全文获取类型
收费全文 | 411078篇 |
免费 | 35661篇 |
国内免费 | 24685篇 |
专业分类
电工技术 | 24225篇 |
技术理论 | 64篇 |
综合类 | 47950篇 |
化学工业 | 53436篇 |
金属工艺 | 21162篇 |
机械仪表 | 21813篇 |
建筑科学 | 42068篇 |
矿业工程 | 18234篇 |
能源动力 | 10732篇 |
轻工业 | 20957篇 |
水利工程 | 16742篇 |
石油天然气 | 16218篇 |
武器工业 | 4018篇 |
无线电 | 36769篇 |
一般工业技术 | 37173篇 |
冶金工业 | 20288篇 |
原子能技术 | 4406篇 |
自动化技术 | 75169篇 |
出版年
2024年 | 1227篇 |
2023年 | 4593篇 |
2022年 | 8726篇 |
2021年 | 11187篇 |
2020年 | 10743篇 |
2019年 | 9102篇 |
2018年 | 8439篇 |
2017年 | 10302篇 |
2016年 | 12338篇 |
2015年 | 14213篇 |
2014年 | 23531篇 |
2013年 | 22014篇 |
2012年 | 27522篇 |
2011年 | 31185篇 |
2010年 | 24532篇 |
2009年 | 25561篇 |
2008年 | 24104篇 |
2007年 | 29761篇 |
2006年 | 27106篇 |
2005年 | 23732篇 |
2004年 | 20054篇 |
2003年 | 17962篇 |
2002年 | 14619篇 |
2001年 | 11670篇 |
2000年 | 10074篇 |
1999年 | 8083篇 |
1998年 | 6180篇 |
1997年 | 5297篇 |
1996年 | 4872篇 |
1995年 | 4057篇 |
1994年 | 3617篇 |
1993年 | 2709篇 |
1992年 | 2312篇 |
1991年 | 1769篇 |
1990年 | 1524篇 |
1989年 | 1289篇 |
1988年 | 1017篇 |
1987年 | 713篇 |
1986年 | 583篇 |
1985年 | 489篇 |
1984年 | 434篇 |
1983年 | 344篇 |
1982年 | 321篇 |
1981年 | 230篇 |
1980年 | 193篇 |
1979年 | 173篇 |
1978年 | 85篇 |
1977年 | 108篇 |
1976年 | 80篇 |
1975年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Various methods have been developed to monitor the health and strain state of carbon fiber reinforced polymers, each with a unique set of pros and cons. This research assesses the use of piezoresistive sensors for in situ strain measurement of carbon fiber and other composite structures in multidirectional laminates. The piezoresistive sensor material and the embedded circuitry are both evaluated. For the piezoresistive sensor, a conductive nickel nanocomposite sensor is compared with the piezoresistivity of the carbon fiber itself. For the circuit, the use of carbon fibers already present in the structure is compared with the use of nickel coated carbon fiber. Successful localized strain sensing is demonstrated for several sensor and circuitry configurations. Numerous engineering applications are possible in the ever-growing field of carbon-composites. 相似文献
92.
Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO3) powders and dicalcium phosphate dihydrate (CaHPO4·2H2O) powders, has been developed. Three different compositions of Ti:CaCO3:CaHPO4·2H2O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO3 to CaHPO4·2H2O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO3) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites. 相似文献
93.
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
94.
95.
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
96.
97.
This paper analyzes the problems existing in the teaching of data structure course, and puts forward the reform from the as-
pects of strengthening basic programming, visualized explanation of abstract theory, combination of C++, Java programming, ratio-
nal use of online platform, and stratification of exercises, aiming at improving students' practical ability, learning interest and self-
confidence. 相似文献
98.
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
99.
In the first critical assessment of knowledge economy dynamic paths in Africa and the Middle East, but for a few exceptions, we find overwhelming support for diminishing cross-country disparities in knowledge-based economy dimensions. The paper employs all the four components of the World Bank's Knowledge Economy Index (KEI): economic incentives, innovation, education, and information infrastructure. The main finding suggests that sub-Saharan African (SSA) and the Middle East and North African (MENA) countries with low levels of KE dynamics and catching-up their counterparts of higher KE levels. We provide the speeds of integration and time necessary to achieve full (100%) integration. Policy implications are also discussed. 相似文献
100.