全文获取类型
收费全文 | 835127篇 |
免费 | 15953篇 |
国内免费 | 4945篇 |
专业分类
电工技术 | 18242篇 |
技术理论 | 4篇 |
综合类 | 4307篇 |
化学工业 | 124649篇 |
金属工艺 | 35005篇 |
机械仪表 | 30194篇 |
建筑科学 | 23146篇 |
矿业工程 | 5153篇 |
能源动力 | 22312篇 |
轻工业 | 67865篇 |
水利工程 | 8672篇 |
石油天然气 | 13065篇 |
武器工业 | 583篇 |
无线电 | 101565篇 |
一般工业技术 | 160922篇 |
冶金工业 | 144084篇 |
原子能技术 | 14913篇 |
自动化技术 | 81344篇 |
出版年
2022年 | 4879篇 |
2021年 | 8260篇 |
2020年 | 6127篇 |
2019年 | 7171篇 |
2018年 | 16685篇 |
2017年 | 17252篇 |
2016年 | 15023篇 |
2015年 | 9649篇 |
2014年 | 14386篇 |
2013年 | 38841篇 |
2012年 | 24728篇 |
2011年 | 36278篇 |
2010年 | 29819篇 |
2009年 | 31688篇 |
2008年 | 32360篇 |
2007年 | 33471篇 |
2006年 | 24991篇 |
2005年 | 24881篇 |
2004年 | 22332篇 |
2003年 | 21649篇 |
2002年 | 20363篇 |
2001年 | 19656篇 |
2000年 | 18254篇 |
1999年 | 19065篇 |
1998年 | 43988篇 |
1997年 | 31444篇 |
1996年 | 24561篇 |
1995年 | 18809篇 |
1994年 | 16680篇 |
1993年 | 16339篇 |
1992年 | 12027篇 |
1991年 | 11351篇 |
1990年 | 10994篇 |
1989年 | 10410篇 |
1988年 | 10029篇 |
1987年 | 8591篇 |
1986年 | 8473篇 |
1985年 | 9925篇 |
1984年 | 9231篇 |
1983年 | 8142篇 |
1982年 | 7551篇 |
1981年 | 7592篇 |
1980年 | 7091篇 |
1979年 | 6891篇 |
1978年 | 6620篇 |
1977年 | 7802篇 |
1976年 | 10356篇 |
1975年 | 5615篇 |
1974年 | 5341篇 |
1973年 | 5296篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
边坡位移的时间序列曲线存在复杂的非线性特性,传统的预测模型精度不足以满足预测要求。为此提出了基于变分模态分解的鸟群优化-核极限学习机的预测模型,并用于河北省某水泥厂的边坡位移预测。该方法首先采用VMD把边坡位移序列分解为一系列的有限带宽的子序列,再对各子序列分别采用相空间重构并用核极限学习机预测,采用鸟群算法优化相空间重构的嵌入维度和KELM中惩罚系数和核参数三个数值,以取得最优预测模型。最后将各个子序列预测值叠加,得到边坡位移的最终预测值。结果表明:和KELM、BSA-KELM、EEMD-BSA-KELM模型相比,基于VMD的BSA-KELM预测精度更高,为边坡位移的预测提供一种有效的方法。 相似文献
12.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a... 相似文献
13.
Multimedia Tools and Applications - In this work, a new fuzzy logic-based algorithm is proposed for the enhancement of low light color images. A generalization of a fuzzy set known as an... 相似文献
14.
Leibetseder Andreas Schoeffmann Klaus Keckstein Jörg Keckstein Simon 《Multimedia Tools and Applications》2022,81(5):6191-6215
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized... 相似文献
15.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical... 相似文献
16.
Shannon Lee Scott L. Carnahan Georgiy Akopov Philip Yox Lin-Lin Wang Aaron J. Rossini Kui Wu Kirill Kovnir 《Advanced functional materials》2021,31(16):2010293
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials. 相似文献
17.
Xiaoyan Dong Xu Li Xiuli Chen Hongyun Chen Congcong Sun Junpeng Shi Feihong Pang Huanfu Zhou 《Ceramics International》2021,47(3):3079-3088
Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO3-xBi(Ni2/3Nb1/3)O3(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni0·5Nb0.5)O3 boosts the insulation ability, thus obtaining a high breakdown strength (Eb) of 440 kV/cm in xBNN ceramics. A high energy storage density (Wtotal) of 4.09 J/cm3, recoverable energy storage density (Wrec) of 3.31 J/cm3, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of Wrec ≤ 0.4% over 5–100 Hz and Wrec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm3) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems. 相似文献
18.
19.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy... 相似文献
20.
Seredin P. V. Radam Ali Obaid Goloshchapov D. L. Len’shin A. S. Buylov N. S. Barkov K. A. Nesterov D. N. Mizerov A. M. Timoshnev S. N. Nikitina E. V. Arsentyev I. N. Sharafidinov Sh. Kukushkin S. A. Kasatkin I. A. 《Semiconductors》2022,56(4):253-258
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid... 相似文献