全文获取类型
收费全文 | 140680篇 |
免费 | 29721篇 |
国内免费 | 5466篇 |
专业分类
电工技术 | 11660篇 |
技术理论 | 4篇 |
综合类 | 9335篇 |
化学工业 | 28529篇 |
金属工艺 | 5277篇 |
机械仪表 | 8460篇 |
建筑科学 | 17453篇 |
矿业工程 | 3477篇 |
能源动力 | 4421篇 |
轻工业 | 11357篇 |
水利工程 | 4429篇 |
石油天然气 | 5747篇 |
武器工业 | 1688篇 |
无线电 | 15986篇 |
一般工业技术 | 24476篇 |
冶金工业 | 3858篇 |
原子能技术 | 833篇 |
自动化技术 | 18877篇 |
出版年
2024年 | 313篇 |
2023年 | 1007篇 |
2022年 | 2210篇 |
2021年 | 3015篇 |
2020年 | 5752篇 |
2019年 | 7691篇 |
2018年 | 7118篇 |
2017年 | 8343篇 |
2016年 | 8516篇 |
2015年 | 8649篇 |
2014年 | 10750篇 |
2013年 | 10655篇 |
2012年 | 11281篇 |
2011年 | 11102篇 |
2010年 | 8637篇 |
2009年 | 8286篇 |
2008年 | 7752篇 |
2007年 | 8531篇 |
2006年 | 7724篇 |
2005年 | 6567篇 |
2004年 | 5568篇 |
2003年 | 5001篇 |
2002年 | 4521篇 |
2001年 | 3893篇 |
2000年 | 3289篇 |
1999年 | 2303篇 |
1998年 | 1326篇 |
1997年 | 1079篇 |
1996年 | 997篇 |
1995年 | 810篇 |
1994年 | 633篇 |
1993年 | 474篇 |
1992年 | 427篇 |
1991年 | 262篇 |
1990年 | 245篇 |
1989年 | 207篇 |
1988年 | 131篇 |
1987年 | 78篇 |
1986年 | 74篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 34篇 |
1981年 | 30篇 |
1980年 | 70篇 |
1979年 | 54篇 |
1965年 | 26篇 |
1964年 | 34篇 |
1959年 | 33篇 |
1956年 | 31篇 |
1955年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
腐蚀阴极尖端的新方法 总被引:1,自引:0,他引:1
给出一种腐蚀阴极尖端的新方法,使得对阴极常用金属材料(W,Mo,Ir,Ta等)制作的阴极尖端的腐蚀效果明显,针尖对称性和重复性都很好,成品率和质量都有所提高. 相似文献
202.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %. 相似文献
203.
B. Ma P.I. Djurovich S. Garon B. Alleyne M.E. Thompson 《Advanced functional materials》2006,16(18):2438-2446
Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula C∧NPt(μ‐pz)2PtC∧N (where C∧N = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (~ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (~ 5 %) and brightness (~ 600 Cd m–2 at 10 V). 相似文献
204.
新安江流域安徽省地区水环境状况分析 总被引:2,自引:0,他引:2
统计分析流域内点源污染、面源污染产生量与污染物入河量的调查监测数据,结果表明:安徽省辖新安江流域点源入河系数约为面源入河系数2~3倍,点源污染是流域内主要污染来源,但面源污染的作用不容忽视,尤其是总磷,有近2/3来自面源,相对省辖淮河、长江两流域来说,面源污染贡献率明显增大。指出流域污染防治必须综合考虑点、面源污染两个方面;在点源污染不太严重的情况下,对面源污染的治理必须引起足够的重视,才能取得实效。 相似文献
205.
Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry 相似文献
206.
207.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
208.
光纤通信技术的飞速发展带动了光纤测试仪器的发展。主要对两种利用弯曲损耗对光纤进行检测的仪器——光纤识别仪、光纤对线器的原理、结构及其在光纤通信工程中的应用进行了阐述,两种仪器可以在不中断光纤通信的情况下对光纤进行检测,极大地降低了对光纤通信系统的影响,对光纤通信系统具有重要意义。 相似文献
209.
电子产品研制阶段可靠性增长试验研究 总被引:1,自引:0,他引:1
结合工程实际经验,深入讨论了可靠性增长过程及实现途径,在保持试验条件和改进过程不变的条件下,实施了对具体型号电子产品的可靠性增长试验,达到了预期的可靠性增长目标,并且利用可靠性增长试验的数学模型(AMSAA模型)来评估产品的可靠性增长,对开展可靠性增长与可靠性增长试验工作具有重要的实际意义. 相似文献
210.