全文获取类型
收费全文 | 67527篇 |
免费 | 6354篇 |
国内免费 | 2661篇 |
专业分类
电工技术 | 3702篇 |
技术理论 | 4篇 |
综合类 | 3643篇 |
化学工业 | 11617篇 |
金属工艺 | 3691篇 |
机械仪表 | 4406篇 |
建筑科学 | 4476篇 |
矿业工程 | 1727篇 |
能源动力 | 2350篇 |
轻工业 | 4950篇 |
水利工程 | 1206篇 |
石油天然气 | 2792篇 |
武器工业 | 555篇 |
无线电 | 8521篇 |
一般工业技术 | 9465篇 |
冶金工业 | 3636篇 |
原子能技术 | 954篇 |
自动化技术 | 8847篇 |
出版年
2024年 | 193篇 |
2023年 | 1045篇 |
2022年 | 1653篇 |
2021年 | 2632篇 |
2020年 | 2037篇 |
2019年 | 1843篇 |
2018年 | 2157篇 |
2017年 | 2187篇 |
2016年 | 2208篇 |
2015年 | 2688篇 |
2014年 | 3477篇 |
2013年 | 4290篇 |
2012年 | 4741篇 |
2011年 | 5118篇 |
2010年 | 4354篇 |
2009年 | 4275篇 |
2008年 | 4024篇 |
2007年 | 3684篇 |
2006年 | 3428篇 |
2005年 | 2908篇 |
2004年 | 2250篇 |
2003年 | 2032篇 |
2002年 | 2096篇 |
2001年 | 1824篇 |
2000年 | 1493篇 |
1999年 | 1446篇 |
1998年 | 1236篇 |
1997年 | 969篇 |
1996年 | 850篇 |
1995年 | 711篇 |
1994年 | 526篇 |
1993年 | 433篇 |
1992年 | 329篇 |
1991年 | 247篇 |
1990年 | 214篇 |
1989年 | 161篇 |
1988年 | 149篇 |
1987年 | 103篇 |
1986年 | 113篇 |
1985年 | 66篇 |
1984年 | 51篇 |
1983年 | 46篇 |
1982年 | 28篇 |
1981年 | 32篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 30篇 |
1976年 | 34篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
61.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
62.
Shuaishuai Ding Yuan Tian Xiang Liu Ye Zou Huanli Dong Wenbo Mi Wenping Hu 《Nano Research》2021,14(1):304-310
The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe3O4with drastic change in structure,conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator.However,such modulating effect of Fe3O4in OSV has not been comprehensively investigated,especially below the Verwey transition temperature(Tv).Here,we highlight the important role of Fe3O4electrode in reliable-working and controllable Fe3O4/P3HT/Co polymer spin valves by investigating the magnetoresistance(MR)above and below 7V.In order to distinguish between different contributions to charge transport and related MR responses,the systematic electronic and magnetic characterizations were carried out in full temperature range.Particularly,the first-order metal-insulator transition in Fe3O4has a dramatic effect on the MR enhancement of polymer spin valves at 7V.Moreover,both the conducting mode transformation and MR line shape modulation could be accomplished across 7V.This research renders unique scenario to multimodal storage by external thermodynamic parameters,and further reveals the importance of spin-dependent interfacial modification in polymer spin valves. 相似文献
63.
Oh Seung-Jun Yoon Jeong-Hwan Kim Si-Pom 《Journal of Mechanical Science and Technology》2021,35(3):1065-1073
Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically... 相似文献
64.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
65.
Dong‐Wook Kim 《ETRI Journal》2006,28(1):84-86
This letter presents a small‐sized, high‐power single‐pole double‐throw (SPDT) switch with defected ground structure (DGS) for wireless broadband Internet application. To reduce the circuit size by using a slow‐wave characteristic, the DGS is used for the quarter‐wave (°/4) transmission line of the switch. To secure a high degree of isolation, the switch with DGS is composed of shunt‐connected PIN diodes. It shows an insertion loss of 0.8 dB, an isolation of 50 dB or more, and power capability of at least 50 W at 2.3 GHz. The switch shows very similar performance to the conventional shunt‐type switch, but the circuit size is reduced by about 50% simply with the use of DGS patterns. 相似文献
66.
从目前电力系统的发展来看,不论是华北电网还是晋、蒙电网都存在着调峰能力不足的问题。为更好地利用黄河托龙段的水能资源,改善下游河道的水流条件,为地方经济建设提供清洁可靠的能源,建设龙口水利枢纽工程已经提到日程上来。龙口水利枢纽工程开发任务为发电、对万家寨电站进行反调节、兼有滞洪削峰等综合利用。根据电力系统的需求、泥沙淤积情况、动能经济指标和反调节等要求,综合考虑,选定正常蓄水位898m,装机容量420MW。龙口水利枢纽工程的建设符合国家关于调整能源结构,优先开发水电和加强基础设施建设,拉动经济增长的部署。 相似文献
67.
Dong Yuancheng Duan Yongsheng Zou Shiying Wang Jian Ye Xingbin Yang Jianxin 《中国炼油与石油化工》2006,(3):27-32
1 Introduction With the successful completion of the construction of the China-Kazakhstan oil pipeline the refinery at Dushanzi Pet- rochemical Company will process the Kazakhstan-Russian mixed crude at full steam starting 2007. The high sulfur, nitro- gen and heavy metals contents in the Kazakhstan-Russian mixed crude would have a serious impact on the secondary processing units of the Dushanzi refinery, in particular on the distillate hydrocracking unit, which mainly operates on vacuum g… 相似文献
68.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
69.
70.
新会计准则对会计准则质量的影响 总被引:4,自引:0,他引:4
年初,国家财政部发布了新的会计准则,这是中国会计准则建设史上的重大事件。新会计准则体现出会计准则质量的几个重要标准,提高了中国会计准则的质量。同时,分析新会计准则质量方面仍存在的一些不足。 相似文献