘效果,APW similarity的相似用户的关注/粉丝重合百分比为1.687%,优于提出的其他三种算法,分别提高了26.3%、2.8%、12.4%,并且比传统的文本相似度方法Jaccard相似度、编辑距离算法、余弦相似度分别提高了20.4%、21.2%、45.0%。因此APW方法可以更加有效地挖掘出用户的相似用户。 相似文献
6.
随着市场的发展,精品超市和改造店铺逐渐增多,需要一种更加适合的制冷机组来满足市场的需求。本文提供了一种新型的解决方案,解决了现有机组存在的高噪音和高成本问题,不仅提高了制冷效率,而且节约能源,保护环境。 相似文献
7.
ZHAO Pengfei TIAN Yuming LIU Aiping KONG Xiangchen CHAI Yuesheng LI Zhangang BAI Pinbo 《中国耐火材料》2015,(2):36-41
Based on the needs of the market,a new 52 MPa medium-density and high-strength ceramic proppant was prepared by adopting third grade bauxite and clay as raw materials and using the solid phase sintering method,and the effect of the firing temperature on the microstructure,phase composition and mechanical properties of the ceramic proppant was studied. The broken resistance mechanism of this ceramic proppant was also discussed. The results show that the main phases of the prepared ceramic proppant are mullite and corundum; the broken rates are 3. 92% and 7. 21% under 52 MPa and69 MPa,respectively. 相似文献
8.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
9.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献
10.
The low energy density of supercapacitors, especially supercapacitors based on aqueous electrolytes, is the main factor limiting their application, and the energy density is closely related to the operating potential window of the supercapacitor. The polymer electrolyte is the main contributor to the safe operation and good ion conductivity of the supercapacitor. In this study, a crosslinked quaternized poly(arylene ether sulfone) (PAES) membrane was prepared via crosslinking during membrane formation with a thermal-only treatment and applied in an electric double-layer capacitor (EDLC). The pre-prepared PAES membrane formed a polymer electrolyte with 1 mol/L Li2SO4 and was then fabricated into an EDLC single cell. The properties of both the membrane and ELDC were investigated. The preferred cPAES-N-0.2 polymer electrolyte showed an ionic conductivity of 1.18 mS/cm. The optimized EDLC exhibited a single-electrode gravimetric capacitance of 104.92 F/g at a current density of 1.0 A/g and a high operating potential window (1.5 V); it, thereby, achieved a high energy density of 8.20 W h/kg. The EDLC also exhibited excellent cycling properties over 3000 charge–discharge cycles. The crosslinked structures promoted the tensile strength and thermal stability of the PAES membranes; this was accompanied by a slight decrease in the ionic conductivity. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47759. 相似文献