全文获取类型
收费全文 | 29218篇 |
免费 | 3593篇 |
国内免费 | 5027篇 |
专业分类
电工技术 | 959篇 |
综合类 | 5724篇 |
化学工业 | 4494篇 |
金属工艺 | 1657篇 |
机械仪表 | 4453篇 |
建筑科学 | 723篇 |
矿业工程 | 444篇 |
能源动力 | 1345篇 |
轻工业 | 2260篇 |
水利工程 | 384篇 |
石油天然气 | 592篇 |
武器工业 | 319篇 |
无线电 | 5414篇 |
一般工业技术 | 4139篇 |
冶金工业 | 1134篇 |
原子能技术 | 129篇 |
自动化技术 | 3668篇 |
出版年
2024年 | 67篇 |
2023年 | 595篇 |
2022年 | 826篇 |
2021年 | 1109篇 |
2020年 | 1235篇 |
2019年 | 882篇 |
2018年 | 962篇 |
2017年 | 1187篇 |
2016年 | 1278篇 |
2015年 | 1457篇 |
2014年 | 2407篇 |
2013年 | 2548篇 |
2012年 | 3366篇 |
2011年 | 3791篇 |
2010年 | 2595篇 |
2009年 | 2617篇 |
2008年 | 1762篇 |
2007年 | 2273篇 |
2006年 | 1697篇 |
2005年 | 764篇 |
2004年 | 371篇 |
2003年 | 334篇 |
2002年 | 405篇 |
2001年 | 349篇 |
2000年 | 423篇 |
1999年 | 388篇 |
1998年 | 325篇 |
1997年 | 323篇 |
1996年 | 318篇 |
1995年 | 290篇 |
1994年 | 212篇 |
1993年 | 207篇 |
1992年 | 110篇 |
1991年 | 95篇 |
1990年 | 92篇 |
1989年 | 73篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
1.
2.
《Ceramics International》2022,48(14):20062-20069
Photocatalytic N2 fixation is a promising and sustainable manufacturing process of ammonia (NH3); however, the NH3 production rate by this method is very low, thus severely restricting further application of this sustainable technology. Therefore, developing an efficient photocatalyst for N2 fixation under mild conditions is urgently required. Herein, ferroelectric Bi2WO6 materials with different surface oxygen defects were prepared, and the concentration of corresponding defects was controlled by adjusting the thermal reduction time. The abundant oxygen defects in Bi2WO6 can provide more reactive sites to promote the effective adsorption of N2, and the photogenerated charge carrier can be efficiently separated benefiting from the internal electric field. These would weaken the N2 triple bond and reduce the activation energy barrier for the conversion of N2 to NH3 under mild conditions. In the absence of sacrificial agents and cocatalysts, the optimized Bi2WO6 with oxygen defects shows an indigenous NH3 yield of 132.175 μmol·g-1·L-1·h-1, which is more than two times higher than that of the original Bi2WO6. Surprisingly, the Bi2WO6 with oxygen defects produced more than eight times NH3 (471.13 μmol·g-1·L-1·h-1) than that of the original Bi2WO6 when assisted by an external magnetic field, thus providing a new perspective for further enhancing the N2 fixation performance. 相似文献
3.
中国沉积盆地内火山岩分布广泛,松辽、准噶尔及四川等盆地不断取得重大突破与发现,火山岩已成为我国油气勘探的重要领域之一。松辽盆地长岭断陷发育火石岭组和营城组火山岩,是油气增储上产的重要领域,但其勘探成效直接取决于对火山岩圈闭的识别与刻画成果。与碎屑岩圈闭相比,火山岩圈闭成藏条件要求更为苛刻,储层条件、侧向及顶底板封堵条件是控制火山岩圈闭有效性关键要素。在解剖已发现火山岩油气藏基础上,通过攻关研究,提出了火山岩体刻画和火山岩储层的描述是火山岩圈闭识别的重点。以火山岩岩性圈闭为例形成了火山岩岩性圈闭识别描述“五步流程”,并实际应用于龙凤山鼻状构造带。钻后结果表明,火山岩岩性圈闭与钻前认识整体一致,圈闭落实可靠,验证了火山岩岩性圈闭识别描述技术方法的有效性,推进了长岭断陷火山岩的油气勘探,对国内其他盆地火山岩油气勘探具有一定的指导应用价值。 相似文献
4.
Water Resources Management - The low impact development (LID) concept aims to control storm runoff and pollution through decentralized, small-scale source control to bring the development area as... 相似文献
5.
《Ceramics International》2021,47(22):31852-31859
The primary purpose of this work is to introduce the second phase of graphene (G) into non-stoichiometric TiO1.80 successfully and optimize the thermoelectric properties of this composite material through high pressure and high temperature (HPHT) technology. The purpose of doping Ti powder under high pressure is to create a closed reducing atmosphere to change the ratio of titanium to oxygen in the titanium oxide base. The addition of graphene can considerably improve the electrical properties of the material and reduce its resistivity. An X-ray diffractometer, X-ray photoelectron spectrometer, scanning electron microscope, and transmission electron microscope were used to analyze and characterize the phase structure, chemical bond, micro morphology and crystal morphology of the samples. An abundance of grain boundaries and lattice dislocation defects can inhibit the lattice thermal conductivity. We also tested and analyzed the thermoelectric performance of the high-temperature and high-pressure synthetic samples through a variable temperature system. The variation of the absorption intensity of the ultraviolet UV spectrum with wavelength shows that high pressure can reduce the band gap, which is beneficial to the carrier transition and improves the conductivity of semiconductors. HPHT optimizes both the electrical and the thermal parameters of the sample. At a final sintering pressure of 5.0 GPa, the dimensionless figure of merit (zT) of the bulk composite material G/TiO1.80 was found to be 0.23 at 700 °C. 相似文献
6.
Lili Hao Jiaxiang Li Peng Wang Zongliang Wang Zhenxu Wu Yu Wang Zixue Jiao Min Guo Tongfei Shi Qigang Wang Yoshihiro Ito Yen Wei Peibiao Zhang 《Advanced functional materials》2021,31(15):2009661
The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine. 相似文献
7.
8.
针对某乘用车发动机转速在1 573 r/min,压缩机开启时车内噪声异常的问题,对样车进行试验分析与诊断,对压缩机-支架系统进行仿真分析,提出改进方案并验证改进效果。利用LMS声振信号采集系统采集振动噪声数据,采用频谱分析、阶次追踪等方法,并结合压缩机-支架系统模态仿真结果,确定车内异常噪声是压缩机轴频21阶与压缩机-支架系统3阶模态频率接近发生共振造成的。通过优化支架结构来提高压缩机-支架系统3阶模态频率以此来避免共振,并换装橡胶驱动盘缓和压缩机输入扭矩波动。将改进结构进行整车试验,结果表明:匀速工况空调开启时问题转速下,车内噪声降低了2.5 dB(A);匀加速工况空调开启时发动机转速1 500~1 650 r/min区间,车内噪声无峰值,其余转速空调开启时改进前/后车内噪声基本不变,噪声波动趋势平缓。 相似文献
9.
10.