全文获取类型
收费全文 | 89536篇 |
免费 | 10485篇 |
国内免费 | 6293篇 |
专业分类
电工技术 | 7810篇 |
技术理论 | 5篇 |
综合类 | 7830篇 |
化学工业 | 12041篇 |
金属工艺 | 5617篇 |
机械仪表 | 6261篇 |
建筑科学 | 7588篇 |
矿业工程 | 3375篇 |
能源动力 | 2630篇 |
轻工业 | 7092篇 |
水利工程 | 2358篇 |
石油天然气 | 3946篇 |
武器工业 | 1306篇 |
无线电 | 11025篇 |
一般工业技术 | 8679篇 |
冶金工业 | 3298篇 |
原子能技术 | 1395篇 |
自动化技术 | 14058篇 |
出版年
2024年 | 470篇 |
2023年 | 1607篇 |
2022年 | 3611篇 |
2021年 | 4938篇 |
2020年 | 3634篇 |
2019年 | 2627篇 |
2018年 | 2951篇 |
2017年 | 3198篇 |
2016年 | 2893篇 |
2015年 | 4532篇 |
2014年 | 5703篇 |
2013年 | 6521篇 |
2012年 | 7856篇 |
2011年 | 8133篇 |
2010年 | 7389篇 |
2009年 | 6833篇 |
2008年 | 6596篇 |
2007年 | 6022篇 |
2006年 | 5131篇 |
2005年 | 3946篇 |
2004年 | 2711篇 |
2003年 | 1811篇 |
2002年 | 1673篇 |
2001年 | 1277篇 |
2000年 | 1063篇 |
1999年 | 766篇 |
1998年 | 453篇 |
1997年 | 391篇 |
1996年 | 336篇 |
1995年 | 283篇 |
1994年 | 220篇 |
1993年 | 155篇 |
1992年 | 112篇 |
1991年 | 99篇 |
1990年 | 69篇 |
1989年 | 60篇 |
1988年 | 52篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 22篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
针对领域自适应问题中源域和目标域的联合分布差异最小化问题,提出两阶段领域自适应学习方法.在第一阶段考虑样本标签和数据结构的判别信息,通过学习一个共享投影变换,使投影后的共享空间中边缘分布的差异最小.第二阶段利用源域标记数据和目标域非标记数据学习一个带结构风险的自适应分类器,不仅能最小化源域和目标域条件分布差异,还能进一步保持源域和目标域边缘分布的流形一致性.在3个基准数据集上的实验表明,文中方法在平均分类准确率和Kappa系数两项评价指标上均表现较优. 相似文献
34.
35.
Huimin Zhao Wensi Wang Yunmei Du Yu Yang Minghui Wang Shaoxiang Li Ruixin Chen Yanru Liu Lei Wang 《International Journal of Hydrogen Energy》2021,46(18):10763-10772
In this work, we synthesized Se doped MoS2@Ni3S2 with nanosheets coated nanorods structure supported on Ni foam (MoNiSeS). Firstly, MoS2@Ni3S2 (MoNiS) nanorods was synthesized by hydrothermal method. After selenization treatment, MoSe2 successfully formed on the edge of MoS2 nanosheets and particle Ni3S2 transformed into NiSe, in which MoSe2 and NiSe acted as new phase in MoNiSeS. The obtained MoNiSeS only needs a low overpotential of 68 mV to reach the current density of 10 mA cm?2, and has a low Tafel plots of 72.77 mV dec?1 and good electrochemical durability, whose electrochemical activity is much better than that of MoNiS and NiSeS, implying the introduction of Mo and Se is beneficial to improve the electrocatalytic performance of NiS for HER. In addition, the proper amount of Mo source, which has an effect on the morphology of product, has also been investigated. For MoNiSeS, the typical nanosheets coated nanarods expose more active sites and the synergic effects is good to the improvement of the catalytic activity. Meanwhile, WNiSeS has also been prepared using the same method and the corresponding results show that the electrochemical activity of WNiSeS is much better than that of NiSeS, proving the universality of this strategy. 相似文献
36.
37.
以2,6-二甲基苯胺为原料,通过重氮化反应制备2,6-二甲基苯腈,经水蒸汽蒸馏法提纯后,采用75%硫酸酸化,再经酸碱法对产物进行脱色和纯化得产物2,6-二甲基苯甲酸,总收率68.4%。工艺简单、操作安全、适合工业化生产。 相似文献
38.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed. 相似文献
39.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献
40.