全文获取类型
收费全文 | 110612篇 |
免费 | 8264篇 |
国内免费 | 4160篇 |
专业分类
电工技术 | 5823篇 |
技术理论 | 11篇 |
综合类 | 6607篇 |
化学工业 | 18370篇 |
金属工艺 | 5806篇 |
机械仪表 | 6705篇 |
建筑科学 | 8634篇 |
矿业工程 | 3053篇 |
能源动力 | 3112篇 |
轻工业 | 6600篇 |
水利工程 | 1707篇 |
石油天然气 | 6159篇 |
武器工业 | 693篇 |
无线电 | 13938篇 |
一般工业技术 | 14142篇 |
冶金工业 | 5718篇 |
原子能技术 | 1235篇 |
自动化技术 | 14723篇 |
出版年
2024年 | 295篇 |
2023年 | 1670篇 |
2022年 | 2283篇 |
2021年 | 3825篇 |
2020年 | 3002篇 |
2019年 | 2535篇 |
2018年 | 2959篇 |
2017年 | 3334篇 |
2016年 | 2916篇 |
2015年 | 3843篇 |
2014年 | 4891篇 |
2013年 | 6272篇 |
2012年 | 6591篇 |
2011年 | 7222篇 |
2010年 | 6284篇 |
2009年 | 6207篇 |
2008年 | 6178篇 |
2007年 | 5767篇 |
2006年 | 6056篇 |
2005年 | 5435篇 |
2004年 | 3721篇 |
2003年 | 3212篇 |
2002年 | 2855篇 |
2001年 | 2766篇 |
2000年 | 2879篇 |
1999年 | 3376篇 |
1998年 | 2905篇 |
1997年 | 2533篇 |
1996年 | 2237篇 |
1995年 | 1903篇 |
1994年 | 1530篇 |
1993年 | 1211篇 |
1992年 | 955篇 |
1991年 | 726篇 |
1990年 | 588篇 |
1989年 | 491篇 |
1988年 | 381篇 |
1987年 | 284篇 |
1986年 | 194篇 |
1985年 | 166篇 |
1984年 | 93篇 |
1983年 | 76篇 |
1982年 | 86篇 |
1981年 | 56篇 |
1980年 | 45篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
41.
42.
43.
44.
在天然海水侵蚀和冻融循环作用下,与普通混凝土对比,对掺加磨细矿渣(GGBS)海工混凝土的抗冻性和抗氯离子渗透性的耦合性能(简称冻渗性)以及孔结构的细观性能进行了研究.用R值代表混凝土冻渗性指标进行分析讨论,结果表明:掺加磨细矿渣的混凝土,无论掺加引气剂与否,水胶比增大,R值逐渐减小;不掺引气剂,矿粉掺量增大,R值减小;掺加引气剂,矿粉掺量增大,R值增大;引气剂掺量增大,R值增大,但引气剂掺量超过一定极限,R值增长不明显;抗压强度等级在40~60 MPa范围内,其强度值与R值没有明显的规律性.MIP结果表明:掺加矿粉和引气剂的海工混凝土经过冻渗后,无害孔和少害孔的数量较多;R值与最可几孔径大小有明显的反比关系. 相似文献
45.
46.
不同折流板结构螺旋折流板换热器传热性能的比较(英文) 总被引:1,自引:0,他引:1
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
47.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. 相似文献
48.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献
49.
50.