全文获取类型
收费全文 | 56375篇 |
免费 | 5634篇 |
国内免费 | 3391篇 |
专业分类
电工技术 | 4010篇 |
技术理论 | 2篇 |
综合类 | 4120篇 |
化学工业 | 8737篇 |
金属工艺 | 3214篇 |
机械仪表 | 3760篇 |
建筑科学 | 5115篇 |
矿业工程 | 1599篇 |
能源动力 | 1555篇 |
轻工业 | 4864篇 |
水利工程 | 1123篇 |
石油天然气 | 2599篇 |
武器工业 | 570篇 |
无线电 | 7009篇 |
一般工业技术 | 6211篇 |
冶金工业 | 2156篇 |
原子能技术 | 750篇 |
自动化技术 | 8006篇 |
出版年
2024年 | 290篇 |
2023年 | 1057篇 |
2022年 | 2045篇 |
2021年 | 2766篇 |
2020年 | 2008篇 |
2019年 | 1608篇 |
2018年 | 1731篇 |
2017年 | 1926篇 |
2016年 | 1771篇 |
2015年 | 2391篇 |
2014年 | 3036篇 |
2013年 | 3401篇 |
2012年 | 4104篇 |
2011年 | 4265篇 |
2010年 | 3974篇 |
2009年 | 3747篇 |
2008年 | 3491篇 |
2007年 | 3370篇 |
2006年 | 3126篇 |
2005年 | 2605篇 |
2004年 | 1777篇 |
2003年 | 1500篇 |
2002年 | 1461篇 |
2001年 | 1279篇 |
2000年 | 1189篇 |
1999年 | 1116篇 |
1998年 | 727篇 |
1997年 | 718篇 |
1996年 | 642篇 |
1995年 | 515篇 |
1994年 | 430篇 |
1993年 | 285篇 |
1992年 | 222篇 |
1991年 | 151篇 |
1990年 | 127篇 |
1989年 | 120篇 |
1988年 | 86篇 |
1987年 | 58篇 |
1986年 | 46篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
3.
Changbai Long Ning Ji Li Yang Wenjie Zhou Kun Zheng Wei Ren Laijun Liu 《Journal of the European Ceramic Society》2021,41(6):3369-3378
With co-substitution of (Li0.5Sm0.5) at A site and W at B site, the electrical properties of modified Ca0.92(Li0.5Sm0.5)0.08Bi2Nb2-xWxO9 [(CLS)BN-xW, x = 0, 0.015 and 0.03] piezoceramics with ultrahigh Curie temperature (TC) of > 930 °C were enhanced dramatically. The increased resistivity induced by the co-substitution ensure them to be polarized under an enough high field. Combined with the increase of spontaneous ferroelectric polarization (PS), the significant enhancements in the piezoelectric, dielectric and ferroelectric properties can be obtained in the composition x = 0.015. Furthermore, the piezoelectric activity (d33) and bulk resistivity (ρb) of (CLS)BN-0.015 W can be further enhanced at an appropriate sintering temperature. This optimum composition sintered at 1170 °C shows ultrahigh TC of ~948 °C, d33 of ~17.3 pC/N and ρb of ~6.9 MΩ cm at 600 °C, which are comparable to those of the reported high-temperature Aurivillius piezoceramics with TC > 850 °C. 相似文献
4.
A novel CdS/CaFe2O4 (CS/CFO) heterogeneous p-n junction was created by thermal deposition of CaFe2O4 nanoparticles on CdS rods. The CS/CFO hetero-structured photocatalysts exhibited increasingly efficient visible light harvesting compared to the bare CdS. The CS/CFO composites also presented higher photocurrent and slower decay of photoluminescence, suggesting a better separation of the photo-generated electrons and holes. The photocatalytic H2 evolution quantity on the optimized CS/CFO composite from water in the presence of ethanol was up to 2200 μmol after 3-h visible light illumination, which is more than twice that of the pristine CdS. The chemical interaction between CdS and CaFe2O4 was confirmed by the shifts in the XPS peaks, which made it possible for the charge carriers to transfer across the p-n junction interface. This research highlights the importance of forming an interfacial p-n heterojunction between two semiconductors for efficient charge separation and improved photocatalytic performance. 相似文献
6.
7.
Telecommunication Systems - Machine to Machine technology has a broad application prospect in the 5G network, but there is a bottleneck in the energy consumption of intelligent devices powered by... 相似文献
8.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献
9.
10.
Dan Ye Kaiyu Wang Haijiao Yang Xingang Zhao 《International Journal of Adaptive Control and Signal Processing》2020,34(11):1677-1696
In this article, an adaptive fuzzy output feedback control method is presented for nonlinear time-delay systems with time-varying full state constraints and input saturation. To overcome the problem of time-varying constraints, the integral barrier Lyapunov functions (IBLFs) integrating with dynamic surface control (DSC) are applied for the first time to keep the state from violating constraints. The effects of unknown time delays can be removed by using designed Lyapunov-Krasovskii functions (LKFs). An auxiliary design system is introduced to solve the problem of input saturation. The unknown nonlinear functions are approximated by the fuzzy logic systems (FLS), and the unmeasured states are estimated by a designed fuzzy observer. The novel controller can guarantee that all signals remain semiglobally uniformly ultimately bounded and satisfactory tracking performance is achieved. Finally, two simulation examples illustrate the effectiveness of the presented control methods. 相似文献