全文获取类型
收费全文 | 359595篇 |
免费 | 29138篇 |
国内免费 | 19827篇 |
专业分类
电工技术 | 20127篇 |
技术理论 | 53篇 |
综合类 | 42109篇 |
化学工业 | 63237篇 |
金属工艺 | 18869篇 |
机械仪表 | 16655篇 |
建筑科学 | 39124篇 |
矿业工程 | 16132篇 |
能源动力 | 12071篇 |
轻工业 | 20583篇 |
水利工程 | 14609篇 |
石油天然气 | 16010篇 |
武器工业 | 3062篇 |
无线电 | 25907篇 |
一般工业技术 | 32698篇 |
冶金工业 | 19365篇 |
原子能技术 | 3818篇 |
自动化技术 | 44131篇 |
出版年
2024年 | 943篇 |
2023年 | 4030篇 |
2022年 | 8119篇 |
2021年 | 9616篇 |
2020年 | 8799篇 |
2019年 | 7707篇 |
2018年 | 7098篇 |
2017年 | 8580篇 |
2016年 | 10144篇 |
2015年 | 11017篇 |
2014年 | 19080篇 |
2013年 | 18529篇 |
2012年 | 23548篇 |
2011年 | 26426篇 |
2010年 | 20931篇 |
2009年 | 22563篇 |
2008年 | 20550篇 |
2007年 | 26052篇 |
2006年 | 24371篇 |
2005年 | 20824篇 |
2004年 | 17635篇 |
2003年 | 15702篇 |
2002年 | 12870篇 |
2001年 | 10665篇 |
2000年 | 9159篇 |
1999年 | 7401篇 |
1998年 | 5660篇 |
1997年 | 4829篇 |
1996年 | 4484篇 |
1995年 | 3813篇 |
1994年 | 3450篇 |
1993年 | 2574篇 |
1992年 | 2207篇 |
1991年 | 1664篇 |
1990年 | 1449篇 |
1989年 | 1227篇 |
1988年 | 943篇 |
1987年 | 654篇 |
1986年 | 505篇 |
1985年 | 437篇 |
1984年 | 395篇 |
1983年 | 280篇 |
1982年 | 289篇 |
1981年 | 207篇 |
1980年 | 161篇 |
1979年 | 138篇 |
1978年 | 76篇 |
1977年 | 86篇 |
1976年 | 67篇 |
1975年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献
82.
《Measurement》2015
The evaluation of functional features of manufactured workpieces is based on GO- and NO-GO-test results, which are obtained by comparing measured geometric characteristics with nominal dimensions and tolerances specified by the designer. These geometrical specifications are based on a tolerancing system, which was originally defined for the function mating capability. Against the background of upcoming lots of other new functions (like reduction of flow resistance, light absorption, reduction of friction, diffraction of light, self-cleaning or mass transmission) are to be realized with our products – particularly by micro- and nano scaled features. If the verification process will deliver the prediction of the achievable degree of functionality, the usability of a part can be assessed more accurately and in consequence quality and economics can be improved. So, a new principle for tolerancing and verifying turns out to be necessary. In this paper the fundamental deficit of the actual tolerancing and specification systems GPS and ASME Y14.5 is derived and the path for enlarging the system by preposing a functional model is shown. To verify the functional capability of the workpieces an approach based on simulations done with the parameterized mathematical–physical model of the function is suggested. Advantages of this approach will be discussed and demonstrated by examples with microstructured inking rolls, crankshafts and injection valves. 相似文献
83.
This paper presents a fast distance relay for series compensated transmission lines based on the R–L differential-equation algorithm using the theory of equal transfer process of transmission lines. The measuring distances based on the proposed algorithm can fast approach the actual value of fault distance when a fault occurs in front of the series capacitor. When a fault occurs behind of the series capacitor, the fault loop, including the series capacitor, does not match the R–L transmission line model, so the measuring distances fluctuate severely. Based on this, the relative position of the fault with respect to the series capacitor can be judged effectively according to the fluctuation range of the measuring distances, and the accurate fault location can be obtained fast. A variety of PSCAD/EMTDC simulation tests show that the new relay has fast operating speed and high accuracy when applied to the long series compensated transmission lines. 相似文献
84.
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。 相似文献
85.
86.
Qi Yang Qilong Wu Yang Liu Shuiping Luo Xiaotong Wu Xixia Zhao Haiyuan Zou Baihua Long Wen Chen Yujia Liao Lanxi Li Pei Kang Shen Lele Duan Zewei Quan 《Advanced materials (Deerfield Beach, Fla.)》2020,32(36):2002822
Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1−xBix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (−0.67 to −0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm−2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO. 相似文献
87.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
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 / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / 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
88.
冯鹏一 《信息通信技术与政策》2020,(1):12-15
以电信用户入网协议为切入点,电信用户的携号转网行为应受到《合同法》《消费者权益保护法》等私法规范的保护与限制。该行为引起的格式条款解释、合同终止、违约责任、损失赔偿等问题,不能仅靠《电信条例》等公法规范来调整。应当积极引导广大消费者用户以私法领域相关规定为依据,转变争议解决思维,拓宽纠纷处理途径,合理选择维权手段,以保护自身合法民事权益,与行业监管部门共同推动电信行业有序发展。 相似文献
89.
90.