首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   53015篇
  免费   5592篇
  国内免费   2784篇
电工技术   3615篇
技术理论   6篇
综合类   4075篇
化学工业   8764篇
金属工艺   2836篇
机械仪表   3381篇
建筑科学   4500篇
矿业工程   1595篇
能源动力   1759篇
轻工业   4022篇
水利工程   1104篇
石油天然气   2544篇
武器工业   548篇
无线电   6254篇
一般工业技术   6119篇
冶金工业   2221篇
原子能技术   631篇
自动化技术   7417篇
  2024年   313篇
  2023年   1110篇
  2022年   2006篇
  2021年   2669篇
  2020年   1932篇
  2019年   1604篇
  2018年   1741篇
  2017年   1921篇
  2016年   1682篇
  2015年   2328篇
  2014年   2807篇
  2013年   3308篇
  2012年   3680篇
  2011年   3727篇
  2010年   3528篇
  2009年   3365篇
  2008年   3218篇
  2007年   2830篇
  2006年   2828篇
  2005年   2233篇
  2004年   1608篇
  2003年   1351篇
  2002年   1442篇
  2001年   1264篇
  2000年   1115篇
  1999年   1142篇
  1998年   843篇
  1997年   718篇
  1996年   678篇
  1995年   514篇
  1994年   463篇
  1993年   317篇
  1992年   280篇
  1991年   202篇
  1990年   151篇
  1989年   132篇
  1988年   82篇
  1987年   60篇
  1986年   45篇
  1985年   32篇
  1984年   27篇
  1983年   19篇
  1982年   18篇
  1981年   13篇
  1980年   17篇
  1979年   7篇
  1974年   2篇
  1970年   2篇
  1959年   4篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
With the emergence of large-scale knowledge base, how to use triple information to generate natural questions is a key technology in question answering systems. The traditional way of generating questions require a lot of manual intervention and produce lots of noise. To solve these problems, we propose a joint model based on semi-automated model and End-to-End neural network to automatically generate questions. The semi-automated model can generate question templates and real questions combining the knowledge base and center graph. The End-to-End neural network directly sends the knowledge base and real questions to BiLSTM network. Meanwhile, the attention mechanism is utilized in the decoding layer, which makes the triples and generated questions more relevant. Finally, the experimental results on SimpleQuestions demonstrate the effectiveness of the proposed approach.  相似文献   
12.
目的研究蛋类礼盒包装结构的缓冲性能。方法以蛋类尺寸为基础,建立可发性聚乙烯(expandable polyethylene. EPE)缓冲单元结构和组合结构,进行静态仿真分析和实验验证,比较结构在形状、叠合层数、组合形式等参数变化时的载荷与位移。结果结构层数变化相同时,单元结构的极限载荷从143N增加到236 N,组合结构的极限载荷从224 N增加到476 N,均呈近线性增长。结论蛋类礼盒包装中,组合结构的承载能力优于单元结构,通过单元结构的组合,可满足不同蛋类的包装要求。  相似文献   
13.
郭红霞  刘园 《现代化工》2015,(2):9-12,14
在新型二次电池产业的发展中,氢镍电池市场不断萎缩,锂离子电池市场正处于黄金时代。通过对日本和中国新型二次电池产业发展历程分析,我国主要针对低端市场,高端市场为日本占据,并从日本发展经验中提出了可供我国锂离子电动车电池发展的借鉴之处。  相似文献   
14.
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active edge 1T‐MoS 2 / edge Ni ( OH ) 2 heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich edge 1T‐MoS 2 / edge Ni ( OH ) 2 sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions.  相似文献   
15.
Yuan  Zhongchen  Yan  Li  Ma  Zongmin 《Requirements Engineering》2020,25(2):213-229
Requirements Engineering - In software reuse, the reuse of UML class diagram produced in design phase has received more attention due to the important influence on the following developing process....  相似文献   
16.
陕南山地烟田不同植烟年限土壤养分的变化   总被引:1,自引:0,他引:1  
为给陕南山地烟草生产布局及有针对性的施肥措施提供依据,分析了陕南山地烟田不同植烟年限(0~15年)与土壤养分含量的关系。结果表明:随着植烟年限延长,有机质线性下降,全氮和速效钾显著上升,有效磷先上升后下降;氯、有效铁、有效锰、有效硼和有效铜无显著变化或变化很小,有效锌则在第1年急剧下降,之后保持稳定,10年后再次显著下降。认为陕南山地烟区烟叶生产中应适当增加有机肥的施用而合理控制氮肥、磷肥和钾肥的施用,并要注意锌肥的补充。  相似文献   
17.
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices.  相似文献   
18.
使用气-质联用仪测定餐饮废油生物柴油(WCME)和-10号柴油(-10PD)的组成,使用冷滤点试验器和运动黏度试验器测定WCME的低温流动性,同时使用调合、添加低温流动性改进剂的方法改进WCME的低温流动性。实验结果表明,WCME主要由饱和脂肪酸甲酯和不饱和脂肪酸甲酯组成,质量分数分别为27.63%和71.81%;WCME冷滤点为0℃,运动黏度(40℃)为4.41mm2/s;WCME与-10PD调合后,冷滤点降低,其中B20的冷滤点最低,为-13℃,运动黏度随着WCME的体积分数的减少,逐渐接近-10PD的运动黏度。通过添加低温流动性改进剂,WCME,B10,B20的冷滤点分别从0,-8,-13℃降至-4,-26,-25℃。  相似文献   
19.
20.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号