全文获取类型
收费全文 | 242316篇 |
免费 | 28658篇 |
国内免费 | 26628篇 |
专业分类
电工技术 | 28298篇 |
技术理论 | 11篇 |
综合类 | 17965篇 |
化学工业 | 42037篇 |
金属工艺 | 11636篇 |
机械仪表 | 19418篇 |
建筑科学 | 10689篇 |
矿业工程 | 4936篇 |
能源动力 | 6763篇 |
轻工业 | 17663篇 |
水利工程 | 3359篇 |
石油天然气 | 5058篇 |
武器工业 | 2355篇 |
无线电 | 34117篇 |
一般工业技术 | 23796篇 |
冶金工业 | 6355篇 |
原子能技术 | 3474篇 |
自动化技术 | 59672篇 |
出版年
2024年 | 1383篇 |
2023年 | 4407篇 |
2022年 | 7948篇 |
2021年 | 9075篇 |
2020年 | 8727篇 |
2019年 | 7565篇 |
2018年 | 7062篇 |
2017年 | 9572篇 |
2016年 | 10334篇 |
2015年 | 11674篇 |
2014年 | 12651篇 |
2013年 | 15228篇 |
2012年 | 18177篇 |
2011年 | 20096篇 |
2010年 | 14485篇 |
2009年 | 14372篇 |
2008年 | 15363篇 |
2007年 | 17565篇 |
2006年 | 16749篇 |
2005年 | 14336篇 |
2004年 | 11973篇 |
2003年 | 9607篇 |
2002年 | 7480篇 |
2001年 | 5826篇 |
2000年 | 4865篇 |
1999年 | 3984篇 |
1998年 | 3219篇 |
1997年 | 2625篇 |
1996年 | 2082篇 |
1995年 | 1758篇 |
1994年 | 1538篇 |
1993年 | 1151篇 |
1992年 | 904篇 |
1991年 | 702篇 |
1990年 | 598篇 |
1989年 | 456篇 |
1988年 | 365篇 |
1987年 | 218篇 |
1986年 | 206篇 |
1985年 | 245篇 |
1984年 | 216篇 |
1983年 | 163篇 |
1982年 | 219篇 |
1981年 | 102篇 |
1980年 | 103篇 |
1979年 | 33篇 |
1978年 | 21篇 |
1977年 | 25篇 |
1976年 | 17篇 |
1959年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
提出了一种基于MSP430和CC2530的低功耗无线传感器网络节点的设计方法。从硬件和软件两个方面阐述了这种设计方法及其具体实现,通过实验完成了对节点消耗电流的测量和分析。应用结果表明,采用这种方法设计的节点能够在低功耗的条件下稳定可靠地工作。 相似文献
992.
993.
为了将知识、信念、愿望和意图以及害怕、焦虑和自信对决策行为的影响的强烈程度进行形式化,把无穷值的卢卡斯维茨逻辑的真值取值范围从[0,1]扩展到[-1,1]。知识情感等级BDI主体的决策行为通过添加了具体条件的不同背景的不同测度来决定;知识情感等级BDI主体模型清晰地表示了主体的知识状态、心智状态和情感状态的不确定性;此模型可以轻易地向其他类型的主体进行推广。在给出了知识情感等级BDI模型的语言、语义以及此模型的不同背景之间的相互关系之后,对知识情感等级BDI主体的军事决策行为进行了实例分析。此研究旨在为分布式人工智能和军事仿真提供形式支持。 相似文献
994.
Water molecules adsorbed on a double-walled carbon nanotube (DWCNT) serve as charge trapping centers when present in low density and as electron donors when present in high density. There is a discontinuous change between the low- and high-density regions. H2O molecules are apt to be adsorbed on the outer surface of DWCNTs, and in this case the electrical transport properties are extremely sensitive to environment, which suggests that DWCNTs are hole doped and act as an electric dipole with the inner tube. 相似文献
995.
The flame‐retardant and smoke‐suppressant properties of inorganic tin compounds such as zinc hydroxystannate (ZHS) and zinc stannate (ZS) were investigated in a comparison with alumina trihydrate, magnesium hydroxide, and Sb2O3 through the limiting oxygen index test and smoke density test. The flame‐retardant mechanisms were studied through the char yield test, SEM, quantitative analysis, thermogravimetry and differential thermal analysis. The thermal degradation in air of flexible PVC treated with the above compounds was studied by thermal analysis from ambient temperature to 800°C. The results showed that tin compounds such as ZHS and ZS could be used as a highly effective flame retardant for flexible PVC, and it appears that the tin compound may exert its action in both the condensed and vapor phases, but mainly in condensed phases as a Lewis acid. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1469–1475, 2005 相似文献
996.
From in situ polycondensation, a poly(ethylene terephthalate)/Polyamide 6 copolymer/montmorillonite nanocomposite was prepared, after the treatment of montmorillonite (MMT) with a water soluble polymer. The resulting nanocomposites were characterized by X‐ray diffraction (XRD), differential scanning calorimeter (DSC), nuclear magnetic resonance (NMR), dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The results of DSC, 1H NMR, and DMA proved that the nanocomposite synthesized was PET/PA6 copolymer/MMT nanocomposite, not the PET/PA6 blend/MMT nanocomposite. The results of XRD and TEM proved that the dispersion of MMT was improved observably after the introduction of PA6 molecular chain into PET. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2512–2517, 2006 相似文献
997.
提出一种新型的滑模观测器,并分别研究在4种不同的电流控制策略下,基于该新型滑模观测器的PMSM伺服系统的控制问题。该新型滑模观测器引进了Sigmoid函数作为控制函数用来抑制抖振,并根据PMSM的反电动势模型构建了反电势观测器来提取所需的连续信号,因此取消了传统的一阶低通滤波器和相角补偿环节。为了对电机的转子位置和转速进行更加精确的估算,引入了转子位置锁相环结构。在Matlab/Simulink平台基础上建立了4种不同的电流控制策略,基于新型滑模观测器PMSM无位置传感器三闭环控制系统仿真模型,分别对反电动势估算、速度估算、位置估算和突加负载扰动进行了仿真分析。仿真结果表明,该新型滑模观测器在4种不同的电流控制策略下,对电机转子位置和转速的估算、电磁转矩以及定子三相电流有着不同的影响,验证了该新型滑模观测器算法的可行性。 相似文献
998.
Water-soluble single-walled carbon nanotubes (SWNTs) were synthesized by grafting poly(acrylamide) (PAM) from the surface of SWNT via reversible addition-fragmentation chain transfer (RAFT) polymerization. The RAFT agents were covalently attached to the SWNTs by functionalizing SWNTs with in situ generated diazonium compounds. The product was characterized by means of FT-IR, Raman, 1H NMR, TGA and TEM. The results showed that PAM chains had successfully grafted from SWNT by RAFT polymerization. The amount of PAM grown from SWNT increased with the polymerization time. The acrylamide conversion increased linearly with the polymerization time, indicating the “living” characteristics of the RAFT polymerization. TEM was utilized to image PAM-g-SWNT, showing relatively uniform polymer coatings present on the surface of individual, debundled nanotubes. 相似文献
999.
1000.
To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006 相似文献